Split (1)

train · 95.7k rows

source stringlengths 620 29.3k	target stringlengths 12 1.24k
How do you determine the proper rate of descent for landing? I'm trying to use a simulator to learn to land properly. One part that I'm finding really tricky is picking a proper rate of descent. I know I'm supposed to do my best to keep it so I have two red lights and two white lights on the Precision Approach Path Indicator (PAPI), but at the moment I basically am just eyeballing it and adjusting my course whenever the lights aren't right. I have to assume, though, that for any given airspeed there is a rate of descent I can maintain that will keep me right in the middle of the preferred glide slope for that airport. I just have no idea how to figure it out. Is there an application or formula that is preferred for this? Or is it time to learn Vector Calculus? PS- I did check this question to see if it related. But that question is about starting the descent from cruise. I'm talking about rate of descent for final. I did also check this answer, but it's about using the PAPI/VASI lights. I'm looking for a formula to figure out the proper rate of descent during final for a given speed. <Q> Assuming you want a 3 degree glide slope, just take 5 times your ground speed in knots as a starting point. <S> As an example, approaching at 90kt ground speed in a light aircraft, go for 450feet per minute. <S> at 140kt in a jet, try 700fpm. <S> If you're flying a jet outside of 4 miles, and the controller wants you to keep the speed up at 200kt then descend 1000fpm. <S> It's not perfect, but it works pretty well for a first guess, and you can adjust as necessary. <S> Of course, your ground speed is not the same as your air speed, and even for a constant IAS it will likely vary as you descend and the wind changes. <S> Another way to think about this is that a 3 degree glideslope is almost exactly 300ft per nautical mile. <S> If you're 2 miles out and 700 feet up, then you need to descend a bit faster, conversely, if you're at 500 feet, you need to descend slower. <S> A third related rule of thumb is that your final approach speed (in CAS, although IAS is good enough in most aircraft) is 1.3 times your stall speed in the landing configuration (Vso). <S> So if you stall at 100 knots, you want to approach at 130KIAS. <S> IFR approaches are all about having an initial guess at these numbers in your head, trying them out, and then adjusting as the conditions require. <S> If you're good at the guesses then the adjustments will be very small. <A> For most purposes, if you're flying something with a jet engine, you can probably schwag -700fpm for a 3 degree glideslope and be fairly accurate. <S> It will at least give you a starting point. <S> You shouldn't be flying the approach solely off your VSI anyway, but it is useful to determine how large of a correction you are making, or if you're about to bust through the bottom. <A> That way you're not chasing the airspeed, VVI, etc. <S> So how do we figure out what pitch and power settings to use? <S> Well if we look at our ADI in level-flight at our final approach speed we see we are 2 degree nose-high for example. <S> And we know that for each degree of pitch change it equates to 100 ft/NM. <S> With an average ILS the glideslope is around 3 degrees. <S> So we know that this is about 3 degrees low from our 2 degree level flight attitude. <S> This leaves us with about 1 degree nose-low. <S> Fly the approach at 1 degree nose-low, and adjust your power to maintain your airspeed which in the end should result in a VV of about 5 * your groundspeed. <S> Or you can take your groundspeed and convert it to NM/min and then multiply that by 300 ft/NM. <S> If we approach at 160 KTS (2.67 NM/min), we end up with a VV of 800 ft/min which is the same as using our rule of thumb of 5 times your groundspeed. <S> I know this is probably a little more math than what you wanted, but setting a known pitch and power setting and making minor adjustments from that will help improve your approaches tremendously.	It helps to know the pitch and power settings for your jet.
Does European airspace use the metric system? I figured this was probably a no brainer, since Europe uses the metric system, I assume the airspace does... But then I remembered that aviation likes international standards, and I know the US uses Imperial so, does Europe as well? And, yes or no, why do they take that choice? <Q> Some VFR aircraft have speed indicators in km/h, gliders can have altitude and variometer in meters and meters/second and apart from a special ICAO VFR chart being available in metric in Germany, the AIP itself and all other charts always use imperial units. <S> Related question: <S> What is the measurement system used in the aviation industry? <A> Europe uses imperial for distance (nm), speed (knots) and altitude (feet). <S> Russia and China are the only major countries that use meters for altitude - and it causes all sorts of confusion. <S> Some aircraft (more in europe) use kilometers and statute miles/hour on the ASI - but the same is true in the US. <A> As others have mentioned, the basic units to define the airspace are feet and nautical miles. <S> However, some other values are also used when navigating the airspace, and a few are from the SI system. <S> For instance: pressure settings: hPa (aka millibars, mbar) <S> runway lengths: meters <S> visibility: meters temperature: centigrades Regulations (VFR): minimum horizontal distance from obstacles: meters <S> To see the SI units for pressure, visibility and temperature in a real-life setting, just have a look at a TAF/METAR for any European airport. <S> The mixture of units can seem strange, but there is also a method to the madness. <S> You know that whenever you hear a measurement in feet, it is about a vertical distance, and anything expressed in meters (or kilometers) will be horizontal. <S> A small contribution to the clarity of communications.	European Civil Aviation Authorities use the imperial system to depict altitudes and airspace restrictions (feet), speeds (knots) and distances (nautical miles).
Can an outside observer tell if an aircraft is flying through turbulence? As a passenger, when I look out of the window, I can see the wings shaking. What would another plane (not in turbulence) see if they were observing the same plane (in turbulence)? <Q> The wings are more aerodynamic than the body of the aircraft. <S> I.e. the wings are more "responsive", they respond to changed aerodynamic forces more rapidly. <S> As a result of the change in lift in the wings, the body (being connected to the wings) follow the change. <S> Therefore, to an observer who is immune to turbulence, the wings would flex first, followed by the aircraft as a whole. <S> If the turbulence is causing the wings to flex up and down repeatedly <S> (e.g. imagine sine wave), the body of the aircraft can be observed lagging behind the wings and smaller in amplitude. <A> Let's suppose you stand on an unstable bar stool. <S> It shakes a little when you move, but you feel a lot of movement. <S> An observer standing close by will see the stool and you shake a little bit (a few inches at most). <S> If that observer moves a 100 feet away, he might not notice the shaking at all. <S> When the airplane you are on is in turbulence 1 , you will feel a lot of shaking. <S> The airplane is shaking, but to an outside observer which is close, it will feel as much as you feel it. <S> Again, if the observer is moved a mile away, the shaking will not appear as significant as your experience. <S> 1 <S> Minor turbulence. <S> In case of severe turbulence, it will be more evident to an observer. <A> The wings act as a structural dampener to disturbances such as turbulence, similar to the suspension on a car. <S> As they flex, they absorb the sudden energy changes. <S> The aerodynamic forces also take time to accelerate the large mass of the airplane. <S> Because of these effects, most of turbulence will be too small to see from an outside observer's point of view. <S> However, in addition to the wing flexing, the aircraft will also roll, pitch, and yaw in response to the turbulence. <S> The pilots or the autopilot, as well as the natural stability tendencies of the aircraft, will help the aircraft return to its previous state. <S> Here is a video recorded from the X-Plane flight simulator program of a 737 in turbulence. <S> The wing flex and change in flight attitude can be seen.	The wings are flexing because there is a change in lift.
Why is vertical take-off restricted to lighter weight aircraft? Vertical take off is a big advantage, but why it is only limited to low weight? For example, fixed wing like An225 can lift more than hundred tonnes of payload, while the biggest helicopter is 25 tonnes. Why there is no effort to build a helicopter can lift 50 - 100 tonnes. What limits them? Economic or technical problem? I guess it is a technical problem because even the heaviest helicopter is just an experiment, but what is it? <Q> Essentially it comes down to supersonic rotor tips With a plane, in theory you can make it pretty much as big as you like - as long as you have strong/light enough materials, and can keep adding power, an aeroplane design scales pretty well. <S> Bigger wing = more lift. <S> So how does a helicopter produce lift? <S> By using rotors to push air down within a kind of circle. <S> To add more lift we can do (essentially) three things. <S> Make the rotor spin faster <S> , so it pushes more air down in the circle it already uses. <S> Obviously this makes the tips spin faster, so we can only do it to a certain extent. <S> We've already hit this limit. <S> Make the rotor blades longer, so they push a bigger circle of air. <S> Again, though, due to the nature of a circular blade, the outside of a blade is moving faster than the inside. <S> For a certain rotor speed, there's a fixed limit to how large the blades can be. <S> Again, we've already hit this limit Add more blades, so there are more blades producing lift. <S> This works to an extent (hence why smaller helicopters may have two rotor blades, but larger ones have 4, 5 or more. <S> Again, though, this doesn't scale indefinitely - each rotor interferes with the next, you can't just keep adding more <S> There are other slight modifications we can make, such as the airfoil of the rotor, but they don't add significant gains <S> So, basically, we've hit the limit of what we can lift with a single rotor, <S> The only real way to add more lift now is to add more rotors: <S> doing that would be far less efficient than simply using an aeroplane. <S> Which brings me to the final point - helicopters are very inefficient and pretty slow... <S> We simply don't need, except in a few niche circumstances, to carry more weight with them. <A> Jon's answer is correct: "helicopters are very inefficient and pretty slow..." <S> but he misses one important point <S> : helicopters are also incredibly fragile and delicate. <S> Even a regular single-rotor helicopter flying is a miracle. <S> It's been called: "10,000 spare parts flying in close formation." <S> You could add more rotors to gain more lift, the Chinook has two rotors which is part of why it can carry so much. <S> The rear rotor adds complexity but also removes the need for a tail rotor, which is why it isn't quite 20,000 spare parts flying in close formation. <S> But even Chinooks are fragile compared to C-130s. <S> Adding engines adds redundancy in a plane. <S> And remember that if you are in a plane and you lose an engine (or all engines) you can still fly or glide to a safe landing. <S> If you are in a rotorcraft and you lose your engine (either main rotor or tail) or really any single part of those 10,000 parts, then all you can do is pray and try an auto-rotation landing. <S> It gets worse the more rotors you add, not better. <S> This is one of the limitations of rotorcraft and why you for the most part only see multiple rotors (4-, 6-, 8-) used in unmanned drones except for some very experimental vehicles. <A> For a helicopter to take off vertically: $$Lift \gt Weight.$$ <S> The weight grows with length to the third power ($l^3$, <S> weight is proportional to volume) while the lift only grows with $l^2$, because it's proportional to the rotor blades planform area. <S> More lift means higher lift coefficient and more rotorblade planform area. <S> The maximum cirumferential speed at the blade tips is limited (there's the constraint that the tips can't move at supersonic speeds). <S> One would need stiff longer and trapezoidal blades and there is a structural limit to the possible torque on the blade root. <S> Aircraft that cruise at high subsonic speeds exprience the same airspeed at any portion along the wings, unlike a helicopter that has a $v=r \omega$ relationship for the speed along the rotor blade. <S> $v$ is constrained to subsonic speed. <A> The power required to maintain altitude at forward flight is lower than the power required to hover. <S> As horizontal velocity ($V_x$) increases, the induced velocity ($V_i$) at the disc decreases, and induced power ($P_i$) decreases roughly equal to $\frac{1}{V_i}$. However, as $V_x$ increases, parasitic power ($P_p$) increases proportional to <S> $V^3$. Profile power ($P_0$ - the power needed to maintain rotor speed) remains roughly constant. <S> If you chart all of these together with Required Power on the y-axis and forward velocity on the x-axis, you end up with something that looks like this: What this means is that there's an optimum forward speed at which your power is minimized. <S> This is important, because the max rate of climb (and lifting power) is determined by your available power $$P_{av} = <S> P_{tot} - P_i - P_p - P_0$$. <S> If you minimize the power needed to keep the aircraft flying, you have more net power for lifting other things (and for heavy helicopters, they may not be able to take off vertically at all). <S> For this reason, the max rate of climb will always be at some forward speed, and by definition, the max lifting capacity will also be at some forward velocity. <S> A practical demonstration of this principle is that large cargo lifters like the sky crane and the chinook always take off with some forward velocity component. <S> This is why.	As long as you can make the wing bigger without it breaking, and as long as you can add enough power to overcome the extra drag, there aren't many fixed limits With a helicopter, we're limited by the rotor tips: once they go supersonic, they cause a lot of problems.
What advantages are provided by an unstable canard configuration for fighters? Why are most canard fighter aircraft unstable? A stable design would let the canard provide lift. My guesses are: Increase pitch rate Decrease stability while supersonic (supersonic, the aircraft are stable) <Q> This confirms your first guess. <S> Your second guess is also correct: Flying supersonically shifts the center of pressure back and increases stability. <S> If the aircraft is unstable subsonically, it will suffer far lower trim losses supersonically. <S> Please read all about unstable designs in this answer . <S> For conventional, stable configurations it makes most sense to put the control and damping surfaces at the back, and a canard is the better choice for unstable, highly maneuverable aircraft. <A> Most modern fighter aircraft designs -not just canard-wing configurations- <S> are designed to be (slightly) aerodynamically unstable. <S> Stability is ensured through the action of the automatic control system, which issues commands to the control surfaces that stabilize the aircraft. <S> The unstable aerodynamic design together with the digital control system makes the aircraft more maneuverable. <S> A safety feature with the canard providing a downforce for trim, is that the wing stalls before the canard in high angle of attack situations, which ensures that the aircraft still has maneuverability post-stall. <A> A canard surface operates in 'clean' air, not 'shadowed' by the wing, so maneuverability has priority over lift.	You want your control surface to create only little lift, so it has enough margin for maneuvering.
Could fly-by-wire protect against a takeoff tail strike? If the takeoff weight is underestimated, rotation will be done too early and may result in a case of tail strike. One example of such mistake is a 747-400 (F-HLOV) in 2006 (case 8 in this study ). The crew entered ZFW for TOW (100 tons lower), VR was underestimated by 32 kts. Boeing documentation mentions every aircraft can be subject to tail strike, at different degrees. Airbus documentation for tail strike prevention doesn't mention any specific protection from FBW. (source: The Aviation Herald .) UA B744 tail strike on Sydney takeoff (photo may not be the actual May 7th 2010 T/O). I wonder why such basic mistake may be done. Weight could be sensed in some way by the instrumentation, and crew entered values should be challenged if really different. To prevent the crew from being forced (or tempted) to rotate the aircraft beyond the maximum safe angle, isn't that possible to monitor the T/O progress and in case of low performances alert the crew, and provide an opportunity to reject the T/O. Airbus FWB embeds many security systems (compared to Boeing), this is surprising that they cannot prevent such T/O tail strikes. I'm sure there are good reasons, just asking to understand the difficulty. Edit : Based on the answer from Marky Mark, who references the EK407 case, I checked a study published in the aftermath of EK407 tail strike: Take-off performance calculation and entry errors: A global perspective and noted this recommendation for 'TOPMS': While the above recommendation does not preclude data entry and calculation errors relating to take-off performance parameters from occurring, Transport Canada (Department of Transport) agreed that a take-off performance monitoring system(s) (TOPMS) would provide a significant safety benefit. However, before regulatory authorities establish a requirement for the fitment of TOPMS, a certified system would need to be developed (Transport Canada, 2010). Basically, a TOPMS, which assists pilots in determining whether to continue or reject the takeoff, can be defined as (Brown & Abbasi, 2009, p. 7). Are TOPMS now in place? <Q> However, this is not fool-proof <S> and it remains up to the PF to maintain the correct nose-up angle. <A> Boeing has removed the tail skid on the latest B777-300's because they have never had a tail strike and an updated version of FBW will virtually guarantee it going forward. <S> Removing the tailskid saves about 300 lbs. <S> More info: <S> Aviation Week Article <S> Boeing has also decided to remove the tail skid from the 777-300ER as a weight and drag reduction improvement after developing new flight control software to protect the tail during abused takeoffs and landings. <S> “We redesigned the flight control system to enable pilots to fly like normal and give them full elevator authority, so they can control the tail down to the ground without touching it. <S> The system precludes the aircraft from contacting the tail,” Schneider says. <S> Although Boeing originally developed the baseline electronic tail skid feature to prevent this from occurring on the -300ER, the “old system allowed contact, and to be able to handle those loads we had a lot of structure in the airplane to transfer them through the tailskid up through the aft body into the fuselage,” he adds. <S> “So there are hundreds of pounds in the structure, and to be able to take all that out with the enhanced tail strike-protection system is a nice improvement.” <S> The change was implemented on the line in November and will be offered as a retrofit through a service bulletin. <S> “With a retrofit, you can’t save so much weight because the structure is already in the fuselage, but the drag and maintenance savings is still a nice benefit,” says Schneider. <S> “It is also one of things customers are most interested in retrofitting off the aircraft." <S> Tail Strike Protection (TSP) logic has been incorporated in the 777 FBW since the -300ER became available. <S> It is available on the 777-200LR as well (despite shorter body); I believe all other models also have it now through the PFCs (200ER, F). <S> The newer -300ER aircraft have the TSP logic ENHANCED and with it came the removal of the tail skid, which saves 323 pounds (145kg) of aircraft weight besides maintenance costs <S> (it's a hydraulic actuated skid). <A> In principle, yes. <S> The aircraft would have to be able to measure its weight, which rests on the main gear and front gear when on the ground. <S> Measuring a structural displacement which increases with more weight and decreases with less weight, one could determine the aircraft weight.	On Airbus aircraft, the guidance law provides attitude protection on take-off which should prevent a tail strike.
Are there non-economic barriers to a 1000 passenger aircraft? I know the number 1000 is just an arbitrary number that happens to have some zeros in it, but is there any non-economic obstacle to making a 1000 passenger aircraft? Also, assume normal-ish space-per-passenger constraints, so 1087 people on a 747 isn't really a 1000-passenger aircraft. <Q> If money is no object, and we ignore terminal constraints, then no, there isn't. <S> The A380 already supports 850 passengers in a single-class layout, and Airbus has plans to make a stretched version (the wings are designed to give room to stretch the fuselage without needing too much redesign). <S> 1000 passengers isn't really that much of a stretch; we can basically get there now. <S> The issue is that economic obstacles are very real obstacles to building planes; no one has a need for a 1000-person plane on any route (the A380 isn't even used today with max capacity, it's used to give lots of space to first-class passengers with a bit over 500 passengers). <S> There are certainly at least two airfields out there that would be able to handle a 1000-passenger A380; unfortunately, neither is a commercial airport (the two are Edwards AFB and the Shuttle Landing Facility; the SLF has a 15,000 foot runway that's 300 feet wide, while Edwards has a similarly-sized paved runway). <S> However, if operation is uneconomical, you won't see anyone building a plane to do it. <A> Yes, there are some barriers: <S> To evacuate 1000 passengers within 90 seconds from half of the available emergency exists will require clever engineering. <S> First the scaling laws: When you increase the size of an aircraft, its area will grow with the square of the increase while its volume will grow with the cube of the increase. <S> This demands proportionally bigger cross sections of all load-carrying members. <S> For the same reason ants cannot be scaled up and elephants have much bigger legs than antelopes. <S> The A380 is already pushing the envelope, and any bigger aircraft will be even more problematic to design. <S> But not impossible. <S> The emergency slides on the A380 were one of the most challenging parts to design. <S> While normal slides can be mercifully short, lowering a passenger by 8 meters from the upper floor such that he or she will reach the ground at a survivable speed is hard. <S> The slide must be much longer and still is not allowed to buckle. <S> This required the development of new materials. <S> Now that this has been done, a stretched fuselage with another two or four type <S> I exit doors <S> will make the 1000 pax version possible. <S> But when a future design plans to have a wider fuselage with more seats in a row, this will be one of the first limits to adding seats. <A> Aside from finding a route that would make such a large aircraft profitable, the biggest barrier is probably that the existing infrastructure couldn't support such an aircraft. <S> Terminals would have to be enlarged to handle the enormous passage of 1,000 riders. <S> I'd guess that most taxiways probably aren't large enough either. <S> Even the A380 has run into trouble finding suitable airports to operate out of. <A> NASA sponsored a program to answer just this question. <S> It was called the Ultra Efficient Engine Technology project, or UEET. <S> If you Google it I believe you will find the best estimates for max aircraft size, around the turn of the century when this project concluded, was 2.5 million pounds MTOW. <S> That is a bit more than 2X the size of the A380, and with current tech, that number is probably around 3 million pounds MTOW.	Scaling laws tell us that the structural mass fraction of such a big airplane would increase, reducing its efficiency.
How many passengers can an Airbus A380 carry? What is the passenger capacity of an A380, and how many suitcases could it carry? <Q> Wikipedia lists three basic configurations for the A380-800: 407-526 <S> (3-class) <S> 644 <S> (2-class) 853 <S> (1-class) <S> However, different airlines have different configurations . <S> The lowest number of seats is Korean Air, with 407 . <S> The highest number of seats is Air France, with 538 . <S> Emirates has discussed plans for a configuration with 644 seats but it does not appear on the list ( or on SeatGuru ). <S> As far as baggage, this thread states that the A380-800 might carry 19 LD-3 containers of baggage, or 3002 cubic feet, which is for about 471 passengers. <S> The bulk hold, which is for loose baggage, can hold 1,525 kg or 14.2 cubic metres (501.5 cubic feet), and the A380-800 can carry 8,000 kg of cargo in addition to a full passenger load according to Emirates . <S> An average suitcase is about 0.1 cubic meters in volume. <S> If the bulk hold is 14.2 cubic meters, then it could theoretically fit 142 suitcases. <S> But an average suitcase weighs 50 lb, so 142 suitcases would weigh 3220 kg, which is over twice the weight capacity. <S> The LD-3 containers add an additional 85 cubic meters of space, or 850 bags. <S> This is a total of 942 bags, which for around 500 passengers sounds very reasonable. <S> But wait, there's more! <S> What if the rest of the cargo capacity was filled with luggage? <S> Emirates above claims a total of 12 PMC and 44 AKE of cargo capacity. <S> The properties are as follows: <S> PMC 23 cubic meters ( max ) <S> 6700 kg capacity <S> AKE 4.3 cubic meters <S> 1497 kg capacity <S> This is a total of 465.2 cubic meters of capacity, or 4652 suitcases, or 105,505 kg. <S> The containers could hold a maximum of 146,268 kg. <S> So the bulk plus container capacity is 4794 bags by volume. <S> This is assuming every container could be packed completely full of bags with a density of 227 kg/cu m, so the actual numbers would probably be lower. <A> In theory, up to a maximum 853 passengers in a single-class setup (ie if the whole plane was set up for the maximum possible number of economy passengers) <S> For example the upper deck contains a small number of First Class seats (front) and a larger number of Business Class (rear) While the lower deck contains all economy class passengers <S> Reference: <S> airbus.com Airbus has some vague plans to introduce a 1000-passenger all-economy (ie single class) "stretched" version of the A380, <S> but these don't appear to be in the pipeline for production anytime soon. <S> The A380 was originally designed with this in mind, though. <A> The Daily Mail and Seat Guru both show Emirates having a two class version with 615 seats total, 557 economy. <S> And, while Emirates only shows three class versions if you actually look up the route mentioned by the first link (Dubai - Copenhagen) <S> you will see it only has Business, Economy. <S> Clicking on the "View services" link will also show the First class missing. <S> So, despite the Daily Mail being a rag and Seatguru not being 100% reliable to say the least I must say the evidence strong for this configuration.	Luggage isn't a limiting factor for the A380, as it can hold approximately one suitcase per passenger in the luggage hold, and a further 2-4 suitcases per passenger in the bulk hold (depending on whether other cargo is being carried) In practice, it's usually configured for 525 in a typical "three class" (First, Business, Economy) layout, which is standard (with fairly minor variations) for most airlines as this is both more profitable to the airline, and better suited to actual real-world demand.
Can I become a pilot if I am under treatment for Attention Deficit Disorder? I know that before you even begin training in flight school, you are required to get a physical examination from a doctor to determine if you are fit to fly. Online articles stressed the importance of being completely honest with the doctor about any existing conditions. I was just recently diagnosed with ADD (or rather, I described my issues to my regular physician and simply started receiving medication to treat it) and this is something I would naturally disclose at the physical examination. Does FAA disqualify someone from getting their pilot's license on the basis of ADD? I take medication for this once a day and it resolves any issues I face from it. <Q> I'm going to assume you're asking about US/FAA requirements <S> - If not what's below may not be particularly helpful. <S> you may need to undergo additional testing in order to receive a medical certificate. <S> Also some of the medications used to treat ADD/ADHD may be disqualifying (I know that Adderall, Focalin, and Ritalin were all on the FAA's "No Fly" list - I'm not sure if they're still an absolute NO <S> or if you can get approval for them). <S> AOPA has a pretty decent drug list that you can search to see if what you've been prescribed is permitted - it's a little easier to search/cross-reference than <S> the official FAA " <S> Do Not Issue/Do Not Fly" list <S> and they do a good job keeping it up to date, and a brief article on ADD/ADHD & medical certification . <S> They also have a service to assist you with getting your medical (as part of Pilot Protection Services ) which can be helpful. <A> You can get a Pilot certificate under the Light Sport Category. <S> This does not require a medical, only a current Drivers license. <S> I've never seen a doctor for flying <S> and I've had my ticket for a few years. <S> You will be limited to VFR flight and aircraft size restrictions.(small plane, two seats to name few restrictions) <S> But there are lots of options for Light Sport Aircraft, and many more manufactures getting on board with new equipment. <S> Your CFI will teach you almost everything a beguining private pilot learns, because you have to be able to operate in the same airspace system with the rest of the VFR world. <S> The training time requirements are less than PP and many pilots are starting with Sport and then moving up. <A> You wrote that it was only your normal medical doctor that wrote the prescription. <S> I would go back to him and verify that he did not write an official diagnoses of ADD in your medical records. <S> And if he did, I would ask him if he is willing to amend the record and call it "possible ADD". <S> I am pretty sure he would not have written that you have a diagnosed ADD condition as it takes more than a conversation with a general practitioner to make such a diagnosis. <S> Assuming there is no official diagnosis of ADD in your record, all you have to do is get off the medication, wait three days (instead of 90 as folks with an official diagnosis have to) and then take the three neurotests. <S> You will not have to find a psychologist who is willing to "un-diagnose" you. <S> See https://www.aopa.org/go-fly/medical-resources/health-conditions/mental-health/add-and-adhd for more details. <A> Be forewarned: I hold a multi-engine instrument rating but can no longer fly due to the loss of my medical certification. <S> I attended Embry-Riddle Aeronautical University through an extension campus at Hillsboro Aero Academy. <S> I completed all of my flight tests and exams in the minimum required time. <S> I had the entire staff behind me when confronting the FAA on the matter of ADD. <S> Unfortunately, the FAA's requirements to get a waiver are quite strict (which includes taking the Wisconsin card sorting test before acquiring a medical certification). <S> According to the three psychologists that I visited in trying to acquire a waiver, the tests are difficult to pass for even the most focused individuals. <S> I didn't at first <S> and that's how I got so far. <S> It was only when trying to get a class 1 medical certificate that I admitted to having once been diagnosed with ADD. <S> I hadn't taken any medication in five years at that point and had no symptoms, but few psychologists will un-diagnose you due to the severe liability it could pose on them and others. <S> I spent thousands of dollars trying to acquire a waiver and invoked the AOPA legal insurance that I had, but nothing helped. <S> The FAA's job is to deny you. <S> Until these things are looked at more seriously by the FAA, I would suggest not saying anything.	ADD is not a disqualifying condition, however if you have a formal diagnosis of ADD or ADHD My recommendation is to not say anything.
What aircraft can make these sharp 90-degree turns? I took this photo when I saw a plane make a crazy 90 degree turn. What kind of aircraft could do this? I have a plane finder app for commercial aircraft and this plane did not show, which is the first time that's happened. <Q> It looks like a 90 degree turn, but it isn't. <S> You're not looking vertically up at it; you're looking at a fairly shallow inclination, maybe only 20 degrees elevation at the corner of the turn. <S> It means that the actual course change is probably only about 20 or 30 degrees, and just looks like more because of the optical effect of foreshortening . <S> As for the aircraft, pretty much anything capable of flight at high altitude - probably 30,000 to 40,000 feet - any jet airliner or many business jets. <A> We looked at how tight a turn a Boeing 747 can make in this question . <S> The answer gave a radius of just 6.11 km. <S> Your contrail photo clearly shows that the airplane has either one or two fuselage-mounted engines. <S> The 747 was assumed to have a limit of 1.5g for the 6 km turn, but if the aircraft in your photo has a higher buffet and airframe limit, much tighter turns would be possible. <S> The turn radius <S> $R$ can be determined when airspeed $v$ and bank angle $\Phi$ rsp. <S> load factor $n_z$ are known: <S> $$R = <S> \frac{v^2}{g\cdot tan\Phi} = <S> \frac{v^2}{g\cdot \sqrt{n_z^2-1}}$$ <S> If your airplane was traveling at Mach 0.7 in FL300, its speed would have been 212 m/s. <S> Let's further assume it could pull 3g at this speed and altitude, and your turn radius becomes 1.624 km or just about one mile. <S> It is very hard to judge the radius of the contrail's turn section, but it is quite easy to list the characteristics which help to make the radius small: <S> Low wing loading enough thrust to sustain high load factors enough strength to allow for high load factors enough lift capability to allow for high load factors <S> One could add the capacity to fly high enough to be able to form contrails, but this is already implicitly contained in the other conditions. <S> We need something with big wings and a powerful engine - a lightly loaded fighter aircraft in other words. <A> Such a turn from a long distance could look like it is seen in the photo you posted. <A> As Federico said, there is definitely a possibility of an acrobatic or stunt aeroplane, and the first thing that came to my mind when I saw this picture was an Extra 300S . <S> The contrail looks to me like more of a smoke trail (Extra 300 series planes are usually equipped with smoke generators), as towards the beginning of the line the trail seems to be 'bunched up', or wavering. <S> Also, a couple hundred feet (at best guess) from the turn, the line shifts, possibly as a result of wind shear and/or turbulence.	As we do not know which airplane were you observing and neither the airspace it was moving in, one possibility, aside for military aircrafts, it could be that it was an acrobatic one, maybe training on specific maneuvers.
What are the spiral marks in the center of the engines? When I get a chance to peek inside an engine, I noticed that many have spiral marks painted in the center. What is the purpose of these? Pictures: <Q> The benefit of these white markings inside the engine is twofold: <S> The ground crew can tell if the engine is running or not. <S> When an airplane is at the gate before departure, there are several personal attending the airplane. <S> They would be loading luggage, refueling, removing waste products, loading food, etc. <S> etc. <S> . <S> Not all of these people are in constant contact with the pilots and they can come very close to the engines. <S> Although there are several precautionary measures taken before the pilots turn on the engines, it is a very clear visual indication by looking at the spirals to tell if the engines are running or not. <S> Rotor or prop blades sometimes have their tips painted for the same reason. <S> The birds keep away. <S> During flight, when the engine is running, birds see the spinning spiral as opposed to just a black hole, and hence they stay away from it. <S> It is like an anti-bird signal because if there was nothing in the middle it just looks like a cave or black void that birds tend to fly toward. <S> Even though it looks like a blur to us, birds can see motion better. <S> Wikipedia mentions this also: ... <S> it appears as a white circle which discourages birds from flying into the engine. <S> Rolls-Royce brochure (PDF) quoted the following (identified by user BowlOfRed in comment below ) : <S> In flight these swirls flicker as the engine rotates at high speed, scaring birds and allowing them to fly clear of the engine. <A> Not only do they tell you the impeller in spinning, but once the human eye can no longer identify the swirl pattern, it is spinning with enough speed to be an induction hazard (it can suck you in). <S> When parking an airliner, the crew lead guides the aircraft using aircraft marshaling wands. <S> When he/she turns both tip toward each other, the crew set chocks around the wheels. <S> Then NOTHING happens until that crew lead can see those spinning spirals clearly in all engines. <S> Then and ONLY then, does that lead clear the crew to continue operations and begins comms with the flight crew. <A> The spiral on many GE engines is a stylized "G": <S> Source Rolls Royce has a longer spiral. <S> The design helps with ground crew safety, as Farhan's answer discusses . <S> However, it is not required and not all engines have them, suggesting that they are also a matter of style between engines and manufacturers. <S> This page from Boeing about bird strikes says that there is no scientific evidence that spinner markings, airplane colors, landing lights, or weather radar deter birds. <S> On the other hand, the Museum of Flight states that "research has shown" the spiral deters birds. <S> Though I suppose this research could have been unscientific. <S> The AOPA says that "one air carrier detected slightly reduced bird strike rates after painting the jet engine spinners white. <S> " If there is indeed an effect here, it would seem that a spiral would be less effective than painting them white. <S> This paper notes mixed results on using eye spots on aircraft. <S> When used on the ground, the birds seem to get used to them quickly, just as they do with the noise. <S> As costly as bird strikes can be, it would seem that aircraft operators would widely adopt anything shown to help prevent them.	Our aerospace engines have swirls painted onto their spinners in order to indicate when the engine is rotating while on the ground. As a long time ramp agent for Delta and Southwest Airlines, I can tell you they are a critically necessary element to ground crew safety.
Can a passenger request to visit the cockpit during a flight? As a kid, I remember going to the cockpit of a plane with my mom (I believe the airline was AOM French Airlines ). Is this still possible now? I understand the answer might differ with different airlines/countries, I'm mostly interested in European and Asian airlines/countries, specifically Japanese. Is there some specific regulations for international flights, or does it depends on departure/arrival locations? <Q> This stopped after the World Trade Center attacks. <S> You might be able to get a kid in briefly before the plane takes off. <A> Generally speaking, you will not get very lucky unless you are a pilot yourself and are carrying your license with you (and even then, this is airline dependent). <S> If this is the case, you might even be able to ride in the jump seat for a portion of the flight <S> On the ground a lot of pilots/cabin crew are friendly and would be happy to show you around. <S> Use common sense though and ask to go after landing for the best chance - before take off the crew will be quite busy with pre-flight checks. <A> This is usually the case with major airlines with any destination in Europe, or the U.S., not sure abut Asia though <A> Can I ask to go to the cockpit during a flight ? <S> Of course you can. <S> The answer will be a firm " <S> No <S> " and you will be watched very closely by the cabin crew and any plainclothes security onboard until you land. <S> It's possible the police will be waiting for you. <S> Can I ask to go to the cockpit after a flight ? <S> Of course you can. <S> If it's a longer stop the crew are often happy to show off their office. <S> If it's the end of a 12 hour intercontinental flight with a bad-weather landing they might decline. <A> It's a security and/or safety risk to allow any persons in the cockpit these days. <S> This accident happened as a pilot allowed his children to take control during flight. <S> With the autopilot active, Kudrinsky, against regulations, let the children sit at the controls. <S> I've seen flight crashes, in which persons in the cockpit have interfered with the flight in one way or the other. <S> Based on these experiences, unauthorized persons in the cockpit is totally not allowed these days. <A> About 30 years ago I did this during flight when I was a kid. <S> These days I manage to do it for my daughter but only while boarding.	Usually the cockpit is restricted during any phase of flight besides boarding/de boarding.
Why must the throttle be moved slowly? User 'Calphool' writes : For example, in a real plane, if you jam the throttle forward too quickly, you can kill the engine or make it backfire. This may sound like a trivial detail, but people have died on takeoff because they never learned proper throttle technique. Why and how? What accidents were caused by mishandling of the throttle levers? <Q> There are a few ways rough throttle handling on a propeller airplane can get you into trouble: Gyroscopic yaw and torque: a rotating prop creates yaw 90 degrees to its spin which are offset by control inputs (mainly rudder), throttling up or down requires changes to these control inputs. <S> This isn't that big a consideration on lower-powered aircraft but it is on high-performance aircraft. <S> In the first case that comes to mind an inexperienced P-51 pilot rammed full throttle in on a go-around and it flipped the aircraft on its back. <S> At low airspeed it's possible there wasn't enough control authority to manage the forces even if he had been prepared for them <S> Pitch changes <S> : most aircraft will have a pitch change when the throttle is increased or decreased, again quick changes require coarser changes in controls while slower changes mean smoother and better controlled inputs. <S> Again more applicable to higher performance aircraft Engine and carburetor: <S> The engines in most light propeller-driven airplanes represent the pinnacle of 1950's technology. <S> Fuel mixture, priming, and throttle control are all completely manual - there are no electronic systems to help smooth things out during throttle changes. <S> Many airplane engine carburetors do not have an accelerator pump to shoot extra fuel to prevent the engine stalling during a quick throttle up. <S> Given that an engine stall when airborne is a life-threatening emergency it's in your interest to make smooth, controlled changes <S> Although not usually a safety issue wear and tear is also a consideration. <S> Smooth, gentle changes are better for the levers, plungers, and cables in the engine control system. <S> Less wear and tear means better reliability and less costs. <A> This actually happened to me about two months ago. <S> On a very cold night, I went to do my night-currency (3 takeoffs and landings) in a Cessna SkyCatcher (C-162). <S> The plane was hard to start due to the freezing temperatures, but eventually got it going. <S> I did the normal run-up checks, took off, and did one loop around the pattern, coming back for a normal landing. <S> I made a full stop on the runway, reset the flaps, and pushed the throttle forward. <S> The engine instantly died. <S> I told the tower <S> I was stuck on the runway, and he held up some other traffic that was looking to land. <S> Multiple attempts to get the engine restarted failed. <S> Eventually, the FBO sent a tug out to pull me off the runway. <S> Later I talked to the Chief Pilot who was aware of the problem, and most frighteningly of all, said that it definitely could happen in the air. <S> If I had decided I needed a go-around on short-final, and pushed the throttle too quickly, it may have killed the engine when I needed it most. <S> I do not think that I "jammed" the throttle forward, but I may have pushed a little aggressively. <S> I will always be very gentle on my throttle from now on. <S> But what concerns me is those times when you need power quickly (such as a go-around near the ground), you just may not have time to do a slow-and-easy acceleration. <A> Straight from the FAA knowledge tests: Overly-aggressive throttle movements <S> /RPM changes can lead to de-tuning of the crankshaft counterweights.	Quick changes require bigger changes, slower changes give a pilot more time and allows smoother transitions.
Can commercial aircraft dump luggage or cargo mid-air? In a situation where the pilot realizes that weight of the aircraft is too high, can they dump luggage / cargo mid air, similar to dumping fuel? <Q> No they can't. <S> The cargo doors are secured and will not open mid-flight. <S> Cargo holds are usually pressurized so opening the door anyway would cause depressurization. <S> Also if the weight was too high the pilot should never have lifted off in the first place. <S> Then after you theoretically throw the stuff off board think about what happens after to the stuff. <S> It will drop down hard probably on someone's roof. <S> Only some military cargo planes with a back hatch are designed to jettison cargo. <A> There are various examples in history where luggage and/or cargo was dump during flight to reduce weight: Embraer EMB-110P1 Bandeirante, 29 July 1998 : To lose weight, the left overwing exit was opened and luggage of the passengers was jettisoned. <S> Lockheed L-149 <S> Constellation, 29 May 1972 : <S> Cargo was jettisoned, but the aircraft continued to lose altitude. <A> Today? <S> No, not practical... aside from sudden depressurization, the high speed of the aircraft means that anything jettisoned from the aircraft stands a chance of striking tail surfaces with enough force to damage or destroy them. <S> Same goes for the cargo hold - it is also pressurized, with similar problems on sudden depressurization. <S> Unintended opening of the cargo hold in flight has caused more than one crash, and several emergency landings. <S> In those days, aircraft were unpressurized, and flew through the weather, not over it. <S> Aircraft speed was low, <S> around 100-150kts, so things could be tossed out without risking damage to the tail. <S> The lack of ILS at airports meant that those airports would close more frequently due to poor visibility. <S> It was possible for an airliner, even with good fuel reserves, to run low on fuel if heavy fog closed all airports within the range of the aircraft. <S> One way to keep the plane in the air longer was to dump luggage to lighten the aircraft. <S> In his book Fate Is The Hunter , Ernest Gann <S> describes preparing to dump luggage from an ice encrusted DC2 - up to four inches thick in some places on the aircraft. <S> They didn't take that step, but were prepared to.	In the early days of commercial aviation, dumping luggage due to low fuel was not unknown.
What type is this aircraft, appearing in the movie "Kingsman"? In a scene of the movie Kingsman: The Secret Service the young aspiring agents have to skydive from an airplane. I didn't recognise it: which airplane is it (assuming it actually exists)? I could only find a picture from inside and one from below . <Q> - (Image Source: WikiPedia - Author: Adrian Pingstone) <A> It was built in Belfast at the Short Brothers facility, near to the then RAF Sydenham - now George Best Airport. <S> My father worked for Shorts as a senior design engineer. <S> In the late 1960s I was able to visit the assembly floor. <S> I was aged nine or ten. <S> I saw part-completed early variant Skyvans. <S> from time to time, I saw the finished planes over Belfast Lough as they were subjected to test flights. <A> It is the Shorts SC-7. <S> You can see the short nose compared to the C-23 Sherpa. <S> I too thought C-23 because I worked on them in the US Air Force.	That distinctly squarish shape looks like a Short SC-7 Skyvan 3-100 , especially since the registration on the photo from below is visible: G-BEOL . Indeed, this is a Skyvan.
What is the minimum distance allowed between two parallel runways? Is there an international regulation for this matter or does it differ from one country to another? <Q> In the United States, the FAA has published Advisory Circular 150/5300-13A, <S> Airport Design , which includes standards and recommendations for airport design, including parallel runway separation. <S> In summary, <S> For simultaneous IFR operations, "Dual simultaneous precisioninstrument approaches are normally approved on parallel runwaycenterline separation of 4,300 feet (1311 m). <S> On a case-by-casebasis, the FAA will consider proposals utilizing separations down toa minimum of 3,000 feet (914 m) where a 4,300 foot (1311 m)separation is impractical. <S> This reduction of separation requiresspecial high update radar, monitoring equipment, etc." <S> Note: <S> Simultaneous Offset Instrument Approaches allow as little as 750 ftbetween runway centerlines. <S> International regulations do differ. <S> ICAO have their own standards. <S> Here is an example of a document which prescribes airport standards compliant to ICAO Annex 14. <A> Based on ICAO doc9157 Aerodrome Design Manuel Part1 Runway, the minimum distance between centre lines of 2 parallel( or near-parallel ) runways is For Visual Meteorological Conditions (VMC) operation: 210m for category 3( runway length=1200m-1800m ) and category 4( runway length>1800 <S> m ) <S> 150m for category 2( runway length=800m-1200m ) <S> 120m for category 1( runway length<800m ) <S> And for Instrument flight Condition (IMC) operation: <S> 1035 <S> m for independent parallel approaches ( radar separation minima between aircraft and adjacent centre line is not prescribed) <S> 915m for independent parallel approaches <S> ( radar separation minima between aircraft and adjacent centre line is prescribed) <S> 760m for independent parallel departures or Segregated parallel operations (one exclusive for departure and another for landing) <S> PS: It can be reduced by 30m for each 150m arrival runways is staggered toward arrival aircraft down to 300m between centre line of two runways; and vice versa (but no maximum) <S> When two runways are closer than the regulations above, only one can be "operated" at the same time (eg: LGW). <S> Even though only one of the parallel runway would be operated at the same time, the separation of the runway have to follow the "Runway strip rule", which is 75m each side from the centre lines for category 3/4 40m each side for category 2 30m each side for category 1 <S> Therefore minimum distance of two parallel runways is the sum of the strips,ie: minimum distance of two parallel 4E/F runways is 75+75=150m from their centre lines. <S> The above is global standard which represents the minimum requirement of runway , other aviation authorities such as FAA in US may have stricter standard. <A> The distance between the runways is not the issue. <S> Some of them are just a hundred feet apart. <S> The issue is that the closer the runways are, the more separation the planes using those runways must have, and the higher the IFR minima. <S> For example, below is a picture of Oakland International. <S> The two smaller GA runways (28L and 28R) at the top are close together, but when the field is IFR, only one of them can be used for IFR operations. <S> The runway at the bottom (29) is a commercial runway, but it is far enough from 28L that Oakland can have simultaneous IFR operations on 28L and 29. <S> This page gives you a pretty good idea of what to expect.	"For simultaneous landings and takeoffs using VFR, the minimumseparation between centerlines of parallel runways is 700 feet (213m)."
Can VOR indication be reliable if one of its antennas breaks? What will be the reliability of the VOR indication inside the cockpit if one of the two outside antenna is broken ? Can we trust it to make a VOR approach? What will be the consequences assuming that we are in a general aviation aircraft like cessna 150 / 172 / 182 . Picture of antenna: (Image Source: http://www.simmer.fr/ ) <Q> No, it should not be used. <S> Twin antennae, as you have shown, are balanced and fed into a balun ( BAL anced to UN balanced) to feed the single transmission line to the receiver. <S> Together, they provide the correct impedance for the aerial system. <S> With an antenna broken, it is likely that the impedance of the circuit is wrong and therefore, the input to the receiver is, at best, suspect. <S> [GUESSWORK] <S> It's impossible to predict the indicated behaviour without knowing precise details of the aerial fit but a reasonable guess would be that the standing wave ratio in the feed will be altered and therefore, a phase error will be introduced. <S> The magnitude of the error will vary in proportion to the sine of the actual phase angle so my guess would be that the bearing will be accurate when due South or North of the VOR then increasingly inaccurate as you move round with an maximum error at 90 or 270. <S> [EDIT] Early in the morning when I first wrote this <S> but I think I am wrong about being accurate due North or due South. <S> It will be accurate somewhere on the compass and at 180 degrees opposite to that, with increasing inaccuracy as you move towards 90 degrees away from that somewhere. <S> Only calibration would tell you where the somewhere is. <A> The literal answer is, who knows? <S> The only way to find out for sure would be to calibrate the VOR and observe the deviation - if any - from the expected readings. <S> The instrument manufacturer might have some general guidance, but no one can predict the results of physical damage accurately. <S> But having said that, it doesn't really matter anyway <S> : you shouldn't be doing anything that requires a VOR if you know that the equipment is broken. <S> Even if it still seems to be accurate despite the missing antenna, what happens if you lose the other antenna? <S> Or some broken wiring starts causing intermittent false readings? <S> And although this is getting away from the exact question that you asked, there are regulations to consider. <S> You didn't mention a specific jurisdiction, but let's assume US/FAA for now, <S> I'm guessing the general rules are very similar in most places. <S> If you're VFR then you don't need a functioning VOR anyway: by definition, you will never be relying on it for anything because you're navigating visually. <S> It might be helpful to have a VOR in VFR, but it isn't required . <S> ( 14 CFR 121.349 does allow for VFR flights on routes where you can't use pilotage, but it also requires two independent navigation instruments.) <S> On the other hand, if you're IFR then it would probably be illegal for you to rely on a VOR that you know is damaged. <S> 14 CFR 91.205 requires "navigation equipment suitable for the route to be flown", and I think it would be difficult to convince the FAA that a VOR with a broken antenna is suitable for navigation. <S> But the most basic point of all is that relying on broken equipment is just dangerous, especially for an instrument approach where you're relying on the accuracy of the instruments to prevent you from colliding with the ground or an obstacle. <S> In my opinion, taking that chance would show very poor decision-making and general airmanship. <A> This means that you may only pick up the VOR when the "good" antenna element is closest to the beacon, and its lower efficiency will mean that the range from the beacon you get a signal will be decreased. <S> The navigation information is all carried in the 30 Herz modulation on the main carrier and the FM subcarrier: nothing in the VOR receiver ANTENNA can affect the phase relationships of the 30 Herz. <S> If the warning flag is not showing, there is adequate signal and the VOR bearing will be accurate. <S> Not good practice to leave an antenna broken in this way, but it is not an issue regarding safety as long as you've got enough signal (i.e. no warning flag). <S> Exactly the same applies if you're receiving an ILS localizer - the information is in the 90 and 150 Herz modulation in this case. <S> As long as the warning flag isn't showing the information WILL BE ACCURATE. <A> VOR's direction doesn't come from the aircraft seeing where it comes from. <S> VOR works by a pulsing omni-directional beacon and a sweeping narrow beacon. <S> The pulse happens each time the sweep is north. <S> Then the heading from the compass is used to see where the beacon is relative to the airplane. <S> (Image Source: Wikipedia - Author: <S> Orion 8) <S> Does this mean that you can use it for navigation with a missing antenna? <S> Not unless the system was designed to compensate for a missing antenna.	The only effect of a broken VOR antenna is that the polar pattern of the antenna will be altered, and its efficiency as an antenna decreased because it will be mismatched to the feed line.
Do aircraft have siren to warn public in case of a crash over land? The recent crash of a Taiwan aircraft, got me thinking, do aircraft have built in siren, which can warn people on the ground of a possible crash to give them some headway. If that is not practicable or feasible, then what solutions are feasible, or one should abandon the idea altogether and think of making planes safer in the first place? <Q> I understand where you are at with this, I'm going to start off with a bit of math to show how it's not workable. <S> Commercial airliners move quickly, even in a controlled glide one is going close to 3 miles (4-5 km) per minute. <S> To give people on the ground enough useful warning to perhaps find some sort of cover you would need to give at least 20 seconds. <S> This siren would have to be able to penetrate the walls of buildings and houses and cut through the background noise of a built up area at least a mile ahead. <S> This is a very powerful siren and you'll have the following challenges: <S> At close range you would deafen anyone nearby, injuring the people you are trying to warn The mechanism to generate this siren would likely be large, heavy, and challenging to design into an aircraft frame <S> You would need a great deal of mechanical or electrical power to generate that amount of noise. <S> If you have no engine power you won't be able to sound the siren, and if your engines are working you won't need to as the engines make very good sirens already <S> There are very, very few cases where a siren such as this would save very few lives compared to justify the costs. <A> No they don't. <S> If you think about it, it is very rare for an aircraft to crash into a built-up area. <S> Anyone hearing it might be as likely to run into the path of the aircraft rather than run away from it. <A> No they don't, crashes over land where the plane was stable enough to provide enough warning to the people on the ground <S> are very rare. <S> The only incident that would have benefited from it which comes to mind is the gimli glider . <A> No, and even if they did you would probably not hear it. <S> Engine noise should be enough to alert someone who is paying attention, but the truth is that the average pedestrian has no cognizance of unusual noises. <S> Also, the odds of hitting a pedestrian are extremely remote. <S> Most people move around in cars. <S> Unless you are landing on a park or a beach there will generally be noone around. <S> I did hear of one case a couple of years ago where a guy ran out of fuel and landed on a beach and killed a jogger. <S> The jogger didn't hear him because he was wearing headphones. <S> When you come down it all happens really fast. <S> A pedestrian, even with a lot of warning would have to be paying attention, be alert and react right away. <S> Most people are absorbed in what they are doing and a siren going off 1000 feet away and 300 feet up is not going to be on their radar. <A> They did design one plane with a siren to warn people on the ground. <S> The aircraft was called the "Stuka"The pilot would diligently turn on the warning siren right before he nosed down and dove at 300 miles per hour to accurately release his bombs onto the people he was warning. <S> The warning siren terrorized the general public, so they stopped using it out of consideration for the bomber pilots, who didn't like getting shot down by the military employed to protect the public.	People on the ground would have very little time to hear a siren from an aircraft approaching at a hundred miles per hour or more.
What does it mean for a door to be armed? What does "arming a door" mean? Is the orange tape that's applied over a window related, perhaps as an indicator to people outside that the door is armed? <Q> Prior to departure (usually before engine startup), all the aircraft doors are placed into the armed (or automatic) mode by the cabin crew. <S> Methods of arming vary from aircraft to aircraft, but ultimately the girt bar (a metal bar attached to the door end of the slide) is physically attached to brackets either in or adjacent to the door sill. <S> [...]If a rapid evacuation is required and the doors are opened while "armed", the opening of the door pulls the slide pack out of the bustle (because the girt bar is physically attached to the aircraft floor) <S> This is also the reason for the famous All doors in flight announcement : DOORS TO ARRIVAL AND CROSSCHECK <S> “Flight attendants, doors to arrival and crosscheck.” <S> Meaning: Occasionally heard as “disarm your doors and crosscheck,” and announced by the lead flight attendant or purser as a plane approaches the gate. <S> The intent is to verify disarming of the emergency escape slides attached to the doors. <S> When armed, a slide will automatically deploy the instant its door is opened. <S> Disarmed, it needs to be deployed manually. <S> On departure the slides are armed to facilitate an emergency evacuation. <S> (You might hear this as “doors to automatic.”) <S> Upon docking, they’re disarmed to keep them from billowing into the boarding tunnel or onto the apron during servicing. <S> The orange or yellow tape is a visual indicator for ground workers or ramp agents that the doors are armed or not armed. <S> The visual indicator can vary, it can also be built into the door lock mechanism, triggering a visual indicator externally if the door is locked and armed. <S> In the following picture, the orange tape is not strapped over the window, which should indicate an unarmed door. <S> In the video that this image is taken from, the flight attendant has just locked and possibly armed the door, the other flight attendant would place the orange tape over the door window during "cross-check". <S> (Image Source: YouTube " <S> B757-200 Door Closing" - Author: Exupery747) <A> When the door is armed, the slide will deploy when the door is opened. <S> The tape is indeed an indicator to people outside that the door is armed. <A> Yes. <S> Someone can (and unfortunately has) opened an aircraft door while still armed. <S> Some aircraft have an indicator that is visible from the outside indicating the door is still armed. <S> Other aircraft require indincation from flight attendants (such as a thumbs up) indicating the door is disarmed. <S> Older single isle aircraft <S> (727 DC-9) the slides would fall out of slide pack but not inflate. <S> Flight attendants would have to pull an inflation handle at the part of the slide attached to the floor of the aircraft after opening the aircraft door. <S> This was an economic feaure for airlines as slide deployment are expensive. <S> If the slide deploys but not inflated they were just rolled back into the protective covering. <S> However these were dangerous in actual emergencies as flight attendants would have to reach down and inflate slides and could be pushed out. <S> The ones that automatically inflate are dangerous if opened accidentally if they are deployed into a jetwat or catering vehicle	If a door is put into armed mode , it will trigger the evacuation slide when the door is opened.
Do emergency services helicopters fly VFR when leaving base? I've recently been watching an interesting documentary on helicopter paramedic teams. As you all probably know, their job consists of a lot of sitting around doing nothing before a scramble and then a short (or not-so-short) flight out to the middle of nowhere and back again. On the (UK) documentaries I've seen, the aircraft are usually based at reasonably large commercial airports, physically located close to the fixed-wing runways. In order to find the guy lying injured in the field and help him out of asystole, they have to rapidly launch from a presumably busy airspace, and get there ten minutes ago. Do airports have procedures that allow them to always assume an "exit route" is always okay, under some ceiling? Do they have to get take off clearance as other private aircraft would? I understand that they get given priority ATC clearance when in controlled airspace , but quite often their target call-to-takeoff times are less than two minutes, and it seems unlikely that the nearby 777 on FA would be done that quickly. What happens if it's not possible to be VFR entirely on route? I have seen cases reported where difficulties are encountered due to fading light halfway through treating a patient -- meaning that the pilot is worried he can't take off again. It seems rather odd that, if a pilot was able to land in a field comfortably with good visibility, he can't ask for a route to be cleared, file a flight plan, and go to hospital IFR. For that matter, how do police helicopters chase the bad guys at night in zero visibility? Disclaimer : I've never set foot in a helicopter in my life, but have a single-digit number of hours in light aircraft -- sick people are more my forte. <Q> If the helicopter is operating at an airport, it needs clearance like a regular flight, otherwise it would be a very dangerous situation for the helicopter and any other traffic in the area. <S> Usually the ATC will give priority to the emergency helicopter (as much as possible), so it will leave the area without delay. <S> Regarding the weather conditions, there are two aspects that need to be considered: <S> The regulations allow emergency helicopters to fly VFR below VMC minima (this is true in Europe, I have no idea about FAA). <S> So, an emergency helicopter, can continue VFR with visibility down to 1km, or even 800 meters for short periods of time. <S> If the helicopter is IFR equipped and <S> the pilot(s) IFR rated, it can switch to IFR if necessary. <S> On the way to the accident site this might not be very useful if the weather will not allow safe descent and switch to VFR, but on the way back to the airport/hospital, it can be very useful, provided <S> the landing site has some kind of IFR procedure. <S> Again, ATC will usually offer full cooperation in all this switching of plans and flight rules. <A> I dont fly rotorcraft but I do interact with emergency choppers in 2 ways. <S> I'll speak form what I have seen, I am in Philadelphia (PA, USA) so all my experience is with the procedures around here (FAA). <S> Storage And Takeoff: I am currently doing my training at Northeast Philadelphia Airport (KPNE) where the local police and news choppers are stored (I think the medical choppers are there as well <S> but I have yet to see them there). <S> I have seen them depart often and generally they can get in the air and get out of the way <S> so fast they don't interrupt normal aircraft traffic. <S> I have, on a few occasions, been instructed to extend my downwind for one of them to land or take off <S> but again they are out <S> so fast it's almost a non-issue. <S> Keep in mind that KPNE is not Philly international <S> so I don't know what its like at other cities and if they hold traffic for them. <S> I would think they try to store the choppers at smaller airports near the city for this reason. <S> Most major cities have a few airports anyway. <S> Landing At The Hospital: My apartment happens to be next to one of the major hospitals in Philadelphia <S> and I have the pleasure of looking right at the pad on the roof from my window. <S> That being said I also have the "pleasure" of watching them practice and make approaches at the hospital. <S> I can confirm that they have made landings (and frequently at that) in IFR conditions or even what seems below IFR minimums. <S> I would say in the time frame I am home (after 5pm every day) they make on average one landing every other day or more. <S> If the weather is good, they will try and get more in, I would assume these are practice <S> but I can't see the doors of the chopper <S> so I can't be sure. <S> Bottom line is in my area the rescue choppers do fly IFR. <S> I'll try and capture a picture today <S> (it's very cloudy) if they are on approach. <A> I don't fly rotocraft, but I can tell you if the airport is of any size they have to get a clearance unless they want to be turned into a hood ornament. <S> If the helicopter is pre-flighted and ready to go, it only takes few seconds to get a clearance, so it will not normally cause a delay. <S> Concerning IFR Flight: rotocraft require special equipment to fly IFR and it is much, much more dangerous than flying aircraft IFR because you are landing off field. <S> Note that flying at night is not the same thing as flying IFR. <S> If the sky is clear it is VFR, even if it is night. <S> Being on a medivac crew is the most dangerous regular job in the United States and hundreds have died doing it.	Each operator and pilot have different policies, but in general police helicopters will rarely if ever fly IFR, and medivacs will only fly IFR if they judge it safe.
Why do jet engines use kerosene rather than gasoline? Could you run a jet with gasoline? Why do all jet engines use kerosene? <Q> You can persuade a turbine engine to run on just about anything that can burn. <S> So the decision of which fuel to actually use depends on the side factors including, but not limited to: availability cost emissions <S> hot section temperature chemical reactions with engine parts Specific examples: <S> Coal dust is rather difficult to pump around, and the rampies don't like shovelling liquid hydrogen (used in the Space Shuttle) requires a lot of storage and has the nasty habit of freezing anything it touches, like rampies. <S> ethylacetylenedecaborane is unpleasantly toxic (rampies union again) and the combustion byproducts were rather abrasive to the engine's innards trimethylaluminum would reduce the engine complexity (no igniters needed) because it has the nasty habit of igniting instantly upon contact with air, so leaks are rather dangerous. <S> natural gas is commonly used as a turbine fuel in pumping stations: it's already there and thus is "free". <S> The required pressure vessels make it impractical to use as an aircraft fuel. <S> So kerosene basically became the standard turbine fuel because it's: <S> cheap: kerosene makes up a rather large fraction of crude oil. <S> When you measure your fuel load in tons a few cents per litre makes a difference. <S> safe to handle: relatively non-toxic, doesn't ignite all that easily storable and transportable in common structural metals <S> doesn't clog up the engine <A> In a modern turbofan engine, fuel is not only burned in the engine and used to lubricate parts such as fuel pumps and controls, it is used as a hydraulic fluid as well -- <S> this is used to power things like inlet guide vanes and variable stator vanes in many engines, as well as more exotic accessories such as movable nozzles and inlet ramps. <S> This means that gasoline is often not tolerated by larger aviation turbines, as it boils at such a low temperature that it could boil off inside fueldraulic (or other fuel system) parts and interfere with their operation, atop the lubricity and lead fouling issues that it obviously would pose. <S> Even wide-cut jet fuels such as JP-4 and Jet-B are prohibited for service in some larger turbofans due to the volatility issues they pose (this is a quote from the 777 QRH Limitations section): <S> The use of JP–4 and Jet B fuels is prohibited. <A> From my training, the limits on the PT6 use of avgas is related to its ability to lubricate the engine's fuel pumps, and the lead fouling of the hot section which will result from the avgas. <S> I can't say about other engine's tolerances, but some military jet fuels have much more volatile components than straight kerosene and marine gas turbines run on diesel. <S> A turbine's fuel isn't always decided by what it can burn, but by what it's practical and economic to feed it. <A> Apologies if this is tangential but other properties of kerosene (aka kerosine) as turbine fuel were brought up. <S> Another property of jet fuel that was not mentioned is freeze point where viscosity drops because of wax formation and pumps and filters begin to clog. <S> Ordinary kerosene (as used in lanterns and space heaters) rarely has to deal with sub-zero temperature (e.g. -40C) and 30,000 feet altitude. <S> Also important is volatility which can be reduced at low temperatures and impede combustion. <S> see <S> http://www.shell.com/global/products-services/solutions-for-businesses/aviation/shell-aviation-fuels/fuels/types/civil-jet-fuel-grades.html for different fuels and <S> their freeze points. <A> The very high temperatures of jet engines cause gasoline to be a poor fuel because it tends to burn too fast. <S> Kerosene, which is routinely called "Fuel OIL" some places, avoids pre-ignition problems (and some safety hazards) just like higher-octane gas avoids spark-plug knocking. <S> The ultimate control of ignition comes from using Diesel Fuel (which ALSO is routinely called Fuel Oil some places), and that's why big trucks use Diesel <S> : that control gives them the best fuel efficiency their engines can have; but Diesel wont' run a jet engine. <A> We ran Olympus Gas turbines for fast power and speeds when I was in the Royal Navy. <S> These happened to be the same turbines that Concord used when she was in service. <S> We ran them on Marine Quality Diesel and had no problems. <S> Again may be its the - temps could be a real issue, and the fact you get more power from Higher octane fuels, with all the technology these days you would think their would be a cheaper alternative.	Gasoline is too volatile for a jet engine; Diesel fuel is not volatile ENOUGH for a jet. To my knowledge, all "Jet fuels" (intended for aircraft use) are based on kerosene.
Do planes return to service after non-fiery crashes? A Turkish Airlines flight recently ran off the runway and ended up on its belly in a field. The landing gear were damaged, but the plane didn't burn and the fuselage remained intact. Are planes involved in this sort of accident repaired and returned to service, or are the planes usually scrapped? <Q> If the aircraft can be economically repaired (there is no major structural damage, and we're not talking about an aircraft already scheduled to be retired) <S> then it's likely the aircraft will be repaired and returned to service. <S> When you spend several million on an aircraft you aren't going to throw it away for a few tens or hundred thousand dollars worth of damage, particularly as it's probably insured. <S> If the aircraft is structurally compromised to the point where repairs would not be economical (or if we're talking about an older aircraft which has given many years of service and is due for retirement) it would probably be written off and scrapped for any salvageable parts (either repairing it to a condition where it could be ferried to a " boneyard " or dismantled and cut up at the accident site - whichever option is less expensive for the airline). <S> As one particularly famous datapoint, the Gimli Glider had an off-airport landing with a nose gear collapse in 1983. <S> The aircraft was repaired, returned to service, and flew until 2008 (a little under 25 years of additional service after its incident). <A> Yes, some even after a fairly fiery crash. <S> Here are some photos and a video illustrating some very interesting cases (ALCI Lidia 2012-13 crash and recovery and ALCI Mia accident in 2009). <S> Here they even say that the airframe was totaled ten years prior to this accident and repaired a year after that. <S> Edit : Factual corrections about the video <S> (thank you @DeltaLima). <A> I don't know about large aircraft, but for smaller aircraft it is usually dependent on whether a structural member was damaged, especially a bulkhead.	If a structural member is bent or crushed, then usually a small plane will be unsalvageable, but if structural members are intact and undamaged, then usually the aircraft can be repaired.
How can an airplane land if a hail storm damages the windshield? I understand hail can be very damaging to an aircraft, in particular to the engines and windshield. In the event that a windshield becomes cracked so that visibility is impossible, can pilots pop out the windows when at a lower enough altitude in order to see the runway? <Q> In the EMB-145 the abnormal procedure for obscured windscreens is to secure items in the cockpit, open the side window and look through its opening. <S> There are more aircraft that share this procedure. <S> Here is the QRH procedure for "Impaired or cracked windshield" in the EMB-145: <S> Associated Windshield Heating .............................. <S> OFFIF <S> only the outer layer (glass) is cracked, no action is requiredIF inner layer of glass is cracked, proceed as follows: <S> Cockpit Door ......................................... <S> CLOSE <S> Maximum Altitude ....................... <S> 10,000 FT. <S> , OR MEA, WHICHEVER IS HIGHER Pressurization Manual Controller ........ <S> 1 <S> O'CLOCK POSITION Wait 15 <S> Seconds Pressurization Mode <S> Selector <S> ........................... <S> MAN Cabin Delta-P <S> ........................... <S> SET EQUAL TO 1 PSI <S> Note: <S> Pressurization Manual Controller must be used to set and maintain Cabin Delta-P at 1 psi while descending Airspeed .................................... <S> BELOW 250 KIAS Smoke Goggles .......................................... <S> DON <S> In case both windshields are impaired: Cabin (below 10,000 ft) ....................... <S> DEPRESSURIZE <S> Airspeed ................................. <S> MAXIMUM 140 KIAS, <S> MINIMUM VrefIF <S> forward view through both wind screens is impossible, secure loose objects in cockpit and proceed: <S> Note: <S> Intercommunication will be impossible with window removed. <S> Direct Vision Window ................................ <S> REMOVE <S> Landing must be made looking through the direct vision window <S> * * * * <A> They use instruments instead. <S> BA flight 9 had it's windscreen rendered somewhat opaque by volcanic ash <S> As Flight 9 approached Jakarta, the crew found it difficult to see anything through the windscreen, and made the approach almost entirely on instruments, despite reports of good visibility. <S> The crew decided to fly the Instrument Landing System (ILS); however, the vertical guidance system was inoperative, so they were forced to fly with only the lateral guidance as the first officer monitored the airport's Distance Measuring Equipment (DME). <S> He then called out how high they should be at each DME step along the final approach to the runway, creating a virtual glide slope for them to follow. <S> It was, in Moody's words, "a bit like negotiating one's way up a badger's arse." <S> Although the runway lights could be made out through a small strip of the windscreen, the landing lights on the aircraft seemed to be inoperable. <S> After landing, the flight crew found it impossible to taxi, due to glare from apron floodlights which made the already sandblasted windscreen opaque. <S> From Wikipedia <A> If the windscreen is damaged, blocked, or iced-over, the captain can fly on instruments to the airport, then land by opening and looking out the little window. <A> If the aircraft has what is known as auto land, the auto pilot can land the airplane, so the pilot has that as an option. <S> However, you can approach the runway in what is known as a forward slip. <S> Using a lot of rudder, the tail will move to one side, this moves the nose to the opposite side, allowing the pilot to see forward, looking out the side window. <S> The pilot also simultaneously uses opposite aileron, to counteract the turn, using the rudder would initiate. <S> Once over the runway, at about 50 feet, the pilot would straighten the plane out, and begin the landing flare. <S> He can then use the view of the the runway edge line, out his side window, to keep the plane aligned with the runway. <S> A radar altimeter gives precise reading of how many feet he has to go, as he descends to the pavement. <S> So, the pilot knows where he is. <S> These things are practiced by flight crews in simulators twice a year. <A> Pilots tend to use the view out of the side windows in their peripheral vision to judge height above the runway, so provided you could see the approach lights at some point to know you are on the centre line, its not as bad as it sounds. <S> There are numerous examples in history of aircraft landing with oiled up, or iced up windscreens. <S> Also it might be possible in some situations/aircraft to fly a curved approach then use the side windows in the final seconds of flight. <S> My view is that the reason why the wind shield is opaque was probably a bigger risk to the aircraft than actually landing with it in that condition.	Some airplanes, like the Pilatus PC-12 pictured below, have a captain's side window that can be opened during landing so that the pilot has a direct view of the runway.
Will ATC proactively route traffic around bad weather? When thunderstorms or other severe weather crop up, will the Air Traffic Control in the area proactively route traffic (horizontally or vertically) around the trouble area, or do they leave it up to the individual pilots to request an alternate route? My intent was asking about commercial aircraft flying IFR , however the information about general aviation and VFR is appreciated <Q> Yes, ATC will reroute flights that are operating on Instrument Flight Rules (IFR) . <S> There are lots of videos of flights getting routed around severe weather floating around on the internet! <S> Atlanta is a great example, as is Memphis, FedEx's hub . <S> In addition, NASA is working on a product called Dynamic Weather Routes that will help controllers be smarter about amending planned or unplanned weather reroutes. <S> Sort of, for aircraft operating VFR. <S> VFR flights that are talking to ATC may get advisories about weather and suggested headings from the controller. <S> I've received notifications about things like 'moderate to heavy precipitation 5-10 miles ahead' many times when operating on VFR flight following. <A> The system is a combination of both. <S> The controller will have a view of the weather radar for the area, and can route traffic around bad areas. <S> However, the pilots have a better view with the weather radar on their plane, and the pilots have the ultimate decision as to what they will do. <S> The pilots may see a weather return they don't like and ask for deviation around it. <S> Even if ATC denies the request, the pilots are ultimately responsible for the safety of the flight, and should do what they feel is best, even if that means deviating without permission . <S> There is an interesting article here that is a bit dated, but should still apply to the general idea of how ATC handles bad weather. <A> My experience from flying Commercial IFR in Europe is that ATC never proactively re-route around bad weather, but are however usually expedient handling requests from pilots (heading changes to circumnavigate), based on airborne weather radar data.	They will at least advise the pilots of the bad weather that they can see, and can offer the pilots a deviation or let them know what previous flights have done.
Why are aircraft external lights round, not tear-drop shaped? I saw this image of a Cessna 172's tail posted on another question and it made me wonder why the beacon light is basically a cylinder, and not a more aerodynamic, teardrop shape? Image source <Q> That beacon lens (and most of the strobe lenses shaped like it) are actually Fresnel lenses . <S> They are optically designed to produce a specific plane & intensity of coverage, and tinted for a specific color. <S> (The color, intensity, and plane are specified in the FARs & applicable Technical Standard Orders if you want to go hunt down the requirements.) <S> The lens optics are easier to see on the split <S> (Red/White) lenses: <S> A Fresnel lens is not the only way to meet these requirements, some anti-collision lights do it by sheer intensity (while retaining the "jar" shape, mainly for installation compatibility), and as GdD pointed out there are more aerodynamic options available . <S> The Fresnel lens method is usually adequate for smaller/slower aircraft however, and the drag penalty at relatively low speeds isn't significant enough for designers to worry about. <A> Your assumption that all are round is faulty, plenty are teardrop shaped. <S> You'll see round ones on many slower aircraft where streamlining isn't as big an issue, however on faster aircraft they are almost always aerodynamic. <A> Taking a look to the photograph you are showing not only the lights are not very aerodynamic, you can see as well that the fairing on the tail could have a softer transition, the rivets used are not the ones used in commercial het airplanes and transition between plates is also not smooth. <S> You can see that the aerodynamics is open to improvements. <S> Cessna 172 is an small airplane of 3 passenguers and one pilot. <S> Customers of this airplane will be mainly of 2 kinds: <S> Small airlines making short flights between 2 places very close. <S> Private use. <S> Notice that although the airplane has an autonomy of 1200km, usually is not able to compete in routes of that distance as airplanes like A320 will be able to offer a cheaper ticket. <S> Is a typical airplane for travels between islands with low traffic. <S> In that context... <S> For the airline, as there will no be a big traffic, the main cost will be amortization of the airplane, also trips between 2 points will be usually very short, so the most part of the use of the airplane will be in ground taxing the airport. <S> For the private use, it will be an airplane not used regularly and the flying time, in the life of the airplane, will be really limited. <S> In the overall context of the lifetime of the airplane the fuel consumption (driven by the aerodynamic drag) will be smaller than the effect of the amortization of the airplane (capital costs) and maintenance. <S> In order ot reduce aerodynamic drag and fuel comsuption in general (weight reduction), that will imply extra costs on each manufactured airplane: <S> Add-hoc design of components not using standards. <S> Higher quality standards and control. <S> Higher costs of development (NRC). <S> High costs materials. <S> More costly manufacturing shapes. <S> Basically the manufacturer (Cessna) needs to make a decision between: Making a relatively cheaper airplane with higher fuel consumption. <S> Making a costly airplane efficient in fuel consumption <S> In that trade-off, for this specific model and my understanding of the customer objective, is more attractive to create a cheaper airplane.	The answer is overall airplane optimization.
What is the difference between "flight level" and "altitude"? I have seen references to "FL180" and "FL300", and I know that they stand for Flight Level 180 and Flight Level 300. I've also seen references to "an altitude of 18000ft" or "an altitude of 30000ft". What is the difference between flight level and altitude , how do they relate to each other, and when and why would one be used instead of the other? <Q> Flight levels use QNE or pressure altitude, while altitude references QNH or local pressure adjusted to sea level pressure. <S> Altitudes are used at low levels and flight levels at higher levels. <S> The transition between altitudes and flight levels differs by country and is generally just above the highest obstacle in that country. <S> In the US the transition altitude/level is 18,000' / FL180. <S> Some countries transition as low as 5000' <S> / FL050 and the transition altitude/level may vary from airport to airport. <S> In the altitudes knowing accurate elevations relative to the ground and obstacles is important for collision avoidance and this is the reason QNH is used here. <S> Each airport will report QNH and controllers will issue the current QNH as needed. <S> You need to know the QNH for obstacle / terrain avoidance but you need to be using the same QNH as those around you for aircraft vertical separation. <S> Above all terrain/obstacles the only thing we care about is vertical separation, so we no longer need to know about the actual pressure and instead use a standard reference pressure, QNE / 1013.25 hPa / 29.92" <S> Hg. <S> Note that flight levels drop the last two zeros of the corresponding altitude and so 30,000 is FL300, not FL30000. <S> When checking in with a controller, FL300 would be pronounced flight level tree zero zero . <S> It is also worth noting that an altimeter cannot actually determine altitude. <S> It can only determine pressure (technically local static pressure compared to a reference pressure). <S> It converts this pressure to an altitude using a calibrated non-linear scale. <S> To illustrate the point, look at this map of 500 mb heights: 500 mb correlates to 5500 m or 18,000 ft in a standard atmosphere. <S> In a real atmosphere this height varies and is not actually level. <S> An airplane flying "level" at FL180 from LAX to NYC last night will have actually descended almost 300 m while indicating a constant altitude. <S> These deviations in true altitude from indicated altitude are acceptable, however, since they effect everyone equally in the same locality and separation is maintained. <A> FL180 and FL300 stand for Flight Level 180 and Fight Level 300. <S> Flight levels are spaced 100ft apart on an altimeter that is set to the standard sea level pressure (QNE) of 1013.25 hectopascals or 29.92 inches of Mercury. <S> So indeed, FL300 means 30,000 ft. <S> Altitude 18000 means that the altimeter indicates 18,000 feet and that the altimeter is set to the QNH, which is the pressure reading on the ground corrected to sea level pressure using the standard atmosphere. <S> When there is a low pressure area, the QNH will be lower then 1013.25 hPa. <S> When you compare two altimeters; the first set to QNH < 1013.25 hPa and the second one is set to the standard setting of 1013.25, the first altimeter will indicate a lower value than the second altimeter. <S> QNH setting is used at lower altitude where obstacle and terrain clearance are important. <S> But for long distance traffic it is a nuisance to change the altimeter setting as the aircraft flies through different pressure areas on the ground. <S> Therefor the Flight Level concept was introduced, allowing everybody on higher altitude to use the same setting. <S> This also reduces the chance that aircraft have a different altimeter setting in the same airspace, which would cause vertical separation problems. <A> Altitude The vertical distance of an object measured from mean sea level. <S> Flight Level <S> To display correct altitude, a pilot re-calibrates 1 the altimeter from time to time, according to local air pressure. <S> Flight levels solve this problem by defining altitudes based on a standard pressure of 1013.2 mb (29.92 inches Hg). <S> All aircraft operating on flight levels calibrate to this same standard setting regardless of the actual sea level pressure. <S> Flight levels are then assigned a number which is the apparent altitude ("pressure altitude") to the nearest thousand feet, divided by one hundred. <S> Therefore an apparent altitude of 18,000 feet is referred to as Flight Level 180. <S> Note that aircraft may be at some other actual height than 18,000 feet, but since they all agree on a standard pressure, no collision risk arises. <S> Flight levels are not used close to the ground, for perhaps obvious reasons - obstacles are fixed to the ground and so their absolute height needs to be known. <S> The altitude of the lowest flight level varies from country. <S> 1 <S> : Re-calibration of altimeter is done to avoid airplanes flying at the same height, though their altimeters show different altitudes. <S> This is safety issue.	To understand a flight level, we should understand how altitude is measured in an altimeter, which is essentially a calibrated barometer - it measures air pressure, which decreases with increasing altitude.
What are the pros and cons of a pulsejet? I've heard pulsejet powered aircraft can fly at very fast speeds but are there any drawbacks to this type of engine? And are the disadvantages greater than the advantages or vice versa? <Q> Consequently, it needs speed to work well. <S> If the pulse jet is on the ground, it is not easy to start - it needs to be fed with compressed air, and once it runs (it can run even when not moving because the oscillating pressure wave inside the tube will compress the inflowing air), it develops litte thrust. <S> Thrust will go up with airspeed, so you need additional thrust sources for initial acceleration and take-off. <S> In case of the V-1, this was done by a steam catapult or by air-launching the device. <S> Note that the V-1 was accelerated to 370 km/h on a 45 m long catapult which means more than 100 m/s² (10g) average acceleration. <S> Most of the development work went into making the airframe withstand this acceleration. <S> A modern design would need additional engines as well, and once those are included, the rationale for pulse jets becomes very weak. <S> They make sense if you have an air-launched, disposable application, such as long-range air-to-air missiles. <S> This is a niche in which their higher-speed cousins, the ramjets, will still be used . <S> Pros: <S> Runs and produces some thrust when at rest (as opposed to ramjets). <S> Cons: <S> Thrust grows with flight speed. <S> This can be seen as a pro, but normally requires additional means of acceleration. <S> Therefore listed as contra here. <S> Low fuel efficiency. <S> The fuel energy is converted to other forms of energy: Just listen to the videos of Colin Furze to get an idea. <S> High levels of vibration due to the intermittent operation. <S> When the Heinkel 280 was tried out with Argus pulsejets , the aircraft experienced unacceptable vibration. <S> Need heat-resistant materials. <S> The central part will get very hot in operation, so at least nickel-chrome stainless steel is needed if air cooling is insufficient. <S> Cannot go supersonic. <S> For this, there are ramjets . <S> EDIT: <S> NACA tested the As 014 pulse jet and wrote a report , from which the performance data depicted below is taken: It seems that Bruce Simpson over in New Zealand has improved the pulse jet design a lot: He needs no compressed air for starting and makes clever use of surrounding cold air to increase mass flow and keep material temperatures down. <A> First of all they are loud <S> there is a reason that the V1 bomb is called the "buzz bomb". <S> They are also fuel hungry due to the low compression ratio. <S> The biggest advantage it that they are very simple. <S> Once you have them ignited they will continue to burn until they run out of fuel or the airflow is disturbed. <A> Pulse jets were big during WWII but the have a few issues. <S> Advantages: <S> Aside from throttle flaps pulse jets have essentially no moving parts which makes them not only simple to build but simple to maintain. <S> People build them in their garages at home all the time. <S> From a war time standpoint this was great since you could make many of them in a short time. <S> Disadvantages: <S> Noise: <S> Pulse jets are much louder than their spinning counterparts. <S> This makes them some what less useful from a stealth/wartime standpoint and from a commercial standpoint in regards to general noise pollution concerns. <S> Low Impulse: <S> From my understanding of them pulse jets have a low specific impulse due to their more piston like ignition pattern. <S> They don't deliver the kind of thrust their fan like counterparts can. <S> Size: <S> If memory serves they are also much bigger than a regular jet (for a given power output). <A> Disadvantages : <S> Very low thermodynamic efficiency due to very low compression ratio. <S> Therefore they are not very fuel efficient. <S> They consume a lot offuel. <S> Reed valves fatigue quickly. <S> Reed valves can also be subjet to heatand loose their temper. <S> Bruce Simpson has done a great deal of workto improve the lift of reed valves. <S> High temperatures involved. <S> Valveless pulse jets tend to be less efficient than valved (but a lot simpler). <S> Most of the literature on valveless pulse jets is substantially incorrect as to what is happening with the gas flow within the engine. <S> Advantages : <S> Simplicity <S> Pulse jets can be designed to develope maximum thrust at stand still or at any particular sub-sonic speed. <S> If they are designed for maximum thrust at a reasonably high speed then their stand still thrust will be low. <S> A low velocity pulse jet will suffer from the flame tending to be blown out the back of the engine as the forward velicity increases. <S> There are ways of making pulse jets so they can develope maximum thrust over a wide speed range. <A> One other advantage of pulse jets is: they are dirt cheap to build, as compared to other forms of aircraft engine. <S> A primary reason they were used in the V1 was their very low cost. <S> One other disadvantage: they really have only one efficient power output: their maximum. <S> While this does vary with airspeed, it also means that pulse jets can't really be throttled down without risking a flameout. <S> That would make landing a pulse jet aircraft a challenging affair. <S> Since the V1 was never designed to make a controlled landing with a pilot on board, that wasn't an issue.	The pulse jet engine works because it uses the dynamic pressure of air for compression. Very easy to build, very light. They are very very noisy.
Why is there a compressor in an air cycle machine? I'm a curious high school student. Why is there a compressor after the first heat exchanger in an air cycle machine ? I've read that compressing the cold air is for the cause of efficiency because compressing hot air uses much more work than cold air, and the effect of this is that the compressed air temperature increases. But if so, why compress at all when the air itself is going to be cooled again in the second heat exchanger? Why not leave the compressor and place the turbine as it is from the ACM? <Q> If I understand your question correctly, you don't really understand how the ACM works. <S> The idea of an ACM is to create 'cool' air. <S> Especially on the ground <S> (imagine landing on your tropical holiday destination), this means that the air must sometimes be made cooler than the outside (ambient) temperature. <S> The second law of thermodynamics (and in this case, the law of common sense) states that you can't just cool your air against the warm ambient air, so you will need to do some special tricks. <S> In this case, the special trick is compression. <S> You compress the air, which will make it quite hot ( increase the temperature ) <S> (search for adiabatic compression on the internet). <S> Then, this hot air can of course easily be cooled against ambient air, which happens in the second heat exchanger. <S> In fact, the hotter the air after compression is, the more heat is exchanged in the second heat exchanger. <S> This means the heat exchanger can be made smaller, which is especially useful since air-to-air heat exchangers are inefficient and thus relatively big . <S> Now, you expand your air again, which will cool it ( decrease the temperature ). <S> However, since you already cooled it down in the second heat exchanger, it will now be cooler than when it originally encountered the compressor! <S> This makes sense, since you removed energy from the air in the second heat exchanger. <S> So, this way, you can cool the air down further than would have been possible by a heat exchanger (search for reverse Brayton cycle on the internet). <S> So, this system has two advantages: <S> It is possible to cool down air beyond ambient temperature, so it functions as 'airco' on the ground or at low altitude. <S> It is possible to cool hot compressed bleed air with a relatively small, light heat exchanger for pressurizing your cabin while not cooking your passengers medium-rare. <A> Because there is an expansion stage, the energy of the compressed air can be used to run a second compressor. <S> Doing this allows to cool the precompressed air before it is fed to the second compressor, thus improving overall efficiency. <S> For the same reason, some turbocharged engines use two turbocharging stages with an intercooler between the compressor stages. <S> You could also extract the air at a later stage of the engine compressor, cool it and expand it in a diffusor, but then the engine compressor has to do more work and the cooler needs to be bigger due to the higher temperature and lower density of the compressed air. <S> But somehow you still need to shed the pressure energy in the air, and running it through a turbine is an ideal way to achieve this. <A> The ACM has a nozzle in the turbine which compression and rapid expansion of air through the conical holes of the nozzle, and inducer and exducer blades of the turbine wheel pulling and pushing air at high RPM's produces the cold air. <S> Primary cools down bleed air from engine for perameter required, then temperature leaving compressor discharge into secondary heat exchanger cooling down air sufficiently for turbine inlet air temperature requirements and turbine discharge temperature. <S> Example, testing HONEYWELL ACM for 757, and 767, from primary to compressor inlet is 197 to 207 deg. <S> F. comp discharge temp is about 285 deg. <S> entering secondary then exiting at 205 deg. <S> F entering turbine inlet and outlet discharging at 25 deg. <S> fer. <S> or less. <S> from turbine scroll. <S> Also, the RPM is 46K to 51K. <S> Some smaller ATR ACM's go over 100k.	It keeps the volume of air low and allows for smaller, more efficient turbochargers.
How quickly could a commercial airline integrate advances in technology into its fleet? How quickly would a commercial airline be able to integrate significant advances in technology into its fleet? Specifically I am interested in large commercial airlines and advances in technology that would substantially increase the efficiency of fuel consumption in passenger aircraft, but I don't have enough of a background in commercial aviation to make an educated guess and have not been able to find a comparable historical example. If someone could provide me with either it would be much appreciated. <Q> It depends on the advance. <S> Generally, there are three ways how airliners can be improved: Operations and procedures: This can be as simple as faster turn-around times so aircraft will be more profitable, or as complicated as doing away with airways which would help to shorten trips, but depends on changes in regulations which have been in place for decades. <S> Better equipment: All parts of an aircraft are designed to be individually replaceable, and swapping old engines for newer, more fuel efficient ones will bring already two thirds of the efficiency benefits of replacing the whole aircraft. <S> Other examples could be less heavy furnishings or more precise instruments. <S> But there are limits, and every change needs to be approved by regulatory authorities. <S> Newer aircraft models <S> : This brings aerodynamics, engines and equipment up to the status quo, and is done by airlines on a regular basis to improve both their attractiveness and their profitability. <S> Examples are Singapore Airlines , which pride themselves on an average age of their fleet of just seven years, or Vueling , which thanks to a recent expansion has lower seat-mile cost than all their competitors. <S> Generally, the days of dramatic technology advances are long gone. <S> Today, years of research are justified by single-digit percentage advances, and a new development like the A380 is started with a promise of just 15% less seat-mile cost when compared to airliners which are two decades old by the time the new plane is put into service. <S> To answer your question directly: Changes which produce meaningful improvements need years of preparation and testing for approval by the authorities. <S> Quick gains are not possible anymore. <A> If pressed (each plane is grounded until it is installed)? <S> As fast as it's maintenance guys can pump them out per plane. <S> Doing so would require getting the plane to the shop and having the mechanics installing the "advance" which could take a few days. <S> They would then also take the chance to do some of the regular checks . <S> If not then the install would be scheduled along with the other regular check already planned in its lifetime depending on how labour intensive the installation is. <S> Before all that can actually happen the guys doing the install must be trained and the supervisors must be able to certify the installation, that will also take time. <A> In general, a large carrier will have a heterogeneous fleet in which the most recently purchased aircraft will be more performant and fuel efficient than the older aircraft. <S> A carrier can generally "buy" fuel efficiency simply by selling older airframes and buying new ones with new engines. <S> Another way carriers can improve fuel efficiency is by how they load the airframe. <S> Seats and other fixtures onboard are removable and the carrier can reconfigure aircraft in various way and improve the way the equipment is constructed to make it lighter. <S> Carriers are always looking for upgrades that will lighten the load or balance the load better to improve fuel efficiency. <S> There are also computational ways to fly more efficiently. <S> For example, if the flight plan and route planning can make use of winds aloft more efficiently significant fuel savings can be realized. <S> Advanced software can also be used to tune engines or fly the aircraft so that engines use fuel more efficiently. <A> I would try to give some structure to the answer. <S> Firstly, take into account that any technological innovation on the airplane itself it is not performed by the airline, is done by the airplane manufacturer like in car industry. <S> For giving you a more concrete answer I would divide in three: <S> Only renewing improving the fleet by a new one. <S> A way to get the latest technology is just by selling to other airlines or transport companies the old models and buy new airplanes. <S> Typical life span of a airplane is aroud 20-30 years, so that will be how often airlines do that. <S> Another way is implementing retrofits, airplane manufactures offer some improvements as retrofit of the airplane like the A320 sharklet . <S> However you need a business case, not all retrofits are implemented because they are not interesting, apart from the cost of buying from the manufacturer the retrofit the airline will have the airplane in ground during the retrofit. <S> Usually to maximize the business case the airline waits until a complete overhaul (revision) is perform on the airplane to take the advantage is already grounded. <S> Finally: as soon as possible. <S> Just take a look to the recent battery issues on B787 airplanes were grounded during a long period to avoid reducing safety standards. <S> When this kind of situations happen, airlines try to implement technology changes (or just modifications) as soon as possible. <S> Business case is really possitive... <S> Finally, I think the right question is... who pays the modification in the last situation?	Immediately in some cases.
Is it required to memorize checklists for better efficiency? Military pilots are instructed throughout training that they must learn all checklists off-by-heart (in the RAF anyway). This way things get done much quicker, primarily in the event of an emergency when the immediate actions must be performed like 2nd nature. A recently PPL-qualified pilot friend of mine informed me that he refers to his reference cards for every set of checks. The checks for a Cessna-152 were much much more brief than for military trainers. I was wondering what the standard is for general aviation, and whether there is a requirement to learn at least engine-failure immediate actions? <Q> As mentioned in that video "appropriate" leaves some room for common sense interpretation (clearly your first course of action if your engine dies in flight should not be to open the operating manual to the Engine Failure In Flight checklist and begin reading: <S> That would NOT be "appropriate"). <S> I expect most other countries have a similar view on the subject. <S> As far as what gets memorized, the checklists for most simple aircraft (for our purposes let's say that's anything with a single piston engine, unpressurized, with 6 seats or less -- your average Piper/Cessna/Citabria/etc.) <S> can be memorized. <S> They're not that long <S> and there's not that many of them. <S> Time permitting a good pilot will generally still refer to the printed checklist even if they did the entire thing from memory, if only to read off each item and make sure they didn't miss anything. <S> More complicated checklists (like what you might find on a 737 or a C-130 for example) will usually have a set of Immediate Action Items (often called "Red Box Items" because many manufacturers put them inside a big red box at the top of Emergency or Abnormal checklists). <S> It's generally expected that the flight crew have the Red Box Items committed to memory and be able to complete essentially on instinct. <S> After completing the Red Box Items all the really important stuff is done, and there is hopefully enough time that it's now appropriate to pull out the checklist (or Quick Reference Handbook), verify that the Red Box Items have all been done, and run through the rest of the items. <A> However, the idea behind it is sound -- normal checklists are a check list, not a reference for how to operate the airplane day-to-day. <S> As a result, commercial operators and private pilots use flows (i.e. a series of control movements, sequenced for efficient performance and checklist compliance) in conjunction with their checklists for normal procedures and memory items, and modern (i.e. "glass cockpit") transport aircraft provide checklist prompts through the ECAM or EICAS display system that are used for non-normal conditions and the non-critical portions of emergency checklists. <S> See <S> this answer for an excellent example of how an emergency checklist (engine failure) and its matching flow work together in a light aircraft. <A> I don't know of any standard, but it is definitely a wise idea to learn the emergency procedures very thoroughly. <S> One reason for this is that every flight is different. <S> Even routine stuff like the run-up tends to have some new quirk or difference every time. <S> If you have the checklist down pat, it makes it much easier to deal with whatever unique thing is happening. <S> During a fire, for example, if you are fumbling with a checklist and do not already know the procedure thoroughly, valuable seconds will be lost while you are reading through the items. <S> You want to know it so well that all you have to do is glance at the item and say "ok now I do this". <S> In other words, the checklist should just be a reminder to what you already know. <S> In the United States there is no absolute requirement to know the checklists thoroughly ahead of time, but an applicant's likelihood of failing a practical test will definitely increase if they don't, because your chance of making a mistake or getting flustered is greater if you do not know the checklist by rote. <S> Also, I would note that in US practice you MUST use physical checklist or the FAA examiner will fail you in a test. <S> Memory is not considered an acceptable substitute for a physical checklist by the FAA.	The upside of memorized checklists is that you can execute the checks much more quickly; the downside is that many of the detailed troubleshooting checklists used for non-normal conditions that arise in commercial aviation are much longer than a pilot can reasonably memorize. In the US the closest thing to a standard, and the requirement ( per the FAA's practical test standards ), is that you make appropriate use of checklists.
Did commercial airliners have microwave ovens in the past? So I went on 2 long (total of 16 hours) flights with a major US airline, and they did not provide a free in-flight lunch (grr) during either flight. I had brought a sandwich with me just in case, but when I asked the flight attendant if they could heat it up they said that they did not have microwaves. This was I think a 757 or similar aircraft. When I landed I was asked about my trip, the microwave thing came up and was told (by an older person) that airlines did have microwaves and that mothers with children would often ask the flight attendants to warm up bottles of milk for them...?! So now I'm curious, did aircraft used to have microwaves in the past? Were they removed? I now know the food they serve on airplanes is "heated via hot air ovens" but why would there not be a microwave on board? Even if just for crew use? <Q> Generally speaking, airliners do not have microwave ovens for safety reasons. <S> Probably some smaller business jets have them. <S> As also mentioned by sweber in comments to the question, meals are not heated at the airport. <S> Airline catering companies like LSG Sky Chefs prepare the meal near the airport and deliver it to the airplane. <S> Inside the airplane, they use convection ovens to heat it. <A> I flew for TWA International from 1970-1990. <S> It took a long time to train <S> the older F/A's on their operation. <S> Prior to their installation we cooked in convection ovens which cooked meals for 30-40 minutes depending on if they were frozen. <S> Now you're telling me I can do this in 3-5 minutes? <S> We destroyed so many Filet mignons by turning them into hockey pucks. <S> Plus we had to warn the passengers with heart monitors that microwaves were onboard and in use. <S> It was quite a learning curve. <A> For the most part, no, they did not have microwaves onboard passenger aircraft. <S> When serving large numbers of passengers a microwave would be a luxury taking up valuable space. <S> Having said that I did work for an airline that did have microwaves onboard. <S> It was an all first class airline with a small fleet of B727's. <S> The aircraft were configured for 33 passengers. <S> There were no menu items that were ever designed with the microwave in mind as a preparation method. <S> Some chefs would use it to reheat a plate of food in a crunch <S> but it was against policy and <S> it would create fireworks onboard as the English bone china had a gold emboss on it that would spark. <S> Hot water would be the only way a baby's bottle could be heated. <S> Even if they had the ability to heat your sandwich they are correct in not allowing that due to health, food and safety regulations. <S> Above all else, most passengers with manners would agree, it's a rather tacky request. <A> AA has Microwave Ovens on its 777-300 First Class Galley.	Some flight attendants mention that they can warm your food, but some say that they will not for legal and health reason. We had microwave ovens on all of our 747's. I could not find any reference where commercial airplanes used to have microwaves.
How often do people fly SVFR? I was going over Special Visual Flight Rules (SVFR) with my instructor recently and he told me that he has only requested it a few times, and that it is mainly used if you are flying from deteriorating weather into improving weather. In other words, you are sure that where you are going is clear. I got thinking about it and felt that if there were ever an SVFR situation, I would most likely ground the flight (until I get my instrument rating that is). That being said, how often do pilots request SVFR? It seems like it would cause people to end up in situations that they can't handle i.e. weather deteriorates more instead of getting better, does this happen often? It has been mentioned that SVFR rules vary from country to country, I am asking about peoples experiences in the USA but am happy to hear of other similar situations around the world as well. <Q> From my experience in the US at the facilities I've worked, and the discussions I've had with other controllers, it depends heavily on the area's weather patterns. <S> Other places, like coastal or areas where fog banks are common, SVFR can be useful, esp if only half the field is covered in clouds, and you need to make it in or can easily get out. <S> Personally, I'd probably just file IFR and cancel when I got to a good spot VFR, if I just wanted to go out and enjoy, versus just flying to a destination. <S> Also, note, SVFR in terms of separation is only one SVFR aircraft(and really aircraft period) in the airspace at a time. <S> So, you'll be delayed to come in if there's IFR, or other SVFR aircraft ahead of you. <S> Helicopters generally do request it more than fixed wing aircraft in my experience. <S> Also, realize a pilot has to explicitly request SVFR, a controller can't prompt or hint at the correct terminology to use to request like saying "Do you have a SPECIAL request" <A> I've done it once, or maybe twice in 1200 hours of flying. <S> The first time was when I was stuck at an airport in the LA basin which was below standard VFR minimums due to how thick the smog was. <S> I filed SVFR to take off, and by 5000 feet I was above the smog layer and it was blue skies <S> the rest of the way home. <A> Also, Copter instrument approaches can terminate at the MAP with an SVFR clearance to the airport. <S> Such approaches may even be noted on the flight plan. <S> For example, the MAP for JFK COPTER RNAV (GPS) 028 <S> ° <S> (PDF) depicts various VFR routes to the NYC heliports. <S> These can be flown SVFR. <A> The below was posted before the OP clarified in his question that he was interested in FAA-based data and anwers. <S> I am not aware of any statistical data, but I can answer the second question in your text. <S> Remember that SVFR is not only about visibility, but also about staying clear of clouds. <S> Airspace D in Germany requires cloud distances of 1.000ft vertically and 1.5km horizontally. <S> You are also required to remain at least 500ft above ground during flight, except for landings and takeoff. <S> If your cloud base drops below 1.500ft, you could technically no longer maintain VMC, even though maybe your visibility was more than 10km. <S> In this case your only option is to request SVFR. <A> Like requesting access to military routes (MR on your area maps) it seems to be something that lots of people don't use but those who know how to use them discover they are great! <S> I have found that traffic control (especially the non-tower sites you address as e.g. "Radio Hawthorne") <S> love hearing these requests and are eager to help you figure out the details you need to get what you want - probably because it's a bit more interesting than most of the requests they hear :) <S> Caution, Opinion ahead : <S> I highly recommend you learn to use it and memorize a few of the versions more relevant to your location (e.g. "SVFR to VFR on top" to get above spotty low clouds). <S> You'll sound like a pro and traffic control will usually be quite friendly and receptive about it. <S> In fact I can't recall ever being turned down on such a request, although I have received advice to change my strategy once or twice (including once when I was guided into a channel to see about a dozen military craft go by at close enough range to count mustaches). <S> SVFR is a fun and powerful tool for the general aviation pilot and an excellent way to build skill. <S> Do them with your instructor too while you have the chance because they are indeed a skill that is worth working on.	The facilities I've worked, it's been usually a tool, when people are trying to get in right before the weather hits, or they're seeing good improvement in neighboring airports and at the main one, and know that it'll be good enough to make it between the two areas. Copters fly SVFR more often than fixed-wing for a number of reasons: SVFR minimums are lower (see 91.157), can be done at night, and are not subject to the "NO SVFR" of Part 91 Appendix D Section 3 that prohibits SVFR at large Class B airports. I've flown SVFR a lot.
Why would a helicopter climb in a spiral? I was just watching the James May's Toy Stories Christmas Special Flight Club * , and in it he commented that the helicopter was making a spiral climb to 8,000'. Why would the pilot spiral, not just essentially go straight up? * An excellent series if you're a big kid who enjoys toys, and as a bunch o' GA pilots, I'd think that covers most of you! <Q> A helicopter will achieve its best climb rate at a moderate forward speed. <S> Climbing in a spiral helps to have forward speed in what is essentially a vertical climb. <S> In a hover all the airflow which is available for lift creation must be generated by the rotation of the main rotor. <S> This means that a small amount of air must be accelerated by a lot. <S> If the helicopter adds forward speed, it can achieve a higher mass flow through the rotor, and now less acceleration is needed to achieve the same lift. <S> This improves the efficiency of lift creation. <S> If the helicopter goes faster than its speed for maximum rate of climb, aerodynamic drag grows too high and reduces efficiency again. <S> The difference can be dramatic: Below is a plot of the speed versus altitude of a generic helicopter and turboprop plane in comparison to the V-22 tilt rotor. <S> Remember that the available power is roughly proportional to air density, and you can start to see how much more power is available for climbing when the helicopter flies with a moderate forward speed. <S> Flight envelopes of a generic helicopter, a turboprop plane and the V-22 tiltrotor (picture source ). <S> Thanks to @mins for inspiring me to expand the answer a little. <A> <A> See my question here . <S> The reason I performed a spiral climb is for the reasons given above plus a couple more. <S> Forward speed is safety. <S> In the event that the engine should quit, having forward speed gives you a lot more options. <S> When climbing vertically, you have a lot more pitch on the blades than in forward flight. <S> If the engine does quit, the blades will slow down very quickly reducing the time available for the pilot to dump the collective and enter autorotation. <S> You are also storing kinetic energy, as well as potential energy, in the system and therefore have more energy to play with if the donkey does go quiet. <S> In the R22 I was flying, I would probably have about one second to react correctly in a vertical climb. <S> Perhaps 2-2.5 in forward flight. <S> I wanted to remain clear of the danger area since I didn't have a clearance and had limited options for flying around the sides. <S> I did ensure that I was not over any houses and moved the spiral a couple of times so that my noise footprint was not over the same spot.	In the spiral, the helicopter generates translational lift , which is added to the lift generated by the downwash of the rotor system, improving its ability to climb.
Is ATIS information - including identifier - available on the internet? According to Section 2-9-1-a of the FAA's Air Traffic Organization Policy, a phonetic letter is assigned to each tower-issued ATIS update. This information is available on the ATIS VHF frequency for an airport, or via a phone call to a designated ATIS number for the airport. There is a passing reference on the Wikipedia page to ATIS being available electronically via a service named "D-ATIS", although I've never heard of this. I'd love to be able to view this information electronically, rather than having to get my VHF handheld, or the plane's radio going and tune it in before flight. The voice system is frequently engaged. If it was available via the internet, it'd be super-easy to access. Is there a means accessing the ATIS - including the identifier - for a given airport in electronic form via the internet? If so, how? NOTE: I know it's possible to get METAR reports, but they are typically automatically generated, not manually adjusted by the tower (as ATIS sometimes is), and don't include the phonetic letter designation issued by the tower and required for initial tower contact. <Q> The short and general answer is: No . <S> In the case of D-ATIS, the information can only be obtained using ACARS , other systems such as CPDLC require special equipment. <S> With modern technology and communication, some airports have started to use Twitter to broadcast ATIS, however they should not be used for flight purposes, but are only for entertainment. <S> (Image Source: <S> Twitter - Account: @yssyatis) <A> In Australia the full ATIS and identifier is available on the internet in text form (along with all the weather and NOTAMs) - but it is only available to pilots. <S> The information is provided by Airservices Australia (which is basically our government-owned version of NATS) through their online service called NAIPS. <S> NAIPS is free but to register you need an Aviation Reference Number issued by CASA, which are only available to pilots or engineers or other important people. <S> To illustrate, here is the ATIS from Sydney (YSSY) from a bit earlier today, they were using identifier K: ATIS YSSY K 260229 <S> APCH: <S> EXP INDEPENDENT VISUAL APCH. <S> DO NOT PASS THRU, ASSIGNED RWY CL <S> RWY: <S> 34L AND R FOR ARRS AND DEPS OPR INFO: PARL RWY OPS IN PROGRESS. <S> INDEPENDENT DEPS IN PROGRESS <S> WIND: <S> 260/12 XW MAX 12 DW MAX 3+ VIS:+ WX: <S> CAVOK+ CLD: TMP: <S> 27+ QNH: 1015 <A> I dont know of a site that has it for every airport <S> but this site has lots of live streaming ATC. <S> It seems they have ATIS for some airports (I found it for JFK) <S> but chances are they will only have it for the big airports however depending on where you fly out of you may get lucky. <S> Again this is the actual audio feed so you will still need to listen to it. <A> In the US ATIS information isn't available on the internet. <S> The tapes (or an equivalent written record) are retained like any other ATC communication though (3-4-2 item "k") and are available via FOIA requests if you have a pressing need for them. <S> If all you're interested in is the weather most airports that are large enough to warrant an ATIS broadcast are also large enough to have a weather station reporting METARs, which means you can use one of the many available METAR archive search websites (or if you prefer you can dig around on the NOAA website - I used to know the URL for the archive <S> but it's apparently been moved).	The ATIS is only a VHF recording, but even when recorded digitally, it is not available in a text-base form in many cases which would allow being made public on the internet.
Why aren't there more passenger helicopters? I've observed helicopters being used often in the military for medical flights for other special use purposes, such as sightseeing and news reporting Why aren't there any commercial passenger transport helicopter flights? Or are there any examples of this? Are airplanes simply that much more efficient? <Q> Airplanes are much more efficient, much faster and scale better. <S> Helicopters are limited to around 150 knots because when flying forward the tip of the advancing blade must not exceed the speed of sound while the retreating blade must still move aft fast enough to produce lift. <S> Helicopters are also difficult to make large, because for efficiency the rotor disk needs to be large, but the diameter is again limited by the tip speed having to remain subsonic. <S> And the material requirements to make the blades strong enough without making them too large to keep drag low. <A> Jan Hudec's answer has already detailed why helicopters are not widely used for mass transportation or have been scaled up to ferry passengers more often. <S> The few exceptions exist where landing space is limited and the helicopter's maneuverability is more advantageous. <S> Offshore Oil & Gas Rigs <S> (Image Source: www.wn.com ) <S> Where transport by ship is not fast enough or not possible due to heavy swell, the use of helicopters allows quick access to the offshore platforms. <S> New York Helicopter Taxi <S> (Image Source: www.americanbestgetaways.com ) <S> The New York Helicopter Services allow quick access to the airports around New York for business travelers who would otherwise take more time to arrive in Manhattan. <A> Even with a pair of decent ear defenders on it's not exactly quiet. <S> OK, so a commercial 'air bus' is never going to match a Mercedes or even a plush executive helicopter for levels of NVH, but there's nothing particularly attractive about the experience other than getting somewhere much quicker than you might otherwise. <S> The noise also means the 'go anywhere' ability of helicopters is severely curtailed if noise means they can't actually go many places. <S> Add to that <S> the high cost <S> and it's pretty much a non-starter except for edge cases as in SentryRaven's answer where an increase of speed of an order of magnitude or more, or the circumvention of otherwise impossible access outweigh these concerns. <A> There are a few commercial passenger flights, but not so many because of the costs. <S> In Sao Paulo, Brazil, there are about 500 registered helicopters , with about 700 flights per day, which include transporting CEOs and politicians from one part of the city to another. <S> Some might also cite safety concerns, but this is unlikely to play a major role. <A> There was regular helicopter service between Tallinn, Estonia and Helsinki, Finland during the mid-2000's. <S> It was mainly used by business travellers between the two cities. <S> I think the flight time was something like 20 minutes and the heliport was on both sides conveniently in the middle of the city. <S> The regular plane service has a flight time of 30 minutes with additional time spent for airport procedures and taxi rides to and from the airport, so there definetely was a business case there. <S> However there was an unfortunate crash and the company never quite recovered from that. <S> They use their copters for oil rig flights now, if I am not mistaken. <S> See Wikipedia Copterline Flight 103 . <A> When I took flying lessons, I looked into a helicopter certification. <S> The rental cost was 2-3 times more than a fixed wing aircraft at the time. <S> I don't know what it costs now, but I assume it's still really expensive. <S> There are passenger helicopters, usually used by corporations or very wealthy individuals. <S> Some companies maintain their own fleet or charter when needed (which is probably cheaper). <S> One company I worked for early in my career maintained an intra-site fleet of helicopters (if your manager would approve it and the weather held, an hour drive became a 20 minute helicopter ride). <S> I never got to use it because this was one of the first things to go when the company went into decline and needed to cut costs.	Several factors contribute to this: Frequent traffic issues leading to unpredictable delays in major roads; Presence of an elite having enough money to afford such flights; Availability of a sufficient number of helipads. Spending years being ferried off and on shore by helicopters, I'd say the biggest problem is noise.
Can a software "hard freeze" or serious hardware problem completely disable the whole cockpit? I think that the glass cockpit of a modern plane has some sort of a central power supply or at least some central controlling software. What happens if this central power suddenly disappears, or the central software freezes? Yes, of course, this would be a severe failure and would put everybody's life on the plane in serious danger. Is such a failure possible? <Q> If the power suddenly disappears to any aircraft (ie, a total electrical failure including the batteries), then all the aircraft systems will be failed regardless of whether or not they were glass. <S> This is highly unlikely because there are several power generation backups that would have to fail, including the batteries themselves, before this ever became a reality. <S> Unfortunately though, if the aircraft only has electrically controlled, hydraulically actuated control surfaces (fly-by-wire), vice actual mechanical linkages (or backup controls), then a total electrical failure would be 100% fatal if power cannot be restored. <S> The control surfaces would not be movable. <S> However, more to the question regarding software bugs, all primary flight instruments are backed up to prevent such disasters from happening. <S> I have personally lost all the digital displays in my cockpit and flown a no-gyro, surveillance approach in bad weather using nothing but a peanut gyro. <S> Its possible, but definitely not a good time. <S> Anything is possible. <S> However, even though the odds of a total electrical failure, or complete loss of instrumentation (including backups) is nominally greater than 0%, the statistical probably can still probably be rounded to 0. <A> All of this, of course, depends on the presence of actuator hydraulic power - <S> if you have no hydraulic power and no electric power on a FBW Airbus or Boeing (including a loss of the dedicated FADEC/EEC backup permanent magnet generators), you're toast because not even "fly by thrust lever" a la UAL232 and OO-DLL will save you in that case. <A> But, is such a failure possible? <S> The answer to if such a failure is possible is on some level yes. <S> But for what its worth no. <S> There are a few things to consider. <S> Redundant and Independent systems: <S> Aircraft typically have not only redundant systems but independent systems in other words not only are there back ups <S> but they are often separated so that a failure in a single system or set of systems should remain isolated. <S> From a power standpoint a plane gets is electrical power from the turbines driving a generator. <S> Each turbine has at least one generator (maybe more <S> Im not sure) <S> so if a single engine were to cut out you would not lose power generation. <S> You may need to shut the lights off to not over draw the generator <S> but you could still power the key systems. <S> Aircraft also have batteries in the case of total engine failure. <S> keep in mind that in a total engine failure you will be on the ground long before you kill the batteries I would think. <S> Multiple Electronic Busses: To my knowledge larger airplanes have multiple electric busses each of with can be independently tied to and disconnected from the main buss as well as joined if needed. <S> If one buss fails you can switch over to the other to draw power for the aircraft. <S> Keep in mind that if a surge causes the failure the components would be protected by the fuses. <S> This is even finding its way into smaller GA airplanes. <S> It is possible to order some small planes with 2 alternators now <S> I believe the Cirrus SR-22 can be had in such a configuration. <S> Now that we have established that there are actually multiple central power connections lets look at why its so remote they fail. <S> If you take 2 systems that are (for the purpose of this example) created equally, have the same run times on them and are serviced the same etc. <S> they would have the same chance of failing at any given moment in time. <S> That being said the chances of them both failing at the same point in time is so remote it can almost be ignored. <S> The idea here is that we can accept a single system failure, complete the flight, and then send the plane in for repair. <A> There have been incidents where the primary flight displays have failed somewhat as you describe: example 1 , example 2 (one each for Boeing and Airbus <S> so I'm not taking sides). <S> That said, there's a lot of redundancy in these systems. <S> Cockpit display systems are somewhat separate from flight control systems, so the failure of one may not impact the other. <S> As UnrecognizedFallingObject notes, there are even some options for manual control in the event of a total fly-by-wire failure. <S> Modern glass cockpit aircraft have a small display, usually toward the center, with standby instruments (Airbus calls it the Integrated Standby Instrument System). <S> This is a separate LCD display, powered independently by the emergency bus and driven by its own computer, designed to display altitude, airspeed, and attitude. <S> This provides the crew with essential information toward making an emergency landing.	So yes, things can fail, causing cockpit displays to go blank and other problems. While total electrical failure in a transport-category aircraft is extremely remote, even fly-by-wire airliners such as the A320-380 and B777/787 have redundant backups that would work under the scenario: in the case of the Airbus, you'd fly using the rudder pedals for yaw and roll and manual stabilizer trim for pitch, while Boeing uses a pair of spoiler panels for mechanical roll backup instead of the rudder.
Are two people required in cockpit at all times on large commercial aircraft? It would seem reasonable on large commercial airlines to require that there be two people in the cockpit at all times. For example when the pilot goes to the toilet a member of the cabin crew must enter the cockpit until the pilot's return. Such a rule would greatly reduce the probability of pilots being locked out and reduce problems should they be locked out. Do any airlines enforce such a rule? <Q> EDIT: please see at the bottom of the answer the update from EASA <S> Are two people required in cockpit at all times on large commercial aircraft? <S> No. <S> From EASA, pag. 101-102 : (emphasis mine) <S> CAT.OP.MPA.210 Crew members at stations Flight crew members <S> During take-off and landing each flight crew member required to be on duty in the flight crew compartment shall be at the assigned station. <S> During all other phases of flight each flight crew member required to be on duty in the flight crew compartment shall remain at the assigned station, unless absence is necessary for the performance of duties in connection with the operation or for physiological needs, provided at least one suitably qualified pilot remains at the controls of the aircraft at all times . <S> During all phases of flight each flight crew member required to be on duty in the flight crew compartment shall remain alert. <S> If a lack of alertness is encountered, appropriate countermeasures shall be used. <S> If unexpected fatigue is experienced, a controlled rest procedure, organised by the commander, may be used if workload permits. <S> Controlled rest taken in this way shall not be considered to be part of a rest period for purposes of calculating flight time limitations nor used to justifyany extension of the duty period. <S> Do any airlines enforce such a rule? <S> As other answers mention, yes. <S> EDIT: <S> On the 27th March 2015 EASA has issued the following Safety Information Bulletin : <S> operators are recommended to implement procedures requiring at least two persons authorised in accordance with CAT.GEN.MPA.135 to be in the flight crew compartment at all times, or other equivalent mitigating measures to address risks identified by the operator’s revised assessment. <S> This still does not mean that 2 people are required, but are recommended. <A> It's not required by a regulation, but, yes, it is required by the procedures of some airlines, at least in the U.S. <S> A flight attendant taking the seat of an absent pilot to ensure there are always two people in the cockpit, <S> and/or blocking access to the open door with a trolley, are often seen on US flights, but not necessarily on others, Hansford said. <S> For instance it is not a requirement on Australian flights. <S> Source: <S> http://www.theguardian.com/world/2015/mar/26/germanwings-crash-safety-of-cockpit-doors-on-all-planes-questioned <S> I've also heard numerous U.S. airline passengers claim to have witnessed this frequently, though I don't recall having seen it personally. <A> The FAA has very similar rules about flight crewmembers leaving their station. <S> § <S> 121.543 Flight crewmembers at controls. <S> ... <S> (b) <S> A required flight crewmember may leave the assigned duty station — (1) <S> If the crewmember's absence is necessary for the performance of duties in connection with the operation of the aircraft; (2) <S> If the crewmember's absence is in connection with physiological needs; or (3) <S> If the crewmember is taking a rest period, and relief is provided—... It goes on to describe the requirements of a relief crewmember, but this is only if the pilot is taking a "rest period". <A> only exceptions are a few very small commuter airlines that fly single-pilot in Cessna 402s and Caravans and Piper Chieftains in remote places like Alaska, Hawaii and the V.I. (and Nantucket!).	The "Two Crewmember Rule" has been mandatory for all US passenger airlines since 9/11 as well as for all foreign airline flights in and out of the US.The
What vertical flight profile could be expected from an aircraft if the pilots were incapacitated? If there were nobody at the controls what kind of vertical profile could be expected from, for example, a modern airliner? After reaching the cruise altitude I assume the pilot just sets a nav route and altitude on the onboard computer or at least set the trim to avoid having to constantly adjusting the altitude manually. <Q> Emergency descent (like during a decompression event where you need to get from cruise to 10k ft ASAP to make sure the people in the back survive) shouldn't make a nice curve. <S> It only wastes time you don't really have. <S> Normal operation means the pilot activates the autopilot during cruise which will fly the programmed course set by the pilot. <S> It will stay follow that course (or put itself in a holding pattern on the final fix) until it runs out of fuel or the pilot intervenes when it is cleared for descent. <S> This happened with Helios Airways Air flight 522 ; both pilots were incapacitated shortly after ascent and the plane put itself in a hold and crashed when it ran out of fuel after more than an hour. <S> A plane where there is nothing controlling the altitude (when control is lost due to loss of hydraulics for example) will follow a phugoid cycle . <S> That is a series of dives and climbs as the elevators gain and lose bite on the air with speed. <A> Large commercial aircraft are not expected to descend if their pilots just walk way. <S> At least, not quickly. <S> Large planes generally cruise on autopilot, which will keep altitude until told otherwise. <S> In fact, airliners generally have flight management computers that will fly the entire route before holding near the destination. <S> When the plane runs out of fuel, it will slow down and then, finally, it will descend until it crashes. <S> This was seen in Helios 522. <S> I don't know what that descent profile would look like. <S> The Helios 522 accident report shows the following Aircraft enters from bottom right. <S> AP lines up aircraft with Athens International airport runway. <S> after overflying airport, AP turns SE and puts aircraft on holding pattern (loop at bottom). <S> Fuel exhaustion causes one engine to flame out and AP to disengage. <S> Aircraft starts to bank (assymetric thrust) and turns. <S> Second engine flames out. <S> Final descent is on a roughly spiral track. <A> Any descent profile can be expected of an unpiloted aircraft, but generally nothing severe would be expected uncommanded and without stall occuring. <S> Aircraft control surfaces (rudder, elevator, aileron) can be "trimmed" to maintain coordinated level flight. <S> Elevator trim, in particular, is constantly adjusted (by the pilot or autopilot) so that if nothing was flying the plane it would maintain its present airspeed. <S> A consequence of this is that a properly trimmed airplane will climb or descent to maintain the airspeed it is trimmed for. <S> Give the above we can say <S> The above assumes no autopilot or an autopilot in speed hold mode. <S> An autopilot in altitude hold mode will attempt to maintain altitude as long as possible, and depending on the programming that might mean until stall occurs. <S> When the stick shaker activates preceding the stall, that should disconnect the autopilot and this may be followed by stick pusher activation. <S> In the end, if stall is avoided, the airplane will descend at the airspeed that autopilot last trimmed it for, which is likely a slow-ish airspeed (close to but above stall speed at present altitude). <A> All certified airplanes are designed to have a (very slight) spiral instability. <S> The opposite case, dutch roll <S> instability is not acceptable. <S> This will make a plane that is trimmed out straight and level and then left alone without pilot, autopilot wingleveler or other automation to slowly enter a spiral dive with gradually increasing bank angle and sink rate. <S> Spiral instability is achieved by having the lateral tail area large enough so when a wing drops slightly by external disturbance and the plane starts to slip in the wing low direction, the tail will turn the plane in the same direction as the wing drop. <S> This is a gentle and harmonic movement, it feels natural to the pilot. <S> If uncorrected it leads to a spiral dive at increased bank angle and speed. <S> Dutch roll is the result of to small tail area, so when the plane slips for instance to the left, the nose will go right and up. <S> The speed will go down, and if uncorrected will lead to a stall. <S> It is not the case that a plane left unattended (no pilot or autopilot on duty) will largely stay on course and altitude until the fuel runs out. <S> If a plane was stable by itself, flight in low visibilty would not be a problem. <S> One famous example is the John F. Kennedy Jr. accident. <S> http://en.wikipedia.org/wiki/John_F._Kennedy_Jr._plane_crash	a properly trimmed aircraft with no pilot input could be expected to roughly maintain altitude and once out of fuel it will descend at whatever rate is required to maintain its trimmed airspeed.
How can the breath of a pilot be recorded? On a plane, as a passanger, I can't hear my own breath. I can't hear my own breath even in a silent room. On a plane, there is a continous background noise. And the microphone recording the noises in the cockpit, are probably not directly at the lungs of both pilots. I am really wondering, how can the breath of a pilot simply be recorded on the cockpit, if it wasn't designed specifically for that (or it isn't a very high quality recorder placed directly to the body of the pilots)? <Q> One of the channels of the Cockpit Voice Recorder is the microphone on each pilot's headset. <S> This is much closer to the source of the breathing noise than your own ears. <S> The microphone may also not have a wind filter so breathing on it will generate a lot of noise. <A> Pilot's breath is not recorded on a flight data recorder, as it is not one of <S> the data parameters . <S> A reference to this can be found in the press conference summary for Germanwings flight 4U9525, which states: ... <S> the only sound to come from Lubitz is the sound of him breathing, picked up by the microphone on his headphone set . ... <S> “We could hear human breathing inside the cabin,” said Mr Robin, “and this breathing noise we heard up until the moment of final impact. <S> That means that the co-pilot was alive. <S> Apparently he was breathing normally, so this is not someone having a heart attack, for example. <A> You can actually hear breath on the mic (see ratchet freak's answer above). <S> If you have multiple pilots, you can hear the other guy breathing on the channel intermittently. <S> You do not hear every breath, just the sniffs, intakes, coughs, etc, all the little noises he makes. <S> In other words, when they say "breathing" for that incident, that includes all kinds of little noises that are associated with normal breathing.	However, if a pilot is breathing abnormally, the cockpit voice recorder may easily detect that as the breathing sound is captured by the CVR.
What can airline pilots do if they are no longer in the position to fly, career-wise? I was having a discussion with a friend about the incident in the past days (4U 9525) and more specifically the what could be described as 'Taboo' of Psychological problems among pilots. We came across a few points: They will only reluctantly admit that something is wrong, since risk losing their Medical (hence being 'grounded'). It will only be easier to loose and harder to get back I suspect after this event. At least for the younger bunch who might have difficulties they will have substantial debt from training that is difficult to pay off. Furthermore, they will have worked hard to get where they are. Any airline that does suspect something will most probably not allow them near the cockpit again. Should anything happen the airline will be held to blame, since they did allow him to fly despite knowing of the problem. This brings up the question: What can a pilot do, career-wise, if they feel they are unable to exercise the profession? It seems pretty cornered to me. Perhaps work in dispatch/ network control was the only one I figured their knowledge could come to use. Switching to the simulator I suspect might also be possible, but not for the younger individuals. <Q> When I worked in the design department of an aircraft company, I had two types of coworkers: Those with and those without a pilot's license. <S> You could easily spot the difference. <S> In aircraft-related engineering decisions it was soon obvious. <S> See it this way: All managers in car companies have a driver's license, so they have at least some contact with what their companies make. <S> All higher managers where I worked had no pilot's license, and it made work outright awful. <S> They were trained as beancounters, and that restricted their viewpoint. <S> They were simply incapable of telling good engineering from bad. <S> If you have managed to get a CPL, adding an engineering degree on top is not hard. <S> That is my advice to grounded pilots <S> : Go to engineering school and enrich the workforce with your experience. <A> Pilots are intelligent. <S> They can retrain and become good at some other type of work: aviation mechanic, computer scientist, engineer, law. <S> Some of these fields will pay much better than a pilot career <S> will anyway, so don't worry about the sunk cost of pilot training. <S> If you are not fit to fly, no amount of bargaining/rationalizing is going to fix that — you've got to move on. <S> The root cause (psychological problems, in your example) is a red herring. <S> You may have to change careers for many reasons: injury, family, health, etc. <A> Commercial glider and balloon flights don't require a medical, nor do certain kinds of instrument instruction. <S> Someone who's is healthy but wouldn't pass a first or second class medical can have a career teaching, or flying commercial flights like sightseeing and advertising.	I mightily preferred to work with other pilots - they would have a much better grasp of "what looks about right" and not pursue hare-brained, outlandish ideas.
Is head-on or trailing wind better? Does a powered aircraft fly faster when in a head wind or with a trailing wind? The question revolves around the head wind should provide 'better' lift, and trailing winds have very little to 'push' against. <Q> A tailwind provides a faster groundspeed. <S> The aircraft moves through the air so whether the ground is moving relative to the mass of air has no relevance to the aerodynamics of an aircraft at cruising altitude. <S> a British Airways passenger jet approached supersonic speed this week as it rode a surging jet stream from New York to London. <S> from The Telegraph, <S> 10 Jan 2015 <S> They mean groundspeed - <S> so the term supersonic is moot. <S> The Boeing 777-200 jet reached a ground speed of 745mph as it rode winds of more than 200mph across the Atlantic. <S> At ground level, the speed of sound is 761mph. <S> Aircraft often use the predominantly westerly† jetstream when flying from the USA to Europe, From Japan to California or across the USA. <S> Flying the other way they pick an altitude to avoid it. <S> Wikipedia <S> The Jetstream is a high speed, high altitude, wind that blows moderately reliably in one direction. <S> Metcheck <S> † Westerly means "blowing from the west" - towards the east. <A> Headwind is good for take-off and landing. <S> It adds extra speed for free at the start of the take-off run, rsp. <S> allows to come in slower for landing, reducing the landing distance. <S> Tailwind is good for enroute flight. <S> It pushes the aircraft forward and adds extra miles per hour for free. <S> The speed relative to the surrounding air is the same at the same power setting and altitude regardless of wind speed, but when measured relative to the ground the wind speed must be added to the air speed. <S> But on the way back from a tailwind leg the aircraft has to fly in a headwind, and the added time and fuel expense is higher for the sum of both trips in comparison to trips made when no wind is blowing. <S> Why? <S> Let's assume the aircraft will fly at the same power setting, and will achieve 200 mph in still air. <S> The trip to a destination 1000 miles away will take 1000 / 200 = 5 hours in still wind for a roundtrip time of 10 hours. <S> Now add to that a 50 mph tailwind, and the trip will take 1000 / 250 = 4 hours. <S> On the return trip we need to subtract the wind: Now it will take 1000 / <S> 150 = 6 hours 40 min to fly back. <S> The total flight time with wind is 10 hours 40 min, and those 40 min of longer flight time consume proportionally more fuel and crew time. <S> Tailwind is only good when you don't plan to return, or when the wind will have changed when you go back. <A> Constant wind does not affect the lift or drag of an aircraft. <S> As stated by others, you will travel faster in relation to the ground with tailwind but your airspeed will stay the same no matter what wind you have. <S> Shortly after you are in the air, the aircraft travels with the wind, rather then with the surface of the earth. <S> The aircraft wouldn't notice any wind. <S> For an airborne aircraft, the air always stands still. <S> Wind is only the movement of air in relation to the ground, and the aircraft doesn't relate to the ground once it is airborne. <S> This is why you take off into the wind: <S> Your airspeed (the speed the aircraft travels through the air, so the sum of windspeed and groundspeed) is higher with a lower ground speed. <S> Here the maths <S> : Let's say you have 10kt headwind <S> and you are standing at the runway. <S> When standing still your airspeed is already 10kt eventhough your groundspeed is 0kt. <S> As you start moving, the airspeed will always be 10kt more then your groundspeed. <S> Conclusion: <S> The wind doesn't make an airplane faster in relation to the air, but in relation to the ground the wind can change the speed of an aircraft, but not by producing more lift/drag, but by simply moving the aircraft along in the air. <A> The question actually has nothing to do with aerodynamics. <S> It's a matter of relative motion, which is traditionally considered physics, but IMO is really nothing more than simple vector arithmetic. <S> Consider this equivalent question: Before you board your airplane, you walk through an airport. <S> You approach two parallel "pedestrian conveyor belts," one moving away from you and one moving toward you. <S> Which one should you walk across if you want to get to the other side faster? <S> Now replace your body with the airplane, and the conveyor belts with "wind" (moving masses of air). <S> Does that make it more clear? <A> When looking at the physics, the speed of an aircraft is the speed relative to the air . <S> For this, it is not relevant how the air moves relative to the Earth - or any other planet, for that matter. <S> The aircraft does not even "know" the direction of wind. <S> So there can not be a difference in the aerodynamics, in a very fundamental way . <S> If you ask about the speed relative to the ground, you can just add the vectors of both speeds.	If you are having tailwind, the aircraft will travel with the same speed through the air, but with an increased speed over the ground.
Is there a legal requirement to tell your doctor you are a pilot? Specifically if I visit a doctor in Canada who is not a CAME for my regular aviation medical, do I have to tell him/her that I have a pilot's licence? You can imagine why I'm asking. I just explained to someone that I'm supposed to mention this to any doctor I see. However, it's been ages since I've flown and I would no longer do this as I haven't even kept my medical up to date. I've just searched the CARS and can't find any reference to this being a law. Is it possible I was told this by mistake, or as something that's just recommended? I do recall doing this once or twice and the doctor didn't just pat me on the back and say "good for you". He nodded and just acted like it was a normal thing to be told. Not sure what tags are available, but I'm interested in answers from other countries as well. <Q> However, on the application for a medical certificate ( Form 8500-8 ) you must list all "visits to health professionals" in the last three years, including type of professional and the reason for the visit. <S> The medical examiner uses that information to guide questions to ask about your medical history: a yearly checkup with your family doctor will not be remarked on, while a visit to a specialist might invite scrutiny about that area of your medical status. <S> Depending on any existing conditions, you may need a letter from your primary doctor explaining your condition, but you would specifically ask for this rather than expect it to be provided. <A> You don't have to. <S> The reason is because you do have to tell your CAME about everything at your next aviation medical exam anyway. <S> The reason you are not required to tell your doctor that you are a pilot is because section 602.02 and 602.03 of the CARS give you the responsibility to not fly if your medical condition or drug you are taking renders you not fit to fly. <S> There is contact info for Civil Aviation offices and they can help you with that determination: Civil Aviation offices . <S> The CARS are available at one big 4mb web page here . <S> 602.02 <S> No operator of an aircraft shall require any person to act as a flight crew member and no person shall act as a flight crew member, if either the person or the operator has any reason to believe, having regard to the circumstances of the particular flight to be undertaken, that the person (a) is suffering or is likely to suffer from fatigue; or (b) is otherwise unfit to perform properly the person’s duties as a flight crew member. <A> It's not in the Canadian Aviation Regulations, but in the Aeronautics Act which enable the CARs. <S> It's section 6.5(2) , <S> and yes, if you are a pilot, you have to advise any doctor of that fact, and they in turn must advise the "Minister" if there is a possible aviation hazard. <S> Here it is ("Canadian Aviation Document" means your pilot licence): <S> 6.5 <S> (1) Where a physician or an optometrist believes on reasonable grounds that a patient is a flight crew member, an air traffic controller or other holder of a Canadian aviation document that imposes standards of medical or optometric fitness, the physician or optometrist shall, if in his opinion the patient has a medical or optometric condition that is likely to constitute a hazard to aviation safety, inform a medical adviser designated by the Minister forthwith of that opinion and the reasons therefor. <S> (2) <S> The holder of a Canadian aviation document that imposes standards of medical or optometric fitness shall, prior to any medical or optometric examination of his person by a physician or optometrist, advise the physician or optometrist that he is the holder of such a document. <A> In Norway all Your medical records are stored in one database. <S> Every doctor, public or private, have access to this register, they will also add Your visit in the database. <S> Only way to get around this database is to visit a witch doctor or see a doctor outside the country. <A> In the UK, like the other countries mentioned, you're not required to tell a doctor you're a pilot. <S> However, if you have a medical problem that may impede your ability to fly, you are required to tell the CAA (the national aviation body), who will probably suspend your medical certificate until you get checked out by your medical examiner. <S> I've been advised by more senior pilots that you shouldn't tell doctors you're a pilot if you can avoid it. <S> Doctors who don't normally deal with pilots are unlikely to know the criteria for a medical certificate, so may overreact to minor ailments. <S> They might not even know that you get checked out by another doctor anyway! <S> One colleague reported that when his doctor treated him for high blood pressure (that was still within the acceptable limit for his class 2 certificate), she got very agitated when he told her he was a pilot. <S> She thought he shouldn't be allowed to fly with high blood pressure, and was worried that she might be required to tell someone or face legal consequences. <S> Even so, it might be necessary to tell your doctor for practical reasons. <S> For example, some medications are not allowed for pilots, so you may need to explain to your doctor that they can only prescribe certain drugs or treatments for your condition, which will necessarily involve telling them you're a pilot. <S> Although I don't know about the rest of Europe, I would expect it's one of the things that is harmonised across the EASA region.	In the US, you are not required to inform a doctor that you are a pilot.
What kind of sunglasses are good for flying? I'm a beginner at aviation. I'm currently in training for gliders license.Our instructors mentioned that sunglasses are very important if not mandatory. What kind of properties do I need to look for in sunglasses to determine whether they are good for flying? <Q> No polarizing glasses, they make reading anti-glare instruments difficult and sometimes even limit your outside view if the cockpit windows are polarized as well. <S> Good fit <S> , you don't want to loose them in the slightest of turbulence. <S> Consider fitting a strap so you can temporarily hang them around your neck. <S> They also need to be comfortable if you wear a headset over them. <S> Neutral colour (grey, grey-green, brown) of the lenses, which does not distort the natural colours too much as that would make distinguishing navigation lights more difficult. <S> Actually the FAA have published a safety brochure on sunglasses which covers many aspects. <A> No matter what type you get in the other answers, make sure they're comfortable. <S> Realize the headset will be pressing the arms into the side of your head. <S> I used some Oakleys that I think left permanent dents in my skull. <S> One thing you may consider as a student is the sunglasses ability to accept a pair of flipdown blinders??(not sure of the name) that are used for IFR training. <S> Waay better than the hood, but still not as fun as real IFR. <A> There are some good answers to a similar question here which may help you on some general things. <S> But as mentioned no polarization due to its issues with glass cockpits. <S> There are lots of low profile sunglasses out there that may look cool but let a lot of light in on top and bottom of the lenses. <S> Also as mentioned they need to fit under your headset nicely <S> so some larger frame stuff wont work that well. <S> I prefer the Ray-Ban aviators (non polarized) with the classic green lens. <S> They sit will under head sets and have nice coverage. <S> Avoid any lens that has a gradient tint, I tried to fly with a pair of gradient tinted aviators I also own and it was miserable.	Good eye coverage is key and this will depends on your eyes and how different glasses sit on your face.
How are GA aircraft ferried from factories? It's relatively easy to transport jet aircraft like Airbus and Boeing: most of them have a long range, and a few hops at most would get them to the owner. But how would a Cessna manufactured in U.S. be delivered to Dubai? It would not have the range to cross the Atlantic. Taking a brand new single-engine aircraft across a large ocean also sounds very risky (to the occupants). Same story applies to Hawaii. Getting there may also require many hops (e.g. Texas -> California -> Canada -> Alaska -> Japan -> Taiwan -> Singapore), making the transportation long and costly. Are they put on trailers and shipped like cargo? If yes, how is the aircraft taken apart? (I'd imagine even the wing span of a 172 would be too wide for roads in many countries) EDIT: the linked question addresses airliners. I am specifically interested in GA airplanes. <Q> Ferry flights are quite common; the recent Cirrus ditching in the Pacific was a ferry flight to Hawaii. <S> As well as planning a suitable route and dealing with permits and paperwork, refueling etc., the ferry company may install extra fuel tanks to give more range, and provide the pilot with specialized survival and communications gear. <S> And an airline ticket home, of course :-) <S> This might all seem expensive, but considering that a new top-of-the-range Cirrus SR22 has a list price of almost USD 800,000 you can imagine that ferry costs aren't necessarily a big deal in comparison. <S> The second option is to put the aircraft in a container and ship it, and there are some companies who specialize in this (the page has some small photos of aircraft in containers). <S> The major concern in this case is removing the wings: gliders and many experimental (e.g. home-built) aircraft are designed to have their wings removed for storage and transportation (towing behind your car) but most typical Cessnas, Beechcraft etc. <S> aren't. <S> You need to have the aircraft professionally and carefully prepared and then re-assembled and checked after delivery. <S> Which option is best depends on the costs of each option and the value of the aircraft. <S> There's also the consideration that if you buy a 60-year old aircraft from the other side of the world, ferry companies may decline to fly it to you because of the risks of subjecting it to the stresses and weather of a very long series of flights. <S> Or their/your insurance company may refuse cover for a ferry flight for the same reason. <S> Or perhaps the aircraft is certified for VFR only, which would make a long ferry journey much more difficult to plan and execute. <S> In those cases, container shipping may be the only available option. <A> You can often get to Reykavic airport in Iceland for crossing the Atlantic. <S> If that hop is still too far you can install extra fuel tanks in the cargo hold and/or passenger area temporarily. <A> I can't tell you, if this applies to Cessnas or not, but at least some of the lighter planes are simply shipped by ship or cargo planes. <S> They take those apart. <S> Not completely of course, <S> but they take off the wings and tail. <S> Once they are arrived, they put them back together or leave that part to the new owner. <S> I don't know whether this applies to all or some planes, but at least my boss's was transported this way. <S> He went to Rotterdam to pick it up. <A> Newly manufactured US general aviation aircraft are usually flown by pilots who work for (or contract to) delivery companies. <S> As an example, Piper contracted a lot of their deliveries to a company who specialized in worldwide aircraft delivery pre-GPS. <S> Anthony Vallone was one of their pilots and wrote Air Vagabonds which clarifies the dangers of flying small GA aircraft solo to various parts of the world. <S> Some companies provide delivery flights to their region for used and new GA aircraft. <S> Clamback and Hennesey are notable for to/from Australia deliveries and have had to ditch in a near new Cessna 182 due to engine failure. <S> Atlantic crossings now mandate IFR and so VFR only aircraft are more likely to be container shipped. <S> However Vallone's book details temporary fitment of nav/comm to comply with over ocean requirements like HF radio. <A> All the new aircraft deliveries I have been involved with were done by the buyer or the leasee. <S> The normal process involves a physical inspection of the aircraft, paperwork, accessories, making sure the correct documentation is in hand, as well as one or more test flights to assure aircraft performance. <S> In every delivery I have accepted, there is usually a squawk list, and the manufacturers are great at performing seeming miracles overnight. <S> It is not uncommon that there is a couple of days of squawks. <S> I often invite a factory test pilot along on the flights, as that helps identifying issues. <S> Some of the things I check include the rigging and trim of the aircraft, the power plant performance, the radio installations (which can require some coordination when picking up a plane mid-continent and testing HF), the autopilot systems, and the ECS. <S> Funds are transferred and paperwork is filed, and a flight to the destination is accomplished. <S> Normally close fuel and power plant monitoring is done for that flight, and things like WX radar, strike finders and other avionics are extensively run. <S> If we don't have someone who has significant experience in the aircraft, we take training at a place like Flight Safety, in a simulator. <S> Training is normally classified as initial or recurrent. <S> The training outfit can tailor the training to include the specific equipment and engines that are included in the delivered aircraft. <S> The bulk of the aircraft I have personally accepted of delivery on are turboprops and jets, but it also includes a few piston aircraft. <S> Some local flight schools, charter and FBOs have hired me to accept delivery of aircraft for them. <S> In my opinion the acceptance of new aircraft is more than just kick the tires and ferry the aircraft. <S> It is a through systems checkout, and verification that all documentation is in place, cosmetics are good, and so, verifying that the end user receives a plane which is unlikely to have any issues, and that it performs as advertised.	As you've guessed, there are two options: a ferry flight, or shipping the aircraft in a container.
Does Daylight Saving Time affect local airspace? Only some countries use Daylight Saving Time. In Canada, some provinces use and don't use DST (such as Saskatchewan). However, in remote and local regions where this is not observed, what would happen? What happens when areas that do not observe DST are controlled by areas that do. (Cleveland controls parts of Southern Ontario). How does this affect local airspace? Does it affect global airspace as well? What are the safety implications? How does it affect Air Traffic Controllers operating these different spaces? <Q> This is from the FAA's AIM, but other countries do the same for obvious reasons: 4-2-12. <S> Time a. <S> FAA uses Coordinated Universal Time (UTC) for all operations. <S> The word "local" or the time zone equivalent must be used to denote <S> local <S> when local time is given during radio and telephone communications. <S> The term "Zulu" may be used to denote UTC. <S> This question covers in much more detail why UTC is used in preference to GMT , and <S> this question explains why pilots need to know the time in the first place, at least under IFR (which applies to almost all airline flights). <A> Does daylight saving time affect local airspace? <S> Yes <S> and No. <S> In aviation Flight plan information, weather, etc. <S> all use Zulu Time (UTC). <S> This provides a single time standard everyone in the world can use, and avoids misunderstandings based on various national rules for "Daylight Saving Time", "Summer Time", etc. <S> The airline / airport / travel agent / etc. are responsible for properly converting UTC times to the local timezone for passenger convenience. <S> Similarly active times for restricted airspace, TFRs, etc. are all published as UTC times to eliminate any possible ambiguity in this regard. <S> Not everything is based on UTC however: <S> The (FAA-operated) tower at the field I fly from operates from 0700–2300 Local Time . <S> When the United States messes with the clocks twice a year the UTC hours of operation/effective hours for the Class D airspace will change to remain aligned with the same "local time" operating period. <A> Air Traffic Control uses UTC or Zulu time which is the same, all the time, the whole world over. <S> Local only flights will use local time. <A> Yes it does, some Major international airports, notably SYD, have a curfew in place. <S> Commercial passenger aircraft land between 0600 and 23:00 AEST or face sanctions. <S> This in turn affects patterns in Dubai, Singapore, KL, LAX, DFW etc. <S> This is a "must depart by" issue for some of these. <S> This is a politically motivated rule to appease voters in the flight path and is tied to "local" time. <S> Aircraft arriving early are slowed and fly laps over suburbs, sharing the joy. <A> It does have an effect, look in St-Hubert, they have to work an hour longer in the summer! <S> That might be true anyway, <S> but when reading times in the CFS there are always adjustments for the time change. <S> Essentially the airport (or parts thereof) opens and closes at the same local time but the zulu time changes. <S> TWR St-Hubert 118.4 352.5 (E) 1045 <S> -05Z‡ <S> Apr-Oct; 1045-04Z <S> Nov-Mar <S> You may think that doesn't happen in Sask. <S> , <S> but look- <S> TWR Saskatoon 118.3 244.7 (E) 1200-0445Z <S> Mon-Fri Mar 11-Nov 3, 1245-0445Z <S> Sat-Sun Mar 11-Nov 3, 1245 <S> -0445Z <S> Nov 4-Mar <S> 10 <S> They also have to make adjustments to their times to accommodate traffic from other provinces. <S> They also work longer in the summer. <S> This is from an old CFS I found online, don't land and say I said they would be open. <A> In all air traffic control systems, all time is UTC (called "Zulu time"), which doesn't have daylight savings. <S> Local time is only used when communicating with passengers (departure/arrival boards, announcements, boarding tickets, etc). <A> Some class D towers are only open part time based on local time. <S> So yes, daylight savings time will impact when the tower and class D airspace is active.	Aviation always uses UTC time .
What would prevent a solar powered aircraft staying aloft forever? Focusing on aircraft, not balloons, I found this question that led me to some basic research on atmospheric satellites . I imagine the technology has evolved since NASA's research more than 10 years ago. Given the following points: The aircraft cannot stay in flight forever, as it must land for maintenance (as would any aircraft). In 2001, NASA planned a 40h long trip based on solar powered technology. A fuel-powered UAV can stay up to 33h in flight . The Qinetiq Zephyr stayed aloft about 2 weeks. Redundancy can be added to continue operation in case of equipment failure (as in any commercial aircraft). 'Real' satellite can stay airborne for several years (payloads seem to be able to operate several years without maintenance) If the aircraft can land, the payload and equipment do not have to be as reliable as they would on 'real' satellites, as they could be changed or repaired. For an atmospheric satellite based on solar-powered airplane technology such as the NASA's Helios, operated in normal conditions, what is the most restrictive element that make landing compulsory? <Q> The most common failures in planes start with: a human mistake or a mechanical failure . <S> Where, of course, mechanical failures are much more likely to happen on moving parts. <S> Satellites have very little moving parts: you get couple servo motors to adjust the angle of your equipment such as the solar panels and the antennas. <S> Both happen in units of full rotations a day. <S> You also often have some small rocket engines to correct the satellites course, but they are rocket engines whose moving parts comprise more or less just one valve. <S> In a plane, however, you have pieces that move very fast and fluids of all kinds (not only fuel which you need not have on a solar-powered plane, but also lubricants, hydraulics etc.) <S> , also very sensitive mechanical sensors whose non-stop operation is crucial for the flight. <S> This all needs to be inspected, oil levels checked, hydraulics checked. <S> Last but not least, the weather in the space is quite calm, compared to the atmosphere. <S> Depending on how high you fly, you meet clouds, storms, birds, temperature changes etc., which all can add to the wear of things and make things require maintenance. <A> Other than mechanical or human factors, the other key considerations would be the weather and the season. <S> The weather would affect even a high-flying solar powered aircraft because they descend (albeit slowly) during the night cycle. <S> Note that thunderstorms, jetstreams and even mountain wave can reach into daytime flying heights as well. <S> There needs to be a trade off between how high the aircraft can fly in the thin air and the size, weight and fragility of the resultant design. <S> This would put the aircraft at eventual risk during one or more phases of the flight. <S> The season (in combination with the aircraft's position) would affect the amount of energy it could receive from the sun. <S> Whilst a solar powered UAV may fare well in the summer months in the northern hemisphere, it may not be possible to fly it continuously in the winter months, for example. <S> As most applications are location specific, and typically over industrialised regions, this precludes moving the aircraft to the equator or flying a sinusoidal pattern between the two tropical circles. <S> In your mechanical assumptions it would also be worth accounting for ionising solar radiation (which may affect onboard computer and memory chips) and stronger UV light, which is likely to have a degrading effect on most of the materials used to build the aircraft. <S> Finally, just a mention that redundancy may be a sensible approach for when there is spare payload and/or energy, but would be less desirable when these were both at a premium. <A> One that I can think of is the charge/ discharge effectiveness of the battery. <S> the more charge/ discharge cycle applied to a battery, the less effective the battery can hold its charge, down to 70%. <S> Eventually, the batteries need to be replaced before running out of power at night. <A> There are some practical matters which factor into this issue. <S> With satellites there is a high launch cost, and servicing them in space is also very expensive. <S> So the systems are designed for an economic life which is derived from the expected failure rates of all the systems, and things like the depletion rates of RCS used for station keeping, etc. <S> So there is a high economic incentive to design systems that have a long life. <S> With solar powered UAS, the costs are much lower, and certainly the launch cost is a couple of magnitudes or so less. <S> The cost to service is low, if the aircraft can be retrieved, maintained and relaunched. <S> So really there is little economic incentive to make the investment to have a UAS which can stay on station for years. <S> So in my opinion, it is possible to have solar powered UAS which will station keep for very long times, but there is little economic incentive to develop the high reliability systems (perhaps including redundancy) because the cost to retrieve and relaunch is low. <S> One such application for aircraft like this is to provide data connectivity over cities or even remote areas, kind of like launching an airborne hotspot.	In addition, their design requires a very carefully managed flight envelope: an unstable air mass could easily destroy the aircraft. I'm not sure which would be the limiting factor, but I think that either some equipment wouldn't be operational without maintenance, or you would get a mechanical failure of some kind.
Are military jets always scrambled when communication to a commercial aircraft is lost? I've heard that in case a commercial flight does not respond to Air Traffic Control, military jets would always be scrambled to check the state of the flight. The benefits of scrambling jets are clear. My question is, are they always scrambled in every case? <Q> Basically you are asking if there are exceptions to that rule. <S> I think there are a few. <S> First of all, ATC will not inform the military of every instruction that is not reacted to; there wouldn't be enough jets. <S> Pilots do miss instructions occasionally, sometimes aircraft are handed of to the wrong frequency by ATC, wrong frequencies are entered into the radio etc. <S> All these things usually sort themselves out in matter of minutes and it would be a waste of resources to scramble. <S> If no contact is established after a certain amount of time, only then the military will be involved. <S> However if an aircraft starts to deviate from earlier acknowledged instructions without reacting on the radio, it is safe to assume that the time to alert the military is considerably shorter. <S> And then of course the aircraft must be in range of military jets. <S> An aircraft halfway across the Atlantic is simply too far out for most interceptors so until the aircraft is getting closer to shore <S> I don't think there is much reason to scramble jets. <S> Some more information about loss of communications, causes and prevention can be found in this Skybrary briefing note . <S> For obvious reasons the exact procedures for scrambling military aircraft are not publicly available. <A> There are well-defined procedures for communication loss and even for interceptions (at least in the US, but I guess other countries are similar). <S> However those procedures are vague on when an interception is required: <S> In conjunction with the FAA, Air Defense Sectors monitor air traffic and could order an intercept in the interest of national security or defense. <S> Intercepts during peacetime operations are vastly different than those conducted under increased states of readiness. <S> The interceptors may be fighters or rotary wing aircraft. <S> The reasons for aircraft intercept include, but are not limited to: (a) Identify an aircraft; (b) Track an aircraft; (c) Inspect an aircraft; <S> (d) <S> Divert an aircraft; (e) Establish communications with an aircraft. <S> As you can see, there are no significant details there and certainly no one is saying that intercepts will always be ordered. <S> But there are a couple of reasons why it's difficult to say anything more. <S> First, it's security-related, and <S> the people who know the real answers won't give them anyway. <S> See here for some related discussion. <S> Second, as this question explains, there are various reasons for launching jets: a political gesture, a demonstration of a country's military capabilities, and/or a piece of security theater . <S> It's probably a safe bet that most developed countries have processes in place for when to launch an interception, but they certainly aren't public. <A> I would answer: No. <S> In the U.S. there is a "lost comm" procedure which is detailed in the Airman's Information Manual 6-4-1 . <S> I <S> this procedure, the crew should enter the lost comm code, 7600, into the transponder. <S> If in radar range, this signals to ATC that the aircrew knows that it's radio has failed, and ATC may presume that the crew will follow normal lost communications procedures. <S> As long as this is happening, and it looks like procedures are being followed, there is a good chance fighters will stay on the ground. <S> If, on the other hand, The crew keys in 7500, the hijack code, I would presume chances of a scramble are significantly elevated. <S> Basically the procedures look like this: <S> In Visual conditions, or if Visual conditions are encountered, land as soon as you can. <S> In instrument conditions, do your best to follow your flight plan as it was most recently cleared. <S> More details are in the manual. <S> It is interesting that there are a few ways to re-establish communications. <S> For example, ATC or flight service can utilize the voice feature of available navigation beacons, and may issue an instruction like, "Airline 1234, if you read, turn to heading 150." <S> If the crew can pick this up, they may be able to respond with a turn and they can continue from there. <S> The situation being under control, no need to send up interceptors. <A> Are military jets always scrambled ... <S> Some regions are protected by armed platforms in continuous orbit.	Over Europe and many other parts of the world, the general rule is that if an aircraft in controlled airspace does not reply to instructions from Air Traffic Control, military jets will be scrambled to intercept the aircraft. Back to the question, NO .
Why does manifold pressure increase with power? Whilst writing an answer to this question , I remembered something I don't really understand. The partial vacuum in the inlet manifold is caused by the piston descending with the inlet valve open during the "suck" phase of the Otto cycle. It is this vacuum that causes fuel to be pushed into the intake, the greater the vacuum, the greater the fuel added to the inlet charge and the greater the power. Since the needle valve is on the manifold side of the throttle butterfly along with the input to the MAP gauge, why does the manifold pressure increase with power? I would have thought more power, more "suck", lower pressure; more pressure, less "suck", less fuel. I'm obviously wrong since that's not how it works but why? The answers to this question get close but I'm still missing something (and I'm sure will soon be embarrassed by the obviousness of the answer). <Q> Manifold pressure is actually a measure of the vacuum pressure between the throttle and the cylinders. <S> The more the throttle is opened, the closer that manifold pressure returns to atmospheric pressure. <S> The amount of fuel provided to the engine depends on the pressure difference between the manifold and the throttle body. <S> The throttle body pressure will decrease as the throttle is increased, because of greater rate airflow across the venturi <S> (faster air -> lower pressure). <S> The manifold pressure will increase as throttle is increased, due to the greater flow of fuel/air mix into the manifold (greater mass of air flowing into a fixed volume -> higher pressure). <S> So the pressure difference will get larger as the throttle is increased. <S> This link has a pretty good description of what's going on. <A> Manifold pressure is the pressure in the fuel\air mixture between the throttle and the engine. <S> When the throttle is at low power, then it is preventing fuel\air from flowing which causes a reduction in pressure. <S> This is because the engine is trying to pull fuel\air, but throttle is preventing it much like sucking on a straw stuck into thick milkshake. <S> When the throttle is wide open, then the fuel is able to freely flow & you should see normal pressure just like outside (i.e. 29.92). <S> In other words, the pressure is actually decreased when at low power & at "normal" pressure when at full power. <S> For more info check out this link <A> I'm answering my own question since the existing answers are good, but do miss a key point in my question which ultimately was the source of my confusion. <S> I mistakenly thought that the fuel needle valve is on the manifold side of the butterfly. <S> Therefore, I could not understand why more vacuum (less power) did not result in more fuel (more power). <S> The reason is that the valve is on the intake side of the butterfly and therefore, the more open the butterfly, the lower the pressure on the intake and therefore, the more fuel. <S> So, increasing throttle opens the butterfly which lets more air into the engine faster, which causes a drop in pressure (because of the venturi) in the intake which draws more fuel. <S> Sorted! <A> The intake stroke creates a vacuum in the cylinder. <S> This vacuum allows the fuel air mixture into the cylinder. <S> That constant cycle keeps the manifold pressure lower than the atmospheric pressure while the engine is running. <S> The amount of mixture available to the cylinder is controlled by the throttle valve. <S> The more the valve is open the greater volume of mixture available to the cylinder. <S> That is why manifold pressure is the lowest at idle and the greatest when the engine shut down. <A> Manifold pressure controls power production and the throttle controls manifold pressure. <S> Pressure does not increase because more power is being made, rather, more power is made because opening the throttle (increasing pressure or reducing vacuum) allows the engine to pump and burn more fuel/air mixture. <S> A carburetor contains the throttle for controlling airflow into the engine. <S> It also contains a venturi which meters the amount of fuel mixed into the air. <S> The ratio of gasoline to air must remain approximately 14:1 in order to burn properly, so as airflow increases through the venturi vacuum in the throat also increases, pulling enough more fuel to keep the ratio correct. <S> More fuel without more air or vice versa would cause the engine to quit. <S> Also shown is the choke plate, which is used to get extra fuel into a motor before it is up to operating temperature. <S> Closing the choke adds manifold vacuum to venturi vacuum to pull more fuel into the intake. <S> Fuel does not fully vaporize when the motor is cold and it will not burn if not vaporized, so the extra fuel makes enough vapor for the motor to run. <S> As the motor comes up to operating temperature, the choke is opened so the normal amount of fuel is mixed with the air.	The amount the throttle is open determines the pressure in the manifold.
How does a CVR / FDR determine when to stop recording? For example, the CVR records only about 2 hours of data. Overwriting important data must be avoided, and thus the recorders should know if a catastrophe has happened. Then they can stop recording (to protect the already recorded data from overwriting), and start signaling the rescue team. What is the logic used to stop recording? <Q> The CVR and FDR have impact switches to stop recording when they experience high acceleration. <S> In incidents and accidents that don't involve high enough acceleration, the plane remains intact enough for the boxes to be immediately found and switched off manually. <A> In the United States, CVRs and FDRs have a 10 minute (+/- <S> 1 minute) battery requirement to allow any available post-crash voice and data to be recorded, with power removed once a timer limit is reached. <S> While I'm not familiar with the internals of the FDR, simple circuitry could trigger the timer to start based on current flow from the battery, if not for an acceleration-based impact sensor suggested. <A> In crash the last two hours before the crash is most important, so the recorder always recording and stopping when the plane crashes either because of crash sensor or simply due to loss of power and input as the wires leading to it are torn by the impact forces is the right thing. <S> However in some incidents ¹ the data would also be useful. <S> When the crew realizes something occurred that needs to be reported as incident, they are supposed to pull the circuit breakers after landing and tell the appropriate safety board to come for the data (which must be done before next flight). <S> Alternatively if the aircraft is equipped with quick access recorder ² they can instead preserve those data, which can be done by any maintenance worker, so the plane can be dispatched again. <S> However sometimes the crew fails to realize they should preserve the data (or fail to report the incident altogether and it may be reported by someone else like another crew, traffic controller, maintenance etc.) and get scolded for it. <S> ¹ Incident is any occurrence in which safety margins were reduced, but nobody was hurt and there was no or only small damage (with damage to engines or landing gear always considered small). <S> The kind of incident where investigators would most want to have CVR and FDR data and don't always get them is TCAS activations (near misses); they generally have ATC voice recordings and radar tracks, which ATC records in much longer loop, but the on-board recorders often get overwritten either before the planes land or because the crews fail to preserve them. <S> ² <S> The quick access recorder is not crash-worthy and not mandatory, but most airliners have it these days. <S> It usually has longer recording loop and records more parameters, but the main advantage is that any mechanic with portable computer can download the data in couple of minutes and the aircraft can be dispatched again instead of waiting for the safety board investigator to come around.	In more serious crashes, the boxes stop recording because of the physical destruction of everything but the memory units (only the memory units are built to survive crashes).
How much does it cost to give an airliner a fresh coat of paint? Just a random thought I had: the weather gives a jet's paint job a battering; meaning they need to be resprayed approximately once every 5-10 years. (See How often is a passenger jet aircraft painted? ) Roughly what might a paint job for a 777 like the one shown in the YouTube video below, cost an airline? Bonus: I believe afterwards that the weight of the plane has to be recalculated, so as not to affect weight-and-balance . How is this calculation done? <Q> <A> A news article that linked that video said it took Emirates Airlines 6550 hours to repaint 21 aircraft, an average of 312 hours each. <S> They run a round-the-clock operation, with 26-30 people working at any given time, so that translates into roughly 8500-9000 man hours to complete each plane. <S> If the average entry level salary there is similar to the US at \$18/hr, that's upwards of $175,000 just in labor. <S> And if a paint job weighs 555 lbs on a 747 (and that's after it dries – think of the lost moisture), and your spray efficiency is around 50%, we're talking closer to <S> 2000 lbs of wet paint to purchase to get the job done. <S> At around 9.0 lbs/gallon, that's about 220 gallons of paint. <S> Sherwin Williams sells paint for around \$50/gal, so that's another \$11,000 for the paint. <S> Then facility costs for electricity and cooling, but I don't have to get into that, as we're already nearing the upper estimate of the per-aircraft cost vasin1987 cited in his answer . <A> £900'000, apparently , in the case of the Royal Air Force's Airbus A330 Multi Role Tanker Transport . <S> I know it's not exactly an airliner. <S> For reference, this is what a paint-job costing a little under £1 million looks like (both photos below from BBC News ). <S> It's not clear to me why this particular repainting job should be so expensive. <S> Perhaps it reflects the British Prime Minister's famed ability to obtain excellent value for tax-payers' money on prestige projects. <S> Here's the plane in its original livery: <S> I am not a military aviation expert, so I cannot say whether it is a good thing for a dual-use air tanker to be made more conspicuous. <A> The cost depends on a lot of factors, how many planes, how many colors, how desperate the manufacturer is for your business or if you have your own paint shop. <S> But given the care that must be taken to use the correct paint, the correct solvents, dispose of everything and the FAA requirement that the paperwork for the job must weigh more than the paint - I'm guessing several $10K. <S> Boeing have some data on the amount of paint and if you should paint or polish including the fact that the paint scheme on a 747 weighs nearly 0.5Ton <A> Not an expert far from it, though have inspected large aircraft paint finish for Government contract job and £84million hanging on the outcome, once. <S> It is a specialised area, much stripping, pre-treatment, tie-coats, preparation, not your average paint and partial stripping of components may well be required. <S> It feels like, say £900,000 for a multi-colour finish, might be something of a bargain. <S> A previous comment suggested weight gain about 550 lbs (American?), sounds reasonable, but factor in stripping losses first. <S> Specialised labour, working at heights, safety regime, security requirements, safe disposal of waste, it's a big project <S> so project management team and large facility, (American?)it all adds up. <S> Hope this is helpful and not pompous.	According to WallStreetJournal article , Tom Horton stated in an interview that : A 777 paint job can cost \$100,000 to \$200,000, depending on the number of colors involved, and a smaller Airbus A320 can cost $50,000 or more.
Is "General Aviation" a well-defined term in the US, in the EU and/or elsewhere? In this earlier question I tentatively assume that GA means civil aircraft operations other than scheduled passenger transport - what I think of as "airliner" operation though it could include quite small aircraft operating a scheduled fare-paying passenger service. It has been suggested to me that GA can sometimes or often be used to mean all aviation in general - perhaps in some contexts more than others. I had thought that most people here used GA to mean aircraft operations other than scheduled service, but now I have my doubts. So, is there an authoritative definition of GA in the USA (and elsewhere, or worldwide) or is it a vague and varyingly interpreted general phrase that I should avoid to prevent misunderstanding? <Q> The FAA does not include a definition of General Aviation in CFR 14 (aka Federal Aviation Regulations) <S> Part 1 (General Definitions and Abbreviations), but, from a functional perspective, in the US, GA is generally used to refer to any civilian operations falling outside of Part 121 and some Part 135 operations (Commuter and Charter Operations - regional feeders have and may still operate under this section if they can meet the requirements, as it is more relaxed and easy to comply with than part 121). <S> With respect to the FARs, it's important to remember that Part 91 covers ALL types of flight operations UNLESS its provisions are EXPLICITLY overriden by another paragraph (as would be the case with an air carrier's Operating Specifications, part 121, 135, and other sections dealing with more specialized aerial applications). <S> Part 119 also deals, in a very general sense with conducting flight operations for compensation. <S> IMO, you're not likely to go wrong using the term to refer to everything civilian outside of scheduled carrier and medium/large cargo operations (e.g. Atlas, Evergreen, FedEx, UPS). <S> The caveat is, of course, that GA operations are so diverse that this is more of an "everything else" category rather than the much clearer images conjured up by a flag/commutter/regional carrier or a large cargo operator. <S> If you're unclear about whether a specific application or air operator falls under GA, go ahead and ask. <S> The FAA division of airports is more likely meant to reflect that certain airports have certain primary intended purposes (e.g. many of the nation's largest airports do not allow Part 91 operations, only air carriers) and may require certain types of infrastructure in order to allow them to perform those roles. <S> And yes, using a 737 as a personal plane under Part 91 would fall under GA - Boeing <S> even makes a specialized version just for that, see the BBJ. <A> In the Pilot/Controller Glossary , the FAA now defines General Aviation as: <S> That portion of civil aviation that does not include scheduled or unscheduled air carriers or commercial space operations. <S> and it gives the ICAO definition: <S> All civil aviation operations other than scheduled air services and nonscheduled air transport operations for remuneration or hire. <S> Both these definitions are closely tied to commercial operations, and they go out of their way to point out that non-scheduled air carriers are NOT general aviation. <S> Note that "civil aviation" would mean "not military". <S> Historically the term has been very colloquial, and to some extent you will still find different definitions from everyone. <S> However, IMHO these are the most clear definitions available. <A> The term "General Aviation" is used differently by different organisations. <S> It may be best to either avoid it or only use it where it's meaning will be clear to international or non-expert readers. <S> From what I've read, Use vs Type <S> These sorts of classification apply to the use (i.e. "operation") rather than to the aircraft <S> type <S> (make and model) - you could use a 737 as a personal airplane and your use would not be governed by regulations that apply to 737s operated by typical airlines for scheduled passenger transport. <S> FAR lore <S> I've read people say that, in the USA, GA means anything under FAR 91 and FAR 135 but scheduled airliners come under FAR 121 <S> (I may have the numbers wrong, please correct) <S> AOPA say "General aviation (GA) is all civilian flying except scheduled passenger airlines. <S> " <S> ICAO define general aviation as all civil operations other than scheduled air services (plus a bit of hand-waving) <S> Transport Canada say "General aviation (GA) is all civil aviation operations other than scheduled air services and non-scheduled air transport operations for remuneration or hire". <S> FAA divide airport operation into Commercial Service, Cargo Service, Reliever and everything else "commonly described as General Aviation Airports". <S> But I couldn't find an FAA definition that applied specifically to the aircraft (or to aircraft operations other than at an airport). <S> EASA seem to define operations primarily into Commercial Air Transport (CAT) and Non-Commercial (NC) and use the phrase "general aviation" in a more general all-encompassing sense.	In common parlance, "General Aviation" typically means "not-airline".
Is there a maximum lift to drag ratio? If I recall correctly, the best competition gliders have a L/D ratio as high as 60:1. What imposes this limit? Is there a maximum theoretical L/D ratio, or could sufficiently advanced materials allow a glider with a L/D ratio of, say, 200:1? <Q> Gliders need to fly in tight circles to use updrafts, and the larger the wingspan becomes, the bigger the speed difference between inner and outer wing will be. <S> Also, landing such a wide wing without dropping a wingtip will be very hard. <S> Smaller wings with a high aspect ratio will have a low chord length, leading to smaller Reynolds number s, which translates into a steep increase of friction drag if the aspect ratio is increased without increasing wing area. <S> Therefore, only adding wing span will help, and this runs into a soft wall beyond the 30 m of designs like the Eta . <S> In addition, the current mass limit of 850 kg will make bigger aircraft unattractive for competition pilots. <S> The Concordia (pdf!) is claimed to have an L/D approaching 75, but I have learned over the years to see theoretical predictions as invariably optimistic, and realistic performance, with bugs on the wing and all, will never quite measure up to the hoped-for ideal. <S> Werner Pfenniger proposed to use boundary layer laminarisation by suction (pdf!) to reduce friction drag and proposed glider designs with L/D ratios in excess of 100. <S> Turbines at the wingtips would drive the suction pumps, so these would still be unpowered aircraft. <S> But so far nobody has dared to turn his visions into reality. <S> While laminarisation avoids the increase in friction drag of a turbulent boundary layer, a moving wall would eliminate viscous losses altogether. <S> Now the friction generation is between the moving wall (this could be a taut foil running between two cylinders at the forward and aft end of the wing) and the fixed structure. <S> With current materials there is no hope of reducing drag this way, but who knows what tricks will be possible in the future. <S> A glide ratio of 100 or more looks rather unlikely in the next 50 years. <A> With any measure of aircraft performance, we must begin with the airfoil section. <S> All reasonable real-world airfoils start at about a 120:1 best L/D. <S> This is because with a testable airfoil you typically have an optimal combination of Cl = 1.2 & Cd = 0.10; hence the L/D of 120:1 (read "Abbott and Von Doenhoff" for more theoretical and practical considerations). <S> As you add the drag of extraneous components to your airplane like: cockpits, wheels, control surfaces, dirt, doors, screw heads, antennas, wing tips, ventilation, panel seams, and so on; you chip away at the best achievable configuration L/D. <S> For airplanes like the Space Shuttle you'll end up with a L/D of less then 5:1 <S> (hence the phrase "Flying Brick"). <S> A typical general aviation aircraft on the other hand, has about a 9:1 L/D. <S> For a sophisticated sailplane where extreme attention is made to the details, the configuration suffers only a 50% performance loss and achieves the aforementioned 60:1 L/D. <S> Higher performance is certainly possible, but is likely to be incremental in nature. <S> The starting point in designing an airplane often sets the initial configuration such that wing-skin friction drag is equal to the mathematical lift-induced drag. <S> Following that calculation, we start adjusting things until an acceptable configuration emerges. <S> The more realistic the first guess, the sooner the configuration emerges. <S> When evaluating advanced concepts like boundary layer suction or blowing, the performance cost of powering the air pumps is often ignored in testing; as is the reality that many microscopic pores quickly clog and are rendered ineffective, so be careful about taking the boundary layer control performance data at face value. <A> Loosely speaking, <S> L/D ratio is limited by the aspect ratio of the wing (its length to its chord width) and the friction of the wing surface (which is why frost/ice on the wing is a bad thing -- it dramatically increases wing friction). <A> Yes, you can have a L/D as high as you'd like. <S> But I don't think you'd enjoy flying in milliKelvin liquid helium superfluid which has zero viscosity... <A> The lift and drag coefficient are defined with a fixed and uniformed pressure. <S> Therefore, gravity and Archimedes' principle should not be involved in this topic. <S> The maximum lift-drag-ratio is obtained with infinite wings. <S> 2D airfoil optimization with genetic algorithm give the following optimization for the lift/drag ratio: <S> 1/0.00166/0.002=300 000 <S> https://optimization.mccormick.northwestern.edu/index.php/Wing_Shape_Optimization <S> This is a theoretical limit of course.... <S> which do not have some much sense in the present real world with finite wings, clear-air turbulence, surface roughness, water on wings,etc...	With current technology the L/D might go up to 70 or 75, and going higher would require an almost impractically large wing span.
Why don't fighter jets take off vertically? I've heard the claim repeated many times that some modern fighter jets have an installed thrust greater than their weight, so theoretically they could accelerate straight up. I've never actually heard of this being done, however. It sounds useful, though, especially on the deck of an aircraft carrier. Imagine: we could take out the whole catapult system, and replace it with some sort of a system to pick up an aircraft and turn it vertical. Why is this not done? <Q> They can climb vertically, but this works best if they are several tons below their maximum take-off mass. <S> Fighter jet engines need a lot of fuel, and at the beginning of the flight the aircraft will be too heavy for vertical climb. <S> Also, the landing gear would need to be rearranged if the plane is to take off from any airport. <S> Even a thrust/weight ratio slightly above 1 at maximum take-off mass will not be enough, because the aircraft needs some airspeed for its control surfaces to become effective. <S> The Harrier VTOL jet uses bleed air which is ducted to nozzles at the extreme ends of fuselage and wing for low-speed attitude control. <S> It is conceivable that the fighter will hang vertically on a wall, with its wheels locked in clutches which will release it when the needed thrust is reached. <S> With thrust vector control the aircraft could be controlled over the full trajectory until it transits to horizontal flight, and could even land vertically. <S> But this would need specially prepared airfields and use much more fuel than a conventional take-off, leaving less fuel for the mission. <A> Yes, they can accelerate straight up (even at max weight in some cases), but to accelerate straight up from 0 airspeed requires some kind of control to keep the aircraft stable. <S> All of the aircraft's normal control surfaces only work with air flowing across them, so if you stood it up and pushed the throttles forward it would simply tip itself over. <S> This is why VTOL aircraft always have more than one point creating thrust, they use thrust to stabilize the aircraft as it rises. <S> The other consideration (as Peter mentioned) is that it's less efficient to climb this way, meaning less fuel for the mission, lower takeoff weight, or some other tradeoff. <A> The closest the US ever got to it is the ZEL program for the F-100 Super Sabre. <S> Basically, put the F-100 on a cruise missile launch rail, strap one hell of a big rocket booster to its arse, and run for cover. <S> Used to have a 90 minute VHS tape about the project, they got so far as to design underground launch ramps with nuclear blast proof doors to launch the fighters after Soviet bombers. <S> Never went operational though, by the time it had progressed to where it could work in practice the Nike SAM system was mature enough the ZEL program was no longer needed. <A> Well they sometimes do. <S> A pilot or flight lead can request an unrestricted climb to cruising altitude for the purposes of practicing intercepts or other training maneuvers as this F-22 Raptor demonstrates. <S> But this does employ a conventional takeoff and accelerating the jet to a pre-determined speed before going vertical. <S> In regards to an engine thrust greater than 1:1, this applies to static conditions at sea level, generally using full afterburning. <S> As you increase in altitude, the rated thrust that the engines can produce degrades with decreasing air density. <S> The idea of a pure VTOL fighter has been explored with the "tail sitter" designs such as the Convair XFY-1 <S> Pogo or Lockheed's entry . <S> These designs were feasible for a proposed cruiser based fighter interceptor, but the configuration made it difficult to land and the project was abandoned shortly after a series of test flights. <S> Both the Harrier series of attack aircraft and the new F-35B can take off and land vertically, but at a greatly reduced fuel an dpayload required for hovering; These aircraft prefer short take-off operations from ship with a warlord, then land vertically once this is depleted with completion of a mission. <A> One other factor to consider: if a fighter with a thrust to weight ratio of greater than one can launch vertically off of a ship, how does that fighter land back on the ship? <S> Being out in the ocean, there's no where else to land, and if the ship has a flight deck for landing, may as well use it for a much safer conventional takeoff with a much higher combat load. <S> This was the issue faced with the three tail sitters the US financed in the 1950's, from Convair, Lockheed, and Ryan. <S> The bottom line: landing on the tail, with the pilot looking over their shoulder in the attempt, turned out to be far too difficult, on stationary land, with a huge landing pad, and no battle damage. <S> Trying to land a tail sitter on a moving ship after carrying out a combat mission would have been even more difficult. <S> All three efforts were abandoned as being impractical in military conditions.	If no thrust vectoring is installed, the aircraft will be uncontrollable in its initial ascent.
Why do airline pilots have shoulder harnesses? On airliners, passenger seatbelts are simple lap belts. However, flight crews seem to have at least shoulder straps, and often five-point harnesses. Why do flight crew have more restraints? <Q> pilots need to be able to do work during turbulence. <S> passengers don't really like to be fully restrained. <A> They're required. <S> ICAO Annex 6 <S> , Part 1 states: <S> 6.2.2 <S> An aeroplane shall be equipped with: ... c) 3) a safety harness for each flight crew seat. <S> The safety harness shall incorporate a device which will automatically restrain the occupant's torso in the event of rapid deceleration <S> It also confirm's Ben's comment that they are also meant to restrain an incapacitated pilot: Recommendation. <S> – <S> The safety harness for each pilot seat should incorporate a device to prevent a suddenly incapacitated pilot from interfering with the flight controls. <A> I recall early in my glider training when I was about 17 before Id gone solo. <S> My instructor used to keep his shoulder straps loose <S> so I started doing the same. <S> On my 1st actual cable snap on the winch tow <S> I whacked the stick forward and the glider went into -ve g. <S> It was an open-cockpit glider with no canopy <S> and I was half hanging out and only just managed to reach and get fingertips of one hand onto the joystick to pull myself back into the plane. <S> I stabilised the glider, pulled my straps tight, but then found out my instructor behind me was not responding. <S> I landed safely and then found out he was unconscious. <S> He had bashed his head on the wing above him and passed out. <S> I always had my straps fastened properly after that incident. <A> <A> In airliners, shoulder harnesses are not installed for passengers because: it is not not mandated by law <S> it is too much for average passengers to deal with <S> it requires money to install <S> it is superfluous in a crash when compared to the same safety from a lap belt Flight crew is required to use the shoulder harness (when installed) as it is the law ( 14 CFR 91.105 ): (a) <S> During takeoff and landing, and while en route, each required flight crewmember shall— <S> (1) Be at the crewmember station unless the absence is necessary to perform duties in connection with the operation of the aircraft or in connection with physiological needs; and (2) Keep the safety belt fastened while at the crewmember station. <S> (b) Each required flight crewmember of a U.S.-registered civil aircraft shall, during takeoff and landing, keep his or her shoulder harness fastened while at his or her assigned duty station . <S> This paragraph does not apply if— (1) <S> The seat at the crewmember's station is not equipped with a shoulder harness; or (2) <S> The crewmember would be unable to perform required duties with the shoulder harness fastened. <A> If the plane is in turbulence, and the passenger is jostled about, injured, or even knocked unconscious, well, sucks for him, but he will recover. <S> The more extreme the situation, the more important it is that the pilot be conscious, uninjured, and stable. <A> For passengers, while flying I feel fully restrained around the hips by a lap belt fully tightened- it would be more comfortable to have the belt load spread out. <S> A full car seat belt compared to a lap belt allows you full motion. <S> Its more likely the cost and difficult of having more anchor points on all seats especially when they spread them across the plane- a place to join the belt to the seat at higher point. <S> They might also have to design the seat to handle its load being more spread out. <S> Let alone having to work out if having such "improved" belts actually helps survivability with the greater risk of being unable to unclip.	There have been some "unusual attitude" instances where the crew have recovered the aircraft but would have possibly been thrown from their seats or unable to reach the controls through excessive G if not fully restrained.
Why are commercial airplanes painted at all? While there was debate over why airplanes are painted white and a question about how much a new paint job costed , what hasn't been asked is why airplanes are painted at all. I remember one airline company sent out a press release in the 1980s or 1990s that keeping its planes unpainted (i.e, a nice silver) saved several hundred gallons of paint as well as considerable cost savings because the plane was also lighter and used less fuel. If there are considerable positives to keeping planes unpainted, why do airline companies bother painting them? This is prompted by a recent flight I had on an US Air airplane that had just been repainted in the American Airlines livery. The captain joked that the paint was still so new that we shouldn't try touching it. Both companies are famous for always being in severe debt -- so saving every penny should have meant going for the 'naked' look. Related: A quora question on how much money would be saved if airlines stopped painting their liveries and a Boeing white paper on painted vs unpainted <Q> I remembered hearing that paint actually reduces the drag of the plane. <S> Searching a bit I found this Boeing document describing it. <S> Of course there is the billboard effect too. <S> From the report: <S> In response to numerous questions raised by Boeing customers regarding the efficacy of surface coatings to reduce drag, Boeing has investigated some possible airflow physics explanations. <S> Possible explanations postulated by Boeing aerodynamicists include: Increased regions of laminar flow due to reduced surface roughness. <S> Reduction in surface roughness resulting in lower skin friction drag, when flow is turbulent. <S> Reduction in dirt and/or insect adhesion resulting in reduced roughness and hence reduced skin friction drag. <A> Quite apart from the paint preventing corrosion, which puts the lie to the idea that AA flies unpainted aircraft (they don't, they use a clear paint on metallic parts and metallic paint on non-metallic parts), there's the economic factor. <S> Those aircraft are flying billboards for their owners. <S> That's why they're repainted or at the very least have stickers applied when rented/leased out to other operators. <A> Painted aircraft can be kept looking clean with a relatively quick wash, while unpainted metal requires comparatively more effort and time (thus, money) to be kept shiny. <S> The fuel savings may simply be more than offset by the maintenance fees. <A> I think more importantly it also helps the ground crews and the air traffic control tower responsible for ground traffic. <S> When looking at a line up of planes from a distance, you can eliminate a majority of planes right away because they are either the wrong airline or wrong type. <S> Now you only have to compare the tail numbers of a couple aircraft. <S> Several years back I was getting a tour from a friend of orlando's control tower, and as you can imagine it is a pretty busy place especially up top where they are relying on their eyes to organize the traffic on the ground. <S> When tracking an aircraft that's taxing, they have two pieces of information, tail number and airline. <S> So if you have a lineup that goes AA, United, UPS, United, Frontier for instance, you don't even have to break out the binoculars to know what their tail numbers are except to maybe to differentiate between the two united flights. <S> Speeds up the process and also cuts down on careless error. <A> Why are aircraft painted at all? <S> Because of the flying billboard function. <S> Marketing determines the colour scheme, not techical reasons such as weight savings (which is true) or drag reduction from paint (which is false). <S> Because of protection. <S> The paint protects against small scratches from sand etc which may start fatigue cracks. <S> If the polished skin is re-buffed 3 times a year it is closely scrutinised - but preventing is better than curing. <S> Polishing removes a very thin layer of aluminium oxide and I could find no references that the amount of removed material would be a problem during the lifetime of an aircraft. <S> On a 737-800, the coat of paint weighs about 70 kg, on a B-777 about 200 kg. <S> The cost increase due to higher maintenance requirement is about 60 kUSD <S> in 1998 dollars or 85,000 dollars/year now, for an airline with 100 B737s <S> this equates to higher maintenance cost of 8.5 mUSD/year. <S> This is offset by the reduced fuel costs from the weight savings, depending on air miles. <S> Corrosion prevention is an often quoted reason for the coat of paint. <S> However there is a specific type of corrosion occurring only on painted aircraft. <S> From a Boeing document : Polished surfaces are protected from corrosion by regular buffing after washing. <S> Painting protects against oxidation, salts, and jet fuel spills. <S> However, unrepaired chips and cracks in paint collect dirt and moisture and so may become corrosion sites. <S> Painted surfaces are also susceptible to filiform corrosion, or worm corrosion, which begins between metallic surfaces and paint and erodes both. <S> It creates hydrogen and lifts up the paint layer as it travels across the surface. <S> Another Boeing document addresses claims that paint may reduce drag. <S> It effectively refutes these claims, stating that both painted and polished aeroplanes are aerodynamically clean. <S> It does recommend to keep them that way, by washing all planes at least three times a year, due to accumulated dirt and insects which do cause increase of drag. <S> Something that was found by the regular buffing of polished aircraft, I believe that in the past polished aircraft were found to have lower operating cost which was first attributed to weight savings but later turned out to be due to less insect residue. <S> All in all, aircraft are painted for good reason. <S> And sometimes they are not painted, also for good reason.	Another interesting thing is, that planes are regularly repainted to keep the drag low. So the painting reduces the fuel costs, instead of increasing them. They are a major part of brand recognition.
Why are number of landings logged? I have flight logs for a WW II B-24 navigator who flew with a combat crew in China Burma India. There is a column for number of landings. The entries range from 1 to 5 or 6, mostly 1 or 2. The time can be as long as 8:00 to 10:00 or more. Why is the number of landings recorded? Is that still done today? <Q> Yes, it's still done today, at least in military aviation. <S> It's to ensure that the undercarriage does not excede the number of landings it has to endure before being checked/overhauled/replaced. <A> I'm not sure if this is specifically a military question or a general question. <S> In general aviation (FAA) you are required to do a certain number of landings every 3 months to stay current. <S> So landings are logged for this reason. <S> The specific regulation is 14 CFR 61.57 (a) (1) , which says ( emphasis added ): <S> […] no person may act as a pilot in command of an aircraft carrying passengers or of an aircraft certificated for more than one pilot flight crewmember unless that person has made at least three takeoffs and three landings within the preceding 90 days […] <S> I am not yet rated for IFR, so I'm not sure on the specifics about IFR currency mentioned in this regulation. <S> The currency for VFR related flight differs from day and night; however, 3 night landings in 90 days will count to keep you current, while 3 day landings will only keep you current for daytime VFR. <S> A note on military training: <S> I was able to find this book/article that alludes to the training of navigators during the second world war; on P.585: Before 1933 instruction in navigation was given only as part of pilot training. <S> If the individual in question had a military career and joined before '33 he may have been a pilot first and simply continued with the same log book. <S> Why the landings were logged may just be force of habit. <S> Either way its an interesting read on how difficult it was to be a navigator at the time and exactly what it took to become one. <A> Landing is not the easiest thing on an airframe! <S> It imparts a lot of stress, and everything we build is designed and evaluated by some statistician to endure a certain number of uses + or - some standard deviation that he/she defines. <S> Even the keys on your keyboard are meant to endure a certain number of presses. <S> Additionally, if you CAN collect data that you suspect may be useful later, why not? <S> You never know when you may want to use it for something you didn't intend to. <S> Not sure about the navigator though. <A> I suspect it has to do with the fact that pilots want/need records of that for certification purposes and <S> Pilot In Command <S> can change in the middle of a flight. <S> Seems silly for a navigator though.	Landing an aircraft can typically be the most stressful regime of flight in terms of loading of certain bits of the aircraft, so it is pertinent to log how many times it happens per flight.
What is a vortex generator? I saw a vortex generator mentioned in an aircraft listing. What is a vortex generator? <Q> The angle of the plate causes the air to swirl, creating a vortex behind it. <S> This effect allows the air flow to remain "attached" to the surface even at points where the flow without a vortex would separate from the surface. <S> One of the most common uses of vortex generators is on aircraft wings forward of the ailerons. <S> When the aircraft wing stalls , the flow detaches from the wings. <S> This means that the flow will detach before it reaches the ailerons, making them ineffective. <S> The use of vortex generators helps the ailerons to provide control even if the rest of the wing is stalled. <S> Source <S> Of course, these also add drag, even when the wing is not stalling, so they are only added where needed. <S> They are also used in other places, such as the engine, as in Farhan's comment above , and also on the tail of the 737 . <A> I will try to explain the physical mechanism, adding extra information compared to previous answers. <S> As mentioned before, the vortex generator is usually taking the shape of a plate. <S> What this plate is doing is generating an small vortex. <S> This vortex is basically a region where the flow is rotating around its axis. <S> Basically this plate extracts energy from the flow generating this rotation on the flow. <S> Ok, this rotational flow has got energy and, if properly oriented interacts with the boundary layer over the wing providing further energy to it. <S> With that extra energy the boundary layer is more resistant to separation, that means, that you can increase the angle of attack further and obtain a higher lift coefficient for the same wing. <S> Now comes the why?. <S> A vortex generator is always creating drag, always but it might reduce the fuel consumption of the airplane. <S> How? <S> Think about overall design of the airplane, for a given flying condition the amount of lift generated can be obtained big lift coefficient times wing surface. <S> Imagine now, that we are designing the airplane and we have found that the condition that is dimensioning the needed size of the wing is, for example, the maximum runway length at take off, in order to reduce it you need to generate more lift at an specific speed. <S> For being able to accomplish that you can either increase the wing surface or increase the maximum lift you can obtain from the wing, and you can accomplish that by introducing vortex generators smartly designed for that condition. <S> A trade off is later on made between increasing the wing surface (with the impact in drag and weight) and including the vortex generators. <S> So, although adding those vortex generators are adding drag compared to a clean wing, it might be the case that you are actually reducing fuel consumption because the other alternative is adding more wing surface and the optimum solution became the vortex generators. <S> There are several location of vortex generators, some of the on the vertical plane improving rudder efficiency, others in the upper surface of the wing, others over the engine affecting the slat during take-off or landing. <S> Another use of vortex is after designing the airplane as quick fix to solve “unexpected issues”. <A> They're little winglet type things that you install on the surface of the wings to encourage laminar flow of air and to discourage stalls. <S> Think of them as "cheap insurance for when you're not monitoring your airspeed very well". <S> Edit for future readers: Should be attached flow, not laminar flow. <S> See below comments for explanation.	To be more general, a vortex generator is a small angled plate installed on an outer surface of an aerodynamic body.
Why can't I exactly match the same points on different VFR sectional charts? I am taking a trip from somewhere on the Phoenix sectional up to the grand canyon. I wanted to just splice the two sectionals together on my computer and then print them out. I picked a coordinate to align (as you can see in the first image), and with that coordinate aligned, almost nothing else on the map matched up. Why aren't the sectional maps standardized to people can do this more easily? I would have loved to make a "custom" map out of the Phoenix sectional, Vegas sectional, and Grand Canyon map, but it's virtually impossible without modifying them further, which I don't want to do in case of messing up the scale and/or orientation. <Q> This is by no means specific to aviation charts. <S> Most likely it's simply general property of local maps. <S> Maps are flat, but earth surface is (approximately) spherical. <S> So to represent ground features on the flat map a projection is needed and this projection can't preserve all relations—angles, distances and areas—precisely. <S> So there are many different projections that distort different properties. <S> While such projection does not preserve exactly any properties out of the centre, the distortion grows with distance from the centre, so for small areas it's appropriate. <S> This however means, that each section uses different projection and that near the edges the maps will be distorted each in a slightly different way. <S> That's why the maps can't be easily laid out to form a bigger map. <S> You would have to lay them out on a sphere. <S> You could try using some software for stitching panoramatic photos ( here is one such you can use for free). <S> That should be able to apply suitable transformation to make the maps match. <S> At the cost of increasing the distortion. <A> The FAA's graphical index of sectional charts shows all the charts for the coterminous 48 states laid out on a singlemap projection, but the areas covered by the charts do not all alignwith the rectangular boundaries of that projection. <S> If you were to obtain copies of all the charts and attempt to lay themout according to that projection, you would have to rotate the westerncharts clockwise and the eastern charts counterclockwise. <S> So even if the charts are truly drawn to the same projectionand are perfectly executed, you will not be able to align them perfectlyjust by moving them up, down, left, or right. <S> You will need some rotation as well. <A> There are a few reasons that may cause this. <S> First off I assume you are getting your images from here in which case if you look at the 2 PDF downloads in question the maps were issued on different dates. <S> Although its unlikely it is possible that things were moved on the map between these 2 issue dates. <S> I cant tell where you are trying to join the maps but if you are trying to join them mid map (not edge to edge) <S> you may have issues even though they should line up. <S> This is a decent write up of the different kinds of map projections and how distortion comes into play when projecting a spherical surface on a flat piece of paper. <S> This distortion could cause some of the issues. <S> I would also thing some error can end up in maps when they are printed. <S> If you use apps like foreflight or the like you will see that the points which are often GPS based dont always line up perfectly with the map. <S> Lastly, you should NOT make your own maps to be used for actual navigation. <S> There are many issues this could create that I will not go into as it does not have to do with the answer to the question. <A> WAC and sectional charts use Lambert conformal conic projections. <S> the scale error varies with lattitude to preseve great circle as straight lines. <S> Cones have flat edges <S> sphere's do not. <S> https://en.wikipedia.org/wiki/Lambert_conformal_conic_projection	Any two contiguous charts might or might not be rotated at the same angle;charts directly north or south of each other (several pairs along thenorthern edge of the 48 states) might be aligned, but other pairs of chartsthat have an east-west offset (most of the other adjacent pairs)are likely to be rotated at a different angle. Small area maps are usually drawn in azimuthal projection with the central point in the centre (or significant point near the centre) of the mapped area.
What does "radar contact" mean in ATC calls? When ATC mention 'radar contact', what does that mean? In what conditions ATC might contact you and mention 'radar contact' in the call? and what would be the appropriate responses? <Q> The FAA's Pilot/Controller Glossary gives both US and ICAO definitions: <S> RADAR CONTACT - a. Used by ATC to inform an aircraft that it is identified on the radar display and radar flight following will be provided until radar identification is terminated. <S> Radar service may also be provided within the limits of necessity and capability. <S> When a pilot is informed of “radar contact,” he/she automatically discontinues reporting over compulsory reporting points. <S> [...] <S> b. <S> The term used to inform the controller that the aircraft is identified and approval is granted for the aircraft to enter the receiving controllers airspace. <S> (See ICAO term RADAR CONTACT.) <S> RADAR CONTACT [ <S> ICAO]- <S> The situation which exists when the radar blip or radar position symbol of a particular aircraft is seen and identified on a radar display. <S> RADAR CONTACT <S> LOST - Used by ATC to inform a pilot that radar data used to determine the aircraft <S> ’s position is no longer being received, or is no longer reliable and radar service is no longer being provided. <S> The loss may be attributed to several factors including the aircraft merging with weather or ground clutter, the aircraft operating below radar line of sight coverage, the aircraft entering an area of poor radar return, failure of the aircraft transponder, or failure of the ground radar equipment. <S> Note that this is not a universal term, Canada uses "radar identified" instead. <S> Their equivalent of the P/CG is the Glossary for Pilots and <S> Air Traffic Services Personnel : <S> Fr: <S> « Identifié radar » <S> And: “Radar contact” U.S.: Expression for: “Radar identified” <A> No specific response is typically necessary (although acknowledging that you heard the transmission with a callsign or "roger" is appropriate). <S> The call means that the controller sees your aircraft on radar & has confirmed that "this" target is "that" aircraft, i.e. your aircraft. <S> He is now capable of providing ATC services that require the use of radar, such as radar vectors, separation, traffic calls, minimum altitude monitoring, etc. <S> Not saying that he necessarily IS providing all of those things; there's a little bit of context to such things. <S> You can also hear, "radar contact lost" either when you are below the radar horizon due to terrain, or over the water too far away from from the radar site. <S> This means that you're now, if flying IFR, operating under non-radar IFR rules, and things like making position reports at the mandatory reporting points now applies. <S> (You don't have to make those reports while in radar contract.) <S> Interestingly, you may also (rarely) hear a military fighter call "radar contact" in response to a traffic call, meaning that he sees the traffic on radar, but not visually. <S> Not sure if that's standard terminology for them in an ATC environment or not, but I've heard it a few times. <A> Context: You will typically get this the first time you contact an ATC facility <S> and they reply with a squawk code . <S> "Radar contact" is to tell you that they now know which blip (aka contact) on their radar display is you and are thus able to provide various radar services--though whether they actually will is another matter. <S> Notably, if you don't hear this, you're likely either below their radar coverage or talking to a facility that doesn't have radar at all. <S> Obviously, they're not able to provide radar services in that case. <S> They're likely to ask for position and altitude next <S> so they know where you are relative to other aircraft. <S> If they do see a primary radar return at the position you give them but <S> no secondary, it's likely your transponder isn't working; in that case, they probably won't ask position again but will ask your altitude occasionally--and near a busy class B/C airspace, will likely tell you to keep out because having to verify that every time another plane comes near adds too much work. <S> Responses: If all they say is "radar contact" and nothing else, just acknowledge it with your callsign. <S> Usually, though, they'll start giving you traffic advisories, and you'd reply to those with "looking" or "in sight". <S> If you didn't specify why you're calling them on your callup, they may also ask you to "say intentions" <S> so they know what to do with you--and may start giving you vectors accordingly, which you would need to repeat back as usual.	“Radar identified” An expression used by ATC to inform the pilot of an aircraft when radar identification is established.
What's the advantage of using short wings rather than long wings? To clarify the question, I mean the type of wing used on a Concorde or a fighter jet, vs a glider's long and thin ones. What is the aerodynamic reason for using a short wing when the plane is faster? <Q> Another reason to have shorter wings on high-speed or maneuverable aircraft deals with the aircraft's aspect ratio , which is the ratio between its length to is breadth/chord. <S> Longer wings (high aspect) bend more under load, and may twist, which causes structural issues. <S> Additionally, aircraft with shorter wings (low aspect) can roll much quicker. <S> This means that a fighter jet with short wings may roll at rates up to 720 degrees/second while a large airliner or cargo plane may roll at 15-60 degrees per second. <S> A third reason is parasitic drag. <S> From the linked wikipedia article above: While high aspect wings create less induced drag, they have greater parasitic drag, (drag due to shape, frontal area, and surface friction). <S> This is because, for an equal wing area, the average chord (length in the direction of wind travel over the wing) is smaller. <S> Due to the effects of Reynolds number, the value of the section drag coefficient is an inverse logarithmic function of the characteristic length of the surface, which means that, even if two wings of the same area are flying at equal speeds and equal angles of attack, the section drag coefficient is slightly higher on the wing with the smaller chord. <S> However, this variation is very small when compared to the variation in induced drag with changing wingspan. <S> For example, the section drag coefficient $c_d$; of a NACA 23012 airfoil (at typical lift coefficients) is inversely proportional to chord length to the power 0.129: <S> $$ c_d \varpropto <S> \frac{1}{(\text{chord})^{0.129}}.$$ <S> Since parasite drag increases with airspeed, and high aspect wings have higher parasite drag, it makes sense for high-speed aircraft to have the wing that creates less drag at high speeds, and the slower aircraft to have the wing that creates less induced drag. <S> You can see this in a simple graphic of the drag curves: (Since the induced drag is lower at high speeds anyway, there is little point in minimizing that, rather minimize the type of drag that is a much larger factor at high speeds) <A> You may want to take a look at this and this <S> but generally it has to do with the fact that many things change at super sonic speeds mainly <S> The primary advantage of the delta wing is that, with a large enough angle of rearward sweep, the wing’s leading edge will not contact the shock wave boundary formed at the nose of the fuselage as the speed of the aircraft approaches and exceeds transonic to supersonic speed. <A> At low airspeed, the aerodynamics of long thin wings are great. <S> The longer and thinner, the lower the induced drag (the drag inherent in creating lift, very dominant at low speeds). <S> However, aero requirements always seem to be contrary to structures requirements. <S> Savings in aerodynamics are often offset by increased weight of structures, and a balance needs to be struck for the best fuel economy. <S> The wing shape is very dependent on the maximum design speed of the craft, roughly as follows: <S> Subsonic < Mach 0.6: long, thin and straight please. <S> Induced drag is the dominant design factor. <S> High subsonic < M0.85: friction drag becomes more dominant, induced drag is less due to higher speed, and compressibility effects start introducing quite a bit of extra drag. <S> Wing sweep is introduced. <S> A long, thin, swept wing creates a high amount of torsion, heavier structure etc, so unfortunately we need to keep the wings a bit shorter and stubbier. <S> New materials and wing profiles enable longer and thinner wings again with less of a weight penalty. <S> Transsonic between M 0.85 and <S> M1.2: Compressibility is such a dominant factor that the area rule <S> is much more important in reducing drag than the wing shape. <S> Whichever wing shape fits the area rule is best. <S> But fuel economy in this speed region is always questionable, either slow down like all pax planes or speed up like Concorde. <S> Supersonic <S> > <S> M 1.2. <S> Compressibility drag is all dominant, and now we want to mainly limit this form of drag. <S> Induced drag is of no concern anymore. <S> A very good way of limiting shock wave drag is to make sure that all of the wing stays within the shock cone streaming from the nose tip: within this cone, airspeed is lower than outside the cone. <S> Even for military planes where fuel economy is not the dominant design factor, the performance penalty of having the wing stick out of the shock cone is considerable. <S> Source <A> Short wing means less structural weight. <S> But an airplane needs an optimum wing surface area (optimum for its weight, in other words the wing it needs to generate enough lift for the size of the airplane). <S> A longer wing is much more efficient (generate more lift for its surface) but at the expense of weight (you need a beefier structure to maintain the integrity of the wing, so there is a sweet spot in between)	So for the same lift, a shorter wing would be lighter, but study have shown that lift is not generated on the full span of the wing, so a short wing would not be efficient.
Can a commercial cargo aircraft be converted into a commercial passenger aircraft, and vice versa? Just saw a video in a news, a military cargo plane carrying people stranded in some country. The seats were like in a commercial airliner. This led me to ask the question. Would it be possible to see some examples where it was done, along with the procedure? <Q> Image courtesy of canalblog.com <S> Image courtesy of airliner.net <S> Nice film to show the process. <S> Military transport aircraft can also be fitted out with stretchers or seats, or whatever other combo of stuff you want. <S> To the best of my understanding these lock in like any other cargo pallet in the floor. <S> They are less concerned with aesthetics and more with practicality: Image courtesy the DOD via Wikimedia Image courtesy of aarcorp.com <A> It applies to helicopters too. <S> When on holiday in the West Indies, one of the locations offered helicopter rides. <S> If anyone booked one, they contacted the local freight helicopter company who put the seats back into the helicopter, then they flew you round the bay, then took the seats out again to continue their bread-and-butter freight work. <S> The pilot told us helicopters come with seats, they took them out and put them in the shed. <S> They formed the company to shift building materials to construction sites. <S> One day a man approached them and asked if they could do sight-seeing rides for tourists. <S> They checked the seats were still in the shed and said "of course". <A> I used to fly a Twin Otter aircraft that was used in the UK to carry cargo (newspapers) at night and passengers in the day. <S> The seats were carried in the rear of the aircraft and the pilot who flew it at night put the seats in before he went home. <S> No certification was needed as there were no modifications.	There are such a thing as "Quick Change" aircraft, allowing entire 'pallets' of chairs to be exchanged for cargo.
Why don't big airliners have bigger doors? Reading this question I saw this picture in MikeFoxtrot's answer and noticed how easier it would be to board the plane using that huge door: I understand that for single aisle planes you wold need to form a single line anyway, but for two aisle planes having a wide door could speed up the boarding process a lot. So, is there a reason why it is not done? What is the limiting factor in the door size? <Q> Multi-aisle commercial aircraft adopt a multi-door boarding strategy rather than a single-huge door (see the A380 or the B747, both use two doors). <S> A door interrupts both frames and stringers and weakens the overall aircraft structure. <S> A huge door interrupts many more frames than a small one and two small ones can be set apart from each other to have some continuous frames between the two, restoring some rigidity. <S> The complex closure systems ensure that part of the stresses are carried by the door material, but it will never be perfectly transmitted as it would be without a door. <S> As mentioned before, the stresses are heightened if the compartment is pressurised (as when passengers have to be transported). <A> Before answering your question, please take a look at the excellent answer to <S> Why aren't planes loaded from both ends? , which talks about increasing efficiency in boarding passengers. <S> Airliners do not need bigger doors for boarding people because people are not like big crates which are loaded into airplanes using forklifts. <S> To incorporate a wider door, we need to do the following: have a bigger foyer inside the door <S> All space on a passenger airplane is fully utilized to the maximum extent. <S> Having a large area just to greet passengers and help them to their seats is not a very efficient use of that space. <S> size of jet bridge New jet bridges will be needed, which can allow more than two people walk side-by-side. <S> gate procedures <S> Most of the airlines have designated their seats into zones 1 . <S> When boarding, people are called in a manner which expedites the boarding process. <S> With a bigger door, this process needs to be adjusted for boarding more people at the same time. <S> At present, only A380 has an upper deck for passengers, which extends the length of the aircraft. <S> They already have multiple jet bridges to maximize the boarding process: <S> Image Source 1 : <S> Not talking about travel classes . <A> A door involves reinforcement of the structure around it (on the fuselage), so a bigger door involves more structural reinforcement, which means it adds more weight (because of the beefier structural reinforcement). <S> In airplane, whatever you do, you want to keep the weight of the structure as low as possible, so you can carry more people. <S> It's economic reason (the airline is a business). <S> Technically windows need structural reinforcement as well, but without window it would be boring, and probably less people would fly (they would feel less safe to not see outside). <S> The cabin is pressurized, so the bigger the door, the more pressure pushing to pop it open (which is why it would need beefier structural reinforcement)	This helps under the structural viewpoint: the presence of a door (cargo or passenger that might be) induces design problems that are amplified if the compartment has to be pressurised.
Does an A320 revert to Direct Law if both engines flame out? In the case of a flame-out in both engines on the two-engine A320, does the aircraft revert to Direct law or does it maintain Normal Law ? An example is US Airways 1549 (the landing on the Hudson). <Q> The airplane needs a primary source of electrical power in order to remain in normal law (among other things of course). <S> If both engines lose power, then the generators on those engines also lose power. <S> The only other primary electrical source is the APU generator. <S> In addition to the batteries, the RAT (ram air turbine) is also available to supply electric power (along with hydraulic power) in an emergency situation. <S> In this mode, the flight controls reconfigure to alternate law until a generator is brought back online. <S> From the US Airways 1549 report , page 88: ...the captain started the APU, which improved the outcome of the ditching by ensuring that a primary source of electrical power was available to the airplane and that the airplane remained in normal law and maintained the flight envelope protections <A> When both engines have failed, the A320 reverts to alternate law. <S> However the pitch law is replaced by the direct law upon landing gear extension. <S> The side stick movement directly controls the elevator position. <S> It means that side stick input is proportional to flight control output. <S> The THS is mechanically controlled from the trim control wheel. <S> No protection is included. <A> According to https://www.skybrary.aero/index.php/Flight_Control_Laws As is the case with ALT1, some failure cases that result in ALT2 will also cause the autopilot to disconnect. <S> ALT2 is entered when both engines flame out, with faults in two inertial or two air-data reference units, with faults to all spoilers, certain aileron faults or with a pedal transducers fault. <S> In Alternate Law 2 (ALT2), Normal Law lateral mode is lost and is replaced by roll Direct Law and yaw Alternate Law. <S> Pitch mode is in Alternate Law. <S> Load factor protection is retained. <S> In addition to those protections lost in ALT1 (Pitch Attitude and Low Energy Protection), Bank Angle Protection is also lost. <S> In some failure cases, High Angle of Attack and High Speed Protections will also be lost.	The airplane will no longer be in normal law mode if both engines fail and no other electrical generator is online.
How should I deal with a passenger experiencing hypoxia over the Grand Canyon? I am taking my mom for a trip over the grand canyon. My mom lives at sea level, whereas I live at 5000ft, and workout at 8000ft daily. The VFR lowest route over the Grand Canyon is 11,500ft MSL. If I am flying over this with my mother and she starts to exhibit signs of hypoxia, what are my options? It is the law to remain at the prescribed altitudes and headings while flying around the Grand Canyon. That being said, obviously passenger safety comes before anything else. If my mom gets sick, I would have to drop in altitude, but what kind of consequences would I face for this? In the event of hypoxia in one of these corridors, what would be the best way to deviate while remaining safe and courteous? <Q> First, let's be crystal clear on something: <S> A person experiencing symptoms of acute hypoxia is an emergency which requires immediate action to ensure the safety of that person. <S> In an in-flight emergency requiring immediate action, the pilot in command may deviate from any rule … to the extent required to meet that emergency. <S> ( FAR 91.3 (b) ). <S> So if you're over the Grand Canyon at 11,500 feet and your mother starts showing signs of hypoxia you key the mic and let ATC know you have a passenger showing signs of hypoxia, tell them you are descending to a lower altitude, and ask for vectors to an airport where you can land. <S> If they give you any trouble about it you respond with "N12345 is declaring a medical emergency ". <S> All that said, there are sensible things you can do to mitigate the risk of hypoxia and avoid the need to declare an emergency. <S> If you intend to spend an extended period of time at altitude (which I personally define as "Over 10,000 feet" for an average healthy non-smoker): Bring a portable oxygen system Ideally with enough cannulas/outlets for yourself and your mother/other passengers). <S> Carry <S> a relatively inexpensive pulse oximeter Check your SpO 2 periodically to catch hypoxia early - before clinical symptoms develop. <A> You can treat the hypoxia with low cost bottled oxygen supplies specifically made for this situation . <S> , a top of oxygen is all she's likely to need. <S> A pony bottle should let you get through your flight if she exhibits some symptoms, at 12 bucks a pop you can buy 2 just in case. <A> The simple answer is to rent or buy a supplemental O2 system for Mom. <S> Don't fake this one. <S> As Voretaq7 said in the first answer, "A person experiencing symptoms of acute hypoxia" Focus on the word "acute". <S> Just having your Mom feeling a little light-headed is probably not going to hold up as a valid reason to divert lower in any faa action. <S> And if their google-fu is good and they find this website, you will not be able to claim that you were not aware of the potential for a problem. <S> The reason for my warnings: They are serious about the altitude restrictions over the Grand Canyon. <S> Diverting should be reserved for a truly unexpected emergency. <A> In principle at least, you can begin to experience hypoxia at 5000ft. <S> By 10,000ft, it's affecting your eyesight, and probably starting to affect your judgement a little. <S> At 15,000ft, your judgement can be measurably impaired, and you'll often experience euphoria, so you can't TRUST your judgement even if you think everything is okay. <S> Your personal experience and thresholds may vary. <S> FAR 91.211 spells out supplemental oxygen requirements. <S> At 11,500, you're close enough to the FAR regs (12,500) that you really ought to be carrying supplemental oxygen. <S> These regs are known to be very liberal. <S> Bring some oxygen for both of you and no worries.	If a full oxygen system isn't an option bring one or more "boost cans" These can provide temporary/limited relief for symptoms of hypoxia – probably enough to get yourself back on the ground, or at least to a lower altitude. At 11,000ft it's unlikely lack of oxygen will make your mother really ill Just get the supplemental O2 system and you are covered. You don't have to divert, in fact it may be a bad option depending on conditions (I would recommend you don't go if conditions will make diverting dicey though).
Why do propeller blades not have winglets? On the first look this question might sound ridiculous and maybe it is. But as propeller blades act by the same physical laws as wings, and winglets reduce the induced drag by quite a bit, then why are they not put on propeller blades? I could imagine that it might be a material problem. But are there any more reasons? And why exactly might it be a material problem? <Q> Winglets on wings help because they increase the volume of air on which the wing can act. <S> Extending the wing span would be much more efficient , but when span is restricted or the maximum wing bending moment is limited, winglets bring a small improvement in efficiency at high lift coefficients. <S> On propellers , however, the winglets would run through air which is already affected by the tips of the propeller. <S> No additional air will be involved, so no efficiency increase will be possible. <S> Please note that propulsive efficiency is increased by accelerating more air by a smaller amount. <S> The formula for the propulsive efficiency $\eta_p$ <S> of an air breathing engine is$$\eta_p = \frac{v_{\infty}}{v_{\infty} + <S> \frac{\Delta v}{2}}$$where $v_{\infty}$ is the speed of the inflowing air and $\Delta v$ <S> the speed increase of the air affected by the propeller disc. <S> A smaller $\Delta v$ acting on a higher mass flow makes the engine more efficient. <S> This effect is most pronounced when $v_{\infty}$ is low. <S> The prop tip winglets would operate in a region of high dynamic pressure and generate more friction drag without contributing to the prop's efficiency. <S> By the way: Whoever tells you that winglets reduce induced drag quite a bit has something to sell to you, but I digress. <A> Hartzell make propellers that appear to have winglets (tips bent aft) called Q-tips. <S> The name seems to refer to them being quieter. <S> I have read that they do the same job as a slightly larger diameter prop. <S> They seem to have no life issues. <S> Since noise costs energy, and a smaller prop does the same job.... it is possible that they are more efficient. <S> The bent tip is small - on the order of a couple of inches. <A> Winglets on propellers look like propellers that have gone through "ground strike" and the FAA grounds prop-driven aircraft with propellers damaged due to ground strike. <S> It's simply more expensive to manufacture, certify, and maintain; even though it does provide improved thrust in take-off position; but potentially more drag during cruise and feather conditions (based off propeller pitch, will be different with different propellers). <S> BERP tips most likely more effective overall considering take-off, cruise, and feather conditions <S> (feather is the desired pitch during engine failure to prevent wind-mill and drag from the prop free rotating). <A> Pros: <S> Winglets on a prop would limit span-wise flow, leaving more air to work on, because it does not "fly away". <S> Furthermore, winglets can be designed in such a way so as to suck air inboard towards the prop hub, further increasing the amount of air being worked on. <S> They would also reduce induced drag from tip vortices. <S> Anyone who says winglets are trash can explain that to all competitive gliders, Boeing, Airbus, Cessna, and any other modern aircraft manufacturer, most of whom use some sort of wingtip device. <S> Because of the strong outboard flow along the prop, the low pressure air from the top of the blade, and the high pressure air from the bottom of the blade both end up outboard of the propeller, where the low pressure region sucks high pressure air from the bottom of the blade onto the top, thereby reducing the high pressure on the bottom, and increasing the low pressure on top, resulting in a completely useless portion of the blade, which produces very little thrust but still creates drag, and requires more power to turn the propeller. <S> For all of the above reasons, a propeller of the same diameter that is placed into a shroud can potentially create up to 85% more thrust using the same engine, as a propeller that is not shrouded. <S> Cons: <S> A wingtip located on the tip of a propeller would be constantly accelerated outboard, if a regular propeller blade deals with this acceleration rather easily, because it is an axial load on the blade, the winglet would be a cantilever beam, and the forces would rapidly add up creating a rather formidable force on any significantly large winglets on the tip of a propeller. <S> Besides the magnitude of the force, and the fact that it is a cantilever type load, it is also a variable load which is less on low RPM, and higher on high RPM, which quickly leads to material fatigue and structural failure. <S> The cost to manufacture such a propeller would be higher. <S> The weight of the propeller would be higher to account for the structural loads listed above. <S> Boils down to cost, weight, reliability. <A> The concept of 'winglets' was applied in early days of aviation by the inventions of Henri Coanda, patents: 1937GB191112740, 1910; CA370885, 1937; and to boat propellers; you can have a look, also in ESPACENET, at patents: <S> ES-0444150, Inventor: 'Gonzalo Perez Gomez', and ES-8300608, 1987, same; and ES-0293837_U <S> by 'Ramon Ruiz Fornella', all from: 'Astilleros espanoles'. <S> 'NASA <S> Technical Memorandum 87771', by Milton A. Beheim: 'NASA Research in Aircraft Propulsion', shows a propeller with 'winglets'.	I'd say that one of the reasons for winglets in wing tips is to reduce the marginal vortex, due to the compensation of the difference in pressures between the upper and lower surface of wing, this 'vortex' or 'swirl' increases drag, and thus impairs overall airplane efficiency.
What are the advantages of Chemical Oxygen Generation over Gaseous Canisters on board of aircrafts? I'm looking to get a bit of info on Chemical Oxygen generation, especially as done on aircraft. I understand the process of Chemical Oxygen Generation. I'm also aware that weight for weight it produces far more oxygen than Oxygen gas canisters. What I want to know is are there any other advantages? Does it have added safety benefits when compared to high pressure gaseous oxygen storage? The Oxygen candle burns extremely hot when it goes off but I'd imagine high pressure gas canisters could be far more dangerous and prone to exploding if damaged? <Q> Pressurized oxygen tanks have two big minus points: they are heavy, and they are essentially a small bomb. <S> But they have two big plus points: they can be refilled easily and they don't generate any heat when you use them. <S> Chemical oxygen generator plus points are they are lightweight, self-contained and more-or-less maintenance-free (they don't leak). <S> As nearly everything in aviation is a balance of good and bad, we often see both systems being used at the same time. <S> The flight crew will use oxygen on a regular basis - sometimes procedurally, sometimes just to clear up a headache. <S> They need to be able to turn it on and off, and the airline doesn't want to replace the system each time. <S> Passengers rarely need oxygen, and when they do it's only until the plane descends to breathable altitudes (which will happen really quickly). <A> An oxygen bottle is extremely heavy. <S> And when you are on fire you don't want to have oxygen around. <S> And in general when you have to use oxygen in an aircraft, something went wrong. <S> A big jet is about 40 meters long which means you have at least 40 meters of oxygen pipe. <S> By requirement oxygen should be provided from maximum altitude to around FL100 which means 20 or 30 minutes. <S> 435 passengers needing 30 minutes of oxygen means 1 ton of deadload. <S> Replenishing an oxygen bottle is a pain for maintenance (tank temperature, pressure, ...). <S> Maintenance and weight are key factors in the decision. <A> The disadvantages of stored oxygen are that the cylinder can be very heavy, and it contains pure oxygen which can explode on contact with fire or a source of high temperature. <S> However, it can last longer <S> the flow is by demand when the person inhales. <S> This means it can last longer than the chemical generator oxygen supply. <S> The cons are it is one time use and can only supply oxygen for about 15-20 minutes. <S> This means the pilot will only have enough time to descend to a lower altitude. <S> Another disadvantage that it is a continuous supply device, whereby it will continue to supply the oxygen even when you don't need it. <S> Once it is activated it won't stop until all the Sodium Chlorate is used up to produce oxygen.	The chemical generator is cheap, doesn't need frequent maintenance and checks, and can supply oxygen for a larger number of people without adding weight to the aircraft because the oxygen is a byproduct of the burning of Sodium Chlorate. Minus points are they are single-use, time-limited and cannot be shut off.
Why is a control surface that allows two sides of airflow better than those that allow one? For example, ailerons allow air to flow past both the top and bottom surfaces, which makes it more aerodynamic than speedbrakes. Also, plane rudders have air flowing on both sides, which is apparently mote efficient than a spoiler. Why does this happen? <Q> For low drag, you want to minimize the surface changes presented to the air flow. <S> Large changes in the surface will create turbulence and pressure changes that contribute to drag. <S> Small changes will minimize these sources of drag. <S> When you move a control surface like an aileron or elevator, air is flowing past both sides of the airfoil. <S> Although this changes the direction of the flow, which gives the control force as well as some drag, the air can still flow past both sides. <S> In the case of a spoiler, the air cannot flow past both sides. <S> This increases the frontal area presented to the flow, and creates a low pressure area behind the deployed surface. <S> Creating a low-pressure area behind an object is a big contributor to drag, which is why aerodynamic bodies tend to have a teardrop shape . <S> Spoilers on the wing also have the effect of reducing lift. <S> By disrupting the smooth low-pressure flow over the upper surface of the wing, they reduce the effectiveness of the wing, effectively stalling the affected portion . <S> For an illustration of both principles in action, see this video of a speed brake on a Mooney. <S> This shows how even a relatively small object, when disrupting the air flow, can add a significant amount of drag. <A> The reason is that both sides of a control surface experience pressure changes, both ahead and aft of the hinge line. <S> In case of spoilers and speed brakes, only one side is affected, so the effectiveness is only half as big. <S> Please see the pressure coefficient plots of an airfoil for three different flap deflections below. <S> Upper and lower surface pressure are shown by color-coded lines, and lower lines belong to the lower surface. <S> Dashed lines show the inviscid pressure, and solid lines the pressure distribution with friction effects added. <S> The wider two lines of the same color are apart, the more lift is created. <S> Note the contour plot below, which follows the color scheme of the pressure plots. <S> While control surfaces normally are deflected by less than ±20°, regular spoilers are extended by 60° or more to create as much drag as possible. <S> But even if they are extended by similar angles to those of a control surface, the air will have no chance to flow orderly along the leeward side. <S> Instead, this side will only have separated, chaotic airflow, while the windward side will show a flow pattern very similar to the windward side of a control surface. <S> The pressure in separated flow will not change with deflection angle, so this side will not contribute any lift effect. <S> Note in the picture above that the pressure level over the whole chord is pushed up or down by the flap, because the flap is located in the aft portion of the airfoil. <S> In contrast to that, spoilers are mounted mid-chord, where their influence over the pressure level is smaller. <S> This reduces the lift effects of spoilers even more. <A> The main answer is drag. <S> A spoiler will create more drag than a surface that allows flow over both sides. <S> In the case of speed brakes this is what you want to happen as you want to slow the plane down. <A> I think you question comes to the difference between aerodynamic body and blunt body. <S> It is no so much linked to exposing one or two surfaces to the external flow, but more linked to the shape exposed to the external flow. <S> An aerodynamic body has a shape which produces low drag, aerodynamic bodies have a very small size normal to the direction of flight. <S> For example, the wing is really thin in the vertical direction, but huge is the direction the plane is expected to flight. <S> A blunt body is the oppossite way around, exposes a big surface in front of the moving direction. <S> The spoilers are a very good example. <S> I can give you a practical example, you hand. <S> When you are in your car (in movement) <S> and you extend your hand outside the car, having the hand parallel to the ground <S> , you don't notice significant "pressure" or "force" over your hand (please use some nice speed...) <S> however is you set your palm looking to the direction the car is moving, the "pressure" over you hand is much bigger as you are exposing a bigger surface. <S> Example <S> the same phenomena with your hand is happening with ailerons, rudders and airbrake. <S> We use an airbrake to stop the airplane, that is why we use like your palm in the car. <S> Stop the airplane. <S> Ailerons and rudders are intended to not stop the airplane, but control it. <S> That's why the intention is to have low drag.	With control surfaces you want to alter airflow with out creating excess drag.
How might one start a new logbook for an engine that had one lost? About 6 months ago in a hangar at a local (KLWT), I saw a Piper PA-30 Twin Comanche and instantly wanted it. When I got home, I did a look up on the Registration (N) number and found out that the aircraft was de-registered in 2005. I did some asking around the airport the next day and discovered that the owner had passed away. After some more research, I discovered that the airplane had one engine and its prop totaled. It had the propeller and engine replaced, but neither had logbooks and that was why the plane is collecting dust. I really would like the airplane, because it is actually in good condition, yet it sits in the back of the central hangar and is ignored by everyone. So in a nutshell, the airplane is in good condition with airframe, avionics and logbooks for the right engine and prop. There are just no left prop or engine books. The current owners (the estate of the deceased pilot) do not seem to even realize that the airplane is still sitting there, so I do not think that they would put much thought into selling the plane and I might be able to pick it up relatively cheaply. The only thing that I seem to need is a logbook. So I was wondering if it would be possible to somehow just start a new log after purchase? The other option is to just buy a new engine with books. Any advice? <Q> One way to get a new engine logbook is to send the engine for a factory overhaul. <S> Your engine will be regarded as a usable core, and will come back with all tolerances within "as new" limits and a new logbook. <A> As a bonus, there's a good chance the airframe log will have the installation date and time <S> so you might come up with TSMOH too (if not total time). <S> If you can determine TSMOH, there is probably little value reduction due to the missing log assuming you can determine <S> the engine/prop is airworthy. <S> (it's a missing airframe log that really devalues an aircraft) <S> But alas there is airworthiness (the strict FAA meaning of airworthiness) of the engine or prop. <S> You want to know that it meets its type design or properly altered configuration and that it is in a safe condition to operate. <S> So AD compliance does come into question here. <S> If the aircraft went through an annual inspection since the engine/prop replacement, and was declared airworthy, although it is possible that the AD status went with the missing logs, it probably didn't. <S> Typically most shops print out a status report for the aircraft including airframe, engines, props, & appliances and staple the whole report together and place it in the logbook pouch. <S> This happens more often than not so if it's there <S> you're good as long as the inspector signed that any applicable AD was properly dealt with... <S> even the "Previously Complied With" ones. <S> That list then becomes the complying record. <S> Most shops use some sort of computerized aid for AD status. <S> Usually they save the aircraft profile and report in memory <S> so they have less work next year. <S> If your lucky, maybe they can reprint and resign the list. <S> If the airframe logbook has an entry for installing the engine maybe there is a hint of where the engine was overhauled. <S> If so, that overhaul agency should be able to pull up a work order and if your lucky, give you more info like total time and <S> what ADs were complied with at that point, etc. <A> First of all, if the engine hasn’t been run since 2005, it is likely corroded internally and is junk. <S> Don’t worry about the logs, that engine will never legally fly on a certified aircraft unless it is overhauled and receives a new logbook. <S> The other engine and the whole airframe may also be corroded beyond saving. <S> Answering your question more directly: you can buy a new logbook. <S> Your A&P mechanic must list everything known about the engine from whatever receipts the FBO might have, and he must also verify AD compliance. <S> An AD is a mandatory Airworthiness Directive issued by the FAA. <S> The A&P will verify which ADs apply to that airframe/engine and inspect the plane to insure the work has been done. <S> After the A&P completes his work for an Annual Inspection, the airframe will be legal to fly. <S> Sitting for 10 years is very bad for engines and airframes. <S> Be careful going forward. <S> This plane could be a money pit!	For an engine or prop, you can simply start a new log with the appropriate explanation as the first entry.
Is there a fuel injector cleaner additive available? I have not seen any additives (such as those used in automobiles) to clean and maintain fuel injectors in aviation engines. Is there a reason for that such as the use of lead in 100LL or something else? The fuel injectors will eventually constrict or clog as the avgas leaves residual deposits. Is there some technical reason or is it just that no one has gone through the certification process or at least (like AVBlend or CamGuard) received the "will do no harm" approval from the FAA? Removing, cleaning, reinstalling fuel injectors is not only expensive but you also risk damaging them and if you have the GAMI injectors you can have quite a bill coming at you. <Q> Fuel injectors in GA piston engines are actually fixed nozzles, so short of fuel contamination, are not so easy to clog,since the only thing that can be deposited with clean fuel is the blue dye in the avgas. <S> In 8 years maintaining a fleet of 6 to 8 injected Continental engines, running 200-700 hours / year <S> , I did not see a fuel-deposit blocked nozzle. <S> Deposits did change the flow rate enough for us to routinely clean them ultrasonically (our pilots were cruising lean of peak, and would start complaining), but removing, cleaning and reinstalling the injector nozzles was a routine, straightforward and scheduled event in my experience. <S> With position tuned nozzles, as current Continental ones are, you need to be careful to get them back to their correct position, just like GAMI ones, but it's not rocket engineering. <S> The torques for installation are in the manuals, and they are not the most challenging item to work on (one b-nut and one pipe thread per nozzle) on the average GA engine. <S> There's no need for special additives. <A> If your injectors are blocking due to lead deposits a tricresyl phosphate additive may help improve lead scavenging and prevent the problem, but it's probably not going to clean a clogged injector. <S> (TCP is also pretty nasty stuff – leaning your engine more aggressively can often accomplish the same thing without the chemicals.) <S> Frankly 100LL is a pretty darn good solvent: it even dissolves that blue dye they put in it which nothing else ever seems to budge. <S> If your injectors are blocked due to contamination that 100LL won't dissolve having your mechanic take them off and bench-clean them is probably a good idea ( <S> as Thomas pointed out this isn't rocket surgery - any competent mechanic should be able to do it without damaging anything). <S> As far as other "pour it into the gas" cleaning additive, as with many things <S> There's an Advisory Circular that covers this (AC 20-24D) - at least to some extent: That Advisory Circular deals with fuel specifications for type certification of aircraft/engines/APUs, but it contains this interesting nugget: <S> (1) Fuel additives that are incorporated into ASTM, governmental or military specification, or other industry-based consensus organization specification, are considered to be identified in sufficient detail to be accepted by the FAA under existing operating limitations on TCs, amended TCs, STCs, or ASTCs, provided there are no changes to those operating limitations. <S> So if you can show that the injector-cleaner chemical you want to use is an approved additive according to ASTM D910 (the standard that governs 100LL avgas), your use of the additive is in accordance with the specification ("not more than X% or Yppm"), and the additive is not contraindicated by the manufacturer (of the engine, airframe, or any components) <S> you should theoretically be OK to use it. <S> Navigating that legal morass is something you probably don't want to do though <S> : The risks of getting it wrong are not just paperwork-related: some additives can damage your fuel system, or even lead to an engine failure. <S> A bench cleaning of your injectors is probably the easier and safer option. <A> Keep fuel injector clean by using fuel injector cleaners isn't a bad choice at all. <S> I have been using them for years. <S> Try Chevron, Lucas or BK44 to see different between before and after.	I'm not aware of any FAA-approved (or FAA-accepted) products for on-engine fuel injector cleaning.
Do French, Spanish, Italian, and Greek controllers still speak to their native pilots in their native language? At the time of my retirement in 1999, controllers in France, Spain, Italy, and Greece typically spoke to their native pilots in their native language in spite of the fact that English was/is the international language of aviation and is specified as such by ICAO. Not following the ICAO convention deprived non-native speaking pilots of valuable situational information. Does anyone know if any of the aforementioned countries have come around to having their controllers always speak English? <Q> Well, I just pulled up LEMD on LiveATC and heard some Spanish there. <S> So Madrid clearly speaks Spanish sometimes, although it's probably not very busy right now (5:30 AM there). <S> Archives from midday for LFPO and LFBD (Orly and Bordeaux) have plenty of French. <S> Archives from midday for LGAV (Athens) approach has something definitely non-English <S> (I can't tell if it's Greek or not, but I can't imagine anything else it'd be); LGAV has heavy use of English, but it's not exclusively English. <S> And LiveATC has no feeds for Italy. <S> So, for three of them the answer is definitely "yes, they still speak not-English;" for the last, LiveATC can't answer. <A> As per ICAO Annex 10 PDF , it is no longer a recommendation, but a requirement that all controllers be able to speak English with an ICAO language proficiency of at least level 4. <S> ICAO Annex 10 states: <S> 5.2.1.2 Language to be used 5.2.1.2.1 <S> The air-ground radiotelephony communications shall be conducted in the language normally used by the station on the ground or in the English language. <S> Note <S> 1. <S> — <S> The language normally used by the station on the ground may not necessarily be the language of the State in which it is located. <S> A common language may be agreed upon regionally as a requirement for stations on the ground in that region. <S> Note 2. <S> — The level of language proficiency required for aeronautical radiotelephony communications is specified in the Appendix to Annex 1. <S> 5.2.1.2.2 <S> The English language shall be available, on request from any aircraft station, at all stations on the ground serving designated airports and routes used by international air services. <S> 5.2.1.2.3 <S> The languages available at a given station on the ground shall form part of the Aeronautical Information Publications and other published aeronautical information concerning such facilities. <S> This however doesn't mean that countries cannot still work with their own language and countries like France <S> still work IFR & VFR traffic in their local langauge, whereas some countries like Germany limit German to VFR traffic and emergencies, where plain language can be used. <S> IFR traffic in Germany is conducted in English only. <A> In France pilots and ATC have to speak french if they are French <S> This is described in the radiotelephony procedure https://www.sia.aviation-civile.gouv.fr/dossier/texteregle/RADIOTEL_V2.pdf section 2.4 2.4 Use of French language:	The rules of air indicates that the ATC must be able to speak english if they have to deal with international traffic. The French language is used (except for training purposes or particular cases) between French pilot and ATC
Are all the engines on a multi-engine plane the same? In general, are there any differences between the engines on a multi-engine aircraft? Are engines designed to be specifically for the left or right wing, or inboard or outboard for a 4-engine aircraft? What about the tail engine on a tri-jet like the DC-10? Is it the same as the two wing-mounted engines? <Q> Generally yes, but not always. <S> If you include the APU as an engine, the answer would need to be different, but I understand your question concerns just the engines used for propulsion. <S> For jets, the direction of rotation doesn't make much of a difference, so the same engines can be used on all stations. <S> However, with propellers the swirl does influence flying characteristics, especially at low speed, so special left- and right turning versions of turboprop and piston engines are available. <S> Maintenance and logistics become much simpler if only one type of engine is used. <S> In the past, not so much emphasis was placed on this, so some airplanes used different types of engines. <S> Examples were: Convair B-36B , which combined piston and jet engines in the same airframe Junkers G-38 , which used a Junkers L88 inboard and a Junkers L8 outboard. <S> Later, the outboard engines were also changed to the L88. <S> This can be seen from the number of propeller blades: If the outer engines drive a two-bladed propeller, it is the earlier version with the L8. <S> Hawker-Siddeley Trident 3 , which was almost a four-engined jet, because it had a small, tail-mounted RB-162 engine in addition to the three tail-mounted RB-163 Spey to provide thrust on takeoff. <S> Rutan Voyager , which used a bigger front and a smaller rear engine. <A> The place to find the true answer is in the Type Certificate Data Sheet. <S> This document will tell you exactly what engines can be installed on an aircraft. <S> For example on the DC-10-10: <S> 3 General Electric CF6-6D, CF6-6D1, CF6-6D1A, CF6-6K or CF6-6K 2 Turbofan Engines. <S> (CF6-6D and CF6-6K engines may be intermixed in accordance with Appendix XXII of the applicable FAA Approved Airplane Flight Manual. <S> CF6-6D1 and CF6-6D1A engines may be intermixed in accordance with page 2.1 of Section IVB of applicable FAA Approved Airplane Flight Manual.) <A> As this image shows the Navy flew a plane with two propeller engines and two jet engines. <S> Read more about it here. <S> From wikipedia: Beginning with the P2V-5F model, the Neptune became one of the first aircraft in operational service to be fitted with both piston and jet engines. <S> The Convair B-36, several Boeing C-97 Stratofreighter, Fairchild C-123 <S> Provider, and Avro Shackleton aircraft were also so equipped. <S> To save the weight and complexity of two separate fuel systems, the jet engines on the P2Vs did not burn jet fuel- <S> they burned the same fuel as the piston engines: 115–145 Avgas. <S> The jet pods were fitted with intake doors that were kept closed when the J-34s were not running to prevent them from windmilling, allowing for economical piston-engine-only long-endurance search and patrol operations. <S> In normal U.S. Navy operations, the jet engines were run at full power (97%) to expedite and assure all takeoffs, then shut down when the aircraft reached a safe altitude. <S> Also, the jets were started and kept running at flight idle during low-altitude (500 feet during the day and 1,000 feet at night) anti-submarine and/or anti-shipping operations at sea as a safety measure in case one of the radials developed problems. <A> As mentioned in an answer earlier the rotation direction of jet turbines doesn't affect handling, however, the engines installed on either sides must have same thrust as to make the handling easier. <S> One example for differing engines however is A380, where the inboard engines are equipped with thrust reverser and outboard engines don't have them. <S> There are several reasons for doing this, not having thrust reverser makes engine comparatively simpler to build and maintain. <A> The "Super 27" replaced the outer engines of the Boeing 727. <S> The problem with re-engining a trijet is the necessity of re-engineering the center engine's casing and intake, wspecially if an S-duct is involved. <S> That is so complicated that re-engine plans typically left that engine alone . <S> So it was with the Super 27 with a swap to the more powerful JT8D-217. <S> I have jeard of schemes to put even more modern engines on the outer pylons, but cannot find the link.	Usually the Engines on the same plane are of the same model (or type).
What is propeller / engine sync and how does it work? In some models of multi-engine airplanes there is a switch labelled something similar to "prop sync" or "engine sync". My questions are: What is engine synchronization? How is it achieved? Why is it important to use? What happens if you don't use it? <Q> I don't know how it is achieved, but here is the reason: <S> If you have two sources of the same noise, with nearly the same frequency, the sum of both noises will be a noise of slowly increasing and decreasing volume. <S> It's called beat and can become very annoying. <S> The math says $$\sin(2\pi f_1t)+\sin(2\pi <S> f_2t)=2\cdot\sin\left(2\pi <S> \frac{f_1+f_2}{2}t\right)\cdot\cos\left(2\pi <S> \frac{f_1-f_2}{2}t\right)$$ <S> To demonstrate this, there you see two sinus-tones of almost same frequency, and what happens if you mix them: <S> The blue curve is of frequency $( <S> f_1-f_2)/2$. <S> As example, one machine running at 3000rpm and one at 3030rpm results in a noise which increases for one seconds before it decreases within one second again. <S> As said, I don't know how it is done, but synchronization must be done very precisely to avoid this beat. <S> Edit: <S> Here is what happens if the two noises do not have the same volume. <S> One of the curves has three times the amplitude of the other. <S> The envelope is not a pure sin function, but the blue function fits it quite well. <A> On the Junkers Ju-52 the pilot had two little discs which rotated with the beat frequency between two engines. <S> The upper left one would show the beat frequency between the left and the center engine, and the lower right one that between the center and right engines. <S> The pilot would try to stop them rotating by advancing or retarding the throttles, equalizing engine speed in the process. <S> I highlighted the synchronization indicator in the picture above ( source ). <S> Running all engines at the same speed helps to fly straight and reduces vibrations. <S> Not only is one distinctive engine frequency removed by equalizing it with the other, also the beat frequency is deleted. <S> Sorry, I cannot answer this for the Beech Baron. <S> I've flown it only once and don't remember any instruments (other than my ears) which would help with synchronization. <A> According to Wikipedidea <S> As for why its used the article states Propeller synchronization serves mainly to increase the comfort of crew and passengers, since its primary purpose is to reduce the “beats” generated by propellers that are turning at slightly different speeds. <S> As for what happens if you don't use it, according to the article Synchronization is not normally necessary for proper operation of the aircraft. <A> The engines using prop sync will be constant speed props. <S> Constant rpm is maintained with a governor of some kind that adjusts the pitch. <S> This governor can be tuned by the prop sync to speed up or slow down one prop by adjusting it. <A> It's just an automatic system to do prop speed and/or blade location synchronization. <S> On a multi without it, one does it manually by adjusting the prop pitch controls. <S> If the automatic system is not used, it can still be done manually. <S> Prop sync is typically required to be turned off during critical phases of flight (takeoff/landing). <A> 4 engine prop planes turn at exactly the same(RPM) or percent depending on the type of engine. <S> Number 3 is usually the boss and all the others slave to it. <S> Every blade has to cycle between the other blades on the same wing or it causes a harmonic vibration so fine if cannot be felt by the crew but can shake nut or other tightened safety devices loose. <S> If 4 blades crossed when they are at their closest proximity, you'd have blades which are near the speed of sound crossing about 4000 times a minute, so they must take turns crossing the center line. <S> On 2 engined aircraft it is not a critical.	In aviation, propeller synchronization is a mechanism that automatically synchronizes all propellers of a multi-engine, propeller-driven aircraft so that they rotate at the same speed.
Are there risks if the side joystick must be handled with a pilot's weaker hand? Suppose that a first officer were left-handed and a captain were right-handed. Both are NOT ambidextrous. Even after training, what if their weaker hands' control and degree of versatility remain worse than their dominant hands'? In other words, in commercial (and not just military ) cockpits, joysticks (on the side) must be grasped with only one hand. But does this fact presuppose or require perfect ambidexterity? <Q> I can't speak for all pilots everywhere, but I've flown both sticks and yokes from both the right and left seat (as well as the front and the back seat in tandem aircraft) and found the adjustment process between switching from right to left hand to be very quick. <S> I found getting used to sight picture differences to be a much bigger challenge and, like many others before me, sideloaded my first few landings (along with climbing/descending during turns) until I got the hang of it. <S> Other pilots I've spoken to about this have expressed the same feelings; there is a learning curve, but it is by no means insurmountable. <S> At any rate, flying is far more of a mental activity, with masterful physical coordination being surprsingly far down the list of innate qualities a pilot needs. <S> And no, I am not nearly ambidextrous; in fact, my coordination abilities with my non-dominant hand are hilariously poor, as anyone who's ever watched my try to toss a tennis ball during a serve can attest. <A> No, flying with your non-dominant hand is not really an issue at all. <S> This is because most airplanes are designed to be flown from the left seat and most people are right-handed. <S> When in the left seat, you fly with your left hand on the yoke and your right on the power (or other controls, as necessary.) <S> When in the right seat, you do the opposite. <S> As far as the amount of force is concerned, for larger aircraft, the force you have to apply to the stick is created more or less artificially (or, at least, it's mechanically scaled down, such as with pneumatics/hydraulics.) <S> In newer aircraft with electronic controls, the resistance force to the pilots' input is created entirely artificially. <S> If the controls were linked directly to the yoke in a large/fast aircraft (think a jet airliner,) it would be physically impossible to manipulate them by hand, due to the forces being applied to the control surfaces by the wind. <S> Small aircraft, however, do often have direct linkages from the controls to the control surfaces, but, even so, it's very normal to fly them with your non-dominant hand, even for pilots who have never flown before. <A> Can you drive a car with either hand on the steering wheel at a time? <S> I know I can. <S> I can also hold a hold with either hand and control the plane without any noticeable differences. <S> I think hand dominance only comes into play when it comes to more precision, dexterous things like writing. <S> Flying, however, is done with feel for the most part so as long as you know how to fly with the forces felt on the hand from the controls, there shouldn't be any problem using either hand. <S> Another analogy is with bicycles. <S> I noticed some people can't ride with just one hand on the handlebars because they end up pushing the side of the handle bars they are holding and thus causing the bike to turn. <S> Usually, such people can't ride with one hand with either hand. <S> Why? <S> Controlling a bike isn't exactly a precision thing where precise angles are achieved. <S> Rather, its done by feel so if you can ride bike with one hand, you can do so with the other.	In fact, most pilots learn to fly with their non-dominant hand, even in aircraft with traditional yokes.
Is there a cockpit which can recognize the voice of the pilot and help him/her to fly? Is there any new cockpit that uses voice commands (think for example Siri from the new iphones) that can identify the voice of the pilot and help him/her to fly? <Q> Voice recognition works because it learns from the user over time, something that is not possible in a cockpit environment with crew resource management. <S> There is a prototype in development by Honeywell at the moment, but it's in early stages of development. <S> Related reading <S> : The benefits of a Speech Recognition enabled cockpit by Adacel PDF <A> Yes...kind-of. <S> There was a product by a company called VoiceFlight which would allow you to program Garmin GPS systems (GNS 430/530), which was FAA-approved by STC for a good number of light General Aviation aircraft. <S> While it was not capable of flying the plane by voice instruction it could be used to program a route into the GPS, which a coupled autopilot would then be able to fly. <S> The VoiceFlight product has been discontinued as competition from the newer GTN 650/750 (which require less knob-twiddling to program a route) and other technologies like Connected Panel ate into the company's business to the point where it was no longer viable to remain in business, but the core idea of voice technology in the cockpit has been proven possible (and according folks who tried it, even practical). <S> It may make another appearance some day. <A> Yes - Typhoon uses a "Direct Voice Input" (DVI) system. <S> This has a limited vocabulary which allows the pilot to control non-safety critical items via voice input. <S> The current system uses an uploaded template specific to the pilot to enable recognition. <S> Although developments are looking at various updates including removing the dependency on pilot templates.	No, voice recognition is currently not used in aircraft as it would have to be built into the aircraft to pass certification for the aircraft and with rotating crews on aircraft, the voice recognition would need to be able to work with too many different voice types: high pitch, low pitch, male, female, accents, dialects and many more factors.
Are there items bigger than an aircraft section transported by air today? This question about engine transportation made me wonder what is the size of the biggest item ever transported. Then I remembered that it should have been a space shuttle (either Buran or the American Space Shuttle ), but those items are no longer transported. Nowadays whole aircraft sections are transported, thanks to A300-600ST and B747LCF . Are there cargo items bigger than a high by-pass ratio jet engine or an aircraft section that are transported by air today (in 2015)? How are those item handled? <Q> According to Wikipedia, the An-225 is the world's largest cargo aircraft and it's transported both the heaviest and longest items of cargo ever carried by air: <S> At 16.23 metres (53.2 ft) long and 4.27 metres (14.0 ft) wide, its consignment, a generator for a gas power plant in Armenia along with its loading frame, weighed in at a record 189 tonnes (417,000 lb) <S> [...] <S> On 11 June 2010, the An-225 carried the world's longest piece of air cargo, when it flew two new 42-meter test wind turbine blades from Tianjin, China <S> It's also carried the Buran spacecraft (the 'Soviet space shuttle'), which was actually what the aircraft was originally built for. <S> The An-225 is still in operation and the operator gives some examples of large cargo that can be carried: <S> The aircraft has the spacious cargo compartment with length of 43.32 m, width of 6.4 m and height of 4.4 m, that allows carrying a variety of cargoes inside. <S> For instance, sixteen standard aeronautical containers of UAC−10 type; 50 cars; single piece of cargoes up to 200 t (turbines, generators, dump trucks − Belaz, Kamatsu, Euclid, etc.). <A> When you are not restricted by the size of a cargo hold, your cargo can become much bigger. <S> See below how a Mil-26 lifts the fuselage and wing root of a Tu-134. <S> I have not checked whether this is a record, but I would expect that the world record will involve the Mil-26 somehow. <S> Mil-26 lifting a Tu-134 carcass, seen from below ( source ) <A> I'm not sure if this counts since it's still in development and production, but <S> Scaled Composites' Stratolaunch Carrier Aircraft (dubbed the Roc ) will almost certainly shatter any existing records for payload capacity. <S> Its mating system is designed to hold up to 500,000 lb (230,000 kg.) <S> Its intended payload, like that of WhiteKnight and WhiteKnight 2 , is a rocket stack mounted between the twin fuselages to be air launched. <S> At least as of December 2011, the first flight test was indeed scheduled for 2015 , so I guess it technically does meet the 'in 2015' criterion for this question. <S> :) <S> The specific 'item to be carried' in this case is the Pegasus II rocket stack with a gross weight of 465,000 lb. <S> (211,000 kg,) according to Aviation Week . <S> Stratolaunch carrier aircraft carrying a Pegasus II: Source: BusinessInsider <S> The carrier aircraft will also have the largest wingspan of any aircraft to date: Source: Wikipedia	On 11 August 2009, the heaviest single cargo item ever sent via air freight was loaded onto the Antonov 225.
Would it be viable to install a screen in front of jet intakes to prevent them from sucking in birds? Why isn't there a protective screen with large diameter holes (approx 2') mounted in front of the jet engine intake to protect the turbine blades? This would keep larger birds and large ground debris from getting sucked in, which can cause serious internal engine damage. <Q> Modern high-bypass turbofan engines work by pulling in immense volumes of air and accelerating it. <S> A screen as proposed would make that task far more difficult, which would ruin the efficiency of the engine. <S> It's also pretty well unnecessary. <S> Jets worldwide take plenty of birdstrikes every day. <S> Unless the pilots see it (hitting the windscreen will do that) or hear it (hitting something near the cockpit) or the bird goes into the engine core (which causes the smell of burned bird in the air conditioning), the chance that the crew knows about it before the next walk-around inspection is pretty slight. <S> The vast majority of birdstrikes are utterly inconsequential. <S> (Except for the bird -- ruins his day pretty thoroughly!) <S> Yes, there are a small number of very highly visible events where birds do disable an aircraft -- the "miracle on the Hudson" and the loss of an AWACS in Alaska come to mind, and there are others. <S> And it's possible for a birdstrike on an engine to cause significant damage IF the bird is large enough <S> AND it goes into the core, but in the big picture, that is actually pretty uncommon. <S> Thus, the aircraft manufacturers and operators end up accepting the risk of a catastrophic birdstrike, because the alternative of protecting the engine as suggested is too expensive when the effects on the efficiency of the engine are considered. <S> One other point, bird flesh is pretty easy for an engine to chop up and digest. <S> If a big bird hits a metal shield at high speed, there would be the risk that the shield could be damaged enough that some of the metal would break apart and go into the engine as well, and THAT would cause far more damage than just the bird. <S> Fun video of stuff being shot into an engine during testing <A> If you look carefully at the picture of the Me-262 V3 below, you can see the spherical screens on both engine intakes. <S> Today, screens are used only in ground tests. <S> See the picture below for the Rolls-Royce version: <S> The big surface of the sphere reduces aerodynamic losses, which are small under static conditions anyway, but this contraption would obviously be totally impractical in flight. <A> The assumption was that they would operate from damaged runways or roads and the engines would need protection against Foreign Object Damage (FOD). <S> Right air intake of a MiG-29 with main doors closed and louvres on the wing root opened. <A> There are three problems with this idea: (1) To make a screen strong enough to withstand the body of a 15-to-20 pound bird hitting it at 500 miles per hour, would require thick wire which would significantly block air flow. <S> (2) <S> Such a screen would be very liable to collect ice, so it would have to be heated to high temperature. <S> This would be expensive and would increase the maintenance burden for the aircraft. <S> (3) <S> If part of the screen failed and broke off for any reason and went into the rotors, it would destroy the engine. <A> When flying any surface that is exposed to the air will generate drag. <S> That screening, although full of holes, will create significant drag when exposed to the air that is entering in the airplane. <S> Also, it will distort the air entering the engine reducing the efficiency of the engine and increasing fuel comsuption. <S> Globally, the extra drag and the higher fuel consumption is more costly than the increase of weight needed for generating extra protection on the engine nacelle.	Screens were actually used on the first prototypes of the Me-262 , but soon abandoned when they were found to be more of a burden than a help. A few Russian/Soviet fighters had retractable FOD screens on their engine intakes (MiG-29 and Su-27 IIRC).
Why should I request a long landing? I fly in/out of a small international airport occasionally, the runways are quite long. It is not unusual to land half-way or even three-quarters down the runway. When doing this, pilots request long landings from ATC. I once did not request a long landing and did anyway and got chewed out a bit from ATC. My question is: Is it mandatory to request a long landing or is it more of a courtesy? Where is this information documentated? <Q> There's no mention that I can find of "landing long" ("landing deep" is sometimes used outside the US) in the FAA's P/CG , AIM or ATC procedures . <S> So it's fairly safe to say that it's an unofficial instruction (assuming I didn't miss it somewhere). <S> The main reason for doing it is to avoid a long taxi after landing, but I suppose there could be other reasons too, like coming in too high on a long runway or avoiding wake turbulence. <S> The point of requesting it - and not just doing it - is that it may mess up sequencing at a busy airport because you take more time to clear the runway, with the result that the tower has to instruct the aircraft following you to go around. <S> As my first instructor said, "once you're cleared to land it's your runway". <S> I've never been asked by ATC to do it <S> but I have been asked by the tower to "land short", to minimize my time on the runway and let an airline flight take off ASAP. <S> However, it was clearly phrased as an informal request, not an instruction; something like this: <S> N12345 Clear to land 36L, appreciate a short landing if you can manage it <S> So I think the conclusion is that landing "short" or "long" is simply an informal way for pilots and ATC to make things work a bit more smoothly. <A> When you are cleared to land, you own the entire runway until you exit. <S> Use it all if you must. <S> (One exception to this is at Oshkosh, during the annual AirVenture when as many as three airplanes are cleared to land on the same runway at the same time: one short, one medium, and one long as demarcated by colored dots.) <S> Having said that, at a busy airport you are expected to land reasonably close to the arrival end, and to exit the runway promptly. <S> This is an important component of keeping traffic moving smoothly at a busy airport, so if you want to land long you should inform the tower of your request. <S> A good reason to land long: <S> If the controller has positioned you too close behind a large airliner so that wake turbulence is an issue, tell the controller that you want to land long. <S> Wingtip vortices stop as soon as the aircraft lands, and you want your touchdown point beyond the large airliner's touchdown point. <A> But you should state your intentions clearly as a courtesy to the controller and by effect other aircraft that you share the airport with. <S> The controller will expect a small aircraft to take the first runway exit. <S> They plan the arrival stream accordingly. <S> From experience they know it will take a Cessna 150, for example, 40 seconds between overflying the threshold and vacating at the first exit. <S> Thus they can space the next aircraft appropriately so that they can give a landing clearance in time after you vacate. <S> When you unexpectedly fly all the way to the second half of the runway before landing it will take much longer between overflying the threshold and vacating the runway. <S> This will make the margins for giving the landing clearance to the aircraft behind you much smaller and may even force the controller to order the big jet on your tail to go around. <S> For screwing up somebody else's plan and causing others to go-around you get shouted at sometimes. <A> Long landings are requested mostly by GA pilots (although airlines can do it too) on longer runways. <S> ATC is informed about it. <S> If the aircraft is parked near the end of the runway, or needs to get there, long landing is used as it is faster to fly at 80 knots than to taxi at a much lower speed. <S> I'm not sure why ATC didn't like it in your particular situation. <S> It could be that they were expecting you to get off the runway sooner, which you didn't. <S> This PDF explains this. <S> I couldn't find any regulations related to it. <A> ATC doesn't like unannounced long landings because unless they are informed of what you're doing, they will be concerned that you're just too fast or too high and might run off the end of the runway. <A> This tool is called Reduced Runway Separation and requires the preceding aircraft to be beyond a certain distance measured from the runway threshold, before the subsequent approaching aircraft can be cleared to land. <S> Related question: <S> When is an aircraft cleared to land?	In EASA land, you can also be asked to make a long landing because the controller will want to clear another aircraft to land behind you, although you are still occupying the runway. I don't think it is documented anywhere that you must inform the controller if you want to land long.
Can a drone hitting a plane be mistaken for a birdstrike? Could a bird-sized consumer drone be digested by a jet engine, and not be recognized as a drone, mistaking it as a bird strike? I'm thinking of the situation during the flight - like an engine making a short unusual noise, but works OK; not sure that can even happen eating a small bird? As was pointed out, the debris of the object will look different in obvious ways when checking the engine after flight I would assume a major factor is how the engine handles the drone, in terms of defects or running anomalies. The battery comes to mind, hitting a turbine blade might be a problem - depending on the battery size. There are certainly drones with very small batteries, that I assume will do no obvious harm, and certainly ones with batteries big enough to do harm for sure. <Q> Would one be able to tell the difference before landing? <S> Not likely in many scenarios. <S> Case 1: <S> Bird hits windshield: blood & guts are immediately visible. <S> Drone hits windshield, cracks are visible but not much else. <S> The crew CAN immediately figure out, if they've ever see a birdstrike on the windshield, that this was something else. <S> (Of course, it could just be a shattered outer pane -- <S> those do fail sometimes, not necessarily due to any collision. <S> Never had one go in flight, so <S> I don't know if the sound of the pane shattering might be mistaken for a collision {or vice-versa}, or not.) <S> Case 2: <S> Bird hits near the cockpit but NOT on a windshield. <S> Sounds like a sharp crack, like a piece of gravel hitting your automobile windshield at highway speeds. <S> If a drone did the same, it would probably sound pretty similar, and without the blood/guts to see (or not see), the ability to notice what's missing may not be there. <S> Case 3: <S> Bird hits the engine, and it starts running poorly. <S> Sometimes you will smell the guts cooking in the core of the engine (i.e. they get into the bleed air system & thus into the air conditioning), and that's a clear sign that your engine ate a bird. <S> But the bird CAN miss the core and still cause problems with the fan blades. <S> Most birds that miss the core are chopped up by the fan blades & the crew had no idea until after landing that anything happened, but a big enough bird can cause damage that way. <S> So if the engine starts running rough, hot, and with some vibration, the absence of "cooked goose" odor isn't necessarily going to drive the conclusion that the collision had to be with something other-than-a-bird. <S> Now, all of this assumes that the crew doesn't see the object that they hit. <S> Which they very well might. <S> Everything in that case is obviously an entirely different discussion. <A> A small drone, like those commercially available, is not much bigger than your average raptor or even a goose, but the material it's made of is much harder. <S> Not very many geese have aluminum shoulders affixed with stainless-steel screws and supporting carbon-fiber wing struts. <S> As such, a drone will do much more damage to the turbine blades (or the windshield or any other leading surface). <S> This is one of the big reasons for current restrictions on UAV operations; current rules treat them similarly to model aircraft, and that means a ceiling of 400 feet and a no-go zone five miles from any controlled airspace unless you have comms with the tower for the space you enter. <A> It's really dependant on 1) size and 2) type. <S> I.E. <S> if it's a DJI Phanatom, then it will just get shredded as its made out of plastic, possibly doing damage to the engine. <S> On the other hand, if its a large multi rotor that's made of metal/carbon fiber, then the engine will most likely be damaged pretty badly. <S> So, TL,DR: if it's a consumer one, probably won't be much evidence, about as much as a bird, but with less blood. <S> Of its large, then imagine a crane made of carbon fiber.	One might suspect that a lot of damage with no smell seems unlikely to be a birdstrike, but there are cases where some engine component has failed & caused engine damage (ranging from barely noticeable up to catastrophic), and you can't really know much about causality for the engine doing what it's doing until you're on the ground.
Why is full carb heat recommended when reducing power below normal setting? In my first flight lesson today, my instructor asked me to apply full carburetor heat when we had to reduce power to 1900 RPM in our Cessna 152. I was surprised by this as I didn't remember learning this in ground school, and I later checked the Jeppesen textbook I am using, and referring to the section on carburetor icing, I saw that when power is reduced below normal operating limits, full carb heat is recommended (must have missed it when studying the ground material). My understanding is that the cause of carb icing is the sudden drop in temperature in the venturi due to drop in pressure as the fuel speeds up. If I am reducing power, I am reducing fuel flow, so shouldn't this reduce the chances of icing? So my question is why is full carb heat recommended when decreasing power below normal operation? <Q> When you close the throttle for descent, the airflow is constricted. <S> This constriction is going to cool the air more than it is during cruise configuration, and may increase icing. <S> From This AOPA document : Throttle ice is formed at or near a partly closed throttle valve. <S> The water vapor in the induction air condenses and freezes due to the venturi effect cooling as the air passes the. throttle valve. <A> At full throttle, manifold pressure is high, close to ambient pressure at that altitude. <S> At partial throttle or at idle, manifold pressure is low. <S> It is the transition from higher pressure (ambient) to low pressure (in the induction manifold) that causes cooling. <S> Think of why ambient temperature is cooler at 10,000 feet MSL than it is at 1,000 MSL. <S> So moving the throttle to a lower power position will cool the carburetor. <S> The advice is right, follow the instructions in the POH. <A> At lower power settings in particular, the butterfly valve of the throttle has a smaller opening, which effectively act as venturi, making the carby more conducive to icing. <A> The other answers are good, but I'll contribute the physical reason. <S> When a gas is expanding due to pressure differences, the temperature of the gas will drop. <S> This is stated in the Ideal Gas Law . <S> While air is not an ideal gas, it's close enough that we can use the law to calculate the temperature drop - within reasonable limits. <S> PV=nRT, where P is pressure, V is volume, n is number of moles of gas, R is the ideal gas constant (8.314 J⋅mol−1⋅K) and T is temperature in Kelvin. <S> When you close the throttle, pressure in the manifold will drop , and the air entering from ambient pressure to manifold will have to expand. <S> This cools it down - and as it cools it can hold less moisture as well, so you risk water vapor condensing out of the air, and potentially very cold air. <A> When the engine is running at full power, it is creating a lot of heat. <S> When you throttle down rapidly, suddenly much less heat is being generated, but the engine is still being rapidly cooled. <S> This rapid cooling can create stress as the metal parts of the engine contract at different rates. <S> Applying Carb-heat directs available heat into the carburetor, and by association, the overall engine, which slows down the cooling of the engine and reduce the stress from rapid cooling. <A> The final authority on the use of carb heat is the POH, unless the POH itself leaves it to the pilot to make a judgement call, in which case you have to reference your knowledge of carb icing formation, the specifics of the aircraft's system, your intended operating parameters, and current atmospheric conditions. <S> Your instructor asking you to use carb heat when reducing power is likely both in line with the POH (can't remember for certain, it's been years since I've seen a -152 POH) as well as general prudence when operating carbureted aircraft, especially something with an engine that small.	I learned that applying carb-heat when throttling down has nothing to do with Carb-Icing, but instead is to prevent shock-cooling.
Is there an aircrew bunk in the 747 cockpit? Reading this article , I came across the quote : Pilots also enjoy its creature comforts: at BA the 747s are known as the ensuite fleet. “Our little bedroom is within the cockpit: you can stick your pyjamas on and clean your teeth without anyone seeing you. And coming out the bunk when you wake up, it’s a different light and you’re in a plane cockpit in the sky,” he says. I know there are crew sleep areas on large aircraft but I've never heard of there being a bunk. Does anyone have a floor plan for the cockpit which would illustrate how do they fit those cabins there? <Q> Yes, there is a crew rest with two beds (bunk) connected to the cockpit on the 747. <S> As MainMa notes , this can be found on 747-400 or 747-8 models, but not the older models. <S> It can be seen on the seating charts here: <S> The crew rest is directly across from the two lavatories. <S> While the lavatories open into the aisle of the cabin (grey area), the crew rest opens into the cockpit. <S> There is a layout here <S> that shows a how the upper deck is arranged. <S> It's a freighter, but is was converted from a passenger plane, so it has the same crew rest location. <S> With the introduction of the 747-400, the position for the flight engineer was removed (seen below), with those functions being replaced by computers. <S> This opened up a bit of room behind the pilot seats. <S> Source <A> The answer depends on the precise model of Boeing 747. <S> For instance, the Boeing 747-8 (third generation of 747) features two beds which are clearly visible here, in blue: <S> The original image of the complete aircraft is available here . <S> The setup is very close to the one shown in fooot's answer . <S> In the same way, Boeing 747-400 has two bed as well, as can be seen on this schema . <S> On the other hand, the much older Boeing 747-300 doesn't seem to have any beds: <S> See the original image here <S> Other sources (including <S> the detailed 8300x3800 cutout of Boeing 747-100 ) confirm that there are apparently no beds on older Boeing 747-100, 747-200 or 747-300 models. <A> I found it difficult to find a specific floor plan. <S> No floor plan, but there are several location with photos available of the rest area on the -8. <S> CNET has one. <S> No longer on the Boeing web site, there is an archived copy of the crew rest area for a -400 freighter that has a floorplan for the area. <S> This page isn't as detailed, but shows the crew rest area on a 747 to scale with more of the upper deck. <S> Unfortunately it lacks detail with how it connects to the cockpit. <S> And not a 747, but here is a page with a graphic of the 787 crew rest area.	I've seen references that the 747 had a lot of different plans, with many airlines having a crew rest area in the rear of the upper deck rather than off the cockpit.
What are the indications that your turbofan engine has "thrown a blade?" In an airliner, such as an A380, what indications do the pilots have that an engine has thrown a fan blade? Will that always result in destruction (of the engine)? <Q> Turbofan engines are designed and tested to contain a fan blade failure . <S> However, this is a violent event and will cause serious damage to the engine. <S> The engine and surrounding components are subjected to large forces and vibrations, and the engine can ingest debris from the damage to the fan, causing further damage. <S> There will likely be an investigation, and the engine will probably be scrapped due to the widespread damage to different components. <S> To the pilots, it will seem like a bird strike, but probably worse. <S> There will be a loud noise as the fan blade separates and collides with the fan case and following blades. <S> The fan will then be out of balance, so heavy vibrations will follow as the shaft loses its rotational energy. <S> The pilots will be able to tell which engine has failed by the loss of thrust, as well as the indications of vibration and failure on the instruments for that engine. <S> If the fan does not get stuck, it will continue to windmill, which will result in ongoing vibration from that engine. <A> engineer and pilot here - formerly of JPL. <S> I've seen blade loss tests and any modern high performance engine will violently destroy itself if a blade is lost. <S> You can see tests of this on youtube for example at that link or by searching on "jet engine blade-out test" (without the quotes). <S> (User fooot gave a longer example video as well.) <S> In these tests they typically use a (very small, prebalanced) explosive charge to separate one blade from the spindle and then the engine vibrates itself to pieces. <S> Modern engines are constructed near the very limits of the materials used. <S> In fact there is a special joint venture company in the US that makes a lot of the fan blades and which exists just for this purpose. <S> They use special tools to X-ray every blade and measure the center of gravity as the slightest bubble in composites or weight anomaly would be enough to destroy an engine. <S> When a blade is lost, the off center mass causes an engine to vibrate itself violently to death. <S> In person you can't really hear anything but the vibration and destruction at these tests - I couldn't even hear the explosive charge when it went off (although it seems audible in some of those videos). <S> As fooot noted above, the pilots are informed through the usual engine-out detection methods such as loss of telemetry (and it may start a fire which would be noted and dealt with by fire suppression systems on a larger jet). <S> Many companies including, I know, Rolls-Royce will invite the public to fan blade out tests to show how their engine bodies control the resulting carnage. <S> It might be a fun afternoon if you're the type to visit aviation stackexchange :) <S> They post videos online for the same reason and you can see a lot of very nice slow-motion videos on the subject. <A> To give some idea of the forces involved, losing a fan blade from a large turbofan will create an force of about 100 tons on the engine, oscillating at a few thousand RPM until the rotor slows down. <S> In a worst case scenario, the aftermath is enough to shake the entire aircraft to the level where walking about in the passenger cabin is difficult. <S> But aircraft have survived that and landed safely, and for long distance flights over water the plane is certified to survive the consequences for up to 3 hours flight time before reaching the nearest land. <S> On the other hand, if the tip of 10mm long high pressure compressor blade cracks off in the engine core, you might not even know about it until the next time the engine is stripped down for a full inspection. <A> Provided the engine survived the event, we are looking at all the engine parameters from the cockpit displays. <S> Those indications are different depending on engine manufacturer. <S> N1, N2, EGT, Oil pressure, ITT, engine vibrations indicator (VIB) and source, EPR (...). <S> Just by looking at the numbers you cannot tell for sure if a blade separated. <S> And it all depends also from the compressor stage the blade separated (first, last...) <S> or if it was a fan blade.	If you lose a "large" blade like a fan blade, or a "heavy" blade like most turbine blades, the engine vibration monitors will instantly go off the scale and the engine control system should shut the engine down automatically.
In what circumstances could a 787 stay powered on continuously for 248 days? The FAA has issued an airworthiness directive for the 787 : SUMMARY : We are adopting a new airworthiness directive (AD) for all The Boeing Company Model 787 airplanes. This AD requires a repetitive maintenance task for electrical power deactivation on Model 787 airplanes. This AD was prompted by the determination that a Model 787 airplane that has been powered continuously for 248 days can lose all alternating current (AC) electrical power due to the generator control units (GCUs) simultaneously going into failsafe mode. This condition is caused by a software counter internal to the GCUs that will overflow after 248 days of continuous power. We are issuing this AD to prevent loss of all AC electrical power, which could result in loss of control of the airplane. I'm curious: Are there any circumstances under which a 787 would remain powered continuously for 248 days? [Edited to add a follow-on question:] Boeing has said "If there is a definitive record of a powercycle within the last 120 days, no operator action is immediately required." Does that happen? 120 days? What is the longest period a passenger aircraft might conceivably be continuously powered on? <Q> Aircrews seldom have to power off an aircraft completely (also known as a cold and dark cockpit). <S> Airliners usually stay powered on at the gate. <S> This is known as a "short turn-around": <S> engines are stopped, the APU is stopped, but electrical power and air conditioning is still supplied by ground equipment. <S> This has the advantage of minimizing turn-around time (after all, airliners are meant to stay in the air to make money). <S> The cabin also has to be cleaned and prepared for the next flight at this time, so something must power the lights. <S> It is theoretically possible to stay on this way for 248 days. <S> However, airliners have scheduled maintenance, which completely powers off the aircraft. <S> So, in reality, it's very unlikely to have an airliner powered continuously for 248 days. <A> There have been issues with the 787 giving "nuisance" messages after starting up. <S> One solution would be to start the process earlier, to leave time to deal with them. <S> Another is to just never shut it down. <S> However, the plane does need to be shut down sometimes for regular maintenance. <S> A Boeing spokesperson said: No airplane in the fleet experienced that condition. <S> The issue was discovered during lab testing, and while it would be unusual for a plane to be on for 248 days straight, it's not impossible, so Murphy says that it will occur at the worst possible time . <S> So in the interest of safety, the FAA is making operators aware so that they can be sure to shut down their planes regularly and avoid the issue. <A> This is a bug Boeing found in the 787. <S> This bug, which was found during laboratory testing , is: ... <S> plane’s power control units could shut down power generators if they were powered without interruption for 248 days, or about eight months <S> This bug wasn't found in any airplanes in line operations. <S> Boeing states <S> that: ... power was shut down in all airplanes in service in the course of the regular maintenance schedule ... <S> Airliners stay on for very long times, but their proper maintenance requires them to be power cycled regularly. <S> About this issue, Boeing says : If there is a definitive record of a powercycle within the last 120 days, no operator action is immediately required. <S> So, the answer to your question is there aren't any .	They are also powered off if the expected time at the gate is long.
What is the difference between slice, segment and leg? I have heard of the terms slice , segment and leg . Since I am a newbie in travel industry, I would like to know and understand the basic differences between the three. Could someone please explain the three, using some kind of example? <Q> I'm pretty sure those terms are not used consistently across all organisations in the air travel industry. <S> They are not defined in an IATA glossary <S> I looked at <S> but I did find this: Definition of Flight Segment <S> The International Air Transport Association (IATA), the international trade body for airlines around the world, defines a flight segment as the operation of a flight with a single flight designator between the point where passengers first board an aircraft and the passengers' final destination. <S> A flight designator includes an airline code, which has two letters or a number and a letter in combination, and a flight number of up to four digits. <S> A flight segment can include any number of stops where passengers board and deplane the same aircraft operated by a single airline. <S> Comparison of Flights and Legs <S> A flight is defined by the IATA as the operation of one or more flight legs with the same flight designator. <S> Unlike a flight segment, a flight may involve one or more aircraft. <S> The IATA defines a leg as the operation of an aircraft from one scheduled departure station to its next scheduled arrival station. <S> From eHow <A> From IATA passenger glossary : <S> Leg: <S> The operation between a departure station and the next arrival station. <S> Segment: <S> Sometimes referred to as "City Pair". <S> The operation between board point and any subsequent off point within the same flight number. <S> Leg vs Segment in layman terms <S> : A leg stops when the plane lands. <S> A segment stops either when you change flight number of when youarrive at one city where you want to spend time. <S> One segment includes one or more legs from the same flight number. <S> Sometimes a plane lands to refuel or to load other passengers but is technically the same flight number. <S> Every ticket's coupon represent a segment. <S> It is the first time I have heard the slice term. <A> As defined by others: A leg is always a single non-stop flight. <S> Example, UA123 from BOS-EWR is a leg. <S> A segment is a flight operated by a single flight number, but may have an intermediate stop.... <S> Example - UA 234 from BOS-ORD-SFO is a segment <S> "Slice" is a newer and less used term in the travel industry: <S> A slice can be a single flight segment or multiple flight segments to get from origin to destination, possibly with a connection, but without a stopover. <S> Example- <S> round trip itinerary with two slices Slice 1 - UA123/15NOV BOS-EWRSlice 1 - UA234/15NOV EWR-SFO Slice 2 - UA345/25NOV SFO-BOS <A> I am directly quoting from the book 'A Dictionary of Travel and Tourism Terminology' by Allan Beaver. <S> "sector, segment or leg: <S> A sector is, by definition, a portion of an itinerary, or journey, which may consist of one or more legs or segments. <S> A leg is the portion of a journey between two consecutive scheduled stops on any particular flight. <S> A segment is that portion of a journey, from a boarding point of a passenger, to a deplaning point of the given flight. <S> Although the passenger may not leave the plane, it may tough down to take on or let off passengers at several points, so that a segment may be made up of a leg or group of legs."	A flight segment can include one or more legs operated by a single aircraft with the same flight designator.
What is Transponder Code 2000 actually used for? On What is the significance of a squawk code? @DeltaLima gave a fairly concise answer. In it he listed several 'standard' codes used for things like emergencies. Also in the list was Code 2000, for which he included the description: Used when entering a Secondary Surveillance Area and no code has yet been assigned So, if I'm in the US, under VFR (code 1200) and I enter a Secondary Surveillance Area, I automatically change to Code 2000? Why wouldn't I have already been given (a specific) designator? <Q> The purpose of squawk code 2000 is to prevent aircraft entering a Secondary Surveillance Radar (SSR) area from transmitting a code that is the same as a discrete code assigned by ATC to an individual aircraft. <S> If you are flying in the USA under Visual Flight Rules (VFR), you will be assigned (implicitly) code 1200. <S> Upon entering a SSR area you might get assigned another code, but often you will keep code 1200 if you are not near class C airspace. <S> If you are flying Instrument Flight Rules (IFR) outside a SSR area (e.g. entry into the US from oceanic airspace), you will use code 2000. <S> Upon radar contact you will then get assigned a discrete code. <S> From FAA Advisory circular 91-70A - (Oceanic and International Operations) <S> : <S> 2. <S> EXPANDED OCEANIC CHECKLIST. <S> ....... <S> g. <S> After Oceanic Entry (1) Squawk 2000 . <S> Thirty minutes after oceanic en try, crews should Squawk 2000, if applicable. <S> There may be regional differences such as Squawking 2100 in Bermuda’s airspace or maintaining last assigned Squawk in the West Atlantic Route System (WATRS). <S> Crews transiting Reykjavik <S> ’s airspace must maintain last assigned Squawk. <S> It is standard practice in many airlines to select code 2000 after arrival at the gate. <A> You'll often hear ATC (Oakland Center or Los Angeles Center) tell aircraft that are heading out over the Pacific something along the lines of "UAL ###, radar services are terminated, squawk 2000, contact ARINC on HF frequencies" when they hand off control to the oceanic ATC. <S> The 2000 code simply means that the aircraft IS being controlled, but NOT right now by any radar controller. <S> If they kept whatever squawk they had leaving Oakland or LA center, then there would be the possibility of a conflict as they entered somebody else's radar coverage (Hawaii, Guam, Japan, etc). <S> So instead of sorting out what the aircraft that are no longer in radar contact are squawking, they simply give them all the standard 2000 code, and when the aircraft is back in radar contact with (whoever), then that controller assigns them a code that works with his center. <A> The US ATC procedures say that 2000 is to be used for departing IFR aircraft (section 5-2-6): <S> Code 2000 to an aircraft which will climb to FL 240 or above or to an aircraft which will climb to FL 180 or above where the base of Class A airspace and the base of the operating sector are at FL 180, and for inter-facility handoff the receiving sector is also stratified at FL 180. <S> The en route code must not be assigned until the aircraft is established in the high altitude sector. <S> It looks like the specific information you quoted from the other answer simply doesn't apply in the US. <S> The term "secondary surveillance radar area" isn't in the P/CG and Wikipedia says that the use of 2000 in relation to SSR areas is for ICAO countries only: <S> The code to be squawked when entering a secondary surveillance radar (SSR) area from a non-SSR area used as Uncontrolled IFR flight squawk code (ICAO countries) <S> It does give this information for the US, though: Non-discrete code assignments in accordance with FAA Order JO 7110.65, 5-2 <S> *Also for use in oceanic airspace, unless another code is assigned by ATC (USA) <S> The Order it mentions is the ATC instructions. <S> I have no idea about oceanic operations, so I can't comment on that part. <S> As for VFR, the AIM simply says that all VFR traffic must squawk 1200 unless otherwise instructed by ATC.	Another use of code 2000 is on the airport: before power up you can select code 2000 to avoid code conflicts that could occur when you would maintain your code from a previous flight.
Is there a database of airport ceilometer raw data? I am interested in obtaining raw ceilometer data, to test some cloud/aerosol layer identification algorithms. Is this type of data freely available or will I need to ask for it directly from the airport? Do airports keep an archive of raw data or simply of cloud heights as determined by manufacturers algorithm and provided in METAR reports? <Q> OGIMET looks like it goes back to 2005. <S> It seems like you need to plug in dates one at a time <S> but there are plenty of ways to skim a page <S> and im sure you can ask them for a data dump if you know what you need. <A> Weather Underground is a great site, although finding the specific link for archived METAR reports is more difficult than it should be. <S> The following link is an example that gives all METAR reports for a given airport on a given day; you can either use the fields given on the page to find other dates & other stations, or you could edit the URL itself to find what you want (and perhaps even automate that into a screen-scraping app): <S> Weather Underground Link <S> You can also get the same data in a CSV file with a separate link . <S> If you don't mind doing a little bit of coding, you can also subscribe to their API, which allows you to get historical data with some fairly straightforward calls to their API. <S> The "developer" subscription is free but limited in how many calls you can make; more expensive subscriptions allow more calls. <S> The following link is where you can start learning about their API. <S> ((This answer is as much an answer to this question , which is now closed and marked as a duplicate of this one. <S> It is a slightly different question, and this answer is really more aimed at that question, but it addresses this question as well.)) <A> I have been looking for this kind of historical data for a long time, and I finally found it! <S> Check out <S> Iowa State University of Science and Technology's site , called IEM (Iowa Environmental Mesonet). <S> There is even a python script <S> you can use to download it programmatically if you wish! <S> It has various forms of data (maybe not for all networks) going back to 2000 for ASOS and 1995 for AWOS. <S> It has worldwide data, you just have to switch to the network you want and choose the reporting station!	My favorite weather site Weather Underground has historical data.
What makes flight recorders harder to find than tagged sharks? It really bothers me that we can't find planes that weigh tons with black boxes (AFAIK) technology that's almost obsolete, on the other hand shark tags (AFAIK) work great for long time and we can monitor shark movement, depth, temperature, etc., all the time. So, why? <Q> They're different usage cases, and have to be engineered differently. <S> Three major points: <S> It adds a lot of padding and weight, and limits the kind of battery that can be used. <S> Sharks also don't dive to a depth much greater than 3000 feet on most occasions . <S> A planes flight recorder is designed to survive to a much lower depth, under much larger amounts of pressure. <S> Not to mention being designed to survive all sorts of other things . <S> Another point regarding depth, it is much harder to search for a signal at a depth of 15,000 ft, than it is even at a depth of 5000 ft. <S> This article shows how big of a difference you get between even 20 meters and hundreds of meters (not thousands), it gives a good idea of what I mean. <S> If a shark tag fails, nobody cares. <S> If you tag 100 sharks and 30 of the tags survive, you still have some pretty good data. <S> But if one airplane crashes and its black box fails, it's considered unacceptable. <S> They are required to survive 100% of the time. <S> All this conspires with the difficulty of getting a receiver deep into the ocean to make finding FDRs/CVRs really difficult. <S> That's not to say they couldn't design one that is much better, it just becomes extremely expensive (as all things are on airplanes). <S> And you have to determine if these edge cases (like flight MH370) are worth making an airplane a few million dollars more expensive (between R&D and certification, the later being quite expensive). <S> I think the theory was they should be able to find any one of these within a month, and that may take some rethinking (maybe 3 months, or a year perhaps?) <S> But they'll never be as successful as shark tags just because the requirements to be able to find one at that depth <S> 100% of the time are quite different from the needs of a shark tag. <A> Shark tags work by only sending the logged data when the shark resurfaces. <S> Between those it just stores the data in memory until it can send it. <S> Sending underwater takes a lot of power otherwise. <A> Because they're located in the wreckage, which can be at great depths. <S> The only signal that can be sent at great depths is an audio signal, and that takes a lot of power (relatively speaking, the CVR and FDR are battery powered) <S> Sharks (or whales, they are often tagged) either remain in relatively shallow waters, or occasionally swim near the surface, where a radio signal can be detected. <S> The practical solution would be a realtime data feed of data now being recorded on the FDR to a remote receiver, sort of a super ACARS. <S> In fact, ACARS data factored in determining the cause of the AF 447 crash long before the wreckage and black boxes were found - it showed a stall after loss of airspeed from frozen pitot tubes.	A shark tag doesn't have to survive a 500mph impact ( #7 on the list ) with the ground, and a flight recorder has to be able to do so. All of these differences combined mean that black boxes are manufactured to much higher standards, and as a result they are bulkier, have different sorts of radios and require much more battery life (to support the larger systems) than a shark tag.
What is the function of the tail section on a fixed-wing aircraft? In a generic fixed-wing aircraft like a Cessna, what is the function of the tail section, i.e. the rudder and elevators? <Q> First off lets be clear that a tail section does the same thing on small aircraft that it does on large aircraft. <S> Second off lets be clear that a tail section is not necessary for flight and there are planes like the Northrop Grumman B2 that dont have a tail section they are affectionally called "Flying Wings". <S> The short answer is that the rudder (vertical part) controls yaw and the elevator (horizontal part) controls pitch. <S> A plane is capable of movement and similarly adjustment in all 3 dimensional axes. <S> But lets dig in a bit: The Elevator: <S> This is usually located in the back but by no means has to be. <S> Burt Rutan has implemented many designs that have forward mounted elevators. <S> As to functionality they essentially allow you to alter the pitch of the plane which in turn alters the angle of attack of the wing which furthermore has a direct effect on the lift generated by the wing. <S> In a simple world we could say that when you pitch up you climb and when you pitch down you descend. <S> The reality is that the engines thrust plays a large factor in this. <S> For example if you are flying at a level attitude and increase thrust your will increase speed (and the speed of air over the wing) which will generate greater lift and cause the plane to elevate with out a pitch increase (you will have to apply some force to keep the plane level though). <S> The elevator provides a way to easily alter the pitch of the plane (and angle of attack) so you can climb when you want. <S> Generally speaking you will also add power for the climb. <S> For a more lengthy explanation check out the wikipeidea article . <S> The Rudder: <S> The rudder is mainly to control the left-right yaw of the aircraft. <S> In a single engine prop plane this can be used to help overcome the left turning tendencies created by uneven force of a spinning prop ( P-Factor ). <S> In a more general case the rudder is often used to correct yaw when a heavy crosswind is present on landing. <S> It is also used in flight to ensure your turns neither skid or slip <S> (stay coordinated) remember "Step On The Ball" . <S> For more reading check out Wikipedia <S> This picture shows the axes of movement pretty well. <A> The function of the tail section of a conventional fixed wing aircraft is to provide stability. <S> It also holds two important control surfaces; the rudder and the elevator. <S> If the aircraft is in a side-slip, which means the nose of the aircraft is pointing left or right of the direction of the relative airflow, the vertical tailplane will create an aerodynamic moment forcing the nose into the wind. <S> The vertical tailplane also contains the rudder. <S> The rudder is a control surface which controls the aircraft's yaw moment. <S> The pilot controls the rudder by using the rudder pedals. <S> This allows the pilot to correct disturbing pitch moments which might come from the propeller or to bring the aircraft intentionally into a sideslip, for example for a crosswind landing. <S> During turns the rudder is used to ensure the turn is coordinated (keep the sum of the weight and centrifugal force pointing down the vertical axis of the aircraft) <S> The horizontal tailplane, or horizontal stabilizer is for longitudinal stability. <S> Usually it provides the horizontal stabilizer gives and aerodynamics down force, thereby keeping the nose up. <S> That may sound counter intuitive, but is essential for the stability of conventional aircraft. <S> When the airspeed increases the aerodynamic forces increase as well. <S> Due to the increase of the lift force on the main wing combined with an increase in down force on the horizontal stabilizer the nose of the aircraft will be forced upward. <S> This causes the aircraft then to trade kinetic energy for potential energy and the speed will reduce again. <S> The horizontal stabilizer also contains the elevator. <S> This control surface allows the pilot to control the pitch moment of the aircraft. <S> Aircraft can be trimmed such that they maintain a constant pitch angle at constant speed without the need to constantly give elevator inputs. <S> This trimming is done by either a small trim tab on the elevator, but in other aircraft the angle of whole horizontal stabilizer can be changed to trim the aircraft. <A> Good answers, but let me make it short and simple. <S> The tail (empenage) mainly contains the vertical stabilizer and the horizontal stabilizer. <S> This video shows what happens when the vertical stabilizer is lost. <S> The plane has no way to stay pointed into the wind - very bad. <S> When the horizontal stabilizer is lost, the plane instantly noses down.(I tried to find the video of the dam-busters practice where the Lancaster bomber is going along above the water. <S> It drops the cylinder, which hits the water, bounces up, and slices off the tail of the bomber, which noses into the water, at 100+ mph.)	The vertical tailplane, also called vertical stabilizer helps the aircraft's nose facing into the direction of the relative air flow.
What is different between a Cat IIIA, Cat IIIB, and Cat IIIC ILS approach? In terms of aircraft equipment, approach minimums, procedural differences, and anything else relevant, how do the 3 types of a Cat III ILS differ from one another? <Q> ICAO and FAA CAT III definitions <S> A CAT III operation is a precision approach at lower than CAT II minima. <S> Sub-categories are listed below. <S> A category <S> III A approach is a precision instrument approach and landingwith no decision height or a decision height lower than 100ft (30m) and a runwayvisual range not less than 700ft (200m). <S> A category III B approach is a precision approach and landing with nodecision height or a decision height lower than 50ft (15m) and a runway visualrange less than 700ft (200m), but not less than 150ft (50m). <S> *I've omitted the JAA definitions. <S> Source Airbus Flight Operations Support documentation . <S> FAA Reference Material <S> The below links are to comprehensive FAA publications covering the areas as titled. <S> FAA AC120-29 for CAT I/II . <S> FAA AC120-28 for CAT III . <S> Thanks <S> @Sports Racer for the comment with links to these documents. <A> From: AC 120-118 https://www.faa.gov/documentLibrary/media/Advisory_Circular/AC_120-118.pdf CAT I (FAA)An instrument approach operation with a minimum descent altitude (MDA), decision altitude (DA), or decision height (DH) not lower than 200 feet (60 m) and with either a visibility not less than ½ SM, or a Runway Visual Range (RVR) not less than 1800 feet (550 m). <S> CAT I (ICAO)Any precision approach and landing operation with a DA/H of 60 m (200 feet) or higher and with a minimum visibility of 550 m RVR or greater will be termed a Standard CAT I operation. <S> CAT II (FAA) A precision instrument approach operation with a DH lower than 150 feet but not lower than 100 feet and a RVR not less than 1000 feet. <S> CAT II (ICAO) <S> Standard CAT II operations are made to a DA/H below 60 m (200 feet), but not lower than 30 m (100 feet), with associated RVRs ranging from 550m (1800 feet) to 300 m (1000 feet). <S> CAT III (FAA) A precision instrument approach and landing operation with a DH lower than 100 feet (30 m) or no DH, or a RVR less than 1000 feet (300 m). <S> CAT IIIa (ICAO) A precision instrument approach and landing operation with a DH lower than 30 m (100 feet) or no DH and an RVR not less than 175 m (600 feet). <S> CAT IIIb (ICAO) <S> A precision instrument approach and landing operation with a DH lower than 15m (50 feet) or no DH and an RVR <S> lower than 175m (600 feet) <S> but not less than 50m (200 feet). <S> CAT IIIc (ICAO) A precision instrument approach and landing with no RVR limitations. <A> Cat III A 600 feet (180 meters) <S> Runway Visible Range (RVR) CAT III B <S> 150 feet (46 meters) <S> RVR CAT III C zero visibility <S> No decision height in any CAT III approach (CAT II is 100' and CAT <S> I is 200')	A category III C approach is a precision approach and landing with nodecision height and no runway visual range limitation.
How do manufacturers engineer their aircraft to deal with tail strikes? I have been told that tail strikes on take off and landing are rare but do occur. I think, in my mind, the tail touching the ground at all would just make the tail fall off, but it appears I was wrong. In most of cases of tail strikes I've read about the plane is able to either continue on it's journey or can simply circle back to the field it departed from. So I'm wondering, what do big commercial aircraft manufacturers (like Boeing and Airbus ) do to keep tail strikes from turning into a major disaster? How do they engineer the plane to survive the incident? <Q> During testing, the rear fuselage is protected by a beam made of oak or even steel to distribute the tail strike loads and to protect the aircraft skin. <S> A340 during tail strike tests. <S> This one is literally blazing along the runway … For normal operations, the protection is removed. <S> However, tail strikes must not cause flight-critical damage, so a few precautions are taken during design: <S> No hydraulic or electrical lines must run along the bottom of the rear fuselage. <S> If there are still mechanical control elements like pushrods, they and their collapsing supports must not be close to the bottom of the fuselage. <S> The tail strike location must be outside of the pressurized part of the fuselage. <S> The main protection against tail strikes, however, is procedural: <S> The rotation speed must be high enough to allow lift-off before a critical pitch attitude is reached. <S> Delta wing aircraft are much easier to over-rotate, so the Concorde used a retractable tailwheel for tail strike protection: <A> The 777-300ER locks the gear bogey in the horizontal position during takeoff making it considerably more difficult to tailstrike <S> (Boeing said they hit the ground 12 times during testing with the -300, but only got within 18 inches on the -300ER). <S> Source See these documents: 1 , 2 <A> Firstly, this article from Boeing explains how tail strikes occur. <S> And this Boeing informational note gives more practical information on tail strikes and prevention: A short excerpt from that note:"... <S> some 777 models incorporate a tail strike protection system that uses a combination of software and hardware to protect the airplane. <S> However, these devices do not guarantee protection for landing tail strikes and some takeoff tail strikes. <S> They also reduce tail clearance distances."	And some models of the 737, 767, and 777 have a tail skid that prevents damage from most takeoff tail strikes.
What are N1 and N2? When I'm reading something about jet engines, it's common to see references to N1 and N2. I've never fully understood what N1 and N2 are on engine instruments and how they relate to thrust and the position of the throttle. <Q> N1 and N2 are the rotational speeds of the engine sections expressed as a percentage of a nominal value. <S> It is similar to the revolutions per minute (RPM) of a piston engine, expressed in percentage instead of in the actual rate of rotation. <S> They are different because they are characteristic on two-spool engines (see the figure below). <S> The first spool is the low pressure compressor (LP), that is N1 and the second spool is the high pressure compressor (HP), that is N2. <S> The shafts of the engine are not connected and they operate separately. <S> Image credit: Emoscopes / Wikimedia <A> Conceptually, N1 is the fan (or, fan speed ) and is most related to your thrust (since the fan produces more thrust than the core on today's big motors). <S> As long as you have N1 rotation before lighting the engine off, N1 isn't all that important during the start. <S> But once it is running, power is generally set with reference to the N1 (or fuel flow or EGT or EPR) rather than the N2. <S> This picture of 727 instruments shows, from top to bottom, the N1, EPR, EGT, N2, and Fuel Flow indicators. <S> You can tell (hopefully) how the N1 and N2 are both tachometers, showing percentages instead of values, because it's a lot easier to talk about 52% N2 than 6350 N2 RPM. <S> The picture below shows an example of the engine stack displayed on a modern EICAS panel, with the N1 and the EGT displayed prominently, and everything else just shown as digital values (with no EPR indication in this aircraft). <S> This is a typical in-flight presentation, showing you the two things you most care about with large displays, and everything else available if you really need it. <A> It's dependent on the aircraft and engine installations but these refer to the rotation speeds of the engine spools. <S> As listed above, usually the N1 refers to the spool which the fan and LPC/LPT are on and N2 is the HPC/HPT spool in the gas core. <S> The displayed values for N2 and N1 are often given as percentages of their maximum rotational speed. <S> Therefore the HPC spool will often display as running much faster than the LPC/Fan spool. <S> This isn't always the case; For instance the engine speed gauges in the Aero Vodochody L-39 display the HPC spool as '1' and the Fan/LPC speed as '2'.	The N2 is the engine core, and the N2 gauge is used mainly during engine start: on initial starter engagement, the N2 starts turning first, and things like adding fuel+ignition and then later disengaging the starter are based on specified N2 speeds.
Regarding N1 and N2, what does the "N" stand for? I initially phrased this question in a comment to another question regarding what N1 and N2 mean, hoping it would be that sort of low-hanging fruit that is easily answerable and not worth a proper question in its own right. But then I starting searching and came up short. This Yahoo Answers page has lots of guesses on it, from "nominal" to "Newell". (And we all now are reminded why nobody goes to that site for real answers.) Many other pages explain what N1 and N2 are, but not where the "N" part comes from. I'm wondering if it might have its origin in German, as a lot of early developmental work on jet engines was done in Germany. Or was it simply an unused letter that fit? <Q> Many thanks to ROIMaison's answer for steering me in the right direction. <S> In Turbomachinery: Basic Theory and Applications, Second Edition , Earl Logan, Jr. provides a symbol reference list at the end of each chapter starting in chapter 2, defining $N$ as rotor speed , in units of rad/s; an angular change per unit time, and $N_s$ as the specific speed , a dimension-less quantity derived from a ratio of the flow and head coefficients. <S> N1 and N2 seem to be derived from both. <S> Wikipedia mentions the speed as a percentage paradigm as a human factors consideration, though as of 5/14/2015 there are no references to support this. <S> However, there may be a scientific basis behind this as well, since a change in N is proportional to the resultant change in airflow (i.e. thrust produced): <A> Here at Tech ops , they say it comes from specific speed. <S> However, it does not explain why the letter N was chosen, but perhaps this knowledge might help lead to an answer. <S> This source mentions: <S> N is the symbol for "specific speed". <S> Specific speed is defined as "the speed of an ideal pump geometrically similar to the actual pump, which when running at this speed will raise a unit of volume, in a unit of time through a unit of head". <A> For rotational speed, $n$ is a common symbol. <S> While the English Wikipedia article uses $\omega_{cyc}$, I can find many English-language sites using the symbol. <S> To be honest, $\omega_{cyc}$ is a really combersome symbol for something that is used as often as rotational speed is. <S> In German (see the corresponding Wikipedia article ), it is definitely the standard way of representing rotational speed in revolutions per time unit (as already mentioned by Peter Kämpf above). <S> The origin of this is probably harder to determine, but I imagine that it has something to do with the number of revolutions always being a natural number. <S> After all, $n$ is the go-to symbol for any unit-free integer value in engineering and physics, in my experience. <S> The usage of the capital letter, which is inconsistent with this, is a little more dubious in my opinion. <S> But I have a theory for that, too: <S> The majority of all software working with the value has, for the last 50 years, probably been written in Fortran. <S> Fortran variable names are, by convention, capitalized. <S> So anyone working with the value or displaying it might have just adopted the name of the variable as the symbol for N1 and N2. <S> Any pre-Fortran occurence of the terms might disprove that theory.	As far as I can tell, the N comes from the physics behind turbines in general, whether they be water pumps or wind turbines, a subset of mathematics called fluid dynamics .
Why don't most fighters have thrust reversers? With the exception of the Panavia Tornado, fighters do not have thrust reversers. Why is this? Why does the Panavia Tornado have them? <Q> It is not a very efficient means to reduce the speed of a landing aircraft either, and other methods (e.g. brakes or drogue parachutes ) are much better suited. <S> The biggest advantage of thrust reversal is that it cancels out the idle forward thrust working against the aircraft. <S> Canceling out idle thrust isn't an issue on most fighters, as they have an engine nozzle that is open at ground idle to prevent any thrust from being produced. <S> This nozzle probably also makes it a bit difficult to integrate Thrust reversals, but the Panavia Tornado proves it can be done. <A> It has nothing to do with cost or wasting fuel. <S> A military jet is notoriously designed to do the best it can, to hell with how much it costs. <S> If expense of construction was a concern, they'd think it was ridiculous to build from exotic components just to shave a few pounds. <S> Fuel efficiency and fuel cost is only a concern in terms of being economical as possible in order to have the best range to attack the enemy, or to loiter on station on patrol. <S> Wasting a little fuel on landing is inconsequential; why else would jet fighters have fuel dumps? <S> It's common to jettison any few thousand extra pounds of fuel to get landing weight down, and it's also common to take extra fuel on from the tanker just in case. <S> So you take three times as much fuel as you need to get back to base, then when you get there safely, you just dump it <S> so you're light enough to land. <S> They don't include reversers because the extra weight and space they need would be better used for something else like fuel or avionics. <S> Military jets, especially fighters, are ridiculously expensive to operate, not just buy. <S> Commercial aircraft, on the other hand, need to do things cheaply, with little maintenance and short turn-around times. <S> Passenger aircraft and airlifters are far larger and heavier than fighters; that's why they need reverse thrust. <S> A big enough parachute is a real pain to pack back up again, and replacing worn out brakes is expensive. <S> A thrust reverser is extra initial expense, but it pays for itself. <S> They may also need to turn themselves around for takeoff; while a fighter could be pushed by hand in a pinch, a C-5 Galaxy, not so easy. <S> It's not surprising, in the few fighters that have a reverser (the Tornado and the Saab Viggen), landing on short or icy runways was a primary motivation, coupled with rapid turnaround, and the fact that parachutes are only effective at high speeds. <A> Fighter aircraft are specialized tools optimized for a specific purpose: to destroy enemy forces (in the air and on the ground). <S> Everything that is not vital to that mission is quite literally dead weight that reduces the performance of the aircraft as it relates to its specific purpose. <S> Jet fighters are not required to "taxi back" on the tarmac, and simpler "speed brakes" are more effective at slowing down in flight.	Military large airlifters use thrust reversers to quickly unload and return for more, and to land on short runways; that's rarely a concern for a fighter. Thrust reversal is a complex system (equals money) and it uses significant amount of fuel (also equals money).
Is wing flex good? I've noticed that the wings of the 787 and A380 tend to flex a lot. Does wing flex help an aircraft in any way? <Q> The wings of the Boeing 787 are so flexible because its carbon fiber material can be stretched more, and the high aspect ratio of 11 will magnify this effect. <S> In flight the consequences are: Less shaking due to gusts, because the wing will dampen load changes more effectively. <S> Delayed aileron response, because the lift change due to aileron deflection will first bend the wing before it starts to roll the aircraft. <S> On the ground one consequence is: <S> The wing might have less tip clearance, because less in-built dihedral is needed - the rest is supplied by the wing's elasticity in flight. <S> In general, wing flex is like the suspension in a car. <S> It costs a little bit of performance but gives a much smoother ride. <A> I will try to add over @PeterKampf answer. <S> Flexibility is finally another parameter, when you make your design allowing your airplane to be flexible, you are introducing a new variable. <S> As in all optimization problems adding new (smart) parameters allows you to create a more optimized design. <S> Just taking the example provided by @PeterKampf , if the airplane is less shaking due to gusts the requirement over the aerodynamics/structure of gust response is more easily achieved. <S> That makes relaxation in some areas of the structure making it lighter. <S> So, altohugh there is a potential cost in aerodynamic performance, it might end in savings in fuel as the airplane will be lighter for the same gust response. <S> There is also an effect that is not seen in the picture, what you is the flexion produced by the lift, but also the lift is producing cambering , which can be also exploited by the wing to have a more optimized design. <A> To add to the other answers, a stiff wing is a heavy wing. <S> If flex can be permitted then the wing can be made lighter.	Flex does increase the risks of things like fatigue cracking (metal), delamination (composite), excessive strain and aerodynamic surprises, but if these are all allowed for in the design then the plane will be lighter and have a better payload-range than the equivalent stiff wing.
Why is an unpressurized takeoff performed? Why would an aircraft perform an unpressurized takeoff? What conditions lead to this being beneficial? <Q> Typically, the pressurization system is run by engine bleed air. <S> Using that bleed air means you have less engine power available than is maximally available with the bleeds off. <S> If you're on a runway that requires all your power, you do a no-bleeds takeoff, which means you have no pressurization. <S> Shortly after takeoff you would turn the bleeds on. <A> Packs off doesn't mean that the cabin is unpressurized. <S> The outflow valve(s) are closed and the cabin pressure remains steady at aerodrome level. <S> This will give better engine thrust as mentioned above. <S> Unpressurized cabin would mean outflow valve in open position and cabin pressure would be equal to ambient pressure. <S> This is not allowed on commercial flights (at least JAA/EASA regulations).I flew one ferry flight unpressurized and almost popped my ears on takeoff because of the high climb rate. <A>	One reason for an unpressurised takeoff would be if the aircraft's pressure hull is damaged, and it's making an unpressurised ferry flight to somewhere it can get repairs.
What is the purpose of a dorsal fin such as on the Boeing 737? I've noticed that the 737 has a rather unusual vertical stabilizer, with an extension at the front. Is the 737 the only plane equipped with such a vertical stabilizer, and what is its purpose? <Q> The "extension" at the front is called "dorsal fin". <S> Its main purpose is to improve directional stability in high side-slip situations (asymmetric flight due to engine failure, crosswind landings, etc). <S> The double-sweep of the leading edge of the vertical stabilizer helps the vertical stabilizer to be effective at a larger range of side-slip angles (high lateral angles of attack). <S> The stabilizer is an airfoil, much like a wing. <S> The amount of lift (or in this case, sideways force) <S> it generates, varies with its angle of attack (AoA, or $\alpha$), or in this case, sideslip-angle ($\beta$) something like this: Lift coefficient ($C_L$) increases with increased $\alpha$, until it reaches $C_{L_{MAX}}$. <S> This angle is called $\alpha_{crit}$. <S> Generally, the more sweepback an airfoil has <S> , the lower its $C_{L_{MAX}}$, <S> BUT the higher its $\alpha_{crit}$. <S> This means that the non-dorsal-fin-part of the stabilizer (low sweepback) will be able to generate its $C_{L_{MAX}}$ (sideways lift) at a lower $\beta$ than the dorsal fin. <S> Increasing the side-slip angle beyond its $\beta_{crit}$ decrease the amount of sideways force it generates. <S> By using a secondary airfoil (the dorsal fin), with a higher sweep angle, (ie, higher $\beta_{crit}$), the net loss in sideways force with increased side-slip may be avoided, or at least mitigated. <S> Further, at high $\alpha$, (or in this case, with a vertical stabilizer $\beta$), a delta with high sweepback will generate a vortex, which will follow the upper side of the surface down-stream of it, adding kinetic energy to its airflow, thus enhancing its effectiveness. <S> The current version of the dorsal fin was added to the Boeing 737 with the Classic (−300 and onwards), but the design is not unique for the Boeing 737. <S> Look the Cessna 172 for instance (Wikimedia Commons): <S> The ATR 72 doesn't have a "pronounced" dorsal fin, but you can still see clearly how the sweepback of the vertical stabilizer changes along its length (Wikimedia Commons): <S> Or, on the other side of the speed spectrum (Wikimedia Commons): <A> The vertical tail stabilizes the aircraft in the yaw axis. <S> The fuselage is unstable, so a stabilizing fin must be added. <S> Since the vertical has a much higher aspect ratio than the fuselage, it will stall first . <S> Beyond the stall angle of sideslip, the vertical will not be able to overcome the still increasing instability of the fuselage. <S> To remedy this, a delta wing with high sweep has been added ahead of the lower part of the vertical. <S> It will not stall but continue to increase its sideload with higher angles of sideslip, thus stabilizing the whole plane in yaw even when the vertical tail itself is stalled. <S> Since the high sweep will produce a vortex at high sideslip, this will also help to make the lower part of the vertical more effective. <A> For planes that fly at high speeds (near or above the speed of sound) that strake helps with area ruling . <S> As the craft nears speed of sound the characteristics of air change and the change in cross sectional area over the longitudinal axis becomes an important factor in drag forces. <S> Keeping this smooth as possible will decrease drag in the transonic regime. <S> That strake will let the rudder itself be smaller and move more of its volume forward and smooth out the transition to the rudder proper.	Adding the fin extension or strake will keep the aircraft stable into higher angles of sideslip.
How should a pilot respond verbally to being cleared for takeoff? When ATC says "cleared for takeoff", what's the correct answer from the pilot? <Q> This is how FAA recommends (PDF) : <S> A typical takeoff clearance may state, for example, “(Callsign) <S> 123 RNAV to MPASS, Runway 26L, Cleared for Takeoff”. <A> Same phraseology you're given: cleared for takeoff with your callsign, and if applicable, the runway or instructions ("turn left heading 200" for instance) given in the same transmission. <S> Anything else is nonstandard. <S> Not on the roll nor on the go nor <S> cleared for departure nor anything else, <S> no matter how cool it sounded when somebody else said it on the radio. <A> Quite simply, you readback the runway identifier and the clearance - exactly like you receive it. <S> or <S> In case you get other instructions in connection with the takeoff clearance, you need to read those back as well. <S> Note that you should not read back any wind information given, since it is just that - an information - not a clearance or instruction. <S> ICAO Document 9432, section 4.5	The expected pilot response is, “(Callsign) 123, RNAV to MPASS, Runway 26L, Cleared for Takeoff”.
Which airplane designs have the greatest longevity? What airplane designs have been around the longest, from first flight through last retirement from active commercial or military service? My guess is that the DC-3 will win, since it has been around since before WW II and is still in service, although there are enough other designs out there I'm not familiar with that I'll be interested to see where I may be wrong on that. (Russian designs come to mind as an obvious source of possibilities.) Can anything out there beat the DC-3? What's the runner up? (The wikipedia page on the DC-3 says its first flight was December 17, 1935.) <Q> If any commercial or military service will do then there are a few designs which are older. <S> The Noorduyn Norseman is still used for air tours and cargo work and it was first flown a month before the DC3. <S> The Ford Trimotor was introduced in 1925 and I think there's still one or two doing tours. <S> Apart from tours the DC3 is still the one I'd think of as still doing really serious service. <A> This is a community-wiki mashup of the other answers - I thought a table would be useful <S> Date Aircraft Commercial Introduced Type Service (2015) <S> 1909 Bleriot XI <S> Flown by Shuttleworth collection UK, <S> entrance fee.1932 <S> JU-52 <S> Sight seeing flights by Ju-Air, Switzerland.1932 Tiger Moth Flight experiences, e.g. Cheltenham UK.1934 Dragon Rapide <S> Sight seeing flights, <S> London.1935 DC-3 <S> Many commercial flight-experience/other operators.1935 PBY Catalina <S> Still used in aerial firefighting role.1938 <S> Piper Cub <S> Many still in private/GA use and in flight <S> schools.1952 <S> B-52 <S> 76 still in service with USAF. <S> Projected service to 2045?1952 Tu-95 <S> In service with Russian air force. <S> Projected service to 2040? <A> The Shuttleworth Collection , at Old Warden aerodrome in Great Britain, has a flyable Bleriot XI which was built in 1909 and served at a flight school into the Thirties. <S> It is still regularly displayed in flight. <S> You might argue that this is no commercial service, but to witness the display, you need to buy a ticket, and ticket sales help to support the collection. <S> So I enter it as a contender here. <S> Having flown first in 1932, the Ju-52 is also older than the DC-3 or even the Dragon Rapide. <S> Several are still in commercial service - you can book scheduled sight-seeing flights with the Swiss operator Ju-Air. <S> Ju-Air's three Ju-52 served from 1939 to 1982 in the Swiss Air Force. <S> Wikipedia has an exhaustive list of current Ju-52 operators. <A> The legendary Piper Cub which was used as a trainer during WWII and first flew in 1938 is still a popular plane and although not by Piper <S> is still made in some form of variants today. <S> I dont think its in service any more (at least as far as I know) <S> but there are still loads of them flying. <A>	There's a de Havilland Dragon Rapide still in commercial service doing air tours around London, that's first flight was in 1934. The USAF B-52 first flew in 1952, stopped production in 1962, is still a frontline bomber, and is projected to continue service until 2045 http://en.wikipedia.org/wiki/Boeing_B-52_Stratofortress
Why does the Harrier jet have four landing gears? I was looking at pictures of Harrier jets and I noticed something. They have four landing gears. That seems pretty unusual for a fighter jet - most have only 3 in a triangle formation. What is the reason for this 4 point configuration? It seems to just add complexity and cost without really increasing stability. <Q> The main load bearing landing gear is in a bicycle setup, with 2 outriggers for stability. <S> The Lockheed <S> U-2 also has its gear in the bicycle configuration and takes off and taxies with detachable "pogo" outriggers for stability. <A> The Harrier is designed around its rather large centerline engine with its 4 non-standard exhaust ports. <S> In order to balance properly, the engine's nozzles have to be in just the right place and we can't have annoyances like landing gear doors opening just before landing and deflecting the thrust stream that is keeping the thing in the air. <S> Fighter jet wings are typically too thin to fold the gear into them like on some airliners (and the bombs / missiles get in the way too). <S> So, the gear gets to fold up into the space just behind the aft nozzles where it doesn't disturb anything important. <S> In almost every other jet fighter the engine occupies this space instead. <S> Yes, tricycle gear makes for easier landings but as this plane is designed to land straight down that isn't a big issue. <S> And we tend not to put green pilots into the things either <S> so if they do need a regular runway the driver should be fairly good. <A> And if the Harrier had been a conventional terrestrial fighter, it probably would have used a ubiquitous tricycle landing gear. <S> The driver for Harrier's unusual landing gear configuration is the requirement to hover via an unconventional single engine vs available fuselage space. <S> This necessitated that the Rolls Royce Pegasus engine to be located directly over the center of gravity for the aircraft. <S> Consequently, this dictates the placement of the engine right on a/c centerline about midway along the fuselage and <S> the engine now occupies much of the fuselage space which could normally be used for stowage of a tricycle landing gear when retracted. <S> The rotating engine nozzles and their associated exhaust also would interfere with a tricycle main gear located on the fuselage. <S> Designers both at Hawker Siddley in the 1960s and McDonnell Douglas in the 1980s looked at the problem and concluded that a bicycle type landing gear mounted fore and aft of the engine with retractable outrigger gears on each wing represented the best solution in regards to weight and balance, structure, and drag for the aircraft. <A> The Harrier's wings have large anhedral, the wingtips are close to the ground. <S> Without the outriggers there is a risk that payload carried back to base on the outer pylons gets damaged if the pilot sets down the aircraft with a roll angle or a roll rate causing a roll angle to build up.	This allows the gear to be lighter, stay close to the center and out of the way for the jet blast.
Why is the nacelle outlet of the tail engine of the L-1011 Tristar lower than the engine itself? I've noticed that the nacelle outlet of the Lockheed Tristar is situated below the engine itself. It is at the end of the fuselage. The nacelle outlet of the tail engine of the DC-10 on the other hand, is at the same height as the engine. Why did Lockheed choose to lower the nacelle outlet? Perhaps this picture will help show you guys what I mean. <Q> As Federico points out , the engine is located directly in front of the exhaust portion. <S> This is true for almost all engines with ducted arrangements. <S> It's much easier to duct the cool, slow intake air to the engine than duct the hot, fast exhaust air away from it, for both temperature and drag reasons. <S> Putting the nozzle higher, like on the DC-10 series, means the rudder is pushed higher up the tail. <S> This arrangement keeps the rudder as close to the vertical center of gravity as possible, which reduces the stress on the tail and limits the rolling motion induced by the rudder. <S> It also keeps the engine forces close to the vertical center of gravity. <S> This configuration also allows the supports to tie in to the existing structure at the rear of the fuselage. <S> Placing the engine further up the tail would add surface area (and therefore drag), and require additional structure to support the engine above the fuselage. <A> This arrangement of placing the engine intake duct above the fuselage is called S-duct <S> (Thanks Terry ). <S> The answer of why would be <S> it is how it was designed, probably as a differentiating feature. <S> This is vaguely mentioned here : ... <S> a small vertical fin [is] between the bottom of the middle engine intake and the top of the fuselage. <S> From the pictures below ( images' source ), it appears that what Federico stated appears to be true. <A> I have discovered some more information regarding the S-duct design in an L-1011 marketing book. <S> S-Duct Payload Benefits <S> The S-duct center engine location benefits payload by its lower fuselage weights. <S> It allows a longer constant fuselage section thereby adding seating space. <S> The more effective rudder allows the engines to be located further outboard on the wings and provides an optimized center cabin door location. <S> The exhaust efflux provides an effective fineness ratio increase and hence reduces drag. <S> Center Engine Position <S> In the S-duct arrangement the engine is 10 ft. <S> lower than a fin mounted engine. <S> This permits easier access for maintenance or engine changes. <A> The 'nacelle outlet' you speak of is actually Engine #2. <S> It is fed air via an 'S' shaped duct running through the tail section of the aircraft, starting at the dorsal intake just forward of the vertical fin.	In this cutaway you can see the intake duct leading down to where the engine is: Source Putting the exhaust nozzle lower allows more room for rudder above it.
Why do English-speaking pilots and ATC say "Niner" instead of "Nine"? Besides the fact that it's now a standard, why do American-English-speaking pilots and ATC say "Niner" instead of "Nine"? None of the other numerals are pronounced in an atypical fashion. For what was "Nine" being mistaken that resulted in the "Niner" standard being adopted? <Q> According to Wikipedia : The pronunciation of the digits 3, 4, 5, and 9 differs from standard English – being pronounced tree, fower, fife, and niner . <S> The digit 3 is specified as tree so that it is not pronounced sri ; the long pronunciation of 4 (still found in some English dialects) keeps it somewhat distinct from for ; 5 is pronounced with a second "f" because the normal pronunciation with a "v" is easily confused with "fire" (a command to shoot); and 9 has an extra syllable to keep it distinct from German nein 'no' . <S> The phonetic alphabet is not a random selection of words. <S> It was created very carefully taking dialects into account, so as not to confuse any of the letter with possible mispronunciations. <S> Although they are "English" words, the choices were made with the world in mind. <S> As mentioned on the same article : <S> The final choice of code words for the letters of the alphabet and for the digits was made after hundreds of thousands of comprehension tests involving 31 nationalities. <A> The reasons I've heard behind the pronunciations: <S> Three / Tree: <S> Tree is better pronounced and better understood by all people, regardless of accent. <S> Five / Fife: <S> Much of aviation has a military history. <S> On a poorly heard transmission "Five" can sound a lot like "Fire", which is both a military command to "shoot", and an aviation emergency! <S> "Fife" avoid that ambiguity. <S> To keep it clear that this is a digit and not a negative-reply, "Niner" is distinct from the "Nine" <A> "Niner" is spoken for the numeral 9 to avoid it being mistaken for 5.	Some non-native English speakers have trouble both pronouncing and understanding the "TH" sound. Nine / NinerGerman is a commonly spoken language, and "Nine" is "No" in German.

Subsets and Splits

No community queries yet

The top public SQL queries from the community will appear here once available.