Is it okay to use magnetized tools on airplanes?

The answer: In most cases, no. There are a few exceptions.

The most common exception is when adjusting any sort of magnetic compass system. Flux valves, whiskey compasses, etc... are usually supposed to be adjusted with tools made of brass.

Even then, your typical A&P will adjust the whiskey compass, for example, wait for the thing to stop spinning like crazy, and then make a slight adjustment back the other way. He'll repeat that process until he gets it right. I'm not saying it's right, but it's what most of them do.

The only other scenario I can think of would be bringing those tools too close to a CRT-based display system. Magnetized tools can make the display go a little wacky.

There may be others, but that's all I can think of off the top of my head.


Why can’t air traffic control radars determine the altitudes of primary targets?

without knowing its elevation angle, it could be located anywhere along a circular arc extending from the horizon to the zenith at the specified distance from the radar

Well, not quite.  Aircraft are generally much more restricted in their vertical positioning.  If there's a return from 30 miles away, that aircraft can't be overhead.  (And radars normally have a maximum elevation to the beam, often around 70 degrees).

This document suggests that (at least as of 1989) determining elevation angle was very difficult for ATC primary radar.  It was possible by cross-correlating information from multiple feeds, but that this was not routinely done.  The document focuses on how useful that would be for helping to remove ground clutter.

Even if some elevation information were available, that data might not be presented to controllers unless it were of a useful precision.  If the precision were worse than say 1500 feet, would that be useful?

  Besides, military radars can and do provide altitude information for primary targets

Radartutorial suggests that vertical discrimination (or 3D radar) requires extra equipment and is therefore more expensive.  Since ATC can get this information by secondary radar, the expense of gathering it via a 3D primary system is avoided.

Besides cost, older 3D radar would scan a region more slowly than a 2D radar.


To understand how a helicopter works (and in fact the mechanics of other aircraft too), it's helpful for you to be familiar with a key concept in physics, called Newton's Third Law of Motion. It says, in general terms, "for every action, there is an equal and opposite reaction".

Here's a simple thought experiment. Picture yourself wearing a pair of rollerskates, standing up, holding a basketball. Now, throw the basketball out in front of you using a two-hand pass (bring it to your chest and push it out in front of you). You'll find yourself moving backwards on the skates. You won't be moving as fast backwards as the ball will be moving forwards, because you have more mass than the ball, but you'll move, because the force of you pushing the ball out forward created an equal force moving you in the opposite direction.

A helicopter, and in fact most powered aircraft, work the same way. when a helicopter's rotor moves through the air, it pushes air downwards through a combination of its airfoil design, which moves air downwards as it passes over the top of the rotor, and an upward angle to the blade relative to the oncoming air that pushes the air with the underside of the rotor. By Newton's Third Law, the force pushing the air downward creates an equal and opposing force pulling the rotor, and the helicopter attached to it, up into the air.

To hover, all that's required is for this force pulling the helicopter up (you can consider it as either "lift" or "thrust") to equal the force of gravity on the helicopter, which is its weight. If these forces balance, the helicopter will remain the same distance off the ground. If lift is greater then weight, it will rise into the air, while if weight it greater, it will sink or fall.

Now, normal aircraft have to move forward through the air in order for their wing to get the airflow needed to generate lift. A helicopter, by rotating its wing, can produce the airflow over the lift surface without the entire helicopter having to move forward (or backward or sideways for that matter). So, it can rise straight up into the air and truly hover over a single spot on the ground.

The tail rotor of a helicopter is necessary to counter another force produced by the helicopter; torque. Torque is similar to force - really it is a force - but it's being produced in a circular direction instead of a straight line. The helicopter's engine uses torque to spin its rotor. Again, by Newton's Third Law, if the rotor of the helicopter is being spun clockwise by the engine, the helicopter itself will begin to spin counter-clockwise.

To counteract this torque, most helicopters have a second, smaller rotor which works the same way as the big one, but directs the force of its thrust sideways in the opposite direction to the way the helicopter's body wants to spin.

This sideways rotor doesn't necessarily have to be on the tail, but it works best if it's on the end of a long lever arm, such as the tail boom of the helicopter. The closer it is to the main rotor's shaft, the more thrust it has to produce in order to counteract the torque of the main rotor.

It doesn't have to be on the side of the tail either; many modern helicopter designs have the tail rotor spinning inside an aerodynamic duct in the middle of the tail:

Helicopters also don't necessarily have to have a tail rotor at all; all that's required is equal, opposing torque to that of the main rotor. A common substitute for a tail rotor is a second, counter-rotating main rotor:


How is a 14 CFR 101 sUAS NOTAM filed for an unregistered aircraft?

All part 107 aircraft must be registered, regardless of weight.  The question addresses the case of Part 101 flyers, who were exempt from registration.

Regulations have changed, and the Exception for Recreational Flyers now requires aircraft above 250g, used for recreational flights, to be registered.  Hence a registration number would be available for drone NOTAM filing.

In the case of aircraft below 250g, which are not required to be registered under the Exception for Recreational Flyers, an identifier may be offered by the filer of the NOTAM.  (eg: MONGO2025551212, which might be a name and phone number)


Are aircraft with counter-rotating props or Down Between Engines less likely to develop asymmetric icing?

Ice accretion is a very complex phenomenon on airplanes that depends on several factors. One of the main factor is the composition of the cloud that the airplane is flying and the exposure time.

Another significant effect are the conditions on the imprigment surface on the airplane, which depends of the flow path and the pressure over the surface.

So, having the properlers rotating in the same direction means that the propellers are providing energy in a different direction. Also that will mean that, for optimizing the airplane, the fuselage will be slightly assymetric (very difficult to notice).

So, to the first statement you are mentioning, I can confirm you that the imprigment areas affected by this assymetric effect will develop different ice shapes.

What I can tell you is that FAA and EASA employ real experts for airplane certification and they are concious of this effect, and I can tell you that any doubt they have about aircraft performances will request the manufacturer to demonstrate in flight.

My answer to your question is that those airplanes are not protected in the sense that they will develop assymetric iced conditions but are strongly protected in the sense that this condition is considered and very likely tested with airtificial iced shapes, so the airplanes are really safe. So globally, yes, the airplane is "protected" by design.

For your questions about 4-engined airplane, the answer is the same but having more complexity due to the number of engines.

I can tell you as well that in iced conditions, due to the complexity of the phenomena and the prediction and simulation difficulties, there is a lot of conservatism in the way manufacturers design the airplane and significant cost in airplane testing. FAA and EASA are really doing a good job.


Can you help me identify a vintage airplane in a painting?

The aircraft in the painting (I’m not sure it is a painting?) is a North American P-51C Mustang in the Tuskegee Airmen colors of the U.S. Air Force in WW II.
I cropped the image above and then used TinEye Reverse Image Search to find the photo.
My search has expired on that website, but you can copy the “fuzzy” photo and try it yourself on the same site.
Search photo

Search Result

P-51C Mustang in Tuskegee Airmen (Minnesota wing of the Commemorative Air Force)


The flaps on a glider wing are mainly for shifting the laminar bucket of the wing to the right lift coefficient. Yes, they help to increase maximum lift, too, but for gliding this is less relevant.

The goal in glider flying is to get in the shortest time from A to B. This can be achieved by flying faster than the best glide speed, because it gives the pilot more time to climb up in the next thermal. The stronger the thermal, the faster the optimum glide speed. You can read a great discussion about the finer points of this speed-to-fly theory here, courtesy of John Cochrane.

A fixed airfoil needs to have a wide laminar bucket, so drag can be minimised both when gliding and thermalling. This, however, will result in a less deep bucket which means that the drag coefficient within the bucket is higher than for a flap airfoil with optimum flap setting. Since adjusting the flap allows one to shift the laminar bucket to the desired lift coefficient, the laminar bucket of a flap airfoil can be made narrower and deeper.

The direct answer to your question is: no, negative flaps do not increase the maximum glide ratio but help to fly fast at low airfoil drag. If you look at the L/D at high speed / low lift coefficients, then yes, negative flaps improve the L/D at that part of the polar. They also help to limit the maximum lift a wing can produce and allow to fly faster in gusty weather.

Positive flaps reduce both drag at high lift coefficients and sink rate, and they are essential to reach the polar point of minimum sink in high performance gliders because that optimum is at very high lift coefficients due to the high aspect ratio of the wings. If you fly fast with positive flaps you will greatly increase drag and the sink rate, however.


How fast do four Tire-Propellers have to rotate to lift 2000 lbs?

Let's do a back-of-the-envelope estimate. As a simplifying assumption, assume that a propeller generates lift by accelerating air through an opening of a particular size, at one particular speed. The formula for the amount of lift generated in this case is:

$$\text{Lift} = \text{Opening area} \cdot \text{Air density} \cdot \text{Exhaust speed}^2$$

For each propeller, the needed lift is 500 pounds force, and the area of each opening is $\pi \cdot (\text{$9$ inches})^2$.

So we can calculate the needed exhaust speed using Wolfram Alpha: square root of (500 pounds force / (density of air * pi * (9 inches)^2))

The answer comes out to 230 mph. That's the speed that the air has to move downward through the rotors. I don't know how fast the propeller will have to move in order to make this happen, but it will be a comparable speed.

The amount of power required can be found by multiplying this number again by the amount of lift. According to Wolfram Alpha, that comes out to 307 horsepower (229 kilowatts) per rotor. So about 1,200 horsepower for the entire aircraft, if the rotors were 100% efficient.

Good luck with that.


What is the purpose of these "stickers" in the F/A-18 Super Hornet fuselage?

It may or may not be being used in this application, but they are location markers, usually used in weapons separation tests to record the movement and behavior of stores in the airstream as they separate from the jet.  Camera pods, usually mounted on the wingtips or other optimal vantage points record the process for engineering purposes.


Will this diagnosis from my cardiologist prevent me from getting a Class 1 JAA medical?

i passed my medical exam and it was good, this issue wasn't a big problem at all even its not a problem.


Is there a forced retirement age for Part 135 pilots?

There is no FAA mandated retirement age for part 135 operations, although there was in 2017, a proposal in Congress that would limit the maximum age but only for certain operators. As of the date of this answer there is no regulation for 135 pilot ages.

It's up to the operator then to decide if they want to hire somebody who can only fly domestic routes. For some this may not be an issue, for others it may be a deal breaker.


Everyone collectively went "Oh god, not this one" because this same question has sparked some intense debates in the past. Aircraft rely on airflow over the airfoil (wings/tail etc) to produce lift - which is independent of the movement of the tires. This means that with enough air going over the wing, the aircraft will fly even if it isn't moving forward at all relative to the ground.

This is why aircraft on ramps at airports need to be tethered to the ground. This isn't only to prevent them from rolling around, but from taking off should the air flow get fast enough over the wing.

If you are interested in an entertaining segment, the MythBusters did a fairly scientific experiment of this.

             Although it isn't perfect, I think it does a good job of explaining the concepts.


Which is the airliner with the most passengers per lavatory?

This is not necessarily an attempt to answer your question directly. But I do have some interesting information.

I use to be the night shift supervisor for Continental Airlines in Anchorage Alaska from 1998 to 2005. We primarily serviced B757 and B737 flights from Newark NJ or Houston TX via Portland or Seattle each day (4 winter, 6 summer flights). About half the flights had lavatory problems.

The MEL (minimum equipment list) only required the lavatory closest to the cockpit to be operational for a flight. We averaged about 190 pax (max was 230-290). Imagine a B757 with 200 passengers with only one lavatory for a 5hr flight between NJ and WA (WA to AK was 3hrs) - how inhumane! And I did rarely see flights with only two toilets that worked (never one).

This was an eye opener to me that the FAA (govt) is not looking after the best interest of the public. I could tell you other bone chilling experiences but this is not the proper place or time :(

So with due respect, I am warning that there is a difference between the number of toilets in an airplane, and the number of toilets that actually work!


What is the regulatory definition of AOG?

There is no regulatory definition of the phrase "Aircraft On Ground" as used in work orders or repair orders in the FARs (14CFR), it is used by convention to indicate that the order is urgent as the parts or repairs specified must be completed in order to fly the aircraft.

What causes the aircraft to be grounded can be a functional issue that (such as a damaged control surface: The aircraft is grounded until it's repaired or replaced) or a regulatory one (for example, an airspeed indicator is part of the Day VFR required equipment, if it fails even though the plane can physically fly it's not legal to do so - your new airspeed indicator would be an AOG parts order).


How are "charter" and "passenger" flights defined in the AIDX standard?

I know this question is 3 years out of date, but I thought I'd answer anyway. My answer is only applicable to Aviation Info Data Exchange (AIDX) schema 16.1.

As far as I know, there is actually no item in the format specifying the type of flight. But most systems I've come across have some coupled business logic that will make an AIDX request with the form of SheduleRQ and push this to a database.
If the flight isn't in the database it will make a further PublicStatus request to determine if the aircraft info should be shown to the public.

This might be a work around at the moment, but soon enough (2023-2025) AIDX will be integrated into AIDM and with all luck, unacknowledged requests will be a thing of the past.


Really love aviation but have a computer science degree. What kind of jobs could I possibly get which involve aviation?

I'm not sure if this question comes within the scope of this site the way it is phrased.

Anyway, Aviation industry is highly interdisciplinary and has a lot of scope for computer science engineers like,

Design of aircraft subsystems
Development of programs for design and analysis of aircraft components (CAD, CFD etc).
Instrumentation and testing of aircraft systems
Development of aircraft control systems (e.g fly by wire)
Aircraft testing and telemetry.
Aircraft maintenance, which is becoming software intensive.
Software for Airborne (avionics) and Ground based systems (e.g. Air traffic Management).
Development of aircraft display systems.
Software for communication systems for UAVs.

This list is by no means exhaustive. In most parts of aviation, there is a requirement for computer science engineers.


Why is there a helicopter visibility reduction restriction for this approach?

Helicopters may operate under special VFR when in flight visibility is less than 1 SM.  Therefore, the approach can be flown at lower visibility than that published on the approach plate.  However, the note must be published to further restrict these types of operations:  "The procedure is annotated with 'Visibility Reduction by Helicopters NA.' This annotation means that there are penetrations of the final approach obstacle identification surface (OIS) and that the 14 CFR Section 97.3 visibility reduction rule does not apply and you must take precaution to avoid any obstacles in the visual segment."1


How to scale the data of a wing aspect ratio to correspond to the case of another aspect ratio?

For reference, here is figure 5.21, which is originally from NACA report 116 (1921):

Each curve represents a wing with an aspect ratio as labeled. In modern terms, $C_a=100C_\mathrm{L}$ and $C_w=100C_\mathrm{D}$, where $C_\mathrm{L}$ is lift coefficient and $C_\mathrm{D}$ is drag coefficient.

Anderson derives eq. (5.66), which scales the drag coefficient of a given wing (subscript 2) to that of a wing with aspect ratio of 5 (subscript 1):
\begin{equation}
C_{D,1}=C_{D,2}+\frac{C_{L}^2}{\pi e}\Bigg(\frac{1}{5}-\frac{1}{\mathrm{AR}_2}\Bigg)
\end{equation}

The original NACA report states that this formula has "been found to hold for distributions of lift [that] do not deviate too much from elliptical ones, although strictly speaking [it applies] only to the latter." I'm not sure why Anderson doesn't include this important point, but the implication is that we can safely take $e=1$.

Now proceed as follows: Select a curve from figure 5.21 and plug the corresponding aspect ratio into eq. (5.66). Then pick any $(C_w,C_a)$ pair off the curve and plug those into the equation. Plot the resultant $C_{w,1}$ on a figure against the same $C_{a}$. Continue with as many coordinate pairs as you want from the same curve; plot them all with the same symbol. Then select another curve and repeat but using a different symbol. Include a legend. The result should look something like figure 5.22:


On the 737NG, after deployment of spoilers automatically after landing, do the spoilers automatically go back down?

The spoilers on the 737 after auto deploy will re-stow automatically based on TLP (thrust lever position). This is a function for a rejected landing which will automatically lower the boards & retract the levers for go around... most pilots after taxi off the runway quickly advance the throttle to let the actuator reset the system in leu of pushing the lever forward (it has a clutch in the linkage to allow manual positioning as well)


Are landings easier during the day or at night?

I'm going to answer this in somewhat of a more general sense but first let's clear up a few things.

  During the night the runway is brightly lit and all the guiding lights
  are clearly visible, but the actual tarmac is more difficult to spot.

This is not always the case. Maybe at large international airports the runway is quite well lit with lots of extra lights, but there are plenty of airports in the US that are poorly lit (granted not all of them service commercial traffic); it's worth noting that not all runways are well lit. Runway lighting varies quite a bit as well.

  During the day there is flare from the sun

Only if the sun is right in front of you, there are lots of runway directions and you may often land with the sun behind you.

  ...and the lights are less visible but on the other hand the tarmac is clearly visible.

The lights are not visible at all, they are off, but yes the tarmac is easy to see during the day.

A "good" landing by a proficient pilot should not be greatly affected by day or night conditions. What will affect a landing is the prevailing wind and weather conditions. Generally speaking wind (and thermal activity) dies down at night so the air is far more calm. In my experience night landings are smoother because of this. During a hot summer day, even in super clear weather, with the wind whipping and the clouds kicking thermals around you are bound to have a "fun" approach.
(from the FAA's handbook on night operations)

  Night approaches and landings do have some advantages over daytime
  approaches, as the air is generally smoother and the disruptive
  effects of turbulence and excessive crosswinds are often absent

More recently LED light technology has allowed some extremely bright landing lights to be installed on even the smallest of aircraft, this has greatly increased pilot visibility on short final at night.


Why don't aircraft carriers have multiple sets of arresting wires?

Having a second set of 3-4 wires would need a longer deck. But if one set is damaged, so would this landing area, so we need 2 runways:

Doubling the size of the flight deck would result in a massive ship, and scaling doesn't favor something getting too big.

Consider the 1967 USS Forrestal fire, even if the deck were to be double the size allowing two landing runways, an attack or an explosion would spread easily across a flat surface and render the whole ship out of action when it comes to air ops.

Note that USS Forrestal was already engaged in combat. But since you have tagged it redundancy, the answer would likely be (although not this site's scope) military planning redundancy, not an engineering one, i.e., if engaged in combat, having more than one carrier is the redundancy to continue engaging in said combat (and land the other planes).

Of course not all freak accidents can be anticipated. Let's say something bad happens to the deck during peacetime, what's the worst that can happen? The airborne aviators unable to land will eject, and the rescue helicopters will bring them back, it's a monetary loss, but not loss of airborne lives.


The 'Y' in YF stands for prototype according to the Tri-Service aircraft designation system. The 'F' stands for fighter, so YF stands for prototype-Fighter. These aircraft are operated by the US Department of Defense (USAF or USN).

For example, YF-22 is the prototype (technology demonstrator) version of the F-22 Raptor.

The 'X' series is the name given for strictly experimental aircraft; i.e. they are not prototypes.


What protections and feedback does the fly-by-wire on the Boeing 777/787 provide?

1. Do they have the Alpha Floor or Flight Envelope protections Airbus aircraft have?
The Alpha Floor protection on an Airbus overwrites the thrust setting commanded with the thrust levers to TOGA. Boeing does not do this. The autothrottles (if armed) will engage to prevent a stall, but the computer never overwrites the actual thrust lever position in the cockpit:

With the autothrottle armed, the autothrottle automatically activates if not autopilot
or F/D is active or and autopilot or F/D is in VNAV XXX, ALT, V/S, or
G/S, and:

speed less than FMC calculated value for one second
thrust below reference thrust
airplane altitude above 100 feet RA on approach, or airplane barometric    altitude 400 feet above airport on takeoff

Note: During a descent in VNAV SPD, the autothrottle may activate in HOLD mode and will not support stall protection.

(Boeing 777 FCOMv2 4.20.9 - Automatic Flight - System Description)
Also, unlike an Airbus, this protection can be disabled by simply disarming the autothrottle using the switch on the MCP.
The Boeing 777 and 787 do however have Flight Envelope Protections. These also work a bit differently than in a modern Airbus, where sidestick inputs are simply ignored or limited by the computers. In a Boeing, the flight envelope protection will use artificial forces on the yokes to provide the following:

Flight Envelope Protection
The flight envelope protection system reduces the possibility of
inadvertently exceeding the airplane's flight envelope. The flight
envelope protection system provides crew awareness of envelope margins
through tactile, aural, and visual cues. The protection functions do
not reduce pilot control authority. The protection functions are
described later in this section and include:

stall protection
overspeed protection
roll envelope bank angle protection.

(Boeing 777 FCOMv2 9.20.5 - Flight Controls - System Description)
It says that the pilot control authority is not reduced because the pilots can always overpower the simulated forces on the yoke and command the aircraft to go beyond the protected flight envelope.
Essentially, the philosophy for the control authority differs:

Airbus will not let you do control inputs that might get you killed.
Boeing will stop you from accidentally making control inputs that might get you killed, but you can overwrite them.

See also:

What are the main differences piloting Boeing vs. Airbus aircraft?
How does envelope protection work in Airbus vs. Boeing aircraft?

2. Do they have force feedback/force feel?
Yes, unlike an Airbus sidestick the Boeing 777 and 787 simulate the forces on the yoke and therefore provide force feedback:

The primary flight control system uses conventional control wheel, column, and
pedal inputs from the pilot to electronically command the flight control surfaces.
The system provides conventional control feel and pitch responses to speed and
trim changes.

(Boeing 777 FCOMv2 9.20.1 - Flight Controls - System Description)
You won't see the yoke shake in turbulence like on a 737, but you will see or feel the autopilot inputs as the yoke moves.
See also: How does the Boeing 777's yoke of both the captain and the first officer have synchronized movement?
3. When banking (without any pitch input), will the aircraft start to descend, or does the system counteract it like in an Airbus?
It will counteract like an Airbus, up to 30° bank angle, so you can fly a turn by rotating the control wheel only:

The PFCs also provide compensation for flap and speedbrake configuration
changes, and turns up to 30° of bank. The PFCs automatically control pitch to
maintain a relatively constant flight path. This eliminates the need for the pilot to
make control column inputs to compensate for these factor. For turns up to 30°
of bank, the pilot does not need to add additional column back pressure to
maintain altitude. For turns of more than 30° of bank, the pilot does need to add
column back pressure.

(Boeing 777 FCOMv2 9.20.10 - Flight Controls - System Description)
The PFCs here are the three Primary Flight Computers.


Why is the F-35B's elevator not in neutral position when in vertical flight mode?

In this video you can see it better I think:

I drew on a screenshot of the video from the side where you can see the air moving under the aircraft.
Compare this to the Fig. 1 in the paper linked by "Anonymous Person" here in the comment section of your question: http://ltces.dem.ist.utl.pt/lxlaser/lxlaser2016/finalworks2016/papers/03.2_3_366paper.pdf
As you can see angling the tailerons down significantly widens the gap between the leading edge of the tailerons and the trailing edge of the wings which allows air to be pulled along with the exhaust gases (drawn in blue). The paper calls this "entrainment".

Again I drew on another screenshot of the video and illustrated possible air currents that can freely move around the airframe: aft of the exhaust duct and to the left and right of the vertical stabilizers. As you can see the flaps are also extended which helps guide the air around the wings. There probably is a similar airflow around the front section of the fuselage where the wings are not blocking the flow and the fan is pushing the air down.
In a vertical descent or climb the tailerons also create less aerodynamic drag in this configuration than in a leveled attitude so the pitch inducing effects due to the large surfaces at the rear are reduced.
It could also be beneficial to angle the tailerons trailing edge down for a vertical landing or a short takeoff to increase the lift at the rear end by blocking the escape path for air trapped under the rear end of the aircraft. Essentially preventing the cushion of air to escape at least when in ground effect.


What is the correct procedure for operating the engine fire extinguishers on an ATR72?

As I understand it, pilot must pull the red handle and twist 90 degrees. This will stop the engine. Pilot must then press the discharge squib button in order to deploy the extinguishers. is this correct?

Yes, this is correct, except that the handle does not need to be twisted as far as I know. When the handle is pulled, the following things will happen:

The propeller on this side is feathered.
The fuel LP (low pressure) valve is closed.
The bleed air and HP valves are closed.
The deice and shutoff valve is closed.
The DC and ACW generators are disconnected.
The hydraulic to prop brake is closed on the other engine.

Pressing the squib button will then discharge the extinguishing bottle into the engine.

What would happen if the pilot pressed the discharge squib button before pulling the red handle?

Nothing, the button is not armed at this stage:

AGENT/SQUIB
armed when T handle pulled.
Discharges bottle.
(DC EMER/HOT MAIN BAT)

Am I correct in assuming that if the system has detected an engine fire, then the "fault off" buttons would be lit and there would be an audible alarm? If this is the case, would the alarm stop when the discharge squib button is pressed, or only when the fault off button is pressed?

Yes, both FAULT lights would be on and the alarm is triggered, if both loops A and B detect the fire:

The pilots would be alerted of the fire by:

master WARNING light flashes
ENG 1/2 FIRE light illuminates on the CAP (Crew Alerting Panel)
FUEL SO illuminates on the respective condition lever
respective fire handle illuminates
aural alarm sounds

A single FAULT would indicate a fault in the detection system, not a fire itself:

LOOP/FAULT
change in resistance, inhibits fire signal until turned off.
Loop on CAP (DC emer)

You would press the button to turn off the respective loop such that the other loop can detect a fire alone:

OFF
takes respective loop out of parallel circuit. Allows other loop to activate fire signal alone.

Above the buttons it is written: "Agent 1 Loop A" and "Loop B Agent 2". what does this mean and what is the difference between the two systems? In what circumstances would the pilot have to press both discharge squib buttons or both fault off buttons? In what circumstances would they only have to press one?

There are two fire extinguishing bottles and each can be discharged into either engine (Agent 1 refers to the bottle on the same side and Agent 2 to the one on the other side):

The correct procedure for an IN FLIGHT ENG FIRE is:

PL [Power Lever] affected side ... FI [Flight Idle]
CL [Condition Lever] affected side ... FTR [Feather] THEN FUEL SO
FIRE HANDLE affected side ... PULL
if condition persists after 10 seconds:
AGENT 1 affected side ... DISCH
if condition persists after 30 seconds:
AGENT 2 affected side ... DISCH
LAND ASAP

(ATR 72 QRH)

Source: ATR Systems Training Document
Also have a look at this YouTube video found by Jpe61.


How to reasonably determine minimum safe altitudes over city? (fixed wing)

Let's say I'm over a city. For the sake of being specific, I'm not talking about downtown areas with skyscrapers, I'm referring to residential / commercial mixed areas, typical "suburbia". If the city is 15 miles in diameter and densely populated, I would think (erring on the side of caution) I would consider my glide distance when determining a MSA.

Yes, that's what the FAA expects you to do per 91.119(a): Consider your aircraft's characteristics (glide ratio, landing distance required), your altitude, and the availability of landing areas. Select an altitude that lets you land (ditch, crash, whatever) with minimum risk to persons and property below you.

  If I was directly over the center of this city, that would easily make my MSA 4,000ft AGL (using a Piper Cherokee 140 in this example).

That is not an unreasonable determination if the area you're overflying is heavily congested (streets are full of cars/people, no parking lots, fields, or parks to dead-stick into without hitting a person/car/building).
Note, however, that your emergency landing doesn't have to be a pretty one: Light planes routinely fly through the Hudson River SFRA at low altitudes - well below 4,000 feet - and the West Side Highway or Hudson River Park are not particularly hospitable landing sites (you would be hard-pressed to execute an emergency landing without endangering persons or property). That means your "emergency landing" strategy is going to be the same as US Airways Flight 1549: You're ditching in the river. You can safely do that in a Cherokee or a Cessna from 1000 feet or less most of the time since the surface of the river is not as congested as the streets and parks of Manhattan: You can turn out over the river and be clear of people and vessels.

To address your specific bullet point questions:

  What would be considered a reasonable landing spot over a congested area?

One in which you can set your aircraft down without undue hazard to persons or property. (Yes, I realize that's very close to a circular definition.)
You don't have to make the landing pretty: you may damage the plane in the process, and you might damage some property or even kill a person on the ground in the process - sometimes you just can't foresee all the problems - but you should be looking out for landing areas that minimize the risk of injuring or killing people (priority #1) or damaging other stuff.

  What would be considered "undue hazard?"

"Undue Hazard" is a legal concept, and it will be up to your lawyer and the FAA's lawyers to determine if the hazard posed by an emergency landing you make is "undue" (excessive, disproportionate to what operating at a "normal" altitude would have imposed).
For a common-sense definition look at your operation and imagine you were standing on the ground: If you would be asking yourself "What the heck is that pilot thinking flying so low?!" then there's a good chance your altitude is low enough that an emergency landing would constitute "undue hazard" to the folks on the ground.

  What other elements come into justifying an MSA?

We already talked about the big ones: Aircraft performance & what kind of area you're flying over.
You also need to consider at least two other factors:

Pilot Skill
You know what the best short-field performance of your plane is from
the POH, but can YOU reliably execute a landing and hit those
numbers? Would you bet someone else's life on it?
Weather Conditions
What if your only landing area has a tailwind?
What if you have to fly into a headwind to reach your landing area - will you make it given your best glide speed and glide ratio?


What is this metal plate below the door?

@Greg is correct. It is a scuff plate, to protect the fuselage from damage due to GSE (like jetbridge etc). The image below shows it.

Image from slideshare.net

The image below shows an example made out of Ti from a manufacturer's site.

Image from exoticmetals.com


FAA: May I log as cross-country a flight with two or more short legs?

From a 2008 FAA interpretation sent to E. Thomas Sisk:

… cross-country flight time is defined as time acquired during a flight that includes a point of landing that is at least a straight-line distance of more than 50 nm from the original point of departure, not the original point of any flight leg. There is no requirement that any specific leg must be 50 nm. Moreover, a cross-country flight may include several legs that are less than a straight-line distance of more than 50 nm from the original point of departure. Nevertheless, at least one leg of the cross-country flight, however long by itself, must include a point of landing that is at least a straight-line distance of more than 50 nm from the original point of departure (i.e. of the flight, not of that particular leg).
Given the above analysis, the answer is each cross-county flight used to meet the aeronautical experience requirements under 14 CFR §61.1 (b)(3) must include one leg that includes a landing that is at least a straight-line distance of more than 50 nm from the original point of departure.

From the above, it is pretty clear that the order of flying does not matter and you can log the whole flight.
Also, see this AOPA response.


A Question about Departure Procedures at KLRU

The only takeoff departure at Las Crucas, NM (KLRU) is a visual climb over airfield (VCOA).

Typically you would depart the airport and visually see and avoid the obstacles around the airport while you climb.  If you are in IMC conditions (at this airport) you need 2500' ceilings and 3SM visibility to circle and climb above the airfield.  In essence, the procedure is for you to avoid the obstacles while you are climbing in a confined space.

ATC wants to know about your intentions of flying VCOA so they can plan accordingly.  It is one thing to climb over the airfield to the MEA vs. reaching the MEA 30NM from the airport.

From AIM 5-2-7

  A VCOA procedure is a departure option for an IFR aircraft, operating in VMC conditions equal to or greater than the specified visibility and ceiling, to visually conduct climbing turns over the airport to the published "climb-to" altitude from which to proceed with the instrument portion of the departure.  VCOA procedures are developed to avoid obstacles greater than 3 SM from the departure end of the runway as an alternative to complying with climb gradients greater than 200 FPNM.  Pilots are responsible to advise ATC as early as possible of the intent to fly the VOCA option prior to departure.


What does Hawaii ATC do in the case of ICBM warnings?

Here's an account that NATCA shared on their facebook page:

Veteran Honolulu Control Facility (HCF) member Steve Olson, recounting the experience of working yesterday:
“8:07am I was plugged in working airplanes like I do every Saturday morning, when the day took a turn into the surreal. Pilot after pilot started to check in with the same question. ‘Center, can you confirm the missile launch?’
“Then, as questions on the control floor were asked, it seemed like every phone in the room started ringing. The word ‘confirmed’ stung like a knife in the gut. As I started to advise the pilots on frequency that the missile launch is confirmed, the frequencies grew silent.
“As I did the only thing I could, continue to take care of the planes in my charge, all I could do was think about the ones I love, my loving wife and amazing kids. With less then 10 minutes there was nothing I could do.
“We found out rather quickly that it was a false alarm, but it seemed like forever.
“With my heart racing and my stomach in my throat, this is what was in my mind. Every day, for the last 29 years, when I leave home for work I hug Meagan, kiss her and tell her I love her. It may sound silly and trite, but today, for 10 long minutes, it mattered.
“Don’t take anything or anyone for granted.”


In missiles, what actuators are used for the control surfaces?

Battery powered servo actuators.
From www.acc.af.mil, for the AIM-120 Scorpion:

The control section consists of control electronics, actuator batteries, and four independently controlled servo-actuators.

Further on the actual AIM-120 control mechanism:
(Courtesy of the Turkish AF http://web.deu.edu.tr/atiksu/ana44/air3.html)

The Weapons Control Unit (WCU)-11/B consists of four independently controlled electro-mechanical servo actuators, four lithium-aluminum batteries connected in parallel, and a steel fuselage section that is bolted to the propulsion section aft skirt. Each actuator consists of a brushless DC motor ballscrew, an infinite resolution potentiometer directly coupled to the output shaft, and pulse width modulated control electronics. The output shaft is engaged directly to a squib actuated lock so that it does not interfere with the fin (control surface) installation and removal.


How to start an approach in IMC loss of communication under IFR?

The FAA says (per 14 CFR 91.185):

  If the clearance limit is not a fix from which an approach begins,
  leave the clearance limit at the expect-further-clearance time if one
  has been received, or if none has been received, upon arrival over the
  clearance limit, and proceed to a fix from which an approach begins
  and commence descent or descent and approach as close as possible to
  the estimated time of arrival as calculated from the filed or amended
  (with ATC) estimated time en route.

This seems to answer your question unless you have a more specific one. You can descend to an IAF as you see fit and commence any approach. ATC will clear the way.


Is there an aircraft that can go supersonic at sea level without using afterburner?

According to Wikipedia, the BAC TSR-2 was capable of supercruise (no reheat) at Mach 1.1 at 200 feet (~60 m) altitude.  The TSR-2 first flew in 1964.  The English Electric Lightning had demonstrated supercruise several months earlier, but only at higher altitudes (above 20,000 feet, appr. 6 km).


Why do jet engine fan blades have a twisted shape?

I don't think it's accurate to say that the desired thrust is the same along the entire blade. For a large turbofan blade like the one in your image, the outer part is designed to act more like a propeller (efficient for the bypass air) while the inner part is designed to act more like a compressor (efficient for the core). You're not incorrect in stating that the twist does help optimize the angle of attack with the speed of the section, but that's more about not breaking the speed of sound at the tip than keeping thrust constant along the blade.

For any specific engine, though, the blades are highly optimized based on an incredible amount of complex CFD and wind-tunnel analysis for which there is no simple or intuitive summary. The design of a turbofan blade is driven by several factors, mainly

aerodynamic efficiency,
structural efficiency,
noise,
temperature,
vibrations, and
bird-strike resistance.

All of these go into the resultant shape, but you're unlikely to find specifics that are non-proprietary to the manufacturer and available for anyone to analyze. The twist specifically is just another parameter in the extensive, complicated optimization.


Why do private jets such as Gulfstream fly higher than other civilian jets?

There are several reasons and none of them really have to do with a private jet being more aerodynamic than a commercial jet.

Private jets have better power to weight ratio than commercial jets so it is easier to ascend to greater heights. Commercial jets also carry more fuel which needs to be burned off to lighten the plane to go higher.

It’s easier to pressurize smaller cabins than larger ones (this is a significant factor for commercial jets).

Flying higher is usually better for avoiding weather that can even affect commercial airliners in the 30ks.

There is much less traffic up above 40k and it allows the private jets to fly more direct routes at a faster speed and more safely as well.


Is the FAA the only authority with specific medical requirements for transgender pilots?

As several commenters have noted, medical rules are different in each country. ICAO provides guidelines and recommendations, but it's up to each country to actually implement them. ICAO's personnel licensing requirements are in Annex 1 which is not freely available but their Manual of Civil Aviation Medicine implies that transgender pilots should be considered 'higher risk':

  Applicants with disorders of behaviour (for example regarding habit,
  gender identity, sexuality) should be assessed on the basis of their
  ability to put aside the disorder (or any conflicts related to the
  disorder) in order to attend to the aviation task at hand. These
  persons may have significant conflicts with their environment, leading
  to further difficulties, which may become an impediment for them to
  hold an aviation licence.

Looking at specific countries, the FAA may be an unusual case by explicitly mentioning gender identity issues. I couldn't find any mention of them in the EASA, Canadian or UK medical requirements. But all countries' medical requirements include something general like this (this example is from EASA):

  (g) Personality or behavioural disorder Where there is suspicion or
  established evidence that an applicant has a personality or
  behavioural disorder, the applicant should be referred for psychiatric
  opinion and advice.

That catch-all clause would - I assume - include gender identity disorder and therefore require psychiatric evaluation of the pilot. And in cases where a pilot has had gender reassignment surgery and/or drug treatment, the surgery and drugs regimen would almost certainly trigger additional testing and investigation (so would any other major surgical procedure or long-term drug treatment).

Finally, it's worth noting that whatever the general rules are, every case is different and the only way to get a specific answer for an individual is to consult with an aviation medical examiner for that jurisdiction.

(Disclaimer: I know nothing about medicine except that it's complicated. Consult an aviation medical specialist if you want a real answer.)


Does the DC-3 passenger airliner have slats?

Although it's technically possible, you aren't going to find slats retrofitted to a DC-3 (nobody would ever pay for it).

But yes, in theory you could improve the DC-3's stall behaviour and single engine performance very cheaply with Vortex Generators which can be thought of as a "poor man's slat".  VGs increase stalling AOA by between 1/3 to 1/2 of what you get with a slat (say, about 18-20 deg, vs 25 with slats) depending on the airfoil.

VGs have huge benefits on light twins, reducing stall speed, taming stall behaviour, improving aileron response, and often reducing Vmc to the stall when installed on the fin.  They are quite miraculous, although they can be a headache because they are usually glued on and if the kid you pay 20 bucks to wash your plane knocks off too many, you are grounded until you fix them.

I can't find anybody that sells a VG kit for the '3 although it does seem to be possible to install them on a wing with boots. Possibly the DC-3's airfoil requires VG placement far enough forward that the boots are in the way (each airfoil has a chord wise sweet spot and if they are too far aft they don't do anything).  Or maybe nobody has thought of doing it yet.


Is the ratio of HP to weight constant for identical air frames of different sizes? (See Scenario)

In an aircraft, engine power is used to overcome drag. Drag is related to weight, but not in an 1:1 ratio.
There are several types of drag:

Parasite drag: related to the surface area of the aircraft, incl. all the aircraft components that don't produce lift.
Lift induced drag: this is related to lift, which is related to weight.
Wave drag: we'll ignore this for low speeds.

(I'm simplifying things here)

Total drag depends on airspeed. like this:

When you scale an aircraft, things get more complicated. The weight scales with the volume of the aircraft. Your 1/6 scale aircraft won't weigh 1/6 of the original, but (1/6)^3.
Drag scales with surface area, so it'll be closer to (1/6)^2. I suspect lift scales with surface area as well.

So as your aircraft gets smaller, its weight drops faster than its lift, so the wing loading gets lower.

This also means the control surfaces become more effective, and the roll/pitch/yaw rates go up.

This means your takeoff and landing speeds become lower.

In practice, model aircraft fly at much lower speeds than their fullsize counterparts. So they're in a different part of the drag vs. speed graph shown above. This complicates the calculation of how much engine power you need for a model.

If you made a video recording of a full-size aircraft and sped it up, you'd get a decent approximation of what the scaled aircraft would look like.


Could vortex generators be used to preserve aileron authority during a stall?

Vortex generators re-energize the boundary layer and can slightly postpone flow separation at high angles of attack. Therefore, adding them in front of a control surface is a realistic way of retaining authority. In fact there are real life examples:

[picture by Peter Kämpf]

That being said, these devices are a crutch that is best avoided on clean-sheet designs. They add drag in every flight condition in exchange for some more margin at high alpha, this margin could be achieved by designing the aircraft better in the first place. That is why you will mostly see vortex generators applied as fixes late in the design process or as outright aftermarket modification kits. This constant penalty is compounded by the extra maintenance needed to keep the VGs clean and in good condition.

Ultimately, re-energizing the boundary layer can only do so much to prevent separation. A hard down aileron input at high angle of attack can stall the wing even with VGs, they are not a silver bullet.


What is the best strategy for landing when a flock of birds is on the runway?

I think the answer depends on what the birds are doing, but all options are basically "at the pilot's risk" - the tower is just advising you there are some birds hanging around the airport, but nobody can say how they're going to react to you trying to land there too.

If the flock is airborne and flying across the final (completely neglecting to coordinate their movements with tower, as birds are wont to do) you can request an extended downwind until they've moved on.
This has happened to me twice, and in my experience birds tend to be far less interested in airports than pilots. They're usually gone in a minute or two.
If they're sitting on the runway somewhere you can try a low pass over the field to scare them off, but my preference would be to ask the tower/unicom operator if they can chase them away for me with a ground vehicle (so I'm not near the flock in case they decide to disperse "upward" instead of "outward").
If they're just pecking around in the grass near the approach end of the runway looking for lunch Skip Miller & p1l0t have the right idea with a go-around or low approach/overflight to scare them off.
(This is part of why a low pass over an unattended uncontrolled field is often advisable -- you'll hopefully scare off any critters on the runway that you wouldn't want there when you actually land.)
If they're "airport birds" you might want to just land.
Some of the airports by me have resident flocks of birds that I'm convinced just sit there and rate people's landings - I swear I saw the same birds every day shooting touch-and-gos.
These are the kind of birds that aren't going to scatter when you do a low pass unless you hit them with your landing gear, so just be aware of where they are (in case they lose their minds and try to commit suicide by propeller) but they probably won't bother you.

I don't think I'd ask for a downwind landing because of birds (unless we're talking geese or hawks or something), but if it's a calm-wind day, the pattern is empty, and you're more comfortable with that idea go ahead and ask. The worst the tower can do is say "unable".


This answer is written for air transport category aircraft.
Introduction
During take-off there are three operationally significant speeds that ensure a safe take-off:

V1 - the take-off decision speed
VR - the rotation speed
V2 - the take-off safety speed

In addition there are three technically important speeds:

VMU the minimum unstick speed
VMCG the minimum controllable speed on the ground in case of an engine failure
VMCA the minimum controllable speed airborne in case of an engine failure

V1 is the take-off decision speed. Below V1, take-off can aborted safely without overrunning the end of the runway. Above V1 the aircraft is unlikely to be able to stop before the end of the runway so in case of an engine failure it is safer to get airborne. V1 needs to exceed VMCG to ensure the aircraft doesn't veer off the runway when accelerating to take off with a single engine.
VR is the rotation speed. At this speed the aircraft should be rotated and will get airborne soon after. The rotation speed ensures that, in the case of an engine failure, lift-off is possible and
V2 is reached at 35 feet at the latest. At the end of the rotation manoeuvre, the aircraft should be airborne. Otherwise the tail will hit the ground. Therefore, VR will need to exceed VMU.
V2 is the minimum speed that needs to be maintained up to acceleration altitude, in the event of an engine failure after V1. Flight at V2 ensures that the minimum required climb gradient is achieved, and that the aircraft is controllable. V2 speed is always greater than VMCA to ensure the aircraft is controllable in flight if an engine failure should happen.

Answer
What will happen if we just pick a VR that "feels good"?
If VRfeel is lower than VMU, we will end up with a tail strike. Even if the rotation would stop just before the tail strike, the increase in aerodynamic drag (lift is generated) will cause the take-off run to be longer than needed, risking not being able to climb over objects at the end of the runway. In addition, if the aircraft has an engine failure during rotation, it may not be able to reach V2 and could become uncontrollable and crash.
When VRfeel is too high, the aircraft risks exceeding the maximum safe tire speed. There is also a risk of not reaching VRfeel before the end of the runway.

References
Airbus operations briefing note on takeoff and departure operations; understanding takeoff speeds
Boeing article: exceeding tire speed
rating during takeoff


How can I tell from the location of flow separation if an airfoil is stalled?

The boundary layer separates usually at somewhere around 10-15% of chord near stall AOA (which is where you place vortex generators when using them to delay stall AOA).  Separation will start at the trailing edge and move forward.  If it was me I'd tuft the entire lower surface from just behind the LE, maybe 10% so you can really see everything that's going on.  Doesn't hurt to put too many on.


Why are the runways on Denver Int'l very separated from the terminals?

FAA has published Advisory Circular 150/5300-13A, Airport Design, which includes recommendations for parallel runway separation for US airports.

It summarises:

  Quadruple simultaneous precision instrument approaches are currently
  under study by the FAA. In the interim, the FAA, on a case-by-case
  basis, will consider proposals utilizing separations down to a minimum
  of 5,000 feet (1524 m). Quadruples may require special radar,
  monitoring equipment, etc.

  Simultaneous non-radar departures require a parallel runway centerline
  separation of at least 3,500 feet (1067 m), and Simultaneous radar
  departures at least 2,500 feet (762 m).

Back to the case, Denver airport is one of the busiest airports in terms of aircraft movements. It needs 6+ runways to support 550K aircraft movements every year. However, the more runways an airport has, the higher the chance air routes will interfere with each other. More separation between runways (and thus the terminals) can reduced distributions.

In fact the airport masterplan (PDF) shows that the operator is planning to build runways further separated from the terminals.

PS1: Denver is not the only case. Many mega airports have been built or are planned to be built with runways far from the terminal buildings, including Dallas/Fort Worth, Washington Dulles, Houston George Bush, as well as Dubai Al Maktoum Airport, Seoul Incheon airport and Shanghai Pudong airport.

PS2: Even though built in less populated area, Denver airport still have noise issues. More details can be seen here and there.


Is it common for jets not to have backup manual control system for emergencies?

On any large jet (the DC-10 was a wide-bodied plane, seating around 300 people), the control surfaces are simply too large to move without hydraulics. Manual control is impossible, and multiple redundant hydraulic systems are provided. This applies to any large plane.

It's considered unlikely that all the hydraulic systems will fail independently. The specific problem on United flight 232 was that the failures weren't independent: all three hydraulic systems were severed by the engine in the tailplane failing and spewing lumps of metal into the narrow conduit that carried the hydraulic lines.


Does the rate of turn increase or decrease by turning at a higher speed?

The first formula is a function of bank angle $\phi$ and the velocity $v$. By varying only $v$, you are keeping $\phi$ constant. As a consequence, to keep the turn "steady" and coordinated (that are the assumptions needed to write that formula) you need to increase the radius of turn $r$ and decrease the turn rate.

The second formula is a function of $r$ and $v$. Once again you change only $v$, $r$ will be constant here (while before was $\phi$). This leads to a turn with a higher $\phi$ (again to mantain valid the assumptions behind the formula) and higher rate of turn.

So, to conclude, assuming that you whish to perform a coordinate turn, whether the turn rate increases or decreases is a function of what you whish to keep constant when you change speed:

if you have a constraint on the bank angle, an increase of the velocity will decrease the turn rate and increase the turn radius
if you have a constraint on the radius, an increase of the velocity will increase both bank angle and turn rate

To complete the set of equations and see this in practice, you would need to flip each equation and apply it after the other. That means:

Case 1:

$$\dot\psi=\frac{g \cdot tan\phi}{v}   \;\;\;,\;\;\; r = \frac{v}{\dot\psi}  \;\;\;,\;\;\; \phi = const.$$

Case 2:

$$\dot\psi=\frac{v}{r} \;\;\; , \;\;\; \phi = atan\left( \frac{v \cdot \dot\psi}{g} \right) \;\;\; , \;\;\; r= const. $$

Note in case 2 how $\phi$ is computed through an $atan()$ function. This means that increasing $v$ will make $\phi$ approach $90^\circ$. The validity of the model used to derive this equations is no more guaranteed at that point.


Why is the VOR reference and variable signal modulated at 30 Hz?

In VOR early days, the 40s, the stable phase locked loop frequency generator was not available. A common frequency reference was the very stable public AC power grid frequency. The angular velocity of a synchronous motor is locked on the power source frequency, such motor can be used to actuate a variable resistor or capacitor to generate a stable wave which frequency is locked on the power supply frequency.
A VOR relies on two 30Hz signals: Reference signal and variable signal (more on the VOR principle here). The US grid is 60Hz, a synchronous motor with two pairs of poles turns at 1800 rpm, that is 30 rounds per seconds.
The reference modulated the frequency of a 9,960Hz subcarrier (332x30Hz) with a modulation index of 16, meaning the subcarrier swinged between 9,480Hz and 10,440Hz. Here is the description of the mechanical assembly used:

A tone wheel is driven by an 1800 rpm (30 rps) motor; and on this
wheel are 332 teeth which are arranged in a slightly staggered manner
so as to impart a cyclical variation between 9480 Hz and 10,440 Hz
with the rotation of the motor. The frequency modulated signal from
this tone wheel is then used to amplitude modulate the VOR carrier
signal.

(Source: A comparative analysis of area navigation systems in general aviation, by Stephen Malcolm Dodge, NASA -CR-132504, 1973.)
The motor also drove the rotating dipole broadcasting the variable signal:

Early conventional VOR with rotating beacon, source
Here's what the rotating/modulating assembly looked like for a Collins VOR station:

Motor, tonewheel and dipole of a Collins conventional VOR, 1954. Source: Collins
A single motor used to generate both the reference and the variable signal ensured the two signals remained coherent, and therefore allowed a simple phase angles subtraction to get the bearing.
If the VOR had been designed in Europe, the same motor would have turned at 25 rps, and the signals frequency would have been 25Hz instead of 30Hz. There comes @Sanchises question below, about the consequences of the different grids on the VOR compatibility around the world... While the motor angular velocity is the first to be impacted by a different power supply frequency, harmonic interference must also be considered, for example:

In the ILS there are two reference frequencies at 90 and 150Hz, also chosen as multiples of 30 and remote enough from harmonics of line frequency (60, 120, 180Hz, ...). However 50Hz harmonics include 150Hz and interferences may occur on a 50Hz grid.

Modern solutions to solve both the angular velocity problem and the harmonic interferences problem are straightforward, but they were not 60 years ago. It seems designers at this time chose to recreate a 60Hz source locally and dismissed 50Hz AC for the related portion of the equipment. I got this schematics from a 1968 issue of the French aeronautical navigation engineering group bulletin:

Mechanical generation of 90Hz and 150Hz signals in an early ILS. Source: STNA bulletin, page 88
A 1,800 rpm synchronous motor is used to generate mechanically the two frequencies. But France has opted for a 50Hz grid. A static inverter is used as a local 60Hz power supply. As mentioned in the source document, the inverter frequency is stabilized with a 1% accuracy.


Nose gear failure in single prop aircraft: belly landing or nose landing?

The standard procedure is whatever is in the POH for your aircraft. This is from a C182RG POH:

  LANDING WITH A DEFECTIVE NOSE GEAR (Or Flat Nose Tire)

  Movable Load -- TRANSFER to baggage area.
  Passenger -- MOVE to rear seat.
  Before Landing Checklist -- COMPLETE.
  Runway -- HARD SURFACE or SMOOTH SOD
  Wing Flaps -- 40°
  Cabin Doors -- UNLATCH PRIOR TO TOUCHDOWN.
  Avionics Power and Master Switches -- OFF when landing is assured.
  Land -- SLIGHTLY TAIL LOW.
  Mixture -- IDLE CUT-OFF.
  Ignition Switch -- OFF.
  Fuel Selector Valve -- OFF.
  Elevator Control -- HOLD NOSE OFF GROUND as long as possible.
  Airplane -- EVACUATE as soon as it stops.

That assumes that you've already run the gear extension failure checklist without success, of course.


What exactly causes pitch moment in the Phugoid mode?

Everything. When we are talking about flight dynamics and stability in particular, it is the balance of forces or moments that we must consider. For simplicity of analysis, we often choose reference points that allow us to isolate some effects and make them independent of some variables, but if you are interested in the "physics" of it, then you should keep in mind that, in general, the forces and moments are everywhere, and they change.
Specifically, you seem to think that the tail load is zero in the trimmed condition. Not true. It could be true only for aircraft with neutral static longitudinal stability, which normally wouldn't display phugoid oscillations.
In the trimmed conditions, both the tail and the wing create moments (with respect to CG), but they balance out to zero. The essence of static stability is that upon the disturbance, the balance is offset such that it leads to restoration of the initial conditions.
In pure phugoid motion, the upset is airspeed but not angle of attack (AoA). Now, an airplane may have a tendency to have a pitch moment directly in response to speed, which we can designate $M^V$, or better as a coefficient $c_m^V$. This can be related to the nature of its thrust and/or moments from other parts. But this is not strictly required, and we can consider the simplest classical system of just a wing and a fixed tailplane. This system will not see a balance change simply due to airspeed. But consider what will happen:

Say, airspeed is suddently reduced due to wind shear. This is the only change, and AoA remains truly the same.
The moment balance remains the same, becuse lift of the wing and the tailplane changes proportionally. Thus no pitch change yet.
Lift will drop and will not sustain level flight anymore.
The aircraft will start accelerating down (while still in the same attitude!)
This acceleration has an effect of increasing AoA (due to the vertical component of speed). Notice that this angular effect depends on the absolute forward airspeed, which suggests that the effect will be lower at higher speeds.
Now the normal short-period static stability (the $c_m^{\alpha}$ or $c_m^{c_L}$ derivative) will cause a nose-down moment (if the system was stable) and will restore the original trimmed AoA.

This restoration effect normally happens much quicker than the speed change, especially for larger airplanes. So with a good approximation you could analyse just speed changes and assume AoA = const throughout the process. But physically this is not true, which, I guess, is the source of your confusion.

With the nose down, the aircraft will gain airspeed.
QED: the aircraft tries to negate the initial airspeed upset, which is the definition of static stability.
However, what happens next can be interesting. Due to high inertia, the aircraft will inevitably gain more airspeed than needed, and the process will reverse. Oscillations will ensue, and this is what is usually called "phugoid motion". The dynamics of this motion depends on several factors (absolute speed was already mentioned). Typically, this motion is much less dampened than the short-period AoA stability, and can even be dynamically unstable (i.e. have increasing amplitude). But this is not necessarily a problem: because the motion is slow, pilots can control it.

If you want derivatives, they have already been mentioned. Omitting derivation and with some simplifications, they combine to
$$\sigma_V = c_m^{c_L} - \frac{V}{2c_L} c_m^V$$
This $\sigma_V$ is the measure of static stability by airspeed. It is negative for stable aircraft. As can be seen, aircraft without direct speed-moment response ($c_m^V \approx 0$ - think gliders, for example) will have speed stability fully determined by the short-period AoA stability.


Go to college and get an engineering degree, preferably in Aerospace Engineering or Mechanical Engineering with an Aerospace emphasis.  You may also want to pursue a Masters in this area after your Bachelors.
Seek out the best schools you can get into; the biggies in aero are Georgia Tech, University of Michigan, Purdue, University of Washington, and MIT.  But there are a lot of other schools out there with fine aero programs as well and attending there doesn't limit your job opportunities.
Study hard and get good grades.  If you can't hack your freshman and sophomore years, engineering may be a bad choice as a field for you; seek a different major.  On top of that, I strongly suggest you get involved with extra curricular engineering projects or clubs in your department.  This will give you a lot of hands on engineering experience and help build up a knowledge base for you of how to be a good engineer.
I'd also get involved with either a RC airplane club, or better yet, join a chapter of the Experimental Aircraft Association and participate in the flight testing of home-built aircraft.  Again, it starts giving you a lot of hands-on experience in the flight testing of airplanes, which looks really good on a resume.  You can also get a couple of good references this way.
In your junior or senior undergraduate years, start looking for co-op or internship opportunities at the major OEMs, i.e., Boeing, Northrop-Grumman, Cessna, Beechcraft, Airbus, Piper, HondaJet, Gulfstream, etc.  Preferably seek out internships in flight testing.
Finished with school?  Time to land your first job in flight test.  Attend your school's career fair and chat with the reps from the OEMs.  File applications for jobs on OEM careers sections.  Get your LinkedIn page set up.  It's now time to get references from your internship supervisors.  This first job is always a challenge as many OEMs are looking for experienced people and there are very few entry level roles.  You first job may not be in flight testing and will probably not be very glamorous.
Aerospace is a limited and challenging field to get into.  Work is also limited to certain areas of the nation, primarily Seattle, LA Area/SoCal high desert, Dallas, Wichita, Greensboro, or Savannah.  In addition, the business is quite fugitive, having many boom and bust cycles.  Layoffs happen very frequently and you may have to move from place to place to find work.  Starting salaries and benefits packages can be spartan.
Flight testing may or may not be as glamorous as you think it is.  Your primary duties will be generally doing test plans and reports for flight test operations, rigging aircraft of a/c systems with sensors, wiring and data collection boxes, possibly some 3-D CAD modelling.  Even the engineers on the aircraft are sitting at crew stations monitoring data collection.  After that you'll be doing data analyst activities, crunching numbers, etc.
A PPL or CPL is not necessary to be a flight test engineer.  Test pilot is another story altogether and is considerably more difficult.  There are civilian routes into this business but are extremely difficult to obtain.  Most test pilots get their education by becoming military pilots and attending either the USAFTPS at Edwards AFB or the USNTPS at NAS Pax River.  In addition, most of the test pilots at the major OEMs come from the military route and, IMO favor the military guys over non-military, particularly in flight testing high performance military aircraft.  Near as I know there are no requirements from the FAA to become a test pilot but the only private test pilot school in the nation is the National Test Pilot School in Muroc, CA.  They require applicants to possess an engineering degree, a CPL and at least 750 hours total time in fixed/rotor wing.  With an 11 month course to obtain a Masters of Science in Test Piloting costing an astounding $960,000.00, you will definitely need corporate sponsorship.  There are a few firms which will do this.  Burt Rutan's Scaled Composites in Muroc promotes test pilots from its engineering corps.  So does Cirrus in Duluth, MN.  But the competition to obtain these slots is fierce.  All in all, if you want to be a test pilot, go the military route, either in the Military Academies or a ROTC unit at your college.


Who controls VFR flights in class B airspace in Europe?

I'm assuming you're referring to this where a Cessna 172 had a near miss with a 737: http://www.havarikommissionen.dk/~/media/Files/Havarikommissionen/Havarirapporter/Luftfart%202014/Preliminary%20ATI%20Bulletin%20HCLJ510_2014_273.ashx

Regarding who the VFR pilot should have been talking to, that depends. For example if you're flying in Los Angeles you might get clearance into the bravo for LAX from SoCal Approach if you're taking the "coastal route" through the bravo, or you might get clearance from LAX tower if you're flying the lower altitude "mini route" which directly overfly's LAX runways and tower and you'd be talking to whoever you got clearance from until they handed you off.

It really depends how they've set it up. The  terminal area chart (TAC chart) for the bravo airspace contains VFR flyways and procedures including who to contact for clearance. So if you're interested you can get the TAC chart for Kobenhavn and look (usually) on the back of the physical chart where it has more info.

However, having said that: I think this VFR pilot accidentally flew into bravo airspace and will probably lose his/her license. Here's why:

Pilot did not have a Mode C altitude reporting transponder which is REQUIRED to fly in to Bravo.

From the report:

  Aircraft B was reported to fly at 4000 feet with no radar presented altitude readout.

I'm not sure how "Sweden control" hands off to Denmark, but if he's flying to bravo in Denmark you'd expect him to be talking to someone in Denmark, either the bravo airport's tower or Copenhagen Approach which is who the Boeing 737 involved in the incident was talking to.

If he was in Bravo legally he should have been assigned an altitude, heading and squawk code and ATC should have maintained separation between those two aircraft and the bravo controllers are the best in the world at doing exactly that. So I think he accidentally flew into bravo and was talking to the wrong controller.

Edited: To remove irrelevant detail about VFR altitudes above 3000ft AGL.


You dont have this tagged with a jurisdiction and the answer may vary a bit by country regulations but here in the US under the FAA the requirements do not explicitly state the sign must be in the middle of the aircraft:

  § 25.812 Emergency lighting.

  (b)Emergency exit signs -

  (1) For airplanes that have a passenger seating configuration, excluding pilot seats, of >10 seats or more must meet the following requirements:

  (i) Each passenger emergency exit locator sign required by § 25.811(d)(1) and each
  passenger emergency exit marking sign required by § 25.811(d)(2) must
  have red letters at least 1 1/2 inches high on an illuminated white
  background, and must have an area of at least 21 square inches
  excluding the letters. The lighted background-to-letter contrast must
  be at least 10:1. The letter height to stroke-width ratio may not be
  more than 7:1 nor less than 6:1. These signs must be internally
  electrically illuminated with a background brightness of at least 25
  foot-lamberts and a high-to-low background contrast no greater than
  3:1.

  (ii) Each passenger emergency exit sign required by § 25.811(d)(3)
  must have red letters at least 1 1/2 inches high on a white background
  having an area of at least 21 square inches excluding the letters.
  These signs must be internally electrically illuminated or
  self-illuminated by other than electrical means and must have an
  initial brightness of at least 400 microlamberts. The colors may be
  reversed in the case of a sign that is self-illuminated by other than
  electrical means.

So if its easier due to electronic cabling, head room, brackets, or any other factor manufacturers are free to mount the sign off center.


FAA Aircraft Registration Form AC 8050-3 doesn't exist

That's because 8050-1 is the Aircraft Registration Application, and 8050-3 is the Certificate of Aircraft Registration.
You submit 8050-1, and the FAA sends you 8050-3.


It's a STOL (short takeoff and landing) plane, landing in strong headwind. It's perfectly possible.

You can find more examples on YouTube.


What are these things on strings after the loss of cabin pressure?

They are the holders for the oxygen masks, they are packed into the plastic retainers and stored in the overhead, when the masks drop, they fall out of the containers. Not all systems have these retention pieces that I can find, but some do.

The "black" tubes (actually clear, but look black in the picture) you see are the oxygen mask tubes and the mask itself is dangling from the end of the tube, you can see they have green/red labels on them that signify they are oxygen. The oxygen generator for that group of seats/masks is under the label in the top "HOT HOT", oxygen systems get very hot when generating oxygen (just ask ValuJet).


Why could increases in cockpit voice and image recording potentially raise privacy concerns?

I will answer this question with the caveat that it is asking for an opinion, and therefore your experience may vary due to different regulatory authorities. I answer this question from an Australian CASA context but note that while there are differences between CASA, EASA and FAA, they operate so similar that in many cases the courseware I teach to students to become an engineer under those systems is almost identical. Therefore, I feel like I am able to make an informed opinion on the matter even though the courseware I teach is primarily designed for a CASA context. Having said that, If your aviation regulatory authority is not based under those I have just mentioned, I have no idea. Go consult their regulations if that is the case.

I will now paraphrase from an avionics textbook on module 13 (avionics instruments other - Cockpit Voice Recorder system) under the CASA part 66 licence outcomes:

-It is an offence under the Air Navigation Act 1920 to disclose any information on a cockpit voice recorder for the purposes other than that listed in part 2A of this act. This means that unless it is directly related to the investigation of an accident it will not be made public.

-CVR recordings may not be used as evidence in any criminal or civil proceedings within Australia

-CVR recordings cannot be used as grounds for any disciplinary action by employers

-It is an offence to make public any CVR recording. Large fines apply

-Only the investigative authority in the course of investigation or court order is to disclose the recording for the express purpose that it is relevant to understanding the cause of an accident

My text goes on to mention things like if the recording is distressing then a transcript should be made and the original recording not played if it does not add anything to the investigation.

My textbook does not specifically mention video recording systems but I would say they fall under the definition in the Air Navigation Act 1920 and therefore treated the same. But this is something lawyers can fight over.

To some up then, due to the points raised above, I feel like there are no grounds to feel concerned about your privacy if there were increases in recording. This is due to the protection given for your personal data under the act. Each nation should have a similar act that protects people in a similar way. If it doesn't, I would hope your workers union could lobby for change. There are no downsides I can see to increasing recording time and increasing the use of video in the name of safety, especially where a rigid protocol of non-disclosure exists in the form of appropriate legislation. Privacy concerns can only exist in a world where you are not confident in the system providing the protections.

I will finish by adding another opinion on the subject. The only time I wouldn't recommend increasing recording is on very light airframes where space and weight is an issue. There is an ongoing trend in the last 40 years or more and more flight parameters being recorded under the regs, so it makes sense to also find new and innovative ways to record video and voice in the cockpit as well.


Why do I hear the "real" engine noise only when the plane is on the runway?

When you have the thrust levers of, say, a 747 all the way back to idle, the airplane still has enough power to move. In fact, you will have to use the brakes to keep it from taxiing too fast. If you didn't use the brakes, it would finally accelerate to somewhere around 45 knots or so, far too fast for taxiing, but much too slow to take off. At the idle power setting, relatively little noise is produced by the engines.

To take off, if the 747 were at max gross, you would have to accelerate to around 180 knots. That would require a power setting approaching the maximum, depending on the length of the runway. The noise produced by the engines is relative to the amount of power they're producing. Hence, taxiing at idle produces little noise relatively speaking, on the runway taking off a whole lot of noise.


The faster an aircraft is, the wider range of elevator deflections it needs. And so do aircraft with large change of weight (amount of fuel used) during flight. However larger elevator deflection causes higher drag. It is more efficient to move the whole horizontal stabilizer instead. Therefore jet aircraft generally have the forward part of the horizontal stabilizer movable.

Now it would be possible to simply have the whole stabilizer move. And supersonic aircraft generally have just that. It is called stabilators. However having the stabilizer split lends itself to elegant solution for trim.

This takes advantage of the fact, that the aerodynamic forces tend to put the elevator in the position of lowest drag almost straight (slightly bent in direction of less lift) behind the forward part. So when the forward part is moved, the lift changes without changing the force on the elevator. So the elevator is used for the small adjustments where the elevator is intended to return to the neutral position, which the aerodynamic forces help with, and the stabilizer is used to trim for current airspeed.

In aircraft with mechanical controls, the elevator force (or a fraction of it via power drive) acts directly back on the control column and the pilot can feel it, while the horizontal stabilizer is actuated via mechanism that holds selected position (may be electrical with jack-screw like on DC-9 or hydraulic, but with no feedback) and connected to the trim, which is usually pair of large wheels on the sides of the centre console.

Now in Airbus A320 and all newer models the side-stick does not have mechanical link and the pilot does not feel the force on the elevator anyway. In normal law, the ELACs automaically adjust the elevator and stabilizer so that with side-stick in neutral position, the aircraft maintains 1 G vertical acceleration and therefore straight flight (at any flight path angle). Since the trim wheel does have direct mechanical link, it turns as the ELACs (or SECs) adjust trim.

However the distinction between elevator and trim is still useful in case of failure. When the system degrades into direct law, the side-stick position corresponds to the elevator deflection and the trim wheel position corresponds to the stabilizer position. Since the side-stick still returns to neutral position, the distinction of using the elevator for momentary adjustments and trim to balance the aircraft to fly (approximately) straight at current speed holds (just because the side-stick is spring-loaded, the force needed to deflect it does not increase with speed as it does for mechanical controls).


What common forms of deice and anti-ice exist and what future alternatives are being researched?

In general, deicing (removal of ice after it had formed) and anti icing (prevention of ice formation) methods used are:

Image from GKN Technology: Leading the way toward more efficient aircraft

Mechanical which simply pushes the ice off the leading edges. An example is the pneumatic deicing boots, which is the oldest method used where an inflatable rubber boot is used for removing accumulated ice from the leading edges.

Source: quora.com

"Deicer (PSF)" by Pearson Scott Foresman - Archives of Pearson Scott Foresman, donated to the Wikimedia Foundation→This file has been extracted from another file: PSF D-240001.png.. Licensed under Public Domain via Commons.

Heating In large aircraft, the wing (and tail) leading edges are heated by engine bleed air (electro-thermal heaters in case of Boeing 787) for anti-icing and de-icing.

Image from Aircraft Anti-Icing Systems by Leslie Mehl and Annie Parsons

Chemical de-icing systems use dry or liquid chemicals designed to lower the freezing point of water (various salts or brines, alcohols, glycols); or by a combination of these different techniques.
Fluid de-icing systems which use de-icing fluid from a storage tank and fed through micro-filters to a number of porous metal distributor panels. As the fluid escapes, it breaks the adhesion between the ice and the wing and the airflow carries it away, creating the so called 'weeping wing'

There are a number of other de- and anti- icing methods are also available/under development, such as:

Electro-impulse method used high-voltage capacitors, which are rapidly
discharged through the coils installed just inside the skin of the aircraft leading edge, resulting in a electromagnetic repulsive force (on the aircraft skin), throwing ice in all directions. However, the electromagnetic interference and structural fatigue associated with this method limits its application.
Electro- Expulsive Separation System An electric current runs through parallel layers of flat, copper ribbon. When a large pulse of current is passed, a repelling magnetic field is created, causing the upper conductor to jump less than a twenty-thousandth of an inch. The resulting high acceleration causes the the ice to break into tiny particles that fall from the airplane's surface.

Electro-Expulsive Separation System shatters and ejects ice from a wing model in a wind tunnel test from ipp.nasa.gov

Electro-Mechanical Expulsion Deicing System, whose principle of operation is given by the developer as,

  A microsecond duration high current electrical pulse delivered to the actuators in timed sequences generates opposing electro-magnetic fields that cause the actuators to change shape rapidly. This change of the actuator shape is transmitted to the erosion shield of the LEA causing it to flex and vibrate at a very high frequency. This rapid motion results in acceleration-based debonding of accumulated ice on the erosion shield.

Image from An Overview of the Deicing and Antiicing Technologies with prospects for the Future by Zdobyslaw Goraj

Ultrasound Some research is also going on into vibrating the wings using ultrasound to remove ice formed.
Shape memory Alloys have also been proposed to be utilized for deicing and anti icing, with their shape changing properties being used for ice removal when required.

Image from An Overview of the Deicing and Antiicing Technologies with prospects for the Future by Zdobyslaw Goraj

There has also been some research into usage of carbon nanotubes for this purpose.


What is the process to disconnect ground electric power before pushback?

When is the GPU disconnected?

Airports rules are applicable, for example airports may prevent the use of APU when the aircraft is at its stand (to reduce noise and pollutants release). The airline operating procedures also provide directives regarding when to start APU and engines.

The general principle is that GPU energy is cheaper than APU energy, hence unless an engine is running, GPU is used until pushback starts.

Disconnection

When the crew is ready for the pushback they make sure they have the APU running and the GPU isolated from the electrical bus.

B737 overhead electrical panel, source

The ground operator is in contact with the crew through the flight interphone system. The crew asks for the pushback procedure. The ground operator now has to disconnect conditioned air and ground electrical supply.

On the ground power receptacle panel there are usually lights to indicate whether the GPU is connected and in use.

B737 external electrical panel, source

The operator checks the white light is on, which indicates the GPU is not in use and using a switch on the plug electrically disconnects the ground supply. The "CONNCT" light goes off and the cable is physically disconnected. At this time the GPU may be shut down, if applicable.

Chocks are removed, brakes are released and pushback can start.

More on ground handling procedures:

Cello Aviation B737 procedures

Currents required for 90 kVA under 115 V are about 1 kA. If the connection is broken when such current flows, the components just disconnected can melt down, and liquid metal can be projected around (it's similar to arc welding).

GPU are fitted with some protections to prevent hot disconnection. Let's look at this aspect.

Cable layout

A GPU delivers three-phase 115 V / 400 Hz, the GPU cable/plug contains therefore 4 main conductors and pins: one neutral used as common ground (N or G) and three phases (A, B, C). When the system is balanced, there is no current in the neutral, electrons move in phases only due to the voltage 120° phase angle difference.

N, A, B, C wires are connected to corresponding pins of the plug (E/F pins are explained below):

Plug (source)

At 400 Hz the reactance of the GPU cable is 8 times the reactance at 50 Hz, and is able to alter the phase angles at the aircraft interface, leading to significant power losses and under-voltage. Inductive reactance is due to the existence of a strong magnetic field near the conductors. This field can be cancelled by distributing the phase conductors around the neutral.

As the phase conductors have a large diameter, doing so leaves some empty space between the conductors. This means conductors may move within the cable when the cable is used. One solution to minimize this space is to split each phase conductor into two separate smaller conductors connected to the same power connector pin:

Source

Other solutions exist like twisted individual cables.

In addition an adequate mechanism can be used to tweak the reactance and/or the voltage when the cable is moved and its curvature is altered and/or when the electrical demand varies. This can be done by injecting some capacitive reactance into the circuit and/or adjusting the transformation ratio.

E/F control pins

Two smaller pins (E and F) of the cable plug are used for status exchange between the aircraft electrical system and the GPU. F carries 28 VDC from the aircraft. E and F are usually shunted in the GPU plug.

Standard wiring for civil aviation (source)

This way, when the plug is disconnected, the aircraft electrical system can inhibit its ground power input and the GPU can shutdown its power generators.

E/F are connected to corresponding smaller control wires visible between the phase conductors (when E and F are shunted, a single wire is needed).

Additional features

Control wires can be used to connect optional systems to the GPU:

Red/green (ON/OFF) push-buttons for remote control of the GPU.
E/F pins fitted with a small switch to know when the cable connector is 90% inserted within the aircraft panel socket and the connection can be seen as established.
When the cable comes from cable from the loading bridge, additional push-buttons for reel control: UP/DOWN, IN/OUT.
Sensors to detect reactance variation, hot cable/plug or broken neutral.

Conversely, LEDs on the plug can be switched on or off by the GPU using the control wires.

More information:

AXA 2300 GPU Manual


Are landing fees due for an aborted landing in USA?

I commuted to work in my plane into an airport with a landing fee for a few years (I was doing it frequently enough that I paid for an annual subscription with unlimited landings). In Canada you won't be charged if you go around and I can't imagine being charged in the US either.  Although ATC records the landing, the fee is usually levied by the airport authority and is intended to cover airport services, not ATC services.


How Realistic (or not) was the crash scene in Flight?

It's apparently loosely based on Alaska Airlines Flight 261 and like in the actual incident, I don't think he deliberately inverts the plane. In the actual event, the horizontal stabilizer gets jammed in an extreme position thus forcing the plane to invert. Now if it were possible to fly a commercial airplane that big inverted, Alaska Airlines too would've landed safely eventually (which didn't happen, despite the pilots trying to fly it upside down according to the CVR transcripts).


What is the vocabulary used by fighter pilots used to communicate?

There are NATO standard terms.  For example the MiG-29 is known as a "Fulcrum." That's not the Russian name for it but the "NATO reporting name" which you can look up on Wikipedia.

There are also some standard (but not codified) terms such as "angels" meaning "thousands of feet."  And there are some standard terms such as "bent" meaning "inoperative" but I don't know how much those are used any more.

Within a certain operating area or task force, there may be specific code words used that may change from day to day.  These would not be known to anyone outside that area or task force.


How reliable is the Airbus FAC calculated gross-weight?

so after having done some more research this is what I have found.The A320 has two independent gross weight calculations. When the aircraft is on the ground the FMS does the GW calculation. Prior to engine start, the current GW and CG are not defined.; predictions are computed based on the pilot entered ZFW , ZFWCG, blockfuel and the FM calculates the TOW. The GW is calculated  by adding FOB to the pilot entered ZFW (GW=ZFW+FOB)  However I don't know what this iteration rate would be.
When the A320 is airborne, the FACs independently determine the aircraft gross weight (GW) by using the aircraft angle of attack sensors. If a significant difference occurs between the FAC and FMS gross weighs (delta > 7 tons) , the  message "CHECK GW" will be displayed on the scratchpad.


How do general aviation airports inspect their runways?

Runway inspection is usually performed visually. In this answer there is a list with several items which have to be checked in EGNX, but the frequency and exact list check items will be different at each airport. I'm not aware of any binding standard.

In every GA airport I know there is at least one daily inspection performed shortly after sunrise (or before the airport becomes active). This is especially important in grass airfields, where wild boars could have dug holes at night. If something happens during the day there is normally someone who sees it and can either inform the operator or fix it himself. Larger airports operating at night will probably inspect the runway more often.


Why B-52 engines produce lots of smoke only during take-off?

There are a few reasons.

The first is that the engines run more efficiently when the aircraft is moving. As the aircraft moves faster, it's easier for it to get more air into the engine, which helps it run more efficiently.

The second reason is even simpler: like most aircraft a B-52 only rarely runs at full throttle. Most of the time that it's cruising, the throttles are backed off to just overcome the drag and maintain the current speed and altitude (though flying at terrain avoidance level is a rather different story).

The last reason is that the larger amount of smoke is largely an illusion. When the aircraft is moving, it's actually still generating close to the same amount of smoke. We're seeing the smoke from running the engines at full throttle for roughly a minute. During one minute of normal flight, it would generate somewhere close to the same amount of smoke--but instead of being concentrated in the 1 mile or so that we see here, it would be spread across something like 10 miles of sky. In addition, at altitude, you're a lot more likely to have much stronger winds, so exhaust from a minute ago will be relatively widely dispersed, rendering it much less visible than we see here (with air that looks like it's almost perfectly still).


Why is a sweeping second hand required for IFR?

As @fooot mentions in the comments it means that the hand must be concentric with the hour and minute hands, it is not a reference between the difference of deadbeat and sweep seconds as many watch brands commonly reference now. This is a regulation that is intended to clarify the difference between a second hand that references the main dial and one that is on a sub dial. Historically planes may have had more complicated nav clocks like this hamilton where the large second hand is for the chronometer and not the elapsed time clock.

(source)

You can find what looks like one of the early AC's on digital clocks here. It references FAR 91.33 (which seems to no longer be in place) you can find the original verbiage here. I can not find any FAA legal interpretation that further defines "sweeping seconds".

On a bit of a side note, wrist watches (in any form) are not a legal substitute for a mounted clock.