To answer your first question, ADS-B stands for Automatic Dependent Surveillance - Broadcast.

Automatic in the sense that it operates without external stimulus (unlike radar)
Dependent in the sense that the surveillance information is derived from on board systems
Surveillance in the sense that it's primary intended to provide surveillance information to other parties
Broadcast because it transmits to all listeners without knowing who those listeners are, there is no two-way communication.

The capability of an aircraft to transmit ADS-B signals is called ADS-B OUT, the capability of an aircraft to receive ADS-B signals is called ADS-B IN.

ADS-B data contains information about the identity, position, altitude and velocity of the aircraft. The position and velocity information is derived from GNSS (GPS).

There are three technologies defined for ADS-B

1090ES is operating on 1090 MHz, the same frequency used for Secondary Surveillance Radar (SSR) and Airborne Collision Avoidance Systems (ACAS/TCAS). Messages are transmitted by the same transponder that also replies to radar interrogations. This will be a Mode-S capable transponder because the data is formatted in a similar way. Since this frequency is the worldwide used standard for aviation, international aviation will use this ADS-B standard.
UAT (Universal Access Transceiver) works on 978 MHz. A special transceiver is required to use this form of ADS-B. The transceiver is able to send and receive data, it will also receive ADS-B transmissions from other aircraft. UAT is only allowed within the USA and China. The frequency 978 MHz is reserved for other purposes (DME/TACAN) in other countries.  To encourage people to equip with ADS-B voluntarily, the FAA provides additional services on UAT. These are Traffic Information Service - Broadcast (TIS-B) which transmits position of aircraft detected by FAA's SSR's and Flight Information Service - Broadcast (FIS-B) which provides the receiver with weather information and operational data such a airspace restrictions and NOTAMS.
VHF Datalink Mode 4 (VLDm4) uses a frequency in the 118-136.975 MHz block, which is internationally reserved for aviation. Normally these frequencies are used for voice communications, so a special radio is required to support VDLm4. Just like UAT, VDL mode 4 allows for services like TIS-B and FIS-B. VDLm4 was tried in Sweden and Russia, but has not been able to gather much mass. It is unlikely that it will be used on a large scale.

Since you mention 2020 as the year by which aircraft should be equipped with ADS-B I am going to assume you are from FAA-land.

The FAA mandates aircraft in the 48 contiguous states (and D.C.) that operate in class A, B, or C airspace or class E airspace above 10000ft (class E airspace below 2500 AGL excluded) to be ADS-B OUT equipped by January 1st, 2020.
The mandate itself can be found here and the associated Advisory Circular (AC90-114) can be found here.

Aircraft operating below 18000 ft can use either UAT or 1090ES. Above 18000ft, 1090ES is to only approved ADS-B technology.

Countries that have ADS-B mandates are (this list is probably not exhaustive)

Australia
Canada
(Hudson bay)
China
Countries in the European Union
Fiji
Hong Kong
India
Indonesia
Seychelles
Singapore
USA
Vietnam


Of the two possibilities you mentioned, the most likely is the height of the top of the vertical stabilizer from the ground with the plane parked normally. For conventionally-configured tricycle-gear airplanes, this point is the tallest on the aircraft, and therefore this height is useful in determining the required clearance for covered parking areas and hangar openings.

There are a few designs for which a different height measurement is needed. A tail-dragger's tallest point will usually be either the cockpit or a point in the prop's sweep (more likely the cockpit for civilian designs, more likely the prop for old warbirds). The Predator drone uses an inverted V-tail, and its tallest point is actually its communications antenna. The Beechcraft V35 Bonanza's tail tips are within a couple of inches of the top of the cabin. In all these cases a "parked height" figure is required which will be greater than that of the vertical stabilizer.


What is the difference between RFL and ECL in Air Traffic Control?

RFL is Requested Flight Level, ECL is the En-Route Cruise Level. RFL the cruising flight level that has been requested by the flight plan or by the pilots, ECL is the level which has been actually assigned by the controller. The two may be the same or they may be different.

From the EUROCONTROL SPECIFICATION FOR TRAJECTORY PREDICTION Edition: 1.0, page 33

  2.3.2  Enroute Cruising Level (ECL) (3.3.2)

  Domain Knowledge: The  ECL   is  a  notional
  level  that,  in  the  absence  of  constraints,  equates  to  the
  RFL .  In  the  case  where  a  flight  is  not  permitted  to  cruise
  at  its  RFL   for  any  or  a  part  of  its  route,  due  to  the
  presence of a  strategic constraint (level limit) which applies to
  flights between the  aerodromes of  departure and destination, the ECL
  will be limited  to the level defined by the constraint. The ECL may
  also  be  changed  by  instruction from  ATC where  the flight is to
  maintain a different cruising  level, typically due to the proximity
  of a flight at the  RFL  on the same  route.   As with the  RFL ,
  the  ECL  can be changed for different  segments  of the  route  and,
  if different in  the  cruise  phase,  is  changed  to  the  XFL   on
  passing  the  sector   boundary.  The  notion  of  ECL ceases to exist
  after the final  TOD  from cruising level.

This is a complicated way of saying the requested flight level is usually assigned unless there's a good reason for the controller not to (to avoid potential conflicts for example), and the pilots can request a different flight level en route.


How is the moment due to pressure distribution calculated?

If you calculate "component of pdS perpendicular to OQ" you get

$$ dM= (p dS) (cos \theta ~ x_Q + sin \theta ~ y_Q) $$
The pressure times the surface (gives you a force), splited in the two perpendicular forces(along axis) and applied at the $x_Q$ and $y_Q$ distances. Set $y_Q$ to 0 (negligible thickness) and you get the book formula.


What are the factors required to estimate the minimum required power for an experimental aircraft of a specific mass?

A good engineer will first check existing designs: How much power is installed in comparable designs? Use airplanes of similar speed and built quality, such as the Super Diamond Mk 1 which needs 50 to 60 hp. Cruise speed is 90 knots and the MTOW is 450 kg.

Next, try to estimate the minimum wing area. Starting from the minimum speed requirement of 35 kts ( = 18 m/s), and assuming a maximum lift coefficient with flaps down of 1.6, the area to support 340 kg at sea level is $$S = \frac{2\cdot m\cdot g}{\rho\cdot c_L\cdot v^2} = \frac{2\cdot 340\cdot 9.81}{1.225\cdot 1.6\cdot 18^2} = 10.5 m^2$$

Now calculate the drag coefficient in cruise, using the parabolic drag equation. First, establish the lift coefficient at which drag is minimized: $$c_{L_{opt}} = \sqrt{c_{D0}\cdot\pi\cdot\epsilon\cdot AR}$$
The total drag coefficient at this point is simply twice the zero-lift drag coefficient $c_{D0}$, so a low drag design is important. Still, with a fixed gear your zero-lift drag coefficient will hardly be lower than 0.035, so your cruise lift coefficient is 0.938 (assuming an aspect ratio $AR$ of 10 and an Oswald factor $\epsilon$ of 0.8), resulting in a flight speed of just 23.51 m/s = 45.7 kts. Total drag at this point is $$D_{min} = 2\cdot c_{D0}\cdot S\cdot\rho\cdot\frac{v^2}{2} = 249 N$$

To sustain flight at this point only requires $P = v\cdot D$ = 5.85 kW, and assuming a prop efficiency of 0.75, the installed power should be 7.8 kW. But you want to fly faster, so we need the drag at 100 kts ( = 51.4 m/s):
$$D = \left(c_{D0} + \frac{c_L^2}{\pi\cdot\epsilon\cdot AR}\right)\cdot S\cdot\rho\cdot\frac{v^2}{2}$$
There, your lift coefficient is only 0.196 but the dynamic pressure rises to 1,621 N/mm². Since the Reynolds number is higher, your zero-lift drag could drop to 0.031, resulting in a drag force of 550 N. At that speed, the required power is 28.3 kW. Under the heroic assumption that your prop will still be 75% efficient at that speed, the installed power needs to be 37.8 kW or 50.65 hp.

If you "only" want to achieve a TAS of 100 kt at altitude, here is what you need to do in the case of cruise at 10,000 ft ( = 3048 m). First you need the density at that altitude, which is 0.9 kg/m³ or 74% of the value at sea level. This means that the dynamic pressure is 1,191 N/mm² and the lift coefficient 0.267, resulting in a drag force of 419 N. This needs a continuous power of 21.56 kW to overcome. Now I assume the 75% efficient propeller again and that you run the engine at 75% of max. power, so the installed power in 10,000 ft should be at least 38.3 kW or 51.4 hp. Assuming a normally aspirated engine, this would translate to a rated power of 70 hp at sea level.

Considering that similar designs require similar power, this looks about right. Normally, you now need to compute the climb speed with the excess power of 35.15 kW to check how usable this design is, but at 10.5 m/s I doubt this will be not enough.

If you manage to include a retractable gear with your limited mass budget, the zero-lift drag might be as low as 0.024. Now the drag force in cruise at 10,000 ft will be only 324.4 N and the installed rated power at sea level only 40.4 kw or 54 hp.

With piston aircraft, your power needs increase with the cube of airspeed. I leave it as an exercise to you to calculate how much more power the last 10 knots require: Repeat the calculation with only 90 kt cruise and your rated engine power can be as low as 51 hp with a fixed gear.


What is an acceptable phugoid oscillation duration?

Here is the response of a 180 passenger high-subsonic twin-jet simulator: the first period takes about 87 seconds.

Conditions:

  From the trimmed position, excite the phugoid mode by applying longitudinal control in one direction in order to change airspeed by approximately 10 kts, then release.

Initial conditions:

COG 0.2205 MAC
Pressure altitude 35,000 ft
Engine N1 rotor speed 87.47% (both engines)
Calibrated Airspeed 264.54 kts
Gross weight 66,360 kg

EDIT

To answer the additional question of when the resulting motion amplitude would be below 0.1 deg, I made a kind of a digital simulation according to this block diagram:

and then tuned spring stiffness C, inverse inertia 1/M, and damping constant K until the resulting response overlaid the original aircraft one. The resulting motion gets to a max. amplitude of 0.1 deg in about 1,600 sec - 27 minutes.


Could a high absolute difference between heading and course give a hint about weather conditions?

Thinking through the possibilities, if you knew the pressure conditions, and the change of those conditions as plane moves, and you knew the wind direction and speed and its changes as the plane moves, you might be able to have some kind of AI software estimate the location of the pressure centers in the airmass you're flying in, and from that calculate the pressure gradients and wind direction/velocities for some distance around the plane's location.  This might be able to produce a "better than nothing" educated guess as to the wind speed and direction ahead based only on the data being received in real time.
To do this, besides an extremely powerful computer (weather forecasting agencies use multiple Cray supercomputers to predict circulation flows, but maybe you don't need that much power) you would need the normal air data inputs like ambient and dynamic pressure (indicated airspeed), and you'd need to know the airplane's true altitude and true position, which can be provided by a GPS interface.
If the software knew the precise height above the earth so it could measure ambient pressure and continuously calculate barometric pressure and measure pressure changes, and it knew the precise location, track, heading, groundspeed, and true airspeed of the airplane so it can continuously calculate wind velocity and direction (FMS systems on jets do that already), it might be able to create its own pressure pattern map of the immediate area, and from that generate a prediction of wind conditions some distance ahead.


How widely accepted and used is the International Standard Atmosphere?

In most aviation contexts, the International Standard Atmosphere is used universally. This includes things like developing aircraft performance charts, weather forecasts, and flight planning. All flying rules and other aviation standards are all based on ISA.

There are several atmospheric standards. However, for the most part, all of these standards are the same up to about 32km altitude. Since most airliner traffic occurs between about 10km and 20km, there is no need to reference different standards in different locales.

The International Standards Organization (ISO) publishes the atmospheric standard as ISO 2533:1975.  Sometimes this is referred to as the ISO Standard Atmosphere, which would have the same ISA initialization.  However, when used in textbooks, performance charts, flight planning, etc., the term ISA is always understood to mean "International Standard Atmosphere". For the rest of this answer, assume ISA to mean International Standard Atmosphere.

ISA is also an initialization of one of the other standards: ICAO Standard Atmosphere, published by the ICAO in Document 7488/3. The ICAO standard was first published following the 1950 ICAO Council, and underwent multiple changes over the years. in 1979, the Council approved the re-calculation of the data tables to align with the ISO standard of 1975. Once this was complete, the ICAO Standard Atmosphere and the ISA were identical. The ICAO document states that, "any future revisions of the ICAO Standard Atmosphere will be subject of the coordination of the two bodies [ICAO and ISO]".

Because these two standards are the same, AND also have the same initialization of ISA, AND aviation standards world-wide are driven by ICAO, there are frequent mis-uses of the term ISA within the aviation world as being the ICAO standard. However, when used in the application of aviation "things", like calculating True Air Speed, knowing whether the temperature at an altitude is + or - from ISA; it is the International Standard Atmosphere that is meant by ISA.


Is Assumed Temperature used in conjunction with a Derate in the B737 NG?

Yes, that is allowed.
You can combine selection of a fixed derate and an assumed temperature for the takeoff thrust on the FMC N1 Limit page, but only up to a reduction of 25%.

Takeoff Derate
Fixed derates can be selected on the N1 LIMIT page. [...]
Derated takeoff rating can be further reduced by assumed temperature. [...]
Assumed Temperature Thrust Reduction Takeoff
A takeoff thrust less than the full rated thrust may be achieved by using an
assumed temperature that is higher than the actual temperature. The desired thrust
level is obtained through entry of a SEL TEMP value on the N1 LIMIT page or
TAKEOFF REF page 2. [...]
The maximum thrust reduction authorized is 25 percent below any certified rating. [...]
If the assumed temperature method is applied to a fixed derate, application of
additional power should not exceed the fixed derate N1 limit as loss of directional
control could occur while on the ground.
When the assumed temperature method is used with full rate, the reduced thrust
setting is not considered a limitation. If conditions are encountered where
additional thrust is desired, the crew can manually apply full thrust.

(Boeing 737NG FCOMv2 11.32.3 - Flight Management, Navigation - Flight Management Computer)
You can see the current selection on the Upper Display Unit:

2 Thrust Mode Display
[...] Thrust mode display annunciations are:

TO – takeoff
TO 1 – derated takeoff one
TO 2 – derated takeoff two
D-TO – assumed temperature reduced thrust takeoff
D-TO 1 – derate one and assumed temperature reduced thrust takeoff
D-TO 2 – derate two and assumed temperature reduced thrust takeoff

(Boeing 737NG FCOMv2 7.10.2 - Engines, APU - Side by Side – Displays)
What would actually be used by an airline depends on the exact situation. The derate and the thrust reduction via assumed temperature are not the same thing because the derate affects Vmcg, but the assumed temperature does not (see also What is the difference between Assumed Temperature and Derate takeoff thrust?). Today, most airlines will use an EFB (or a separate tablet computer) to perform the TO calculations and the computer will optimize the thrust reduction while taking all legal requirements for V1 (which may be affected by Vmcg, which is a lower limit for V1), second/fourth segment climb gradient, obstacle clearance and possibly noise reduction into account.


Why would lift coefficent change with weight on swept-wing aircraft?

A swept wing has less torsional strength than a straight wing, ie there's less structure at 90d to the root supporting the tip of a swept wing.
Thus a swept wing twists when it's loaded, which unloads the tips and thus generates less lift at higher weights.


Would hydrogen fuel tanks on an airplane increase lift?

Let's do some quick math. Air has a density of about 1.3 g/L and hydrogen has a density of about 0.09 g/L. The best case for lifting force would be storing the hydrogen at the same pressure as the surrounding air. This means that every L of hydrogen can displace 1.21 g of air, reducing the density of the aircraft. The amount of air displaced by the aircraft (and therefore the buoyancy) would not change, but the density of the aircraft in that space would decrease. This would decrease the lift needed, but let's see by how much.

The greatest amount of free volume in an aircraft (that isn't part of the pressurized section of the fuselage) is the fuel tanks. An A380 has a fuel capacity of about 323,000 L. If we consider filling half of that with hydrogen, this would result in a total reduction of about 190 kg. An A380 has a max takeoff weight of 575,000 kg. This change would help but would be very small compared to the total lift needed.

As David Richerby points out, hydrogen needed as fuel would need to be pressurized (if not liquified) to fit enough onboard. This would increase the density above that of any displaced air, which would instead add weight to the aircraft.

Perhaps the hydrogen could be produced instead of stored. Newer aircraft do have something called an OBIGGS, or onboard inert gas generating system. This system generates nitrogen which is used to fill the space in fuel tanks after the fuel is used. Being an inert gas, nitrogen can lower the amount of oxygen in the space below what would be required for ignition of the fuel vapors.

However, this system splits nitrogen out of air, considering that our atmosphere is mostly nitrogen. Hydrogen would have to come from somewhere else, usually water, which would add more weight. Another problem with hydrogen is that when added to air it can be explosive all by itself, which would make the situation even worse. Considering the minor benefit, this would not be a system worth installing on an airliner.

Regarding the feasibility of a hydrogen powered aircraft, NASA did a study and decided that this is not a good source of power for an aircraft. The volume and weight required to store even liquid hydrogen would be too much for the aircraft to be very useful.


Why do drones near airports necessitate cancelling flights?

Re the title question, a plane hitting a crow is enough to take out an engine, as shown in the following video.

Crows weigh about 500–600g. A drone such as a DJI Phantom weighs two to three times as much and isn't nearly so squishy.


During night flying, which color lens for a flashlight is most beneficial?

You will want to use red light.

Why?

See Does red light preserve your night vision? on the Biology StackExchange for a good explanation of the biology and physiology involved, and how it relates to perceptual ability.

As stated in this answer (by leonardo) to that question:

  If one is exposed to red light (above ~650 nm), it would activate the L-type cones mainly (possibly some M-type activation), but no rod activation. Rods are the low light receptor cells in our eyes, and as such, are very sensitive to the photon density, or brightness, entering the eye.

  This is just my speculation, but I think it's plausible that if you were in a completely dark environment with just a red light, filtering out the higher frequencies, night vision could be spared in the sense that we don't activate the rod cells.


Is commercial domestic service using foreign registry aircraft allowed in the USA?

Yes, it's allowed under both part 135 (on-demand) and part 121 (airlines); 121.153 and 135.25 both have the same wording:

  A certificate holder may operate in common carriage, and for the
  carriage of mail, a civil aircraft which is leased or chartered to it
  without crew and is registered in a country which is a party to the
  Convention on International Civil Aviation if— [...]

And US pilots may fly foreign aircraft within the US.


What does the code FU1FU2FU5 mean in this metar?

It's indeed the layer type and okta, but in the remark the layer type is repeated for each reported cloud (smoke) layer. From your example:

FEW037  →  FU1
SCT050  →  FU2  →  1+2=3
OVC250  →  FU5  →  3+5=8

The oktas of the layers are added, that's how OVC is shown as 5 and not 8, by adding the previous oktas it does become 8.

FEW = 1 to 2
SCT = 3 to 4
BKN = 5 to 7
OVC = 8

Similarly for CYCD:

METAR CYCD 012200Z 34010KT 12SM BKN038 BKN051 30/11 A3012
RMK FU5FU2 VIS LWR N-E SLP201 DENSITY ALT 1600FT=

BKN038  →  FU5
BKN051  →  FU2

When no remark is needed for the smoke (French: Fumée), the FU code is placed before the remark:

METAR CYBD 012200Z 29007KT 8SM FU FEW240 28/13 A3019
RMK CC1 SLP225 DENSITY ALT 1400FT=

According to Wikipedia, this is how Canada handles the remark section. Here is what navcanada.ca says:

  Where observed, the obscuration and cloud type amount for each
  reported layer is included in remarks. It may exceed 8 oktas if a higher
  layer is observed through transparencies in a lower layer

(Emphasis mine.)


How can I find out what time an airport was closed due to weather?

The best way to get that information would be to call Airfield Operations at the airport in question.  They can tell you what time the airfield was closed, IF it was the airport itself that was "closed" in that situation.  Oftentimes, however, the field itself isn't technically closed, but the weather was simply so bad that nobody was getting in, and that gets discussed as "the airport is closed" due to weather.  Not technically accurate, but close enough for discussions of "can flights get in there or not."

As for what happened before you left for your connecting city, all sorts of answers are possible.  Perhaps the weather wasn't that bad initially, and it looked like your connecting flight had a good chance of going.  Or perhaps "the system" slipped up, and they should have notified you that the connecting city was as far as you'd be likely to get, and they didn't.  Or perhaps there were PA messages made to that effect that you didn't hear. (It happens.)

Also, an airline wouldn't cancel the flight to the connecting city, since some passengers presumably were trying to get there as their destination, and others had other connections to make to cities that weren't affected.  What could happen if they knew early enough that your second flight wasn't going to go, and recognized soon enough that "this passenger won't get where they're going today", is they'd advise you of the situation, and offer you the option to cancel your trip, rebook the next day, or get to the connecting city so you're that much closer when the weather has passed & flights resume.  Depending on multiple factors, any of those might be a reasonable choice for a passenger to take, so they offer the options, rather than unilaterally cancelling your ticket.

It's also possible that the airport itself made some sort of call that "we're closed" at some point after your first flight had taken off, surprising the dispatchers at the airline.  In that case, you are, plain & simply, out of luck.  Not desirable, but in the millions & millions of airline flights and hundreds of millions of passengers flying every year, it sometimes happens.

Reviewing the weather reports for that timeframe from someplace like Weather Underground might shed light on just how bad the weather was, and when the forecasts were amended.  Making sense of that would require some familiarity with aviation weather reporting formats, though.


What happens if an A320 goes to full throttle with the parking brake set?

The question is simple: What happens?

There is a strong chance this happens:

Credit: spiegel.de

  On 15 November 2007, an Airbus A340-600 due to be delivered to Etihad Airways crashed during ground engine test at Airbus' facilities in Toulouse Blagnac International Airport. The brand new US$250 million aircraft, damaged beyond repair. was written off

Source

And there is a stronger chance that nothing bad will happen, but when you exceed the limits clearly stated by the manufacturer of the equipment without any good reason then your insurance cover flies away faster than the exhaust air so if Airbus tells you to not exceed 75% N1 then it is safe to assume that it is not safe to go 76% N1 on both engines with Parking brakes set.


Checklists before take off - how often must they be performed?

For an airline crew, the Before Takeoff Checklist is performed once before every takeoff.  There is normally no "run up" associated with such a checklist for jet aircraft.

Depending on what else is going on, there are reasons that engine power might be advanced then reduced, and it would be speculation as to what the reason for that was on your particular flight.


What is the maximum weight on the main gear of a large aircraft at rotation and touchdown?

There's more weight on the main gear when the aircraft pushes back from the ramp and is taxiing than on the takeoff roll, due to the lift generated from the wings. When the aircraft rotates the higher angle of attack generates enough lift to 'offset' the aircrafts weight and it takes off.
The most weight a main gear set will take will be on a firm landing at max landing weights (or above in an emergency). On the 737 there is a 'hard landing' G limit of (i think) just over 2G. So in theory temporarily on touchdown the main gear between them are handling twice the aircrafts weight.

As an example for the 737:
MTOW 77 tons.
MLW 65 tons.
4 main gear wheels.

heavy take off = 77/4 tons when parked ready to push back, reducing to 0 on rotation.
ie roughly 20 tons per wheel and tyre.

adding in landing G forces...

firm landing (but in limits) = (65*2)/4 tons on touchdown, quickly reducing back to 65/4.
ie roughly 32 tons per wheel down to 16 when parked up.

emergency landing after take off at MTOW = (77*2)/4 tons at touchdown. 36 tons per wheel!


It depends on exactly how you define "lift" and "weight". You might say intuitively that lift is all the forces acting on the aircraft in the upward direction, like this:

In this case, lift must equal weight, otherwise the aircraft would be accelerating. That is, it's rate of climb would be changing.

But it's more usual to define lift this way:

Here, lift and weight are equal in magnitude, but in different directions. Of course lift doesn't need to be equal in magnitude: it can be adjusted by the angle of attack. But let's suppose lift is equal to weight and see what happens.

Let's do all our calculations with Earth as the frame of reference1. It's useful to decompose lift into a sum of vertical and horizontal components so we can analyze the horizontal forces and the vertical forces separately:

Comparing the vertical component of lift with weight, we can see they are not equal:

Considering only the vertical forces drawn here, there is a net downward force on the aircraft. So why then is the rate of climb not decreasing?

A similar transformation happens to thrust. In a climb, thrust provides an additional upwards component. And of course we must also consider drag. Point being in a steady climb, lift (by the conventional definition) is not equal to weight, but the sum of all the vertical components of lift, thrust, and drag do equal weight.

Let's add an arbitrary amount of drag, and enough thrust to balance the vertical forces.

Now the vertical forces are balanced, but the horizontal forces must also be balanced if we want stable flight. Adding all the horizontal forces in my drawing, there's a net force to the left. So this aircraft may be maintaining a steady rate of climb at this instant, but it's losing speed and probably headed for a stall.

Remember, we initially set lift equal in magnitude to weight, and this is what happens. Without changing the direction or magnitude of lift, there's no solution that results in stable flight.

Therefore, a climbing aircraft requires less lift. To maintain this direction and velocity, this pilot must reduce lift by reducing the angle of attack, and increase thrust such that the vectors add to zero and there's no net force on the aircraft. Reducing lift will also reduce drag.

1 Any other frame of reference could work. For example we could use the aircraft as the frame of reference, which would mean lift is always up, but weight would change direction.


What is the minimum and maximum number of jet bridges used on an Airbus A380?

(Airbus)

The typical is two, one for each level. Three is not uncommon. Any more and the jet bridges will encroach on the adjacent gates, reducing the number of available parking spots at terminal. The right side is busy with other servicing equipment.

Also note the aft-left area being used for catering.

(gulfbusiness.com)

Why do passenger embark on the left side of an aircraft?
Why aren't planes loaded from both ends?
How long does it take to refuel a big jumbo jet?
Airbus patent for detachable cabin (patents.google.com)


If sweep delays compressibility, why does 747 cruise slower than A380?

From Wikipedia, the cruise speeds of the both airplanes are fairly similar:

A380, nominal wing sweep angle 33.5 degrees, cruise speed Mach 0.85

Boeing 747: nominal wing sweep angle 37.5 degrees, cruise speed Mach 0.84 .. 0.9, depending on the model.

So those numbers would contradict the claim in your question, but align with your expectations.
There are several other things to consider. The nominal cruise speed of these planes is more dictated by efficiency, required power for a given speed, and fuel prices. The 747 is an older design, when fuel was cheaper, the general tendancy is that modern airplanes reduced the cruising speed slightly in favor of higher efficiencies.
considering the sweep, raw numbers:

cos(33.5 deg)= 0.83
cos(37.5 deg)= 0.79

So the difference of approx 4% here seems to reflect the difference in cruising mach numbers: the higher sweep of the Boeing 747 reduces apparent Mach number roughly by the same amount that it is flying faster.
Then, for both airplanes, and certainly for the A380, the wing aspect ratio is quite low. So there's a point to challenge how much the sweep actually angles differ, from an aerodynamic point of view. It may be very well that effective angles depend a lot more on local airfoil shapes, low aspect ratios, and other 3d effects than they depend on the nominal sweep angle.
All that said, the swept wing has more advantages than just reducing the apparent Mach number. There is

enhanced aerodynamic stability around the yaw axis (this may even help in the event of asymmetric thrust due to an engine failure)
enhanced mechanical stability of the wing itself under aerodynamic loads
trim properties in transsonic aero regimes

The final design is then a result of many different considerations.
Eg, IIRC, the wing span of the A380 had a limitation so it would "fit into standard airports", and there were likely some trade-offs in aerodynamics for that reason.


They do in fact exist, though they often use smaller helicopters. A Google search on the term "heli taxi" yields thousands of results, and while a lot are probably irrelevant, the first few pages give hundreds of operators around the world, ranging from companies ferrying passengers between airports and major cities to companies servicing oil platforms at sea, islands too small to have airfields, etc.


What is the difference between Distant (D) NOTAMs, Local (L) NOTAMs and FDC NOTAMs in the US?

Short answer: D NOTAMs are about airports and navigation facilities; FDC NOTAMs are about airspace, procedures or regulations; and L NOTAMs don't exist any more (unless you're in the military).

The information on NOTAM types is a bit messy and inconsistent, to say the least. The Alaskan FSS lists 11 types; the PHAK 13-3 lists 3 types (as acpilot mentioned in his answer); the AIM 5-1-3 lists five in its NOTAM section, plus GPS NOTAMs in the GPS section.

And the FAA's military NOTAM site lists yet more types in their FAQ  such as M, V, W and F.

Anyway, here's what the AIM says about D and FDC NOTAMs:

  NOTAM (D) information is disseminated for all navigational facilities
  that are part of the National Airspace System (NAS), all public use
  airports, seaplane bases, and heliports listed in the Chart Supplement
  U.S. [...]  NOTAM (D) information includes such data as taxiway
  closures, personnel and equipment near or crossing runways, and
  airport lighting aids that do not affect instrument approach criteria,
  such as VASI.

  [...]

  FDC NOTAMs. On those occasions when it becomes necessary to
  disseminate information which is regulatory in nature, the National
  Flight Data Center (NFDC), in Washington, DC, will issue an FDC NOTAM.
  FDC NOTAMs contain such things as amendments to published IAPs and
  other current aeronautical charts. They are also used to advertise
  temporary flight restrictions caused by such things as natural
  disasters or large-scale public events that may generate a congestion
  of air traffic over a site.

According to the Alaska FSS page, NOTAM(L) doesn't exist any more for civilian use:

  NOTAM (L):  A NOTAM given local dissemination by voice and other
  means, such as telautograph and telephone, to satisfy local user
  requirements.  This type of NOTAM is now used only in the military
  NOTAM system.  All NOTAMs previously considered NOTAM (L)s in the
  civil NOTAM system are now considered NOTAM (D)s.

That's confirmed by AIR FORCE INSTRUCTION 11-208 (I), which describes NOTAM(L) as a military type:

  4.2.1. Military.
  [...]
  4.2.1.2. Local NOTAM (L series). Local NOTAMs are non-critical and non-safety related information that is essential for the flying and
  support communities to know. Facility managers may establish the
  parameters for local NOTAM determination.

Civilian L NOTAMs are now D NOTAMs that start with the specific facility code. You can find them on the civilian NOTAM site, e.g.:

  !LOU 05/077 LOU RWY 15/33 CLSD
  1605091213-1606222000

And to address your final point, NOTAMs are not obsolete. There needs to be some way to inform pilots about temporary changes or things that happen at short notice, and that's what NOTAMs are for. Many people feel that the system could be improved somehow - pulling up the NOTAMs for even a short flight can give you dozens of results - but there's no doubt that it's needed. Reviewing NOTAMs is an important preflight step, and examiners often test you on it during checkrides. There are plenty of NTSB accident reports that mention NOTAMs, usually in cases where the pilot didn't review them.


Why do some Airbus jetliners at full thrust sound like turboprops?

I'm assuming you mean that buzzing/growly/deep humming sound.
That is the tips of the fan blades in the first stage fan disc approaching the speed of sound, and getting close to forming shock waves. Their noise generation becomes strong at that point.


Does any company (or country) still use Zeppelins or airships? Why not?

Zeppelins had a rigid skeleton and several internal gas bags. None of them are still in operation.

Airships today are blimps, that is, one big gas bag which is kept in shape by internal pressure, which in turn is regulated by ballonets.

The only airships flying today are used for

Advertising (Goodyear blimps, MetLife blimps)
Military observation (Lockheed Martin P-791)
Sightseeing tours (Zeppelin NT)

All attempts (and there were many) to use airships for cargo transport have eventually failed, sometimes spectacularly.


How do aircraft manufacturers determine the elevator size?

There are many factors going into the sizing of elevators, and they are all interconnected with other considerations such as CG envelope, static margin, flight controls, etc.

Here are some factors that will influence up-sizing the elevators. Usually, the minimum elevator sizing is determined by low speed requirements:

Ability to perform early rotation in both all engine operating and one-engine-inoperative conditions (14 CFR 25.107(e)).
Ability to perform go-around in the highest flap extended position (14 CFR 25.119).
Ability to stall the aircraft to demonstrate the intended stall speed (14 CFR 25.201). This may not be obvious, but if you lack the elevator authority to demonstrate the intended stall speed, then you can only declare what you have demonstrated, which negatively impacts all the performance speeds for takeoff and landing.
If the elevator is power actuated (e.g. hydraulically powered), then you also need to consider regular takeoff, landing, go-around, and maneuvering at low speed, with failures (14 CFR 25.671(c)).

Here are some factors that will influence down-sizing the elevators:

Demonstration of static longitudinal stability at Vmo/Mmo. For column based inceptors, the average stick force to speed change must be no shallower than 1 lb per 6kt (14 CFR 25.173(c)). For FBW aircraft, too large an elevator can also lead to residual oscillations.
General over-sensitivity to control inputs at high airspeed.

Of course, most of these aforementioned points are heavily influenced by flight control design, such as anti-servo tab, bob weights, artificial feel force, etc.


Limitations of bird flight as an aircraft design

The movement of the bird wing during the flight is very complex. Not just the trajectory matters, the shape of the wing itself changes as it moves. Angle of attack changes continuously. It is definitely not just about flapping up and down. For a long time, this limited the possibilities of building such machines, while with recent technology it seems possible.

This complex movement also restricts the maximum speed possible, as even small birds cannot beat the wings more than about 80 times per second. The fastest birds, such as the white-throated needletail, may reach 105 mph (168 km/h) in horizontal flight that would not be impressive for an aircraft.


F-111 emergency landing with no wheel; what is done to reduce risks when loosing a wheel?

What are the relative risks of an ejection vs a no-wheels belly landing. I mean obviously the costly loss of airframe. But is the risk to life pretty even odds?

  In a conventional aircraft (e.g. civillian) ejecting is just not an option so belly landings are the norm. But in an F-111 is a belly landing still safer than a controlled, planned ejection?

Ejecting is an extremely violent event, often resulting in the pilot being removed from service for an extended time period, or permanently. 1 in 3 suffer back fractures or other major complications. Ejecting is possibly an end-of-career move for pilots (at best, an end-of-life one at worst). Belly landing on the other hand isn't usually a bad event, typically the aircraft is repaired and returned to service. In an ejection, the aircraft is a total loss, not to mention a rather large unguided bomb.

  Are there no sensors etc. that'd detect they had lost a wheel? Any other indirect indications based on asymmetric drag, hydraulics etc. that one may expect? In other words, how likely is it that one loses a whole wheel but does not know.

No, there are no "wheel fell off" sensors. There are possible sensors to tell the pilot of low tire pressure, and certainly have sensors for hydraulic pressure. That isn't to say though that getting a low tire pressure means a wheels-up landing, landing on a flat tire is entirely possible. Drag probably isn't going to be significant, at least not enough to notice outside of gusts or other factors. That being said, having a wheel "fall off" is an extremely rare event, probably so few that you could count them by hand.

  Are there standard procedures where ATC uses binoculars etc. to check visually whether all seems OK with a landing aircraft (wheels etc.) I know they will check on request, but is there any standard protocol?

Not typically, but ATC often watches departing aircraft with binoculars, not necessarily looking for missing parts though. In clear visual conditions, it would probably be pretty apparent that a wheel fell off to people on the ground, at the very least the next departing aircraft who had to avoid it on the runway. Usually when something falls off the aircraft, the runway needs to be closed while they do a FOD (foreign object debris) removal run.

  Don't military airfields lay down foam for emergency landings? Or is there a downside to foam on the runway?

Yes, military airports can lay down AFFF (aqueous film-forming foam) on the runway, but you don't always need to. The down side is that it causes the aircraft to slide quite a bit further than it may be planned, and it's incredibly hard to clean out. If there isn't much of a risk of fire, its better to just belly it down in the grass. Or just let it slide on the runway. Most military aircraft can dump fuel and land without much fire risk.

By the way, if you think it is impressive to belly-land an F-111 after a wheel falls off, you should watch this video about an Israeli pilot who landed an F-15 with one wing!!!.


How much thrust is available from the Allison T-56-A-15 engine?

From Raymer's "Conceptual Aircraft Design", page 327, equation 13.15:

$$ \eta_p = \frac{TV}{P}$$

Where:

$\eta_P$ is the propeller efficiency
$T$ is the Thrust [kN]
$V$ is the True Airspeed [m/s]
$P$ is the engine power [kW]

Reverting the formula you get that the Thrust per engine is given by:

$$ T  = \frac{P \eta_p}{V}$$


Distance of downwind leg from runway in glider landing pattern?

I was taught (by various publications and compenent CFIs) that angles are a better thing to focus on than distances.  For example, this publication suggests:

  You  should  turn  from  your  crosswind  leg  (or  from  your  45  entry)  onto  your downwind leg when the runway centerline, or an extension of it, is 25-30° below the horizon. Using angles automatically compensates for variations in altitude.

For me, this makes sense for several reasons:

Judging angles is much easier than judging distances.
The AGL pattern altitude might differ depending on the airport/field you are landing at.
If you are landing out, you should ALWAYS fly a normal pattern if possible.  This may force you to fly an abbreviated pattern closer to the ground.

Obvously, adjustments to this will need to be made for a crosswind.


What are the US definition and restrictions on aerobatic flight?

Aerobatic flight is "an intentional maneuver involving an abrupt change in an aircraft's attitude, an abnormal attitude, or abnormal acceleration, not necessary for normal flight."

According to the FAA (91.303), no person may operate an aircraft in aerobatic flight:

Over any congested area of a city, town, or settlement;
Over an open air assembly of persons;
Within the lateral boundaries of the surface areas of Class B, Class C, Class D, or Class E airspace designated for an airport;
Within 4 nautical miles of the center line of any Federal airway;
Below an altitude of 1,500 feet above the surface; or
When flight visibility is less than 3 statute miles.

Aerobatic flight is sometimes considered to be flight with more than 30 degrees pitch or more than 60 degrees bank. This is incorrect. It applies to wearing a parachute. (FAR 91.307)

A normal category aircraft is certified for the following "non-acrobatic" operation: Stalls, lazy eights, chandelles, and steep turns, in which the angle of bank is not more than 60°.

A utility category aircraft is certified for spins (if approved for plane), lazy eights, chandelles, and steep turns, or similar manoeuvres, in which the angle of bank is more than 60 degrees but not more than 90 degrees.

An acrobatic category aircraft is required for other aerobatics.


Has anyone used a 1/4" Y adapter and 3.5mm-to-1/4" converter to pipe in music into their aviation headset?

Commercial 1/4 Jack audio headsets are stereo, signals to top and ring, body is ground... so you need to fiddle the wires so both signals go to the tip... Else you will.only hear one channel .. I don't advocate this use because if you are listening to.music you might miss calls about other traffic etc.. Your call.


Only when on the ground, and at the inlet end, where a strong wind from  the side and behind could influence the engine's ability to draw air in the front at low power settings.  Some engines have limitations or restrictions on how power is applied during takeoff in strong tail or quartering winds, because of initial flow disruptions at the front from air having to make a sharp corner into the intake, where large thrust increases could cause compressor stall/surge.

You might have a procedural requirement to advance power to some intermediate setting, then let it stabilize there before going the rest of the way to takeoff thrust. The GE CF-34 has limitations like this, where winds above a certain speed and off angle a certain amount require a staged application of thrust.

Once you're in the air, there is no such thing as a tailwind as far as the airplane is concerned except insofar as tailwinds add to ground speed.  For the engine, it's all coming from the front as soon as you are moving with any significant airspeed.


Where can I find data sets on jet fuel prices, including futures and options?

Airnav.com lists current fuel prices at most airports (that they can get data for). Keep in mind that airlines may (and most likely do) get a bulk discount based on the volumes they buy in.You may want to take a look at this, and keep in mind they may also trade on kerosene futures as that is what jet fuel is made from.


If the previous 100 hour was overflown but not for hire, is the time still subtracted from the next 100 hour?

According to FAR 91.409 b, the 100 hours can be overflown by ten hours in order to fly the plane to a place where the inspection can be performed, but this time must be included in the next 100 hour period.

If the five hours over the designated 100 hour time limit was for hire (ie not flying the airplane to somewhere the inspection could be performed) then they were technically illegal. And no, that wouldn't change the fact that you must count those hours in the current 100 hour cycle.


Has the design-flaw with the Boeing 737's cabin-pressure switch been fixed yet?

The Wikipedia article on Helios Airways Flight 522 also mentions this wiring issue, and cites a separate report regarding a May 2003 incident in which a 737 had issues with pressurization. During the investigation it was discovered that wiring had shorted and burned in a particular bundle of wires, called a loom, which was important for control of pressurization. The AAIB issued a safety recommendation regarding this issue:

  Safety Recommendation 2004-33

  It is recommended that in order to prevent failure of the cabin pressure control system in the event of damage to wiring loom W298, the Boeing Commercial Airplanes should consider, on the Boeing 737-436 and similarly configured models, separating or protecting the wiring associated with the different modes of operation of this system, which connects the cabin pressure controller to the rear outflow valve, such that any single point failure of the loom would not result in effective failure of the pressurisation control system.

In their 2006 progress report, the AAIB followed up on this recommendation:

  After a review of the issue and the service history of the pressurization system for the 737-100 thru - 500 model airplane, Boeing felt that modifications of the wiring with the intent of separating the outflow valve functions consistent with the subject safety recommendation would not significantly contribute towards a reduction in the overall rate of depressurization events. Their rationale was based on the basic design philosophy and concept of the original system which includes:

  1) A single, mechanical outflow valve which is controlled by a single multi-mode analog pressure controller and driven by independent AC or DC powered electrical motors. Each motor can also be manually commanded open and closed via separate switch on the pressure control panel.

  2) In the event of a complete power/control loss (e.g. - electrical interruption or damaged wiring) either motor will remain in last commanded position. The airplane is equipped with an independent aural warning system (cabin above 10,000 feet) and visual cues (cabin above 14,000 feet) should this condition lead to a cabin pressure loss.

  3) The airplane is equipped with both fixed and portable oxygen supply systems for passengers and
  crew.

  4) If pressure cannot be reliably controlled/restored within a short period of time, the flight crew will utilize procedures (such as rapid reduction in altitude, declaration of emergency and landing at nearest suitable airport) which mitigate the exposure time to low pressure.

  Status - Rejected - closed

So the rationale is that if the system fails, the crew is alerted and may take appropriate action. Note the following regarding an AD published in 2011 with a deadline of March 2014:

  The FAA released Airworthiness Directive AD-2011-03-14 requiring all Boeing 737-100, -200, -300, -400 and -500 types to install two additional warning lights, one for takeoff configuration and one for cabin altitude warning, and introduce updated documentation within 36 months following March 14th 2011.


Why do we have to check that the fuel x feed is properly functioning before departing for an ETOPS flight on the A320?

The main reason to check the Fuel-X-FEED on the ground before the flight is to allow the pilots to use the total fuel quantity on both wings in case of a single-engine failure during flying in ETOPS.
(Due to engine-out scenario you may not be able to feed one engine by both fuel tanks without the FUEL-X-FEED Valve)

in addition to this, the Fuel-X-FEED in the A320 MEL is a NO DISPATCH item by means you can't depart without and that reason tracks back to the EASA Requirments listed in AMC-20 AMENDMENT  - 7 (APPENDIX 4 - FLIGHT PREPARATION AND IN-FLIGHT PROCEDURES):

(11)  Fuel  system
(i)    The aeroplane fuel system should provide fuel pressure and flow to the engine(s) in accordance  with  CS  25.951  and  25.955  for  any  fuel  pump  power  supply  failure  condition not shown to be extremely improbable.
(ii)   The fuel necessary to complete the ETOPS mission or during a diversion should be available  to  the  operating  engine(s)  under  any  failure  condition,  other  then  fuel  boost pump failures, not shown to be extremely improbable2 (e.g. crossfeed valve failures, automatic fuel management system failures).


Is it reasonable for flight economy to correct banking tendencies with stick and rudder?

You might be better off correcting weight imbalance with more fuel in the opposite wing if possible.  Then fly with fuel selector on both as long as you can.  This should give you better economy than trimming aerodynamicly.

Notice this also true for weight too far forward or aft.  Good balance helps in the air.


The same as any other powered aircraft would - controlling their descent with a combination of pitch and power.

Most small GA type aircraft don't have air brakes, spoilers etc anyway, so that's fairly immaterial.

I'd imagine almost any civil aircraft can be landed quite safely without flaps - it certainly forms part of the standard training syllabus for the PPL and you'd likely be expected to demonstrate a flapless landing on your skills test. The only difference is a slightly faster approach and more nose high attitude.


What is the most fuel efficient climb speed for a C172 SP?

First consider the four forces on the airplane in the cruise:

          ⇧
        Lift
⇦ Drag    .  Thrust ⇨
       Gravity
          ⇩

Drag is a function of the airframe, attitude, and airspeed. If the airplane can fly, then drag is more then offset by thrust. The lift is generated by a component of the forward motion when the flying surfaces convert the horizontal force to vertical force. And finally, the lift force is equal to the force exerted by gravity.

Now let's talk about fuel efficiency. That is how much you can do with a quantity of fuel, and you didn't specify whether you're interested in fuel for time (endurance) or fuel for distance, or something else. But let's discuss the major components of fuel usage:

Engine motion. The engine is more efficient in terms of power at its higher rated power setting. So, you would think efficiency would be gained by selecting a higher power (assuming you could also climb with less than 100% power).
Heat. I guess a typical heat engine like a piston engine consumes about 50% of fuel energy to heat (rough guess, it's prob. in the range 35% - 65%). But the heat engine is more powerful the greater the difference between inlet temperature and exhaust temperature. So, the greater time you can spend at higher altitude is probably more efficient in fuel for power.
Cooling. Sometimes you need extra unburnt fuel for engine cooling. For example during climb, when the engine is at higher power and the airflow is reduced.

Now let's discus climbing. During a climb the aircraft has (in theory) to produce all the power necessary for level flight, plus a little extra for the change in elevation. I would posit, without any evidence, that the fuel spent on the elevation change is insignificant compared to the fuel required to stay aloft. (I will gladly accept a reference or metrics if someone has them). But think about it, if you put the aircraft in an elevator powered by a similar motor, it would take a few drops of fuel to raise a few feet. That's a thousand drops for a thousand feet - it is nothing versus constantly offsetting the the weight constantly as it does in flight.

So what is the more fuel efficient climb procedure? It is the technique using:

Higher engine power
Maximizing time at higher altitude; minimizing time at lower altitude
Balancing the mixture to keep the engine as hot as its design will allow. (you said fuel-efficient. You didn't say cost-efficient. Don't violate your POH!)

In summary, to expend the least fuel, climb as early as possible, as quickly as possible (e.g. Vy) and with minimum acceptable richness.

And as long as we are talking efficiency, please also run the tanks dry at your final cruise altitude. This will maximize the most fuel efficient part of the cruise, when you are carrying less fuel.


What is the standard procedure in case of inconsistent sensor readings?

The procedure used would depend on which information is conflicting/unreliable (and of course the aircraft type).

With one or more unreliable airspeed indications (which is one of the more critical ones), the initial action is NOT to start troubleshooting/figuring out which indicator is "the correct one", but to ensure safe speed/flight path by other means. The initial actions on Boeing aircraft is to disconnect automatics (auto throttle, autopilot, flight director) and control the aircraft given memorized combinations of pitch and thrust. With the aircraft under control, and when directed by the checklist, you start analyzing the situation, to see if you can rectify/isolate the faulty source. If a reliable source can not be determined, the aircraft continues to be flown by pitch/thrust settings given in the manual (based on altitude, if known, weight, flaps/gear, desired vertical profile etc).

In the case of unreliable altitude, in case you can't determine a reliable source, you can typically use radio altitude below 2'500 ft. A big caveat is that if the transponder is set to use an unreliable static pressure source, the altitude that ATC sees on secondary radar will also be unreliable. An example of this was seen in the Aeroperú 603 accident, where the aircraft took off, with the static ports taped over, and ATC was asked to assist with altitude and speed information: CVR transcript - Wikipedia

Erroneous airspeed/altitude indications often imply each other, as an unreliable static pressure source will affect both.


Is there a standard format to exchange airspace information in electronic form?

The majority of GPS navigators and FMS have a dataloadable navigation database.  The actual database each uses is typically encrypted and compressed using proprietary algorithms.  The source data for all of these databases normally start out in ARINC 424 format.  Unfortunately, A424 is not available free of charge.

  ARINC 424 is an international standard file format for aircraft navigation data maintained by Airlines Electronic Engineering Committee and published by Aeronautical Radio, Inc.. The ARINC 424 specifications are not a database, but a "standard for the preparation and transmission of data for assembly of airborne navigation system data bases".

The databases are compiled by companies such as Jeppesen. Jeppesen collects the data from the controlling agencies around the world, checks it, and merges it into a world-wide database that they then sell (typically via subscription).

Some information for US airspace is available directly from the FAA.  It is not in a format that can be directly loaded onto aircraft, but may be of use offline.


Can a tail pipe fire occur in cruise? If not, why not?

It comes down to the definition of "tail pipe fire".  A tail pipe fire is normally what you might call a "static fire" of unburned fuel accumulating in the tail pipe with little to no airflow through the engine, and this is normally during ground operations especially during starts.

The tail pipe has an overboard drain for this purpose, but it needs time to let the fuel out.  This is why, during a start, the procedure may require the engine to be dry motored for a minimum time if the start is aborted.  This is to keep pushing air through the engine, to help dry it out you might say, and let whatever unburned fuel has pooled in the tail pipe drain overboard.  If you don't do this and try another start right away, you might end up lighting off the residual fuel in the tail pipe during the start... and a tail pipe fire.

Based on the Air India pics, that wasn't a "tail pipe fire" in that sense (pooled fuel), and was actually case of some kind of engine disruption or malfunction that let the flame move out of the burner can into the turbine section and tail pipe.  This drives the temperatures at the turbine and tailpipe through the roof.  You can see this by the melted turbine blades.  A fuel control problem or air flow disruption problem farther upstream would be the issue here.

You may not get a tail pipe overheat warning in this case because the overheat detection loop (sensing wire) is usually around the section of tailpipe within the cowling, and with the flame originating from the burner can and contained in the tail pipe itself with the airflow, the sensing loops on the outside of the hot section case probably didn't get hot enough.

What should have been obvious to the crew however, was Inter Turbine Temperature (ITT) (or whatever turbine section parameter that engine measures) spiking through the roof at the time the passenger was seeing the flames out the back.

So to question 1: Yes, a "tail pipe fire" is normally a fire from pooled fuel in the tail pipe and is normally only on the ground (but on some engines, could possibly happen during an in-flight relight as well).

For question 2: A tail pipe fire in that sense won't occur in cruise with the engine running.  What is described as a "tail pipe fire" in the article is actually an engine malfunction that caused the flame to move aft out from it's normal place in the burner can, into the hot section, but it doesn't involve fuel pooling in the tail pipe.  Bird ingestion, compressor section malfunction or compressor stall, fuel control going haywire (dumping in too much fuel).  See any videos of airliners ingesting birds on departure and that's exactly what you see.


For a small flying wing, can two motors with different speeds replace the ailerons?

First thing first:
I think you mean yaw not roll. See Yaw definition

If you actually mean roll, then the answer is no.

If you mean yaw; then the answer is yes.
However it is impractical for two reasons:

1) Engines, especially jets but also propellers have a latency when speeding up and down. This will make it impractical, and might create pilote induced oscillations.
Electrics motors are more reactive, but so far they have yet to be commonly used in aviation.

2) Redundancy. If one engine fail.... you have to shut down the second engine, and you lost yaw control.


How big was the F-14 fleet compared to other US carrier-based aircraft in 1981?

During the plane’s heyday, the US Navy maintained 26 active duty F-14 squadrons for the 12 carriers certified for F-14 operations, 4 Test and Evaluation squadrons, 2 Fleet Replacement squadrons and 4 Naval Reserve squadrons.  632 F-14s were delivered to the US Navy between 1973 and 1994.  Each Forrestal-, Kitty Hawk-, Enterprise-, Kennedy-, and Nimitz-Class carrier had two squadrons of F-14s aboard, with 12 aircraft per squadron.  Depending on the cruise air wings aboard, there were approx 85 aircraft aboard ship.  This sets the F-14s comprising about 28% of the air wing’s airframes.

The F-14 was used to provide air superiority in the airspace around the battlegroup as well as escorting strike packages and providing a first line of defense against long range enemy interceptors and cruise missiles.  Later upgrades as well as the F-14D variant allow for precision strike capability against surface targets as well.  The genesis of the AWG-9/AIM-54 weapons system was as a defense against TU-22s carrying Kitchen cruise missiles which had a very real chance of sinking a carrier if the missile found its mark.  A secondary role was given to the F-14 in the early 80s as the primary tactical reconnaissance aircraft for the fleet, replacing the aging RA-5C Vigilante and RF-8 Crusader aircraft by means of a removable Tactical Aerial Reconnisance Pod System (TARPS) which mounted on the center body pylons for the AIM-54 missile.  Later systems included ROVER pods for precision close air support.


What controls the brightness of the MCDU display and keys?

These buttons are to increase and decrease brightness of MCDU. Also, they are used to turn on and off the unit.

As explained here:

  BRT AND DIM KEYS
  Control the light intensity of the entire MCDU. MCDU power up is performed
  with the BRT key and MCDU shut down is performed with the DIM key.

And here:

  Repeatedly clicking on the "BRT" (the top of the paddle switch) will
  switch the unit on and increase the brightness. The reverse is also
  true. Repeatedly clicking on the "DIM" (the bottom of the paddle
  switch) will decrease the brightness and switch the unit off.


How did the propellers attach on a Lazair attach if the shafts had a woodruff key instead of opposite thread?

I believe that while the original engine shafts had a slot for a woodruff key, no key was actually used in attaching the props to the crankshaft. Instead, a nominal arrangement of multiple (6, I believe) bolts attached the props to the crankshaft for mutual transmisal of both engine torque and prop thrust. Presumably the bolts were secured with safety wire, but I have no data on this.


Selection of the profile is only a small portion of the design procedure of the empennage:

Aerodynamic centre of the aircraft minus tail is determined first.
Aft Centre of Gravity is determined.
Static longitudinal stability criteria determine the area of the empennage - upon a disturbance in Angle of Attack, the total aircraft must generate a moment that counteracts the disturbance. Usually, wings and fuselage contribute negative stability, and the tailplane must be sized such that the stabilising moment compensates for this in all circumstances.
Once the area is determined, the aspect ratio, taper ratio, sweep angle and profile thickness are chosen considering a host of factors, including the lift-curve slope, stall behaviour, out-of-trim conditions, structural weight, design diving Mach number.
And then the airfoil shape is chosen. From Torenbeek section 5.5.1.d:

  The basic requirements are that the airfoil section should have a high $C_{L_\alpha}$ and a large range of usable angles of attack. Frequent use is made of approximately symmetrical airfoils with a thickness ratio of 9 to 12 percent and a large nose radius, e.g. NACA 0012. Tailplane stalling - at
  the lower surface - can be postponed by adopting negative camber (e.g. NACA 23012 upside down), upward nose droop, an increase in the nose radius or by means of a fixed slot.

Table 9-2 from the same book contains (dated) horizontal tailplane design data and lists some profiles used:

Cessna 177: NACA 0012/009
Fokker F27: NACA 63A-014 mod.
Lockheed C-130B: NACA 23012 inv.
Cessna Citation 500: NACA 0010/0008
B737/100: 12%/9%
Boeing 707/320: BAC-317


Do elevators have cambered airfoils inverted or symmetrical airfoils

Generally they are either symmetrical airfoils (like NACA 0012) or flat plates (especially on fabric airplanes).  The horizontal tail doesn't have to work as hard, or operate over as wide an AOA range, as the main wing in generating downforce, so you can get away with what amounts to, on most fabric airplanes, a slightly streamlined sheet of plywood.

There are some specialty exceptions. The Zenith 701 family of homebuilt STOL aircraft are unusual in having a heavily cambered flat bottom airfoil for the tail (actually, flat topped, since it lifts downward and is installed "upside down").  They did this to get as much down force as possible at very low speed and since the airplane is a bit of a slug anyway, the draggy tail airfoil wasn't so much of a penalty.

A homebuilt I had started on but never got anywhere with, called the Pegazair, had something similar, having ripped off a few of the 701's design elements.

Also, it was a practice at DeHavilland Canada to use tail airfoils with a bit of negative camber to improve down force at low speed on their STOL designs.  I'm sure there are others.


Why do multi-engine privileges not propagate down to single-engine?

Just like having a SEL Commercial with a MEL PPL doesn't mean you can operate a MEL commercially.

The certification requirements require the demonstration of particular maneuvers like a Chandelle which includes a slow-flight phase. Slow flight on a single is significantly different than slow flight on an MEL because of p-factor and aircraft handling. Same thing with lazy-8's

Another reason is engine-outs. Engine outs have to be demonstrated, and on a Multi, an engine out means you can limp it to your closest airfield. On a single, unless you are in gliding distance, you will be putting it down off-field.

The FAA also has different test standards for SEL commercial versus MEL commercial. Because you've demonstrated satisfaction on an MEL doesn't mean you are proficient in SEL operations for the same maneuvers, so the FAA makes you demonstrate it.


How does the Pseudo-Satellite Zephyr land?

After some power googling...

https://www.airforce-technology.com/projects/zephyr/

  Launch and recovery The air vehicle is launched by hand. Recovery is
  by belly landing as the air vehicle has neither landing gear nor
  landing parachutes.

https://www.ainonline.com/aviation-news/defense/2016-07-11/solar-powered-pseudo-satellite-display-farnborough-2016

  It is hand-launched by a five-man ground crew, and recovered by belly-landing.

http://en.ruvsa.com/catalog/zephyr/

  Launch: hand launch Recovery: autonomous belly landing

It has two-bladed props, so they can be positioned to avoid a ground strike.


Why should autofeather only be used for take off on the Dash-8 Q400?

It's because the critical case that autofeather caters to is engine failure right after V1, on takeoff, where the normal identify/feather drill uses up precious time.  An engine failure on a missed approach or go-around starts well above the low energy state of an engine failure after V1 and there is much more time and energy margin to do the normal feathering procedure.

The system is quite sensitive and there are risks associated with having the autofeather system armed and "ready to fire" you might say.  Mainly, having it put a prop in feather when you don't want it to.  Or even BOTH props in feather.  That risk outweighs the benefit of having it armed outside of the take-off case.

It's a bit like having a policy of taking a firearm off SAFE only when there is a critical need to able to fire instantly when clearing a house.


Is there a practical carbon-free jet fuel?

A different fuel is not necessary. Even the most extreme experiment in diverted jet engine output, the Hunting H.126 did not divert its exhaust flow, it just tapped off compressed air. Its takeoff speed was 52 km/h. All aircraft need forward thrust, and with modern high-bypass turbofans you can get massive amounts of compressed air that's more than enough for blowing any surface you want. The BAe Harrier is a good example; the front nozzles of the Pegasus blow compressed air and match the thrust of the jet exhaust in the rear nozzles.

Fuels roughly fall into 3 categories:

hydrocarbons (everything from methane to jet fuel and diesel). They all contain carbon. Some leave less soot than others: methane is relatively clean. But it's a gas at room temperature, which makes it difficult to store (you need heavy high-pressure tanks).
Hydrogen. Clean, but very difficult to store (needing even heavier high-pressure tanks than methane), and explosive in a wide range of circumstances.
Oddballs like hydrazine and hypergolics. They're all nasty, toxic fuels that require specialized handling which make them unsuitable for civilian use. Hypergolics are two-part fuels that spontaneously combust when in contact with their counterpart.

Some more details on hydrazine:

  Hydrazine is highly toxic and dangerously unstable

Anyone involved in fueling a hydrazine-powered vehicle has to wear a full Hazmat suit. That alone makes it difficult to use a hydrazine-powered aircraft on most airfields as it'd disrupt normal operations.

Hydrazine is also inefficient. For jet fuel, you can pull the oxidizer from the surrounding air. Hydrazine has a specific impulse of 220 s, while jet fuel has a specific impulse in the region of 350 s. So you have to carry 350/220 is 1.5 times more fuel to do the same work.

The exhaust products of hydrazine are extremely flammable (hydrogen). You could burn that in a jet engine, which would significantly increase the specific impulse. Hydrogen is a bit finicky, but hydrogen-fueled aircraft have been tested.


What standard of English are Air Traffic Controllers held to?

You might want to have a look into ICAO Language Proficiency Rating Scale. The article suggests that

  In 2003, ICAO set a deadline of March 2008 for English language
  proficiency at Level 4 and above for all pilots flying international
  routes and air traffic controllers serving international airports and
  routes.

Original text is not in bold.

In the same link, you can also find the description of each rating scale, as described in the Manual on the Implementation of ICAO Language Proficiency Requirements Doc 9835 AN/453, quoted here for convenience:

As of translators on call, I've never heard of such a practice and if I judge from the Level 4 being the minimum, that wouldn't be necessary.


Does the jet blast from a large aircraft pose any risk for other aircraft nearby?

The airplanes in the photo are quite far apart, at least 1-2 lengths between each (it's just the long lens making them look cheek by jowl), and while in line going straight, they are only using a little over idle thrust to get rolling when required, so the jet blast effects are negligible.  The main factor is FOD (foreign object damage) kicked up, and at that distance that would mean sand/dust particles, but the effects of that would be too subtle to measure over the long term in any reasonably clean environment.

That being said, if I was in a desert area where there was drifting sand on the taxiway, I would probably increase my spacing a bit behind the guy ahead.  And you can bet that the guy in the (what looks to be a) King Air that is second in line in the pic - walking with the elephants - is keeping a little bit more distance from the elephant in front as well, owing to the size differential. If I was in the King Air I would be worried about the plane adding a big shot of thrust in both engines to start the turn (hopefully they'll just use the left engine), and the inside engine would be pointing straight at me part way through the turn, and I would be staying  well back.   Airmanship and all that...


Just like normal trimming. However trim the fuel tank use aft fuel tank to achieve the trimming effect. Fuel is pumped between main tank and aft tank to shift CG around to a desire position during flight.

Fuel tank trimming has additional benefit of keeping the airplane in "clean" configuration, creating less drag compare to normal trimming.


Why do military jets seem to always take off using the afterburner?

Military aircraft takeoff with afterburner when it is safer to do so with an exception- carrier pilots always light their cans while taking off (and also when the pilot wants to show off, but lets leave it at that).
The main consideration for using after burner in operational land based aircraft is the available runway length. When the aircraft is loaded heavily with ordnance, the runway required may be more depending on other factors (like OAT etc). In this case, it is better to go for afterburner takeoff. For example, Air Force Instruction 11- 2F- 16V3, F- 16 Operations Procedures specifically states:

3.6 Takeoff
3.6.6 Make an afterburner takeoff anytime the computed MIL power takeoff roll exceeds 50 percent of the available runway.

The same is true for other aircraft like the F-15 too:

3.7 Takeoff
3.7.2 ... For single ship takeoffs, if the  single ship computed  military power takeoff distance exceeds one-half of the available runway, takeoff using afterburner.

Another reason the pilots do it is to check the systems- it is better to check the afterburners on ground rather than finding any problems (like intermittent afterburner) in air. Of course in case of naval aircraft, the afterburners are on till the aircraft clears the ship.
Also, as @Jörg  pointed out, people upload videos that look 'cool'- hence the impression that they always use afterburners rather than the boring military power takeoff.


Has there been a recent change in the airspace configuration at KFYV-- Drake Field near Fayetteville AR?

A little more googling has provided an answer -- on 12/10/18, effective 2/28/19, the extension was greatly reduced in size (and the remaining bit converted to class D) due to the decommissioning of the Drake VHF omnidirectional range (VOR) navigation aid -- see https://www.federalregister.gov/documents/2018/12/10/2018-26498/amendment-of-class-d-and-e-airspace-and-revocation-of-class-e-airspace-fayetteville-ar

I'm not sure why that airspace change was not reflected in any of these documents-- https://www.faa.gov/air_traffic/publications/airspace_amendments/

Actually, it was there, I just didn't see it because they mistakenly used the abbreviation "AK" not "AR" for Arkansas in the table.

Nothing more need be said here--


How many flights follow the North Atlantic Track relative to those that don't?

According to ICAO NAT doc 007 (North Atlantic Operations and Airspace Manual, edition 2014/2015) (PDF), approximately half of the North Atlantic (NAT) flight use the Oceanic Track System (OTS).

  2.1.3: It should be appreciated, however, that use of OTS tracks is not
  mandatory. Currently about half of NAT flights utilise the OTS.
  Aircraft may fly on random routes which remain clear of the OTS or may
  fly on any route that joins or leaves an outer track of the OTS. There
  is also nothing to prevent an operator from planning a route which
  crosses the OTS. However, in this case, operators must be aware that
  whilst ATC will make every effort to clear random traffic across the
  OTS at published levels, re-routes or significant changes in flight
  level from those planned are very likely to be necessary during most
  of the OTS traffic periods.

Note that not all flights in the NAT do cross the Atlantic from East to West or vice versa. For example:

Flights from Northern Europe to Spain / Canaries / Portugal and v.v.
Flights from Portugal to the Azores and v.v.
Flights from Iceland

And then there are a number of fixed routes that allow aircraft that do no meet the minimum navigation performance requirements to cross the ocean. These tracks do not change with the daily winds like the OTS tracks.

All these are included in the 'about half'

But especially in the Northern part of the NAT airspace, covered by the Reykjavik FIR there are many random routes. According to the website of Iceavia:

  In 2010, 92.3% of the traffic in the Reykjavik CTA was on random
  tracks and 7.7% was on the NAT tracks.

But that is mainly because the OTS tracks are usual south of the Reykjavik FIR.

That same page says:

  In effect, where the preferred track lies within the geographical
  limits of the OTS, the operator is obliged to choose an OTS track or
  fly above or below the system. Where the preferred track lies clear of
  the OTS, the operator is free to fly it by nominating a random track.
  Trans-Atlantic tracks, therefore, fall into three categories: OTS,
  Random or Fixed.


What airframe designer/manufacturer is credited with the first retractable landing gear system?

It looks like the first plane that actually flew and had at least a partially-retractable undercarriage was a German racing plane, the Wiencziers Renneindecker, from 1911:

You can see the undercarriage designed to collapse to the rear, using a hand crank in the cockpit to lift the gear. Not a great idea by today's standards as the gear would be prone to collapse on landing, but it apparently worked well enough at the time.

There are plans for retractable landing gear dating back to the late 1800s, before powered flight in such a craft was ever achieved, but they didn't become common on planes until just after WWI. Even then, for relatively slow planes (<200mph) it remains common even today to keep the gear fixed and wrap the wheels in a cowl, as for only a ~4% increase in drag over a full retractable setup, you save a lot of weight and mechanical complexity. Notable fixed-gear craft in military service through WWII include the German Ju87 Stuka and the Nakajima Ki-27 "Nate". Though most of the American wartime air fleet had retractable gear as of just after the start of WWII, practically every WWII air corps draftee trained on either a BT-11 or one of the biplane trainers like the PT-13/17/18. Today, plenty of civvie small craft have fixed gear, such as the Cessna 150, 172 and variants, Piper Cubs and Cherokees, some Beechcraft Musketeers, etc etc.


Would failure to put on an oxygen mask during loss of cabin pressure result in death?

I did high altitude training about three months ago, up to 30,000 feet simulated altitude.  Here's the timeline:

Within 30 seconds (oximeter 100-95): noticed physical symptoms beginning.  I could tell that something was wrong, but felt functional.

Within 60 seconds (oximeter ~90): mild headache.  Still able to write my name.  Not feeling good, but acceptable.

Within 3 minutes (oximeter ~80):  Able to do simple tasks when specifically directed (thread a nut onto a bolt), but completely unable to multitask at even the simplest things (tried to put my pen down...didn't notice that I missed the desk - it landed on the floor.)

Within ?? minutes (oximeter ~70): I am no longer able to perceive the passage of time.  No longer able to take meaningful notes.  My signature is still legible - instinctive muscle memory apparently doesn't degrade nearly as fast.

Within 6 minutes (oximeter unknown): I have taken another pen from my pocket and am playing the knife game from "Alien" with it.  This is much more interesting than paying attention to the directions from the instructors.  I don't notice anything odd about my behavior.

Immediately after:  An instructor gives me a direct command to put my mask on.  I comply.

Total time in chamber: 7 minutes.  Time of useful consciousness in chamber: about 2 minutes

So, to answer your question: It depends.  I can safely say that seven minutes at 30,000 foot environment won't guarantee death (because I've survived it), and it won't guarantee severe brain injury (they let me keep flying) but on the other hand, I'm young and I exercise.  The best answer I can give is the same one that applies to scud running:
Just because the guy before you was able to do it, doesn't mean you'll be able to do it.


When to go missed on a non-precision approach?

Non precision MAP fixes are identified in a number of ways:

Fixes identified by additional terrestrial Navaids eg intersections between the localizer and radial directions from other Navaid beacons like VORs, NDBs, etc..
Fixes identified by DME slant ranges.
Fixes identified by flying a linear course from an identified FAF at a specific airspeed for a specific time.
Fixes identified by area navigation systems.
Fixes identified by specific GNSS waypoints (RNAV GPS).

For the ILS or LOC/DME rwy 5 KCGZ, when flying the LOC/DME, Your MAP is on localizer at MDA at 7.5 NM DME from the Stanfield (TFD) VORTAC.  There is no other means using the equipment required to fly this approach procedure to identify the MAP.

For the LOC rwy 22 into KCDW, your MAP is on localizer at or above MDA when you cross the threshold of rwy 22.  Flying the approach at the correct category airspeed, you can also time it using the table in the lower left corner of the plate.  But the plate clearly says that the MAP is 5.4 NM from the FAF.

For the ILS or LOC 1 into KILG, the LOC rwy 1 MAP is again on localizer at MDA when the aircraft crosses the threshold of rwy 1.  This is defined by the approach timetable on the lower right of the plate.


As a drone hobbyist, is flying below the listed FAA UAS ceiling a violation of controlled airspace?

Short answer:
As of now, since the LAANC pre-authorization system is not yet up and running for recreational SUA flyers, any recreational sUAS operation below 9000' MSL in the lower left corner of the grid square highlighted in the question would be violating the applicable rules.  In the rest of the grid square highlighted in the question, recreational sUAS operation from the surface up to 400' AGL violates no rules.
Now read on for more:
In the particular grid square that is highlighted in the question, the LAANC pre-authorization system will only authorize a ceiling of 100'.  But the questioner is mistaken to believe that the floor of the Class B airspace is 100' anywhere in that grid square.
The lower left corner of the grid square highlighted in the question has Class B airspace extending from the surface upwards.  In that airspace, a recreational sUA flyer can not legally fly a drone without prior authorization.  Since the LAANC pre-authorization system is not even operational yet for recreational sUA flyers, to legally fly in any airspace that is Class B at the surface, a rec SUA flyer would have to fly at a "blue dot" fixed site.  "Blue dot" fixed sites are typically prescribed the same ceiling as the ceiling specified for the LAANC grid square in which they are located, which in this case would be 100 feet.  No "blue dot" fixed site currently exists anywhere in the Class-B-to-surface airspace around Phoenix.
Once the LAANC pre-authorization system is up and running for recreation sUA flyers, a rec SUA flyer will be able to use that system to get pre-authorization to fly from the surface up to 100' AGL anywhere in the grid square highlighted in the question.
But does this mean a recreational sUA flyer is limited to a ceiling of 100' AGL if he or she is flying in a part of the grid square highlighted in the question that does NOT have Class B airspace at the surface?
No it does not.
And does the fact that LAANC pre-authorization is not yet available to recreational SUA flyers have any impact on recreational sUA flight in any point within a LAANC grid square if the airspace at that particular point, from the surface up to 400', is NOT Class B, Class C, Class D, Class E airspace that extends down to the surface and is "designated for an airport", or some other kind of restriction such as those shown by the heavy red markings on the LAANC map?
No it does not.
In all but the lower-left corner of the grid square highlighted in the question, the Class B airspace has a floor of 5000' MSL.  Below that is Class E (E5) airspace down to 700' AGL and Class G airspace from 700' AGL down to the surface.  In that airspace, one can legally fly a drone (sUA) up to 400' AGL with no prior authorization of any kind, either as recreational flyer or as a non-recreational flyer, despite being in a LAANC grid square.
VFR sectional chart view, centered on Phoenix: http://vfrmap.com/?type=vfrc&lat=33.434&lon=-112.012&zoom=10
However, if a rec SUA flyer doesn't fully understand the airspace system or how to read a VFR sectional chart, he or she would be wise to stay on the safe side and avoid any operations within any LAANC grid square until the LAANC pre-authorization system becomes operational for sUA flyers, unless he or she is flying at a "blue dot" fixed site.
The phrase "within the lateral boundaries of the surface area of Class E airspace designated for an airport" refers to Class E airspace that extends down ALL THE WAY DOWN TO THE SURFACE.  More specifically, it refers to E2 airspace, but not E3/E3a/E4 airspace.  To read more about this, visit this outside link to a forum for rc flyers-- "Understanding E4 airspace-- prior authorization not required".
No Class E airspace is present at the surface anywhere in the region depicted in the illustration accompanying the question.


Why do we have to manually tune VOR receivers?

As pointed out in the comments, I think you have things turned around. If you select the frequency of a VOR that has a co-located DME, the system will automatically also select the DME frequency. Thus, I'm guessing that what you perhaps meant to ask is under what conditions do you manually tune the DME frequency. If that is NOT what you are asking, put a comment after this answer to that effect, and I will delete this answer.

Now, if that is what you are asking, the answer in one sense is "never" in that, at least in civilian aircraft, you always select the VOR frequency. However, prior to my retirement in 1999 there were a few, very few as I remember, facilities that provided DME but at which there was no co-located VOR. To get the DME, you selected the VOR frequency that would have been paired with the DME had there been a co-located VOR. and it was the frequency of that non-existent VOR that was shown on the charts along with a clear and obvious note that there was no actual VOR. I have no idea whether in our current airspace system such still facilities exist.

You can find the standard VOR-DME frequency pairings here (PDF) or read about it on Wikipedia.


Block time starts when the aircraft is pushed back from the gate, and ends when it arrives at the corresponding gate.

It is the total time the aircraft is in use, typically only calculated for revenue movements.

Imagine a flight:

Pushback 1000
Taxi 1030
Takeoff 1035
Touchdown at destination airport 1445
Taxi to gate 1500

Total block time is 5 hours


Why is only a single underwater robotic submarine Bluefin-21 being deployed in the search for MH370?

Bluefin-21

  Why not multiple Bluefin-21's

There is only one Bluefin-21.

The other Bluefins 12S, 12D, 9M etc are mostly for shallow water work.

Other AUVs

The Bluefin-21 is not the only commercial Autonomous Underwater Vehicle (AUV) equipped with side-scan sonar.

The US Navy has spent $20M on an order for eight Knifefish (a Bluefin-21 derivative) but these are not due to enter active service until 2017. They are for mine-detection and so (I surmise) may not be well suited to deep-ocean usage.

The Royal Navy has a number of REMUS 600 AUVs but these are not designed for use deeper than 600M

It may be that most existing AUVs equipped with side-scan-sonar are not capable of deep-ocean use.


How does the capacity of 2 parallel runways compare to single runway?

Definition
There are two key performance indicators that are used to measure the key performance area 'airport capacity':

Peak arrival [declared] capacity
Peak arrival throughput.

What is the capacity of 2 near parallel runways?

It depends if the 2 runways are operated in mixed or segregated mode.

For the US, the two active runway case average value (47) is influenced by the ability to operate in mixed mode with independent runways for Tampa (TPA) and Portland (PDX). Otherwise the grouping is more comparable.

The average is between 40-47 arrivals per hour depending on the mode of operation, the higher value being influenced by the mixed mode operation.

How does it compare to mixed mode single runway?

Single runway is 29-30 arrivals per hour. So we are looking at a 33-50% increase.
Declared and IFR
I'd be careful with the interpretation (since you tagged it IFR), because one of the reasons you see a larger gap between the declared and actual for the US compared to Europe is because in the US the capacity is typically declared based on visual meteorological conditions. This is discussed here:

Why are visual approaches (in the US) preferred by US pilots, but not European pilots?
What are the practical impacts of airports in the US being mostly IATA Level 2?

Source of graph and quotations: Comparison of Air Traffic Management-Related Operational Performance: U.S./Europe, 2015, eurocontrol.int (.pdf inside .zip).


Possibly to shatter the canopy into smaller fragments.  Straight dets might just detach a large proportion, possibly leading to unwanted severe secondary strikes on ejecting aircrew.


What is the difference between ADS-B UAT and ADS-B ES?

ADS-B UAT operates on 978 MHz and are available for aircraft that operate below 18,000 FT MSL.  UAT transceivers can display aviation weather products (FIS-B) as well as traffic from ground radio stations (TIS-B).  The airplane must be in a coverage area for TIS-B services.

  TIS-B is intended to provide ADS-B equipped aircraft with a more complete traffic picture in situations where not all nearby aircraft are equipped with ADS-B Out. - AIM 4-5-8

Aviation weather products available over FIS-B through ADS-B UAT transceivers

ADS-B 1090ES operates on 1090 MHz and is required for aircraft operating above 18,000 FT MSL.  The information sent over a Mode S transponder is greater and is called an "extended squitter".  These aircraft will be able to display traffic directly from other ADS-B equipped aircraft and those with Mode S transponders without the need to rely on ground based systems.  FIS-B is not available to these transceivers.

The picture below illustrates where 1090ES and UAT are allowed / required for aircraft after the ADS-B mandate in 2020.

References:

Aeronautical Information Manual 4-5-7 thru 4-5-9
Advisory Circular 90-114A


Would tubofan aircraft benefit from adjustable fan blades?

Both turboprops and turbofans want their blades to be as long as they can be, in all circumstances: that way the largest amount of air is accelerated, and a given amount of thrust created with the highest efficiency. It never pays to reduce the bypass ratio of a subsonic turbofan.

Turbofans with adjustable blade pitch would make sense though, like the constant speed propellers that turboprop engines already have. This article from Flight Magazine 1973 gives the advantages of a high bypass variable pitch turbofan:

  Inherently low noise levels because of high bypass ratio and low fan
  tip speeds.
  Rapid thrust response, allowing thrust modulation for
  accurate rate of descent control on the approach and maximum use of
  reverse thrust during the landing run.
  Reverse thrust available
  without the weight or maintenance penalty associated with reversers
  and spoilers.
  High ratio of take-off to cruise thrust well matched to
  the needs of short-range, Stol aircraft.
  Good cycle efficiency and specific fuel consumption.
  Wide engine operating margins.
  Provides many of the advantages of the turboprop while avoiding vibration,
  ground and fuselage clearance problems and allowing better matching
  with higher cruise speeds.


Does the Airfoil Tools Cd/Alpha Curve include both induced and parasite drag?

To answer the question you have to look at the source:

Induced drag is a drag type which appears on wings with finite span. The polars given are for a 2D profile section and therefore without induced drag.

What about the parasitic drag? Using Wikipedia's definition only skin friction and form drag are taken into account. Interference drag, which is a 3D drag type dependent on the position of other bodies, can't be included either.


Was the Boeing 747 designed to be supersonic?

No. The Boeing 747 was not designed for supersonic flight, though during testing, it was pushed quite close to the sonic speed:

Tom Cole, a spokesman at Boeing Commercial Airplane Co., said original flight tests of 747s conducted in 1969 and 1970 took 747-100 models to speeds of Mach 0.99.

However, the aircraft is not built for sustained supersonic speeds:

... Boeing and the FAA said the 747 is not built for sustained flight at the speed of sound. Its engines aren't powerful enough nor is it designed to deal with a destabilizing shock wave that develops around the speed of sound.

However, it is just possible that the airframe and wings can cope up with the supersonic flight, at least for a little while, though any sustained flight is not possible. There have been cases where the 747 has gone quite near the speed of sound and lived to tell the tale.
China Airlines Flight 006 went into a dive and went near supersonic speeds before the captain could recover it. As a result, large portions of the horizontal stabilizers were ripped off, and the wing was bent permanently upwards.

Damage to China Airlines Flight 006 empennage. By NTSB - China Airlines Boeing 747-SP Accident Report by NTSB, http://www.rvs.uni-bielefeld.de/publications/Incidents/DOCS/ComAndRep/ChinaAir/AAR8603.html, Public Domain, Link
In 1991, a Boeing 747 of Evergreen airlines entered a steep right wing bank and approached sonic speed before recovery was completed. NTSB notes:

... the airplane was in a steep right-wing-down bank. The flight  lost  approximately 10,000 feet of altitude, and the airplane approached supersonic speeds (0.98 Mach) before the recovery could  be  completed.

Later, the Israelis took it close to sonic speed. In these cases, parts of the aircraft certainly experienced local supersonic flow; however, the airframe and wings are not designed for supersonic flow nor are the engines powerful enough. In one case, the aircraft suffered extensive damage (though it was repaired and returned to service).


What makes the F/A-XX twin-engined tailless fighter controllable with engines out?

Those flying wings even before fly-by-wire (FBW) came along are controlled in the yaw axis by asymmetrically deploying the wing-tip mounted split brakes.*
(Source)
With the engines closer to the centerline the effect of one engine inoperative (OEI) is not as pronounced as on jet-liners with the engines far out on the wings. Even with the lack of a vertical fin, the effect will be less than if the engines were more outboard.
In the Boeing 727 it was discovered that an engine out during takeoff did not have a noticeable effect on the yaw, to the point such planes with close engines had different certification for the V-speeds to allow extra time for the identification of the failure. As well as glareshield mounted lights to indicate an engine failure in a clearer manner.
As you can see in the pictures you have, the engines are close, like the 727. And therefore the standard yaw control via split brake rudders* is sufficient.
As for the F/A-XX, it seems it's still a concept. The second image is also a single-engine UAV.

* The aileron-like device that is split at the wing tips. By creating asymmetric drag, the plane yaws.

Unlike conventional aircraft, truly "tailless" flying wings cannot use a rudder for lateral control as it was absent, so a set of clamshell-like double split flaps on the trailing edge of the wingtips were used. When aileron control was input, they were deflected up or down as a single unit, just like an aileron. When rudder input was made, the two surfaces on one side opened, top and bottom, creating drag, and yawing the aircraft. By applying input to both rudder pedals, both sets of surfaces were deployed creating drag so that the airspeed or the glide angle could be manipulated.
(Wikipedia)