Why does the speed of commercial airliners fluctuate, sometimes as high as 1,060 km/h or as low as 800 km/h?

Information displayed to passengers through the entertainment system often gives the aircraft ground speed rather than airspeed.

Wind affects the ground speed, you're right about that.

Few things out of the way first.

Pilots do not use ground speed for flying, instead they use indicated airspeed.
Mach number is not derived from the ground speed, as it is dependent on air temperature, instead it is derived from the true airspeed. Notice we already have two kinds of airspeed. There are more still.
Aircraft type (for example 737 vs. 777) determines "top speed". Not all airliners are the same. Those two types range from Mach 0.77 to Mach 0.85, roughly.

In less words than Wikipedia which I linked:

Indicated airspeed tells the pilot the aerodynamically relevant speed to be used for flying.
True airspeed is the actual speed relative to the surrounding atmosphere.
From the true airspeed, add or subtract tail or headwind, and you get ground speed from that. Typical wind experienced by the regular subsonic airliner is fast (+100 km/h). The tail or headwind component would vary depending on the plane's direction and the wind's direction.
Finally, Mach number is a function of temperature and true airspeed (notice, not ground speed). The higher you are, the colder it is. Also very important, Mach number is a ratio, never a speed. Since the speed of sound varies as the atmosphere changes density and temperature at the different altitudes.

Here's a nice story, a 1200 km/h subsonic flight.

Summary:

Pilots don't use ground speed (for flying), mach number is not a speed.


76,000 feet.  Airbus Perlan Mission II glider, Sept 2, 2018.
The U-2 has a higher service ceiling, 80,000 feet, but it hasn't reached that.
(Perlan II's service ceiling is 90,000 feet.)


What is the reasoning behind using depleted uranium as counterweights in the 747?

Boeing

Boeing would have used DU because it had the right combination of physical characteristics and cost. Their tests showed that the radiation exposure for workers was low (2.6% of the statutory "safe" level). In most cases the exposure was so low as to be not detectable.

Radiation

Passengers on aircraft are exposed to cosmic radiation at much higher levels than people on the ground.

On the ground the average American is exposed to 620 mrem/year from all sources.

Those flying from Washington DC to Los Angeles would be exposed to close to 2 mrem from cosmic radiation. This is not an issue for passengers but is something that airline crew and other very-frequent flyers are aware of.

Exposure to aircraft occupants from cosmic radiation is 600 times higher than from DU counterweights in the early 747 aircraft.

Depleted Uranium

DU is Uranium from which the most radioactive parts have been removed. It is less radioactive than naturally occurring Uranium.

Heavy metals like Lead, Tungsten and Uranium are toxic if ingested. This toxicity is not due to radioactivity. Aircraft crew and passengers are not exposed to these metals in any way that could cause them to be ingested.

Boeing Tests

Boeing carried out safety tests on the material.

Workers

  Boeing
  has
  conducted
  two
  dosimetric
  studies
  of
  exposures
  to
  workers.
  For
  both
  studies,
  whole
  body
  exposures
  were
  measured
  with
  film
  badges
  which
  were
  provided
  and
  processed
  by
  Landauer,
  Inc.
  These
  badges
  have
  a minimum
  detectable
  exposure
  of
  10
  millirem
  per
  issue
  period
  (monthly).
  In
  the
  second
  study,
  extremity
  exposures
  were
  measured
  with
  finger
  rings,
  also
  provided
  by
  Landauer,
  having
  a
  minimum
  detectable
  exposure
  of
  30
  millirem
  per
  issue
  period
  (also
  monthly).
  The
  periods
  of
  the
  study
  were
  December
  1968
  to
  February
  1970
  for
  the
  first
  study
  and
  September
  1977
  to
  April
  1978
  for
  the
  second.

  Both
  of
  these
  studies
  showed
  all
  worker
  whole
  body
  exposures
  were
  less
  than
  2.6%
  of
  the
  exposure
  limits
  for
  occupationally
  exposed
  employees
  (5000
  millirem
  per
  year)
  and
  less
  than
  26%
  of
  the
  limits
  for
  members
  of
  the
  general
  public
  in
  effect
  at
  that
  time
  (500
  millirem
  per
  year).

Crew and Passengers

  Based
  on
  the
  data
  from
  National
  Lead,
  reported
  in
  the
  section
  on
  exposures
  to
  the
  general
  public,
  dose
  rates
  to
  flight
  crew
  will
  be
  less
  than
  0.8
  microrem
  per
  hour.
  During
  a
  2000
  hour
  working
  year,
  this
  results
  in
  a
  maximum
  potential
  exposure
  of
  1.6
  millirem,
  less
  than
  2%
  of
  the
  100
  millirem
  per
  year
  limit
  for
  members
  of
  the
  general
  public.
  This
  is
  only
  1/600th
  of
  the
  500
  microrem
  per
  hour
  increase
  in
  dose
  rate
  from
  cosmic
  radiation
  flight
  crew
  experience
  at
  39,000
  feet.

Boeing Use of Depleted Uranium Counterweights in Aircraft. 1984. Retrieved from NRC

References

Space Radiation, Should Frequent Flyers Worry? 2013. BBC
Tungsten Poisoning. 2014. Retrieved from Patient.info


Why is "proverse" yaw better than no yaw?

I would add that it depends on what you mean by "proverse yaw", and that vertical fin size is key.

Proverse implies "too much" yaw in excess of the appropriate yaw rate for the angle of bank, which would be a skidding turn. That's bad.   If proverse just means an into-turn yaw rate that is appropriate for the bank, that's good.

Airplanes with spoilers-only for roll control suffer can suffer from "bad" proverse yaw in that sense, because the drag of the down-wing spoiler, with nothing sticking up on the opposite wing to offset it, pulls the nose into the turn too much, requiring out of turn rudder to keep coordinated flight (I've heard that the spoilers-only Mitsubishi MU-2 is like that).  But almost all airplanes have the opposite, adverse yaw, to one degree or another.

Anyway, what we want is a natural yaw rate that is appropriate to the bank angle so the tail naturally wants to stay lined up behind the nose in the air stream during the turn. Asymmetric drag effects of flight controls aside, the yaw rate you get in concert with bank to get a turn is a function of the vertical fin (and the rudder, to the extent that it's providing a passive fin-like effect, like with a hydraulic rudder, or a mechanical rudder with centering springs).

It's basically a big weathervane.  If you had no fin/rudder, no weathervaning effect at all, you'd just skew sideways when you bank (even ignoring the dynamic yawing effects of the rolling action or asymmetric aileron drag, which make the slipping worse).

You would think it's desirable to have a fin that can make the tail follow the nose immediately and precisely, when side slip occurs as a result of banking, so the bigger the vertical fin, the better.  But there's a problem with that.  To exploit the self-righting effect of dihedral, to give wings-level stability in roll, you need to have a little bit of side slip occur when the wings are banked, to create the self-righting lift differential.

So you need a weathervane, but not too big a weathervane.  The sizing of the fin itself is a balancing act over the need for strong into-turn yaw, and for roll stability due to dihedral effect.  If the fin is too big, into-turn yaw is too strong and immediate; the airplane will immediately yaw (weathervane) into the turn with little or no initial side slip, and it will want to enter a spiral dive any time it's banked.  Vertical fin too small, and the weathervaning effect is too weak and the airplane hunts and slithers around in yaw too much.

There is a sweet spot for fin sizing that gives good "proverse" yaw to give a naturally coordinated turn that only needs bits of rudder to counteract adverse yaw while the ailerons are displaced, while still allowing just enough initial side slip to allow dihedral effect to apply its self-righting tendency when the airplane is banked slightly by a bump.


What was the Space Shuttle's glide ratio?

As far as I know the space shuttle is no longer in use.  However, the glide ratios (more than one in different configurations) can be found on the Wikipedia page: Space Shuttle Wikipedia page.  There it states that “The orbiter's maximum glide ratio/lift-to-drag ratio varies considerably with speed, ranging from 1:1 at hypersonic speeds, 2:1 at supersonic speeds and reaching 4.5:1 at subsonic speeds during approach and landing.”


Is the 737's autopilot part of the FMS or is it a separate entity?

In Boeing terminology, the FMS, Flight Management System, is comprised of:

Flight Management Computer System (FMCS, which is essentially two FMC's, at least on the 737... other jets may have one FMC, or three)
Autopilot
AFDS (Autopilot/Flight Director System - includes the Mode Control Panel used to select autopilot modes, heading, speed, altitude, etc)
Autothrottle
GPS(s)
Inertial Reference Systems (IRS)
Two (in the 737, three in some other jets) CDU's, which are the "Control and Display Units" with a small screen display and alphanumeric keyboards, used by pilots to view, enter, and edit things such as flight routes & performance data. Many such units are now "Multifunction CDU's", or MCDU's, adding ACARS and/or CPDLC capability.

So in their terminology, the FMS is very broad and includes plenty of things, including the autopilot. The FMC, on the other hand, is the computer that stores your route, calculates the aircraft's position (based on inputs from the GPS receiver(s) + the IRS + possibly other sensors), and does all the navigation tasks. One can couple the autopilot to the FMC guidance - select LNAV and/or VNAV - or not.

It's not uncommon to hear or read "FMC" and "FMS" used interchangably, but they are in fact two separate things. The FMS (the system) includes the FMC (the computer) and the autopilot; the autopilot can be coupled to the FMC, but it is always a component of the FMS.

Sometimes you'll see a CDU referred to as "the FMC (or FMS)" since the CDU is the pilot's main interface with the FMC. But they are separate things; you can have a CDU failure with all FMC's still working, and vice versa.

Clear as mud?


Why are there so few aircraft that had inhabited wings?

There are a few more aircraft with seats in the wings, but you are right as long as passenger seats are concerned: they appeared only in the G-38. Now I could also mention the Soviet Kalinin K-7, which was supposed to seat some of its planned 120 passengers in its wing, but that design never went beyond early flight test of the first prototype.

Professor Hugo Junkers was convinced from the start that the best aircraft would only consist of the wing and engines, but the size of real-world aircraft did require a fuselage to place pilot and passengers. Only when wing thickness grows to 2 meters would it be feasible to place people inside (the root thickness of the Junkers G-38 was 1.7 meters, that of the K-7 was 2.33 meters). That was only possible with the largest aircraft of their time, like the Messerschmitt 323 which had engineer's positions in the leading edge of the wing.

The Illustrated London News article about the Me-323 from 1943 contained the picture above (source) which indicates the engineer's cabin between the two inner engines of each wing.

The simple reason for the scarcity of inhabited wings is the limited chord and thickness of practical wings. Back in the days of propeller airplanes, the relative wing thickness could be 20% or more, but with modern jet transports, even 14% are on the high side (this text contains an extensive collection of data). Next, the wing of airliners is full of other stuff:

Leading and trailing edge devices
fuel tanks
pumps, pipes and control linkages

which leave no space for passenger seats. Only in the days of slow aircraft with low wing loadings was the inclusion of passenger seats even conceivable, and only in the largest wings. The G-38 had a wing loading of only 80 kg/m² while the A380 has one of 680 kg/m², so its wing area is only three times larger than that of the G-38 and its maximum root thickness about the same. If you now consider that just 6 out of the 34 passengers on the G-38 could sit in the wings, it should become clear how infeasible it becomes to place passengers in the wing of even the largest aircraft of today.

Junkers went even farther in turning the blended wing into reality when they (together with Messerschmitt) had to submit proposals for a large cargo glider in 1940. While Messerschmitt scaled up their then-largest aircraft, the M-18d, by a factor of three to arrive at the conventional Me-321, Junkers opted for an all-new design which was only loosely based on the G-38 and blended the cargo volume into the center wing. Their Ju-322, however, turned out to be almost uncontrollable. In the haste of the development, nobody cared to check how effective the far too small and too closely coupled tail section was.

Theoretical concepts of aircraft which place their payload in the wings have focused mostly on freighters, like in this NASA study (PDF!).


Why would a plane perform 360° turns to balance fuel on the ground?

They probably had a fuel imbalance that was marginally outside the limit for takeoff, and perhaps the powered fuel transfer system was unserviceable and was deferred.  Typically there is a gravity transfer capability by just opening a transfer valve and letting fuel run across on its own with the imbalance present, or by skidding slightly.

If they were say 50 or 100lbs above the max lateral imbalance for departure, a spin around on the ramp a couple times with the gravity transfer valve open so that some fuel "sloshes" through the gravity transfer line to the opposite tank, due to the centrifugal force of the turn, may have been enough to get the value in limits.


Boeing1[pdf] specs for 777-300ER:

Max taxi weight: 777,000 lbs (352,442 kg)
Max take off weight: 775,000 lbs (351,535 kg)
Max landing weight: 554,000 lbs (251,290 kg)

Bridgestone2 specs for approved tires:

Main: 66,500 lbs (30,264 kg) x 12 = 798,000 lbs (361,967 kg)
Nose: 44,500 lbs (20,185 kg) x 2 = 89,000 lbs (40,370 kg)
Total tire rated load = 887,000 lbs (402,337 kg)

So at taxi weight on all 3 gear there's roughly a 110,000 lbs / 50,000 kg margin (about 14%).

At max landing weight, main gear only, there's a 244,000 lbs / 110,677 kg margin (44%).

At MTOW there's about a 112,000 lbs / 51,000 kg margin (14%) on all gear, but only a 23,000 lbs / 10,400 kg (3%) margin after nose gear lift off.

But, when the nose gear lifts off the ground the wings are supporting nearly all of the weight. Their numbers are pretty close to what the manufacturers list. I think you're just not accounting for the nose gear at takeoff and the weight difference at landing.

As far as Is the MTOW determined by the wheel maximum supported weight? It's the other way around. The MTOW determines how many tires of what weight rating are needed.

A more important tire consideration is speed. The tires are rated at 204 kt. This paper gives an example of a 747 at 825,000 lb there is a weight margin of 30,000 lb. But liftoff speed is 199 kt, so there's only a 5 kt speed margin.


Lost radio communication after take-off in IMC - what are my options?

The answers to these questions can be found in the AIM in section 6-4-1. All quotes are from that page.
To the first question, you should expect to receive a clearance to 8,000 feet twenty minutes after departure; therefore, don't climb above 4,000 until that time. If you are still in radio contact after 20:55, the "expect" portion of the clearance expires:

If the pilot received an “expect further clearance” containing a higher altitude to expect at a specified time or fix, maintain the highest of the following altitudes until that time/fix:
(1)   the last assigned altitude; or
(2)  the minimum altitude/flight level for IFR operations.
Upon reaching the time/fix specified, the pilot should commence climbing to the altitude advised to expect. If the radio failure occurs after the time/fix specified, the altitude to be expected is not applicable and the pilot should maintain an altitude consistent with 1 or 2 above.

For the second question, the answer comes down to the definition of "briefly". Is your hole big enough for you to get under the clouds, and is the ceiling high enough that you can remain VMC to land? If so, you should do so. But if you just briefly see the ground, or aren't confident that you could safely fly VFR to a suitable airport, then you should maintain IFR and continue flying your clearance. You may inconvenience a few controllers, but if you leave your cleared route only to discover that your intended airport is socked in, getting back to your route to resume your original destination puts you potentially low to the ground, and not along the route that ATC is expecting you:

Pilots should recognize that operation under these conditions may unnecessarily as well as adversely affect other users of the airspace,
since ATC may be required to reroute or delay other users in order to
protect the failure aircraft. However, it is not intended that the requirement to “land as soon as practicable” be construed to mean “as soon as possible.” Pilots retain the prerogative of exercising their best judgment and are not required to land at an unauthorized airport, at an airport unsuitable for the type of aircraft flown, or to land only minutes short of their intended destination.

That said, VFR traffic should always be looking for other aircraft - with and without radio contact. Radios are not required equipment, at least at non-towered airports, so landing among VFR traffic without a radio should not be a big deal.


Is a CFI's 1st-time pass-rate based on the student or the instructor's first attempt?

I believe that your pass rate is based upon your number of students who passed on their first attempt after endorsement vs the number of students you endorsed for the checkride.  I don’t believe the FAA makes any other distinctions here, at least not for §61.197 requirements for the renewal of a flight instructor certificate nor for 89001, Section 13, Issuance of a Gold Seal Fight Instructor Certificate.


ARINC 429 is a defined standard that not only describes the packet structure (32 bits) but also the data formats for different labels depending on the equipment ID. To know how to properly decode an ARINC 429 label you need to know the Equipment ID, which can then be used to look up the meaning of a specific label.

The manufacturer of the device that the data came from may also provide the definition of any non-standard/custom labels

If you know which labels you are looking for you don't have to decode the entire label, you just need to inspect the bits 8-1 to determine the label.

In general though, the ARINC 429 specification provides a guideline for labels:

  Binary coded decimal (BCD) sub-group 001 to 067, 125, 165, 170, 200, 201,230 to 237.

  Binary (BNR) subgroup 070 to 124, 126 to 144, 150 to 154, 162 to 164, 166, 167, 171 to 177, 202 to 227, 240 to
  257, 262 to 265, 267, 310 to 347, 360 to 376.

  Mixed BCD and BNR subgroup 260, 261

  Discretes subgroup 145 to 147, 270 to 276

  Maintenance and discrete data subgroup 155, 156

  Maintenance data subgroup 157 to 161, 350 to 354

  Test word subgroup 266, 277

  Application dependent subgroups 300 to 307

  Acknowledgement subgroup 355

  Maintenance ISO #5 subgroup 356

  ISO #5 message subgroup 357


Could a 30 knot direct crosswind make a Learjet roll over 90 degrees?

It only ever makes sense to talk about cross-wind when the ground is involved. While the aircraft flies, it moves relative to the air and how fast the air is moving relative to ground only affects ground speed and track. If the air is moving smoothly, it can't turn anything over. Only thing that could bank an aircraft over is strong turbulence.

Natural turbulence of a 30 knot wind is unlikely to be strong enough to bank a Learjet 35 significantly, but a wake vortex close behind a heavy aircraft possibly could. The separation minima are there to prevent encountering wake turbulence on approach.


Aircraft with toe brakes have the brake pedals at the top of the rudder pedals.  You press the left one with top of your foot and it applies the left brake(s).  Press the right one to apply the right brake(s).  Normally you press them at the same time and with the same force to keep the airplane from veering to one side (imagine just locking up the brakes on one side of the airplane).

Differential braking is when you press one brake pedal harder than the other.  It is used as an additional form of directional control when:

You have no other forms of steering (either because the steering has failed or there is no nose-wheel steering)
The rudder/nose-wheel steering is not effective enough (because you are going too slow or the wind is too strong).

You want to be careful when doing this, though because you can over do it and create more directional control problems than you originally had.  If you use differential braking during the takeoff roll, it will increase the amount of runway that you use since you are applying the brakes (even though it is only on one side, it will keep you from accelerating as fast).


How much fuel is burned to carry the trip fuel?

The 7:1 rocket figure is perhaps for the unrealized single-stage-to-orbit, getting a payload to low Earth orbit (LEO) is closer to 9:1, and going to the moon and back is 23:1 (Saturn V).
If a soda can's content is the fuel, then the rocket stages that are jettisoned have better fuel to empty mass ratio compared to that soda can, so staging is not the main reason why the figures are higher than the 7:1.

This is important because if a 5-hour flight is getting to LEO, then an ultra-long-haul 16-hour flight is the equivalent of going to the moon and back.

This already tells us there is no general rule of thumb for flight planning (or space flight). But, there is a common figure that is used when highlighting the benefits of carrying the right amount of fuel.
0. A common figure: 15%.
According to Simon Weselby, a Fuel and Emissions Performance Manager at Airbus, that figure is 15%. So to carry 1,000 kg of fuel, an extra 150 kg will be burned.
According to the famous lift-to-drag ratio graph, carrying fuel in cruise is not a big deal as the induced drag decreases with speed. The challenge is getting a heavy plane off the ground and getting it up to speed.*
If the fuel fraction mid-flight for a long-haul jet is 20%. Then that means the thrust required to carry 20% of the weight is 10% of the thrust (if the induced drag equals the form drag at the minimum drag point).
* That's why above a certain range, it becomes more economical to make stops. This takes into account the fuel alone. Not taking into account the passenger convenience, aircraft cycles, the maintenance cost of the extra takeoff thrust, etc.
That relationship is demonstrated by the graph below.
(Wikipedia) Takeoff, climb, step-climbs, etc., are accounted for, i.e., those are the averages for complete flights, not just cruise.
I've used the same 777-200 data that was used in making that graph to come up with different ways to look at your question, which can be answered in more than one way (the previous 15% figure is the easy answer).
1. If the fuel was weightless problem first.
I've used the most economical range (average fuel flow) as a baseline. And from there found out how much fuel is wasted to carry the extra fuel for the extra range.
NM      kg

2800       0    0%
3200     230    1%
3600     420    1%
4000     750    2%
4400    1130    2%
4800    1760    4%
5200    2350    4%
5600    3180    6%
6000    4060    7%
6400    4990    8%
6800    6080    9%
7200    7260   10%
7600    8590   11%
8000    9970   12%

Going from 2800 NM to 8000 NM, 9970 kg are wasted carrying the heavier fuel, or 12% of the total fuel load.
The fuel fractions for 2800 NM and 8000 NM are 18% and 40%. The aforementioned 15% figure for the A330 at 2500 NM matches that of a 777-200 at 2400 NM.
2. Problem two: carrying more fuel for the same trip distance.
This is equivalent to payload. What it does is increase the landing weight (LW). A quick and dirty way to check how much extra will be burned carrying more fuel that will not be used is to use the same fuel fraction for that distance.
This is what the Airbus presentation says, which I've been able to verify in a spreadsheet for 5 different weights 22.7 tonnes apart. (And also for the 737 for good measure.)
(Own work) Click to view full table.
For example, if our baseline flight needs 15% fuel fraction, it will still be 15% of the new higher weight (landing weight + trip fuel). In other words, if the LW goes up, the trip fuel goes up.
For the 777-200, landing weights of 136,100 and 226,800 kg need 25,400 and 37,800 kg of fuel for a 2400 NM trip. Or 15.7% and 14.3% fuel fractions.
An 8000 NM trip needs a fuel fraction of 40.3% for the lowest landing weight I calculated, and 38.8% for the heaviest.
So the quick and dirty rule of thumb is to maintain the fuel fraction for the same trip distance.
3. Percent of Landing Weight (LW) per hour.
A different way to look at it: I've constructed the graph below for the 777-200. As you can see, it matches the trend of the Wikipedia one.
(Own work)
So for a 6-hour flight, it will be 6 times 3.6, or 21.6% of the LW in fuel.
While a 0.5% is negligible for a 737 and maybe even for a 777 on short routes, it is not when it is multiplied by long flight durations.
Below is yet another way to look at the data, the average fuel flow per engine in kg per hour for the different trips.
NM      FF/eng (kg/hr)

 800    2510
1200    2460
1600    2440
2000    2450
2400    2450
2800    2450
3200    2470
3600    2480
4000    2490
4400    2510
4800    2540
5200    2560
5600    2580
6000    2610
6400    2640
6800    2660
7200    2690
7600    2720
8000    2750


What is this single-engine low-wing propeller plane?

That’s a Piper PA-28R Arrow.  Most likely an PA-28R-201 Arrow III, by the looks of it.


Why would a Su-25, which has more power and is much lighter than an A-10, only fly half as high?

Just look at the wing loading: The Su-25 has between 585 kg/m² (regular Su-25) and 691 kg/m² (Su-25TK) when fully loaded, whereas the A-10 has a wing loading of 316 kg/m². This alone should explain why the Su-25 cannot climb as high.

Even when flying at minimum mass, the Su-25 has still 309 kg/m² (345 kg/m² for the Su-25TK), and the A-10 is almost a glider by comparison, having just 208 kg/m² at minimum mass.

Since both are subsonic designs, they have a strict limit on maximum speed. With that, wing loading and the airfoil determine their ceiling if thrust is sufficient.

Another limiting factor is the cockpit: Since the Su-25 was designed for ground attack, it has an unpressurized cockpit. This detail limits the certified envelope, even though a lightly loaded Su-25 can climb higher than 7000 m.


In G1000, how can I intercept a victor airway with multiple legs?

If the airway is too far away to accurately determine which leg you are going to intercept, why would you let the G1000 pick the leg you are going to intercept?

You know best what you want and, as you say, ATC may change your heading anyway.

So you shouldn't intercept automatically until you are fairly sure where you are intercepting. Instead you remain in HDG mode which gives you full control and makes it easy when ATC instructs you to change heading. Then when you are a couple of miles from intercepting you select the leg and let the G1000 do the magic if you want to.

Automation is there to relieve you from difficult or boring tasks. If you find that you spend a lot of time programming your FMS, it may be better to reduce the level of automation and spend the extra time on situational awareness.

I recommend watching this America Airlines training video on automation dependency (a.k.a. "Children of the magenta line"). It addresses the FMS / autoflight dependecies for airline pilots. The video is over 15 years old and by now similar automation systems have entered the cockpits of small aircraft. Although some aspects of the video address a multicrew environment, the main points are equally valid for G1000 equipped single crew / single engine propeller aircraft.


Should the type of plane influence my travel choice?

As a general rule, not really, though there may be some factors that could cause you to consider it as part of your decision-making.

Some short-haul routes may be served by aircraft of significantly different sizes. For instance, some flights between San Francisco and Los Angeles may be on a Boeing 737, while others are on a CRJ Regional Jet. Still others may be offered on a turboprop like the Dash 8 or the even smaller Beechcraft 1900 (or even smaller aircraft, especially serving remote areas). Even those who aren't afraid of flying may be uncomfortable on small "puddle jumper" aircraft, as the seats and headroom are usually physically small and they can be more impacted by turbulence. Such aircraft can also require standard carry-on bags to be checked at the gate (they are usually returned to you at the gate on arrival), as lack large overhead bins.
The Boeing 787 Dreamliner can be pressurized to a lower cabin altitude and has a higher level of humidity than is typical. Efforts were made to lower cabin noise as well. This can lead to a more comfortable flight. Many of these enhancements may be carried over into future next-generation aircraft.
There may be differences in the cabins depending on the aircraft model, especially in premium classes. For instance, first class passengers on Lufthansa may have a separate bed on Boeing 747 aircraft, while those on Lufthansa's A340 will have to make do with sleeping on bedding atop their luxurious seat. Emirates business class is supposedly far better on the A380 (which includes a bar in the back) than the 777, though which you get mostly depends on your route. In other cases, an airline may be rolling out a new premium seat design, which is only available on some aircraft types. While the differences are less pronounced in economy, there may be variations in seat pitch (legroom) and configuration (2-5-2 vs 3-4-3 for example) that can make a significant difference in comfort.
Some people prefer newer aircraft. This can be difficult to guarantee by type alone though, as many aircraft have been produced over a period of decades. Even older aircraft have to go through a rigorous inspection and maintenance procedure though.

That said, most people are choosing their flights based on factors like price, route/time, and frequent flyer membership. Type of aircraft is usually pretty low on the priority list unless you're an enthusiast determined to fly a certain new model.

Also note that aircraft type is never guaranteed, and carriers reserve the right to make substitutions for operational reasons without notice.


What FAA requirements exist for electronic ignition systems on piston engines?

The ignition requirements are pretty straight-forward:

  §23.1165   Engine ignition systems.

  (a) Each battery ignition system must be supplemented by a generator
  that is automatically available as an alternate source of electrical
  energy to allow continued engine operation if any battery becomes
  depleted.

  (b) The capacity of batteries and generators must be large enough to
  meet the simultaneous demands of the engine ignition system and the
  greatest demands of any electrical system components that draw from
  the same source.

  (c) The design of the engine ignition system must account for—

  (1) The condition of an inoperative generator;

  (2) The condition of a completely depleted battery with the generator
  running at its normal operating speed; and

  (3) The condition of a completely depleted battery with the generator
  operating at idling speed, if there is only one battery.

  (d) There must be means to warn appropriate crewmembers if
  malfunctioning of any part of the electrical system is causing the
  continuous discharge of any battery used for engine ignition.

  (e) Each turbine engine ignition system must be independent of any
  electrical circuit that is not used for assisting, controlling, or
  analyzing the operation of that system.

  (f) In addition, for commuter category airplanes, each turbine engine
  ignition system must be an essential electrical load.


What is the Saint-Venant formula for calculating equivalent air speed (EAS)?

I found this snippet

from Flight Mechanics of High-Performance Aircraft, by Nguyen here.

I'm not sure if this answer is consistent with the answer given Ugo..


What alternative designs competed for the C-130 in the 1950s?

The competing companies (ones that elected to compete anyway, more were invited) were Lockheed with two submitted designs, Boeing with one design, Chase Aircraft with three designs, Douglas with three designs and Airlifts Inc with one design. As far as I can tell, these were just designs and Lockheed won the contest based entirely on paper. The YC-130 was ordered and after performance was verified, it went into production in 1954.

It doesn't look like there is any public information on the competing designs since they didn't leave the drawing board. It is unlikely that any of them are "clean sheet" designs. The Boeing submission was probably (and this is a personal guess) based on the C-97 Stratofreighter. The C-130 itself looks to be an up-scaled version of the Fairchild C-123 Provider with design elements from the Chase XCG-20 (which was developed into the C-123).

I'm not sure what you mean by "justifications for the Lockheed design". Given that it is the United States military's most successful aircraft design ever, with 60 years of continuous service, I'm sure every design was driven by a contract or performance requirement. Here is a good article about the C-130 designer, Willis Hawkins that gives some insight into the project.

Most of this information was taken from the Wikipedia page on the Lockheed C-130 Hercules.


Are there any air navigation uses for the HF frequencies?

Current airborne radionavigation systems use MF (NDB), VHF (VOR/LOC, marker beacons), UHF (G/S), and L-band microwave  (GPS/GNSS, DME) frequencies.  (MLS operates in the C-band, and airborne radar in the X-band, but those are niche applications.)

Historically, the only system that used HF was the UK Gee system.  LORAN-A had options for the use of HF frequencies, but these were never used, as MF operation just below the 2 MHz mark gave much more consistent results in both reception range and performance, and LORAN-C migrated into the LF band at 180kHz, partially to avoid the difficulties of being co-located with the amateur radio 160m band.  Decca also used LF frequencies, and the Omega system operated at VLF to provide (imprecise) global coverage.

Furthermore, the FCC frequency table shows no allocations for the Radionavigation service anywhere from 2 to 30MHz, in any ITU region.


Calculation QNE and QNH, with flight level and QNH set lower (higher) than QNE

Since you used the term "Flight Level" (FL75), we must assume that the altimeter is set to 1013.25, and that the altimeter reads 7500'.

The math is basically this: each milibar (or hPa) is worth about 27 feet.  We know that his altimeter is set to 1013 hPa, but the actual QNH is 995 hPa, a difference of 18.

18 * 27 = 486.  So, the aircraft is either 486 feet ABOVE 7500, or 486 feet BELOW 7500.

So.... how do you know whether to add or subtract?  We can remember the phrase "High to low, look out below"... but what does that really mean?

Let's say that an aircraft is in an area where the QNH is really 1013, and is at an altitude of 7500'.  The pilot flies along the route for a while without adjusting his altimeter. The QNH has been steadily dropping (unbeknownst to the pilot) and is now 995 hPa. Since the pilot failed to obtain the local QNH as he passed by various stations (or, by asking Air Traffic Control every hour or so), he has also failed to adjust his altimeter to the new QNH reading.

Here is what has happened: As the aircraft continues to fly from the higher pressure area into a lower pressure area ("High to low"), the altimeter will start to go up. The pilot will unknowingly descend in an attempt to keep the aircraft at the desired altitude of 7500'. The aircraft will continue to get lower and lower ("look out below"), but all the while the pilot thinks he is maintaining straight and level.

So, we know that the aircraft is 486 feet BELOW his indicated altitude.  Therefore, the aircraft is actually at an altitude of 7014'.  He will BARELY miss that mountain peak that is at 7000'. If the QNH was one milibar lower, he would be at 6987'and hit the mountain.


What does this A320 FCTM quote about cold weather and non-precision approaches mean?

I am not sure which part you don't understand, but here is my attempt to explain in more laymen terms.

Short version: When it is too cold, a certain mode for flying non-precision approaches using the Airbus flight computer cannot be used. This is because the altimeter reading is inaccurate when it is too cold, but the computer is not designed to compensate that.

Long version: For all non-precision approaches (i.e. approaches where ground equipment is not providing glideslope signal), there is a minimum Outside Air Temperature.

Since the reading of the barometric altimeter is affected by temperature, when it is too cold outside, the reading can no longer be considered accurate enough for the safety of flight. Corrections should be made (using a mechanical flight computer / lookup table / other tools) to convert the indicated altitude on the instrument to the reading it would have indicated under normal temperature.

Since it is not authorized to make these corrections in the autopilot computer, it is not possible to use the "FINAL APP" mode to fly the approach when the outside air temperature is below this minimum.


What is this old US Army Air Corps plane?

Well gosh, this is a rare bird! The 'DEHAN' monoplane:

From this forum:

  More about Dr.Ing. Jacob Emil Noeggerath (Nöggerath ?),from the first
  Lange's book :

  He had in 19011/12 the HUNGARIAN " DEHAN ":) monoplane designed ,wich
  was flown at München-Oberwiesenfeld.

  There is another short passage about it in the Etrich book by Hanuš
  Salz.

  Dr. med. Theodor Dieterle let built this monoplane in the Otto works
  in Munich in 1913. He was supported by J.E. Noeggerath (not Nöggerath)
  who corresponds with Etrich since 1911 and was probably involved in
  the design too.

  It had an unusual longitudinal stabilisation system with a sort of
  tank? at the front that later was removed.

  Hanuš Salz named it "Dieterle Schwalbe" or "Taube" only. I prefer the
  term "Schwalbe" as the wings are peaked and the tail even it is not
  splitted but inward curved and not Taube-like.

  After this machine was tested with the swiss army, they contacted
  Etrich as well. Only an order for his machines was not realised.

So, it would appear that the plane was a one-off, commissioned by two medical doctors in Zurich, designed by Etrich (hence the similarity of the wings to those of the Taube), built in Munich and flown in Switzerland.

Which does, of course, leave another question: how did it turn-up in Texas in 1918? (Or did it?)

Edit:
There is quite a lot more info on this page under the name 'Dieterle Schwalbe'. In particular:

  Als Besonderheit verfügte die ‚Dieterle-Schwalbe‘ vor der Rumpfnase über eine mit Bleischrot gefüllte, jederzeit verstellbare Metallkapsel von ca. 10 kg. Mit diesem Vorgewicht konnte der Aeroplan während des Fluges ausbalanciert werden. Mit der Lenkbarkeit und dem Sturzflugverhalten von Flugapparaten hat Dieterle sich intensiv beschäftigt und seine Erkenntnisse in mehreren Bulletins des Aero Clubs 1914/15 veröffentlicht. Ob das Resultat seiner Forschungsarbeit in die Entwicklung späterer Sturzkampfbomber wie der Ju 87 eingeflossen ist, kann vermutet werden.

Google translation:

  As a special ordered that, Dieterle Swallow 'in front of the fuselage nose over a column filled with lead shot, at any time adjustable metal capsule of about 10 kg. With this pre-Wicht of Aeroplan could be balanced in flight. With the steerability and the nosedive of Aerial equipment Dieterle has intensively and published his findings in several bulletins of the Aeroclub 1914/15. Whether the result of his research has gone into the development of later dive bombers like the Ju 87, can be suspected.

In other words, Dieterle specially ordered that there be 'pre-weight' canister of about 10kg lead shot attached forward of the fuselage and which could be adjusted in flight to balance the aircraft.

Caption reads: "The 'Dieterle Swallow' with the characteristic Pre-weight; Oberwiesenfeld January 1913"


“All-weather” is a little bit of a hold-over from the WWII days where severe weather was much more of a threat to the aircraft. Between less reliable engines, delicate and finicky instruments like artificial horizons, and limited anti-ice technology, flying in adverse conditions was much harder then. Becoming completely disoriented in low visibility was almost a death sentence.

Special planes were made with the sole purpose of fighting at night, and certain designs were better than others for all-weather operation.

Nowadays, world class military aircraft are all pretty much all-weather because of the 70 years of avionics, propulsion and airframe improvement.


Is a controller at a NFCT required to have an FAA physical? If so what class?

Yes, you would need a current medical certificate. Source is here (page 4).

Although the above document is for NFCT, they do not mention which class is the minimum. However, I found at other places that for ATC, you do require Class II (sources are here and here).

  Second-Class - Commercial Pilot; Flight Engineer; Flight Navigator; or
  Air Traffic Control Tower Operator. (Note: This category of air
  traffic controller does not include FAA employee air traffic control
  specialists).

This flight school indicates the same:

  Applicants must:
  possess a current, Class-2 medical certificate issued through an FAA certified examiner


What are the most common reasons an aircraft to depressurize while flying?

The most common failure leading to depressurization I've personally seen is a pack/air cycle machine failure. The equipment that takes pressurized bleed air from the engine, cools and expands it. I've seen it happen two ways. 1) The aircraft is dispatched with one pack on MEL and the second pack fails in flight or 2) The aircraft is flying at high altitude, 1 pack fails, the other pack switches to high flow mode and fails soon after.

Pack failure is by far the most common I've seen. But have also seen a couple failed fuselage skins and a few burst PAX windows. Typically door leaks are enough to be noisy as heck, but not depressurize the aircraft.


How is a 436 seater A330 fuel efficient?

First of all, keep in mind that the Philippines has one of the shortest average populations on Earth. Their average passenger weighs a lot less than an average American or European, since weight scales roughly with the cube of height. So, 436 Filipinos don't weigh nearly as much as 436, say, Americans or Europeans, assuming average populations from each group. According to Wikipedia, the average Filipino male of age >= 20 is only 5' 3.5" (162cm) and the average female age >= 20 is 4' 11" (150 cm.) Compare those numbers to 5' 9.5" (176 cm) for males and 5' 4" (162 cm) for females for Americans age >= 20. Considering the roughly cubic scale, that's a pretty significant mass difference.

Second, why would putting more passengers on board not be fuel efficient? It will make the aircraft heavier, but it also means that you're carrying that many more people in one trip. My guess would be that you'll burn less fuel per passenger-mile, rather than more. To get a rough estimate, an A330-300 has an operating empty weight of about 274,500 lb. and it can carry about 175,170 lb. of Jet-A. If we assume the average Filipino weighs about 120 lb. (this seems like a reasonable guess based on my experiences in the Philippines,) 436 passengers would come out to 52,320 lb. while the 293 passengers on Delta's A330-300 seat configuration would be 35,160 lb. So, you're increasing mass before fuel by only around 5.5% while increasing passenger count by a whooping 49%. It would be hard to find a scenario in which that does not use less fuel per passenger-mile (unless, of course, you're overweight and can't take off at all.)

Regarding the issue of avoiding being overweight (and, thus, being able to take off,) Cebu Pacific normally doesn't run routes anywhere near the 6,100 nmi range of a fully-loaded A330-300. This means that they won't need to carry a full fuel load. Even a 10% reduction in fuel load from the maximum capacity of an A330-300 would equal the entire added weight of going from 293 passengers to 436. Even at full fuel load, though, judging from the previously-referenced numbers on Wikipedia, we get:

Operating Empty Weight (OEW): 274,500 lb.
Full Fuel Load: 175,170 lb.
436 120 lb. passengers: 52,320 lb.
14 flight + cabin crew x 120 lb. = 1,680 lb.
Total before cargo: 503,670 lb.
Maximum Takeoff Weight (MTOW): 534,000 lb.

So, that still leaves 30,000 lb. for cargo and anything else that's needed, even if they did need to carry a full fuel load for some reason.

The issue of why Cebu Pacific doesn't offer Business/First class cabins was also mentioned. The reasons for this are mostly their target demographic and their route network (combined with the already-explained lack of weight limit.) While there are many business travelers going to and from Cebu City, the routes on which these travelers are typically traveling are already well-served by several high-end airlines that also offer onward connections to Europe and the Americas (e.g. Cathay Pacific to Hong Kong, Korean Air and Asiana to Seoul, Japan Airlines to Tokyo, Emirates to Dubai, EVA to Taipei.) Additionally, Philippine Airlines also already competes in that space (in addition to apparently offering direct flights from Cebu to LAX now, which I think is a rather recent development.)

With their low-cost model and lack of alliance partners for onward connections, it would be difficult for Cebu Pacific to compete for the already well-served premium-cabin demand in Cebu. Instead, their business model is catered to serving Filipinos traveling between islands and to regional destinations where lots of Filipinos work out-of-country. Last I heard, approximately 10,000,000 Filipinos worked outside the Philippines (around 10% of their total population,) so serving that demographic is not a small market. In case it's not obvious, this is an extremely price-sensitive demographic which is well-served by Cebu Pacific's low-cost model.

It should probably also be noted that, while 436 passengers on an A330 is unique to Cebu Pacific, high-density economy-only configurations in general aren't. Lots of regional-service low-cost carriers offer high-density economy-only fleets, even in less cost-sensitive areas like Europe, Canada, and the U.S. In Cebu Pacific's own region, AirAsia and Tigerair also operate similar high-density, economy-only fleets targeting the same demographic (though, admittedly, AirAsia X does have 2 rows of business-class seats in their A330s, but these are on longer routes than Cebu Pacific normally serves, e.g. Singapore-Australia.)


How would SLP997 be calculated on a METAR?

Refer to FAA document, AC 00-45H Aviation Weather Services

  3.1.5.13.25 Sea-Level Pressure.

  At designated stations, the sea-level pressure is coded in the
  following format: the identifier SLP,
  immediately followed by the sea-level pressure in 1 millibars (mb) .
  The hundreds and thousands units are not coded and must be inferred.
  For example, a sea-level pressure of 998.2 mb is coded SLP982. A
  sea-level pressure of 1,013.2 mb would be coded SLP132. For a
  METAR, if sea-level pressure is not available, it is coded SLPNO.


Is it allowed to log actual instrument under IFR in VMC when VFR would be prohibited?

14 CFR 61.51(g) says (my emphasis):

  (g) Logging instrument time. (1) A person may log instrument time
  only for that flight time when the person operates the aircraft
  solely by reference to instruments under actual or simulated
  instrument flight conditions.

  (2) An authorized instructor may log instrument time when conducting
  instrument flight instruction in actual instrument flight
  conditions.

Based on that, the answers to your questions are:

Are you technically even in VMC if you are that close to a cloud? Technically flight is not strictly by reference to instruments, but VFR would be illegal. You're in IMC (i.e. you're operating below the visual minimums in 91.155) but as you said, that doesn't mean you're flying "solely by reference to instruments"
Can an instructor log instrument time? (a PPL would not be allowed to fly through tiny holes in a cloud) If the conditions are IMC, yes (61.51 doesn't require an instructor to operate the aircraft using only instruments)
Does an instrument student need foggles or can it be logged as "actual"? Whether you're wearing foggles or not, you can log instrument time only when you're operating solely on instruments. Practically speaking, using foggles guarantees that you're doing that and can therefore log the time. Without them, some or all of the time might be loggable, i.e. only the part that you really spend flying only on instruments.
Are you still required to see and avoid (obviously still a good idea) Yes, absolutely. According to 91.113(b):

  When weather conditions permit, regardless of whether an operation is
  conducted under instrument flight rules or visual flight rules,
  vigilance shall be maintained by each person operating an aircraft so
  as to see and avoid other aircraft.

It's very common to fly cross country under IFR without logging any instrument time, or logging very little, simply because you're never solely on instruments.


What are the empty weight and maximum takeoff weight of the Moller Skycar?

First of all, Wikipedia does not regard itself as a reliable source, and nor should you. It is only as reliable as the last editor, and since it is the encyclopedia that "anyone can edit" (and frequently does, me included :-) ), that is not saying much. In fact the last editor to touch those stats has messed it up and the stats given do not match the sources cited.
An aircraft's gross weight is the weight of the plane and everything on board. Typically the maximum gross weight is also the maximum takeoff weight (MTOW), although a few planes can take on extra fuel when airborne so that their gross weight then exceeds the MTOW.
As stated in another answer, the M400 is just a recurrent daydream and all figures are estimates provided by the daydreamer. But, with that in mind, the daydreamer's own numbers are clearly the definitive daydream. In other words, go with the website.


Is a pilot allowed to sleep during a flight?

Airline flight crews generally consist of at least 2 pilots. One pilot is designated as pilot flying, the other is the pilot not flying, observing instruments and flight parameters. If required, pilots can use Flight Crew in-Seat Rest:

  Flight Crew in-Seat Rest
  This is the process whereby pilots may take short periods of sleep (naps), while temporarily relieved of operational duties in accordance with carefully prescribed ‘controlled rest’ procedures, when part of a two-man operating crew of an in-flight aeroplane.

This is not communicated to ATC and only allowed with two pilots present on the flight-deck. It is prohibited to have both pilots participate in in-Seat Rest at the same time.

See also these related questions:How do pilots rest on long-haul flights?
What if pilot feels too tired before his flight?


Does lift-to-drag vary with anything beyond geometry?

Yes, it is entirely possible that the airplane will hit a wall where no more acceleration is possible while climbing. This is called the sound barrier. Besides the geometry, both the Reynolds number and the Mach number influence L/D.

As a rule of thumb, the zero-lift drag coefficient at least doubles when accelerating to Mach 1. Slenderness and sweep help to keep this rise down, but some is inevitable. Below is a plot with test data from the linked NACA Research Memorandum A55F06 for wings of different aspect ratio.

Figure 9 from NACA Research Memorandum A55F06 (picture source)

Just so you don't think this can be overcome by clever design, below is a survey of the drag rise of supersonic aircraft, taken from a short course on fighter design by Ray Whitford. While engineers could lower the drag rise with increasing experience, the Sears-Haack body shows that there is a theoretical lower limit that cannot be avoided.

Supersonic drag rise survey by Ray Whitford. Note that here the absolute increase in overall drag is plotted. This graph includes all effects like trim drag which contribute to the supersonic drag rise.

However, this can be overcome by inserting a short dive which helps to gain enough kinetic energy to overcome the drag hump shortly past Mach 1. But you need to start with enough excess thrust so any net thrust is left in the supersonic region.

By the way, the thrust of your ideal rocket will increase on the way up because the atmospheric pressure drops. This will result in an increase in the pressure difference between the thrust chamber and outside pressure.


Why is angle of attack information not displayed in the cockpit?

Many aircraft do include them, because it's very useful.

For example a modern 737:

A Garmin G1000 (one of the more common General Aviation glass cockpits):

Specifically the part that looks a bit like this

And a more traditional analog/mechanical gauge:

The problem is that usually when someone stalls, it's because they've made a mistake - not because they can't see the AoA. Either they're disorientated, or they've made a mistake with airspeed or an obstacle and are exceeding the aircraft's performance envelope.

Typically, the lack of an AoA dial isn't the reason you stall.


Why are only some aircraft in this formation creating contrails?

This 'party trick' is covered nicely on metabunk.org.

  [It's the Su-30's] ability to inject unburnt fuel into the exhaust plume via the afterburner system. The super hot air of the exhaust instantly evaporates the volatile fuel, and then when it mixes with the cold air behind the plane the fuel reforms as a fine mist, essentially a fuel smoke cloud.

(YouTube)


In the early days of flight, were there any cockpit control schemes other than the modern one?

The Dunne D.8 used a pair of levers, each controlling one elevon.


What is the loud noise of a helicopter when the rotors are not yet moving?

The sound you're hearing is the APU (Auxiliary Power Unit) running.

Turbine (jet) engines turn at a much higher RPM than reciprocating engines. This means that an electric starter motor would have to be bigger and heavier in order to produce enough torque to get the engine moving fast enough. The bigger the engine, the bigger the starter (and the batteries to drive it). At some point, it becomes impractical to have an electric starter on a big turbine engine.

That's where an APU comes in. It's essentially a small jet engine. Small enough, in fact, to be started electrically. Once it's running, it feeds high-pressure air to spin the main engine fast enough for it to start. It can also provide electricity, run the A/C, etc.


What is the reason for the poor low-speed characteristics of sweptback wings?

Disadvantages of wing sweep

Lift curve slope is reduced by the cosine of the quarter chord sweep angle. This means more angle of attack for takeoff, which requires a longer take-off run and a longer landing gear to avoid a tail strike on rotation.
If you rotate the airplane, the tips of backward swept wings come down when the aircraft rotates for take-off. This also might drive the requirement for a longer landing gear.
Bending moments in the wing will become torsion moments when you change the sweep angle. And you will need to change it at least in the wing root where the wing connects to the fuselage. This translates into a heavier structure.
If your sweep angle and aspect ratio both are large enough, the wing will show nasty stall characteristics. The boundary layer is swept towards the tips and causes earlier separation when the wing stalls, and the airplane will pitch up or roll uncontrollably. Wing fences help, but cannot completely remedy this.
Wing sweep causes a yaw-induced rolling moment, so less dihedral is needed. On high wing airplanes this requires to use anhedral. Unfortunately, this rolling moment varies with lift coefficient, so your yaw-induced rolling moment on a swept aircraft is lower than ideal at high speed and higher at low speed.
For flying wings, sweep will let the aircraft center pitch up and down when the wing flexes. This creates a powerful interaction between the fast period mode (which is only moderately damped in flying wings) with the wing bending mode, resulting in flutter.

In short, when having a choice, the clever airplane designer avoids sweep whenever he/she can. But sweeping a wing back is still better than forward sweep.

Low Speed Characteristics

An airfoil initially accelerates the air which flows over its top surface and decelerates it again over its rear part. On swept wings, this acceleration-deceleration only affects the orthogonal speed component, so the speed component in span direction remains unaffected. This is the reason for the higher Mach capability of swept wings, but also causes the air to flow first inwards and then outwards while transversing the wing's upper surface.

On top, friction decelerates the air flowing around a body, such that a layer of decelerated air surrounds each surface of an airplane. The thickness of this boundary layer increases with flow length, and on a swept wing this friction will initially mostly affect the orthogonal flow component. At around mid chord you will find air which has been decelerated mostly in its orthogonal speed component (since this component was so high over the forward part) and now will be subject to more deceleration of the orthogonal component, so that only the spanwise component will be left over the rear part of the boundary layer. Now this boundary layer will only flow off in span direction, such that a massive increase of slow, low-energy air will be collecting towards the tips.

A thick boundary layer will cause early flow separation, so when the angle of attack is increased, the flow at the tips of a backward swept wing will separate first. This will cause lift loss, and since the tips are also the rearward part of the wing, will shift the aerodynamic center forward. This in turn will make the aircraft pitch up, which aggravates the stall condition. If the separation happens asymmetrically, the aircraft will roll in addition to pitching up. In case of the F-100, the tail surfaces were too small to stop the pitch-up, so once the aircraft crossed into the stall region, it would uncontrollably pitch up more and stall completely.

Modern swept-back aircraft have an angle-of-attack limiter which will prevent the aircraft from flying into the stall region. Also, wing fences help to keep the spanwise flow in check, and vortex generators help to energize the flow such that the early flow separation at the wing tips is sufficiently delayed to avoid the uncontrollable pitch-up. The F-100 lacked all those remedies.

Wing fences on a MiG-17 (picture source)

Vortex generators on a Boeing 737 wing (picture source)


How low was the Hong Kong Kai Tak landing approach over the city?

As the wikipedia article for Kai Tak, Runway 13 approach states:

  Typically the plane would enter the final right turn at a height of about 650 feet (200 m) and exit it at a height of 140 feet (43 m) to line up with the runway.

Given that some of those buildings underneath the flightpath were 6-storey and therefore ~60-70ft tall, the aircraft were less than 100ft above the highest rooftops. (This I can personally vouch for, since my sister did for a while live in one of those 6-storey apartment buildings and I have stood on the rooftop watching the planes pass over!)


The short answer is that in practice the FAA doesn’t care about “compensation” between family and bona fide friends.
The long answer is that the FAA’s mission is to protect the general public from pilots. (If they also happen to protect pilots, that is a side effect at most.) Your parents and bona fide friends are not the “general public”.
As a practical matter, the FAA could never prove beyond a reasonable doubt in court that any particular dollar that your parents or bona fide friends gave you was for flying vs a gift or for something unrelated, especially when it is likely they would be uncooperative with any investigation or charges against you. If they give you money, and you happen to use some of it to take them flying to a place of your choice, so be it. It’s just not worth the FAA’s time to look too closely at that, so they consciously turn a blind eye.
Where you will get into trouble is flying strangers or acquaintances to a place of their choice. The exact path the money takes is irrelevant; if you accept compensation from the “general public”, then you are operating an illegal charter, and the FAA will hit you like a ton of bricks for that.


How should a newly minted instructor sign an endorsement?

I would think the newly minted CFI should use the same words the FAA uses: "Pending". Can't go wrong with that.


Why did flight attendants need to be seated early landing at Palm Springs?

I can't say for sure, but here's one plausible reason: Palm Springs is in a valley and surrounded by much higher terrain on three sides, which requires more maneuvering to land than at other airports. You can see on the VFR sectional that the airport elevation is 476ft MSL, but there are mountains over 8000ft within 10 miles of the airport. If you check the instrument approach plates for runway 13R/31L (it's the longer one, so most likely to be used by an airline), you can see that the flight paths are far from straight:

RNAV 31L

RNAV 13R

I can imagine the pilot would brief the cabin crew to be seated well before landing for safety while the aircraft flies the approach. Mountains often produce turbulence and high winds too, which would be another good reason to be seated while maneuvering at a lower altitude over that terrain.


What is the minimum separation between two A380's while taxing in-line?

For a Turbojet @ or < slow taxi power, the min distance behind is 30m

Thanks


Is an "atmospheric geostationary satellite" feasible with current technology?

Short answer: No.

Long answer: Your "unlimited time" condition makes the short answer easy. If you need to go up for a limited time, and you have the liberty to choose the time of ascent and descent, the answer is: Possibly.

First, there are two ways of going up there: A balloon and an aircraft. A helicopter would be much less efficient, the tether of a balloon will be too heavy to lift, and you will see that even a glider-like aircraft will struggle to stay for some time at 30 km.

Next, atmospheric pressure at 30 km is 12 mbar, just 1.2% of what it is on the ground. So your aircraft has to go at some speed just to create enough lift. If we assume that you fly at Mach 0.5 to 0.6 (where high-lift airfoils and propellers can still operate), your dynamic pressure is that of a modern glider at low speed. The flight speed actually is between 150 and 180 m/s, however.

Now let's assume your aircraft has an L/D of 50. This translates into a power requirement just to stay aloft of 3 to 3.6 kW per ton of aircraft mass. Your propeller will have no more than 85% efficiency, and your engine will create some loss as well, so your installed power needs to be at least 4 kW per ton of aircraft mass. Since you fly at a glider's dynamic pressure, you will also have a glider-like wing loading of 30 kg/m². Per ton, your wing area is 33.3 m². To operate an air breathing engine at this altitude is a challenge, so I will assume solar electric propulsion. Let's be optimistic and we assume a solar constant of 1.4 kW/m² at this altitude, and you fly at moderate latitudes (say, 45°), so your solar panels can create (20% efficiency) 200 W per m² or 5.3 kW per ton of aircraft mass (assuming 80% of the wing is covered, the rest will have too much curvature). Of course, this is all valid only around noon, so if you want to stay overnight, even in summer there is not enough energy to keep the aircraft up for a longer time, even with very optimistic assumptions. You might want to assume batteries which can provide the power for the climb phase, so you take off in the middle of the night and arrive (with empty batteries) at altitude in the late morning. Then you might really stay there until 2 or 3 pm, when the lowering sun means that your solar panels will not provide enough power to stay up, let alone charge the batteries. And I have not even started to subtract the power for operating any equipment (which would be the reason to go up there in the first place, right?).

To go with a lower wing loading means you will have a very delicate structure which cannot cope with the winds at 30 km and gust loading at lower altitude.

This wind will also be a problem for any ballon. 20% of winds at 30 km are above 76 m/s (Mil Std. 210C), 5% are even above 98 m/s. One cubic meter of helium gives you 10 N of lift at sea level, but only 0.156 N at 30 km. To lift one ton of balloon up to 30 km, you will need 63,000 m³ of volume. This is a sphere with a diameter of 50 m! The wind forces to keep this thing tethered will need a strong and heavy tether, so without going into the details I think that a tethered balloon will be a challenge, to put it mildly.

The "Facebook drone" articles are not serious, they are meant to create some P.R., and don't hold your breath for Internet delivered by drones anytime soon.


What happens if I cross the ADIZ line without a flight plan and no clearance or contact with ATC?

In the late 60's, in a C152. I flew a guy, at a low altitude out of Key West to the Marquessa Islands area to look for sunken Spanish galleons.  On the return trip I was nervous flying at 200 feet above the ocean and climbed up to 3,000 feet.  After a few minutes al said altitude my windscreen flashed black. A F-4 had come from behind and below - zoomed up a few yards in front of me! Looking behind me I saw his wingman, gear and flaps down, S_turning on my six.

A quick call to FSS clarified the situation.

That is what happened to me upon inadvertent entry into the ADIZ. I don't expect it has changed.  There were no followup actions other than the echos of the F-4's pilots laughter.


Why do both east and west isogonic lines tilt toward the west as they go north?

Because the present position of the magnetic pole pole is such, that in central and eastern US states the isogonic lines are tilted to the West. But in western parts of the U.S., those lines are tilted to the East...


What is the relationship between speed, torque and pitch in a helicopter?

I'm afraid that a thorough answer requires the contents of chapters 2 and 3 of Leishman, but here is an outline. The relationship between power and true airspeed from this answer:

Power equals torque times angular velocity of the rotor: $ P = Q * \Omega$. Most helicopters have constant speed rotors, so the relationship between torque and speed would be similar to the power curves.

Rotor blade length and pitch appear as follows. Power P and torque Q equations for momentum theory in the hover:

$$P = C_P \cdot ½ \rho A (\Omega R)^3$$

$$Q = C_Q \cdot ½ \rho A (\Omega R)^2  R$$

At forward speed the momentum based power becomes less due to lower induced power requirements. An inflow equation relates forward velocity of the helicopter with blade tip speed - too much scope for an answer here.

Blade length appears in the rotor disk area A. Torque and power are functions of the rotor solidity $\sigma$, defined as (total blade area)/(disk area). Note that $C_P$ is always the same value as $C_Q$

From Leishman:

..if the amount of lift a helicopter generates changes dependant on pitch, how much does the pitch change..

Thrust T of the rotor Again from Leishman:


Why would a country prefer to purchase Su-35 rather than Su-30MK?

There can be many reasons for such a choice. The first is a single seat air-defense fighter, the other is a two-seat multirole  air-superiority fighter according to Wikipedia. The cost can be another reason; depending on configuration it seems that the two aircraft have an overlap with both types starting around USD \$40 million per aircraft.

Indonesia already operate a fleet of several single-seat types, such as the Su-27, F-5 and F-16, so it might simply be easier to transition to another single seat fighter. They do have a small number of Su-30 already, so it could also be a desire to use each type for the optimal mission, rather than having one type do everything.


Does an increase in inlet temperature affect fuel flow and power output?

Most civil aircraft engines are "flat rated". See What is a flat rated engine?

That means, the thrust (power) produced is constant (flat), as ambient temperature increase, up to a certain temperature, and then the turbine inlet temperature limit is reached, and fuel flow and thrust is reduced as the ambient temperature continues to increase.

So, thrust is initially constant as inlet temperature increases, then decreases. It's a bit harder to predict what fuel flow will need to do to achieve this behaviour. It will certainly reduce in the temperature range where thrust is reducing, but in the cooler temperatures before that, it is probably increasing to keep thrust constant. As the chart shows, in this region EGT and N1 rpm are increasing. I expect fuel flow is probably showing the same behaviour as N1.

Thrust cannot actually be measured in flight, so most engines use either N1 rpm, or engine pressure ratio, (turbine exit perssure/engine inlet pressure) as a way to predict thrust. GE typically uses N1, whereas Pratt & Whitney and Rolls Royce usually use EPR. Using EPR is technically better, beacuse it will account for engine deterioration, where as using N1 assumes the fan mass flow remains the same for a given rpm as the engine degrades. But EPR requires 2 pressure measurements, which are less reliable, so most engines that use EPR have N1 control as a backup mode.  See
What is the difference between EPR and rotor speed as thrust setting parameter?


How do humanitarian flights arrange special permissions to fly when ATC isn't available?

In the U.S. at least, HADR doesn't launch aircraft until a crisis aka disaster has been identified, even if at launch they don't yet know if the problem is lack of potable water or civil unrest over rigged elections.

An already flying commercial airliner won't have a glut of doctors and medicine unless it's been chartered for an already identified crisis, so it's unlikely to divert to this one.

If, after an identified disaster, an aircraft flies there to assist:

A helicopter doesn't need ATC support to land in an off-airport parking lot, of which a major city would have many.
A fixed-wing aircraft, needing an approach path, lacking ATC response, would revert to non-ATC protocols, just like at a small Midwestern grass strip or an Alaskan inlet.  VFR.

Non-aero analogy:  fire trucks and ambulances don't fret over parking tickets.


Is 1N2 (Spadaro) in class G or D airspace?

Strictly speaking class D airspace generally has a radius of 4 NM. If you take a look at the TAC chart or hop on your favorite flight app you will see the field actually sits just outside the airspace.

The sectional is likely drawn this way to allow for 49N and 1N2 to both be properly depicted.

Officially the airport is closed according to the current AF/D it appears to have been shut down in 2016, so it may be listed there simply for visual reference as the physical runway seems to still exist but traffic overlap is no longer an issue.


How much runway is needed for comfortable operations in a PC-9?

TBM quotes the distances for the 700 at

  Take-off: 2,133 ft (650 m)

  Landing: 2133 ft (650 m)

And Pilatus for the PC-9

  Take-off distance over 50 ft obstacle at sea level: 1,300 ft (397 m)

  Landing distance over 50 ft obstacle at sea level: 2,255 ft (687 m)

The PC-9 and TBM 700 are very different beasts (did you mean PC-12?)

comfort is about you the pilot and there are some pilots who operate right down to book minimums. Like anything else in aviation the pilot is the ultimate decider and you can operate both of these planes off a 2256 foot strip in clear weather. I'm not sure I would. I would think 3000ft. is enough to comfortably fly either of these planes. The FBO I rent from at KDYL flys King Air 200's out of there all the time and they only have 3000 ft there. For planes like this, considering their common missions I would also look for a strip with a solid IFR approach, sells Jet-A on the field, enough ramp room to fit your plane, and taxiways wide enough for your wing span as well as sufficient runway length. Its also going to take a lot more than "familiarity" with single engine prop planes to move up to a turbo prop.


What is the A350's procedure for stained cockpit windows?

I am not sure if this applies to modern jets, but pilots of the past were sometimes landing "sideways" by using https://en.wikipedia.org/wiki/Slip_(aerodynamics). That provided some view from the side window.

I believe one example of that could be found in "Fate is the Hunter" by Ernest Gann.

Also general aviation pilots sometimes use this technique if the windshield is iced over.


Is Vy closer to Vbg with a variable pitch prop

Too long for a comment:

My POH does not show Vbg, only the 'normal' V's listed below, and even then only some of these are indicated on the Airspeed Indicator with the Green, Yellow, Red color bands. How would you determine Vbg? Experimentally?

VA,  Maneuvering Speed is the maximum speed at which you many use abrupt control travel.

VFE,  Maximum Flap Extension Speed is the highest speed permissible with wing flaps in a prescribed extended position.

VNO,  Maximum Structural Cruising Speed is the speed that should not be exceeded except in smooth air, then only with caution.

VNe,  Never Exceed Speed is the speed limit that may not be exceeded at any time.

VS,  Stalling Speed or the minimum steady flight speed at which the airplane is controllable.

VSO,  Stalling Speed or the minimum steady flight speed at which the airplane is controllable in the landing configuration at the most forward center of gravity.

VX,  Best Angle-of-Climb Speed is the speed which results in the greatest gain of altitude in a given horizontal distance.

VY,  Best Rate-of-Climb Speed is the speed which results in the greatest gain in a given time.


Is it possible to "pimp up your aircraft" with an audio system?

While there are many great reasons not to do this it would seem from a cursory scan of the FARs that the answer is "Yes, you can." -- At least one company (Alto Aviation) is producing aircraft entertainment systems with relatively "pimped out" audio capabilities.

These systems seem more geared toward "cabin class" aircraft where the crew and passenger compartments are separated (mainly business twin/turboprop/jet aircraft), though I suppose you could conceivably install it in something like a PA-32 or Cessna 206, or even light piston singles if you wanted to.

Such an installation would be subject to the same restrictions as any electrical device installation (requiring a check to ensure it doesn't overload the electrical system, and verification that it won't interfere with navigation or communication equipment), and I would imagine some of the work required may qualify as a "major alteration" as a change to the "basic design of the electrical system" may be involved.
There may also be additional operating restrictions placed on the installed equipment (like "Not permitted for use during taxi, takeoff, or landing" to prevent it from being a distraction/safety hazard during critical phases of flight).


Can a commercial aircraft theoretically reach 60,000ft?

An airliner's service ceiling is the altitude at which its rate of climb drops to less than 100 fpm.  Most commercial airliners can't climb above 40000-45000 on a standard day.  If temperatures are above standard, less than that.  Corporate aircraft can go higher, just above 50000, so they get to avoid pretty much all the traffic because everybody else is below 40.  The Global Express uses low bypass fans and very large wings to do this.

To go toward 60k you need super efficient engines and glider like wings.  P&W developed the U2's engine with virtually no blade tip clearance to be able to operate at 70000ft.

Then you have coffin corner, the spread between critical Mach# and stall.  It gets pretty small at 60000 ft.  In the U2 at 70000 ft the spread between Mcrit and stall is very small, and between Mcrit and the back side of the power curve is just a few knots and they cruise in a tiny speed window, autopilot on in speed mode at all times.  Bit too slow and down you go, bit too fast and mach buffet starts.

At an airliner's service ceiling, you have very little reserve thrust margin, and you may be operating just above min drag speed, not so far from the back side of the power curve in cruise.  If you are at service ceiling and some speed bleeds off because say you hit some down moving mountain wave and the autopilot pitched up to compensate, and you aren't paying close attention, you may have no choice to descend right away as speed decays with no way to stop the decay without resorting to gravity.

Stalls at this altitude take many 1000s of feet to recover from.  In the thin air, a mass has to accelerate over twice the distance through space for the same indicated airspeed increase as down low.  If you get stick shaker at that altitude, you have to push over really aggressively for the recovery, not just lower the nose a bit.  After a fatal Pinnacle Airlines CRJ200 stall incident that started at 41000, airlines started to focus more on training for high altitude stall recovery.

The high altitude world is a dangerous place, even at altitudes in the 30s.


Why does TCAS not issue turning commands as Resolution Advisory?

TCAS gets fairly accurate altitude information from the same source as the transponder. Thus any extrapolation from this information can yield a fairly accurate prediction of whether two aircraft may collide, and provide more certainty that changes in altitude will avert any conflict.

Range information is obtained by measuring the round trip time of the interrogation and response. This will also be fairly accurate.

Direction information is obtained by using the TCAS antenna to detect the direction of responses from other aircraft.

These values are then extrapolated to provide an expected path of other aircraft. Most airliners are required to use TCAS II which only provides the vertical guidance. TCAS III was envisioned to provide horizontal guidance as well, but:

  it was judged by the industry to be unfeasible due to limitations in
  the accuracy of the TCAS directional antennas.

Even if TCAS can be accurate to 3 degrees in direction, this translates to over 300 feet of uncertainty at 1 nmi.

TCAS IV was planned to use more accurate GPS information, but with ADS-B becoming more widely adopted, this development was stopped in favor of some future system that can use existing ADS-B technology.

Another point is that airplanes are generally larger in the horizontal plane than the vertical, and thus would need to change course more horizontally to avoid collision than they would need to vertically. Especially as planes get larger, they also tend to be more maneuverable in pitch than in turns.


If an accident were to occur at a cross-border airport, who would investigate?

By ICAO conventions, the lead investigator is the country in which the accident/incident occurs, unless otherwise delegated. This is fairly common: for example an engine fails in Canadian airspace but they divert to Iceland, it's initially Canada's responsibility.

So you have an argument for whatever country the airplane hit the ground first in your example of a hard landing.

Additionally, ICAO Annex 13 recommends that if the country can't be decided, the state of registry should conduct the investigation:

  5.3 When the location of the accident or the serious incident cannot definitely be established as being in the territory of any State, the State of Registry shall institute and conduct any necessary investigation of the accident or serious incident. However, it may delegate the whole or any part of the investigation to another State by mutual arrangement and consent.

Practically, I would imagine they would delegate the investigation to the country of registry of the aircraft, since that's where the tax dollars were paid.


Why might American Airlines fly a 767 from JFK to EWR?

It's a positioning ferry, to move the aircraft from where it "is" to where it "needs to be" for its next revenue leg (or maintenance, in some cases). These sorts of legs are uncommon because they're expensive; ideally an aircraft is never out of position this way, but sometimes "stuff happens" and you fly an empty plane to get it where it needs to be.


What would be the lift formula for straight wings?

Regardless of the geometrical shape of the wing, you need to know the wing area to determine the lift force as it is one of the factors that affect lift.

Calculate lift using this formula: $$Lift = \frac{1}{2} (C_L * P * S * V^2)$$.

$C_L$: coefficient of lift
$P$: density of air
$S$: surface area of the wing
$V$: velocity of air


What is this large engine doing on a B52?

Testbed Aircraft Cameos

  As a young engineer in the 1960s at Pratt & Whitney Aircraft (now
  UTC’s Pratt & Whitney) in East Hartford, Connecticut, I was involved
  (along with many others) in the development of their 44,000 pound
  thrust (lbt) JT9D turbojet, which powered the first Boeing 747 jumbo
  jet aircraft[ Display footnote number: 2 ]. Because of its then
  ground-breaking large fan diameter (new for the 1960s), P&WA had to
  use a U.S. Air Force Boeing B-52 as a testbed. The Stratofortress,
  with its high wing, allowed the JT9D to be mounted with adequate
  ground clearance for takeoff and landing. In Figure 1, the P&WA
  testbed aircraft is shown landing at the Windsor Locks, Bradley
  International Airport, after a test flight, with a JT9D engine
  replacing two TF-33 inboard engines on the right wing of the
  eight-engined B-52.

  The B-52 continued as a P&WA testbed aircraft until 1981, even after
  being damaged in its hangar by a violent tornado that raced through
  Windsor Locks in 1979. Pratt & Whitney more recently used two Boeing
  747SP aircraft for testbeds, to flight test their new geared fan jet
  engines.


What aerodynamic improvements allow variable geometry wings to be omitted on modern fighter aircraft?

It is more a tactical rather than an aerodynamic improvement.

Wing sweep is helpful when the top speed of the aircraft is well above Mach 2 and should be maintained for more than a few seconds. However, studies of past conflicts have shown that this speed capability was never used and almost never helpful even in hypothetical scenarios.

In addition, the lighter and stiffer structures made possible by carbon composite technology lower the maximum sustained temperature those structures can endure. Now the maximum Mach number is not only limited by aerodynamics, but also the stagnation point heating. In case of the F-22, the maximum sustained Mach number was lowered from 1.8 to 1.6 during development.


Do F-22's use cartridge start to start engines?

It's a Jet Fuel Starter (JFS) system, used by the F-16 and other jet fighters. On-board compressed air (called Stored Energy System) is released onto a turbine, which starts a small gas turbine engine, which then mechanically engages with the engine's gearbox to spin it.

F-22 calls it Auxiliary Power Generation System.

On the F-16 the JFS allows two bursts/attempts, before needing to recharge (re-compress the air). And if I'm not mistaken, it can be charged after two failed attempts using hydraulic pressure from the brake accumulator, as the engine would not be able provide hydraulic pressure to charge the system yet.

Following the release of the high-pressure gas, the sudden expansion and subsequent cooling causes condensation, which is the smoke we see in the video. The two flaps that open prior to the compressed air release are the intake and exhaust doors for the small gas turbine engine.

The F-22 certainly doesn't use a cartridge start (Coffman engine starter). That's mainly for WWII-era reciprocating engines, and some old jet engines.

On an airliner, the equivalent system is an APU. It's started using the battery and then it drives the engine's gearbox using bleed-air. It's a slow process compared to releasing compressed air, especially when you are to scramble as quickly as possible. Technically, both systems are APU's.

This longer video gives us better clues: you can see the JFS's smoke, then see its heat haze, followed by each engine's heat haze. Each step accompanied by sweet music.

(YouTube) Smoke and heat haze from the JFS.


What valve would be the best for a model rocket with a hybrid engine?

It depends on a lot of factors.
Most valves with the specs you need will work really, but you'll have to carefully determine your specs. There's not really a single answer.
What kind of thrust are you designing your engine for? This (amongst other things) will determine your minimum needed flow rate, and will determine the pressures this valve will need to be able to cope with. These things will be the most important valve specs you'll be considering.
I don't know where exactly your valve will be in your engine, but make sure it can withstand the heat its exposed to.
On the flipside, knowing you'll be using GOX, you'll probably just use the pressure from your oxygen tank to power your engine. As the oxygen will be expanding, the MOV might tend to freeze up and lock itself in place. Beware of that as well when choosing a valve.
Not all valves will be able to safely operate in a pure oxygen environment. However, as we're talking model rockets here (the operating time of your engine is quite short I suppose) it'd surprise me if that would turn out to be an issue.
To end with, although maybe not directly related to your question about the valve, make sure you understand hybrid engine throttling. It can get more complicated than you might anticipate.


Turbofan engine 2 spool - Turbine drives the compressor or Starter drives the compressor

The starter drives the entire HP spool (HP compressor, interconnecting shaft, and HP turbine).  The gearbox in question is the accessory gearbox that runs the various pumps and is driven off the HP spool shaft, which by happy coincidence is on the outside of the LP shaft.  The starter is mounted on that gearbox and is able to back drive the HP spool through the gear train for engine starting.

The LP spool, which is the fan and LP turbine with its shaft running down the center of the HP spool, is just going along for the ride during the start.


Can the signature of stealth fighters be uncovered, and then used for future detections?

I would like to make some general comments, as having worked on programs stood up to build sensors for various military threats. In these programs we were always attempting to get data on relevant threats. The more challenging the signature the more it drove the sensor technology, hinting at areas of improvement. In the sensor research we often met with the target community. At times we used their services to look at sensor sensitivities. Perhaps not surprisingly, even though they were on our side, they were at times reluctant to talk about certain sensitive areas.

What I learned from this experience is that, if you are the target you hide your signature as much as possible, and if you are the sensor you hide its characteristics as much as possible. Whenever you give away information you risk exposing your vulnerabilities, and each has its vulnerabilities. An example might be controlling creation of photographic images of sensor optics on an air-to-air missile. This is why some "black" programs hold their technology in war reserve (think hidden in hangers), and are only utilized when the threat warrants exposing this new hardware to the adversary.

As another example, I can point out missions during my cruises aboard the USS Nimitz flying light attack. During this time period the battle group often passed by Libya. The carrier stayed out of the contested waters while the destroyers breached the line drawn in the sand by Gaddafi. Other missions included flying electronic surveillance platforms with fighter escorts close aboard the coast. The radars would light up the surveillance aircraft and that data was captured for further analysis.

My assessment would be that, whenever you bring out a new technology you try to cloak it as much as possible. The other side is out there collecting data on you. Sensors improve, and targets find better ways of hiding. A good example of the evolution of threat can be found looking through the literature on surface-to-air missiles. As soon as the Russians came out with a new SAM we came out with a new countermeasure, which drove them to better sensor technologies.

The findings that a collection activity might obtain will more than likely not allow them to "easily" spot the target. This sort of technology is on the "bleeding edge" and gains are typically hard won and incremental. As we get better sensors, they get better at masking their targets.

One last observation which might not be obvious, but definitely quite important, is that the target might use information about the sensor to develop tactical procedures to minimize its effectiveness. If I learn that your sensor is using microwave electromagnetic radiation I will think about hiding in water vapor or rain storms to minimize its effectiveness. It is truly a cat and mouse game.


Does taxiing in London City (LCY) happen on the runway?

To answer the title question, yes.

There are nice timelapse videos for EGLC/LCY on YouTube, if you want to see it in action. (Example.)

As for the actual operation at the airport, below is the official chart and textual data via the UK AIP:

  6 USE OF RUNWAYS

  b) Minimum Runway Occupancy Time - Arriving Aircraft.

  Pilots are reminded that prompt exit from the runway enables ATC to apply minimum spacing on final approach that will achieve maximum runway utilisation and will minimise the occurrence of 'go-arounds'.
  When landing on Runway 09 pilots should commence back-track as soon as practicable and exit via Hold Echo unless otherwise instructed by ATC. Any aircraft that continues landing roll beyond Hold Kilo may infringe the ILS critical area.
  When landing on Runway 27 A318 and CS100 pilots should plan to exit at Hold Delta (after a back-track if required). A318 and CS100 aircraft are not permitted to exit via Holds Charlie, Bravo, or Alpha. All other aircraft types may use any Hold to exit the runway except Hold Echo which shall only be used when specifically instructed by ATC. Pilots should be aware that use of Hold Alpha will increase Runway Occupancy Time.
  Pilots expecting to use the full runway length to stop (e.g. due aircraft weight/meteorological conditions) are requested to inform Thames Radar on first contact.

(Bold emphasis mine.)

The short version (runway 9): backtrack [on the runway] to vacate as soon as possible (example from cockpit) using the specified exits even if other exits may seem to be available, and if you need full runway length, notify the approach controller (Thames Radar).

(If the pilot does need full length, the approach controller needs to know to add extra spacing for the plane behind.)

For the exits mentioned in the text, reference the chart below:


How are the system development and integration procedure separated for Integrated Modular Avionics?

The Aircraft System Manufacturer is the company developing the system that is being implemented on IMA hardware (supplied by the Avionic Module Supplier). They will likely develop software to load onto the IMA hardware to perform certain functions.

For example:
Airbus would like to implement a Thrust Reverser Control System for their new airplane. The system would take in some parameters gathered from various sensors within the aircraft, perform the necessary logic and/or calculations, and then provide the necessary control commands to the thrust reversers.

Now Airbus doesn't want to develop this specific system, so they contract it out to another company ACME Avionics. They provide ACME with the System Requirements Data, which describes how the system must operate, what inputs it will use, the Design Assurance Level of the system, and the IMA modules the system must use to implement the requirements.


Why is a TFR issued when barometric pressure exceeds 31.00 InHg?

That is because most of the legacy altimeter setting barometers cannot handle such high pressures. Most of them, like the one pictured below has a range from 28 to 31 inches of mercury.

Kollsman Altimeter Setting Indicator, image from analogweather.com
From Aeronautical Information Manual:

7-2-4.  High Barometric Pressure
a. Cold,  dry  air  masses  may  produce  barometric pressures in excess of 31.00 inches of Mercury, and many  altimeters  do  not  have  an  accurate  means of being adjusted for settings of these levels.

As a result, the TFR is triggered by 14 CFR 91.144

(a) Special flight restrictions. When ... barometric pressure on the route of flight currently exceeds or will exceed 31 inches of mercury, no person may operate an aircraft or initiate a flight ...


What's the difference between EFVS and CVS?

The FAA recognizes 4 'vision' systems; enhanced vision system (EVS), synthetic vision system (SVS), combined vision system (CVS), and enhanced flight vision system (EFVS).

EVS and EFVS use either passive or active sensors on the aircraft to enhance the crew's vision of the approach. SVS uses a database to generate a synthetic view of the terrain in  front of the aircraft. CVS combines features of EVS or EFVS and SVS.

It's all spelled out in AC 20-167A Airworthiness Approval of Enhanced Vision System, Synthetic Vision System, Combined Vision System, and Enhanced Flight Vision System Equipment


Is aspect ratio efficiency related to the momentum added to the air?

You're almost there. The difference lies in the kinetic energy required to move a certain mass of air, not in the air's viscosity. Copying freely from one of my earlier answers:

  The force to keep the object aloft is $$F=m_{object}g$$ The force generated by downwards momentum transfer is $$F=\dot{m}v$$ with $\dot{m}$ indicating mass flow (kilogram per second) of the air (not the mass of the object). The energy flow (power) required to  impart this momentum on the airflow is $$ P=\frac{1}{2}\dot{m}v^2$$ Here we can draw an important conclusion. The power requirement is arbitrarily small, by increasing the mass flow and decreasing the downwards velocity.

The power requirement expresses itself in the form of induced drag. By affecting a large mass of air (a long wingspan), you reduce the power requirement, which manifests itself in the form of lower induced drag.


How will the altimeter read in air colder than ISA?

Air expands as the temperature increases and it compresses when the temperature decreases.

image source: aviationweather.ws

When it is colder than ISA, the air column is compressed and therefore you are flying lower than the altimeter is indicating. In other words: the altimeter will over read in cold air.

So to fly safely over an obstacle at a cold day, you have to add extra margin to the obstacle's height, because your altimeter will show a higher altitude than your true altitude.


Have attitude indicators ever had triple failure in a commercial aircraft?

Yes! More or less, it depends on your definition of failure (see later).
As you said, the probability that three Inertial Reference Units (IRUs) fail is extremely rare. This is because IRUs are self-contained, internal to the aircraft, and independents. Instead, air data probes are subject to ice and external factors (for instance, bird strikes), thus more subject to faults. The IRS failure probability is so low, that in the non-neo A320/A330 the ECAM message "TRIPLE IRS FAILED" doesn't even exist (it shows all the three messages: IR1+IR2 FAULT, IR2+IR3 FAULT, IR1+IR3 FAULT).
However, yes, it happened: This is a real picture of an A330-220 (F-GRSQ) flying at FL240 with all IRUs failed in 2014:

According to the BEA report of the F-GRSQ incident (published in 2018), only 2 triple IRU failures incidents in Airbus aircraft happened since 1999: this one and another one in 2002.
In both cases the reasons of the triple failure are unclear. However, the BEA report suggests that the triple failure was triggered by erroneous pilots actions responding to a single IRU failure. In the F-GRSQ the possible explanation is that the pilots identified IR2 drifting too much and decided to switch it to ATT mode (degraded mode, providing only attitude), but they erroneously switched IR3 to ATT. Hours later, when IR2 drifted too much, Autopilot and FBW computer detected the data inconsistency and started to consider IR2 as failed, while IR3 was in ATT mode (and then not used by AP/FBW). Probably, at this point, by following a non-standard procedure, the pilots tried to restart all the IRs to regain the position on Navigation Display, including the  working IR1, which then lost alignment and caused the triple failure condition. Unfortunately, the lack of CVR recordings didn't allow the verification of this theory, but no malfunction was found in IR1 or IR3.

Why do commercial pilots keep ignoring the attitude indicators in case other instruments are assumed to have faults?

I don't think that pilots thought it was an IR problem in the sort of incidents you mentioned.