Did CNN correctly state that AirAsia flight stalled and crashed?

An aerodynamic stall is exactly that: the wing is stalled and is not generating enough lift to keep the aircraft in the sky. The aircraft is falling out of the sky. Whether the stall can be recovered from, and therefore the aircraft can stop falling out of the sky, is an entirely different question.
Some stalls can be recovered from, others cannot... particularly if whatever caused the stall is preventing recovery.

An aerodynamic surface which is stalled is no longer generating significant lift. Most specifically it's not generating enough lift to support the aircraft
An object which is not generating sufficient lift to keep it airborne, and is being pulled towards the earth by gravity, is falling

So yes, CNN is correct - the plane fell out of the sky while stalled. Generally a plane which is at 36,000 ft and is not falling out of the sky, doesn't hit the ground.
As Falstro mentioned in his comment, AF447 didn't realise it was in a stall at all, so therefore couldn't remove it. We don't really have enough information about the AirAsia flight to be sure what happened


Do I have to declare an emergency if I cut into fuel reserves?

There seems to be no regulations that require decleration of emergency in case of using reserve fuel. US DoT InFO 8004 specifically discusses this:

  Emergency Fuel. Although not defined in the AIM or Federal aviation regulations, the  industry-wide connotation typically associated with the
  term “Fuel Emergency” is:

  The point at which, in the judgment of the pilot-in-command, it is necessary to proceed directly to the airport of in tended landing due to low fuel. Declaration of a fuel emergency is an explicit statement that priority handling by ATC is both required and expected.

Noting that pilot declaring minimum fuel is not an emergency,

  The act of using a portion of the reserve fuel assigned to a flight is not,  in its self a cause to declare a minimum fuel state with the controlling agency. Regulations require reserve fuel to enable aircraft to maneuver, due to unforeseen circumstances. Many aircraft safely arrive at their destination having used a portion of the fuel designated as reserve. There is no regulatory definition as to when, specifically, a pilot must  declare “minimum fuel” or a fuel emergency. Air carriers typically develop such guidance for their pilots and include it in their General Operations
  Manuals; such guidance generally  falls along the following lines:

  •Declare “minimum fuel” when, in your best judgment, any additional delay will cause you to burn into your reserve fuel.

  •Declare a fuel emergency at the point at which, in your judgment, it is necessary for you to proceed directly to the airport at which you intend to land. Declaration of a fuel emergency is an explicit statement that priority handling by ATC is necessary and expected.

(Emphasis mine)


Was my latest Air Berlin flight in violation of some in-flight procedures?

The safety pin is in its stowage position - ie. where it is supposed to be stored when not in use, as you can see in this video. The red streamer is usually tucked away out of sight, but some airlines seem to leave it visible. Also, it appears from your photo that the arming handle is over to the right, ie. in the 'armed' position, as it should be in flight.

The Door Locking Indication is green-lettering-on-black for LOCKED, as you can see at 0:28 in this video, or red-lettering-on-black for UNLOCKED. But that lettering may not be very evident unless you are quite close to the door and looking almost directly at the indicator.

As far as I am aware, the Cabin Pressurized light is not normally illuminated in flight - it flashes red if-and-only-if the door handle is moved towards the OPEN position AND the cabin is pressurized, as you can see at 1:04 in this video.


How similar/different are the roles performed by Military and Civil pilots?

The biggest difference is that most everything in commercial aviation is considered administrative in the military.  The tactical employment of our aircraft, the non-administrative portions of flight, is what separates military sorties from commercial flights.  This emphasis on tactical flying has also led to significantly different cultures between commercial and military aviation.  There isn't a commercial pilot I would stand a chance against in a game of FAR/AIM trivia, but I also doubt they'd fare much better if the tables were turned and the questions were related to carrier operations.  We are two separate organizations with two unique mindsets to flying.


There is not an obvious answer to this. I'll outline three effects (among others):

Placement of thrust line. If the thrust line is placed below the CG, it will have a destabilizing effect; the converse is true. That's why wing mounted engines tend to destabilize aircraft as throttles are increased. But that's not the title of your question.
The local increase in flow from prop wash increases the wing lift slope. This tends to decrease the pitch stability. An increase in lift has an associated increase in downwash as a function of AOA. This also tends to decrease stability.
The local increase in flow from prop wash increases the tail lift slope. This tends to increase the pitch stability.

The neutral point contribution is as follows (cited from Etkins, Dynamics of Flight):

$$h_n=h_{n_{wb}}+\frac{a_t}{a}\overline{V_H}(1-\frac{\partial\epsilon}{\partial\alpha})-\frac{1}{a}\frac{\partial C_{m_p}}{\partial\alpha}$$

where $h_n$ is the location of neutral point, $h_{n_{wb}}$ is the wingbody aerodynamic center (AC), $\overline{V_H}$ is the tail volume with respect to the wingbody AC, $a_t$ is tail lift slope, $a$ is the total aircraft lift slope, $\epsilon$ is downwash on the tail, $C_{m_p}$ is the pitch moment contribution from thrust.

Forget about thrust line for a moment, then we have:

$$h_n=h_{n_{wb}}+\frac{a_t}{a}\overline{V_H}(1-\frac{\partial\epsilon}{\partial\alpha})$$

Therefore, increasing the wing lift slope decreases the neutral point, as will an increase in downwash. Increasing the tail lift slope has the opposite effect.

So there is no blanket statement.


How are in-air refuelling craft grounded to each other?

The metal of the tanker's boom (or drogue) contacts the metal of the receiver's receptacle (or probe) first, and that contact is maintained, so that would serve to ground the two aircraft to each other.

It's a good question, but I've never heard of any fuel explosions due to static buildup during air-to-air refueling, so evidently the systems in place alleviate the risks.  Aerial refueling is pretty routine these days, so in relative terms it would seem to be fairly safe.

Purging the fuel lines is a relative term; you could remove the liquid fuel from the lines, but you'd still have vapors, and those are more flammable than the liquid jet fuel itself.  Maybe somebody who flew (or flies) tankers can discuss how far down the boom the fuel goes BEFORE everything is connected and they start pumping; as a receiver I just remember that the fuel flowed into the manifold and then into the tanks.  We didn't do anything special to clear the manifold or fuel lines on our end.

There ARE some inherent risks when refueling between two aircraft flying in close formation that are accepted (i.e. the risk level is okay for the military mission, but nobody does it for commercial airliners), but I don't think this is one of them.


Why are early wing planforms mostly rectangular?

The benefit of tapered wing lies in its proximity to the elliptical lift distribution while retaining much of the structural benefit of a rectangular wing. But we owe this knowledge to a few things:

The Kutta-Joukowski Theorem: published in 1906 by Nikolai Y. Joukowski and influenced a great deal by Martin W. Kutta.
The Lifting Line Theory: published in 1919 by Ludwig Prandtl and inspired by the work of Frederick Lanchester. The term induced drag was coined by Max Munk, a colleague of Prandtl in 1918. Although Lanchester had published some results on aspect ratio and finite-wing aerodynamics as early as 1907, they weren't taken seriously by his compatriots and had very little impact as a result.

The Wright Flyer flew in 1903. By all accounts, the Wright brothers designed it through trial and error. As a result, the insight of tapered wing couldn't have been known to them during the Flyer's design and through much of the First World War.

In any case, most of the early airplanes were bi/triplanes with external struts being their structural members. The drag from the struts would've overwhelmed any benefit gained from tapered wings.


Does Rolls Royce produce any engine that matches the capabilities of the GE9x?

First let's talk about thrust.  Jet engines are designed for very specific thrusts for every specific applications.  For example, look at the GEnx-1B versus the GEnx-2B.  The Boeing 787-8 has GEnx-1B engines rated for ~70k lbf takeoff thrust.  At about the same time as Boeing was developing 787-8, it was also developing the 747-8.  That plane needed slightly less thrust per engine, about 5% less. Boeing could have just put the GEnx-1B on that plane.  But they didn't. Instead they had GE develop the GEnx-2B, rated for 66.5k lbf thrust.  They did that because an engine that had five percent too much thrust was a completely unfeasible option.  The GEnx-2B is smaller and several hundred pounds lighter.  So my point here is that RR is never going to develop an engine the size of the GE9X unless they have a very specific contract for a plane that needs exactly that much thrust.  Every engine RR makes is going to be sized exactly as big as it needs to be and no bigger.

RR certainly could make an engine that big if they had a contract to do so.  If you know how to make an engine that produces 70klbf of thrust, you know how to make an engine that produces 100 klbf of thrust.  Just make everything a little bit bigger. Turbomachinery is not perfectly scaleable, so just because you know how to make an engine with 100 lbf of thrust does not mean you know how to make an engine with 100,000 lbf of thrust.  But from 70k to 100k is not a big leap. Definitely within their capability.

As for everything else, I'd say just look at the market share. There's some interesting statistics here.  http://www.alafco-kw.com/upload/Media_Library__March_2016____Aircraft_Market_Report__March_2016__921.pdf

For example: RR has 59% of the A330 market, a plane on which there are 3 different engine options available (GE, RR, P&W).  RR is certainly behind GE on the 787, but not by a lot.  And RR has an exclusive contract on the A350.  Overall RR is competitive in the market versus the other manufacturers. If RR was "losing out in the technological advancement", you would see this reflected in their market share, but this is not what is happening.


What is the lightest weight operational jet/turboprop fighter ever deployed in combat?

The A-37 Dragonfly is the smallest production combat aircraft I'm aware of.

Empty weight of  6,211 lb (2,817 kg). Max takeoff weight of 14,000 lb (6,350 kg).


If unable to procure Helium, are there any regulations against filling lighter than air craft with Hydrogen instead?

The Hindenburg utilized aluminum flake in a nitrocellulose impregnated fabric.  Materials have improved since then.

In the case of He, diffusion is inhibited by polar surfaces.  For the He to diffuse through the membrane in a balloon, it has to disolve into the fabric layers prior to a barrier such as aluminum. I understand that lithium and beryllium foils have higher impermeability.

In the case of He, poly(ethylene terephthalate) is a reasonable barrier, and PET is commonly available in films (and soda bottles).  It is rather polar, and serves to reduce solubility.

H is a different bird, in that it has low polarity, and different materials will aid in reduction of solubility. Butadiene-acrylonitride co-polymers have low polarity and may perform better with a low polarity gas such as H2.

The gas envelope questions are really materials science questions, and require a fair understanding of not only the mechanical properties, but even more so of the permeability, solubility and diffusivity of the copolymer you might consider.

The legality of using H2 rather than He2 may not be an issue, but even if it were, I am sure that waivers are possible.

A quick check of regs on gas balloons indicates that hydrogen may be used if the aircraft manufacturer approves the gas.  So it appears there is no hard regulatory bar.

Checking with a source at NWS, who indicates their balloons are launched with H2.


Has there ever been a tail-dragger with retractable tail-gear?

Yes, there are. The Boeing B-17 FLying Fortress is one example of an aircraft designed with a retractable tailwheel.

Source: USAAF via Wikimedia, Public Domain (USGOV-PD)

Another example would be the Vought F4U Corsair:

Source: Wikimedia, cc-by-sa-2.0

Doubtless there are also other examples of aircraft similarly equipped with retractable tailwheels.


Is it possible for squawk to change automatically in emergency situations?

Whether or not an airlines is in an emergency situation is not a black or white question. There are millions of different internal and external factors that come into play, any combination of which may or may not be considered an emergency. No computer can be programmed to accurately and consistently calculate whether or not a flight is having an emergency situation - in fact, that's one of the main reasons we still have real, live pilots seated up front.

Could you program a computer to detect a few obvious emergencies (total loss of power, rapid decompression, fire etc.)? Sure. But it wouldn't be able to detect everything.

What's more, setting squawk 7700 is not always the best cause of action in an emergency. In fact, most of the time a flight will already be in contact with ATC and have an assigned discreet transponder code - in such a situation, setting squawk 7700 will often have little or no effect, since you can talk directly to ATC on the radio and explain what's going on. You might even risk ATC losing identification if you start changing your squawk code out of the blue, which could add additional risk. In other cases, squawking 7700 can be beneficial, for example if you are not talking to ATC - or maybe the frequency is very busy and you can't get through - or maybe you don't have time to call ATC, but still need their attention (rapid decompression). ATC might also request that you squawk 7700, to reduce workload on their end.

So to summarize, no, a computer would not be able to necessarily detect when a flight is having an emergency situation. And even if it could, setting squawk 7700 might not even be useful.


Why do countries place limits on what foreign-registered aircraft can do?

Perhaps the biggest reason for this is that countries have different standards of safety.
One example, is a few years ago, Cessna recommended that basically all their piston aircraft have a thorough maintenance inspection known as a SID once they reach 20 years of age. The FAA didn't feel that these inspections justified the fairly considerable cost. Other countries though - Australia, NZ, Germany come to mind - felt the manufacturer knows best, and made the inspections mandatory.
This is just one example of the broader problem of differing standards throughout the world. When an aircraft gains Israeli registration, it must comply with all local laws and airworthiness directives, giving authorities confidence that their standards are being met. Being locally registered also makes it easier to track movements and to target inspections. There could also be tax implications too, as it would become a local asset.


Is the FAA Medical Exam an IRS Medical Expense?

If you're asking whether you can pay for one with an HSA or FSA, then yes, physical exams are eligible expenses, though consult with your insurance provider first if they are covered by your plan.

Physical Examination
You can include in medical expenses the amount you pay for an annual physical examination and diagnostic tests by a physician. You do not have to be ill at the time of the examination.

If you're looking to add it to a list of itemized deductions, as Pondlife explained, it generally has to be business- or workplace related.  If you are a professional pilot, then this is deductible.

What Can I Deduct?
To be deductible, a business expense must be both ordinary and necessary. An ordinary expense is one that is common and accepted in your industry. A necessary expense is one that is helpful and appropriate for your trade or business. An expense does not have to be indispensable to be considered necessary.


How do we find the breaking point of an old braced wing?

Not sure what you mean by "old braced wing", the Spitfires were full cantilever wings from the first prototype 300. From this link:

This link references the original Spitfire specification (without any further references to them):

5 Structural Strength
(a) The strength of the main structure when carrying the load specified in paragraph 3, plus 100 lb shall not be less than as specified hereunder ——
Load factor throughout the structure with the centre of pressure in its most forward position 9.0.
Load factor for wing structure with the centre of pressure in its most backward position in horizontal flight 6.0
Load factor in terminal nose dive 1.75
Inverted Flight
(1) Load factor at incidence corresponding to the inverted stall and with C.P. at 1/3 of chord 4.5
(2) Load factor at incidence appropriate to steady horizontal inverted flight and at the maximum speed of horizontal normal flight 4.5

Most WWII planes still flying are not stretched to the limit regarding g's, to keep exceed the fatigue life. I doubt any current owner would like to test what load the wings are up to at present.


You might be referring to LAPA Flight 3142 (Episode 9 of Season 17). An alarm sounded during takeoff because the flaps were not set, but the pilots ignored the warnings. The aircraft failed to lift off the ground and crashed at the end of the runway.

If that's not the one, this list on Wikipedia should help you locate the episode.


What is the purpose of the 787 engines extending on landing?

Those are the thrust reversers, which cause the engines to produce thrust "backwards" to help slow the aircraft during the landing.

You can see a close-up video of 787 thrust reversers in operation, including a look at the panels at the back of the engine which block the normal flow of air.

We also have a question How do thrust reversers work on a jet engine, and when should they be used?, which describes their operation in general.


How is it possible for the MIG 21 to have full rudder to the left, but the nose wheel move freely to the right and then straight or to the left?

Davidw mentioned the book "Red Eagles".  It has a passage about steering the MiG-17 and says the MiG-21 used exactly the same system.  In the following passage, he is quoting pilot Jose Oberle.
Red Eagles: America's Secret MiGs, Steve Davies, 2011

Taxiing the airplanes was a bit of a trick.  If you wanted to turn
right, you pushed the left [sic][a] rudder bar in and you pulsed this lever on
the control stick.  That dumped the pneumatic pressure to the brake
on the left wheel and transferred it to the right wheel.   You would
get the free-swinging nose wheel to start to turn to the right, and
then as you got ready to come out of that turn you'd have to push the
left rudder bar past neutral and you'd have to start pumping the
little paddle again to get the power back on the left wheel, to get
the nose to straighten out so you could taxi straight!

Per this, the nosewheel is not part of the steering system.
a: most definitely a typo, see for instance the following pilot's experience.
I Was Lucky: I Got to Be a Pilot, Paul "PK" Kimminau, 2017, p. 161

After checking the systems out, I taxied to the runway. That was an
experience in itself!! On US aircraft, the brakes are on the rudder
pedals, that is, you push on the tops which would rotate forward and
apply braking. Also on US aircraft, if you wanted to turn, you pushed
the rudder pedal just as if you were using rudder to fly the aircraft
and power steering would turn the nose wheel. On the MiG-17, the
braking was done with a lever on the control stick. You squeezed it
and applied brakes. If you wanted to turn, you pushed the rudder pedal
in and squeezed the brake lever, and it would apply braking to that
wheel so you turned in that direction.


How well does a composite fuselage deal with lightning?

Lightning striking modern aircraft with composite structures

  Composite parts that are in lightning-strike prone areas must have appropriate lightning protection. [...] Composite structures are less conductive than metal, causing higher voltages.
  Lightning protection on airplanes may include wire bundle shields, ground straps, composite structure expanded foils, wire mesh, aluminum flame spray coating, embedded metallic wire, metallic picture frames, diverter strips, metallic foil liners, coated glass fabric, and bonded aluminum foil.
  Lightning can also damage composite airplane structures if protection finish is not applied, properly designed, or adequate. This damage is often in the form of burnt paint, damaged fiber, and composite layer removal.

  Source: "Lightning Strikes: Protection, Inspection, and Repair", Boeing, 2012

New technology improving the lightning protection of modern aircraft

  Traditional methods to protect composite aircraft from lightning strike damage rely on a conductive layer embedded on or within the surface of the aircraft composite skin. This method is effective at preventing major direct effect damage and minimizes indirect effects to aircraft systems from lightning strike attachment, but provides no additional benefit for the added parasitic weight from the conductive layer. [...]
  A new multi-functional lightning strike protection (LSP) method has been developed to provide aircraft lightning strike protection, damage detection and diagnosis for composite aircraft surfaces.
  The method incorporates a SansEC sensor array on the aircraft exterior surfaces forming a "Smart skin" surface for aircraft lightning zones certified to withstand strikes up to 100kA peak current. SansEC sensors are open-circuit devices comprised of conductive trace spiral patterns sans (without) electrical connections. The SansEC sensor is an electromagnetic resonator having specific resonant parameters (frequency, amplitude, bandwidth & phase) which when electromagnetically coupled with a composite substrate will indicate the electrical impedance of the composite through a change in its resonant response. Any measureable shift in the resonant characteristics can be an indication of damage to the composite caused by a lightning strike or from other means. The SansEC sensor method is intended to diagnose damage for both in-situ health monitoring or ground inspections. [...]
  The SansEC sensor smart skin technology provides lightning strike protection, shielding effectiveness, and opportunity to achieve in-situ damage detection and diagnostics for aerospace composite structures along with other potential beneficial functions not available from the standard LSP method.

  Source: Szatkowski, G. N. at al.: "Open Circuit Resonant (SansEC) Sensor Technology for Lightning Mitigation and Damage Detection and Diagnosis for Composite Aircraft Applications", NASA, 2014 - Download Link

Further information can be found on the internet, see for example "Playing with Lightning in the Name of Aircraft Safety", NASA.

See also this similar question.


How should operations be conducted at a towered airport that is in uncontrolled airspace?

Airport with an operating control tower = talk to it.

From the regulations:

§91.126(d) (concerns Class G) and §91.127(c) (concerns Class E) are identical.

  Communications with control towers. Unless otherwise authorized or required by ATC, no person may operate an aircraft to, from, through, or on an airport having an operational control tower unless two-way radio communications are maintained between that aircraft and the control tower. Communications must be established prior to 4 nautical miles from the airport, up to and including 2,500 feet AGL. However, if the aircraft radio fails in flight, the pilot in command may operate that aircraft and land if weather conditions are at or above basic VFR weather minimums, visual contact with the tower is maintained, and a clearance to land is received. If the aircraft radio fails while in flight under IFR, the pilot must comply with §91.185.


What would happen if an airplane flew through a tornado?

It depends on the strength of the tornado and other variables, but in most cases, a plane Vs tornado will end very very badly for the aircraft and its occupants in a low altitude high speed scenario.
A good example would be the NLM CityHopper Flight 431, a Fokker F-28 that flew into a thunderstorm 8 minutes into takeoff and crashed after the wing was torn off. From the summary of accident report at aviationsafety.net:

At 17:12 the aircraft entered a tornado, which resulted in loads on the airframe increasing to +6.8 G and -3,2 G. The right wing was bent upwards followed by a severe downward sweep. This compromised the structural integrity of the wing, causing a large portion of the outer wing to separate in an upward and rearward motion. Control was lost and the aircraft impacted a railway bridge inverted.

Everyone abroad the aircraft perished. FAA is pretty blunt about flying near one:

Pilots should observe the following rules for any flight routed even potentially near actual or possible thunderstorm activity:
• Avoid all thunderstorms.

And also,

Although pilots have flown through limited state thunderstorms with little or no damage to the aircraft or passengers, these pilots should consider themselves extremely fortunate to be alive.

(emphasis original).
Note: I've used both thunderstorms and tornadoes here. weather.about.com defines them as:

Thunderstorm: A storm (produced by a cumulonimbus cloud) that includes rain showers, lightning, and thunder.
Tornado: A violently rotating column of air that extends down from the base of a thunderstorm to the ground.


What is this US Navy airplane seen at Westover AFB?


Are there certification requirements on Dual Inputs?

Here's what EASA Certification Specifications for Large Aeroplanes CS-25 says about design for dual controls:

  CS 25.399
  Dual control system

  (a) Each dual control system must be designed for the pilots operating in opposition, using individual pilot forces not less than –

  (1) 0·75 times those obtained under CS 25.395; or

  (2) The minimum forces specified in CS 25.397 (c).

  (b) The control system must be designed for pilot forces applied in the same direction, using individual pilot forces not less than 0·75 times those obtained under CS 25.395.

And in many places the requirements state that it must be demonstrated

  ...that exceptional skill is not required to control the aeroplane

The A320 complies. It is designed for control of one pilot at a time, like all other aeroplanes. There is no requirement for a dual control system to be mechanically linked. The B737 columns and wheels can be uncoupled after an elevator or aileron jams, the remaining control provides input on top of that of the jammed circuit.


What additional US-power or ICAO requirements apply to a departing US-based crew with a US-registered aircraft flying to land in Mexico?

The only aviation-related requirements on crossing the US border are:

All flights crossing the US's Air Defense Identification Zone (ADIZ) in either direction must be on an IFR or DVFR flight plan, talking to ATC and have a discrete transponder code.
A list of all passengers and crew must be filed with eAPIS at least 24 hours before crossing, in either direction, and the plane must have an eAPIS decal.

The only difference between leaving vs entering that I'm aware of is that you don't need to leave from a designated port of entry. (Some other countries do require that.)

As a practical matter, there are a handful of aviation-related things that apply to most/all other countries that US pilots don't have to worry about in the US:

The pilot(s) must have ICAO-recognized license(s). FAA Student, Sport and Recreational licenses are not.
The pilot(s) must have appropriate medical certificate(s). No BasicMed.
The aircraft must have a normal airworthiness certificate. No experimental aircraft.
The aircraft and at least one pilot must have FCC radio licenses.

Technically, you don't need passports to leave, but you'll need them to go anywhere else (and to return) by air, so they are effectively required for both.

There are thousands of other laws that apply to all people or goods leaving the US regardless of mode, such as not exporting restricted technology or weapons, human trafficking, fleeing prosecution, etc.  (And there are even more for entering.)  I doubt anyone could list them all, and that is probably off-topic anyway.


Numerous questions regarding ARINC429 protocol

Resolutions in the A429 spec are approximate, so calculate them yourself.

Resolution = Range / (2^significant bits)

Here is one way to do it:
Load your 32 bits into a signed 32-bit integer.
Shift left 3 so the sign bit is now in bit 32.
Shift right (32-significant bits)-1 to form a 2's complement "fixed-point" number.
Convert to float and multiply by the resolution.
Done.

Note that when a signed integer is used the high bit is sign extended on the shift right.

"Fixed-point" is also known as "scaled" in some circles. It's a method of storing and performing math on a real number using an integer rather than using a float. The resolution is the weight of one lsb bit. The resolution is documented somewhere and multiplied by the integer to get the float when debugging and such, but machine code does not "know" that you think of it as a float.

The range is key to fixed -point numbers because it bounds the value. The number of significant bits affects the accuracy. You could use the wrong number of significant bits and still get a "usable"  number but with a possible loss of accuracy if you choose one that is too small. Beware that unused low bits are sometimes repurposed for status flags, etc., so don't expect these to alway be zero. Also, the specs describes an ideal standard but in the real world liberties are taken with labels repurposed as needed.

Because of the way 2's complement integers work, the max positive value possible will be the range minus the resolution. For instance, you can get exactly -180 degrees but not quite +180 degrees.


Why does the Eurofighter Typhoon pitch up on brake release?

When the brakes are on, they apply a backwards force that counters the engine thrust. This force is applied at ground level, and the engine thrust is higher. These two forces result in a moment that forces the nose down, compressing the nose gear slightly.

When the brakes are released, the moment disappears and the nose gear extends.

Another factor here is that the Eurofighter (and F-16) has its air-intake under the fuselage, which forces the designer to put the nose gear behind the intake, closer to the main wheels than other aircraft. That means the nose gear has a shorter lever-arm to resist pitching. It's set up with the same spring rates and damping because it's primary job is to react to bumps in the ground, so it's more sensitive to pitching.


Which operating systems do entertainment systems run on?

According to this article, Linux is at least one of the main contenders in the space, Wikipedia also makes a lose reference to Linux and cites this article as the source. Here is some photographic evidence that its Linux as well. Although I'm sure it varies by maker it seems that Linux is at least one of the main players.


Why do jet engines get better fuel efficiency at high altitudes?

For a quick explanation, you need to know that

Thrust is the difference between the entry impulse of the air entering the engine and the exit impulse of the heated fuel-air mixture leaving the engine. Impulse is mass times velocity, and expressed with a mass flow $\dot m$, thrust T is $$T = \dot m \cdot (v_{exit} - v_{entry})$$
The exit impulse is increased by accelerating the airflow through the engine, and the acceleration is achieved by heating the air.
Each gram of fuel heats up a given mass of air by a certain number of centigrades. The definition of the energy content of fuels is given as the capacity to heat one pound of water by one degree Fahrenheit. The definition of one Calorie is similar but in metric units. Since the heat capacity of both water and air are almost constant at moderate temperatures, the starting temperature makes little difference to the absolute temperature increase when a given amount of energy is added.

Thermal efficiency

Thermal efficiency is the ratio between the mechanical work extracted as thrust and the heat energy spent on heating the air, and it is affected indirectly by the flight altitude. Please see the Wikipedia article on the Carnot cycle. This and similar cycles describe the workings of all combustion engines in thermodynamic terms. Basically, it says that the efficiency of a combustion engine cannot be greater than the temperature ratio between the temperature increase from ambient ($t_{amb}$) to the maximum temperature $t_{max}$ of the process, divided by the maximum temperature. All temperatures must be expressed as total temperatures, where 0° means 0 K or -273.15°C. Operating in colder air makes the ratio bigger and improves efficiency.
$$\eta_t = \frac{t_{max} - t_{amb}}{t_{max}} $$

If $t_{amb}$ is 290 K (16.85°C or 62°F) and the fuel heats up the air to 1400 K (2060°F), the thermal efficiency according to the formula above is 79.3%.

At cruise altitude $t_{amb}$ is only 220 K (-53.15°C or -63.7°F), and the same fuel flow relative to air flow will lift the maximum temperature only to 1320 K (in reality even less; for more precise reasoning see below). Now the thermal efficiency is 83.33%! If the maximum temperature is maintained, both thrust and thermal efficiency will go up; the latter to 84.3%.

In reality, the total efficiency will be lower because we have not included propulsive efficiency, friction effects or power offtake by bleed air, pumps and generators. Propulsive efficiency describes how well the acceleration of air is performed.

Heating the fuel-air mixture

Burning a fuel-air mixture will add thermal energy to it, about 43 MJ for every kilogram of kerosene (if we assume complete combustion). The isobaric heat capacity or specific heat of air (close enough, the mixture has very little fuel but lots of air in it) is 29 J per mol and per K, so those 43 MJ will heat 1000 mol of air by 1483 K. The heat capacity changes slightly with humidity and temperature, but little enough that we can consider it constant for this purpose. If the air starts at 220 K, precompression in the intake will heat it to approx. 232 K, further compression in the engine will heat it up to approx. 600 K if we assume a compression ratio of 25, and this is the temperature at the entry of the combustion chamber.

Those 1000 mol of air weigh about 29 kg, and adding a full kilo of fuel and burning the mixture will heat it to 2083 K. If you want more details about the parameters in a typical jet engine, please see the diagram in this answer. Since the mixture picks up speed as it burns, the fuel mass is also heated and combustion is never complete, the maximum temperature given here will not be reached in reality.

If we start on the ground with an air temperature of 290 K, the temperature in the intake would drop slightly because we will not be flying fast enough for any precompression to happen in the intake. Now the compressor will heat the air to 730 K, and again adding and burning that kilo of kerosene will heat 1000 mol of air to 2213 K. Ideally.

In reality, the engine control will see that the limit temperatures are not exceeded, but here we can play with the numbers as we like. The exact values will certainly be slightly different (more frictional heating in the compressor, heat loss to the outside, slight drift in specific heat with temperature), but the gist of the explanation is correct.

Explanation in layman's terms

Burning the fuel-air mixture heats it and makes the gas expand. This happens at nearly constant pressure and in a restricted volume, so the only way to make room for this expansion is for the gas to flow faster. Nearly constant pressure means that the density of the gas must decrease. The density ratio between the heated and the unburnt gas is proportional to its temperature ratio, measured in absolute temperature.

However, the amount of fuel burnt determines the absolute temperature increase, the difference in degrees between the burnt gas inside the combustion chamber and the unburnt gas at the intake. For a given amount of fuel, the temperature ratio which can be achieved with an absolute temperature increase becomes smaller the higher the temperature of the unburnt gas is. Thus, efficiency decreases with a higher temperature of the intake air.


What are outer marker horizontal dimensions at 3 degrees ILS path?

As Ron Beyer commented, it's more of a flat ellipsoid (egg), not a cone.

Full Image

Another site shows that image:

From the United States Standard Flight Inspection Manual, the tolerances are:

Minor axis being parallel to approach:


Is it possible to have two different makes of engine on a single twin-engine aircraft?

Yes it is possible.

For example :

  A Boeing 777-200ER using GE engines . The first engine = GE90-94B and the second engine = GE90-115B .

This is called engine intermixing.

  On 737 sometimes The more powerful engine is derated to the same level as the other engine, and we had to do full power takeoffs everytime. As long as the FMC is aware of the intermix, pilots are allowed to use autothrottle.

Here are the sources for your further reading :
Source 1
Source 2

Following is another example:

  Models with engine intermix already certified

Aircraft models / Engines        Engines allowed

A310-221 / PW JT9D-7R4D1         1 or 2 JT9D-7R4E1
(48000 lb *)                     50000 lb*
                                 (A310-222)

A310-222 / PW JT9D-7R4E1         1 or 2 JT9D-7R4D1
(50000 lb *)                     48000 lb *
                                 (A310-221)

A310-308 / GE CF6-80C2A8         1 or 2 CF6-80C2A2
(57860 lb*)                      52460 lb*
                                 (A310-304)

A300B4-605R / GE CF6-80C2A5      1 or 2 CF6-80C2A3
(60200 lb*)                      58950 lb*
                                 (A300B4-603)

Note (*): Static thrust limit at sea level for takeoff with OAT 30°C.

For these aircraft models, the new engine(s) is (are) installed with no hardware change nor rating change.


Are animals straying onto the runway considered to be a runway incursion?

The FAA defines a runway incursion as:

  Any occurrence at an aerodrome involving the incorrect presence of an aircraft, vehicle or person on the protected area of a surface designated for the landing and take off of aircraft.

So no.


What is the efficiency of the turbine of a modern jet engine?

Slide 7 of this presentation (shown above) states the latest technology for a turbine with cooling flow is 89% efficient, while an uncooled turbine is about 90% efficient. The table from this presentation comes from the well renowned book by Jack Mattingly, "Elements of Propulsion: Gas Turbines and Rockets".


Why is the critical angle of attack lower in ground effect?

Ground effect creates more circulation around an airfoil (either lifting or downforce-ing). Not going into details about how ground effect works, but the 'mirror-vortex' in potential flow explains this very easily.
Increased circulation will manifest in the pressure field as a higher pressure differential between the top and bottom surfaces of the airfoil. An airfoil always has 2 stagnation points, one at the LE and one at the TE. The CP at these points is 1 (the trailing edge stagnation point is lower in real life because of viscous effects). Because the pressure is constrained at the LE and TE, the suction increase happens along the chord, and usually will increase more at the suction peak (~1/4 chord). Now the adverse pressure gradient from the suction peak to the trailing edge is steeper, because we have a higher suction peak, and the same trailing edge pressure. As the adverse pressure gradient becomes steeper and steeper, the airflow will eventually separate from the surface.
Even for the same AOA, ground effect increases the suction on the suction side of the airfoil, which makes the pressure recovery more susceptible to separation.
RE: not using the terms you mentioned, this is a purely 2D effect and can be seen in infinite span wings and has nothing to do with vortices. However just looking at a pressure field without considering anything else is like trying to figure out how a meal is cooked by just looking at the dirty dishes - you need potential flow to explain this.
Regarding what the resultant pressure field looks like, this is very well covered in literature already, and if you want to see the effects for a previously unstudied section, Javafoil will give you useful results - https://www.mh-aerotools.de/airfoils/javafoil.htm


What information an aircraft responder must give to mode S ground receiver

From Mode-S.org

An ADS-B message is 112 bits long:

+--------+--------+-----------+--------------------------+---------+
|  DF 5  |  ** 3  |  ICAO 24  |          DATA 56         |  PI 24  |
+--------+--------+-----------+--------------------------+---------+

DF is the downlink format, ICAO is the 24-bit ICAO identifier of the aircraft, DATA is the message being transmitted, and PI is the parity/interrogator ID.

There are a number of different message types available:

The messages transmit things like position, altitude, turns, track, airspeed, roll angle, turn rate, etc. But they do not contain any information about the originating airport or the destination.


Why does the Cessna 208 Amphibian have extra tail surfaces?

Well, it's the same reason that the Challenger ultralight demonstrates extreme "adverse yaw" in response to aileron inputs when flown with the doors on, but less so when flow with the doors off.  The floats-- like the doors-- increase the surface area in front of the CG, which has an effect similar to decreasing the size of the vertical fin (which, naturally, is behind the CG.)  "Directional" stability is decreased.
Just like if you took a weathervane and added enough surface area in front of the pivot point, it would stop working.
It's not uncommon for aircraft on floats to have modifications to increase the effective area of the vertical fin, usually by adding a small ventral fin below the fuselage.
Which begs the question-- Why did the Wright brothers take steps to increase the amount of vertical surface area forward of the CG on some of their aircraft?


What are the conditions for an airfoil to be a "thin airfoil?"

There is no hard boundary. Normally it is around 8% relative thickness, details depending on camber and nose shape.

Typical for a thin airfoil is a stall originating from the nose, with a sudden separation of upper side flow, while thicker airfoils start to stall with a separation starting from the trailing edge and moving gradually forward. This gives thin airfoils a nasty stall behavior while thick airfoils stall in more benign ways. The stall behavior depends not only on thickness but also on camber and the geometry details of the airfoil nose, but can be used to separate thin from thick airfoils.

Thin airfoils make sense in two applications:

when the local angle of attack is well controlled, such as in flaps and turbo machinery, and
for trans- and supersonic flight where thickness causes wave drag.

In all other applications thicker airfoils with a blunter nose should be preferred because they allow to store more fuel and to make the load-carrying structure more efficient. The upper limit of practical airfoils is at 20% to 22%, the root thickness of the Davis wing as used in the B-24 and B-29.


Can a turbofan maintain torque when spinning fast?

An initial thought is that at 10X the RPM, it is likely that the blades would be well into Mach numbers, which would have a negative effect on power requirements (that is substantially more torque in particular) to spin the fan, and more importantly the fan would not be effective at those speeds.  There would likely be blade damage as well from the loading.

However this is a rather hypothetical question, where if an engine were developed to do this, there would be other trades to be made in the design of an engine. Changing just one part of a system such as a jet engine, usually does not favorably alter the overall performance.


Does lift coefficient for maximum range change for a glider experiencing headwind?

Your first statement is correct, look at the lift vs AOA chart.  You go faster by pitching down (reducing lift and drag) and speeding up above Vbg(lift recovered now more drag), which effectively changes your trim and lowers AOA.  Why?  Because best gliding "Vbg" is all about covering the most distance per unit altitude, NOT time in the air.

In the most extreme case:  headwind = gliding airspeed you can see that no forward progress is made unless you glide faster.  Forward progress per unit altitude is:

(airspeed - headwind)/altitude

Your new Vbg now factors in ground gain vs increase in parasitic drag.  The result is (obviously) you can't glide as far into a headwind, but (more importantly) you can help making your landing zone in a headwind by increasing your airspeed above published Vbg.


Why are 4 blade propellers often in X or + position when the aircraft is parked?

I have operated twin engine aircraft with four bladed propellers. While not warbirds, the following should illustrate some of the reasoning that goes into positioning aircraft propellers. Each type and situation could vary.

In our operation we have two positions in which we place the blades when the aircraft is parked. The positions are the x and + position you mention, and we will choose the most appropriate one dependent on the situation.

The + Position

When we park such an aircraft on a ramp we may want to secure the propellers so that they cannot turn in the wind. One common method of securing the propellers involves placing the propeller in the + position and securing the bottom blade with a cuff that is tied off to the sides with a bungee.

These propellers are bolted to PT6 series engines in which the propeller section (power turbine and gear box) is free-turning. Securing the prop helps ensure that the gear boxes do not turn without proper lubrication, and helps reduce wear.

The x Position

When the aircraft is parked in a hangar or on a ramp with the propellers unsecured, which is more common for our operation, we want to place the propeller blades in the x position.

This is to put the blades in a position which poses the least risk to people moving about the aircraft. The height at which the blades would sit in the + position would typically put the blade tip right at head level, a dangerous position for a relatively sharp and low visibility aircraft part. Conversely, placing the blades in the x position places the upper blade tips out of the way and the lower blade tips down near knee level.


Can this aircraft be identified by the exposure pattern of its flashing lights?

No, based on the exposure pattern I can't identify the aircraft. But based on the other information you gave, I can. It's an Embraer 175, registration N287SY.

After looking up the exact position of the M13 Globular cluster at the time the photograph was taken, I found that the telescope had to be facing to 64 degrees (East-Northeast), with an elevation angle of 28 degrees.

I used in-the-sky.org to find the position of the M13 cluster.

I then drew the geodesic from  James River State Park in a heading of 64 degrees
I used academo.org to draw the geodesic on the map

Then using Flight radar 24's history/replay function I found the aircraft

The aircraft is an Embraer 175, flight DL3693,  flying at 38000 feet.

If we assume:

the telescope is at 500ft MSL,
pointing up 28 degrees above the horizon,
the atmosphere is ISA, and
the earth is flat,

then we can calculate that the aircraft would be approximately 21.5 km horizontally away.

Measuring that out on Google maps gives the following:

That measurement is perfectly in line with the flight path of the Embraer 175.

The slant distance to the aircraft is approximately 24.5 kilometres. The track angle of the aircraft is 228 degrees, so we see the aircraft almost from straight ahead.

The span is 26 meter, I assume the lights are at the wingtips (they are not). The distance between the traces is thus expected to be 3.5 arc minutes.  Close enough!


Is a "breakover feature" required for airliner seats?

I can't speak to the regs, but my understanding of the brace was primarily to protect your head, not being as exposed to any debris, and not having very far to travel to bang against something.

As far as I understand (and I'm less sure of this), your back being in a curved position like this is better able to absorb impact/jarring than if it's vertical and you drop suddenly, or are whipped forward and backward by suddenly arresting horizontal motion.


Why is there a GPS/RNAV waypoint co-located with a VOR?

In the US, the FAA has done this alot, as in their long term plan to phase out a lot of the VORs. Doing that, they're preemptively just adding a Fix for procedures on top of the VOR so they don't have to update all the procedures when the VOR is decommissioned.


Approx 1948 Brasil Brazil Airliner...what is it? Taildragger?

The airliner in the picture is a Vickers VC.1 Viking, registration LV-AFI, of the former Argentinian operator Flota Aérea Mercante Argentina.

According to this source, the plane served the
Secretaría de Aeronáutica under registration LV-XFJ for less than a month, from 10.9.1947 till 4.10.1947 before transferring to FAMA.

After FAMA, the plane in question served Fuerza Aérea Argentina from 4.5.1949 till 11.11.1951 under registrations T-80 and T-50.

Wikipedia: Vickers VC.1 Viking

Wikipedia: Flota Aérea Mercante Argentina (in Spanish)


How do military fighter aircraft identify themselves and each other?

Military aircraft, like civil aircraft have transponders. Military aircraft  are assigned military codes, and their transponders have special military modes.

An aircraft doesn't need a transponder to be "illuminated" by radar, but the transponder enhances the "blip" and modern transponders transmit additional aircraft information such as altitude (Mode C).

See the "Interrogation Modes" of transponders in this link.

Notice that the Military modes include "cryptographically" secured version of Mode S and ADS-B GPS positioning.


You ask a very broad question. Jet engine technicians can work in various capacities depending on the job they are hired to do.

In my experience, I worked on the flight-line directly on aircraft removing/installing, performing operational checks, troubleshooting and servicing engines and other systems.

Some technicians work on engines out of the aircraft and in a controlled environment like the factories where engines are made. Others work in repair shops tearing down and rebuilding existing engines.


On a calm day, what determines the active runway?

Almost every airport that handles frequent traffic will have a Preferential Runway Use Policy. That policy will cover things such as which runways to use for departures and arrivals when parallel runways exist, and the preferred direction even in calm winds.

It's based on the best noise abatement routes/gradients, taxi distances, terrain, etc.

So much so the preferred direction can be used in tail-wind up to a limit (8 knots component in certain places for example). Basically it's the usage that was envisioned when the airport was designed (which does take into account the historic wind data).

  Westerly Operations is the normal traffic pattern used at LAX during the daytime (6:30 am to
  midnight) throughout the year. Aircraft approach the airport from the east and depart the Airport
  to the west due to the prevailing westerly wind. This procedure routes louder departing aircraft
  to the west over the ocean, while arriving aircraft fly from the east to the west over the
  communities on the eastside of LAX, including the Cities of Los Angeles, and Inglewood, and
  the communities of Athens and Lennox.

Above (source) being the normal traffic pattern, it will remain so during calm winds.

Related:

In calm winds, which runway should I select at an untowered airport?
Why would a commercial flight be landing with a tailwind?


What units are used for the horizontal grid lines on a sectional?

One tick mark along a horizontal grid line on a sectional chart denotes one minute of longitude. At the equator (but nowhere else), this is also equal to one nautical mile.  The further from the equator, the less the distance that is spanned by one minute of longitude.

One tick mark along a vertical grid line on a sectional chart denotes one minute of latitude, which is also equal to one nautical mile, anywhere on the earth's surface.

(The above comments assume a perfectly spherical earth.  Therefore they are not completely accurate, but they are close enough for nearly all aviation purposes.)

It is important to understand that at any given point on a sectional chart-- in fact, at ALL points on a sectional chart-- horizontal and vertical distances are portrayed at the same constant scale.  If you want to measure a given horizontal (or diagonal) distance in nautical miles, you can mark it off on a piece of paper and then hold it against the tick marks on a vertical grid line to get the distance in nautical miles.  Or you can just use a chart plotter.

For larger-area charts, it is necessary to vary the horizontal and vertical scales, to accomodate the curvature of the earth.


What action should the pilot take when a TCAS RA (Resolution Advisory) provides opposite guidance to ATC instructions?

In the 2002 Überlingen mid-air collision, one crew followed the ATC instruction to descend instead of the TCAS Resolution Advisary to climb. This caused the deaths of 71 people.
Equipment and procedures have improved since then. Pilots should always follow TCAS Advisory and there is a FAA rule that deals with this. 91.123   Compliance with ATC clearances and instructions.

91.123   Compliance with ATC clearances and instructions.
-
(a) When an ATC clearance has been obtained, no pilot in command may
deviate from that clearance unless an amended clearance is obtained,
an emergency exists, or the deviation is in response to a traffic
alert and collision avoidance system resolution advisory. However,
except in Class A airspace, a pilot may cancel an IFR flight plan if
the operation is being conducted in VFR weather conditions. When a
pilot is uncertain of an ATC clearance, that pilot shall immediately
request clarification from ATC.
(b) Except in an emergency, no person may operate an aircraft contrary
to an ATC instruction in an area in which air traffic control is
exercised.
(c) Each pilot in command who, in an emergency, or in response to a traffic alert and collision avoidance system resolution advisory,
deviates from an ATC clearance or instruction shall notify ATC of that
deviation as soon as possible.
(d) Each pilot in command who (though not deviating from a rule of
this subpart) is given priority by ATC in an emergency, shall submit a
detailed report of that emergency within 48 hours to the manager of
that ATC facility, if requested by ATC.
(e) Unless otherwise authorized by ATC, no person operating an
aircraft may operate that aircraft according to any clearance or
instruction that has been issued to the pilot of another aircraft for
radar air traffic control purposes.


How does turbine efficiency compare with internal combustion engines if all the turbine power is converted to mechanical energy?

The most efficient IC engines are large Diesels. At the extreme end are ship engines with better than 50% thermal efficiency resulting in a specific fuel consumption of only 0.260 lbs/hp/hour or 158 g/kW-h. But even supercharged truck diesels achieve above 40% thermal efficiency at high load (this NHTSA study gives 42%).

Aerodiesels have achieved 220 g/kW-h already with the Jumo 204 and 205 of the early 1930s. Even the modern Thielert diesels (now sold by Continental) are hardly better, claiming 214 g/kW-h. Also the Napier Nomad, a super- and turbocharged aero diesel with utmost efficiency as its design goal just reached 219 g/kW-h.

Gasoline engines start at about 240 g/kW-h; this value is achieved by the Lycoming IO-390 with fuel injection. Without fuel injection, specific consumption rises to 260 - 280 g/kW-h which is typical for a Lycoming O-360 at 65% power. Note that the Jumo 213, one of the more efficient WW II-era piston engines, already achieved 260 g/kW-h even with 87 octane fuel and a compression ratio of only 6.93:1 at its most favourable operating point. Advanced Innovative Engineering, who have taken over the Norton-Wankel engine, claim 310-350 g/kW-h for their 650CS with 120  PS.

Comparing that with turboprops needs some conversion of thrust into power. This is only valid for a specific flight speed. If you do that at cruise speed, the large turboprops Progress D27 and Europrop TP400 claim a consumption of around 240 g/kW-h. Smaller turboprops rarely achieve below 300 g/kW-h.

To save you from the trouble of looking up and converting the data in the last link, here is a selected list:

Allison 250 $\;\;\;\;\;\;\;$: 370 g/kW-h. This is a typical small helicopter engine.
Garrett TPE331$\;\;$ : 310 g/kW-h. This is used on small turboprops like the Do-228 or the Merlin III.
PWC 126A $\;\;\;\;\;\;\;$: 280 g/kW-h. Getting larger - BAe ATP.
Rolls-Royce Tyne : 237 g/kW-h. This has long been the largest turboprop in the West and used on aircraft like the Canadair 400 / CL-44.

Please note that those turboprops feed on kerosene while the piston engines need gasoline. But by basing the comparison on a per-mass basis, it is valid because the energy densities of both are almost identical. Very large turboprops are as efficient as gasoline piston engines, but diesels still have a small advantage.

Now for turbofans. Here we have thrust which needs to be converted into power first by multiplying it with flight speed. It would be nonsensical to compare the static case – here by definition turbofans do not produce power. For the nitpickers: Yes, I need to look at the gas speeds ahead and behind the engine, but still, this makes for a poor comparison: Most static values are from test stands with all accessories removed and no losses for engine mounts and fairings. I will instead use the figures in cruise given in this answer, using a fuel burn of $b_f$ = 18 g/kNs and a speed of Mach 0.78, which equates to a flight speed of 262 m/s in 11.000 m altitude. Multiply by 3600 for a per-hour value and divide by 262 (the N are in the denominator!) and you arrive at 247 g/kW-h. So again, very similar to good gasoline piston engines but not as good as diesels.

But again this comparison has to be taken with the proverbial grain of salt. Now we need to have a closer look at speed. Thrust-specific consumption goes up with speed and roughly doubles between the static case and cruise speed for a modern turbofan. The GE-90 achieves 8 g/kN-s static and 15 g/kN-s at Mach 0.8 – that would be just 209 g/kW-h and be on a par with the best diesels. For comparison: The installed figures for modern military engines in supersonic aircraft are 20 g/kN-s. And regarding the fuel-hungry turbojets: The old Jumo 004 achieved 39 g/kN-s – just twice as much with a compression ratio of only 3.3:1. Real fuel guzzlers were the Argus 014 of the V-1 with 107 g/kN-s in cruise.

While turbine engines gain in efficiency with altitude due to colder intake air, the diagram below comparing the Jumo 213 A with the J version (source) shows an increase in power specific fuel consumption with altitude. Note that flight speed will also rise with altitude and is not given, so I suspect this is more due to higher speed than higher altitude. Again, these are real-world data from flight test with the engine installed in a FW-190D (source). Going from sea level to 10 km which roughly doubles true air speed raises the specific consumption by 20%.

Comparison chart between Jumo 213 A and J. Flight altitude is given in [km] along the x axis and specific consumption along the right y-axis. Multiply by 1.34 for g/kW-h. The lower set of lines are for partial load operation between 2100 and 2700 RPM (A version) rsp. 3000 RPM (J version) while the upper set of consumption lines are for maximum power operation at 3000 RPM (A version) rsp. 3400 to 3700 RPM (J version), partially with water-methanol injection.


How does altitude affect the TAS and thrust of an electric fan powered aircraft?

The Helios was an electric powered prop driven aircraft that achieved an altitude of over 96,000 feet and maintained it in level flight for more than 40 minutes.

as altitude increases

You maintain wing lift with constant IAS until the wing airflow approaches the speed of sound (TAS increases).  Shaft power output must increase to spin prop faster to maintain thrust or... changing prop pitch is helpful instead of increasing rpm.  This helps avoid the "sound barrier" for the prop.

as motor rpm increases

Even when not limited by supersonic prop tips, increased engine bearing friction from higher rpm requires a greater power draw.  Again, the ability to vary prop pitch is enormously helpful to maintain optimal prop AOA as TAS increases.

can I fly with the same amount of power at 50,000 feet as I can at sea level

You can get a lot closer by designing your aircraft to fly at 50,000 feet by:
 1.  Reducing wing loading by removing weight
 2.  Increasing wing aspect ratio and/or increasing wing area
 3.  Increasing the **area** of your prop so you can push more air at the same rpm.

With props, you must compensate for thinner air, but higher rpm is not the only way.


What are the US Customs requirements upon returning to the US after pre-clearing customs in the US Virgin Islands?

You're required to notify and clear customs if you land in the 50 U.S. states or Puerto Rico from the U.S. Virgin Islands, even though the U.S. Virgin Islands is part of the U.S.

"All private aircraft arriving in the United States via the Gulf of Mexico or the Atlantic
Coast from a foreign location in the Western Hemisphere south of 30 degrees north
latitude, or from any place in Mexico or from the U.S. Virgin Islands, shall also furnish a
notice of intended arrival. Such aircraft must then land for inspection at the nearest
designated airport unless an overflight exemption has been granted under Section
122.25 of the Customs Regulations."


Do jet aircraft have a better glide ratio than propeller aircraft in general? If so, why?

"Glide performance" is measured by "Lift-to-drag ratio":

In aerodynamics, the lift-to-drag ratio (or L/D ratio) is the amount of lift generated by a wing or vehicle, divided by the aerodynamic drag it creates by moving through air

When you look for examples you'll see that for the most part larger airliners do indeed have a more favourable L/D ratio

Boieng 747 = 17:1
Airbus A380 = 20:1
Cessna 172 = 11:1

As to why, that is the way they are designed. A good glide ratio is a favourable feature of an aircraft as less drag will imply better efficiency, and airlines are more concerned with efficiency than, for example, a training aircraft which might be more concerned with stability.
More information can be found here: How far can airplanes glide?


What would be the effect of skinning over the gap in fixed leading-edge slats?

To answer your question, I suggest to look at the effect of slats. NACA technical report 407 studied a fixed slat similar to what is used on the Zenith CH-750, and the result of the optimum geometry is plotted below. Dashed lines are for the airfoil with a fixed slat and solid lines for the airfoil with the slot between slat and wing filled:

Lift and drag coefficients for a wing with and without a fixed slat over angle of attack, from NACA TR 407.

Three conclusions are obvious:

Drag is higher with a slat for no benefit in lift (even a small reduction, actually) up to an angle of attack of 15°. Don't let the scale of the plot mislead you: Zero-lift drag for the slotted wing was 0.0229 compared to 0.015 for the plain wing, an increase of 52.5%.
The maximum angle of attack has been increased by 9° by the slotted wing, from 15° to 24°. This translates into an increase in the maximum lift coefficient of 34.6% (from 1.297 to 1.751)
The stall behavior has changed from benign to outright nasty by the addition of the slot.

While the airfoil studied in NACA TR 407 is quite close, it is not exactly what happens once the slat is removed: While the outer contour of the airfoil did not change in NACA TR 407, those builders removed part of the wing when removing the slat. Therefore, wing area would be reduced and the loss in lift will actually be even greater. NACA TR 400 hints at a lift loss of more than 40%, which would increase the minimum speed of the Zenith CH-750 by about 30%. Note that the take-off and landing distances will grow accordingly - the STOL in the aircraft's name will not apply any longer!

When putting a glove over the slot, the wing area will be maintained and the minimum speed will not go up quite so severely. Using the 34.6% from NACA TR 407, the minimum speed increase would only be 23.6%. The change in airfoil shape (with the glove the point of maximum thickness is further back and the relative thickness smaller than with the slat removed) will not alter the flight characteristics in a significant way - in both cases the airfoil is of the peaky upper surface type with a large nose radius, so separation around stall will start from the trailing edge and move forward with increasing angle of attack. Long laminar runs on the top surface cannot be expected in both cases.

Now I only wonder why you would add vortex generators. I thought the idea was to reduce drag and improve cruise performance?


How did planes measure their speed relative to the ground before GPS?

The other answers seem to make a simple thing way too complicated. Yes there are DMEs or TACANs, that are sometimes used to get a ground speed, but it's only accurate if you're tracking exactly to or away from it. And it certainly wasn't used to calculate speed enroute unless one of your navaids was a VOR/DME or equivalent. Rather than using DME they'd be using INS, which delivers data more similar to GPS.

Calculating ground speed in the past (before INS, or in airplanes without one) was done using the simple method of having checkpoints along your route. These checkpoints where navaids or intersections determined by multiple navaids. Either way their location was known, divide the distance by the time spent travelling between them and you got your ground speed.


What aerodynamic phenomenae can decrease the pressure gradient in Boundary Layer Ingestion?

First, let me explain the context of your question: It is about a concept for a future airliner:

Boeing Blended-Wing-Body Model 450-1U, taken from NASA/CR-2006-214534.

In the artist impression above the engines are podded and sit on struts in order to achieve a uniform flow field at the intake face. However, the strut and nacelle surface area will contribute drag that could be avoided if the engines would be mounted closer to the rear fuselage. The picture below, taken from the same source, shows a CAD rendering of a possible geometry with semi-buried engines:

The disadvantage of this concept is the ingestion of boundary layer flow such that the speed profile over the intake face shows a speed gradient (BMI = boundary layer ingestion). This will result in distorted flow at the compressor and cyclic pressure variations for the compressor blades, which in turn will require a more robust and less optimized compressor geometry or run the risk of compressor stalls and early blade failure. Also, the energy loss within the boundary layer results in lower pressure recovery ahead of and inside the intake, which will increase specific fuel consumption.

Or to quote the NASA page on inlets:

  As the air is brought from free stream to the compressor face, the flow may be distorted by the inlet. At the compressor face, one portion of the flow may have a higher velocity or higher pressure than another portion. The flow may be swirling, or some section of the boundary layer may be thicker than another section because of the inlet shape. The rotor blades of the compressor move in circles around the central shaft. As the blades encounter distorted inlet flow, the flow conditions around the blade change very quickly. The changing flow conditions can cause flow separation in the compressor, a compressor stall, and can cause structural problems for the compressor blades. A good inlet must produce high pressure recovery, low spillage drag, and low distortion.

The question now is: What can be done to keep the semi-buried engine concept but to avoid the intake flow distortion from boundary layer ingestion?

Solution 1:

As it turns out, the same NASA paper proposes a simple diverter ahead of the engines which is supposed to push the slow boundary layer to the side:

Solution 2:

An even better solution is to use a splitter plate; after all, the semi-buried engine has an intake very similar to the side-mounted intakes of trainer and combat aircraft. Below is an example from another subsonic aircraft, the Czech L-39 Albatros jet trainer:

Subsonic splitter plate intake on the L 39 (picture source)

Solution 3:

Less commonly used, boundary layer suction can be employed to remove the slow-moving air close to the surface and to re-establish a more uniform speed profile. Here my example is the Eurofighter EF-2000 intake, where boundary layer suction is used to remove the boundary layer that has accumulated on the splitter plate itself:

EF-2000 intake, here abused as a baggage compartment. The grid of holes is used to suck away the boundary layer.

A similar arrangement was used on the intake cone of the SR-71, but I did not find a good picture. Boundary layer suction, however, is not the kind of passive solution you desire. But it has the advantage of being adaptable to the specific flight situation.

Solution 4:

Also not passive, and not being used in existing airplanes, would be a moving surface ahead of the inlet. This has been tried with rotating cylinders at flap breaks, and there is some literature covering the topic. The moving surface will reverse the effect of the wing ahead of the intake and re-energize the boundary layer right ahead of or inside the intake.

In all cases, you need to check whether the newly incurred losses of the boundary layer manipulation will be lower than the gains in engine efficiency. I did not go into vortex generators: They might help to equalise the speed loss or at least to reduce the speed gradient towards the surface, but they incur new and intense losses all by themselves and would most likely reduce efficiency a lot. If well placed, they will reduce intake distortion, but at the price of a much reduced pressure recovery.


What does Lion Air faking the repair of the AoA vane mean for the Florida repair shop that ceased operations?

The FAA action, while supposedly not directly related Lion Air but more to Xtra's problems with working on parts they were not authorized to work on because they hadn't demonstrated that had everything in place, is obviously politically related to the event because the crash put the spotlight on Xtra and the FAA had to do something once having lifted that particular rock.

So from a strictly legal standpoint, Lion Air's maintenance actions don't help Xtra and what will happen is Xtra will have to make reforms and then go back to the FAA to try to get their repair cert reinstated independently of any Lion Air actions.

Normally what happens is a part goes to a repair facility, and the repair shop puts it though an Acceptance Test Procedure (ATP) as per the manufacturer's Component Maintenance Manual (CMM). There is usually some kind of test rig that has to be made (instructions for making it in the CMM), that runs the specified functional tests on both ingoing and outgoing parts.

So the part goes in, and gets an incoming ATP. If it passes the incoming ATP, it's considered serviceable and gets tagged NFF (No Fault Found) and sent back to the airline as serviceable.  If it fails ATP, it gets broken down and repaired as required.  It then gets an outgoing ATP (the same test normally) to validate function before it is tagged repaired/serviceable.

I can't really tell from the article if the mis-calibration was inherent to the vane as received or was something screwed up when the airline installed it.  Notwithstanding the likelihood that Xtra was turning parts around that they don't appear to be approved to repair, it's not uncommon for parts to come back to an airline NFF, or repaired, and still fail when it's installed on the plane.

So either Xtra had the proper manual, test rig, parts and tools, training etc. for fixing these vanes or they didn't.  The FAA's action makes it sound like they didn't and were maybe just receiving units and doing some other test they made up themselves, or maybe just smiled at it and sent it back out. Hard to say.

In any case, receiving a part back with a serviceable tag is no ironclad guarantee that it will work in service, and "bad from spares stock" happens from time to time.  No system is perfect.  The business depends to some degree on the redundancy of having two and three of everything to cater to random failures no matter the background causes, except in this instance Boeing decided to let that single-point-of-failure spot in the system architecture get through cert, and here we are.


Is the 777X actually the newest Boeing plane?

While the 777X is a derivation from the older 777 Classic family of airplanes, it is, in fact a brand new airplane, similar to the difference between the 747-8 and the 747 Classic line or the F/A-18E/F Super Hornet compared with the F/A-18A-D series. Based on that and the rollout date of the 777X, it would be BCA’s latest airplane.


Why are there speed restrictions applied after deicing an aircraft?

Some deicing fluids can leave a gel-like residue on the airplane. Several incidents occurred with 737s where the residue accumulated in the elevator balance bay, causing severe oscillation/vibration in flight above 270 KIAS. These incidents resulted in the issuance of Airworthiness Directive (AD) 2002-08-20, which required adding the 270 KIAS limitation you discovered into the 737's Airplane Flight Manual (AFM). The required "maintenance procedures" consist of cleaning off the deicing fluid residue. The AD also requires a one-time cleaning and sealing of the elevator balance bay.

  The FAA has received reports of numerous incidents of
  severe airframe vibration, or limit cycle oscillation (LCO), in flight after the horizontal stabilizer had
  been deiced/anti-iced on the ground. The reported incidents occurred on Boeing Model 737-600, -700, and -800 series airplanes. The empennage structure on these, as well as Model 737-700C series
  airplanes, is identical; therefore, all of these airplanes are subject to the identified unsafe condition.
  These events have been attributed to an accumulation of deicing/anti-icing fluid or other residue in
  the elevator balance panel cavities and on the external surfaces of the elevator tab.

A Boeing article on the subject gives some more information and also has some photos showing the residue. Here's what a gummed-up 737 elevator balance panel looks like:

From the article:

  Airplane deicing and anti-icing fluids can leave residue in critical areas in the wings and stabilizers. This residue can rehydrate and expand into a gel-like material that can freeze during flight and cause restrictions in the flight control systems. Therefore, attention to this residue should be part of a regularly scheduled inspection and cleaning process.

...

  Although Type III fluids have not been specifically linked to any events involving flight controls, the composition of these fluids makes them equally susceptible to residue problems as the Type II and Type IV fluids.


Are aircraft with squirrel cage fans as wings viable?

Unfortunately, I can only speak for MAV design, but the lab I work in at the University of Maryland (UMD) has done some work on a similar design called a cyclorotor.  Here's a paper that might have some information for you (https://www.researchgate.net/publication/301680815_Development_of_a_quad_cycloidal-rotor_unmanned_aerial_vehicle?ev=prf_pub), but I'll try to sum up here.

The neat thing about these aircraft is that you have, in theory, a very efficient and simple rotor system.  Instead of a rotor blade where only the outer portion of the blade is moving at a desirable speed, the entire blade is moving as fast as you want it.  Similarly, instead of the complexity of a swashplate and needing to actually tilt a rotor in the direction you wish to travel, you can actuate the pitch of each blade in a cyclorotor arrangement with respect to its location in its rotation (analogous to cyclic blade control) and generate a thrust vector in virtually whatever direction you want...all without tilting the aircraft's body.  I've copied a figure from the paper I linked to illustrate this:

In this image, you have 4 blades rotating around on a drum.  It's not quite the "squirrel cage", but similar.  Each blade is allowed to pitch, as on a Ferris wheel, as it spins around.  To govern this pitching, each blade is attached to an offset bar near the center of the drum's rotation.  Hence, as the blades spin around the drum, their pitch is passively modified, forcing them to generate thrust in a particular direction.  Change the orientation of the offset bar, and the cyclic pitch of the blades changes accordingly, thus modifying the direction of the thrust vector...all without changes the vehicle's flight attitude.  For reference, a helicopter has to tilt over in whatever direction it wants to go (generally speaking), increasing drag area and, based on rotor dynamics as well, limiting its response time.  Plus, it could be handy to keep a stable, level platform that can still move around (say for filming or something like that).  It is a really neat feature to have.

The paper is likewise optimistic about the efficiency of the design.  However, measuring efficiency is a VERY tricky thing to do in a way that you can truly compare two designs.  For example, disc loading is typically measured on a helicopter as the gross weight of the aircraft divided by the rotor disc area.  On a cyclorotor, if you want to compare on that metric...what is the disc area?  The paper utilizes the projected area of the cycloidal rotor (the "drum", if you will, the forms the fan wing concept).  Some argue that utilizing that doesn't give you a true apples-to-apples metric to compare with because well...how IS that projected area and the weight it lifts necessarily comparable to a single-rotor helicopter's disc?  Even for coaxial helicopters, I've heard substantial arguments about how to best reduce a coaxial rotor system to a single rotor system for a true apples-to-apples comparison...and I'm not sure you could find one that involves disc loading for this present case of the cyclorotor.

Power loading (gross weight divided by installed power, so the higher the quotient, the better hover efficiency you have -- more weight for less power) seems like the go-to metric then, since it has less "wiggle room", per se.  However, now that you have that, how do you still say that two helicopters at a given power loading are better or worse than each other?  Power loading doesn't capture everything (only hover efficiency), so an additional parameter is necessary.  What is being held constant between the two designs that gives a basis to say whether or not a given design is actually more efficient than another?  In the UMD paper I've linked to here, it posits disc loading...which, as said, may be a questionable way to do that.  These are the two of the "go-to" parameters of helicopter performance, so we might need to make something new.

Hence, I think that the best answer that I have is that the design is still being felt out, and I'd be wary of people who posit massive efficiency increases.  There is no free lunch, and efficiency is a tricky thing to nail down.  I've seen more CAD of fan-wing designs than I have vehicles (at least, for those larger than the MAV scale), so I'm inclined that think it's not living up to expectations for the larger vehicles, but that's pure opinion.  Also, this said, I know of at least 5 of these vehicles that have been made and flown at UMD, though none over 10 pounds gross weight.


When does the FAA require OEM involvement for the approval of an STC?

It tends to go on a case by case basis.  OEMs tend to steer clear of STC developers because OEM involvement tends to drag the OEM into an implied commitment to support the STC itself, or support the STC's secondary effects on how the airplane is operated, that the OEM would rather not be stuck with.

What will happen is an STC developer will submit a certification application with documentation, test reports and all that, to the regulator, and most of the time the regulator will approve the STC independently of the OEM.  But there may be cases where the regulator's engineering group will demand OEM engineering input, or at minimum an "NTO Letter" (NTO = No Technicial Objection) before approving the STC.

In such a case the ball is in the OEM's court and if the OEM insists on not getting involved, well the STC developer is stuck and the project might die on the vine unless they find some other work-around.

In other cases however, the OEM may actively support an STC application where they would like to see the mod go into service because there is a benefit to the OEM.  You might see this for a mod that improves fleet reliability, or is just really popular with operators, but where the OEM lacks the internal resources to develop it in-house due to budget limitations.


Should helicopters fly when they the lack power for vertical climb out of ground effect?

Up to a certain speed, which will be in the POH, the greatest power requirement is when hovering out of ground effect.  Next is hovering in ground effect and power required in forward flight is the lowest, and decreases up until a point where the increase in parasitic drag starts to increase the power required.

See a typical power required curve.

From the AOPA blog

So it is possible to not have enough power margin to be able to hover OGE but enough to hover IGE.

To perform a normal take-off (ignoring a lot of side effects such as need for pedal), come to a normal hover height, about 2-3 feet, then push the cyclic forward.  Increase collective smoothly to maintain altitude and allow the aicraft to accelerate which it will, since increasing collective increases power and the rotor thrust now has a forward horizontal component. As significant translational lift kicks in at about 10 kts, a reduction in collective is required to avoid climbing early.  You don't want to be climbing with high pitch, and therefore high drag, if the engine quits.  When reaching about 45 kts or so, pull back on the cyclic to adopt a climbing attitude.  The aircraft will settle at about 65 kts.

To perform a "creeping" take-off, increase collective to become light on the skids.  Gentle forward pressure on the cyclic will start a slide on the ground. As translational lift kicks in, apply a little back pressure to lift gently to climb to about 1-2 feet to remain in maximum ground effect and continue to accelerate.  Wait until 45 kts is reached, and off you go.  During this manouver, the collective is left where it is until established in the climb, aside from small adjustments needed to keep the altitude constant during the creep.

I am not sure if it is a certification requirement, but every helicopter I've flown is capable of safely flying when there is not enough power margin to hover OGE, and most helicopters I have flown are on the weak side (R22, B206, B206L, S300, Enstrom 280) so I guess all helicopters can do so.

I checked a few types certs and I can see nothing about creeping take-offs. I am reasonably sure that the only limits that apply are for RPM, MAP, torque, N1, N2, temperatures etc. As long as you don't exceed those and are in accordance with the POH, then it doesn't matter how you get airborne. As you can see from the power required curve, the power required for forward flight is a great deal lower than for hover.

I've copied in your comment:

  I understand that vertical climbing is not hovering, but neither is it
  "flying" in the same sense that translational flight adds lift.
  Positive vertical climb out of ground effect with no translation is, I
  deduce, the hardest thing a helicopter can do. The maximum rate of
  climb in that attitude seems like something you'd have charts for, but
  I don't even know a term or acronym for it.

Because of translational lift, a helicopter requires less power to climb when flying forward than it does to hover, in or out of ground effect.  The greatest power requirement is when hovering OGE and increasing the hover height requires more power still so yes, climbing vertically OGE requires more power than any other regime.  There is no chart, or term for this that I am aware of simply because you should not do it and the POH will detail restrictions, not least, the "dead mans" or avoid curve.

http://flyinghelicoptersinalaska.blogspot.co.uk/2010/04/why-dont-helicopters-go-straight-up-and.html

The only time you should ever climb vertically (a "towering" take-off) is when operating out of a confined area when it would not be possible to get out without clearing the trees, walls or whatever.  Some pros do it all the time, e.g. power line inspection/repairs, logging and so on but they accept a risk of operating outside of the limits and are certified and insured appropriately.

The avoid curve shows the combinations of height and speed in which test pilots (i.e. the best) have demonstrated that a safe landing is possible if the engine quits.  You should not fly in the shaded area so you can see (and that chart is similar for all helicopters) that a towering take-off should never be used unless there is no alternative, and only then, for the shortest possible time.  Coming into a high hover, say 50 feet, or continuing a vertical climb OGE is prohibited by virtue of it being in the shaded area(s) of the chart.

Helicopters are not always intuitive.  Many people are surprised by the fact that climbing needs less power than hovering, and the faster you go (up until that point where the parasitic power increases dramatically), the less power is required.  Imagine a car where less power was required to accelerate and go faster!


Vortex Lattice Method with eliptical panels

Typically in numerical simulations, instead of an ideal(inviscid) vortex, a viscous vortex with a finite core is used to avoid the singularity at the centre. In these viscous vortices, the swirl velocity inside the core is assumed to be linearly increasing from zero at the centre. While outside the core, the induced velocity remains the same as that of the ideal vortex.

There are multiple models that model these finite core vortices; some of which are:

Rankine
$$V_{\theta}=\begin{cases}\overline{r} & \text{if }\overline{r} \leq 1 \\ 1 / \overline{r} & \text{if }\overline{r}>1\,.\end{cases}$$
Lamb–Oseen
$$V_\theta=\frac{1}{\overline{r}}\left(1-\mathrm{e}^{-1.2526 \overline{r}^{2}}\right).$$
Bumham–Hallock
$$V_{\theta}=\frac{\overline{r}}{\overline{r}^{2}+1}\,.$$
Proctor

$$V_{\theta}=\begin{cases}
  \frac{1.4}{\overline{r}}\left(1-\mathrm{e}^{-\beta(1 / \overline{B})^{0.75}}\right) \times\left(1-\mathrm{e}^{-1.2526 \overline{r}^{2}}\right) & \text{if }\overline{r} \leq 1 \\
  \frac{1}{\overline{r}}\left(1-\mathrm{e}^{-\beta(\overline{r} / \overline{B})^{0.75}}\right) & \text{if }\overline{r}>1\,.
\end{cases}$$

Proctor–Winkelman

$$V_{\theta}=\frac{1}{\overline{r}}\left\{1-\exp \left[-\beta_{i}(\overline{r} / \overline{B})^{2} /\left\{1+\left[\left(\beta_{i / \beta_{o}}\right)\left(\overline{r} /_{\overline{B}}\right)^{1.2}\right]^{p}\right\}^{1 / p}\right]\right\}\,.$$

Vatistas
$$V_{\theta}=\frac{\overline{r}}{\left(\overline{r}^{2 n}+1\right)^{1 / n}}\,.$$

In these equations, $\overline{r}=r/r_\mathrm{core}$.


Why battery voltage is lower than system/alternator voltage

This is more of an Electrical Engineering question than Aviation, indeed the exact same thing can be asked about any automobile.
Both of the figures that you quote are 'nominal': The battery cannot be expected to put out a much higher voltage than 12v, so in reality, all systems will work fine down to about 10volts or so, though 'normal' voltage will be 12.5v for a reasonably new, modern battery in good condition.
Conversely, the battery itself requires a significantly higher voltage to charge itself, so the alternator needs to put out 13 to 14 volts, which gets rounded off to 14v for simplicity when talking "in general".
Nearly forgot - for some heavy duty systems, a 12v system is insufficient, so the battery is simply doubled up, so 12v nominal becomes 24 volt, etc., but with the same tolerances.


In current missile, what is the guidance law used at terminal phase in homing missile guidance?

According to this easy to read brief introduction:

Optimal Homing Guidance Laws

  Other Optimal Homing Guidance Laws, many modern guidance laws require
  an estimate of time-to-go (tgo), which is the time it will take the
  missile to intercept the target or to arrive at the closest point of
  approach (CPA). The tgo estimate also is a critical quantity for
  missiles that carry a warhead that must detonate when the missile is
  close to the target.


Which AFDX connections are used in Airbus A380?

There are some resources.
This source shows how AFDX is used as the backbone of the IMA (Integrated Modular Avionics) and lists subsystems such as the air data inertial reference units (ADIRU), Engine Electronic Controllers (EEC) and Electrical Load Management (ELM) Systems as 'members' of the network.

This archived article talks about the development of AFDX to solve real time performance issues with the flyby wire controls of the A380.

Other articles of note would be this. The other articles are behind a paywall but for completeness they are here and here


What is the capacity of the vent surge tank in an A320?

From Airbus flight crew operating manual (FCOM):

The expansion tanks above the center tank allow the center tank to be filled to the maximum. Tanks capacity is 23,858 liters.

The FCOM says the fuel can expand up to 2 % without spillage in the vent/surge tanks. That's about 239 liters per surge tank.

The volumetric expansion of the fuel is about 0.095% per °C. 2% allows for a 21°C temperature increase.

The vent/surge tank communicates with the outer tank on the same side, and fuel can flow back by gravity, when conditions permit.


How does climb-rate vary with density/pressure altitude?

For propeller aircraft, the climb rate is a function of

available power
demanded power
weight
air density
wing lift

Five variables, and wing lift is itself a function of Mach number, Reynolds number, wing AoA, wing area. Available power is a function of air density, throttle setting, propeller incidence - demanded power a function of air speed, air density, angle of attack, Mach & Reynolds numbers. So in total a very large matrix of independent variables - in order to find equations via an analysis, we'll have to make some assumptions and simplifications. For instance that the aircraft thrust vector stays reasonably horizontal so that $T \cdot sin(\Gamma)$ is close to zero and can be disregarded. Also, that lift = weight during the climb.

For the steady climb, the weight equation then becomes $$W = C_L \cdot \frac{1}{2} \rho V^2 \cdot S \Rightarrow V = \sqrt{\frac{W}{S}\cdot\frac{2}{\rho} \cdot \frac{1}{C_L}} \tag{1}$$

For the drag in horizontal flight:

$$ D_h = C_D \cdot \frac{1}{2}\rho V^2 \cdot S = \frac{C_D}{C_L} \cdot W \tag{2}$$

and the required power in horizontal flight $(P_r)_h$ becomes:

$$ (P_r)_h = D_h \cdot V = W \cdot \sqrt{\frac{W}{S}\cdot\frac{2}{\rho} \cdot \frac{{C_D}^2}{{C_L}^3}} \tag{3}$$

The power required to maintain climb speed $C$ is $W \cdot C$ and available power $P_a = (P_r)_h + W \cdot C$, hence:

$$ C = \frac{P_a - (P_r)_h}{W} = \frac{P_C}{W} \tag{4}$$
Combine (3) and (4):

$$ C = \frac{P_a - (P_r)_h}{W} = \frac{P_a}{W} - \sqrt{\frac{W}{S}\cdot\frac{2}{\rho} \cdot \frac{{C_D}^2}{{C_L}^3}} = \frac{\eta \cdot P_{br}}{W} - \sqrt{\frac{W}{S}\cdot\frac{2}{\rho} \cdot \frac{{C_D}^2}{{C_L}^3}} \tag{5}$$

Above picture shows a graph of $P_{br}$ of the P&W Wasp: function of manifold pressure and altitude. This engine had a turbo-charger for improved altitude performance, the engines of GA aircraft may not have these. Plots of variable pitch propellers show a propeller efficiency $\eta$ of about 0.8.

How this ties into the graph shown in OP:

The equations feature air density $\rho$. This is a function of static pressure and of temperature: an equation to convert to static pressure and vice versa can be found here.
Available power for a normally aspirated piston engine decreases as a function of altitude, approximately according to $\frac{({P_{br}})_h}{({P_{br}})_o} = (1 + c) \frac{\rho_h}{\rho_o}$. Tests on some American piston engines showed that for many of them a value of $C$ = 0.132 would be appropriate, refer to figure below which also shows the altitude-power function of a piston engine with supercharger.

All references and pictures from a university lecture book, paper copy only.


Do airline transport pilot trainees ever fly a passenger-less aircraft?

When pilots are trained for flying in an aircraft type they have not flown in before, they go through type rating, then line training. During the type rating, they learn where all the instruments and buttons are, what starts which system, how the plane behaves, how to land and auto-land etc.

During line training, they spend time in the cockpit together with an instructor pilot, usually a senior captain. Most airlines have a 3-person crew in the cockpit when a new F/O is receiving line training. This training is about the airline specific bit of flying, company procedures etc.

Note that before going to type rating, the pilot already has at least a commercial flying license: they can fly already. Depending on the country, the type rating can take place in a Level D simulator for 100%. Some countries still require a couple of actual flights in an aircraft, but there is an increasing trend to use Level D simulators only, for two reasons:

Back when the airlines paid and arranged for type ratings, it was relatively simple for them to arrange for an aircraft for a training flight, empty or not. But now a majority of type ratings is self funded, how does a student find the finance to charter an empty aircraft?
The realism of Level D simulators is incredible. My office used to be not far from the simulators - every once in a while I would hear the siren for the sim coming down at an unscheduled time, for an unscheduled break: the stress level inside is real, you reckon that you are really 30,000 feet up with an engine on fire, alarms sounding, actual (non-toxic) smoke entering the cockpit, etc. After clearing the emergency, some students needed time to reflect.

Boeing predicts that we need 30,000 new pilots every year for the next 20 years. How do we streamline it such that all competent persons can become pilots, not only people with enough money to charter a plane?

As @user71659 points out, at airlines that only fly widebodies, standard entry position is a second officer/relief first officer/cruise pilot on a long haul plane like the 777. (Cathay Pacific, Singapore Airlines, Emirates, for example).


Is "passenger loading bridge" a synonym to "contact stand"?

ICAO Annex 14, which deals with aerodrome design (not really terminals) uses the terms PLB and aerobridge.

Wikipedia lists many names for it, with the official being PBB (Passenger Boarding Bridge). The names listed are jet bridge, jetway ®, gangway, aerobridge/airbridge, air jetty, portal, and skybridge.

Official FAA documents use the term PBB. (Example.)

Contact stand most probably is used to distinguish it from a remote stand, it's not very popular according to Google. Rotunda or pivot describes that a PBB pivots, or perhaps the pivoting / telescoping part.

To answer the main question, yes they all mean the same thing, with PBB being an official name.


Depth and range for FDR/CVR black box detection

The maximum range if it's transmitting on 37.5kHz is usually between 1 and 2 kilometers in poor conditions and around 4 to 5 kilometers in normal conditions and up to 6 or 7 in good conditions. The range depends on the frequency it's transmitting but the ULB's work on 37.5kHz.


How to advise others of imminent danger?

To quote an answer by kevin on another question from last year:

What's the procedure? The procedure is, be creative to save as many lives as possible!
Really. The procedure is to determine a course of action which will likely result in the best outcome for everyone, utilizing all resources and given all constraints. Period. It is as simple as that.
There are infinitely many scenarios, and one cannot be trained for everything.

If you need to communicate something as quickly as possible in order to avoid a disaster, and calling "mayday, mayday, mayday" will be a significant waste of valuable time, then the answer is clear: don't call mayday. Just say what you need to say.
If you know what the other aircraft need to do in order to avoid a collision, perhaps it would be a good idea to announce "Go around, go around, go around!", "Cancel takeoff, cancel takeoff, cancel takeoff!", or "Hold short, hold short, hold short!", as appropriate.
In the case of Air Canada 759, where an arriving airliner mistakenly lined up to land on an occupied taxiway instead of the runway, a pilot on the taxiway announced: "Where's this guy going? He's on the taxiway." This probably wasn't the best possible thing to say, but the airliner went around and avoided a collision.