How long would a cruising aircraft take to crash if everyone spontaneously vanished? I recently saw a movie in which what appeared to be a Lockheed C-130 Hercules was suddenly without occupants. They did not move or exit the craft, they simply vanished. I assume that the craft remained pressurised, and no modifications to controls were made. I assume that any auto-pilot-like features remained either on or off as they were at the time, unless they have some kind of system to automatically engage in certain situations. At the time of the incident, the aircraft appeared to be cruising.

I am wondering how long it would take for a cruising aircraft take to crash if everyone spontaneously vanished?

There is a far more important question (and the real deciding factor)

How much fuel is on board?

If left unattended a plane will fly until it runs out of gas quite literally, the more gas in the tanks the longer you have. This has happened on occasion before. The Helios Airways Flight 522 is about as close as you can get to this hypothetical situation in real life. The plane may travel farther (since its lighter) but it will go until its out of gas. The same thing applies to smaller GA planes as well.

This is all of course assuming that the plane is not intercepted before running out of gas. Helios 522 was intercepted by F-16's before it crashed and they visually established that the crew was incapacitated (although a flight attendant tried to save the plane). I don't know what the procedure is for interceptions like this but if the plane were headed for a highly populated area they may not let it run out of fuel.


What is the difference between F-16C and JF-17 in terms of role? What is the difference between F-16C Fighting Falcon and JF-17 Thunder in terms of role?

When does someone use an F-16C and when does someone use JF-17?

Firstly, you should understand that these two fighters are from different countries (F-16 hails from the US and serves with many NATO countries, the JF-17 is a Chinese design), but were developed along closely parallel project focuses. The F-16 was developed with the advent of highly maneuverable and powerful Russian air-superiority fighters such as the MiG-29 in mind.

Designed along the inherently unstable design idea, the F-16 is pretty much the epitome of maneuverable and agile fighting machines. In addition it was meant to be produced in relatively greater numbers than its much faster, heavier, and air-superiority focused cousin the F-15. This is one aspect that it accomplished very very well as the F-16 was quickly run into mass-production via bulk requests from the USAF which, at the time, had much greater funding that it does now. The F-16 turned out as an affordable fighter that was good enough for the USAF, not too good to be banned from international export, and flexible enough to be used in a variety of roles and ensured its use well into the 21st century.

The more obscure JF-17 is a Chinese design meant to do the same thing the F-16 did when it came out. Chengdu wanted a fighter that was rather maneuverable, and was viable and cheap enough to succeed in the international market. What resulted from a joint project between PAC and Chengdu was a fighter that could compete both in real-life maneuvering and technologically with its peers. In addition at only $15 million per unit for a block 1 type JF-17 it is one of the cheapest 4th generation aircraft of its kind available.

The two aircraft were built with similar roles in mind, and in practice fulfill them similarly as a result. The F-16 is in some ways the superior of the two, having benefited from lessons learned in many deployments around the world, but both are designed for multi-role usage, inexpensive operation, and affordability en masse.


How are engines numbered? On a commercial aircraft, the number of engine is usually 2, 4 or 6. When the technician or LAE was given task to inspect an aircraft engine no 2 on a 4 engine aircraft. Which engine would they go to?

2 different lecturers of mine had 2 different answer for this and both have experience in working with aircraft engine.

Lecturer A said:

Lecturer B said:

Which one is right? Requesting help from Technician or LAE. A brief explanation would be really helpful too.

The Wikipedia article is clear: engines are numbered sequentially, left to right, as seen by the pilot facing forward. That corresponds to the second of your diagrams.

Twin engined aircraft have just engines 1 and 2 on the port and starboard wings respectively.

Three engined aircraft follow the same convention with the number 2 engine in the fuselage centre line.

Since this appears to be an arbitrary convention I'm not sure what more explanation you're expecting.


How do airlines dispose of a passenger jet when it's no longer airworthy? When a plane is finally considered to not be airworthy, what happens to them?  Do they take them apart bit by bit?  Do they sink them offshore to make them into reefs?  Are parts stripped and sold as spares? Are there legal procedures the airlines have to go through?  What happens?

Generally the planes are scrapped by a recycling company. The parts will either be removed and sold as spares, or chopped up and recycled or disposed of. So a lot will depend on how easy it is to remove the part, and how much of a market there is for it. Airplanes are disassembled to a large extent during heavy checks, which can provide an opportunity for substituting in spares.

Engines: Probably the most valuable part of the airplane. These will be removed and either used as whole spares or for spare parts, depending on the condition and how many of the type are still in service.

Cockpit instruments: These will be removed and used as spares as well, if there is enough of a market (everyone wants those fancy glass cockpits these days).

Interiors: These may be removed as well, they can be used as spares.

Control surfaces: These can be removed and used as spares as well.

Windows: These can be removed and reused.

Systems: Pumps, electronics, lights, actuators, etc.: Most of these can be removed and sold as spares.

Landing gear: This can also be removed and reused, depending on the number of cycles it already has.

Tires: The tires may be reused if not worn out. The tubes may not be reused.

Airframe: Although some parts may be able to be used, generally the effort and the fact that there are probably many cycles on the part will prevent much from being used as-is. The metal will be chopped up as scrap. They are already working on recycling major composite structure as well, since manufacturing scrap is already being created. According to Boeing, with modern recycling processes, the metal, plastic, wires/electronics, and carbon fiber composites are used for:

15% High-grade industrial
50% Low-grade industrial
35% Landfill

As it often is with business charts, it's not clear if these are by weight, volume, or what. This company claims to recycle 90% of the weight of an aircraft.

There are of course cases like Steve V. mentions where the plane is donated to some institution, but this doesn't happen to most planes. There are also ways that airplane parts find other uses.


Why did some Caravelles have a very long dorsal fin? (Source)

Why did some Sud Aviation Caravelles have a very long dorsal fin stretching half the fuselage?

Initially I thought it's to keep the fin low to fit in existing hangars as a selling point, but the variant shown above (10B3 Super B) can also be found without this fin:

(Source)

There are two competing theories on airliners.net forums. One of them says it's fuselage strengthening for over-water flights in case of ditching. The other is a housing for an optional HF antenna. As far as I know, an old HF antenna was a stretched wire.

I checked the English, French, and Swedish Wikipedia articles, only the Swedish mentions it:

  The aircraft was also equipped with a long dorsal fin (Google translate).

A Flight issue from 1956 does not show the fin in their cutaway (the article also does not mention it).

The dorsal ridge housed avionics and HF antennas. From this document:

  The most noticeable difference are the larger cockpit
  windows and the removal of the dorsal fin (the long fin on top of the
  fuselage), that housed avionics. The 6R's not built for United did
  have the dorsal fin, though.

This is a non metallic radome. It protects the antenna from aerodynamic effects, and from water and ice which damage antenna electromagnetic characteristics. Closer view:

Source

The HF antenna was required when using long range HF navigation (Loran) and HF communications, typically over oceans and large non populated areas.

These features were not useful when flying over populated land, where VHF aids and VHF communication were possible.

There is a list of C/N without the dorsal fin in this forum. When the antenna is not under a radome, it looks like this:

Source (simulator)

See also: What is this wire going from mid-fuselage to the tail on this 737?

Progress in antenna design and receivers with (hugely) increased sensibility allow for smaller antennas, that can afford to be vertical with some signal losses. Today HF antennas tend to be vertical and under a radome at the leading edge of the vertical stabilizer:

Source

Helicopters, civil and military still use long wire antennas as antenna rails when they need HF:

Source

See also: What is this pipe on the tail of this helicopter?


Are there examples of diverse departure assessment departures in the US or Canada? If there is no published departure procedure at an airport with an approach  then you can use what is referred to as a diverse departure assessment departure. I would think that you might find these in places like Kansas and Florida, but a cursory look in these areas doesn’t yield any examples.

Can anyone give examples of diverse departure assessment departures in the US or Canada?

A diverse departure is a default departure procedure, named "omnidirectional" by ICAO.

To answer your question: It is normally not published. The only thing that is required on aeronautical publications is a wording preventing or limiting the use of this procedure.

  BUCKLEY AFB (KBKF),  AURORA, CO  TAKEOFF MINIMUMS  AND (OBSTACLE)
  DEPARTURE PROCEDURES
  11013
  Diverse departure not authorized.
  Use published  departure procedures
  for obstacle avoidance.

Sometimes there is a reminder that it can be used:

  CANNON AFB (KCVS), CLOVIS, NM
  TAKEOFF MINIMUMS  AND (OBSTACLE)
  DEPARTURE PROCEDURES
  ORIG 15064
  Diverse departure authorized all runways.

This default procedure is valid only when:

Not explicitly prohibited,
There is at least one instrument approach for the airport
No obstacle departure procedure (ODP) and
No standard departure (SID) has been published for the airport.

A diverse departure is conducted this way:

Cross the runway end at 35 ft, maintain heading and a 200 ft/NM gradient until 400 ft above the runway end. The 200 ft/NM gradient is TERPS' minimum climb gradient, and corresponds to ICAO's 3.3% for the minimum procedure design gradient.
Continue or turn in any direction while maintaining a minimum rate of climb of 200 ft/NM.
Maintain this rate of climb until reaching a 1,000 ft obstacle clearance or a 2,000ft obstacle clearance in mountainous areas.

Source

The 40:1 ratio (152 ft/NM) delimits a surface from the runway end, named the obstacle clearance surface (OCS). The diverse departure ensures being above the OCS until enroute.

Whenever the conditions exist for a diverse departure, it is implicit ATC authorities have assessed the absence of obstacle above the OCS. This assessment is named the diverse departure assessment.

Given the 40:1 slope and obstacle clearances, the area assessed may have a radius from 25 to 46 NM.


Why don't airliner winglets have consumer advertising on them? I was looking over the wikipedia article for the 737NG when I came across this picture:

As you can see, the operator of the jet has written their companies web address on the winglet.  Which seems like a waste, I'm already on their airplane, there's no need to sell me, it's not so much an ad as a reminder at that point...

So, I couldn't help but think, when looking at it, that it would be somewhat clever if RedBull bought the rights to advertise on a 737NG and wrote something on that spot that said, "Redbull gives you winglets" (rimshot).

Sillines aside, there is a serious question here.  Generally speaking if there is a public surface that many many people will be forced to stare at for any length of time, then there is an advertisement there.  Bus stops, billboards, the sides of buildings, there are ads virtually everywhere.  Heck, commercial aviation equipment even has a few already with some of the jetways you see at airports:

There are tens of thousands of people who see winglets every day (and even more who see winglets in travel pictures, blogs, etc), so why aren't advertisers taking advantage of the space and, further, why aren't airlines trying to sell the space in order to increase revenue?

I'm wondering if perhaps there are regulations that might make this difficult?  A good advertising spot will change images and products fairly frequently.  On a winglet that would necessitate either a new paint job or, perhaps, a new vinyl wrap (like what is used in NASCAR.)  And I'm wondering if the regulations for commercial aircraft regarding how the winglets are painted would prohibit this sort of "quick switch" activity (are wraps even legal)?  Or perhaps there is a certification process for all new paint jobs that would make it so the amount spent to advertise would never match the increase in sales?

Or is it just that airlines have a sense of pride about their aircraft and respect their passengers enough to not bombard them with ads?  (...yeah, I doubt it's this last one as well ;-) ).

Edit:  I did mark this one for FAA Regulations, but I feel EASA regulations should be similar enough to give some insight as well, so if you want to answer with those regs feel free.

Why airlines don't put third-party ads on winglets

I would assume that a significant part of the answer is that it would look and feel cheap (i.e. not good for the airline's brand image.) They don't usually sell advertising elsewhere on their livery for much the same reason (though they do occasionally dedicate a livery to advertising some charity or some such thing, but that doesn't normally hurt their brand image.) On the other hand, putting the airline's brand image there can possibly help to improve it.

While you are already on the airline's flight, they'd be quite happy if you purchased more flights with them in the future and even more happy if you purchase the tickets directly from their website where they don't have to share the revenue with a travel agent. An additional benefit of mentioning the website is that many airlines now have on-board Wi-Fi and allow you to access their website from it even if you haven't paid for the Wi-Fi. As such, if they can get you thinking about their website and you happen to hop on it and book your next trip while cruising around at 30,000 feet, that's a win for them.

Finally, while they do already have you on board, they're well aware that lots of people post pictures taken while they were on a flight, especially pictures that include the wing (such as the one in the question.) Now your pictures are free (and usually positive) advertising for them.

Vinyl Wraps / Decals

As far as wraps are concerned, as far as I know, yes, they're legal and actually pretty common, even for the fuselage livery. My understanding is that lessors use them pretty frequently. They've also been used for temporary liveries like this one:

It appears that several companies exist for the sole purpose of making aircraft wraps. A quick search found the following:

AdGraphics
AircraftWraps
Plane Vinyl

It appears that 3M makes a lot of the materials used for the wraps.

I also found an FAA document on aircraft coatings that talks about how to apply vinyl decals to aircraft (along with how to paint aircraft, etc.) From page 18:

  Vinyl Film Decals
  To apply vinyl film decals, separate the paper backing from the plastic film. Remove any paper backing adhering to the adhesive by rubbing the area gently with a clean cloth saturated with water. Remove small pieces of remaining paper with masking tape.

  Place vinyl film, adhesive side up, on a clean porous
  surface, such as wood or blotter paper.
  Apply recommended activator to the adhesive in firm,
  even strokes to the adhesive side of decal.
  Position the decal in the proper location, while
  adhesive is still tacky, with only one edge contacting
  the prepared surface.
  Work a roller across the decal with overlapping strokes
  until all air bubbles are removed.

This page from signindustry.com goes into more detail about how to apply vinyl decals to aircraft from a professional installer standpoint.


Is there any legal way to fly an inline twin-engine aircraft with a single-engine certificate? Is there any legal way to fly an inline twin-engine aircraft with only a single-engine endorsement? For example, if it's an ultralight or amateur built?

I understand Rutan's Defiant was an inline twin that could take off, fly and land with either the front engine, rear engine, or both.

I assume you can do this in a twin inline ultralight as there is no twin engine ultralight endorsement in USA or Canada.

I'm asking about the ultralight or amateur built categories in the USA or Canada, not the US LSA category as I understand they are single engine only.

Under United States Part 103 ultralight category, with no license or aircraft certification requirements as long as the the limitations of the category are met (dry weight, fuel capacity, single seat, and level flight maximum speed, permitted flight locations), you can do anything you like.  Whether it's safe or a good idea is up to the pilot.

Last time I checked, Part 103 requires a dry weight (with engine, no fuel, no pilot) under 254 lb, no more than 5 US gallons (though actually called out in liters) fuel capacity, and level flight speed limit of 55 kt (about 62 mph).

I can't answer relative to Canada, as their regulations concerning ultralight/microlight aircraft differ from those in the USA.


How does a flight control computer deal with control surface disengagement? What action does the flight control computer take (under normal law) when it realizes, for instance,

Inboard actuator of aileron/elevator disengaged or
There is a disconnect between the LVDT and the actuator

Is there any backup for this?

Are there any minimum control requirements established for the flight control computer to 'arm' or 'enable' the "backup" if available ?

Well the A320 and A340 have 2 actuators per deflection surface (in case of elevator or aileron, spoilers do not have 2 actuators per 1 surface).

If one of these actuators fail, as in they have no pressure supplied to them by either hydraulic power systems (Blue,Green,Yellow) the other actuator which is supplied by a different pressure supply system (to avoid a single point failure) will take control of the of the surface. The flight control computer would continue working under normal law given that the other 2 Primary flight computers (PFC) are working properly. However, if the secondary flight computers(SFC) take control (after at least 2 failed PFCs), the aircraft would lose the ability of flight with normal law and thus direct law would be activated.

A disconnection between LVDT and a deflection surface would cause a disruption of the feedback towards the PFC. The PFC will notice that it is sending signals but receiving no change in feedback and will consider itself out of order. This would mean the respective PFC will render itself in a passive state and pass control to the other PFC connected to its own actuator. Depending on whether a PFC or an SFC in control, you would have either normal (at least PFCs intact) or direct law (the 2 SFCs are in command)

A Mechanical backup is available in the form THS(Trimmable Horizontal Stabilizer) which is activated by the trim wheel and the rudder which is available through the pedals for the A320 and A340.


Why are commercial flights not equipped with parachutes for the passengers? I understand that commercial flights are equipped with life vests. I also understand that most military jets are equipped with ejection seats. It may be costly and technically challenging to equip passenger planes with ejection seats. Having seen air-borne personnel lining up and parachuting out of a C130, what is preventing flights from equipping each passenger with a life-saving parachute? Is it very technically challenging for an untrained person to deploy a parachute, or are there other reasons?

Qualification: I worked at a sport parachute center as an instructor for 10 years and I hold an FAA Master Parachute Rigger certificate. I believe that qualifies me as an expert on the subject.

The majority of the above other statements here are correct. In summary:

The door of a pressurized passenger plane cannot be opened in flight for the stated reasons.
the door of most larger passenger planes cannot be opened in flight after you depressurize the cabin because they swing forward. Push a sheet of plywood against a thunderstorm-grade wind and see how well you do. Now multiply the wind speed by 5.
even if you blow the door out with explosives, the chances of an orderly exit are slim. At airliner speeds an orderly exit is critical if you expect to survive the jump. Street clothes will be torn to shreds. Oh, and it's COLD up there.
you cannot depressurize an aircraft over 12,000 feet altitude without the passengers passing out rather quickly. If you can control the plane down to this altitude, you don't need the parachutes.
it is extremely difficult to exit an unstable aircraft that is built for sport parachuting (in-flight door, suitable handles, door already open). If the plane is spinning and you are beside the door you might get tossed out and then struck by other parts of the airframe. If it's a larger plane and the door (or you) are away from the current axis of rotation, good luck. Yes, jumpers have successfully exited a crippled jump plane. None of them want to try it again.
modern sport parachutes use steerable ram-air canopies. Jump one of these without any training and you will hurt yourself landing. Most emergency parachutes are round. Jump one of those without any training and you will break something when you land. 200 untrained people jumping ram-air canopies all at once will result in a number of collisions and entanglements, which are typically fatal for all involved.
exiting an airplane below 1000 feet is really not practical. I would do it IF a) the plane is currently under control; b) landing is not practical; c) It's really 1000 feet, not less; d) I'm sitting beside the door. Possible scenario is the engine goes boom and I know there's nothing but rocky land ahead of us. Of course my gear is already on my back ready to go, and I know how to use it.

There have been many cases of a jump plane experiencing engine problems on the way up. By the time the pilot turns around, the cabin is usually empty. There have also been cases where jump planes have crashed on takeoff. None of the (very experienced) jumpers on board thought about anything other than tightening the seatbelt.

Points I disagree with: (although they do not change the outcome)

Emergency parachutes (seat-pack types) are available for far less than sport rigs. Maybe $1,500 each. Weight around 8-10kg. Putting a purpose-built one on would be not much more complicated than a 4-point harness. This was seriously considered back in the 1950's - aircraft seats were designed with parachutes built in. Planes were neither pressurized nor fast back then. Think DC-3 era - the DC-3 makes a great jump plane, I have used one a few times.
maintenance costs would be no more than the escape slides, flotation gear or other similar equipment.


Do pilots ever intentionally land a monowheel glider on the main wheel and a wingtip wheel in crosswind conditions? Do pilots ever intentionally strike a wingtip when landing a mono wheel glider in gusty crosswind conditions?

I understand the Lazair changed from a mono wheel to a standard tail dragger layout for better cross wind ground handling. What about gliders?

Is doing a two-point high-speed ground roll/landing ever done intentionally, with the mono wheel and wing tip wheels (intentional wing strike), instead of slowing down then dropping the wing just before coming to a stop? Say 10 mph crosswind, gusting to 15mph/max crosswind component.

No.

The lever arm of that glider wing is too long and the ground contact force too hard to control. You risk a tailspin which at touchdown speed might very well include a fractured tailboom.

Glider pilots fly their crosswind approach crabbed and try to keep the wings level. After the flare the ideal landing would include a brief kick on the leeward rudder pedal to align the fuselage with the direction of movement just as the wheel touches the ground, but even a slight sideways movement at the point of contact is no problem. Wing tip contact is avoided at all cost and delayed until the glider has slowed down so the ailerons cannot keep the wings level anymore.

The only exception is when there is no safe landing feasible – say on a rocky slope in the mountains. Then the advice is to sideslip the glider into the ground, hoping that the crashing wing will absorb enough energy to let the pilot survive. But that is a single-point landing and quite different to what you have in mind.

But there is one aircraft that can take off from a two-point (actually, counting the tailwheel, it's three, but two of them are the single main wheel and a wingtip) and that is the Akaflieg München Mü-23 motorglider (picture below, source). Starting from a position 90° to the intended take-off direction and with the wingtip pointing into that direction down on the ground, the pilot opens the throttle and lets the aircraft swing around. By the time the aircraft has completed the 90° course change, the wing is level from the centrifugal force and the speed is high enough to keep it there with the ailerons.


What is the relationship between your tail number and air traffic control? Obviously a tail number is used to distinguish yourself from other aircraft, but after the first call, a callsign does the same thing. It is also used for investigation purposes I would imagine, by listening to radio recordings, but are controllers typically even able to read tail numbers from the tower or do they just see a plane around where you say you are calling from and assume that it's you?

Sometimes your callsign is your tail number, particularly on General Aviation flights. For example, if you are flying the Cessna 152 with tail number "N123AB", you would call ATC with "November-One-Two-Three-Alpha-Bravo".
Commercial flights, on the other hand, tend to use their flight number as the callsign. E.g. if an aircraft is operating for Delta Air Lines flight 123, the callsign would be "Delta-One-Two-Three". This is not applicable to GA as GA do not usually fly a particular route or for a particular company. Assigning a flight number to every GA flight would be troublesome, it is simpler to just use your tail number as it is guaranteed to be unique.
Controllers may identify a plane by tail number when you are on the ground, but once in the air it is almost impossible to sight a plane this way. If this is your initial call to the controller, you would describe your location, which allows the controller to identify you on the radar screen. If the controller is unsure, you may be assigned a squawk code and even asked to push the IDENT button. You may also describe your type to the controller, like:

"Tower, N123AB is Cessna 152, 5 miles South of XYZ, (...)"

You are correct that if you do lie about your callsign, ATC as no way of knowing it unless somebody sees you, as described in the "Inside Air Force One" documentary by National Geographic when they tried to pretend to be a GulfStream aircraft to secretly transport the president. If you have ADS-B installed ATC will be able to see your callsign as it was programmed into the ADS-B unit, but even that can be re-programmed.


What is the difference between Body Pitch Rate and Inertial Pitch Rate? ARINC 429 specifies two series of attitude rate labels for ADIRS/AHRS/IRS systems:

Body

326 : Body Pitch Rate
327 : Body Roll Rate
330 : Body Yaw Rate

Inertial

336 : Inertial Pitch Rate
337 : Inertial Roll Rate
340 : Inertial Yaw Rate

What are the differences between these two sets of values? I'm assuming the Body labels are in reference to the airframe, but do the Inertial labels use a different reference?

I'm not 100% sure about ARINC definitions specifically, but in the general aeronautics usage the inertial frame is the ground (flat Earth) frame. The rotation from this inertial ground frame to the body frame is defined by what is known as Euler angles.

Consequently, the inertial angular rates are Euler rates: the rates at which the Euler angles change.

In the body frame, pitch, for example, is what elevator controls, 'up/down' from the point of view of the pilot. Technically, this is pitch motion but not exactly pitch angle control. Euler pitch, the pitch angle per se, is the angle between the horizontal plane and the aircraft body X axis. This angle has a different rate to the body pitch. In an extreme case, on a knife edge (90° roll, zero pitch), body yaw controls pitch angle, and so body yaw rate will match Euler (inertial) pitch rate, and vice versa (minding the sign).

Remember aerospace Euler rotations are in the yaw-pitch-roll order.

Note you cannot rotate angular rates from one frame to another using the same rotation matrix as you use for linear quantities. You need to use the matrix that keeps momentum:

$$
\begin{bmatrix}
\dot{\phi} \\ \dot{\theta} \\ \dot{\psi}
\end{bmatrix} =
\begin{bmatrix}
1 & sin(\phi)tan(\theta) & cos(\phi)tan(\theta) \\
0 & cos(\phi) & -sin(\phi) \\
0 & sin(\phi) / cos(\theta) & cos(\phi) / cos(\theta)
\end{bmatrix}
\begin{bmatrix}
P \\ Q \\ R
\end{bmatrix}
$$

where $\phi, \theta, \psi$ are Euler roll, pitch, yaw; and P, Q, R are body roll, pitch and yaw rates. The aircraft rate sensors measure the latter, so typically you need conversion this way. But for reverse conversion you need to invert this matrix: transposition is not correct for it!

Note this matrix has singularity at pitch ±90°, and indeed, yaw is undefined at such pitch angles. But there are ways to avoid it, e.g. to integrate the whole matrix at every step, or to use quaternions.


How does an airport catch up when it is behind on traffic? When airports fall behind traffic for some reason and delays piling up, how do they catch up? If flights need to be cancelled, who decides (and when) - ATC, airport management, or airlines themselves?

As an illustration, here is a snapshot from this page (taken at approx. 2355 UTC 12/23/15):

Most airports aren't at 100% capacity any of the time: they simply fit in a few extra flights for a couple of hours until they're back on track, causing relatively little delay.
Even those who are at 100% capacity sometimes, aren't usually at 100% capacity 24/7. They can recover by delaying everyone a little for a few hours, with the delay slowly reducing as the airport gets quieter

With a very busy airport (Heathrow is often quoted as an example), however, it's possible that the airport is at/near 100% capacity for long periods. Heathrow runs at nearly 100% capacity (roughly 98%), and much of the "quiet" period is actually at the very start of the day which doesn't leave much slack.

However, there's some scope for "absorbing" flight delays: at Heathrow, most aircraft will sit in a "hold" stack for a while before landing. Aircraft join this stack as they arrive and wait their turn to land. If one plane is a little late, another will simply take its place in the queue and everyone jumps "up" one space until the delayed flight. As long as there are aircraft in the stack, short delays or aircraft arriving early don't really make things too chaotic - there are still 60 aircraft landing in the next hour, it doesn't really matter what order they land in.

However if there's a bigger problem such as ice, which means the overall capacity is reduced, flights must be cancelled as they simply cannot all fit in. In this case the airport will typically reduce capacity across the board and allow the airlines to choose which flights to cancel. In the case of Heathrow, this will usually be the relatively local, high-frequency routes: eg the once-a-day flight to Sydney, Australia will still fly, but one of the once-per-hour Glasgow flights will be cancelled. For the most part the number of cancelled flights is down to the airport/ATC, but the specific flights cancelled are up to the airlines.


Shall We Consider Reversers in performance Calculations? Thrust reversers are featured to help slow down the plane after touchdown.
Moving the thrust levers aft activates the translating cowl to open, closing the blocker doors. This action stops the fan airflow from going aft and redirects it through the cascade vanes, which direct the airflow forward to slow the aircraft.

My question is Shall We Consider Reversers in performance Calculations ?

For airplanes certified under Part 23, both takeoff (AMC 23.55b) and landing (AMC 23.75f) performance can take credit for thrust reverser (T/R) if it's shown to be reliable and safe. As detailed in AC 23-8C, much extra work would be required to take credit for T/R for multi-engine airplanes:

For accelerate-stop distance: demonstration of full T/R with one-engine-inoperative and in a 10kt crosswind and on wet runway for adequate lateral controllability is required.
For landing distance: the landing distance used must be that with one-engine-inoperative; differential braking needed to maintain lateral control for this situation may negate most, if not all, of the advantage of a single T/R.

For airplanes certified under Part 25, only takeoff on wet runway may take credit for thrust reverser (25.109f). Similar situation for landing distance as with Part 23, 25.125c)3) allows credit for T/R, but only for that with one-engine-inoperative; therefore, the same problem as discussed before applies.


Can thrust reversers possibly collapse due to strong crosswinds? I recently watched a YouTube video titled "Dangerous Crosswind Landings during a Storm at Düsseldorftitled" and witnessed at the 2:06 mark, a twin engine commercial jet aircraft landing and noticed only one thrust reverser was deployed.

I am looking for a knowledgeable answer, asking if this was a malfunction.

It is impossible to tell from the video what the reason or cause was, this is all speculation.

Most likely it was a malfunction of the thrust reverser. There is a good change that the crew was aware of the problem before take-off; the Airbus A330 may be dispatched with one or even both thrust reversers unserviceable according to the minimum equipment list (MEL)

Another possibility is that the crew accidentally only activated one thrust reverser. Given the firm landing (as it should be given the strong crosswind) they might have erred in the heat of the moment.

It is unlikely that the decision to use only one reverser was on purpose if two reverser were serviceable. On the ground the aircraft has a tendency to weathercock into the wind because of the vertical tail. Selecting only the windward thrust reverser aggravates that tendency.


Do any propellers/propfans use stator vanes? Why is this not a commonplace feature? I understand that axial-flow turbine engines generally include stator vanes behind every(?) compressor and turbine stage. This makes quite intuitively sense, because without them the rotating blades would mostly swirl the air around through the engine, which would not only prevent the stages from properly transporting/compressing/expanding the air in axial direction, but also put useless rotational kinetic energy into that air. The latter is presumably also the reason why turbofans have such guide vanes behind the fan, too.

All of this applies just as well to unducted fans/propellers. Yet I've never seen stator blades behind an open propeller. There are contra-rotating coaxial propellers of course, the idea of which seems to be similar: get rid of the useless solenoidal air motion. But actively contra-rotating both props adds a lot of complexity, and seems somewhat unnecessary if the goal is mostly to remove large part of the swirling motion. Cancelling all torque is not necessary for a plane.

Especially, I would think stators could also be shaped to help retrieve some energy from the tip vortices like a duct does, without however interfering with the inflow that seems to be the reason why ducts make props inefficient at low speed.

When a compressor rotor stage speeds up the flow, the stator:

Slows it back down, turning kinetic energy into pressure (see image here from the book The Jet Engine)
Presents the flow at the correct angle for the next rotor stage.

A nozzle guide vanes stage (what a turbine stator stage likes to be called) comes before the turbine stage, and it does the same but in reverse (turns pressure into velocity) and adjusts the flow direction for the upcoming turbine stage.

The de-swirl function of the stator stage behind a fan in a turbofan (the outlet guide vanes – OGVs) is beneficial because of how much air the fan has acted on.

The number (and size) of blades tell the whole story. It's often said that propellers move air by a little, and jet engines by a lot. To put that into perspective, the typical pressure ratio rise behind a fan is 1.4–1.6, whereas behind a propeller it's less than 1.02.$^1$

This is where a turbofan's OGVs become beneficial. Adding a static stage of blades behind a propeller (with or without a case) that doesn't accelerate the air by that much to recover meaningful pressure (compared to a turbofan's fan, not much kinetic energy to begin with) in the axial direction won't help. On the contrary it will add drag (air hitting a static object), and weight.

    Actively contra-rotating both props adds a lot of complexity, and seems somewhat unnecessary if the goal is mostly to remove large part of the swirling motion. Cancelling all torque is not necessary for a plane.

A propeller is like a wing, it needs to act on (hit) air to create a normal force. If we substitute the second set of moving prop blades with static ones, we've just lost a lot of thrust.

$^1$: https://history.nasa.gov/SP-468/ch10-3.htm


Is there a physical argument for the Kutta-Joukowski theorem? I am doing the following exercise:

Consider inviscid, incompressible, steady flow. The Kutta-Joukowski theorem $$L' = \rho_\infty V_\infty\Gamma$$ where

$L'$ is the lift per unit span
$\rho_\infty$ is the freestream pressure
$V_\infty$ is the velocity
$\Gamma$ is the circulation taken around the body

was derived exactly for the case of the lifting cylinder. Equation $L' = \rho_\infty V_\infty\Gamma$ also applies in general to a $2$-dimensional body of arbitrary shape. Although this general result can be proven mathematically, it also can be accepted by making a physical argument as well. Make this physical argument by drawing a closed curve around the body where the closed curve is very far away from the body, so far away that in perspective the body becomes a very small speck in the middle of the domain enclosed by the closed curve.

And here is the solution from the author:

The flow over the airfoil can be syntheized by a proper distribution of singularities, i.e, point sources or vortices. The strength of vortices, added together, give the total circulation, $\Gamma$, around the airfoil. This value of $\Gamma$ is the same along all the closed curves around the airfoil. In this case, the airfoil become a speck on the page, and the distributed point vortices appears as one stronger point vortex with strength $\Gamma$. This is exactly equivalent to the single point vortex for the circular-cylinder case, and the lift on the airfoil where the circulation is taken as the total $\Gamma$ is the same as for a circular cylinder, namely, equation $L' = \rho_\infty V_\infty\Gamma$.

Author's figure:

I understand the author's solution until the part that said:

the lift on the airfoil where the circulation is taken as the total $\Gamma$ is the same as for a circular cylinder.

The equation $L' = \rho_\infty V_\infty\Gamma$ is derived from the circular-cylinder case which we have to do the integral of the pressure distribution over the cylinder surface. But I have not understood why the lift on the airfoil is the same for a circular cylinder like author said.

The question as asked in the title is one of the great debates of the discipline of aerodynamics (and you can see by the number of times I've edited this answer that it's still bouncing around in my own head). If you've gotten this far in Anderson and are making this kind of inquiry, you must read McClean. The first 300-or-so pages are devoted basically to answering this very question. Basically: Yes, there is a physical argument (see Peter Kämpf's answer and Anderson 4.5), but saying that lift is caused by circulation is too much of a stretch (which Anderson notes in section 3.16).

Let me turn to your specific example.
Unfortunately, I think Anderson is trying to force the mathematics into the physics rather than start with the physics and describe why the mathematics is a good representation (as McClean sets out to do from the beginning). "Make this physical argument by drawing a closed curve around the body..." basically tells us to make a physical argument by first using a mathematical construction, which to me doesn't actually shed any light on the physics. Further, then we're supposed to be thinking about infinite distances (not physically useful), a "speck on a page" (which has nothing to do with airflow), and really just make use of $\Gamma$ (which is defined purely mathematically) rather than describe a physical flowfield. In short, the closest thing to a "physical" argument here is saying more or less that any two things look the same when viewed from far enough away. This explanation does not seem convincing to me. If you put lots of little vortices around the profile of a cow then reduce it to a "speck on the page," will the cow generate the same lift as an airfoil? To get at the physical generation of lift, we need to remain close to the lifting bodies and determine why their specific geometries create flowfields that produce lift. (Consider, for example, why we need a Kutta condition on an airfoil but not on a cylinder.)

Actually, the mathematical proof (based on conformal mapping) uses the same basic "physical" argument that Anderson makes. Conformal mapping tends to be more of a graduate-level topic, though, so beware of feeling like you need to understand all the underlying math at this point.

In summary, Anderson does not do a good job here of explaining physically why the airfoil has the same lift as the cylinder. If you truly want to understand the physics, read McClean. Anderson's "physical" argument is really just a boiled-down mathematical one.


Will a quad fan arrangement on an aircraft help with pitching moments during VTOL flight transition? The phenomena of ducted fan assemblies inducing pitching moments whilst in transition from vertical to horizontal flight paths is a problem I have seen mentioned by many designers and engineers of VTOL aircraft. I am wondering if the quadratic arrangement(a fan placed at each of the outermost corners of the aircraft) would help alleviate these issues. It would seem to make sense as the front and rear fan pitching moments about a central CG would cancel each other out, though still causing stresses on the airframe.
Are these pitching moments still a problem in quad fan configurations, and has any research been done into the inlets of ducted fans to stop these pitching moments?

The Doak VZ-4 twin ducted propulsor flew in 1958, the Bell X-22 took that up to four in 1966. So yes, people have been thinking about it for over half a century.
Analogously to any tailless aircraft, the side-by-side twin is sensitive to CG in vertical mode and trim must be closely maintained. Although not ducted, the Boeing V-22 Osprey convertiplane suffers from this issue. It is not often an operational limitation, but it does need crew/staff training and careful management.
Similarly the quad arrangement brings the same benefits as the tandem wing in allowing a wide range of CG positions. However the quadrotor does not scale well to full-size aircraft, as discussed at Why haven't quadcopters been scaled up yet?


If maximum speed was a priority for modern military fighter jets and bombers, approximately how fast would they likely be? Burt Rutan talks rather passionately about the lack of innovation in space flight, but also mentions how fighter jet (maximum) speed performance has stalled:

In fact, from what little I know regarding fifth generation fighters, not only has the maximum speed stagnated, but it is degrading.

Traits such as stealth prohibit variable intake geometry and variable wing geometry, the maximum speed appears to never be used in reality, it is probably costly and creates other problems (we only have to look at the SR-71 here). Furthermore, other engine characteristics are probably more desirable, such as supercruise and good acceleration in the range where this is critical and actually useful.

However, in this question I'm asking what, approximately (mach 4, 5, 6?) would the maximum speed likely be, if maximum speed was allocated a similar budget and priority akin to that during the cold war era?

The reason I feel this question can be answered at all, is that I imagine there are some very real, practical problems with very high performance aircraft that require extraordinary solutions to overcome. An answer that identifies where these approximately are would thus go a long way towards a satisfactory answer.

Basically, the crux of this question is to identify if there have been any significant aerodynamic, engine, or other performance related advancements that would enable a fighter jet to travel significantly faster than e.g. the F-15 or MiG-25, while still retaining the same functionality as namely the same types of aircraft.

Similarly for a bomber, it is well-known that sustained mach 3 flight can be achieved by looking at e.g. the XB-70 or SR-71. Even with designs from the 1950s. What is realistic today?

Just to be clear: I'm not expecting an exact figure here, but if there are any studies that have looked into this, it would be a very interesting read. If there are no studies, perhaps someone would want to take the challenge and offer a somewhat comprehensive answer as a conjecture anyway. Any math/physics would be great.

I assume that in order to even begin to answer this question, it must be defined what a "fighter jet" is, must it have an air breathing engine, or can it also have a rocket engine, akin to the X-15? Since I'm asking the question, I will also take the liberty to arbitrarily define this here: The engine type is irrelevant, there may be more than one engine, of different types, of the same type. Whatever would make sense in the context of a fighter jet, or even a bomber. Furthermore, it must be a manned aircraft. If it can reach suborbital flight and beyond, like the X-15, it is still an aircraft (again, arbitrarily defined).

An answer that separates the air breathing and rocket engines as two different categories is fine.

This definition of making if fighter jet/bomber is mostly based on wanting to exclude unmanned experimental aircraft, even if hypersonic aircraft such as the X-43 probably serve as a good reference, I feel they have little root in reality, having no life support, no weapon systems, and perhaps no practical purpose whatsoever beyond data recording.

It may also seem like a pointless question, but this might be quite useful in terms of bridging the gap between aircraft and spacecraft, or any other application one might think of -- suborbital passenger jets, etc.

Increasing the speed of an aircraft results in having to make trade-offs. Drag will increase as the square of the velocity, meaning a doubling of speed will take 4x the power to achieve. This problem is compounded by the fact that it is very difficult to design an engine (and an airframe) that performs really well at super sonic speeds, while still performing well at subsonic speeds.

All design decisions always end up in trade-offs. Increasing maneuverability generally requires doing things that will increase the drag, which means you will require more power to compensate (which then requires a larger engine, which will reduce your maneuverability due to the increased weight).

All of these decisions mean that, in the end, increasing the speed of a fighter inevitably requires the reduction of something else, either turning speed, or weapon payload, or range. While better technology has given us more powerful engines, and new materials and alloys allow us to create more maneuverable aircraft, we've actually seen the top speeds of aircraft go down compared to past fighter aircraft, even though we could create an aircraft as fast as anything from the past, with increased maneuverability and weapon payload in comparison.

These decisions are being made because by reducing the top speed of aircraft, they in return also get better maneuverability, so it's conscious decision to take the higher weapons payload, increased range, and higher maneuverability in place of a higher top speed because a very fast top speed is just not all that useful in warfare compared to everything else. Reconnaissance (which is what the SR-71 was designed for) is better handled by satellites, which can't be shot down in practice, and don't require flying over another country's airspace in a way that is likely to draw their ire. Bombers would rather carry a larger payload, and be fast enough to get to the target, but getting their significantly faster at the cost of a reduced payload won't buy you much. Same goes for fighters, they need to fly around somewhat quickly, but a pure speed advantage over an opponent isn't all that useful either (compared to just having a better fighter). So it's a combination of both physics and specifically what things the military values that just means that there's little value to purely increasing speed.


What special handling characteristics or techniques do biplanes have? How does flying a biplane differ from flying a monoplane? Apart from the increased drag and lift, how does it handle differently, and what effect does that have on manoeuvring?

In particular, I'm interested in differences between a biplane and a hypothetical equivalent monoplane, not differences between vintage airplanes and modern ones, or differences between aerobatic and utility airplanes.

Short answer:

For clarification: Equivalence between biplane and monoplane means than both have the same wing area and the same engine. Then the main differences in maneuvering are:

The biplane has better roll acceleration than an equivalent monoplane.
The biplane has a higher roll rate than an equivalent monoplane at the same speeds.
All biplane flying takes place at lower speeds, resulting in a lower space requirement for all maneuvers. This also means that inertial effects are less pronounced: When pulling up, there is less kinetic energy available for climbing, so (for example) hammerhead turns will end with less altitude gain.

Differences in handling: The biplane has

lower aileron forces for the same roll rate at the same speed
lighter control forces overall due to lower flight speed

Differences in performance:

shorter take-off and landing distances
a lower stall speed
a much lower maximum speed
a lower optimum cruise speed and range
a lower power requirement due to the lower flying speeds, or if both use the same engine, a better power-to-weight ratio

when compared to an equivalent monoplane. These differences are most pronounced if the airplane carries just the pilot and not much payload.

Flying techniques are the same as for monoplanes. Indirectly, differences are likely due to differences in design. Example: Few biplanes profit from having a retractable landing gear while gear retraction makes sense for monoplanes with higher power loading (installed power relative to wing area).

Explanation

Biplanes have two major differences:

Smaller wing span at the same wing area, and
Wire bracing results in very lightweight biplane wings.

The smaller span reduces roll damping and roll inertia, so a biplane will accelerate into a roll more quickly than an equivalent monoplane and will reach a higher roll rate. This is the main difference in maneuvering.

The smaller wing span results in more induced drag if both have the same mass and the same speed. With wire bracing, this condition is unrealistic, and an equivalent biplane will be much lighter. If the structure is a substantial part of the aircraft's mass (this is typical for aerobatic airplanes), the result can easily be less induced drag, despite the lower span, and also lower wing loading. This in turn means that both fly at different speeds: The biplane will be able to fly much slower, but the aerodynamic drag of the bracing will restrict it to low speeds. This also means inertial effects are less pronounced: The lower mass and lower speed of the biplane combine for a marked difference to the equivalent monoplane.

For aerobatic displays this is ideal: All action takes place close to the audience, and the biplane will need a much smaller area for all maneuvers than an equivalent, but heavier monoplane. The downside are low maximum speed and low range.

Another difference in performance are much shorter take-off and landing distances due to the lower wing loading, which results in a lower stall speed. The optimum endurance and optimum range speeds are lower than those of an equivalent monoplane as well, so all biplane flying happens at lower speeds, which is beneficial for training aircraft.

Since control forces are proportional to dynamic pressure, a biplane will have lower control forces than an equivalent monoplane. Here equivalence also means that the relative chord of all control surfaces is the same. In reality, a good designer will select a higher relative chord for the biplane's control surfaces to ensure that control forces are above their required minimum.

The heavy, unreliable engines of the early years made biplanes the ideal way of taking to the air. Once engines became more powerful and allowed higher payloads, the monoplane became better suited to carrying passengers and freight at higher speeds and over longer distances.


What are RNP and ANP in area navigation? What are Required Navigation Performance (RNP) and Actual Navigation Performance (ANP)?

RNP is a numerical value that refers to the level of performance required for a specific published procedure.  If the procedure has an RNP 10, then the on-board navigation equipment must be able to calculate its position to within 10 nautical miles. If the procedure has an RNP 0.3, than the equipment must be able to calculate its position to .3nm.

ANP is the "actual" level of performance being experienced real-time. The on-board navigation equipment estimates the quality of the reception and determines how "reliable" it thinks its own position is.  If the estimate of reliability is high, then the ANP is lower.  An ANP value of 0.6 indicates that the navigation equipment is confident of its own actual position to within .6nm.  Essentially, this means that if the equipment puts a point on the map of where it thinks it is, there is a circle around that point with a .6nm radius and the aircraft is somewhere within that circle.

If the RNP required value is lower than the ANP value, you cannot use that procedure.  If you're using a procedure, you must monitor the ANP value. If, at any time, the ANP goes above the RNP, you must exit the procedure.

Here is an image of a Boeing 737 FMC displaying the current ANP (.06) and the RNP (2.0).  Courtesy of http://www.b737.org.uk


Is there a dedicated emergency frequency? Coast patrol has a dedicated frequency for emergency that must be watched at almost all hours, and even if I recall, it had a "dead silent period" to prioritise whatever emergency might be reported. Is there a dedicated frequency for aviation? Or shall MAYDAYs just be sent to the standard ATC frequency?

If a pilot is already speaking to ATC (or monitoring a frequency) they should continue to use that frequency for any emergency or abnormal situation.
If they are not currently receiving ATC services or on an ATC frequency, attempt to use 121.5. Many ATC providers and enroute airliners monitor this frequency and can relay or provide assistance.
The FAA's AIM (6-3-1) describes emergency use of 121.5 in the United States:

h. Although the frequency in use or other frequencies assigned by ATC are preferable, the following emergency frequencies can be used for distress or urgency communications, if necessary or desirable:

1. 121.5 MHz and 243.0 MHz. Both have a range generally limited to line of sight. 121.5 MHz is guarded by direction finding stations and some military and civil aircraft. 243.0 MHz is guarded by military aircraft. Both 121.5 MHz and 243.0 MHz are guarded by military towers, most civil towers, FSSs, and radar facilities. Normally ARTCC emergency frequency capability does not extend to radar coverage limits. [emphasis mine] If an ARTCC does not respond when called on 121.5 MHz or 243.0 MHz, call the nearest tower or FSS.


How does wing flex reduce wave drag? If I'm reading this post right: What is the effect of airfoil thickness on aerodynamic lift?

Airfoil thickness increases the lift coefficient.

And from here: What are the effects of the Boeing 787's very flexible wings?

Wing flex reduces wave drag.

I'm wondering about the how. My theory is that the air sees a thicker airfoil in a flexed wing, without actually building one. Is that assumption correct? Or is it related to the end-plate effect?

Front view of a flexed wing. Orange indicates that perceived increase in airfoil thickness.

No, it is torsion which reduces wave drag.

The sweptback wing will twist as well as bend, and this twist will reduce the local angle of attack, and with it the suction peak on the top side of the wing. The same mechanism twists the outer part of a forward swept wing to higher angles of attack, necessitating a stiffer structure to avoid aeroelastic instability.

Air will not "see" any difference in wing thickness, regardless of the dihedral or bending. For air, there is no difference between a wing and a vertical surface (which would have almost infinite thickness following your assumption, but obviously doesn't).


Where in the world is it possible to be a foreign air traffic controller (non-military)? To work as an FAA controller, you must be a U.S. citizen. To work as a EUROCONTROL controller, you must be a national of one of their member states.

Per standard governmental employment laws, I assume most countries around the world have similar requirements. Are there any exceptions? Are there any places more open to employment of foreign controllers?

I know there are a few U.S.companies that perform contract air traffic control services in other countries, such as RVA, Midwest ATC, and Serco, but I believe this is mostly for the U.S. Department of Defense. Are there any countries that have foreign contracts for civilian ATC services?

The EUROCONTROL example you give, allows controllers from all member states to work in Maastricht Upper Area Control (Netherlands) and provide ATC over Belgium, (part of) Germany, Luxembourg and the Netherlands. Many of the controllers there are not from any of these four countries so they are foreign air traffic controllers.

Also EUROCONTROL is only providing Upper Area Control above the four countries mentioned above. All member states have their own Air Traffic Control providers, some have more than one.

Within EU countries (note that not all EUROCONTROL member states are EU member states) we have freedom of labour movement. So for EU citizens there should be no official barriers to work as a foreign controller in another EU member state. Apart from the intra-EU rules, some ATC organisation within the EU are open to applications from outside the EU. For example the Dutch Air Traffic Control Organisation LVNL is open to foreign controllers. Applicants are not limited to citizens of EU countries.

ATC at airports is becoming a commercial business. The companies that you mentioned provide civil ATC at various airports around the world. Another example is ATC at London Gatwick Airport: the contract was awarded to a subsidiary of the German ATC organisation DFS.

Outside the EU I know that there are many foreign controllers work in the United Arab Emirates. They are looking for new applications at this moment as well.


Why are magnetized materials dangerous goods? I was reading about Dangerous Goods, and came across the fact that magnetized materials are classified as Dangerous Goods (item 12 in the linked page). We all see magnets every day, and they seem harmless.

Why are magnets dangerous to airplanes and require more careful handling?

98% percent of magnets - the everyday ones - are completely harmless. I believe the concern is with super-strong rare-earth magnets, where they can be problematic. Aside from Simon's valid point on interference to compasses:

Getting stuck to things, such as other bags or the infrastructure itself, in the baggage system.
Attract themselves to other packages and content, possibly damaging these. Think of hard drives and electronics.
Being a nuisance and safety concern should somebody decide to open it, such as customs or security. You can get your hand crushed in the process if you open the box and the thing springs out.

Be aware they do not appear to be banned - just regulated in that they have to be properly labelled and packaged for safe transport. More curiously in that list are 'First Aid Kits' and 'Seatbelt Pretensioners'.


What is the best option when the headwind exceeds the maximum airspeed? In a previous question, Mongo described flying his Cessna with a negative ground speed in a head wind.  In this situation, what is the correct thing for a pilot to do, if there is nowhere to land downwind and upwind ground speed is negative?  Other answers on that page show that, for very light aircraft, descending will not always get you to a low enough wind speed that you can fly forwards.

Before even taking off, a pilot is required to get a weather briefing, including winds.
 Wind speeds are usually predictable and well known.  If a pilot was flying against strong headwinds, with no good landing alternate, he screwed up his flight planning before he even started the engine.  A headwind doesn't even have to be strong enough for negative GS, just strong enough to cause concern.

Winds vary by altitude in both strength and direction.  If a pilot does find himself in such a situation, changing altitude by a few thousand feet, higher or lower, can very likely change both the wind direction and speed to something that is manageable.


Factors to be considered when re-engining aircraft What parts of the aircraft need to be adjusted / refitted / added when fitting new (different type) of engines?
Also what what kind of re-certification regarding airworthiness etc. will be necessary?

This depends greatly on the engine. However, given the 737 MAX situation, I'll assume you mean re-engining with larger, more efficient engines. This still leaves a lot of room for interpretation- what aircraft are we working with? Something like the 757, with tons of ground clearance? Or something like the 737, with very little clearance? I'll answer both.
In the first scenario, re-engining a 757, there's not a WHOLE lot that needs to be changed. The engine mount/pylon, wing structure (to account for a heavier engine), and maybe the FADEC. That's really all I can think of. Maybe the fuel system.
The second scenario is where things get interesting. If you want to avoid a 737 MAX style situation, you'll need to extend the landing gear legs and find some way to stow them. If you can't find anywhere on the airframe that's beefy enough to accept that, then you'll have to find an ideal spot and reinforce it. Then change everything that I mentioned in the first scenario.
I'm no aerospace engineer, and I'm sure I'm missing countless things here, but these are all the major things that I can think of.


How much thrust is lost through a curved exhaust nozzle? In modern VTOL aircraft energy is usually directed through nozzles to achieve vertical lift. How much energy is lost when changing the direction of flow in static thrust conditions?

For the F135 engine in this photo, thrust in hover is only about one per cent less than maximum thrust, if Pratt & Whitney's data sheet is to be believed.

Maximum Thrust Class 41,000 lbs
...
Hover Thrust 40,650 lbs

The Hawker Harrier's maximum thrust was about 20,280 pounds.
An approximation of its maximum vertical thrust at low airspeed is given by its maximum vertical landing weight, 19,918 pounds, again just about one per cent less.


What is the difference between placing wheel chocks on the outer wheels as opposed to the inner wheels of the main landing gear? Recently I am aware of a change made to the IATA Ground Operations Manual (IGOM) in regards to the position of the wheel chock on the main landing gear.

Is there a justification for why one method is preferred or is safer than the other?

If the inner wheels are chocked, the ground crew person would likely have to place their arm/hand in the path of the wheels to grab the rope and pick up the chock.


What is the largest flight school in the U.S. that does not offer a degree? Definition of "largest" for the purpose of this question: the greatest number of flight operations per year on average.

What is the largest flight school in the United States that does not offer a degree?

According to Wikipedia, "ATP Flight School ... is the largest flight training company in the United States."

However, volume does not necessarily mean quality, and the focus of ATP and other big-name flight schools seems to be on students who want an airline career—and pushing them through the training as quickly (and profitably) as they can. If that doesn't meet your goals, or you don't have large amounts of both time and money available to dedicate to it, you are probably better served going another route.


How can I become familiar with flight rules specific to Canada when flying there from the United States? As a US licensed and trained pilot, I know I can fly into Canada, but are there are airspace rules that are different from the American system. Is there a Canadian rules test or conversion you can or should do, or should I just expect to fly in Canada by the exact same rules and procedures as in the United States?

In the specific case of Canada, AOPA and COPA have a lot of information aimed at US pilots. AOPA has a complete guide on documents, customs etc. and COPA has a page with more information, which includes this remark:

  The flying rules are almost indistinguishable - reading the COPA guide
  should keep you legal and out of trouble. Make sure you get a Canada
  Flight Supplement (CFS) and some VNCs (Canadian equivalent to your US
  sectionals), that will allow you to navigate VFR safely.   IFR plates
  are available from Nav Canada as a subscription or the (sample list
  of) vendors included below. (by mail order)

The guide is free but available to AOPA/COPA members only.


Are engine casings expected to contain turbofan blade fragments? On Southwest 1380, initial indications are that a fragment of the engine blade pierced the engine casing, which then hit the airplane window (or perhaps a part of the casing did). According to the BBC,

  Mr Sumwalt also said a casing on the engine was meant to contain any parts that come loose but, due to the speed at impact, the metal was able to penetrate the shell.

Is this an reasonably expected containment failure?  Or is the failure to contain surprising to industry experts?

We don't yet know how or why the engine casing failed to contain the fan blade on Southwest 1380.

But yes: Not only are the engines designed to contain blade failures at fan red-line speeds, but they are also required by 14 CFR 33.94 to confirm they do, typically via destructive "blade-off testing."
(There are a number of good videos of this testing online: Search "turbine blade fail test" or "blade-out engine test.")

As noted here "fan blade-out" failures in the real world are virtually unseen.  (Turbine blade failures are relatively common and can even go unnoticed until major service teardowns.)


Is it required for pilots to contact ATC while flying VFR? Does a pilot need to communicate with ATC while flying VFR (during departure, flight or departure) or does it depend on type of flight (like private, commercial, etc.)?
Or is it required for pilot to inform ATC only during arrival and departure for runway clearance and altitudes?
If a pilot does not remain in contact with ATC during the flight, how does ATC know what pilot's intentions are?

It depends on which class of airspace you are flying in. For airspace classes A, B, C and D, a continuous two-way radio contact with ATC is required for all VFR flights. In airspace classes E, F and G, there is no such requirement.
The below table shows requirements for both IFR and VFR to fly in different airspace classes (source: ICAO Annex 11, Appendix 4). You should notice the second column from the right, which specified the radio communication requirements for a given airspace class.

These are general rules, that apply to all ICAO member states (basically, every country in the world), unless a specific state has decided to deviate from the ICAO standards. Such deviations will be listed in the national AIP, section GEN 1.7. For example, in some countries, two-way radio communication may be required for VFR traffic within certain airspaces classified G, even though that is generally not the case. A table with rules specific for your country will be available in your national AIP, section ENR 1.4, and will probably look quite similar to the above.
At controlled airports, a control zone will be established, which will be class A, B, C or D (cf. ICAO Annex 11 para 2.6, a control zone cannot be classified E). This means that, at a controlled airport, VFR traffic must establish a two-way radio contact with ATC, just like IFR.
At uncontrolled airports, however, this is generally not required.
During the approach, departure and en-route phases of flight, whether or not you are required to be in contact with ATC depends entirely on where you are flying. Very generally speaking, if flying close to controlled airports or above a certain level, you can expect the airspace to be controlled, and thus, contact with ATC is required. At low altitude, away from major airports, the airspace will often be uncontrolled, and no radio contact required.
The above is a very general description, and you really must refer to local charts and procedures to figure out if you are required to contact ATC in a specific area.
As a point of advice, ATC is there to help you. It is a good idea to contact ATC even if you are not required to do so, in order to receive flight information service and alerting service. This allows you to receive important information about traffic, weather, military activity, etc., and if something happens to you, a search and rescue mission can be initiated without delay.


How can I calculate the C.G height for an Aircraft? before I continue I would like to thank you guys beforehand for the help. I am new to this forum and in aviation in general. I am helping my professor to obtain the C.G coordinates in x, y , z for a simulation of a Cessna 172 (we are using Tornado for Matlab). From what Ive read, the C.G in aviation is mostly obtained through the longitudinal axis (x), I assume that the y is centered in most cases, but I am wondering, how can I obtain the height of the C.G, can I use the same method as in the longitudinal axis?

I was also wondering, why is it that for the calculation of the C.G you take into account things such as fuel, passengers, luggage and so on, but not other things like the motor, propeller, fuselage, landing gear, etc.?

Sorry if my questions are a little stupid or obvious. Thank you for your help!

No that's a really good question. Weight and balance calculations for flying are only concerned with the location and value of the variable weights - fuel, pax, baggage. The C of G of the "empty" aircraft with all those components is considered a single unchanging value for the purpose of establishing a starting point before loading, and is established just by weighing the airplane while empty.  The weight of the components is a factor in where the empty C of G will end up, but once established the entire "empty" machine is treated as a whole unit for W&B purposes.

Vertical C of G is not normally provided with A/C weight and balance data.  Although the location is not too big deal with most types of aircraft, for gyrocopters it's quite important because they need to have the engine's thrust line as close as possible to the center of mass for safety reasons (if you unload the rotor on a gyro by pushing over or from turbulence, and the thrust line is significantly above the vertical C of G, the thrust line tries to spin the mass of the machine like a pinwheel about the C of G and the gyro tumbles, with fatal results; the tall and spindly look you see on small gyros today is driven by the need to mount the engine/prop lower to get the thrust line close to the vertical C of G).

On a gyro, the procedure is to hang the loaded ready-to-fly-state machine by the rotor hub, establish a vertical reference line below the hang point, then hang it by another point at the same level that is offset forward or aft using a special "2 hang point" rotor hub fixture, or alternatively if it'll work you can tip the machine back on its main gear until it balances, and establish a vertical reference line extending up from the gear contact point.  Where the line extending down from the rotor hub, and the line extending up from the gear balance point (or the two downward lines if you had a dual hang point fixture) intersect, is the vertical C of G.

To figure this out on a 172 you would need to do something pretty radical, like support it along the fuselage at one point using a suitable resting fixture just forward of the main gear but aft of the C of G, and tip it back until it balances and establish a vertical reference through the balance point, then move the fuselage rest forward to ahead of the C of G and tip the plane nose down to establish a new balance point and vertical reference.  Then where the vertical axis of each balance point intersects, there's your vertical C of G.  Of course you'd want to do this while loaded with people, fuel and bags and you'd probably have to pay them or offer them free beer, after you've found an airplane to use, built a fixture, and all that.  You could also probably do it by weighing on scales with the nose propped up high on a block so it points up at an angle, then reweighing with the mains propped up high on two blocks so it points down on an angle, then do some clever geometric calculations to work it out.

Or, if you are as lazy and cheap as me you could call Cessna's Tech Support organization and tell them what you are doing and what you need, and somebody somewhere should be able to find the data (hopefully) without charging you for it.


What does "airspace above 14,500 MSL is controlled with few exception" mean? I was reading Cessna IFR Training program and came across this line that airspace above 14,500 MSL is controlled with few exceptions.

What does it really mean? Class A doesn't start until 18,000 ft, and although Class E is controlled, it is legal to fly in and out of this airspace without talking to anyone, additionally it also doesn't require communication or navigation equipment. So I have following questions.

If I am away from radar coverage area but inside Class E and flying VFR at 15,500 MSL, is that controlled or uncontrolled, if controlled then controlled by who?
Did they mean to say that as you recall class E is controlled?
What is the real world example of airspace above 14,500 ft MSL but uncontrolled?

Class E airspace starts at 14500 feet MSL except for the airspace below 1500 feet AGL or designated and charted to start lower (SETVODA). There are areas like the US Rocky Mountains that are more than 13000 feet in elevation.

Class E is controlled airspace. Sectionals and charts will give you the information for the controlling agency. But just as if not more important, the minimum VFR weather requirements have to match those of controlled airspace (3-152, 5-111).

§71.71 Class E airspace.
Class E Airspace consists of:

(a) The airspace of the United States, including that
airspace overlying the waters within 12 nautical miles of the
coast of the 48 contiguous states and Alaska, extending
upward from 14,500 feet MSL up to, but not including 18,000
feet MSL, and the airspace above FL600, excluding—

(1) The Alaska peninsula west of longitude 160°00'00" W.;
and
(2) The airspace below 1,500 feet above the surface of the earth.


Which country would employ foreign air traffic controllers? Air traffic controllers from Pakistan hold ICAO approved Licences (ATCL).
Which other country will accept this ATCL for employment acceptance?

As I know, Vietnam is one of the countries employing foreigners for the position of an air traffic controller.


What technology is being moved forward to keep pilots from crashing planes? So it seems that we have three basic issues (and possibly more but not as prevalent):

Pilots can crash planes.  Someone can just be suicidal, be part of an extremist/terrorist group, can have a vendetta against someone or just thinks might as well take more down with me.
Passengers that get into the cockpits.  I know that the cockpits are locked and pilots are armed but on a lot of flights there is opportunity.
Using technology to override aircraft autopilot.

So what is the long-term plan to keep these things from happening from a technology point of view?  Is there anything in the makes that will help solve these issues?  I foresee some sort of technology that requires some sort of dual sequenced unlocking to allow a pilot to make a certain % deviation from flight plan.

Note:  There have been a lot of answers here that basically say "nothing is being done" and offer up reasons why.  To use the recent incident of a pilot dropping a plane into a mountain as an example, my main question surrounding that is, is there a technology that would see that the pilot was well off course?  Is there technology that would see that the plane had a high risk of crashing?  Is there technology that would prewarn flight control (even if it were a few minutes)?  Is there technology that flight control could override plane and right the ship that is going into the mountain?

Nothing.

At present, there are no serious technological plans to prevent pilots from intentionally crashing a plane. There are discussions about making sure that there are always two people in the cockpit, and at some point policies might be changed to make it easier for pilots to enter the cockpit (even if no-one in the cockpit wants them to), but ultimately we trust the pilot to do whatever necessary to ensure the safety of the aircraft (within certain bounds; see the flight envelope protection system in Airbus aircraft).

By limiting pilots' ability to control their aircraft, we seriously limit their ability to legitimately deal with emergencies. See, for example, cpast's example of one pilot having a medical emergency and the other pilot not being able to divert because they can't get approval. Even if both pilots are conscious and able, such a system would slow them down when responding to emergencies.


Why are electric shavers specifically permitted under FAR §91.21 This struck me as a bit strange, 91.21 which covers electronic devices that can be used during IFR flight has some exceptions, one through three make logical sense (not really sure why portable voice recorders are in there though) but number 4, Electric Shavers, is specifically permitted by the regulation. Are that many people shaving under IFR conditions that this needed to be permitted? Is there some historical or practical reason why electric shavers are specifically named in this regulation?

  § 91.21 Portable electronic devices.

  (a) Except as provided in paragraph (b) of this section, no person may
  operate, nor may any operator or pilot in command of an aircraft allow
  the operation of, any portable electronic device on any of the
  following U.S.-registered civil aircraft:

  (1)Aircraft operated by a holder of an air carrier operating
  certificate or an operating certificate; or

  (2) Any other aircraft while it is operated under IFR.

  (b)Paragraph (a) of this section does not apply to -

  (1) Portable voice recorders;

  (2) Hearing aids;

  (3) Heart pacemakers;

  (4) Electric shavers; or

  (5) Any other portable electronic device that the operator of the
  aircraft has determined will not cause interference with the
  navigation or communication system of the aircraft on which it is to
  be used.

This is an educated guess, based on history:

Electric razors were once well known as prone to generating elctromagnetic interference -- the ones available in the 1940s could pretty well blanket a nearby AM broadcast radio receiver.

However, in similar time frames, it was very important for oxygen masks to fit closely on the face, and beard stubble, besides being reportedly very uncomfortable, would compromise the seal (either increasing consumption from the limited store of oxygen available for high altitude flight, or risking hypoxia for the wearer).  Therefore, on long flights, it wasn't at all uncommon for aircrew to shave one or more times before getting where they were going.

As noted in comments, shaving with a blade razor (even the safety razors available when this regulation has its roots) was a bit hazardous in an airplane that might, without any warning, encounter turbulence that could literally knock someone out of their seat if not belted in place.  Wind-up rotary razors existed before 1950, but they were rare, relatively delicate, and expensive.  Electric razors that ran on 115 V were available before 1940 and, with care, would do a good enough job to let an oxygen mask seal well (rechargeable types didn't appear until the late 1950s).

The regulation, then, is to recognize that even with the potential radio interference, an electric razor was specifically to be permitted during flight.


Can ATC separate IFR traffic in class A airspace from VFR traffic in class E? Is it possible for ATC to apply 3 miles separation between an IFR aircraft in class A and a VFR aircraft operating in class E, just below class A?

Keep in mind that ATC only separates IFR traffic from other IFR traffic. So they would not provide separation from any VFR traffic no matter what the airspace (with the exception of Class B).

AIM 4−4−11. IFR Separation Standards

  b. Separation will be provided between all aircraft operating on IFR
  flight plans except during that part of the flight (outside Class B
  airspace or a TRSA) being conducted on a VFR−on−top/VFR conditions
  clearance. Under these conditions, ATC may issue traffic advisories,
  but it is the sole responsibility of the pilot to be vigilant so as to
  see and avoid other aircraft.


Can any aircraft adjust the wing dihedral in flight? Are there any aircraft that can mechanically modify the dihedral angle of the wings whilst in flight? Would this solution give any advantage?

There was one, and it did it to increase directional stability at supersonic speed. I am talking of the North American XB-70, of course. There were three benefits to this configuration:

Improved directional stability. Without the effect of the folded-down wingtips, the XB-70 would had lost all directional stability upwards of Mach 2. The wingtips folded down to 64.5° anhedral (or is it -64.5° dihedral?) which effectively made them into ventral fins. This answer explains how a ventral fin is especially helpful at supersonic speed, because it works in the compressed air below the aircraft.
Less shifting of the aerodynamic center. Since the transition to supersonic flight will shift the aerodynamic center back, folding the wing tips down reduces lift in the aft section of the wing, thus reducing the aftward shift.
Better capture of the compressed lower wing flow for lift creation, which is called a waverider. This increases the pressure on the lower side of the wing at high supersonic speed and allows to fly with a reduced angle of attack, thus reducing drag.

XB-70 landing with wingtips straight (picture source)

XB-70 in flight with wingtips down (picture source)

The XB-70 is also one of only a few types where every aircraft ever built had different dihedral: AV-1, the first prototype, had 0° while AV-2, the second prototype, had 5° dihedral over the whole wing to improve yaw and roll stability. Only the dihedral of the outer panels could be adjusted in flight, however. According to this source (PDF!) they were the largest moveable aerodynamic device ever used on an airplane.

Other cases of variable dihedral were less intentional, though, and there was really no advantage to it:

Like on many Navy aircraft, the wings of the F-4 could be folded for stowage. If the mechanism was not locked, the wings would fold up. The F-4 was even powerful enough to be flyable this way. When only one side folded up, the F-4 would crash, however.


If the static port get blocked, and no alternate static air source is fitted, will the transponder keep provide mode C? If the static port get blocked for any reasons and the aircraft is not fitted with an alternate static source while in Mode C with SSR, will the ATC still get the height information from my transponder?

It will stop reporting correctly as it is connected to the same static air line as the altimeter

  The transponder depends on an external altitude encoder to provide the digitized pressure altitude that the transponder needs for its Mode C replies. The encoder is connected the same static air line as the altimeter and is wired electrically to the transponder

However the transponder may not know the port is blocked and will still report the erroneous information it is receiving. If the port is blocked it’s pertinent to shut off altitude reporting manually.


Why is Mi-35M so huge in size? Why is Mi-35M so huge in size?

What is the benefit of having an attack helicopter to be so big?

If there is no benefit, why wasn't its size reduced?

Apache is not as huge as this.

Apache is pure attack helicopter with just two crew. Hind is a mixed role attack and light transport helicopter with additional room for 8 troops. Different role, different size.


Seating distribution in passenger aircraft Recently I was checking in to a flight and was asked if I'd like a window or aisle seat as usual and choose a window seat. I was then told that there are no more window seats available but I could get an aisle seat without someone sitting next to me and then just take that window seat. The plane was an ATR-72 so the rows were 2+2 seats.

I know about weight distribution to the front/back but I couldn't come up for a good reason to do this. What could be the reason for not giving me that apparently free window seat right away?

There are certain restrictions due to which the airliner didn't give you the seat even if you were ready to pay extra for it (Depends on the operations policy by the manufacturer and the aircraft).

It's mostly the weight restrictions for the flight to take-off as there might be some obstacle for the flight during take-off(hoarding on the end of runway, climate etc.). If the weight is too much then it will result in a disaster so equal weight distribution is mandatory.

Moreover in the end it's airliner which has to suffer because the seat occupancy get's affected and it has huge losses incurred by not leaving to its capacity.


Why Do Airlines Still Use Tractor-feed Printers? Why do airlines still use those old dot-matrix tractor-feed printers at their gate counters? I’ve always thought that was hilarious.

Probably note directly related to aviation, maybe more to airports than airlines:
Well, dot-matrix printers are expensive, but durable and print at very low cost and finally carbon copies (two, three or even four) of forms could be created. And replacing them will require a lot of software adaptions.
I‘ve seen airports using text-user-interfaces (TUI via terminals), which are often working a lot of better (fast and efficient to use) then usual GUI applications. New stuff, is not automatically good.


Are flame holders made of a special material other than that used in combustion chamber? Are the flame holders made of materials which have higher friction coefficients than the combustion chamber in order to create turbulence?

In The Jet Engine, there is no mention of a two-material setup for the flame-holder/combustor. It's all about the design of the diffuser and combustor shape / holes.

One of the fancy things they mention (p. 122, image below) is the lining of the walls in elevated ceramic-coated tiles for internal cooling.

Having to deal with two materials would decrease the structural integrity of the combuster. And to my knowledge, the flame-holder and combustor are one and the same, a single unit.


What airspace are ultralight pilots allowed to use? So I've been watching videos and thinking about getting into ultra-light aviation. Flying in a personal air-trike or paramotor looks like a lot of fun. Being new to the aviation arena I had a couple questions:

How do the airspace restrictions work?
Do you have to file a flight plan like any typical aircraft/pilot at an airport?

For example, say I wanted to take my paramotor to a large park and take off from there? How would that work with the FAA, talking to ATC and other traffic in the area so they know I'm there? Does it work the same as flying in a Cessna?

Ultralights are regulated under 14 CFR 103. There are very few regulations that apply to them, but there are specific rules on airspace in 103.17:

  §103.17   Operations in certain airspace.

  No person may operate an ultralight vehicle within Class A, Class B,
  Class C, or Class D airspace or within the lateral boundaries of the
  surface area of Class E airspace designated for an airport unless that
  person has prior authorization from the ATC facility having
  jurisdiction over that airspace.

That means, you can fly in (most) class E airspace and all class G airspace. You can find more information about those airspace classes in this question.

As for your other questions:

A flight plan isn't required even for aircraft, and ultralights aren't subject to the regulations that would require them anyway
Ultralights aren't required to have radios or talk to anyone; you usually fly so low that you aren't in anyone's way
It's not at all the same as flying a Cessna; in fact, you don't even need a pilot's license to fly an ultralight
See this question for information about launching from national parks; state parks would be subject to state law instead but the principles are probably the same

You might want to look through all our ultralight questions for more information.


Can a GPS waypoint be used when filing a VFR flight plan? This probably equally applies to IFR flight plans, but the general question is can arbitrary (unrelated to an airway or named fix) GPS coordinates be used in the route on a flight plan?

Yes, nothing prevents you from doing so, and it is quite common.

Flying VFR does not require you to actually navigate by means of visual reference, it just requires you to remain VMC in accordance with the airspace class you are in.


Difference in lift generation for a swept wing and straight wing in subsonic condition Would there be any differences in lift for a straight wing and swept wing (front or back) with the same airfoil cross section, same chord length, same wing span, and same area when flying in subsonic condition that is lower than Mach 3?

Since both the lift curve slope and the effective angle of attack are reduced by the cosine of the sweep angle at quarter chord, the lift coefficient of a swept wing at the same geometric angle of attack is reduced by the square of the cosine of the sweep angle.
Also, the pressure distribution over chord differs between straight and swept wings, especially near the center and the tips. All this makes swept wings less attractive, were it not for their ability to delay compressibility effects, basically for the same reasons which reduce their efficiency.
However, lift is generated in the same way: By pushing air down or by a pressure difference between upper and lower wing. Both are equivalent explanations of lift.
Only at high sweep angles and high angle of attack will vortex lift kick in and produce this pressure difference by means of a strong vortex on the upper side of the wing.
Since you ask about "subsonic condition … lower than Mach 3", I wonder whether you actually ask about supersonic flight with a subsonic leading edge. Now things are rather different between a swept and an unswept wing: While the sufficiently swept wing with a subsonic leading edge will still exhibit a pressure distribution similar to that at subsonic speed, the supersonic straight wing will create a shock, resulting in a slowing down of the flow where at subsonic speed an acceleration could be observed, and vice versa. Also, the center of pressure will move back in supersonic flight.


How were the graveyard spiral and other sensory illusions discovered? The graveyard spiral has an infamous reputation for killing even experienced pilots which only have visual flight experience. What the wikipedia article does not mention is how and when the spiral and other dangerous sensory illusions were discovered.

Essentially it means that pilots in the beginning years would be found inexplicably killed by seemingly harmless weather with visual impairment (fog, night). Someone must have survived such an experience and lived to tell the tale. Is there any information about the hunt for the cause of early crashes and when they identified the culprit?

This paper from the website of the Department of Behavioral Sciences and Leadership at the US Air Force Academy reviewed cases dating back to 1913 (note though it doesn't assert that the reports in 1913 suspected Spatial Disorientation (SD)). In the linked paper the author references a previous paper which I can't seem to find: Gibb RW . Historical assessment of visual spatial disorientation
[abstract] . Aviat Space Environ Med 2010 ; 81 : 318 .

  In 2010, the lead author presented an assessment of visual spatial
  disorientation at the annual Aerospace Medical Association conference
  and cited 25 studies dating from 1947 to the present declaring SD’s
  role in mishaps as well as surveys of pilots anonymously sharing their
  SD experiences

The earliest research they reference is a Navy survey from 1947. Quoted from the linked paper

  1947: U.S. Naval aviators, 67 total, reported on their illusionary
  experiences and categorized them into visual, non-visual, conflicting
  sensory cues, dissociative, and emotional ( 48 ). Of note within
  visual illusions categories were confusion with lights, depth
  perception, “ black night, ” and judging height above the
  ground/water. Experienced pilots were still prone to illusions
  regardless of total flight time.

  ( 48 )Vinacke WE . Illusions experienced by aircraft pilots while
  flying .J Aviat Med 1947 ; 18 : 308 – 25 .

The linked article suggests that the aviation community has known about these issues since the early days of flight but the issue was (and they assert still is) an underrated and underreported flight risk which may skew reporting which causes underfunding. Thus the published research may lag the time in which the community started noticing SD.