What is ATR Automatic Thrust Restoration in MD-83?

The MD-80 series has two systems that can increase thrust in case an engine fails during takeoff:

Automatic Reserve Thrust (ART)

This system is independent of the throttle position and can increase the thrust of the remaining engine to the maximum rated thrust in case of an engine failure. It can be turned off with a switch on the glareshield, because it must not be used when using a FLEX takeoff thrust.
Automatic Thrust Restoration (ATR)

This system will use the autothrottle servos to increase thrust up to the go-around thrust setting after an engine failure.

  Thrust Recoveries for Engine Failure During Takeoff

  In takeoff mode, two separate systems attempt to provide maximum available
  thrust when the performance of one engine significantly differs from the
  other. These systems are automatic reserve thrust (ART) and automatic
  thrust restoration (ATR).

  Automatic Reserve Thrust (ART) System

  The ART system combines features of the digital flight guidance computer
  (DFGC) and the JT8D-200 fuel control to provide maximum rated thrust in
  the event of an engine failure during a normal thrust takeoff. Upon actuation
  of the ART system, thrust is increased without throttle movement by the
  opening of a solenoid-operated fuel valve in the engine fuel controls of both
  engines.

  The ART system is READY when the airplane is on the ground, the ART
  switch is in AUTO, either slat is extended, both engines are operating at or
  near idle, and the ART system self-test is complete. The ART system is
  subsequently armed when the N1 on both engines reaches 64% RPM.

  The ART system is actuated when the DFGC detects any one of the
  following: 30.2% differential in N1 RPM, invalid N1, DFGC failure,
  electrical power loss, or manual DFGC switching. Upon actuation, the ART
  system increases the EPR of the operating engine(s) from normal takeoff
  EPR to maximum takeoff EPR (an increase of approximately .05 EPR) by
  opening the solenoid-operated fuel valve in the engine fuel control. Once
  ART is actuated, the maximum takeoff EPR limit is displayed on the thrust
  rating indicator, and the EPR gauge. Once actuated, the ART system is
  latched (ART fuel valve remains open) until the ART switch is moved to OFF.

  The ART has an automatic self-test feature. If the ART system fails the selftest, the ART INOP annunciation illuminates. Dispatch is allowed with a failed
  self-test; however, the ART switch must be moved to OFF to disable the ART
  system.

  The ART switch, with AUTO and OFF positions, is on the upper instrument
  panel. Two annunciator lights are on the center instrument panel. The
  READY light indicates ART has successfully passed the self-test. The ART light
  indicates the system has successfully activated.

  Automatic Thrust Restoration (ATR) System

  The Digital Flight Guidance Computer (DFGC) automatic thrust restoration
  (ATR) is a feature, separate from the ART system, that increases thrust under
  certain conditions in the event of an engine failure during takeoff. Once
  activated, the ATR will unclamp the throttles (if the autothrottle system is
  engaged) and move both of them equally until one of the engines reaches the
  Go-Around EPR Limit.

  The ATR is armed if:

  The flight director pitch axis is in takeoff mode,
  The airplane is above 350 feet radio altitude, and
  Both engine EPRs are below the Go-Around EPR limit.

  After arming, the system will activate if the differences between the engines
  are greater than or equal to 0.25 EPR and 7% N1 (in the same direction), or
  (for DFGC models -930) the airplane’s vertical speed decreases to less than
  zero for 5 seconds. In these cases, the throttles will unclamp (if the
  autothrottle system is engaged) and move to the Go-Around EPR limit.

  If ART is armed and the ATR is activated, the EPR limit will be the
  maximum inflight takeoff rating reduced by the same amount that the ART is
  designed to provide. This correction prevents overboosting the engine if the
  ART system subsequently actuates.

(MD-80 FCOM Sec. 18 - Power Plant)


Is procedure turn considered published approach course?

I’ve been doing a lot of practice approaches lately and if a procedure turn (or hold) is required, they tell me to 'report procedure turn (hold) inbound'. Then they clear me for the approach. I think this is why:

AIM 5−4−7. Instrument Approach Procedures

  b. When operating on an unpublished route or while being radar vectored, the pilot, when an approach clearance is received, must, in addition to complying with the minimum altitudes for IFR operations (14 CFR Section 91.177), maintain the last assigned altitude unless a different altitude is assigned by ATC, or until the aircraft is established on a segment of a published route or IAP. After the aircraft is so established, published altitudes apply to descent within each succeeding route or approach segment unless a different altitude is assigned by ATC. Notwithstanding this pilot responsibility, for aircraft operating on unpublished routes or while being radar vectored, ATC will, except when conducting a radar approach, issue an IFR approach clearance only after the aircraft is established on a segment of a published route or IAP, or assign an altitude to maintain until the aircraft is established on a segment of a published route or instrument approach procedure. For this purpose, the procedure turn of a published IAP must not be considered a segment of that IAP until the aircraft reaches the initial fix or navigation facility upon which the procedure turn is predicated.


The root cause is the nature and theory of aerofoils. The design mission is to use the wing in an optimal way and finally the wing + body combination in the most optimal way to achieve the design goals. Most of the design goals answer to the following questions:

do you want to go fast (speed), or
do you want to lift more weight (payload),

For a given amount of fuel

do you want to go as far as possible (range), or
do you want to stay in the air for the longest period (endurance), OR, combinations such as
do you want to carry a specific weight a specific distance?

There will be an optimal aerofoil for each of these, and new designs can be attempted if there isn't one that fits the requirement or it is felt that there's room for improvement.
There are some aerofoil properties that tend to be common for the bulk of the commercial jet designs, as most of them are chasing similar goals:

generally best efficiency (in terms of L/D) is around 4˚ to 6˚ AoA. This angle is  achieved by combining a level flight pitch attitude of 2˚ to 3˚ with the wing mounted at a 2˚ to 3˚ Angle of Incidence**.

Stalling AoA in clean configuration somewhere around 15˚+, and

most of these aerofoils even produce lift till 1 or 2 degrees below 0˚ AoA.

With high lift devices extended, the typical AoA could vary between 7˚ and 10˚depending on slat/flap configuration.

(** Angle of Incidence: wings are mounted with the leading edge higher than the trailing edge, so the angle between the average chord line and the longitudinal axis of the airplane is fixed and it is called the Angle of Incidence. Thus an airplane rolling down a runway already presents an AoA of a few degrees and inflight, we don't have to cruise at an uncomfortable pitch attitudes of 5 to 6˚ nose up )
The physics of aerofoils and aerodynamics, as mentioned above, dictate that, the airplanes are mostly flown at different nose high attitudes of upto 20˚ including the slat/flap extended regime of flight, and climb phase. Much lesser part of the flight is spent at negative pitch attitudes of 0 to -4˚ for descents. Thus the 'lopsided' stabilizer range.
The Stabiliser settings for take-off depend on the CG, GW (Gross Weight) and T/O Thrust for the flight so as to present a 'standard' stick force and control effectiveness for the pilot and it must be understood that though weight acts through the CG, the GW is actually acknowledging the Lift being created by the wing to lift that weight.
BTW, a symmetric aerofoil produces no pitching moment only at zero Angle of Attack. Mount it at a small angle of incidence and it will produce a lift component acting through CP. It's just that there are other aerofoil shapes that have fewer compromises affecting the typical design goals.


Why did the B-52 never have a JT4A-powered version?

The military designation of the proposed JT4A is J75 (not to be confused with J57).
It was proposed for the G-variant of the B-52, but it would have slowed down the production:

The B-52G was proposed to extend the B-52's service life during delays in the B-58 Hustler program. At first, a radical redesign was envisioned with a completely new wing and Pratt & Whitney J75 engines. This was rejected to avoid slowdowns in production, although changes were implemented. The most significant of these was the brand new "wet" wing (...)
—livingwarbirds.com

Even a simple re-engine (as opposed to re-wing and re-engine) takes a lot of resources and time. The new engines are about 10% heavier, and they would need new nacelles, aerodynamic and flutter testing, etc. So, it was considered, but it wasn't the right time – fast production was needed for its role in the Cold War; 193 B-52Gs were delivered 1959–1961, making it the most produced variant.


Can I land my aircraft on the grass next to the runway at a public airport?

It depends on the airfield. Landing on grass is only recommended if the ground is maintained to a reasonable standard and clear of obstructions. Some airfields have grass strips maintained for that purpose, on others the grass has lights, wires and cables, or just lots of holes/ruts which will be far worse than the tarmac.

Some airfields are only grass, tarmac is not a prerequisite for having an airfield.

You want to know before you go, how to find out depends on where you are. There are flight guides and websites in many countries that tell you what is available, but it always makes sense to call ahead and ask the condition of the available grass, and to find out if there are any unofficial grass areas you can use.

There is also ATC, at a towered airfield you must land where you are cleared, you can'd decide to land on the grass nearby because you want to as it's a violation. If there's grass available you need to make sure you ask for it and they will give it to you if they can, most of the time ATC is helpful. If they say no there's probably a good reason. At an untowered airfield it's at your discretion, if there's grass available and it's in decent condition you would state your intention on the frequency and follow normal procedures.


What is the difference between Body Pitch Rate and Inertial Pitch Rate?

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

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

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

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

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

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

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

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


In the US, aircraft numbers are requested or reserved from an available list by the aircraft owner: N-Number Availability Query.  Then the owner, the manufacturer in the case of new aircraft, submits an application for registration with the reserved or available number.

This order of events (to reserve then request assignment) is important as registration numbers are applied to the aircraft, recorded in logbooks, programmed in computers, etc. before the aircraft certification is complete.

In the US, aircraft manufacturers reserve blocks of registration "numbers" long in advance of manufacture.  A registration request is made to the FAA on the appropriate form at which time a registration examiner at the FAA determines the legitimacy of the request: whether the number is assigned or available to be assigned to the aircraft as requested.

The Canadian process is the same.  Available Marks


Is (L/D)max achieved at a specific speed or AOA?

I'm confused because one source tells me that (L/D)max is achieved at a specific speed. The other source tells me that (L/D)max is influenced by the AOA.

The speed is only correct for a specific wing loading and straight flight at 1g. Only then will the optimum lift coefficient be reached in level flight at that speed.

The angle of attack version is the more generic and better way. Actually, optimum L/D is achieved at a specific lift coefficient, which is closely related to the angle of attack via the lift curve slope.

  The graph shows that the airfoil is the most efficient at a specific AOA. Thus in the ranges between 15° and 18°.

No, it only achieves the highest lift coefficient in that range. This is right before stall and certainly not the position of optimum L/D. Drag will have grown disproportionally over the previous angle of attack range. Without a drag polar it is impossible to say where that specific airfoil has its best L/D.


Are the A320's A and B electrical buses both energized all of the time during flight?

They are both energised all of the time except emergency situations. The essential devices can be switched between them, the non-essential ones will be turned off in such cases.

There is actually a couple more buses than two. The main ones, AC BUS 1 and 2¹, are powered by one engine-driven generator each, and are normally not connected. This has some advantages that

the generators don't have to be synchronized, and
if there is a short-circuit on one, the other remains functional.

The APU generator and external power are connected to a bar that can be connected to either and automatically connects to whichever is not powered. This bar can also be used for connecting the buses in case only one generator is running, and this can be controlled by a switch.

The essential devices, which means most cockpit instruments, are connected to a separate Essential AC BUS, which is normally connected to the AC BUS 1, but can be, manually, switched to AC BUS 2, in case AC BUS 1 does not work. It can also be powered by emergency generator (on RAT) or even an inverter from the batteries when RAT does not work (before it deploys and after landing during roll-out).

The even more important devices, including the flight control computers, are connected to the DC HOT BUSes directly powered by batteries.

So the essential devices can be switched when either bus is not energized. The non-essential devices like galleys, in-flight entertainment and cabin lights, will be powered off in that case. They will also be disconnected if the bus is energised, but does not have enough power (automatic load shedding).

¹ In the document I have they are not called A and B. The document document is (I got it off the internet², so it's not official copy for legal purposes) titled A318/A319/A320/A321 Flight deck and systems briefing for pilots and apparently created by Airbus (in 2007, but it's unlikely they changed this since)

² This or this is a slightly different version (even older, dated 1998), but the chapter 3. Electrical System has the same content. The included image is from the later link.


What are these protuberances on the north edge of runway 10/28 at Mataveri?

It isn't a change in the runway length.* It was last lengthened in the 80s to serve as a Space Shuttle emergency landing site (latimes.com), and the length hasn't changed since.
Between c. 2007 and 2011 (sorry clouds got in the way) the runway was resurfaced in stages. In one stage, the runway was shortened and given a temporary (small; cheap) turnaround pad (with centerline markings as well). When this happens, the declared distances are amended.
When the work was done, a new proper one was built, and the temporary small one became vestigial. Note the X marking in the second image, and note that many runways utilize mid-runway turnaround pads to shorten the taxi time back to the terminal (on the west end).
* well, in a sense, it was


I'm going to assume that when you say 1000 meters above sea level, what you really mean is 1000 meters above ground level. 1000 m AMSL can be underground in many locations.

First, you need to understand that the airplane, once in the air, always moves together with the surrounding air. The surrounding air can be moving relative to the ground – what's usually referred to as wind – but assuming sufficient altitude above local ground, the airplane is largely unconcerned with what the ground is doing under it.

Second, every airplane has some glide ratio. The glide ratio tells you, for each amount of distance covered, how much altitude you will lose. Typical values for light motor fixed-wing airplanes might be around 10:1 to 12:1, while commercial airliners might get 15:1 to 20:1, and high-performance gliders can exceed 50:1. For simplicity, I'll assume a glide ratio of 10:1, which is pessimistic, but which should be achievable by most light motor airplanes. (User XRF pointed out in a comment that these values might actually be on the optimistic side, but I'm sticking with them because the point is to illustrate the principle, not to give an exact calculation.)

Typically, the glide ratio is quoted at speed and configuration of best glide, so your first course of action when losing the engine should be to configure the airplane for best glide, and re-trim to match.

What the 10:1 tells us is that, for each 1*X meters (or feet) of altitude that you lose in a glide, you will cover 10*X meters (or feet) of distance. Since you start out at 1000 meters above ground, this means that you can cover 10*1000 meters or 10 km of distance before your flight path intersects ground.

However, again, that's distance covered through the surrounding air mass.

To figure out how far you can travel along your ground track, you need to figure out the amount of time for which you can remain in the air. Let's say that the speed of best glide in your airplane is 100 km/h indicated airspeed. Since you can travel 10 km through the surrounding air mass, this means that your travel time after losing the engine is 10/100 of an hour, or six minutes.

In six minutes, the 72 km/h wind will push your airplane 7.2 km along the ground, because six minutes is 1/10 of an hour, and 1/10 * 72 = 7.2.

Therefore, if you maintain that tailwind, with this highly simplified example, the point where you reach ground level will be 7.2 + 6 = 13.2 km from where you lost engine power.

If you instead make a 180° turn to head straight into the wind, you now have a 72 km/h headwind and a 100 km/h  indicated airspeed, for a ground speed of 100-72 = 28 km/h. You can still travel 10 km through the airmass before you reach the ground, and this still takes 6 minutes, but in those 6 minutes, your ground track distance is only 2.8 km.

The major advantage of turning into the wind is that when you reach ground, you will do so at a relative speed of 28 km/h, rather than 172 km/h, assuming an unchanged 100 km/h indicated airspeed. (This is why you always land into the wind.)

Therefore, with that wind, depending on which direction you turn into, your point of contact with ground, with these assumptions, will be somewhere between 2.8 km from where you lose engine power, and 13.2 km from where you lose engine power, expressed in terms of ground track distance.

In practice, however, if you lose the engine while in the air, this is all awfully academic. Rather, you'd pick out a nearby spot on the ground that looks reasonably even, level, and large enough to set down on; and head that way. There are virtually always ways to lose altitude, but without engines in an airplane not designed as a glider, very few ways to gain altitude. With experience, you might be able to quickly judge if you'll make it to the runway or not; but any controlled landing, even an outfield landing, is always better than a crash. You can always worry about getting the airplane back to the airport once you're safely on the ground.


How do CFIs typically determine proficiency for complex and high-performance endorsement?

This Advisory Circular describes what should be examined when transitioning (and ultimately endorsing) a pilot for complex operations.

  This publication is offered as a guide to the procedures and standards
  to be followed for a thorough and comprehensive checkout in these
  airplanes. The conscientious application and adherence to the scope of
  coverage recommended in the syllabus should result in a more
  competent, effective, and efficient pilot.

The document is fairly short and I suggest you look through it, for brevity I wont copy it here as its pretty much all relevant. Its important to note that this is simply what the FAA suggests (albeit strongly) and its not required all the described things be covered in a checkout. Although the instructor may be assuming some liability by signing you off without a proper checkout.


Is there any way to estimate the weight difference between a trimmable horizontal stabilizer and a fixed tailplane?

Hard to find a general reference for this one. You're adding the weight of the hinge, the actuator, and the supporting structure now connecting only to the hinge axis.

Torenbeek section 8.4.1 gives a weight estimation for preliminary design purposes for the tail group of high subsonic aircraft: it mentions a weight increase of 10 % over the weight of a fixed horizontal tailplane.


Does EASA allow IFR, NVFR or SVFR in gliders?

It's not possible to get IR for any of those. I think EASA now has flying in clouds rating for gliders. For night flying you will need a glider that is certified to do that. I don't know any manufacturers of night gliders. Blaniks had an option to fly at night but most of them cannot fly now at all.

SVFR may be possible in theory but it will be crazy. Maybe you can be towed in special VFR but this will be dangerous. It also depends on whether the country in which you are flying allows SVFR.


Why do I get a severe headache just before landing?

Your sinus passages were obstructed and it was atmospheric pressure squeezing your skull as the increasing pressure on the descent tried to equalize the pressure.

The air in your sinuses escapes much easier than it goes back in so the problem is always after a descent.

Feels like someone trying to drive a nail into your skull between your eyes.   Plug your nose with your fingers with your mouth closed and blow GENTLY and you will feel the air enter your sinuses and relieve the pressure.

Good idea to take a sinus medication like Otrivin with your travel kit if you are having that problem regularly.


How are range violations during a launch countdown handled?

As far as the FAA is concerned, it's just an airspace violation.  There is a restricted area over the center/base that extends up to 5000 feet.  This is active continuously.  There are other restricted areas that extend up to 'unlimited' that are "Intermittent by NOTAM normally 24 HRS in advance."

So high altitude traffic is not impacted by the continuous restriction and when there is a launch the restriction is published by NOTAM in advance.  This gives ATC the ability to route traffic around the area without any significant impact.  Since the safety area extends out into international airspace, the FAA can't control it as restricted airspace.  They have been defined as FAR 91.143 airspace, which states:

  §91.143   Flight limitation in the proximity of space flight
  operations. When a Notice to Airmen (NOTAM) is issued in accordance
  with this section, no person may operate any aircraft of U.S.
  registry, or pilot any aircraft under the authority of an airman
  certificate issued by the Federal Aviation Administration, within
  areas designated in a NOTAM for space flight operation except when
  authorized by ATC.

So violation of the NOTAMed airspace is a violation of 91.143.

In my experience (5 years working launch ops) the issue usually arises with GA aircraft that want to watch.  If someone enters the area, ATC will try to contact them by radio.  There are also helicopters and or plane that can intercept and escort the aircraft clear.  Space Shuttle launches had the largest contingent of aircraft.  Some small booster ops might have one helo or a King Air to deal with intruders.

The aircraft can also be used to get the attention of boats in the area.

Whether you scrub a launch or not depend on the launch window. I've seen them range from a few minutes to several hours.  A violator at the wrong time will cause a scrub with a short window, while you can handle the delay with a larger window.


What do I need to know to design contra rotating propellers for a powered paraglider?

Using two counter-rotating props does indeed eliminate torque issues. The co-axial configuration has been around for a while, like the successful Breguet Dorand of 1936. The thrust, power and propeller disk issues are a bit complicated, let's start with a qualitative discussion.

Two 2-blade co-axial rotors compared with a single 4-blade rotor of the same size.
To generate a given thrust, two counter-rotating 2-bladed propellers use less power than a single 4-bladed propeller of the same size - if they are mounted far enough away from each other. Separating the two propellers helps in reducing power: the closer together they are, the less the power advantage. Separate them 20% of the rotor radius, and you still have a 7% power advantage over a single 4-blade propeller, as computed by Kamov (reference). Further away results in less power required. Note that the 7% power advantage may not account for losses from the dual gearing trains required.

Co-axial 2-bladed propeller compared with two 2-bladed separate propellers of the same size.
Momentum theory predicts a power penalty of $\sqrt{2}$ = 41% when two rotors are placed co-axially without separation, compared with the two identical rotors being operated in isolation. Test results have indicated that that is an overestimation: 20% is more realistic.

We're limited to commercially available sizes and pitches and are using fixed pitch. That means that we cannot optimise for the exact circumstances. My recommendations for the design process would be as follows:

From your link I see that there are 40" and 49" blades available. Go for the 40" props.
Your link gives an output RPM of 3500. With a 40" prop, the tip speed becomes (3500 RPM * $2\pi$ rad * 0.5 m / 60 sec) = 183.3 m/s, about Mach 0.55. Forward velocity is around 20 m/s. The velocity triangle at the tip has an angle of tan$^{-1}$ 20/183 = 6.2°
A typical symmetrical profile such as NACA 0012 has a maximum L/D at angle of attack = 4° at M=0.6 (reference).

Add this to the velocity triangle and you end up with a blade tip angle of 10°. That equates to a blade pitch of 22 inch for the forward propeller. Select the standard pitch closest to 22 inch (24" ?). The next one up to 22" should be the best choice, because the aft propeller will be pulling in air and add to the free stream velocity.
The aft propeller runs the accelerated air from the forward propeller and must have a higher blade pitch than the forward propeller. Select the next available pitch up (28" ?).
Naturally, one propeller must be clockwise and one must be counter-clockwise.
Both propellers should be 2-bladed. That will result in four blades in total, more than enough for this application. Adding more blades will cost horsepower and not result in any useful thrust increase.

For the thrust per propeller, if I compute that from a $C_L$ of 0.55 and integrate that over the blade radius from 5 cm to 48 cm (to account for tip losses), I get:
$$ T = C_L \cdot \rho \cdot A \cdot \int_{0.05}^{0.48} \omega \cdot r \cdot dr$$
$$ = C_L \cdot \rho \cdot A \cdot \frac{\omega^2}{2} \cdot (0.48^2 - 0.05^2) $$
$$ = 0.55 \cdot 1.225 \cdot 0.05 \cdot \frac{366^2}{2} \cdot (0.2304 - 0.0025)$$
With

$C_L$ = 0.55
$\rho$ = 1.225 kg/m$^3$ at sea level
A = blade area is about 0.05 m$^2$
$\omega$ = 3500*2$\pi$/60 = 366 rad/sec

= 514 N per propeller. Note that there are assumptions on propeller profile and blade area in there. $\alpha$ may not be exactly 4° so lets take a 10% lower value of 450N per propeller = 900 N total.
Power required to generate this thrust is the blade profile power plus the induced power from thrust generation. When I look up the $C_T$ and $C_P$ factors of the propeller disks, I get a $C_P$ of 0.001, resulting in a power P of
$$ P = C_P \cdot \rho \cdot A_{disk} \cdot {V_{tip}}^3 = 0.001 \cdot 1.225 \cdot 0.785 \cdot 183^3 = 5.9 kW $$
So for two propellers with a penalty of 20%, that would be 14.4 kW = about 20 hp. There are some estimates in here and all depends on the pitch size and if my assumptions of blade profile and blade area are correct, but it seems to be in the ballpark. The product would need to be tested for actual thrust and power consumption of course.
If your counter-rotating setup and gearing works, the main selling points would be absence of torque and a low tip speed resulting in low noise.

Update
Some of the comments are on using larger propellers and one 3-bladed and a 2-bladed, and there is a question on using a spreadsheet for single propellers.

The single propeller spreadsheet may be a compilation of experience on using one single propeller. However, you will be driving two propellers.
A main selling point for your set-up is elimination of torque. Use one 3-bladed and one 2-bladed propeller, and the difference in drag will re-introduce torque. You have 4 blades in total already, no need to add a 5th or more for any purpose.
A larger propeller uses more horsepower than a smaller propeller, and you're driving two propellers. If your engine can drive 2 larger diameter propellers, by all means go ahead.
Your vehicle travels at a maximum of 70 km/h, the propellers won't have an issue with attracting enough air.
Increasing output RPM would be a good way to increase thrust!


Does the Fairchild Metroliner have any unusual handling characteristics?

Your question is basically asking for opinions. That said, I'll give you mine plus a bit of objective information. I flew SA-226 and SA-227 Metroliners for about two years, commuter flying (4 to 8 legs a day), mostly in U.S. Pacific Northwest weather, two pilots, no autopilot.

The Metroliner was considered by many to be a high workload, unforgiving aircraft. See this for more on that, but I did not find it unreasonably so. However, anytime you have a high work load, fast aircraft, the potential for incidents/accidents gets a little greater than if either of those things is not true.

It was not an airplane that you could get consistently good landings in if you consider a good landing one that is smooth (whatever that means). Clunkers greatly outnumbered greasers, at least for me. The tires were small and hard, and in my opinion the long landing gear magnified clunkers. You could increase your chances of a greaser by carrying a lot of power onto the runway, but that used a lot of runway.

Nose wheel steering was hydraulically actuated via the rudder pedals. It was not uncommon for the system to be inoperative, and the aircraft could be dispatched without it, in which case you had a castoring nose wheel. New captains dreaded being dispatched with inoperative nose wheel steering. Once you got used to it though, it was no problem. In fact, if you had to do some really fancy maneuvering on the ramp, you could turn off the nose wheel steering and if need be pivot about a main gear.

Far from any aerodynamic deficiency, at least in my opinion, it was great in that respect in that it was fast, but had the ability to slow down quickly.
Controllers liked it (and took advantage of this) that it could fly at jetliner approach speeds from the outer marker inbound until short final. Controllers at SFO would often put us between jetliners going down final, or from a left downwind for 28L clear us from that downwind for an asap short final knowing that we could do it. We would touch down beyond where the jetliners did but still in time to make the turnoff to what was then the commuter ramp. When you dropped the gear and flaps and brought the props back to an almost flat pitch with no power, it quickly slowed and/or came down.


Is this photo showing dozens of airliners in close proximity real, or even plausible?

The image is a composite image of 42 planes taking off from Heathrow over a one-hour period on November 2, 2016.  Here it is on Getty Images if you want to license it for your own purposes;  it is credited to Dan Kitwood.


Why do many fighter jets have double vertical stabilizers?

There are a few reasons many fighter/bomber designs have 2 vertical stabilizers:

one large tail produced more shear force at the root, 2 smaller tails mean less force at the vertical stabilizer root. This allows for a lighter structure
redundancy if one tail is damaged. The US navy philosophy is 2 is better than one, this makes sense given that its aircraft spend much of the time over oceans where there's few alternative landing sites
twin tails are shorter than one big tail, and vertical height is a consideration on carrier aircraft
twin engines spaced apart make for a wide fuselage back which can create a blanking effect with a single tail in the middle, 2 tails mean that there's always one vertical stabilizer that is effective
Twin tails create less of a radar cross section, and allow the tails to be angled to deflect radar signals away from airborne radar sources


What safety requirements are there when designing an electronic device to go inside the cabin of an airliner?

A document called RTCA DO-160 defines the testing for a number of environmental requirements. Within each test standard is normally a number of different test conditions. The level of required testing is normally defined by the customer of the device, who has the task of showing the regulating body (FAA, EASA, etc) that this is sufficient to ensure the aircraft meets all regulatory requirements.
In addition, DO-254 gives guidance for electronic hardware and DO-178 handles software. There are other legacy documents like MIL-specs that define testing as well.


What is the difference between an Non-Directional Beacon and a Compass Locator Beacon?

Normally "Compass Locator Beacons" were co-located with the outer marker for ILS approaches. A "compass locator beacon" is an NDB beacon specifically to drive the radio compass.

A radio compass was a lot simpler instrument than the ADF that worked off of the NDB beacons. Typically it just had a needle that pointed left/right to direct the pilot to turn towards the station. They operate on the same frequencies as ADF/NDB and can be tuned with an ADF receiver.

Radio compasses used the old "loop antennas" that you see on old aircraft pictures. The pilot, co-pilot, or navigator would rotate the antenna by hand (the older radio navigation system required the pilot to turn, so rotating antennas were a step up) to be able to find the bearing to a particular station.

ADF (the "automatic" part of the "automatic direction finder) eliminated the need to rotate the antenna to get the direction to the NDB.

So to answer the question, the NDB and the compass locator beacon are technologically the same, it is the equipment in the aircraft that changed.

See NDB Nav History for more details


How does a CFI know what endorsements to give?

In general, a flight instructor must demonstrate sufficient knowledge so as to be able to provide the proper endorsements for his students. This is covered both in AC 61-65 and in the Flight Instructor Practical Test Standards Task M:

  Task M: Logbook Entries and Certificate Endorsements

  References: 14 CFR part 61, AC 61-65.

  Objective: To determine that the applicant exhibits instructional
  knowledge of the elements related to logbook entries
  and certificate endorsements by describing:

  Required logbook entries for instruction given.
  Required student pilot certificate endorsements, including
  appropriate logbook entries.
  Preparation of a recommendation for a pilot practical test,
  including appropriate logbook entry for:
  a. Initial pilot certification.
  b. Additional pilot certification.
  c. Additional aircraft qualification.
  Required endorsement of a pilot logbook for the satisfactory
  completion of the required FAA flight review.
  Required flight instructor records.

Regarding the question:

  Let's say someone has a helicopter license and wants to get their private pilot? Do they have to take a knowledge test?

According to 61.63:

  § 61.63 Additional aircraft ratings (other than for ratings at the airline transport pilot certification level).

  (b) Additional aircraft category rating. A person who applies to add a category rating to a pilot certificate:

  (4) Need not take an additional knowledge test, provided the applicant holds an airplane, rotorcraft, powered-lift, weight-shift-control aircraft, powered parachute, or airship rating at that pilot certificate level.

So a private pilot looking to add an additional category rating at the same certificate level need not take the aeronautical test.

Regarding the question:

  What if someone is a sports pilot and wants to upgrade to a private pilot, what do they have to do?

you can find the answer in part 61.103:

  Subpart E—Private Pilots

  §61.103   Eligibility requirements: General.

  To be eligible for a private pilot certificate, a person must:

  (e) Pass the required knowledge test on the aeronautical knowledge areas listed in §61.105(b) of this part.

  (j) Hold a U.S. student pilot certificate, sport pilot certificate, or recreational pilot certificate.

So a sport pilot upgrading his certificate to private pilot must take the private pilot test.


At what distance beyond the aiming point is a landing considered a "Deep Landing"?

I believe that needs to be decided by the operator, taking into account their operation and fleets. For a jet on a short, normally wet runway, I would allow for a smaller margin than for a turboprop onto 4000m dry asphalt.

In the absence of any other information, maybe a sensible starting point could also be to look at what assumptions have gone into crew‘s landing performance calculations. On large jets, nowadays often a 7 second (or 1500ft) air distance is assumed between crossing the threshold and touchdown, in line with TALPA ARC recommendations. An air distance longer than that will invalidate the performance calculations (as this value is assumed to contain some margin already, using the full 1500ft will already use up all margin on the air part of the landing) and would thus provide a sensible event threshold. Obviously this would have to be reconciled against runway aiming point markings etc. in the FDM event validation to prevent a non-standard runway marking from generating false positives.


What is the decision- and workflow during a strategical rerouting?

Good question! One major problem of long-haul flights is the age of the wx forecasts in your flight preparation papers vs. the quick and unexpected development of especially convective adverse weather.

If the wx is of such magnitude that passing through it is not possible, ATC will offer reroutings to pilots. But in most occasions, the decision rests on the aircrew, as they have to consider other operational aspects as time in their tanks, navigation equipment etc.
If the adverse weather consists of ISOL CB which can easily be circumvented, ATC will most likely not issue big reroutings and let the pilots do the wx avoidance on a tactical / ad hoc level.

If the aircrew is lucky to work at an operator with savvy dispatchers, they will pro-actively send an ACARS message to the crew, so they can prepare for the wx development ahead.

So most of the time, the flight crew has to come up with an idea. And their means of situational awareness are limited. As of now, the only means to really see what is ahead is the wx radar, usually having a range of 120-200NM. So it is common practice to ask aircraft ahead on track about the wx situation.

After gathering all the facts, the classic decision workflow starts. At my company, we use F-O-R-D-E-C, which stands for

Facts
Options
Risks
Decision
Execution
Control

...where "D" is the point at which you make your decision. Depending on the time available and the task to be solved, FORDEC may take 10 seconds (fire on board) up to half an hour or more (I guess https://en.wikipedia.org/wiki/Qantas_Flight_32 must have been such a case).

The "C" part (for "control" or "check") is a reminder to revisit your decision at a later point in time and check if it is still valid.

In the future, we will see more and more "connected" flight decks, where pilots can receive long-range wx information as live radar pictures directly into their electronic flight bag. This could have saved the lives of the people onboard AF447:

The yellow circle represents the range of the wx radar (what the pilots of AF447 could see) and the red polygons represent the known wx situation from a satellite picture.


Can a SIGMET last less than initially forecasted?

Yes, SIGMETs can be cancelled.

A quick web search uncovered, for example, the ICAO Asia/Pacific Regional SIGMET Guide, 6th edition, May 2017, which on page 3-16 (PDF page 24) says, in part:

  3.5.4. Cancellation of SIGMET

  3.5.4.1. Annex 3, 7.1.2 requires that "SIGMET information shall be cancelled when the phenomena are no longer occurring or are no longer expected to occur in the area”.

  3.5.4.2. As such, it is mandatory for an MWO to cancel any SIGMET that is currently valid but for which the specified phenomena no longer exists or is expected to exist.

It appears that the cancellation is communicated with a new SIGMET, valid until the expiration time of the original SIGMET, specifying "CNL SIGMET XX" where XX is the original SIGMET sequence number. Sections 3.5.4.3 and 3.5.4.4 specify the format of the cancellation SIGMET. MWO is shorthand for Meteorological watch office.

SIGMETs can also be amended or corrected after issuance.

From the same document, the very next section, snipped for brevity:

  3.5.5. Amendment/correction of SIGMET

  3.5.5.1. If it is known that an existing SIGMET no longer accurately describes the existing or expected future evolution of the phenomena a new SIGMET, correctly describing the hazard should be issued, followed immediately by a cancellation of the original, erroneous SIGMET. [...]

So it is entirely possible that on the 31st at 11:00, the SIGMET originally issued with a validity of 310800/311200 is no longer in effect.


Does the pressure at the static ports drop as the aircraft's speed increases?

The comment:

  In fact, the pressure at the static ports will drop as the aircraft's
  speed increases (Bernoulli principle)

is not exactly accurate. The aircraft is a complex aerodynamic shape and static pressure distribution across the fuselage is not linear. An example is provided by the following figure from NASA Technical Memorandum 104316:

[Source: NASA]

If you look at the graphical part of the above figure, you'll see areas where the pressure is above (>0) and below (<0) the reference pressure. As the airspeed increases, the tendency will be for the positive values to get bigger and the negative values to get lower (more negative). So along the line between points 2 and 3, and also between 4 and 5 (over the wing), the pressure will drop as speed increases. Between 1 and 2 (the nose), and between 3 and 4 (just in front of the wing), the pressures will rise with speed.

From the same report:

  Zero static pressure error on the fuselage exists at locations 2
  through 5. One of these locations is chosen for the static port. To
  keep pneumatic lag small, the static port is normally located as near
  the airdata instruments as possible (or the other way around). (To
  determine this location precisely, several static ports are made in
  this area. The optimum location is then selected as a result of
  comparing the various ports with a reference source, such as a
  trailing cone.) This pressure distribution changes with flight
  condition, so a calibration over the flight envelope may still be
  necessary.
  ...
  Even with the selection of the best static port position, some
  pressure errors will remain, and these errors must be determined in
  flight. The difference between the locally measured static pressure
  and the ambient static pressure, which is dependent upon angle of
  attack, airspeed, and aircraft configuration, is called position
  error.

Based on the measured position error, a Static Source Error Correction (SSEC) table is developed. The SSEC is loaded into the air data system when it is installed in the aircraft so that it can make the necessary corrections.


Do all flights with the exception of military show up on FlightAware?

No.
From the Flightaware FAQ:

Can FlightAware track VFR flights?
In the US and Europe, this is not officially supported although some VFR aircraft with flight following are available on the position maps but it is largely unreliable and arrival/departure/flight plan data is often not available.

and

Can I track NASA's Space Shuttle or other space ships (UFOs, etc) on FlightAware during launch or descent?
No, but that would be rather amusing; the shuttle or UFOs would have to be on an IFR flight plan to be tracked or have an ADS-B OUT transponder. However, NASA streams live NASA TV on the Internet.

and

Can I track military aircraft? What about presidential movements in Air Force One?
FlightAware does not track military aircraft and presidential movement flights (e.g., Air Force One, Marine One, etc.) are operated by the US military.

etc.
Also compare this screenshot from FlightAware with a screenshot from another free tracking service:

You will notice that several flights are missing on the FlightAware map. The other tracking site, however, is not perfect either; these kind of internet tracking sites mostly rely on ADS-B, and do not receive radar data. Even if they did, we also still have flights which do not even show up on radar. Aircraft surveillance is complicated ...


Could simple fly-by-wire controls be installed in a prototype as quickly as a mechanical system with an autopilot?

Early civilian FBW systems were prototyped by taking a conventional cable aircraft and feeding the control surface commands into the existing autopilot system and servos.

The earliest was with NASA Langley's 737 which had an aft "research" flight deck. Various instrumentation and control schemes were tested. The airplane's normal flight deck remained in the front with safety pilots.

(NASA Photo)

When Airbus developed the FBW system for the A320, they took a test A300 (F-BUAD), installed the sidestick on the left seat and rigged the FBW system to give commands via the autopilot system.

(Source, Article)

This was the last time this was done; no subsequent Airbus aircraft ever had cable prototypes and to my knowledge Boeing never did. FBW systems are mature enough that there does not need to be cable backup testing. If you need to prototype some new control law or scheme, you can simply modify the software in an existing FBW aircraft.

A fundamental issue is that the intent of testing is to build a new aircraft type. It takes quite a bit of engineering work to design a cable system that would only be used for early stage FBW testing, and would ultimately be wasted. In a modern FBW system, everything is completely tailored to electronic control, from the stick all the way to the hydraulic actuators.


How does fuel economy quantitatively depend on altitude for a jet?

I am adding this community wiki answer to show my current state of research and to provide the plot vs. altitude, which I will update when I learn more. Comments are welcome.
Thermal Efficiency
From this answer by Peter Kämpf, we know that the thermal efficiency for jet engines is given by
$$ \eta = \frac{T_\text{max} - T_\text{amb}}{T_\text{max}} $$
where $ T_\text{amb} $ is just the ambient temperature (from ISA) and $ T_\text{max} $ is the temperature resulting from the combustion. If I understand the answer correctly, this should be about 1100 K above ambient temperature, so I am currently using this term to describe the impact of thermal efficiency on fuel economy:
$$ \epsilon_\text{T} \propto \frac{1}{\eta} = \frac{T_\text{max}}{T_\text{max} - T_\text{amb}} = \frac{T_\text{amb} + 1100 \, \mathrm{K}}{1100 \, \mathrm{K}} $$
I am not sure if the increase in temperature of 1100 K is constant with altitude, so please correct me if this is wrong.
Drag
From another answer by Peter Kämpf, we know that induced drag is proportional to dynamic pressure
$$ q = \frac{v^2}{2} \cdot \rho $$
with $ v $ being the TAS and $ \rho $ the density (known from ISA). Since work required to overcome the drag per distance is proportional to the force, the fuel economy should just scale with
$$ \epsilon_\text{drag} \propto \text{TAS}^2 \cdot \rho $$
Propulsive Efficiency
From this answer we know that the propulsive efficiency for a jet engine is given by
$$ \eta_p = \frac{2}{1 + v_e / v_0} $$
where $v_e$ is the exhaust velocity and $v_0$ is the TAS. As far as I could find, there is no straight-forward way to relate $v_e$ to altitude and temperature. For the moment, I added the propulsive efficiency for a high-bypass jet engine from the following plot from Wikipedia:

(image source: Wikipedia)
Summary
For the combined (relative) fuel economy term, I just multiply all previous terms:
$$ \epsilon = \epsilon_T \cdot \epsilon_\text{Drag} \cdot \epsilon_\text{Prop} $$
The following plot now shows the relative fuel required per distance. Each curve has been normalized to 1 at sea level.

The propulsive efficiency dominates as long as the TAS is increased. Afterwards, the lower drag dominates. The overall fuel use is almost half as low at high cruise altitudes compared to sea level.


What is the rescue arrow decal on a military jet pointing to?

It's a small door leading to a compartment which contains a handle on a reeled lanyard.  When fully extended, the handle and lanyard activate the pyrotechnic charges which jettison the canopy or other enclosure over the flight crew stations, facilitating rescue.

The arrow may also just point towards the external canopy latch in order to expedite cockpit access and rescue.


Why is the airflow in airline cabins downwards?

Temperature stratification is a vexing problem on lots of airliners.  The big challenge is you need a distribution system that is effective when cooling (on the ground and at low altitude when the weather is hot) and heating (as soon as the outside temperature drops to the point where there is a net heat loss that can't be made up by passenger body heat, the ECS will be producing inflow that is warmer than ambient).  At cruise where the  outside temperature is generally -10 to -40C, you are in heating mode, where inflow temperature is above ambient.
The objective is to get a circulation going (air falling along the side walls, and rising at the center aisle) to keep the air mixed and prevent temperature stratification in the small space, with the added factor of a large heat emission from the passengers to cope with. Distribution systems strive to do this.

So you would think that most of the time, you want the air coming in at the floor so there is a natural convective circulation favoring heat from below (most of the time incoming air is warmer than ambient).  Problem is, you have the heat of the passengers, which is significant, rising into the ceiling.  You generally want to measure temperature for regulation purposes at somewhere around passenger head level, and if the heat comes in at the floor, there is a tendency for heavy stratification as the sensor is remote from the incoming heat source and it creates a very long response loop (sense, adjust, wait for the result, adjust again, etc.).
The CRJ200 suffers badly from this problem because the airflow is from Dado panels along the sides at the floor like a home heating system (a design carryover from the Challenger corporate jet, which had different distribution requirements).  The temperature sensor is up by the overhead bin.  When the sensor called for more cooling, or even just less heat, the Environmental Control System would dump in all kinds of cold air, which didn't want to rise being colder than ambient, so it would have to, in effect, fill the bottom of the cabin space with cold air (or really, less hot air) until the "coldness" reached the sensor up at the bin.  Anyone who's ridden in the CRJ200 knows well the cold feet problem with that airplane, even at altitude where it's -30 outside.  What helped a lot was moving the sensor down near the floor to the inflow region to reduce the response loop, and a modification was created to do that which was quite effective, but few airlines bothered with it and having the sensor near the floor is generally suboptimal from a design perspective.
On the later CRJ versions they went with the more common airliner arrangement.  Air is injected up at the overhead bins somewhere and most of it is shot at the sidewall panels, to get a waterfall sort of flow down the sidewall panels, inboard along the floor and up the center aisle(s) (some air may also be injected into the space between the bins to prevent stagnation there).  This works reasonably well even when in heating mode where the air being injected down is warmer than ambient, and allows the temperature sensor to be in a good location with a reasonably short response loop, so variations of this type of distribution system are the most common.


Why do turbofans go faster than turboprops?

To generate a given thrust, a turbofan accelerates less air but faster than a turboprop. This means that turbofans can fly faster. However thermodynamically it is more efficient to accelerate a greater mass of air slower, so turboprops are more efficient and that translates into lower fuel burn.


Why bits are mixed up (interleaved) during ATC transponder mode A and mode C reply format?

Mode 1 transponders only had six bits: A1, A2, A4, B1, B2 and B4, which clearly wasn’t sufficient to identify specific aircraft.  Each day, all pilots would be given a common code to squawk when returning so the air defense folks would know they were friendly, whereas a foe would only have a 1/26 chance of guessing correctly.
Mode 3/A upped this to twelve bits, adding C1, C2, C4, D1, D2 and D4. However, the C bits were cleverly interleaved with the A bits, and the D bits with the B bits, at twice the transmission rate. The result was that (for instance) Mode 1 code “12” and Mode 3/A code “1200” looked the same, at least to the primitive equipment of the era. This was specifically intended so that Mode 1 aircraft could work with Mode 3/A radar sites and vice versa, allowing a gradual upgrade. Where the new equipment was in use by everyone, individual (“discrete”) codes could be assigned to each aircraft.
This is also why, to this day, xx00 codes are mostly “non-discrete”, i.e. they have a general meaning rather than identifying a specific aircraft.


Is the whole world's airspace covered by ATC?

The entire world is divided into Flight Information Regions (FIRs), so in theory there is someone responsible for everywhere.  However, those FIRs are then subdivided into different classes of airspace.

Class A/B/C/D/E airspace is "controlled", meaning there should always be some sort of ATC available.  In remote areas, though, ATC may not have radar coverage, so separation would be based only on position reports (plus ADS-B, for participating aircraft).

Class F/G airspace is "uncontrolled"; any ATC service would be advisory only, and around untowered airports, they'll tell you to use CTAF.  Often the reason airspace is uncontrolled in the first place is a lack of radio and/or radar coverage.


Is there a "pounds per hour" reading that could have signaled the fuel leak to the pilots of Air Transat 236?

Fuel flow is measured by flow transducers in line with the fuel pipes. And they do a very good job at measuring flow, but unfortunately a fuel leak bypasses them. There is no direct measurement of the leak flow anywhere.

The pilots of Air Transat 236 had two indications of the fuel leak:

Increased fuel flow through the oil/fuel heat exchanger caused a drop in oil temperature and a corresponding increase in oil pressure.
Drained fuel on the leaky side caused a fuel imbalance.

It would only be possible to positively identify increased flow as a leak if the leak occurs in between two flow transducers, both mounted in the same fuel line. If the leak occurs after a single transducer, the increased flow gives an indication. Otherwise, the leak flow would have to be observed from available volume, minus legitimately used engine flow. There are fuel tank probes distributed in airliner fuel tanks that give an indication of fuel volume per tank. Picture below shows the six fuel probes in the 747 centre tank (source).

The difficulty here is that leak flow must be derived from volume measurement: unit of flow is $m^3$/sec, the derivative of volume. The wing tanks are long and flat and the probes measure vertical distance, with an accuracy that suffices for Qty indication but lacks the precision of the fuel flow meters which directly measure impulse of the mass flowing through them. Plus they measure mass directly, a more useful entity than volume. Volume per mass changes with fuel temperature, tank levels change with aircraft pitch and roll, the level needs to be derived over time: all of this can only give an indication over the course of hours, when a large amount of fuel has leaked out already, and with a degree of uncertainty that would leave room for doubt.

You're right though, in wondering why there seemed to be no automated way for monitoring discrepancies in fuel quantity. @Waked mentions the estimation messages of the B737NG, which would also only seem to occur after much fuel has been lost aready. The A330 now has an ECAM caution message: FUEL FU/FOB DISCREPANCY, put in place after the Air Transat incident. Lessons learned from this incident would now be incorporated in the fuel management systems and aircrew procedures. The brilliant glide flight of the pilots demonstrates once again why we need pilots in front of the aeroplane.


What does the small fan do that is visible on Boeing 787 Dreamliners on landing?

If you are speaking of the small fan behind the gear in the photo below (click to magnify)

Image from here.

you are speaking of a Ram Air Turbine, usually used in an emergency, not in normal operations.


Why did the north / south runways close at Daugherty Field (KLGB)?

From a Long Beach Post article:

The two runways in question have not been in operation for a number of years and the study ultimately found that removing them will create a safer and more efficient airport for the City of Long Beach.
The removal will allow for new taxiways and possibly opportunities for economic development.

It seems by checking the summer (June) wind rose for Long Beach—shown below—the longest runway 30-12 has the best wind averages, even when the southerly wind dominates the month. It would be cheaper to use than to maintain two old ailing runways.
(Source) 30-12 runway drawn over the wind rose.


What's the relation between speed of an aircraft and takeoff distance?

I think your question is regarding new aircraft under design and not for existing planes?

The dynamics of ground roll/stopping is governed by one equation:

$$m\ddot{x}=T-D-\mu(L-mg)$$

where $T$ is thrust, $D$ is drag, $\mu$ is friction coefficient, $L$ is lift, $m$ is mass and $g$ is gravitational accel. Since thrust, drag and lift are a function of airspeed (and spoilers + brakes + thrust reverser should abort occur), the most naive way is just to numerically integrate the equation twice to get the distance at time.

That being said, don't forget that takeoff distance and accelerate-stop distance must be considered with all engines operating and with the critical engine failed. $V_1$, assuming not limited by controllability, should be selected such that the two distances balance. Also keep in mind that a good portion of takeoff distance is rotating and accelerating to $V_2$ before 35ft with the critical engine failed. The previous equation does not account for that portion.


What is the structural significance of 'dimples' on the fuselage of a Boeing 747?

That's just oil canning of the unsupported areas of skin between stringers and formers, and when pressurized the skin stretches enough to remove them (18:00 in the vid).  The fuselage diameter will swell a little bit, maybe 1/8 or 1/4 inch, when pressurized.


For light, GA aircraft, is there a "standard" turn, and what does that mean?

The FAA Aeronautical Information Manual defines 'standard rate turn' as,

  A turn of three degrees per second.

This results in the completion of a full circle in 2 minutes. Every airplane must be able to complete a standard rate turn in order to be certified. The standard rate of turn is used as the main reference for bank angle.

GA aircraft are expected to turn at the standard rate of turn during holding, intercepting, tracking, approaches, departures etc.

You're correct that the airspeed determines the turn rate. As the turn rate is standardized, the bank angle becomes dependent on the air speed. From FAA-H-8083-15A Instrument Flying Handbook,

  True airspeed determines the angle of bank necessary to maintain a standard-rate turn. A rule of thumb to determine the approximate angle of bank required for a standard-rate turn is to divide your airspeed by 10 and add one-half the result. For example, at 60 knots, approximately 9° of bank is required (60 ÷ 10 = 6 + 3 = 9); at 80 knots, approximately 12° of bank is needed for a standard-rate turn.


What airline academies are available to US citizens?

Many of the Asian ones are only open to their own nationals, to give them the opportunity to become a pilot as well. Pilots are in demand, and particularly captains are hard to find. For the funding, many F/Os are now self funded, low cost airlines do usually not fund initial pilot education.

An outfit like Stella Aviation in The Netherlands did offer bank loans to fund the license, guaranteed until the student found a job.

Unfortunately, we don't see many USA citizens working as expats: they are often very expensive due to having to pay double taxes when working abroad, USA has historically had few tax agreements with other countries.


Can a plane fly backward if its propeller is in reverse?

Fly? No.
Wings generally only produce enough lift to keep an aircraft aloft when air is flowing over them in their intended direction. If you reverse the airflow over the wing (by moving backwards in the air, for example) the wing would no longer be producing the necessary lift, and the aircraft would "descend at an extremely rapid rate" until a normal airflow over the wings was restored. (That's the polite way of saying "the darn thing falls out of the sky like a rock!")

Move? Yes. At least on the ground.
This has been demonstrated on more than one occasion by Fat Albert, the C-130 that supports the Blue Angels.  While the propellers themselves do not reverse, the blade pitch is changed to produce reverse thrust (slowing the aircraft the same way thrust reversers do on a jet engine, and in this case reversing its direction of travel).

Note that there is one notable exception to the "airplanes can't fly backwards" rule, which the article Ethan linked to alludes to: If the wind velocity exceeds the aircraft's stall speed it's possible for an aircraft to "fly" at its minimum airspeed, but be moving backwards relative to the ground.
This is a bit of a cheat though: The airplane still thinks it's flying forward (the relative velocity of the wind over the wings is in the "normal" direction, and the airspeed is fast enough to create enough lift to sustain flight). It just happens the the airspeed includes a headwind component sufficient to give the aircraft a net "negative" groundspeed.
The hypothetical P-51 in your question would require sustained winds of about 83 knots to make this trick work (we generally call that a hurricane), but something like a Piper Cub can do it at much more reasonable wind speeds.


Can a Diesel Aircraft engine be run on Car Diesel?

In at least some cases, yes. Continental's CD-155 diesel engine will run on auto diesel, Jet A or any mixture of both:

  The CD-155 is certified for the use of both jet fuel and diesel (DIN
  EN590) and is running with the two fuels in any mixture ratio.

EN590 is the European standard for auto diesel. The Gemini 125 engine can run on Jet A and diesel according to their website, as can the Austro AE300. So it seems that in general, aircraft diesel engines can indeed run on auto diesel.


What is wrong with a high-speed landing for an ultralight or GA aircraft?

Keeping too much speed in an approach in any airplane can be risky depending on how much runway you have as it all has to bleed off before you can stop. It's a great way to end up in a hedge. Extra airspeed means you'll either float in ground effect for a very long time, or if you somehow manage to get the wheels down you won't get much braking action as the wheels won't have much weight on them on a tricycle configuration, in a tailwheel configuration you will have braking action but you'll have to be gentle or you'll nose in. In fact, trying to hold down an airplane that is far over rotation speed is tricky, and it can all go wrong. There's no good reason you'd want to try this unless you had some sort of condition in the airplane that necessitated it.

Landing fast isn't good for your tires, the extra ground speed will cause more wear on initial contact as the wheel has to spin up that much faster. Your brakes could overheat or at least would wear out faster as well. Other than that I can't think of any particular damage or wear.


How to keep a helicopter steady when close to the ground?

The ground effect can be seen as an increase in air pressure underneath the lifting surface because the down-flowing air cannot stream through the ground. An image from this book::

In the hover, the down streaming airflow is pretty docile, with turbulent whirls only occurring in the transition to forward flight in ground effect. Full scale helicopters are inherently unstable with an eigenfrequency period in the order of a couple of seconds, and the instability gain is not really affected by the ground effect: amount of lift is kept relatively constant by pilot action, and ground effect mainly reveals itself as a reduction in induced drag.

So for full scale helicopters, pitch/roll controllability of the helicopter does not change (much) in ground effect. Depending on objects on the ground and the slope of the terrain there can be changes in trim as the pressure increase influences the horizontal tail for instance, but these do not fundamentally change eigenfrequency period.

For model helicopters, hovering in ground effect is a much more difficult task: the recurring blade period brings on a temporary pressure increase from lift creation. From Prouty:

  The wake in ground effect is not really a steady flow, as is assumed by the theory, but a flow with large-scale fluctuations that can be felt as gusts by an observer standing near the helicopter. Reference 1.21 speculates that these fluctuations are associated with the vortex that is made up of the individual vortices from the blade roots. This vortex apparently writhes like a pinned snake along the ground, causing the entire wake to shift and wobble.

Since scale models have a higher revolution than full scale helicopters, the frequency and distribution of these vortices may be what causes higher instability for hovering.


How safe are airplane tours of the Grand Canyon?

It used to be worse. (Comforting, I know)

Back in the day (1956), commercial airliners traveling coast to coast would often give their passengers a little tour of the Grand Canyon on the way to their destination (air travel was still a novelty).  When a mid-air collision between two passenger planes occurred, the government invested in a $250 million upgrade (1960 dollars!) of the air traffic control (ATC) system. One could say that the crash resulted in the 1958 creation of the Federal Aviation Agency (now Administration) to oversee air safety.

One of the things the FAA did was create a Special Flight Rules Area (SFRA) around the Grand Canyon and make a specific chart just for the area. Additionally, they created approved commercial tour routes (see the orange routes below)

In addition to commercial sight-seeing tours being more regulated, there is a lot more training, documentation and procedures available for pilots with the main interest being safety. For example, the following notice is printed on the chart (References 14 CFR Part 93 Subpart U which gives minimum altitude restrictions, both for safety and noise abatement!)

https://skyvector.com/?ll=35.7929449938479,-112.79126822365794&chart=231&zoom=2

And of course, as mentioned in another answer, commercial operators, even if they are operating what looks like a "small private plane" are subject to increased mechanical inspections and regulations. One thing to look for when you arrive is the level of professionalism exhibited by the crew (it might just be a single pilot), but also the people checking you in and working with you to get you on your flight. There is something called a "culture of safety" in aviation that, while the unforeseen can always happen, if there is a culture of safety, preventable incidents can be minimized or eliminated.


Why did Cessna use a new design for the C162, instead of updating the C150 design?

I think there are a couple reasons: 1) Weight, and 2) the Type Certificate.

For #1, the original C-150 is roughly 100 lbs too heavy (in empty weight).  That's a bit over a 10% reduction, which is huge in an all-aluminum design.  Note that later models need even more weight removed (C-152 included).

For #2, the C-150 is a CAR Part 3 type certificated design.  To sell it as a LSA would almost certainly require a re-designation so as not to conflict with the original type certificate.  This is primarily a paperwork thing, but nobody had done it before (even now, none of the "grandfathered-in" type-certificated designs are still built under their type certificate or by the original manufacturer).  The C-152 is an add-on to the C-150's type certificate, so the same problem applies to it.

As far as why the C-162 failed, I think Carlo's answer covers most of the reasons pretty well (ignoring the "GA is dead" rant), though I'd like to add that Cessna did a terrible job with designing the C-162 and took so long to "get it right" that they didn't start deliveries (of an arguably inferior product) until right after the 2008 economic downturn.


What are the rules regarding airlines picking up passengers at stops in foreign countries?

The short answer to your first question is that an airline can pick up passengers at an intermediate stop as long as it's previously been agreed by all the countries involved (see below). One example is Singapore Airlines SQ12, which flies SIN-NRT-LAX; many passengers leave and board the aircraft in Tokyo.

More generally, these rules are known as the freedoms of the air but they aren't consistently or fully implemented everywhere and a lot depends on agreements between individual countries. Your first question is about the fifth freedom:

  the right to fly between two foreign countries on a flight originating
  or ending in one's own country

As Wikipedia describes, this isn't always straightforward:

  The negotiations for fifth freedom traffic rights can be lengthy
  because in practice the approval of at least three different nations
  is required

If an airline stops in an intermediate country to refuel or for other technical reasons but isn't allowed to board or deplane customers, that would be the second freedom:

  the right to refuel or carry out maintenance in a foreign country
  without embarking or disembarking passengers or cargo

There's an interesting discussion of fifth freedom flights from a passenger perspective here, and you may get better answers on this topic on travel.SE.


How is the change of moment handled in a Weight and Balance calculation with a swept wing aircraft?

In supplement to @Dave's answer and as he said depending on the airplane, the complexity of calculating the c.g. can vary greatly. The manufacturer of every large aircraft I've programmed weight & balance for has had tables for each tank. In Boeing's case for the 747-400, each table line is a tank volume in gallons and the tank c.g. at that volume in inches. For example, and using JSON notation since the OP is JavaScript fluent:

{"vol":3200,"ba":1453.7},
{"vol":3250,"ba":1454.8},
{"vol":3300,"ba":1456.0},
{"vol":3350,"ba":1457.2},
{"vol":3400,"ba":1458.4},
{"vol":3450,"ba":1459.7},

"vol" is the fuel volume in the tank in gallons

"ba" is the balance arm at that volume in inches

Since fuel is loaded by weight, one has to use the fuel density to convert to volume.

Typically, at least for large aircraft, you have to satisfy the c.g. envelope for:

zero fuel weight
ramp weight after fueling
takeoff weight
landing weight

Also there has to be provision for carrying ballast fuel if that is necessary.


Quite simple ― use a (special) towbar! Aircraft with such unique front wheels (like the Antonov An-225 Mriya and Lockheed C-5 Galaxy) carry their own towbar around, which is then attached to the tugs for movement.

For example, here is the Galaxy's towbar:

From left to right: 68th Airlift Squadon loadmasters, Senior Airman Katy Mackey, Master Sgt. Kevin Foerster, Senior Master Sgt. Dustin Burleson, Airman 1st Class Brandon Stone, and Master Sgt. Alfonso Cervantes unload an aircraft tow bar off C-5A Galaxy upon arrival to Cairns, Australia on May 5, 2012. The tow bar was used airport officials to move the Air Force's largest transport aircraft in place to load the U.S. Coast Guard's HH-65C Dolphin helicopter. (U.S. Air Force Photo/Maj. Tim Wade)

And here's that of Mriya:

AN-225 towbar being removed from aircraft; screen grab from this youtube video.

And here's a Galaxy with a towbar:

Troops from the 439th Maintenance Squadron prepare to tow a C-5 Galaxy into Westover's Regional Isochronal dock, May 22, 2013, to test the newly-constructed mobile tail enclosure. Crews broke ground April 1, 2012, for the $5 million MTE, is a moveable structure on rails that will protect maintenance troops from harsh New England weather. The MTE is the largest structure of its kind in the Air Force. (U.S. Air Force photo/SrA Kelly Galloway)

This video shows Mriya's towbar in use.


Are both RVR and visibility minimum required for CAT I ILS?

If RVR (which is both runway-specific and more precise) is available, then it is controlling. If not then visibility (single value for the airfield) is controlling.
For example, typical Cat I minimums might be 1800 RVR or 1/2 Statute Mile (when the runway has an ALSF-II approach lighting system). If the RVR is near 1800 for one runway, the visibility may be low enough at the sensor for the airport that the prevailing visibility is reported as 1/4 SM -- too low to allow you to fly the approach (Part 121 rules, at least). But with the RVR, since it's measured at your runway (and often, right next to the touchdown zone of your runway), you're legal to fly the approach, since that much visibility "right here" means you have an excellent chance of seeing the approach lights at your DA.
Also, for all ILS approaches below Cat I mins (Special Cat I, Cat II, Cat III), only RVR matters.  The difference between each of those mins (1600 for Special Cat I, 1200 for Cat II, 600 for Cat III) are too fine to be captured by a "prevailing visibility" sensor.


Yes.  In fact, before GPS came along, if you were flying somewhere and wanted to use your VOR to get from A to B, that's exactly what you did a lot of the time if it was convenient; fly along the victor airways if they were more or less on your route.  IFR traffic is only separated from other IFR traffic and when VFR in non positive control airspace you can go wherever you want notwithstanding other restrictions.

In the GPS era nobody uses VORs very much any more and you can fly direct almost all the time when VFR (I haven't used the VOR in my plane in eons; mostly I just use a tablet or my phone), but there is nothing to stop you from flying along an airway if you feel like it.


What are the helicopter frequencies on the LA heli charts used for?

This is the frequency for the tower controller who is due to control inbound helicopters. You can see LAX 119.8, HHR 121.1 and LGB 120.5 frequencies noted. These are all frequencies used by the tower controller at these aerodromes.

At LAX, the class bravo transition will be issued by the tower controller on 119.8.


They are called drop tanks. When a drop tank is jettisoned, very likely it is not retrieved and reused. This is also the case with (sadly, discontinued) Space Shuttle external tank. Those tanks were not reused either. I am not talking about the rocket boosters.

What happens to jettisoned fuel tanks?

It depends on where they land. The tanks jettisoned in Vietnam have been used to make boats (more pictures here).

It is worth noting that these external fuel tanks have disadvantage too:

  A general rule is that only about half the capacity of a streamlined
  drop tank actually goes towards increasing the aircraft's overall
  range, the rest going to overcome the added drag and weight of the
  tank itself.


What do the terms "Landing Since New", FC, and FH mean on a Landing Gear RDAS?

Landing Since New - The definition is probably provided in Page 2 of the RAS.

This basically means the number of hours spent Landing from the time the aircraft was brand new . Based on this figure the blades will have to be removed.

FH - Flight Hours - Basic unit for measuring length of time in service/before maintenance becomes due. The flight hour (FH) represents one hour of flight

FC - Flight Cycles - One Take Off and Landing


How is the flow of air through a NACA submerged inlet determined?

The flow through the inlet is determined by the resistance of everything behind the inlet. If the inlet is blocked off internally, there is no flow and $v_i$ = zero.

The mass flow is indeed the way to determine through-flow: mass in = mass out. Which is a function of the pressure build-up (both in and out), cross section area (both in and out), temperatures, etc. A similar process occurs in a jet engine inlet.


On a 777 what would happen if the aft pressurization switch was accidentally left closed?

From my previous source in that incapacitation question:

  Two outflow valves are installed: one forward and one aft. Normally,
  most of the outflow is through the aft outflow valve. This improves
  ventilation and smoke removal. Cabin altitude and full ventilation
  rates can be maintained by either valve. Source


Center of Gravity and Center of Lift stability

If you ever read something along the line that "even the slightest" cause will result in "very bad changes" when before all was stable, you know that the writer was out of their depth. But you have come to the right place.
The way you formulate the question it concerns lateral stability. The combined center of all side forces (= lateral lift) should be behind the combined center of gravity of all components of the airplane to give it weathervane stability. Since the law of conservation of momentum applies also to a flying airplane, all movements should happen around its center of gravity, so all moments should be summed up there to see what effect they will have. In order to see their effect on stability, it is even better to focus on the force changes effected by a change in sideslip. If they produce a moment which will rotate the airplane away from that sideslip, the airplane is laterally stable.
Why only the changes in sideforce with sideslip? This will become more clear when we look at longitudinal stability, which is implied by the graphic in your question. Here the same principles apply, only that a constant downward acceleration is added, namely gravity. To compensate its weight, the airplane needs to produce an opposite force, namely lift. This lift has to act at the same longitudinal and lateral position of the center of gravity. Any deviation would produce a moment around that center of gravity which would start a rotation. In order to shift the center of lift to the desired location, the pilot will deflect control surfaces to modulate the lift force at the extreme ends of the airplane (tail rsp. canard and wingtips) so that any moment around the center of gravity disappears. This is one meaning of "trimming" the airplane (the other one means to remove all stick forces in order to stay at this state).
Theoretically, the pilot could balance the airplane in the desired state using the control surfaces like you can balance a broom on your fingertip. But that becomes tiring quickly. So it is preferable that the airplane itself will produce moments when the trimmed position is left, without any additional control deflections. This is achieved by having the changes in lift force act at a location behind the center of gravity.
The point where all lift forces can be summed up is the center of pressure, (Auftriebsmittelpunkt) whereas the point where all changes can be summed up is the neutral point (Neutralpunkt). Now you know what the author of the Wikipedia article wanted to say but failed to do so. He is by far not the only person to confuse those two points.
In fact, only when the center of lift coincides with the center of gravity will flight be straight and steady. All other positions will cause the airplane to rotate away from its current attitude. In order to return to its old state, only the neutral point needs to behind the center of gravity.


Why were rotary vane compressors never used in jet engines?

The most important characteristic for a jet engine compressor is high mass flow rate with light weight and if possible small size. For the same size, the flow rate can be increased by operating the compressor at higher rpm. But sliding components don't allow that.

Only the axial and centrifugal compressors can achieve sufficient flow rates, so they are used. Centrifugal compressors achieve higher pressure ratio for weight, but are larger, so they were used in many early designs and now remain in small turboprops while larger engines use axial compressors for their compactness.


How realistic is the aviation crisis in the recent Spider-Man movie?

This depends on the aircraft type, the flight rules and weather conditions as contributing factors.

Larger aircraft or medium sized aircraft operating under general aviation or commercial aviation will in many cases be equipped with a technology called Traffic Collision Avoidance System (TCAS) (See: How does TCAS work?), which can instruct both aircraft to take evasive action if a collision is imminent. This is especially important in Instrument Meteorological Conditions, where pilots do not rely on outside visibility, but on instrument flight only operating under Instrument Flight Rules.

In Visual Meteorological Conditions, aircraft would likely be able to see each other and take evasive manueouvers without ATC or TCAS having to warn them, e.g. this is the case for smaller aircraft operating under Visual Flight Rules.

Aircraft receive clearances and instructions to occupy a certain flight level or altitude, sometimes coupled with clearances for approaches or arrival/departure procedures. If pilots do not receive further instructions, they will start to hold over their last clearance limit and commence lost radio/comms procedures, which include holding for a given amount of time and then beginning the descent towards the airport on defined and published approaches. If the power outage is long enough, the airspace is quite busy and all other frequencies are also unavailable, one of the being the distress or guard frequency, there is a probability that two aircraft on the same level will reach their clearance limit at some point and enter a hold at the same flight level, which could result in a collision.

The scenario however assumes that really all failsafes and contingency procedures have failed.

See also ths related question: What happens when an airport shuts down?


When should the half bank mode of an autopilot be used?

Seems like the accepted practice is to use half rate when faster than 250 knots, in cruise, or when flying in icing conditions.

The AIM (5-10-3) also states that pilots should use half standard rate (through probably referring to hand-flying) when on final of a no-gyro approach like a PAR.

The rest of the time, in terminal areas and when holding, standard rate is expected by ATC. When unable to maintain standard rate (icing, for example) in those cases, notifying ATC should suffice.


How to calculate the airspeed for maximum specific range?

Check the units. Using $$W = 50000N$$ instead of $W=5099kg$ you get $$V=83m/s$$ (vs. $V=26.5\sqrt{m}$).


Is it possible to stall a plane so badly that the nose refuses to go down due to lack of airspeed?

Yes it's called a Deep Stall, and is mostly a problem with T Tail aircraft, especially jets with Supercritical Airfoil wings (like the CRJ Regional Jet line).

Such wings stall from the leading edge and the stall's flow separation spreads rapidly and completely across the entire wing all at once, so there is very little residual nose down pitching moment.  Plus the T tail ends up in a spot where it's in the wake of the flow from the wing, and gets blanked out, and loses its ability to pitch the nose over with positive lift since it's sitting there in the turbulent wake of the wing.

So the plane just mushes downward in an unrecoverable, stabilized, well, mush, and will pancake into the ground like that.  A CRJ200 test aircraft was lost in development testing when it got into a deep stall and IIRC, the stall/spin recovery parachute in the tail failed to deploy (or it didn't have one at the time; I forget which).

Such airplanes require, in addition to the usual stick shaker, a stick pusher to force the nose over, by shoving the control column for you if you do nothing while the shaker is going off, before the natural stall can occur, since the natural stall can be unrecoverable.  Generally if an airplane has a stick pusher system it means it has a deep stall mode.


What's the pattern of airflow over the airfoil at high angle of attack?

The question is about the boundary layer, which indeed stagnates and stops at high AoA, as shown for the laminar boundary layer in the picture. Then the airflow will detach from the upper surface, after the point where the boundary layer has stopped.

B. makes no sense to me, I'm only aware of one camber line.


Is there any reason to use only UTC standard time in aircraft and not GMT?

UTC is in principle the same as GMT.

But for accurate applications there is a difference:

  Saying "GMT" often implies either UTC or UT1 when used within informal or casual contexts. In technical contexts, usage of "GMT" is avoided; the unambiguous terminology "UTC" or "UT1" is preferred. Wikipedia

UTC: Is defined by atomic clock with corrections for leap seconds added manually.
UT1: Is defined by the Earth's rotation, hence is more susceptible for change and less easy to calculate than an atomic clock.

However the difference between the two is less than one second. It might matter for your $8000 \frac{\text{m}}{\text{s}}$ satellite or for your $300 \frac{\text{m}}{\text{s}}$ aircraft, but otherwise your can consider them equal for informal applications.


How is the transfer of an aircraft managed when it landed at a different airport than the scheduled one?

The aircraft will most probably be re-positioned to wherever it is needed. Often this will mean sending a crew to wherever the aircraft is and having them ferry it empty. If it is some far-flung place, the crew which landed it there may wait until it is possible to re-position it themselves.


If a pilot's plane suddenly and unintentionally becomes inverted, what is the pilot's best course of action?

What you are describing is Unusual Attitude Recovery (UAR) techniques, which are a standard part of the training for every Private Pilot1

Here is a good description of just such an event.

Almost all pilots do instinctively want to right the plane first, but as I'll explain below, this is a mistake, and the point of UAR training is to change the pilot's instinctive approach.

The actual biggest threat to a plane in an unexpected unusual attitude is speed.   If the plane has too much speed (above VA), sudden control movements can damage the airframe or even break apart the plane.

If the plane has too little speed (stalled or spinning), there may not be effective airflow over the wings and tail, and moving the controls may not do anything at all! (remember, control surfaces need a steady flow of air over them to be effective).

So the very first and most important step in UAR is to manage speed.  Upon recognizing that they are in an unknown and unusual attitude, the pilot's immediate action must be to look at the airspeed indicator:  If its too high (yellow-arc or above), pull the throttle to idle and let the speed come down.  If its too low (white-arc or below), immediately add full throttle and let the speed come back up.

Once the airspeed is anywhere in the green-arc (and precision is not terribly important here, just a manageable speed), then the next steps are to return the plane to roughly level (+/- 10° of pitch), and roll the wings level.

1 I'm unsure if Recreational Pilots and Sport Pilots also get UAR training.


Can I shoot any approach at an uncontrolled airport in VMC without any clearance?

You would have to cancel your IFR flight plan with ATC, fly the duration of the flight and the approach by VFR, but, yes, you could.

Many people fly practice approaches at untowered airports by announcing their intentions over the CTAF.  This can be difficult to do at beehive airports with a lot of GA traffic going into and out of them, but it’s possible.  I’ve done it plenty of time without incident.


If I get my Private Pilots License before college, how far will that set me ahead, if at all?

Well, since you want to go to Purdue specifically, a good place to start would be the Purdue Professional Flight website.  I found this there:

FAQ: Students Coming to School with a Private Pilot’s Certificate. Is there an advantage?

Depending on each individual situation, a student coming in with their Private Pilot’s Certificate can be either an advantage or disadvantage. The only real difference is cost. Sometimes it is more cost efficient for a student to get their certificate from Purdue or an outside flight school. It is ultimately up to the student.


What is the standard power supply and voltage supply on modern airliners?

Typically 115 VAC, 400 Hz for most large aircraft, which can be rectified and stepped down for DC powered subsystems.  Smaller GA airplanes typically use 12, 14 or 28 VDC for their electrical systems.


According to their website, they will start commercial flights using the 737 MAX on 29 December, but will be testing their aircraft on non-commercial flights before than:

We’ll begin with non-commercial flights in early December 2020 before the official return of the 737 MAX. On December 29, we’ll resume scheduled service with 2 flights a day (1 round trip) through January 4, 2021, from Miami (MIA) to New York LaGuardia (LGA). We expect to phase more of the aircraft into our schedule through January, with up to 36 departures from Miami.

(aa.com, emphasis mine)


Is the route which takes the least time always the one with least fuel-burn?

Generally, the least time in the air the better, but it's mostly a maximum miles per gallon over the earth thing and this depends on winds.  In the time/fuel burn equation, there is always a "sweet spot", a speed/power configuration that gives the most miles per gallon for "air distance" traveled, but how this translates to a maximum distance covered for a given amount of fuel depends on the headwind/tailwind component.

If headwinds are strong, the most efficient speed may be faster than what is optimal for winds that are light or there is a tailwind.  It's easy to see if you take it to the extreme; imagine you are in an airplane that cruises most efficiently at 50 mph and can go 80 mph.  Most miles per gallon air distance is at 50, but if you have a 50 mph headwind, you aren't going anywhere are you, and your actual miles per gallon is 0.   Dial that ridiculous example back to something more reasonable and you can see that there are subtle variations with winds that have to be taken into account.

Generally speaking if there is nil wind or a tail wind, you would fly at the most efficient miles per gallon speed but with a really strong tailwind it might be better to slow down even more for best earth miles per gallon.  If there is a headwind, the optimal speed might be little faster than the max air miles per gallon speed to use the least fuel to get there.

There was an incident once where an RJ crew had to do an IFR diversion with the flaps stuck at 45 degrees and the crew had to decide what speed to fly at, limited to flap extension speed and with all that drag, taking into account whatever headwind/tailwind they had.  They landed at their alternate with 500 lbs on board, about 10 minutes worth.  Talk about pressure to get your calculations right...


Is it possible to accurately measure airspeed without pitot tube?

Technically speaking, inertial measurements are not sufficient to derive airspeed. You need pressure measurement (or airspeed measurement, see LIDAR).  Pitot-static probes are the most usual and conventional devices to measure pressure.

However, several researches have been conducted, to replace pitot-static tubes with different technologies. These technologies are mainly based on measuring surface pressure on a part of the fuselage. Of course the measurements (not a single value but several values from various locations) have to be calibrated via flight tests.

With the current popularity of machine learning I think the calibration algorithms will not be the main problem.

Some other technology being investigated

there's also ongoing research and trials about using LIDAR to
directly measure airspeed. Which won't need pressure measurement.
ultrasonic devices are also able to measure airspeed directly,
however their real flight usage is unknown (to the author).


How can an airliner have low altitude stall recovery?

The most important reason for aircraft stalls is due to high angle of of attack, which causes flow separation.

Usual stall recovery procedures consist of reducing the aircraft angle of attack (pitch angle) and increasing power so that the stalled wing starts producing lift and the aircraft forward speed is increased to the required amount. Then the controls are applied in such a way to return to level flight as soon as possible.

The problem with low altitude stall is that stall recovery usually involves some loss of altitude and if the altitude is low enough, recovery from stall may not be possible before contact with ground.

However,the recovery altitude may be decreased to a certain extent by incorporating the following technologies in civil aircraft.

Use of high lift devices- Use of high lift devices like slats and flaps increases the lift coefficient and also delays the onset of stall. In case the slats have not been deployed before stall, they can be deployed to get the airfoil (wing) produce lift again.

Source: zenithair.com

Increasing the power- In general, greater the power applied, the less the loss of altitude. In this case, the engines usually have excess emergency power that can be applied for reducing the loss of altitude.

In general, it is better not to enter into a stall and most of the technologies are geared up towards prevention of stall than recovery due to a number of reasons

In case of civil aircraft, below a certain altitude, stall recovery is usually not possible.
Addition of systems to ensure a soft landing in case of stall increases the cost and complexity and in any case may be impracticable in case of large aircraft. As such, it is better to train the pilots to prevent entering into a stall in first place.


Why are the MSA direction needles not oriented to north?

The arrows are referencing the nav cues, not the VORTAC radials, which define the MSA zones.  It’s cut up that way to define the sectors relative to the reference point that you will be flying in e.g. for the second from left MSA symbol, if you’re flying southeast of the HQM VORTAC between a course heading of 230° TO and 350° TO the VORTAC, this is an acceptable MSA for that segment.  I suspect that choice was made because aircrews are going to be approaching the airport from these areas as opposed to departing and their HSIs, OBSs, RMIs, etc are going to be set to track TO the NAVAID at that point.


What is the name of the system that replaced stairs for disembarking aircraft?

(throughouthistory.com)

Shown above is a telescopic corridor at London Gatwick airport c. 1930's (I had to make it interesting).

For today's system, the name you are looking for is jet bridge. It's also known by other names. There is also a rarer system called mobile lounge.