What is the difference between a propeller and a rotor?

Short answer:

A propeller is used to propel something, the force at stake being called thrust. Thrust is usually horizontal (but not always, think about rockets). This device comes from the navy domain.
A rotor of a rotorcraft is used to control anything, including the altitude, the generated force being called lift. Lift is generally vertical (but not always, think about a rudder). Rotors have generally more than two blades.

Lift and thrust involved are components of the same physical force (the aerodynamic force) to which we refer to differently based on their purpose after an arbitrary breakdown based on the direction they act (compared to the direction of the aircraft or to the gravity field).

For our pleasure, let's also talk about a turbine rotor, which is a rotor/propeller which doesn't produce lift or thrust, but convert the fluid velocity (actually momentum) into torque. For example the wind turbine rotor. A turbine rotor is certainly a propeller, but we don't refer to it as a propeller, as it propels nothing.

Rotor is the most generic name for something spun by a shaft. It can be used for a propeller, the rotating wing of an helicopter, the rotating elements of a compressor or a turbine, etc. You can't be wrong using rotor for any spinning device. Rotor (rotating) is the antonym of stator (stationary). These terms are not specific to aerodynamics, in a electric motor there is usually a stator and a rotor as well.

The rotor of a rotorcraft comprises blades and is comparable to a propeller, if we except blades additional freedom in flapping and leading-lagging to limit vibrations created by repeated force swings encountered while performing a 360° turn.

Source: Wikipedia

But actually the main rotor is a (rotating) wing, and the anti-torque rotor is a (rotating) rudder. Their blades are meant to produce lift like the wing and the rudder they replace. Because lift is involved, we tend to name them rotors rather than propellers.

A propeller also comprises blades, fixed on the rotation axis.

Source.

The purpose of a propeller is to propel the aircraft, that is to push it in the direction of its flight.

Both a rotorcraft rotor, a propeller and a wing create the same aerodynamic force. However the conventions are:

A rotor and a wing are used to eventually counter weight and control altitude, and a propeller to eventually counter drag and control velocity along the flight path (I say eventually because to gain altitude you usually temporary increase thrust, that's a detail)
A rotor and a wing create lift, a propeller creates thrust.

Wing, propeller blade and rotorcraft blades work exactly the same from an aerodynamic standpoint. The resultant of their action is the total aerodynamic force, which is then broken down arbitrarily into lift, drag, thrust and torque to facilitate mechanical analysis.

Notes:

Moving an aircraft along its path (thrust) is easier than maintaining its altitude (lift), and therefore a main rotor is far larger than a propeller for aircraft of the same mass.
The horizontal displacement of the rotorcraft is also produced by the main rotor (cyclic control), so some part of the aerodynamic force can also be seen as thrust, and the rotor also acts as a propeller.
Propeller is used for simple propellers and not in turbine engines. While the fan of a turbofan is comparable to a propeller, participates to thrust production and aircraft propulsion, the fan is still only one part of a system (guide vanes, fan duct and exhaust nozzle greatly maximize final thrust). Bottom line the fan is a rotor, not a propeller.


What procedures are used for midair refueling without air supremacy?

It's actually a problem the US Navy at least has been considering - with improvements in anti-ship missile capability (such as China's Dong-Feng 21D) meaning that carriers are at risk at ranges approaching 900NMi having to keep the ships out of range is taking a large chunk out of the effective range of aircraft such as the F35C which has a range of 1,200NMi and refuelling a "stealth" aircraft with a conventional tanker plane sort of defeats the point.

As a House Armed Services Committee report noted:

  The committee notes that the aircraft carrier air wing has been optimized for striking power and sortie generation and believes that it may not be configured to support the long-range strike required by current and future threat systems. While the introduction of the F-35C will significantly expand stealth capabilities, the F-35C could require increased range to address necessary targets. The committee believes that several options could be used to address this issue to include developing a stealth tanker capability, improved engine technology, or to develop and procure a strike capability that is purposely built to strike at increased range.

The current proposed answer to this is the MQ-25 development of which was approved by the US Navy earlier this year for service in 2024.

The MQ-25 is intended as an un-manned tanker with stealth capabilities delivering fuel for 4-6 aircraft at a range of ~500NMi, as a) a stealth aircraft itself it will be harder to detect and intercept and b) as UCAV if it does get shot down there's no need to think about ejection seats or any other mechanism to protect the crew.


Why do pilots cut the reverse thrust below 40 km/h?

The question speaks of a very old 747 landing tutorial. And as such I take that to mean it would be of a 747-100/200 aircraft, and that's the reference point I'm answering from.

First, concerning the comments below the question that wonder whether you have to worry about unwanted objects on a runway at an international airport, there is no such thing as a completely clean runway, even after sweepers have just finished clearing the runway. There is always some grit—it's a matter of degree—and while ingesting it isn't going to cause immediate problems, over time it will abrade the fan blades and thus the engine performance. This may not apply to higher, body-mounted engines rather than engines mounted below the wing, at least we didn't worry about it when I was flying 727s. If our taxi speed with engines idle was getting a little fast, we would sometimes deploy the reversers of the center, S-duct engine in the tail for the taxi.

Next, why take any risk if there's little benefit to be gained. The greatest effect of reverse power is immediately after touchdown when the aircraft speed is highest. As the speed slows, reverser effect decreases rapidly.

  (...) cut the reverse thrust after decelerating to 40 km/h.

40 km/h is only 22 knots. That's a taxi speed. I spent 10 years on 747-100/200 aircraft at two different carriers, and we never used powered reverse anywhere near taxi speed.

The 747-100/200 reverse levers are on the forward edge of the thrust levers. You can't raise them unless the thrust levers are in the idle position and the air-ground sensors show you on the ground. When you do raise them, they first come to a near vertical position that deploys the reversers but leaves engine power at idle. If you pull the reverse levers aft to get greater than idle reverse thrust, you're doing so against a spring loaded force such that if you relax the pressure, the engines will return to idle.

  What happens if that was ignored all the way to a complete stop? Would the plane start moving backwards?

Staying in reverse down to 0 km/h is simply not done. However, let's say you did it. If you had the reversers deployed but were at idle power, I doubt the aircraft would move backwards.  Reverse thrust is not as efficient as forward thrust. Depending on the engines and how heavy you are, 747-100/200s can start to move forward at idle forward thrust, but the usual procedure is to come to "breakaway" thrust to get the aircraft moving and then go back to idle.

If you came to 0 km/h in reverse with significant engine power, then, yes, you would start to move backward. But, of course, the chief pilot would hear about it, and probably fire you.

I know of one instance where a 747 was backed up using reverse thrust to clear a runway in an extreme situation in a third world country, so it can be done.


What are the effects of adding power to a 45 degree banked aircraft?

The key is that you qualified the turn as coordinated.  If the turn continues coordinated after the application of more power, then the aircraft will climb due to increased energy being converted to altitude.  Unless you decide to "lower the nose" and turn at a faster airspeed.


What happen if an aircraft is more than 10 hours overdue for its 100-hour inspection?

FAR 91.409(b) says:

  Except as provided in paragraph (c) of this section, no person may operate an aircraft carrying any person (other than a crewmember) for hire, and no person may give flight instruction for hire in an aircraft which that person provides, unless within the preceding 100 hours of time in service the aircraft has received an annual or 100-hour inspection and been approved for return to service ...

(Emphasis mine)

According to a literal reading of the regulation, it only applies to operation "for hire" and not to the owner(s) flying it for personal use. So, in theory, what you propose is legal.

However, if an FAA inspector ever reviews the log books and sees that you went over 100 hours between successive 100-hour inspections, you would need to provide evidence that every such flight was not for hire, which could cost you significant time and effort.

So, while it is technically legal, in practice it is unwise. If the plane is regularly used for hire, get it inspected every 100 hours regardless of the nature of specific flights.


Why does the canopy of the F-22 Raptor have a golden tinge?

In order to reduce the radar cross section (RCS) of the aircraft, the F22 canopies are coated with a thin layer of Indium Tin Oxide (ITO), which gives it a golden tint.

From the book F-22 Raptor by Bill Sweetman:

  The F22 Raptor canopy ... comprises two sheets of polycarbonate, sandwiched between two layers of optical glass, fusion bonded in an autoclave and drape formed over a canopy blank ... A metallic coating of indium-tin-oxide is added to the canopy to reflect the radar waves, giving it a golden tint.

They are used in stealth aircraft to reduce the RCS. From globalsecurity.org:

  A window member composed of a transparent resin or inorganic glass with a transparent conducting film such as gold or ITO (indium tin oxide) coated thereon, is used as an electromagnetic wave shield window for stealth aircraft. Applying such transparent conducting film enables, while maintaining transparency to visible radiation, both a radio wave stealth property which scatters radio waves in various directions so as not to be detected by radar, and an electromagnetic wave shield property which prevents harmful electromagnetic waves, except for visible radiation, from invasion into an aircraft.

This technique is used in other aircraft like the EA6B Prowler and the F-35.


Are pilots expected to keep an ear out for conflicting authorizations?

The short answer is yes, they are definitely expected to listen and act accordingly. This is one example of situational awareness in aviation, and pilots are expected to use all useful information sources to maintain awareness of what's going on around them.

A nice example is this one where the crew of a US Airways aircraft avoided an accident. There was heavy fog at the airport, and while the US Airways flight was waiting for takeoff clearance a United aircraft ended up on a runway instead of a taxiway. The controller couldn't see the runways because of the fog and she believed the United aircraft was on a taxiway, so she gave the US Airways flight clearance to take off even though the United pilot said several times that they were on a runway.

The US Airways pilot had heard the discussion (actually, almost a debate) between the controller and the United pilot, and he refused the takeoff clearance because he wasn't confident that the situation was under control. It's well worth watching the whole thing, but the key exchange is this:

  ATC: [...] USAir 2998, runway 5R, fly runway heading, cleared for
  takeoff

  US2998: Uh, tower, USAir 2998, 'til we figure out what's going on down
  there, we're just gonna stay clear of all runways

This level of awareness is expected of all pilots, including light aircraft pilots at uncontrolled fields. Although in that situation there's the additional complication that there may be aircraft around that don't even have radios!


Which kind of aircraft have the lowest operating cost?

150 Miles is perfectly reasonable distance in most small planes and one passenger is a fairly easy load. There are a lot of options out there but arguable the cheapest would either be the Cessna 150/Cessna 172 Or the Cherokee 140/160/180. The factors that keep the price very low,

Fixed gear: less to service and inspect during an anual and less to go wrong in terms of over all maintenance. You never have to worry about the proverbial "gear up" landing.
Some of the most produced air frames in history by companies that still exist so parts are abundant and not all that hard to come buy when compared to some of the more obscure air frames out there.
Very common engines, decent on fuel burn rates and easy to have serviced, inspected, and generally considered reliable.
Very practical useful loads for carrying one other person and luggage.
Common and for sale in most places, would be easy to find a decent air frame.
Common enough you may be able to find a partner to go in on it and help reduce costs.
Lots of mechanics out there who will happily work on these planes, and are quite knowledgeable on them as well.


Can I include my point of departure in the three landings for my commercial solo cross-country?

It depends on how you classify the flight. More importantly, it depends on how the DPE classifies the flight. Most people consider any flight with a stop longer than a fuel break as the end of the flight at the fuel stop, and the beginning of a new flight at the subsequent start up. Some sticklers would consider anytime you shut down the engine on the ground, the end of that flight.
You can log it any way you want. I doubt any DPE will count a flight with an overnight stopover between legs as one flight.
Here is an alternative. Takeoff at Airport A. Fly a closed traffic pattern to a full-stop, taxi-back landing. Fly to Airport B where you perform a full-stop, taxi-back landing. Fly to Airport C where you perform a full-stop landing. As long as the straight line distance between A and C is more than 250 Nautical Miles, your total distance is over 300 Nautical Miles, and you are either solo or performing the duties of PIC with an instructor, you should be good for the FAA Title 14 CFR Part 61.129(a)(4)(i) requirements for a commercial pilot.
Note that the regs don’t stipulate a full stop, taxi-backs. If you are flying solo, it gives you time to set up for the next leg. Although it is hard to believe that there is not another suitable airport in 300 Nautical Miles. In what area are you flying?


Why do landing gear bays in commercial aircraft not have a fire extinguishing system?

Cost/Weight/Complexity, the usual reasons why you avoid to add another systems. But let's analyse if you really need it.
Easy to prevent
From the data of this Boeing document:

at least 62% of the wheel well fires are caused by applying excessive grease
at least 11% of the wheel well fires are caused by hydraulic leaks
at least 3%  of the wheel well fires are caused by incorrect application of solvents

From the fire protection standpoint the landing gear is a quite simple device: maintenance staff should pay attention where and how much grease they put, pay attention where solvents are put, and the only flammable liquid is the hydraulic fluid. An engine is much more complex, you have many flammable fluids (fuel, hyd, oil), many pipes and extreme forces, which make the maintenance error and engine damage more probable. Then, causes can also be external (like bird strikes). This makes an engine fire event probability much more higher.
Moreover, most of all events of wheel well fires appear after landing (i.e., after braking), which is still a serious problem, but not as serious like in-air fire.
Rare
Wheel well fire are 10x less probable than engine fires and 1.5x less probable than APU (source):

There were only 2 fatal accidents related to wheel well fires: Propair Flight 420
 and the Nigeria Airways Flight 2120. In both cases pilots were unaware of the fire and they didn't take any countermeasure.
Easy to solve
Just put the landing gear down. The >= 200 kts air does the rest. If it doesn't work, at least the most flammable materials (rubber, hyd pipes) and the heat source are now outside the aircraft frame and it will take more time to reach the wheel well, so you have more time to land.
Since wheel well fires are caused by high brake temperatures, the procedure is even usually applied before the fire actually exists. For example, the HOT BRAKES procedure of Airbus requires to lower the landing gear (and turn on the brake fan, if available) as soon as the brakes become overheated, potentially preventing in this way the fire event.


What are the properties of the wing (airfoil symmetry, angle of incidence) of an aerobatic aircraft?

There are a few things to consider for a good aerobatic airfoil. The transition between attached and separated airflow has a big influence for spins or snap rolls, and a good aerobatic airfoil needs only a small change in AoA (angle of attack) to fully transition between the two. To achieve this, it helps to shape the forward part similar to an ellipse (a lemniscatic function, to be precise), and to use a nearly straight line for the last 70% of chord. The goal is to have a Stratford pressure rise on those 70% which gives the maximum possible pressure gradient without separation. Increase AoA just a little, and you have fully separated flow over those 70%.

When all works as planned, you can get the plane out of a spin by applying rudder at, say, 45° before the fuselage points in the desired direction and get out of the spin within 10° of that direction. Same goes for snap rolls, they get really snappy. It is a real pleasure to fly such planes, but you need some discipline. There are no aerodynamic warnings before you stall, and stalling comes immediately. On the other side, with the limited lift loss of such an airfoil and the powerful engines of aerobatic airplanes, stalling is no big issue.

A major reason for mounting the wing at 0° incidence is that you need little elevator correction in a roll. Rolling happens about the longitudinal axis of inertia, and if the wing is aligned with this axis, it has 0° AoA at 90° and 270° of the roll and at 180° the inverse of the AoA it had in level flight. With a symmetrical airfoil, lift is always correct, and if the aircraft flies at zero stability, you need not to move the elevator.

Mistimed elevator movement in rolls leads to immediate changes in flight path direction (happens really easily, and is easy to observe from the ground), and it is very hard to pitch the whole airplane just at the right time so it has no lift (read: side force) in knife edge flight, but the right lift in inverted flight. Just for flying inverted, many regular airfoils are just fine, but it is in the transitions where the symmetric airfoil has a clear advantage. A fast roll with a cambered airfoil will result in a corkscrew-shaped flight path because you cannot pitch quickly, let alone precisely, enough.


What are these protruding elements from SU-27's tail?

I believe that these are static discharge wicks.  You can see similarly sized/shaped wicks on a 1/32 scale models of the SU-27, as discussed here, but, more importantly, you can find them labeled with number 53 on the cutaway drawing below.  The label is written as Разрядники статического злектричества, which, according to Google Translate, is "ESD arrestor" (or static discharge wick).

These are distinct from the shape of the wicks found on most GA aircraft in the US (just a straight stub of wire, potentially with some insulation around the base), but, as discussed on Aerospaceweb, the shaping of the wick (particularly the inverted cone shape shown here) contributes to increasing the gradient in the electric field from tip to base of the wick.  This encourages accumulated charge to migrate back into the atmosphere from a controlled point and decreases interference with on-board electronics and radio systems.


Why were the windows on the Concorde about the size of a hand?

The Concorde flew above 15,000m. At this altitude a sudden reduction in cabin pressure would prove hazardous to crew and passengers with most falling unconscious within a few seconds. The low air-pressure would also render the oxygen supply system inefficient and most passengers would suffer from hypoxia.

Thus we have the reason for the smaller windows, should a breach occur then the size of the hole being small would reduce the rate if loss of air-pressure inside the cabin. This, combined with a reserve air-supply to augment the cabin-pressure as well as a rapid rate of descent manoeuvre to bring the aircraft to a safe altitude would reduce the the risk of hypoxia.
So basically the small windows were designed to reduce the rate of air escape from the cabin should a hull breach occur.


What is the FMS Bridge Visual 28R approach at SFO?

The FMS Bridge Visual Approach 28R is a version of the Quiet Bridge Visual Approach 28R which is coded with GPS coordinates and can be included in an FMS database for approved operators.  This allows the procedure to be used when the SFO
VOR is out of service, and also gives ATC additional flexibility by allowing them to clear pilots direct to any of the fixes without needing to intercept the radial on the standard arrival.

The pilot must either tell ATC that they can accept it verbally, or include FMS28R ABLE in the remarks of their flight plan so that they know that the flight is capable of flying the approach.


In 1961 study a plane flew 116,684 miles sampling the air, catching whatever was up there, and managed to capture a single termite at 19,000 feet. This is the highest ever observed.

You just never get above the "bug layer" in a smaller aircraft (Cessna 172 limit is 15,000 feet). Likely this is not a proper naming.


What advantages would a triangular shaped spy plane have over a an SR-71?

The 'triangle' wing design that you refer to is pretty common. It is called the delta wing design and is used in a number of high speed aircraft, for example, the North American XB70 Valkyrie.

In fact, the SR 71 wing planform is also a delta, if one removes the engines. One of the reasons is that the wings of the aircrafts are kept inside the Mach cone formed by the aircraft. The Mach angle is given by,

$\mu = sin^{-1} \frac{1}{M}$,

where M is the Mach number.

As the aircraft speed increases, the Mach angle decreases, which means that the aspect ratio should become smaller and smaller. At hypersonic speeds, the delta wing (or a modified one) is the best option as the wing needs to be pretty short for aerodynamics and structural reasons while able to carry the required fuel and generate lift.

The main advantage of the SR-71 Blackbird is its speed, which was about Mach 3.3. It is logical that its replacement should have better speed characteristics. SR 71 used a ramjet during its high speed dash, while its (rumored) successor is expected to use a scramjet engine.

"Turbo ram scramjet comparative diagram" by GreyTrafalgar - Own work. Licensed under CC BY-SA 3.0 via Commons.

The first one(a) is a turbojet engine, the second one(b) is ramjet, and the third one(c), a scramjet. The ramjet and scramjet engines are similar, though the combustion happens at supersonic speeds in the scramjet engine.

NASA has a hypersonic aircraft for experimental purposes called the X43,which uses a scramjet engine, though the aircraft size is pretty small compared to the A340.

Source: hapb-www.larc.nasa.gov

The closest actual aircraft have come to the shape of the 'Aurora' are the experimental aircraft like the X-37, which has short wings.

"Boeing X-37B inside payload fairing before launch" by US Air Force - http://www.af.mil/News/Photos.aspx?igphoto=2000374856 (direct link). Licensed under Public Domain via Commons.

There are a number of aircraft with triangular wings, most notably almost all European combat aircraft have delta wings.

And by the way, the Lockheed Martin SR 72 Aurora concept looks like this.

"Lockheed Martin SR-72 concept" by Source (WP:NFCC#4). Licensed under Fair use of copyrighted material in the context of Lockheed Martin SR-72" href="//en.wikipedia.org/wiki/File:Lockheed_Martin_SR-72_concept.png">Fair use via Wikipedia.


Operating with BasicMed, may pilot use a medication otherwise restricted under Part 67 Medical Regulations?

Looking at section 2307 of H.R.636, which is the congressional bill which implemented BasicMed requirements, it is clear that the physician who performs the exam, and provides care to the subject is responsible for determining what drug interactions there might be, as well as the impact of medical conditions, and whether they might be disqualifying.

Armed with this, my CFI student and I called a friend who is with FAA counsel, who does not address airmen issues, but rendered the opinion that BasicMed is separate from FAA Class 1, 2 and 3 medicals.  It is separate from Sport Pilot medicals. It is unto itself. Therefore it is their opinion that it was the legislative intent to create a separate certification process.

Therefore, the examining/issuing physician makes the determination as to any medical conditions or drugs and their impact on flying. He is the subject matter expert, and therefore if full disclosure is made, the airman has operated in good faith.

Of course, we were invited to submit an interpretation request, so that we could get an official response.

When talking with attorneys, and especially FAA attorneys (in their unofficial capacity) there many disclaimers, which include neuro, psych and cardio prohibitions.  And the importance of consultation with the issuing physician when there are medical changes.


125 cc engine, 64" propeller 3 blade, 180 kg gross weight, will it climb?

I found a google site that showed: Honda GC 125 - 124cc, 10.8 bhp, @ 9000 RPM.

Seems to me it would be much less at 3000 RPM. Can you use pulley/belt system to achieve high engine RPM (smaller pulley) and lower prop RPM (larger pulley)?

The frontal area you provide:

wings length is 29' feet and width is 4'6" (54") approximately,

sounds similar to a Cessna 150, which has a narrower cabin (just about two adult shoulder width, 38 inches), and that needed 100 HP to fly, coming from a 200 cubic inch engine.  It's overall weight was higher tho, 1600 lbs gross (in my 1971 model) vs the 250kG/552lb you provided. If the extra 16" of width is all in the cabin, that will be a lot of extra drag to overcome with that low horsepower engine.


Flight Following into Class C Airport where I'm Landing

The answer to this depends a bit on what happens in practice as in my experience flight following does not always orchestrate handoffs as well as say an IFR flight would.
In some cases FF may drop you before you get to the class C airspace and you will have to request clearance into the airspace as if you were flying without flight following.
They may hand you off to the approach controller, and you can always ask for a handoff but FF is under no obligation to provide that. Remember flight following is NOT an airspace clearance and you will need to obtain clearance as you normally would (for class C thats positive radio contact that does not include a diversion or hold instruction). They will generally hand you off with time/distance to deal with this but you should have that approach frequency queued up in the radio.
Yes you should always report your altitude and position (when appropriate) and positive receiving of the weather when calling an approach controller for entry to their airspace assume FF has given them no information. You could say:

So Cal Approach Cessna 1234R at three thousand feet, inbound for a full stop landing at KLAX with information X-Ray

You should report position if you are not handed off and/or you feel as though local procedures require it (maybe FF is provided by a non radar entity), you would add something like

5 miles south of KLAX

Once on the ground you can ask ground, or the tower before takeoff for a flight following handoff. In my experience they will orchestrate this if its a quiet day and they dont have a lot else going on, other than that they are likely to tell you to contact approach in the air and request it.
They dont really need to know anything beyond Cessna 172 which gives them the performance information they need.


Most aircraft of that era used hydraulic systems to actuate the flight control surfaces.  And yes, controlling the aircraft is critical to flight safety.


What was the motivation for revoking the licence to the pilots of Northwest flight 188?

According to this CNN article the FAA revoked their licences with a letter containing the following reasons (emphasis mine):

The letter said the pilots were "extremely reckless."
"Not only did you not comply with ... [air traffic controller] instructions, you did not even monitor the aircraft's air-ground radios," the letter said. "You were disengaged and impervious to the serious threat to your own safety, as well as the safety of people for whom you are responsible. This is a total dereliction and disregard for your duties."
[...]
The FAA said the revocations cite several violations of regulations, including failure to comply with air traffic control and clearances and operating carelessly and recklessly.

As Adam pointed out in the comments, this would violate FAR 91.13:

§ 91.13 Careless or reckless operation.
(a) Aircraft operations for the purpose of air navigation. No person may operate an aircraft in a careless or reckless manner so as to endanger the life or property of another.
(b) Aircraft operations other than for the purpose of air navigation. No person may operate an aircraft, other than for the purpose of air navigation, on any part of the surface of an airport used by aircraft for air commerce (including areas used by those aircraft for receiving or discharging persons or cargo), in a careless or reckless manner so as to endanger the life or property of another.


What dialogue would a crop duster typically have with ATC?

The actual operation of a crop duster airplane will almost invariably happen in uncontrolled airspace. In the US, controlled airspace does not start until 700, 1200, or in a very few select areas 14,500 feet above ground level; below that the airspace is Class G, uncontrolled. Crop dusters operate at a few hundred feet above ground level or lower (a quick google shows altitude as low as a few tens of feet AGL). Even if they wanted to talk to ATC at those altitudes, radio reception would be all but impossible.
When not actually working on a field crop dusters must adhere to the standard minimum altitude rules (500 feet AGL over non-congested areas, or 1000 feet above the tallest obstruction within 2000 feet over congested areas). But even if they enter Class E airspace, which is controlled, they do not have to contact ATC unless they want to receive an instrument flight rules clearance.
There are three times when a crop duster would have a dialog with ATC: when they want to come into a controlled airport to land, when they want to transition the airspace close to a controlled airport (where the controlled airspace extends to the surface), or when they want to operate over a field within the controlled airspace near an airport. For the first two situations they would communicate with the tower just like any other aircraft; for the last situation it might sound like this:

Duster: Podunk Tower, hello, Air Tractor 123AT is eight miles to the east, we'd like to operate over a field inside the Class Delta airspace two miles east of Podunk Airport.
Tower: Air Tractor 123AT, Podunk Tower, the Podunk altimeter 2992, proceed as requested and remain east of runway 18/36.
Duster: Proceed as requested, remain east of 18/36, Air Tractor 3AT.


What’s the difference between a tail number and a Manufacturer's Serial Number?

The tail number is the civil registration, and the manufacturer serial number (MSN) is a build number used by the manufacturer.

It is similar to the licence plate on your car, and the vehicle identification number applied by the builder of the car.


What is the english term for "vol en ficelle"?

Update:

I found this translator-help page, which suggests:

  [low altitude] constrained flight path

Perhaps nap-of-the-earth flying (Wiki) is what you're looking for.

According to wikipedia:

  Nap-of-the-earth (abbreviated NOE) is a type of very low-altitude
  flight course used by military aircraft to avoid enemy detection and
  attack in a high-threat environment.

It also mentions other terms such as (emphasis mine)

  Other, mostly older terms include "ground-hugging", "terrain masking", "flying under the radar" and "hedgehopping".

Image source


Are passengers more likely to see other airliners from a window seat on the right or on the left?

Your best bet is flying across the Atlantic, where the Strategic Lateral Offset Procedure (SLOP) is used.

This is where the pilot flies a offset to the route, either 1 or 2 NM, always to the right, chosen randomly (or based on surrounding traffic/TCAS), and is kept from the ATC (no radar coverage, although that is changing with satellite ADS-B).

As shown below, you have a chance to see another plane above/below from either side depending on the pilots' flip of coins.

Source; adapted

Regarding two-way airways elsewhere and with the navigation paradox, where flying accurately is ever increasing, it will be a slim chance except for a crossing traffic (not same airway).

If in a holding pattern, the standard turn is right turns, so the right side gives a better look "inside the track," unless the pattern is non-standard to the left.

Source: Mid-Atlantic Race!!! Virgin Atlantic A340 vs Norwegian 787 Dreamliner


That 65kts "climb speed" -- is that ground speed or air speed?

If it's ground speed, then you already have your answer. Since the question is about ground speed and distance travelled, then the wind doesn't factor in to it.

If it's air speed (which is far, far more likely), then you need to figure out your ground speed first. This is where the wind comes in. Now, you didn't specify which direction you're flying, but we can assume from the mention of "runway 26" that you're flying 260 degrees. That means you're flying into a direct headwind, which means in turn that your ground speed is simply your airspeed minus the wind speed. Then use that value in your distance calculation.


The LIB4 and EWR4 SIDs, and others like them with just a bunch of VORs, are designed to give ATC maximum flexibility and assume radar vectors. Basically, you take off, make a turn or two to get clear of the airport (and any low obstacles), and then ATC will vector and climb you based on conflicts with other planes at that moment, so you'll probably never get the same instructions twice. There is no real plan; it's literally made up on the spot by each controller for each plane.

The PORTT4 (RNAV) SID is completely different: you have various specific routes to follow and detailed climb plans for each. Many such arrivals and departures in an area will be carefully designed to never conflict with each other (the top and bottom altitudes listed usually indicate there's another SID/STAR crossing 1000ft above/below at that point), so ATC just watches to make sure everyone follows the plan—and gives out shortcuts when possible. Unfortunately, that SID is only valid for two of the six runways, though presumably they're the ones used most often.

Note the latter's lost comms procedure is just to follow the charted plan you're expecting to follow anyway, though without any shortcuts, whereas the former has an entirely different (and uncharted) plan that you'd probably never follow otherwise.


N43941 (USAF 53-7801) Convair C-131B.

Link to history.

It saw better days:


What would be the general steps for making a flight in a biplane?

First follow @Jim's advice for getting the plane set up and the engine running.

A biplane is most likely a taildragger, which means that it has two main wheels and a third all the way in the back. This will give the plane a nose-high ground attitude, and taxiing to the runway will involve Scarlet to wiggle the plane left and right because the forward fuselage is obstructing her forward vision. This is not made easier by the fact that tandem two-place biplanes, the most common type, are flown from the back seat in order to get the center of gravity right.

Next, she should wait until engine temperature is high enough to run the engine at full load. I would expect that in a pursuit she skips that step but will worry that oil temperature has not reached the required temperature. The next step would be the magneto check which she will also skip.

In the takeoff run she will first orient the aircraft into the wind and then gently apply throttle so the aircraft doesn't end up in a headstand (meaning the propeller pulls the nose into the ground without the wheels moving). This also requires her to pull the stick all the way aft so the empennage (horizontal tail) keeps the tail low. A headstand is shown in the second picture of the second linked answer (this one).

Airfields back then were mostly round grassy patches, so the take-off direction could be freely selected in order to take off directly into the wind. However, you might want to add some suspense when Scarlet finds her biplane at the wrong end of the field and has no time to taxi across it, but takes off with a tailwind. This will make the takeoff run longer and the climb after takeoff more shallow, so she might just barely escape collision with an obstacle there.

When the aircraft picks up speed she should reduce back pressure on the stick and move the stick to a roughly central position in order to reduce downforce on the tail so the tail can lift off the ground. Bonus points for mentioning the gyroscopic effect from the propeller as the aircraft lifts its tail which requires the brief application of rudder to keep the nose pointed into the desired direction.

Liftoff is rather unspectacular and happens when the aircraft is fast enough. However, if elevator trim is set the wrong way, the aircraft will stay on the ground for too long (too much nose-down trim) or lift off too early at a too slow speed (too much nose-up trim). Trim means that either a spring in the elevator linkage or a small auxiliary flap is set such that it pulls the elevator to a certain deflection angle. This is helpful for adjusting control forces according to the desired flight speed and center of gravity location, but if it is set the wrong way on takeoff, Scarlet might be surprised by unusual stick forces.

While the takeoff is flown at full rich mixture, once in the air Scarlet should adjust the fuel to air mixture in the engine according to flight height. You might want to add a dramatic moment where the engine runs rough or even stutters due to too lean mixture.

After that, the escape should be easy.


Do airlines weigh passengers and baggage before loading the aircraft?

While I'm not a pilot, I think it goes along these lines:

Airlines typically assume a value for passengers depending on gender and age. This distribution in the cabin will typically be quite random and a little variation does not do any damage.
Baggage however is weighed on the scales at check in. Each bag is
normally scanned as it is passed onto the plane, so that they know
where is bag is located. The values are then passed onto the pilots
who are able to work out that the numbers are ok. Sometimes there are preferences to load up bags in a certain way for fuel issues, so this is very important to make sure this is still resonable.

These values are then plugged into computers or worked out manually on a paper loadsheet to make sure they are good and within limits.

In fact the weight systems you are referring to are quite unusual I think, see this question.


Is it possible to fly VFR above the IMC floor or VFR-On-Top without a specifically filed route, both using an IFR flight plan to go through IMC?

This question probably covers some of your points but here's some more information. See the AIM 5-5-13 and ATC Orders 7-3-1 for more details.

Can I get an IFR clearance for an area and operate there VFR-on-top?

Yes. VFR-on-top by itself is only a clearance to use VFR altitudes, it isn't a clearance to deviate from your course. But ATC can clear any IFR flight to operate within an arbitrary, defined area (ATC Orders 4-4-1):

  EXAMPLE−
  1. “Cleared to fly east of Allentown VORTAC between the zero four five and the one three five radials within four zero mile radius.”
  2. “Cleared to fly east of Crystal Lake radio beacon between the two two five and the three one five courses to Crystal Lake within three
  zero mile radius.”
  3. “Cleared to fly northeast quadrant of Philipsburg VORTAC within four zero mile radius.”

Same as above, but foregoing the VFR-on-top and accomplishing it purely as IFR.

I don't know exactly what you mean here: VFR-on-top is an IFR clearance. If you're asking how to change altitude as needed under IFR without using VFR-on-top, you can request a block altitude clearance.

Can I file two flight plans?

What would the departure point be for your second flight plan? I suppose it might happen if you departed IFR, requested climb to VFR-on-top, cancelled IFR in VMC, then called back for a pop-up IFR clearance to shoot an approach. But I don't see the point: why not just work with ATC in the first place and stay in contact with them for the whole flight?

All in all, the simplest thing here is just to ask ATC for what you need. Except in very busy terminal areas, they're very good at accommodating pilot requests, whether VFR or IFR.


Is it legal to begin pilot training on a jet?

There is nothing in the US regulations and no references that I can find that prohibits a pilot from learning to fly in a jet aircraft.  There are multiple systems on a jet aircraft that are not found in small GA aircraft and the same systems are more complex.  A lot of professional pilots who fly the same jet for a career don't fully understand the different systems on their jet.

The issue isn't with the FAA though; it is with the instructor and insurance companies.

I certainly would not agree, as a CFII, to train a new student pilot in a jet.  I personally don't want to take on the liability for the payment I would receive for my services.

Most insurance companies will not ensure a student pilot to learn to fly in a jet.


What does "mission mixing" mean for long-range aircraft?

Mission mixing appears to be running computer simulations (or other probabilistic analyses) to assess aircraft engine components' reliability also under non-typical or non-designated use. All for the purpose of design or maintenance/inspection strategies, I would assume.

So, mission mixing is not something you would purposely do with actual aircraft. (Or maybe you would, but then it is not called mission mixing.)

Here are a few articles mentioning it:

https://arc.aiaa.org/doi/pdf/10.2514/1.13142
https://asmedigitalcollection.asme.org/GT/proceedings-abstract/GT2012/44731/439/247656

http://en.cnki.com.cn/Article_en/CJFDTotal-HKXB902.017.htm
https://www.astm.org/DIGITAL_LIBRARY/STP/PAGES/STP14812S.htm


When do commercial aircraft tail numbers change?

I was under the false impression that tail numbers don't change

Tail numbers (AKA registrations) are changeable by definition since each country is allocated codes with different prefixes and formats. If an operator from country X buys an aircraft from an operator in country Y, then the tail number must will most of the time be changed to a valid tail number of country X. Depending on local laws, in some rare cases a tail number of another country will be used, for tax purposes (much more common with sea vessels). This is why some Aeroflot aircraft have VP-B* registrations that belong to Bermuda.

What does not change is the manufacturer serial number (which may be analogues to a road vehicle VIN).

I think the source of the confusion is that the Wikipedia article that you linked to uses "tail number" of civil and military aircraft interchangeably, and that is wrong. Military aircraft's tail numbers do not conform to their countries' ICAO-issued civil registration format, and they may or may not be changed whenever said air force want.

  Already know that different carrier + same tail number may mean different aircraft

This assumption is wrong. Tail numbers are unique. However, they can be re-used over time.

  Under what circumstances do tail numbers of commercial aircraft typically change? That is, other than arbitrary whims (which I assume are rare), when do airlines/aircraft owners go through the number changing procedure?

As mentioned above, the most likely case is when an aircraft is being bought from an operator from another country than the previous operator.

Sometimes the new operator will change the tail number even if the aircraft was bought from an operator in the same country in order to fit the registration scheme that said operator may use (for example, N737* for 737 aircraft, N747* for 747, etc).

Other than the mentioned cases above, it's impossible to answer this question in general terms. Every operator may or may not change tail numbers of aircraft it buys. An operator may even decide to change tail numbers of aircraft it already owns just because.


Is there any way for the baggage carrier to add some fake luggage?

The exact process varies quite a bit from airport to airport and even sometimes from terminal to terminal within an airport. But assuming a relatively modern terminal at a relatively busy airport, most of the process is heavily automated to reduce both labor and error.

Bags will be taken by conveyor to a security station, where a human watches them pass through various scanners. Then they get sorted by machines onto belts going to various parts of the terminal, and then belts going to each gate. This is why bags all get a big white tag with one or more barcodes on it, connected to a database that (hopefully) knows where each barcode should be sent.

Once the bag arrives at the gate, a human will transfer it (just a few feet) from the belt either onto a baggage cart (for smaller planes) or into a Unit Load Device (for larger planes), where it then waits to be loaded onto the plane. Notably, all bags on the same cart or in the same ULD will be waiting for the same plane.

At the other end, a human transfers the bag from the cart or ULD onto to the belt, and it goes back up into the system to be scanned and sent either to a different gate or off to baggage claim.

A single baggage handler can't really change much. They could intentionally misload a bag on the wrong aircraft (heck, they do it often enough by accident), but that is only easy if the "right" aircraft were at the same gate, or at least near enough to move the bag without another handler noticing the odd behavior, and there's no guarantee they'd be assigned to that gate at the right time since baggage crews move around a terminal pretty fluidly as planes come and go. And the "mistake" would be quickly detected when the plane was unloaded at its destination, unless of course a handler there was part of the same conspiracy. Many airline employees have been caught smuggling drugs this way, and presumably many more haven't been caught, so it's completely realistic.

More practical for a true conspiracy, though, would be planting, bribing or blackmailing someone who can simply change the database that says where a particular barcode should go. There are systems that check to ensure a passenger and their luggage aren't separated, so you'd need to attach the bag to someone who you'd be certain wouldn't miss the flight, and then detach it at the other end so you didn't get caught.

Overall, it is a lot simpler to trick "the system" into unwittingly doing your nefarious work for you rather than having a grand conspiracy of humans trying to outwit said system. But it may not make as good of a story.


How to completely track a plane, not a flight?

If you want to look for the airplane that flew a certain flight (U22604/EZY42EA for your case), you could go onto flightradar24.com/data and search for that specific flight to find the list of aircraft which flew with the callsign and if you select any one of the planes, you can find out the flight history of that plane for the past few months. You could also search flightaware.com/ for flight history too.


How does an ADIRU convert ram air pressure from the Pitot tube into Airspeed?

Usually there is an intermediate module ADM (air data module) that makes the conversion from analog pressure into digital numerical value. One ADM will do this for  the ram air pressure, another ADM will do the same for  the static pressure.
Their data are sent on Arinc numerical buses to the Air Data part of the ADIRU.
Airspeed is basically the difference of the received data.
Please refer to the following diagram:

https://upload.wikimedia.org/wikipedia/commons/f/ff/Airspeed_indication_system_-_fly_by_wire.png

Inside the ADM you have:
first of all a PIEZO that will convert the mechanical pressure into electrical voltage, a piezo is somehow what you have in a balance you may use to get your weight. In the balance you have too an analog digital converter since the weight is displayed as a number.

Similarly in the ADM, the next item is an analog/digital converter that will convert the electrical voltage into a binary number that will be sent on the ARINC bus to the ADIRU

You might wonder why the ADM is apart and not inside the ADIRU, it is done like that to have the shortest possible pneumatic tube.
 I do understand I haven’t been enough clear in my previous answer that has been deleted, therefore it is important to understand the following:

The ADIRU managing Air Data and Inertial data, is located in an electronic bay, the pneumatic piping is not sent to the electronic bay, that will make a long distance, therefore no pressure conversion is done by the ADIRU, but by intermediate modules, the ADMs


What is the proper procedure for leaving class D airspace?

The AIM covers this from an operations / legal standpoint:

  3-2-5. Class D Airspace

    4. Departures from:

      (a) A primary or satellite airport with an operating control tower. Two‐way radio communications must be established and maintained with the control tower, and thereafter as instructed by ATC while operating in the Class D airspace. [emphasis mine]

While operating in Class D airspace, you must maintain two-way radio contact with the tower – monitor the frequency and be prepared to respond.

You may leave the frequency once you are either clear of the airspace, or receive instructions to that end from ATC ("N1234, frequency change approved").

Whether or not controllers are bothered by you letting them know that you've left, I can't say, but it would probably qualify as frequency congestion. If they want to get in touch with you, they'll try ("N1234, are you still with me?"), but once you're outside the Class D airspace they're generally only providing advisory information.


A helicopter can hover without the CoG being directly underneath the rotor hub, because the rotor hub can apply hinge moments:

Fully articulated hubs with a hinge offset and fixed hubs apply direct mechanical moments to the fuselage, which line them up with the rotor angle.

The rotating blades are subject to centrifugal forces, which pull the rotor hub in the plane of the rotor deflection. As soon as the rotor plane changes as a result of cyclic stick input, the resulting rotor hinge moment will change fuselage angle accordingly, providing the desired feedback cue.
Any helicopter, regardless of the type of rotor hub, has an aerodynamic coupling between fuselage attitude and rotor attitude. A teetering rotor such as on Bell 212 and R-22 does not produce above mechanical rotor hinge moment. In flight, a helicopter is suspended from its rotor, with the Centre of Gravity underneath the centre of lift, unless the rotor can apply a hinge moment to the fuselage. With a rearward CoG and no hinge offset, the following could happen:

The helicopter has taken off vertically, nose tipped up first, and cyclic forward was input. If the rotor had a hinge offset the fuselage would tilt forward, but with a teetering hinge like in the question there is no centrifugal force acting on the hub, and fuselage position now depends only on CoG location. The upward nose angle has consumed some of the useful forward tilt of the cyclic stick. Visibility is impeded. Fuselage tilt provides no direct feedback of the cyclic position.

Fortunately there is an aerodynamic rotor hinge moment, created by the aerodynamics of flapping. The picture is from Helicopter Performance, Stability and Control by Raymond Prouty. It shows that at first, the rotor acts as a gyroscope and stays in its plane. But the blade feathering is referenced to the shaft, and angle of attack of the right hand blade is increased, left hand blade decreased. The rotor will then flap until it is perpendicular to the shaft. With teetering rotors, there is an indirect aerodynamic coupling between fuselage and rotor shaft: the fuselage attitude still follows the rotor attitude but at a slower rate.

The CoG cannot be placed anywhere, it must remain in the area where the moment caused by gravity pulling on the CoG is lower than the maximum hinge moment. But with all helicopters, there is a region of useful CoG.


Which frequencies does VDL Mode 2 use when used via the ATN (rather than ACARS)?

Some additional information (and corrections)...

The slide is not totally correct (sorry for Airbus) as the same VDL-2 ground stations are used to transport both FANS-1/A CPDLC (A623) and ATN CPDLC over the AVLC protocol (VDL-M2). The two networks are interconnected... But depending on the media access scheme (Plain Old ACARS (POA - refered as VDL-A on the slide) or AOA (VDL2)) the modulation and the frequencies used differs.
In Europe, VDL-M2 is used between 136.7 and 137 (ICAO).

As by 2020 ATN-B1 CPDLC above FL285 will be mandatory, datalink will only be performed on this band using VDL-M2 and no POA.

However, it is true to say that there are two CPDLC. The  ICAO-standaridzed  one (or compliant to the ICAO-ATN  -- as used in Europe) and the non-ICAO compliant initially developed by Boing (as used in the US and oceanic -- also known as FANS-1/A). The two CPDLCs have very similar features and capabilities contrary to what have been told previously. The difference between the two is the end-to-end performance requirements and insurance of delivery (PM-CPDLC - PM=Protected Mode) available on ANT CPDLC and not for FANS-1/A CPDLC (there is no way to ensure a message have been successfully transmitted with FANS-1/A).

FANS-1/A CPDLC is transmitted via the ACARS network using Plain Old ACARS (POA - refered as VDL-A on the slide) or AOA (VDL2), while ATN CPDLC is only transmitted via VDL2 (SATCOM is being validated at the time of writing).

Link2000+ is the name of the development project of VDL2 (US and Europe).

ATN-B1 refers to the implementation of specific CPDLC services and/or messages standardized by ICAO. At the time of writing ATN-B1 is implemented in Europe and tests are being conducted for ATN-B2. ATN-B2 adds some new CPDLC messages but also the ADS-C which is the precursor for I-4D trajectory management.
ATN-Bx refers to the ground implementation, and FANS-xx refers to the airborne implementation (FANS-2/B refers to the ATN-B1 airborne implementation, FANS-3/C to the ATN-B2 -- Don't try to find logic here ;-) )

Have a look in the book "Aeronautical Air-Ground Data Link Communications" for further information between the two (with some historical background).


How is the same takeoff performance achieved by a specific engine type on aircraft of different sizes?

There are several model variations of that type engine.

Refer to the Type Certificate Data Sheet (TCDS) for the Boeing 737.  You will find listed the specific model number numbers and thrust for each approved engine.

For example, here are the CFM engine models approved for specific model/serial numbers of the 737.  You will have to get the latest revision of the TCDS for new models, like the 737 MAX.  This excerpt from the 737 TCDS shows the model variety of one type engine (the CFM56-7B) as approved for certain 737s:


How is TACAN different from the VHF Omnidirectional Range (VOR) system?

A very short question, but the answer calls for describing several techniques which are by themselves difficult to summarize without taking liberties with reality, so the post is rather long and should be read by sections of interest rather than totally at once. And for those not interested in the design techniques, fortunately there is a...
Short answer
Design principle:

A TACAN uses UHF to increase bearing precision. It consists on a single integrated system performing bearing and distance determination at once. In this system, the ground station is a transponder and the interrogator is on-board the aircraft (contrary to the SSR transponder). Frequency is like graduations on a scale, when frequency increases the graduations on the scale are more dense, and readings are more accurate.

A VOR works on VHF for bearing determination. No aircraft action is required to trigger the ground station signal which is permanent. To determine distance, another independent system, the DME, is used. The DME has been borrowed to military and is actually a TACAN without its bearing components (so it is a transponder interrogated by the aircraft).

When selecting a VOR frequency in a civilian aircraft, the avionics actually sets the VOR receiver on this frequency, and the standalone DME interrogator at some "paired" UHF frequency obtained from the ICAO standard pairing table (page 6). VOR and DME share nothing on board beyond the frequency pairing table.

Station antennas:

The original TACAN antenna is made of two small rotating drums with parasitic antenna elements (see details below). A TACAN can be installed on ships or mobile stations. The TACAN antenna is externally similar to a conventional VOR. A TACAN in Alaska during an exercise:

(Source: Wikipedia)

The cylinder contains the rotating antenna system. In more modern TACAN, the mechanical rotation has been replaced by electronically scanned arrays, reducing the size:

Transportable TACAN, source

Doppler VOR (DVOR) are more common than conventional VOR (CVOR), because they can be located on airfields (CVOR: See below for details). The DVOR antenna is a large circular array with a central reference antenna and a large counterpoise under the array.  VOR are sometimes colocated with a DME station, in that case the DME vertical antenna is above and coaxial to the VOR system.

Lambourne VOR/DME, DME antenna on top of the central VOR reference antenna. (source: Wikipedia)

Because the DME part is common to VOR/DME and TACAN, it is technically possible to associate a VOR to a TACAN to obtain a VORTAC station. Military use the TACAN, civilian use the VOR and the DME information of the TACAN:

A full TACAN in place of the previous DME antenna. Source

In addition VOR (CVOR/DVOR) uses Alford loop antennas which are horizontally polarized and radiate low on the horizon. They are sensitive to reflection on obstacles. An electrical counterpoise is required to hide the ground and raise the radiation angle. This artificial ground plane can be very large:

PFN Vortac (decommissioned), source

Signals:

A VOR transmits bearing information continuously.

A TACAN only sends reply pulse pairs when interrogated (see the explanation below). These pairs encode both the bearing and DME information.

A TACAN is usually more powerful than a VOR and has a larger range of use.

I'll focus on explaining bearing determination systems, and explain the DME as an integral component of the TACAN. In addition there are two types of VOR, conventional and Doppler, which work very differently even if they deliver compatible signals to the (unsuspecting) common receiver.

Bearing determination principle
The common principle of bearing determination is to send two signals from the ground station:

A reference signal telling any receiver around the current orientation of the active signal.

A variable signal allowing a particular receiver to determine when the active signal is "pointing" to the receiver (pointing is not the accurate word as the DVOR signals are omnidirectional, see more in this answer).

The receiver determines its relative bearing by comparing these two signals. Both signals are sine functions, the orientation value is represented by the current phase of this function. Both VOR and TACAN use this basic principle, albeit they realize it differently.
The signal phase has the major role in this story, so let's be sure we agree the meaning:

Any periodical (repetitive) signal can be seen as the result of a vector turning at some rate $\small \omega$. The sine function for angle $\small x$ is $\small y = sin(x)$. Applied to a sinusoidal wave of frequency $\small f$ and peak amplitude $\small A$, this becomes $\small y=A.sin(\omega t+\varphi)$ where $\small \omega = 2 \pi f$. The angle $\small \omega t+\varphi$, has been split between the phase $\small \omega t$ and the phase at origin $\small \varphi$. $\small \varphi$ is null if we start a cycle at time 0, this is usually the case. More simply, the quantity $\small \omega t$ represents how much the vector has turned at time $t$. It is an angle, reset after a full turn, therefore it indicates in the end which portion of a full cycle has already been spent (which phase we are in the cycle). Visually:

Phase angle of a sine wave
From that, it is clear that comparing phases of two signals with the same frequency (simple to do with electronics) is equivalent to comparing how much time one lags behind the other (time is actually difficult to measure).
VOR types
Conventional VOR (CVOR) and Doppler VOR (DVOR) stations are perceived identically by the receiver, though they transmit very different signals. The DVOR use tricks to mimic a CVOR and deceive the CVOR receiver. CVOR have nearly disappeared from sight because, due to their sensitivity to reflections, they cannot be located on airfields or close to roads. However en-route/high altitude CVOR can be found at isolated places, the reason is they are more compact and have a smaller cone of silence than DVOR and reflections can be minimized, e.g. when the VOR is located at the top of a hill.
Understanding the DVOR tricks without knowing how a CVOR works is difficult, and doesn't give clues on how the bearing is really determined. So I'm afraid we need to understand the CVOR before the DVOR.
Conventional VOR: CVOR
Early CVOR antenna used to be an array of four Alford loops at the corners of an imaginary square, known by their conventional names: NW, NE, SW and SE. NW+SE loops form the first pair, NE+SW loops form the second pair.

CVOR with four Alford loops
Alford loops are horizontally polarized and very sensitive to reflections on surrounding obstacles (multipath).
Recent generations of CVOR use a slotted antenna, which is a fixed cylinder with vertical slots (generally four slots):

CVOR with slotted antenna and the DME antenna on top. Source: AviaTecho.
A counterpoise is placed under the array to hide the VOR shelter and the ground and raise the radiation direction, it has the dual effect of minimizing undesirable reflection on the shelter and the ground and reducing the cone of silence above the VOR.
CVOR creates and uses reference and variable signals this way:

A low frequency generator creates three 30 Hz signals, identical except their phases. Two audio signals are derived from a reference signal: The sin signal has a phase at origin of -90° and the cos signal has a phase at origin of +90° (the point is sin and cos signals are in phase opposition).

The phase of the reference conceptually represents a direction and is often called the goniometer. As this signal frequency is 30 Hz, the imaginary direction it represents sweeps 360° 30 times per second (1,800 rpm, this is pure abstraction, there is no rotating parts in a CVOR).

A low frequency generator creates a 9960 Hz signal which is FM modulated by the reference. This signal is known as the reference subcarrier.

Conventional VOR block diagram

A HF generator creates a carrier of frequency f (f being the VOR frequency), this carrier is split in three parts:

one part is AM modulated by the reference subcarrier.
another is AM modulated by sin.
the last part is AM modulated by cos.

The HF signal with the reference subcarrier is sent to all antennas. This way the reference can be received identically regardless of the position of the receiver around the CVOR.

The two other HF signals have first their carrier removed, so that only the sidebands subsist. This is to prevent carriers to interfere in space, interferences must occur only between sidebands.

Then one signal is sent to the NW+SE pair of antennas, the other signal is sent to the other pair (remember the two pairs are perpendicular).

The space modulation magic does the rest. The sin and cos sidebands are added as field vector values, sometimes the individual amplitudes are added, sometimes they are subtracted, in variable proportion. This results in an unbalanced cardioid pattern (more precisely a Limaçon de Pascal) which rotates around the VOR antennas at 1,800 rpm, the direction being linked to the phase of the reference (or sin or cos, as they are all linked by fixed values).

The signal resulting from space modulation appears like being a carrier AM modulated according to the direction of the virtual "rotating antenna". The AM modulation is also a 30 Hz signal, and is known as the variable signal.

The resulting signal also contains the unmodified (and constant amplitude) carrier with its reference subcarrier.

CVOR spectrum

To determine the bearing (the radial) of the receiver relative to the CVOR, one only needs to compare the phase of the variable signal with the phase of the reference signal. Both are contained in the resulting signal. The phase of the reference signal and the phase of the variable signal are equal when the reference "points" to north (per principle at this time both phases have a value of 135°, the sum of 45° and 90°, but the actual value has no influence, only the phase difference is meaningful):

VOR: Determination of the bearing by comparing phases

Now we know the principle of the CVOR, it more easy to understand the principle of the DVOR. The DVOR was created to make up for some weaknesses in the CVOR: The CVOR is not terribly accurate unless the installation site is very carefully selected (no obstacle). That means isolated points, not airfields. That's not the preferred option for maintenance and this often precludes having the CVOR aligned with the runway for a VOR approach.

From CVOR to Doppler VOR, ensuring retro-compatibility
The lack of precision of the VOR is rooted in two design choices:

The antennas are close to each other, any default in their placement has great consequences in the accuracy.

The variable signal is AM modulated, AM modulation is deadly subject to errors created by electromagnetic noise and multipath.

In the Doppler VOR (once again... there are two types of DVOR, the single sideband and the double sideband, I'll describe the DSB here):

The two active antennas are at a large distance from each other (diametrically opposed).

The variable signal is FM modulated.

In order to be compatible with the CVOR receiver, other changes had to be made:

As the receiver still compares two signals, one being AM, the other FM, the reference signal must be AM modulated.

Because the result of the phase comparison is now inverted (variable minus reference becomes reference minus variable), the direction of rotation of the pattern must also be inverted (anti-clockwise instead of clockwise).

Because the pair of antennas used for the variable signal creates deliberately a Doppler effect, the reference must be sent on a specific central antenna preserved from the Doppler effect.

Doppler VOR: DVOR
The principle of a Doppler VOR is to create the frequency modulation by Doppler effect rather than by electronic modulation. The Doppler effect occurs with a moving wave source: In spite the source has a constant frequency, when it comes closer to the receiver the apparent frequency is higher than the actual frequency. How much higher depends only on the closure rate.

Doppler effect on train noise: Sound is higher-pitched at the front than at the rear
In the DVOR, pairs of opposed antennas (still Alford loops) are constantly switched on/off, scanning the full array anti-clockwise, the full scan being done 30 times per second. Actually there are two groups of antennas rather than two antennas involved to allow for blending (smooth transition from one pair to the next), but let's simplify for a second. From a receiver standpoint, the signal seems to come from a moving source, and therefore a Doppler shift will occur in a proportion which depends on the apparent direction of the move.

DVOR Doppler effect
To allow for compatibility with the CVOR receiver, this shift must be at most 480 Hz, 480 Hz being the FM swing of the subcarrier in the CVOR. A simple calculation shows the array diameter must be about 14 m (46 feet).
To generate the FM modulated signal, the unmodulated 9960 Hz subcarrier is sent on the "rotating" pair of antennas. The Doppler shift is maximum when the receiver direction is tangential to the pair trajectory and minimal when the pair is perpendicular to the direction of the receiver. This shift is exactly representative of the aircraft bearing and is the variable signal modulation we need.
From a radio signal perspective, only the sideband frequencies are used to transmit the 9960 Hz subcarrier (VOR frequency f +/- 9960 Hz). The carrier is itself sent on the central antenna, AM modulated by the reference signal. This way the carrier is not subject to the Doppler shift.
Bottom line... Like in the CVOR, the receiver sees the composite signal: A carrier AM modulated with a 30 Hz (which is the reference instead of the variable signal), with a subcarrier FM "modulated" as the result of the Doppler effect, at 30 Hz (the frequency of the scan, it now represents the variable signal instead of the reference) and with a swing not far from the expected 480 Hz.
Blending: If a pair of antennas were used one at a time, the number of measurable bearings would be equal to the number of antennas in the array (about 50). To create a more continuous scan (and therefore a larger number of measurable bearings), the antennas which precede and follow the main antenna are also fed by the subcarrier signal, but with a smaller power. This "blends" the transition from a scan position to the next one.
See also What causes the phase to change in a VOR? for a better explanation of the DVOR.
TACAN bearing
A TACAN is based on a stationary antenna plus a rotating parasitic system. The base antenna is vertical and common to the distance and bearing measurement instruments.
Parasitic elements in the aerial field refer to passive antenna elements added to the actual active radiator. A reflector decreases the gain on its side, a director increases the gain on its side (more). The well-known Yagi directional antenna (here in an horizontal polarization) has the two types of parasitic elements:

(Source, modified)
These elements are used in the TACAN, but they are rotating around the active element:

(Source, modified)

The central element, which is the one also used for the DME portion, transmits a constant amplitude signal.

A rotating drum with a reflector electrically adjusts the radiation pattern, adding a signal dip (low gain) that rotates at 900 RPM, which is equivalent to a 15 Hz amplitude modulation. The radiation pattern in the horizontal plan takes the shape of a cardioid:

(Source: Advances in Electronics and Electron Physics, Volume 68, modified)

Another drum with a set of 9 directors, mechanically linked to the first one, creates a 135 Hz (9x15) additional amplitude ripple over the 15 Hz modulation:

(Source: Advances in Electronics and Electron Physics, Volume 68, modified)

Now we need to start again the reasoning taking into account that the TACAN signal isn't transmitted permanently, but only keyed (switched on/off) by bursts of information. Burst are of two kinds:

Reference bursts
DME responses.

Reference bursts are generated according to the orientation of the modulation pattern:

When the 15 Hz peak faces North a main reference burst is sent. The burst consists of 24 pulses

with an asymmetric duty cycle.

When any of the 135 Hz peaks faces East, an auxiliary reference burst is sent. The burst consists of 24 pulses with a symmetric duty cycle.

(Source: Advances in Electronics and Electron Physics, Volume 68. Modified)
The duration of these bursts is only a portion of the 15 Hz cycle, meaning that if there is few aircraft DME interrogations, most of the time the TACAN signal is not keyed, therefore not transmitted. This lack of transmission would create a difficulty for the aircraft receiver:

To adjust its receiver gain (AGC) to counter fading.
To identify the 15 Hz and 135 Hz modulations.

To maintain the capability of reception, the TACAN signal is instead keyed at a constant rate of 2,700 pairs of pulses per second, adding squitter pulses if necessary to fill the blanks. The more the DME interrogations are received by the TACAN, the more DME reply bursts are sent, the less squitter pulses are necessary (more in MIL-STD-291).

The 135 Hz signal has been removed for simplification (Source)
The 135 Hz modulation is used for the bearing determination. By comparing the time between an auxiliary burst and the subsequent reception of one of the 9 signal peaks, it is possible to determine the aircraft bearing relative to the ground station. The main burst (15 Hz) is used to disambiguate which of the 9 lobes was used, and therefore which of the 40° (360/9) sector is actually relevant for the bearing.
In theory the use of the top end of the UHF band and the 135 Hz ripple increase the bearing accuracy by one order of magnitude compared to the VOR. In practical this is less, but still better than the VOR.
The DME principle is to measure the time a radio signal takes for a roundtrip to the ground station. As radio waves travel at light speed, knowing the time is knowing the distance. "The aircraft interrogates the ground transponder with a series of pulse-pairs (interrogations) and, after a precise time delay (typically 50 microseconds), the ground station replies with an identical sequence of pulse-pairs." (Wikipedia).


Is seating distribution planned in airliners or is it left to casuality?

People tend to travel by themselves or in small groups. They sit all over the airplane, either selecting their own seats or having them assigned by the airline's ticketing system. When you go to select your seats, the system shows you what seats are available, but it does not show you other passenger's ethnicities. Airlines also don't necessarily know passengers' ethnicities when assigning seats in advance, except to the extent that they could conceivably guess based on names (they may know what country's passport someone is traveling on, which is not the same as their ethnicity, but even so, they may not know this information until well after a seat assignment is in place).

So lots of people check-in and have their seats assigned basically randomly. The expected result is that small groups of people of different ethnicities would be mixed throughout the plane fairly randomly. I'm not understanding why you think this is something an airline would deliberately need to do, as it would already happen naturally.

Using ethnicity for seating purposes could also violate anti-discrimination laws in many countries, if this was something an airline even wanted to do.

It is sometimes the case that a large group of passengers largely of the same ethnicity will book a block of seats together as part of a group booking, such as a Japanese school trip or German musicians. Such groups may, if space permits, be seated together, and if the group is relatively ethnically homogeneous, you may find a number of travelers of one ethnicity seated together for this reason.


Could an inflatable wing be installed on a Silent glider aircraft?

Here are some of my thoughts. I'm not fully convinced about the tradeoffs though, which would require a little more work to figure out if it was beneficial:

The wing appears a lot thicker in the article than in the silent glider, adding more drag than the solid wing which it currently uses. To get it as thin would be challenge, since the article suggests that the benefit of adding pressure is marginal for the same wing, so you could only make it thicker. In an convential design, the fabric can be a lot thinner than here were it's got to hold a lot pressure. I'm sure you have to add metal wires to maintain the shape under load, adding a weight penalty.
Using a pure air-based system, I'm also somewhat unconvinced about the 'responsiveness' at the controls, since You'd only be transferring the loads at a single point into the (flexible) structure, rather than across an area as in the article example. An analogy of this is to think of trying to apple a torque force to the center of a pool noodle in water, and to observe the ends relative to the center. You might end up having to make a rather extensive wing root structure to make this work.
The benefit would be portability, but since the silent glider has an engine, this would probably not be of a huge concern, since you could get it where you wanted it.

My verdict: It could probably be done, but I'm doubtful about the performance benefits. Then again, I'm only a first year aerospace engineering student, so you're welcome to come with thoughts and any criticism :)


How can I read airport maps when choosing a seat as a passenger?

It seems you already know to look up the layout of the airport, and how to check a map for which direction from the airport you want to look. The piece of the puzzle you're missing is the wind direction.

Aircraft both take off, and land into wind. So it does not matter that you are "coming from the North", if the wind is blowing from the North an aircraft will go all the way round and land on the Northerly runway. So if you were to check the weather and there is a definite Northerly tendency you would want to sit on the Right side of the aircraft.

This is nice and easy when there is a wind, and it is forecast accurately, and you can select your seat close enough to departure to take advantage of this info. Unfortunately there are many things that can throw a curve ball here

Changing wind patterns
Lack of wind / operational reasons to
Multiple runways

About the best you can do is be aware of the prevailing wind, and hedge your bets on which runway will be in use. You'll win some (most?) and lose some. But you'll certainly get a good view some of the time.


Can flight crew book tickets for themselves, on the same flight?

Since the pilot won't check-in their flight bag, the booking will be cancelled (no-show).
They won't board with the passengers, so they won't be counted, same end result. Answer is no.
Many airlines now prohibit active duty (including relief) flight-crew from mingling with the passengers. Long gone are the days of the pilot walking up and down the plane.
That would be the most expensive shower in the history of showers. A first-class Emirates long haul flight is easily $24,000 (SFO-DXB).
Crew rest areas are beds for a reason, a shower goes against the idea of sleeping (may not be a universal thing though). But I wouldn't want to see my flight-crew in a robe going to bed after a nice warm shower. Unless the robe comes with epaulets.


Is it true the F-16 has never lost a dogfight?

migflug.com has a page for combat statistics for all the aircraft currently in use, from which:

The F-16 has 76 air kills, 1 air-to-air loss, and 5 losses to ground fire.

The one air-to-air loss (actually two F-16s colliding) was during the Aegean dispute:

  One of the routine interception maneuvers led to a fatal accident on 23 May 2006. Two Turkish F-16s and one reconnaissance F-4 were flying in the international airspace over the southern Aegean at 27,000 feet (8,200 m) without having submitted flight plans to the Greek FIR authorities. They were intercepted by two Greek F-16s off the coast of the Greek island Karpathos. During the ensuing mock dog fight, a Turkish F-16 and a Greek F-16 collided midair and subsequently crashed. The pilot of the Turkish plane survived the crash, but the Greek pilot died.

You may consider it zero since it was a "mock" dogfight.


Why do piston engines have a lower fuel consumption with higher temperatures?

I don't have a reference, but the physics behind is not that complicated.

The key is that you have constant RPM, constant pressure altitude and constant manifold pressure.

A motor sucks in lots of air, but since the throttle restricts the air flow in the intake, the air pressure between throttle and motor is low. This is the manifold pressure1. At idle, i.e. almost closed throttle, the pressure is very low, while at full throttle, it ideally equals ambient pressure. And in turbocharged motors, it is even higher than ambient pressure.

Finally, manifold pressure together with RPM and displacement of the motor is a measure of how much air volume is aspirated by the motor per time interval.

Since you keep everything constant, this volume also is constant. But warmer air is less dense and contains less oxygen molecules per volume.
Less oxygen molecules means less fuel can be burned. This is why fuel consumption is lower.
But it also means less power. To compensate, the throttle could be opened a little more to let in a little more air volume. This would also increase the manifold pressure.
But if the throttle is already fully opened to get max. power, you can't open it further. So, max. power is lower at higher temperature.

1) NOTE: For simplicity, I'm speaking about absolute pressure here. The gauge in the cockpit displays the under-pressure with respect to ambient pressure, so a high displayed value means a low absolute pressure. And since ambient pressure changes with altitude, manifold pressure does, too, even if the displayed value is constant. The benefit of this is that the displayed value is a good measure of the power with respect to the max. power achievable at that altitude.


How to do a Rapid Descent in a jet with inoperative spoilers?

The answer is actually quite simple.

FOLLOW THE MANUFACTURES PROCEDURES.

In some aircraft (I don't have a 737 flight manual handy) there is an altitude limitation if the spoilers are inop for just this scenario.  When the aircraft was certified, they needed to demonstrate an emergency descent (in the allowable time) without them, and that might not be possible from the certified ceiling. If that's the case in the 737, then descend to the max altitude with spoilers inop (assuming that you started above it).

If there is no altitude limitation and no special spoiler-inoperative emergency descent procedure (I have never seen one of those, but there's nothing to say that a manufacturer couldn't have one) then you simply fly the regular procedure without spoilers.  The manufacturer had to demonstrate this during certification and it must have been acceptable at the time.

As rbp says, most of the time you fly Mmo/Vmo at idle power after you don the oxygen mask.  IF the flight manual/checklist says that you can put the gear down (some do) then you may, but I wouldn't otherwise.  I certainly wouldn't slow to gear speed (unless the manufacturer says to....  Unlikely in a jet like this) because you are decreasing the drag by slowing, and taking time at altitude to do so.


Should I connect the AR6203 COM radio to the GMA324 audio panel using symmetric or asymmetric wiring?

Since you're talking about a DC power system, chassis ground and power ground should be the same. So the power ground is commonly used for grounding shields. The question is: should you ground one end of the shields or both?

The purpose of the shields on the audio connections is to prevent induced audio frequency noise. To do that, the shields must have at least one ground point. RF engineers I've worked with will explain that the best solution is to have the shields grounded at both ends if the units at both ends are properly grounded and bonded. That's a big if, especially in general aviation avionics where slide-in mounting trays are used.

While the connections may be good when you install them, over time the connections can degrade and resistances increase. When that happens the "grounds" at the connected units are no longer at equal potential which can induce current flow through the shields. This 'ground loop' can induce a lot of noise into the lines.

Most installers I've worked with recommend terminating the shields only at one end thus eliminating any possibility of a ground loop. The key to this method is making sure any 'gap' necessary in the shield at the open end connector is as small as possible while still ensuring it doesn't make a connection. The small gaps aren't a big concern here as you're dealing with audio frequencies.


Why does Ryanair always fill its flight plans with the same remark?

It's a contact number for their "HQ". Putting it in the remarks ensures they are easy to get on the phone if necessary for any issue/emergency.

Regarding the redundancy of putting "SCHEDULED" in the remarks - I assume it's for the same reason - ease of locating information.


How does an aircraft form wake turbulence?

Origin of the vortices

Wake turbulence is easy to understand once you know how a wing creates lift: By deflecting the air flowing across it downwards. In this answer, I had used the simplification of just accelerating downwards all the air flowing through a circle with a diameter equal to the wingspan, and leaving all other air unaffected.

This helps to understand the principle of lift creation, but is too simple, of course, because the downward movement of air will create a void above it, and the air below has to make place for that downward moving streamtube. Also, the pressure field around the wing will affect the air in the vicinity of the streamtube as well, and in consequence air from below will be pushed sideways already by the wing, and the air above will start to flow towards the low pressure area over the wing. This sideways movement will become more pronounced aft of the wing, such that air will continuously be pressed outwards below the wing's wake, move up left and right of it and inwards above the wake. The inertia of the downwash keeps it moving downwards for several minutes, continuously displacing the air below it and sucking more air into the space above, and that will result in two vortices swirling behind the wing. This is the rolling up of the wake (see the sketch below, taken from this source).

The vortices are just a consequence of the downward movement of the wake, and this in turn is a consequence of lift creation. Please note that the cores of the vortices are closer together than the wingspan! This by itself should make clear that they are not caused by air flowing around wingtips, a hard to extinguish misconception. The table below gives calculations of this vortex spacing.

The table is also from the Carten paper of 1971; note the inclusion of Boeing's 2707 project!

Strength of the vortices

If we again come back to the simplified streamtube approximation, lift is proportional to the mass of air flowing through it per unit of time times the deflection angle. If lift is equal to the aircraft's mass (as it should be), heavy aircraft need to either accelerate more air (wider span) or accelerate air more (higher deflection angle) than light aircraft at the same speed. A higher deflection angle will produce more powerful vortices. For that reason, a heavy aircraft at low speed and with a small wingspan will produce the strongest vortices.

Since more air flows through the streamtube at higher flight speed, flying faster will require less deflection, making the wake vortices weaker. If the aircraft climbs, air becomes less dense with altitude, and less mass flow over the wing is available, so the vortices grow stronger if the flight speed does not change. Normally, aircraft accelerate when climbing, and the vortex strength will stay the same if the aircraft flies at constant dynamic pressure.

Vortices can be avoided in three ways:

Infinite wing span (meaning infinite mass flow, so no deflection is necessary for any lift)
Infinite speed (again, gives infinite mass flow)
No weight of the aircraft. Flying a zero-g parabola does indeed produce almost no wake turbulence.

End of the vortices

Inertia will keep the wake moving downwards and the vortices spinning, but friction will let those air movements die down within a few minutes. If the aircraft flies high, the wake is dissipated long before it hits the ground. The wake of low flying aircraft, however, does hit the ground and is deflected. The vortex tube now acts like a wheel and starts moving outward, and if there is a sufficient crosswind, the windward vortex can be arrested as in the right sketch below (also from the Carten report).

Photographic evidence

There are far too many pretty pictures around of wake vortices to not include some, so I will add a few here:

You can see that the outer contrails of this Boeing 747's engines wrap around the contrails of the inner engines. This shows how the air is pushed down in the wake of the wing and that the centers of the vortices are slightly inboard of the outer engines.

The condensation traces originating at the winglet tips of this A340 move in- and upward, again showing that the vortex does not originate from the tips but forms behind the wing and with a distance between the two vortex cores of substantially less than the wingspan.

These two pictures show how the downwash of the wake is cutting a furrow in the clouds.

KLM MD-11 on a moist day, flaps set for landing (source © Erwin van Dijck). One, it shows how insignificant the tip vortex is compared to vorticity shed at the flap tips, and Two it shows how the tip vortex moves inward and starts to be sucked into the wake vortex. Note also the tip vortices from the tail!


Are there safety countermeasures for test flights that simulate crashed flights?

The test was flown on a DC-8-72. This model aircraft is certified to have its inboard thrust reversers deployed during flight, which means that the test was either within standard operational guidelines or not too far outside them (it's possible it's not supposed to have reversers deployed at Mach 0.8, but it's allowed to have them deployed at speeds over 190 knots per @UnrecognizedFallingObject's comment, thrust reversers are allowed up to Mmo). In addition, both inboard thrust reversers were deployed; the TV show is wrong when they claim that there were 3 normal engines and one reversed one. As the test found, there was some buffeting, but there wasn't the need for too much lateral control input, because of the symmetry (there was a bit of asymmetry when deploying reverse thrust, but not once both were deployed). Also, crucially, the flight crew was prepared for this, and they had the outboard engines fully spooled up (so while there was high sink rate at high speed, they had the power to come out of the dive safely). The test protocol had them maintaining airspeed, idling the reverse thrust engines before the end of the reverse thrust run, and then having engines at full thrust already to pull up.

In short, the reason it wasn't a suicide flight was that the flight crew was prepared, the plane could take some degree of reverse thrust in flight, the reverse thrust was symmetric, the outboard engines were both spooled up and pitch was adjusted to maintain airspeed, and in general it was a controlled test environment. The TV show implies it was to see if it was possible to recover. That was not the purpose of the test; they set up the test so they knew they could recover, and the purpose was to see the effect on airflow over the wing in as controlled an environment as possible.

Source: NASA report on the test flight


What material is used to make luminescent placard on civil aircraft?

I don't know what exactly AD400 TV25/3881/83 is, but if you are talking about a sign like this:

It appears to be plastic and Larchfield sells them. This material AD400 TV25/3881/83 could very well be a type of plastic, but I don't know about it.

In my opinion, you can contact companies which make or sell them (Larchfield or this or this) to get more reliable information.


In what circumstances do passengers or flight attendants have to take their shoes off?

Passengers are usually asked to remove their high-heeled shoes during an emergency evacuation as they may damage the slide. In other cases, it is better to leave the shoes on during emergency as once you are outside, you're worse off without them. The usual policy is to remove only the high-heeled shoes. For example, FAA says:

  FAA Policy. The FAA believes that the proper procedure regarding shoes during an aircraft evacuation is to leave them on. In the case of a forewarned evacuation it is desirable to remove high-heeled shoes and stow them in an approved stowage area such as an overhead bin. They should not be placed in the seat pocket.

This was the result of cases where the passengers sustained injuries while evacuating as they wore no shoes. For example, during the crash of Southern Airways Flight 242, the NTSB noted:

  The feet of a number of the survivors were cut and some were also burned because they had no shoes for protection. In accordance with standard evacuation procedures, the flight attendants had briefed the passengers to remove their shoes to prevent damage to evacuation slides.

  Had pillows and blankets been distributed and had shoes been worn, some of the passengers' injuries probably would have been less severe and more passengers probably would have been able to escape from the wreckage.

As for removing the shoes during flight, some regulatory authorities are against it, like the Australian Civil Aviation Safety Authority:

  The most common injuries to feet during accidents or emergencies can be prevented by wearing suitable footwear. ... Avoid sandals and high heeled dress shoes. Keep your footwear on during the flight.... High heeled dress shoes will have to be removed before using the escape slide.

As are some airlines, like the American Airlines:

  American may refuse to transport you, or may remove you from your flight at any point, for one or several reasons, including but not limited to:

  ...

  Are clothed in a manner that would cause discomfort or offense to other passengers or are barefoot.

I understand that there was an old rule to this effect, at least in US. Having the shoes on and taking them off both have their advantages and disadvantages. Except when challenged by a FA, I guess you can have/remove your shoes as you like (As long as the one sitting next isn't complaining). If the cabin crew asks though, its better to comply.

As far as the cabin crew is concerned, I'm not aware of any rule which says when they have to remove their shoes, so I guess its upto them, though it would be better for them to leave it on so as to take care of any sudden requirements. IATA recommends shoes which won't come off easily:

  Cabin Crew Uniforms

  ... The  following  is  intended  to  serve  as  a  guideline  for airlines
  when selecting new uniforms for their cabin crew:

  Shoes or boots should be flat or low-heeled and closed with laces or traps so that they will not be lost or thrown off;

Interestingly, this forum indicates that some airlines (including Aeroflot) require their FAs to wear high heels outside aircraft, which are changed to slip-ons (or other manageable ones) once in aircraft. From a news article:

  ... female flight attendants working for one of the world’s largest carriers, United Airlines, are required to wear shoes with a heel height of between one and three inches. Women crew members can only switch to a lower heel—it still has to be at least one-fourth of an inch high—during the service portion of the flight. ... Female attendants then have to switch back to the higher heels once the flight begins its initial descent.