Is aluminum electrical wire used on aircraft?

Cable is not just the metal wire. It's also insulation, installation, cable channels, extra space at tight bends where cable flexibility is insufficient, and maintenance of said cable. Aluminum corrodes in a lot of conditions and happens to be one of the most fatigue-susceptible metals.

For these reasons, most aircraft wiring is copper and silver-plated or nickel-plated copper. Such wiring is reliable even under imperfect conditions.

But there are cases where different considerations prevail. Sometimes it's just the need to have some minimum cable thickness, for mechanical and handling reasons. Other times it's a thick bus bar where weight makes a difference and quality is easy to ensure.
So beside copper there is some steel, copper-nickel plated aluminum, copper-nickel plated steel, and pure aluminum wiring in aircraft.

In aircraft, safety is ensured and validated with engineering and testing; risks of the kind one can take with home wiring are not accepted. The price of aluminum wire is installation and maintenance complexity instead. The ends need to be cleaned and crimped or welded, sometimes the aluminum wire is terminated with a bimetallic insert. As a result, aluminum wiring is more expensive than copper, not less. It will likely require more maintenance work in the future.

Until recently, aluminum has been mostly avoided for these reasons, and used only for thick wires and bus bars. Currently there is enough confidence in quality management and maintenance that aluminum wiring is getting more use in attempts to save some weight, the A380 in particular uses aluminum wires up to 22 AWG. Such weight savings come at the cost of more parts and more work, both in production and later in service.

Specific percentages vary widely, but generally non-copper wiring accounts for more than 10% and less than 50% of overall wire weight in a production commercial aircraft.


if center of pressure moves forward with angle of attack, then does it move forward of center of gravity also at a particular angle?

Longitudinal stability is related to Neutral Point (NP) rather than CP. Exactly because CP moves around, it is not a convenient reference point.

There is no strict requirement for the tail to create downforce for a stable airplane, even though this is a common arrangement.

It may well happen that CP may move ahead of CG and the aircraft remains stable. But it won't keep doing it indefinitely: at some point the wing will stall, CP will move back (this will depend on the wing plan form though), and NP will cease to exist as such. Stability analysis is difficult in such regimes.


Is any readback required when ATC uses the phrase "RADAR CONTACT"?

No. It is an information by the controller to let you know that you have been heard & identified. As he doesn't pass any relevant or critical information, there is no need to readback.
The same goes with e.g. wind information given by ATC.


How is the cargo hold volume for passenger aircraft designed?

The cargo compartments are not only for luggage. Commercial cargo also travel on passenger aircraft, besides cargo aircraft. With luggage alone, there are plenty of spaces in the cargo deck.

In fact, if you fill all the seats, all the cargo space and sufficient fuel for a long trip in a B777, the plane won't takeoff - its GW (Gross Weight) exceeds the MTOW (Max Take-Off Weight).

Airlines are smart people - if a flight is not full, dispatch will put more cargo on the aircraft to utilize it. A lot of passenger airliners also offer air delivery service.

Some passengers complain, "I can't book the flight. The staff says it's full, yet there are many empty seats!" Commercial cargo yields more revenue than an economy seat. Thus, given the weight limitation, an airline may prefer cargo vs passenger.

I don't have info about A380, but I'd guess that the A380 has less extra cargo space than the B777. But as long as it's enough, it isn't a problem.


What methods are used to make a turbofan engine spool up quicker?

Several things come to mind, but they will all reduce efficiency and/or cost money, so they will not be popular with engine users:

For turbofans: Reduce the rotational inertia of the spinning parts by reducing the bypass ratio. Inertia is mass times distance, so making the engine diameter smaller should have the biggest effect.
Increase temperature margins for the turbine. Today, the electronic control (called FADEC for Full Authority Digital Engine Control) will limit the amount of fuel that can be injected into the combustion chamber to limit the temperature in the turbine. By running the turbine hotter for a few seconds the turbine torque can be increased, at the cost of a reduction in the lifetime of the turbine.
For turboprops: Reduce blade pitch momentarily to unload the propeller, so more torque is available for spooling up the engine core. This, however, reduces thrust when it is needed most.
Reduce secondary loads by disconnecting generators and closing bleed valves. This is already done by todays engine control, however.

The best way of dealing with the slow engine response is operational: Avoid situations where the need for a rapid spool-up might arise or enter those situations not with engines set to idle, but to some medium power setting. Carrier pilots do this routinely by spooling up the engine shortly before touchdown, so they will have the required thrust at their disposal if the tail hook fails to catch any of the arrestor cables.

Thanks to RalphJ for pointing out that turboprops use the same tactic. Helicopters never let the engine run in idle while in flight. If less thrust (turboprops) rsp. lift (helicopters) is needed, both adjust pitch to set the desired thrust/lift and keep engine RPM up. Now the mass flow through the engine core is the same as at full thrust, only the amount of heating in the combustion chamber is reduced to adjust the power output of the engine. When more thrust/lift is needed, the pilot adjusts pitch and fuel flow to set the desired thrust/lift level. Since the engine is already running at top speed, the change is not delayed by inertial effects.


What are the advantages of more than 4 propeller blades?

You are right, more blades are bad for efficiency (follow the link for the definition). Ideally, a propeller should have only one blade. Every additional blade will cause disturbances which interfere with the flow on the other blades.

When engine power increases, the propeller disc area should also grow, but this growth is limited by the resulting speed of the blade tips. Once the flow speed there becomes supersonic, the drag at this section of the blade increases without a corresponding increase in thrust. To avoid that, the next best option is to increase the solidity ratio of the propeller, called also the activity ratio. This is done by either increasing blade chord or the number of blades.

Make no mistake, this is bad for efficiency. But if there is enough power available, adding more blades is the best way to transform that engine power into thrust.

Take the Supermarine Spitfire:

The prototype, powered by the 1,030 hp Rolls-Royce PV-12, had a two-bladed propeller
From the Mk II, a three-bladed propeller was fitted to accommodate the increasing power of the RR Merlin (1,470 hp for the Spitfire Mk V).
With the Mk IX, a four-bladed propeller was needed for the 1,575 hp of the supercharged Merlin 61.
From the Mk XII, the more powerful Rolls-Royce Griffon made a five-bladed propeller necessary. Engine power was raised from 1,735 hp to 2,300 hp for the last variant, the Mk XXIV.

Rolls-Royce Griffon-powered Supermarine Spitfire (picture source)

A lower prop speed allows to increase its diameter, but while tip speed will drop by less than the reduction in prop speed (after all, flight speed should not change), the available thrust from this propeller will drop by the square of the speed reduction, since thrust is proportional to the dynamic pressure on the blades. And thrust you get only from the circumferential fraction of the local speed at the blade; flight speed does not count here and does not help to mitigate the reduction. Consequence: You cannot make the propeller bigger and spin it more slowly for a given power.

An extreme example for a propeller with a high activity ratio is the Aerosila SV-27 contra-rotating propeller of the D-27 propfan engine powering the Antonov An-70:

SV-27 propellers on the An-70 (picture source). Eight blades in the forward disc and six in the rear, running at only 1200 RPM. In order to reduce Mach effects, all blades have a swept tip and deep chord.

This can only be topped by something like an ungeared turbofan with a ducted propeller. A turbofan, in other words.


Do carriers such as Janet Airlines carry ADS-B transponders?

You can just look them up. Here's a screenshot from Flightradar24 taken at about 1410 UTC on 22 May 2017.

I imagine in an emergency they'd be given priority just like any other aircraft in distress. The crew might have specific orders covering that situation that requires them to head for a military base. Their operation is so secret, though, that I doubt we'd find out unless a emergency occurs.


What is the relation between aircraft stability and control?

You are right.

Stability is the tendency of a system to return to its old state after a disturbance, be it a gust or a control input. It needs more control effort to change the state of a more stable airplane, such that stability can be measured by measuring control forces instead.

A famous example which is often mentioned in literature is the BE.2, a British two-seater which was designed as a training aircraft in 1912. As a trainer, it had ample stability, so its control responses were sluggish. That proved to be its undoing when war broke out in 1914. The BE.2 was easily outmaneuvered by dedicated fighters, so it had to be withdrawn from frontline service.

Quote from Wikipedia:

  While it proved fundamentally unsuited to air-to-air combat it had a
  relatively low accident rate, and its high degree of inherent
  stability actually proved helpful in its artillery observation and
  aerial photography duties (although it also made it more difficult to
  maneuver quickly)

BE.2 (picture source)


Why are inlet vanes used instead of variable geometry inlets to prevent compressor surge/stall?

What you propose is used as a dust filter for helicopter engines, but even there the plug is not variable. Instead, air spills over the rounded edges of the intake if less is needed.

Intake vanes never close to a point where they would block the intake; instead, they direct the flow such that it hits the compressor blades at the desired angle of attack. They can be moveable to adjust flow to a range of compressor speeds but they never block the flow. Flow control is simply achieved by pumping more or less air into the compressor by means of varying compressor speed. If less air is pumped, more ram pressure builds up in the intake and forces more air to spill over the intake lips. If no separation occurs, this causes little drag and is preferred over something that adds more mass and complexity.

A variable intake body similar to what you propose is only used on supersonic intakes when the shock originating from the tip of such a spike needs to be positioned close to the intake lips in order to achieve uniform flow conditions at the intake face and high precompression efficiency.


Why is the 787 tail cone made out of titanium?

Whenever you see titanium being used on aircraft, look for heat sources. The metallic alternative aluminum is usually lighter and much cheaper.

In most commercial aircraft the APU (Auxiliary Power Unit) is in the tail, behind the rear pressure bulkhead and the empennage.

(modified from aerospaceweb.org)

The APU is a small turbine and its exhaust gases are very hot (I don't have exact data and it depends on the APU model, but the exhaust temperature should be somewhere in the range between 400°C and 800°C). Aluminium has not only a low melting point (660°C), but its mechanical properties degrade fast once it gets hot. On the other hand, titanium has a higher melting point (1668°C) and still performs very well at high temperatures without significantly loosing strength.

While carbon fibers don't lose their mechanical properties at high temperatures, the resin types used as a matrix are very far from being able to withstand these temperatures. Even PEEK, probably the best resin for use at "high" temperatures, has a glass temperature of 143°C (melting point at 343°C). This makes resin-based composites inappropriate. An alternative would be using ceramic materials as a matrix (CMCs). However, the simple geometry of the tail cone probably makes the production with titanium cheaper than with CMCs.

Here's an image of the cone (source: flight.org):


Does the EASA LAPL(A) have a FAA equivalent?

I'm not sure about their equivalence (meaning one cannot fly in US with a LAPL right way), but the closest that comes is the Recreational Pilot license.

The requirements are roughly similar:

30 hours flying experience; however, the FAA requires 3 hours of solo flying and cross country requirements are slightly different.

The limitations are also roughly similar:

Recreational pilot license doesn't allow the pilot to have more than one passenger, while the LAPL does (upto three).


Did older Airliners use a pitot-static system?

They used the same kind of pitot probes and static ports as modern aircraft, but prior to the 70s they didn't use Air Data Computers  that processed the pitot static information in a central location for electronic distribution to other systems that needed the data (that had to wait for the Integrated Circuit and Microprocessor revolutions of the 60s).

Prior to that the pitot and static pressure was routed directly to the instruments and devices that needed to measure it, so you had the plumbing itself routed to both the pitot static instruments and electronic devices that needed it, pretty much like with light aircraft, but with way more plumbing.  The adoption of ADCs reduced the plumbing requirements to just that required between the probes and ports and the ADCs.

Computations and conversions of pressure data (like deriving Mach#) were done by analog mechanical or electronic means directly within the instruments themselves.

So, an airplane like a 707 in the late 50s would have lots and lots of low pressure pneumatic plumbing running up behind the instrument panels and to various analog computing devices in the avionics bay.


What is breaking away/peeling off in military lingo?

I believe these are slang terms for element separation, where a leader and wingman break formation from each other either in order to reform in a new formation for tactical purposes e.g. Spread formation etc. fly a tactical maneuver to defeat a threat like a champagne or in order to land flying an overhead approach.  Wingovers are aerobatic maneuvers, very similar to Lazy Eights, intended to teach student pilots the art of flying the airplane with constantly varying stick and rudder inputs and are not involved with element separation.


Strange plane-shaped object at UK airport

That's a training rig for airport fire crews. They can usually be set on fire through whatever controlled means and the crews can practice approaching and working around aircraft.

In fact, after a cursory Google it's either the one at Heathrow or is near identical to it.


Did the Westland Lysander have a helmet/face mask for radio communication during WW2?

Since they were not suited for combat, they transitioned to supporting clandestine operations where, to quote the  Royal Aviation Museum of Western Canada,
To give it the long range it needed, the aircraft had to be lightened by removing all unnecessary equipment such as guns, armour protection and excess radio equipment, retaining only the radio/telephone for communication with the ground.
It appears that they did have radios, not sure about how they were used. But if you look at the video in the linked page at about 2:33 the pilot appears to be wearing a helmet with built-in headset and a face-mask type microphone. At 6:19 the rear crewmember looks like he is wearing a mask as well.
This is the same aircraft that features prominently in Code Name Verity by Elizabeth E. Wein.


Would a rotating skin design mitigate the heating problem limiting hypersonic flight?

TL;DR Probably not.

Assuming we would have a very good mechanical solution/design we would still need a way to get rid of the heat, i.e. a heat-sink.

Imagine the panel (or what ever we will call a part of the skin) is rotated away from the flow (into the inside of the vehicle), than we would need to cool it but where would we store the heat? We cannot extend a heat-exchanger. So the inside of the vehicle would heat up indefinitely.

Essentially we need to come up with a way to discharge entropy from the vehicle. This can be done by either a heat- or mass-flux from the vehicle into the ambiance.

One possibility is related to your second idea: using a cooling system. This requires you to have a fluid propellant. Using the fluid propellant as a cooling fluid first you would not only cool your airframe but you would also enhance your efficiency. This also solves the heat/entropy problem because you would discharge mass (the propellant).

But given the fact that we assumed to have a matured mechanical design of the ‚skin-rotation‘ mechanism you could have multiple panels with ablative coating. So after the first panel is consumed you could (hypothetically) rotate a new one into the flow.


Do US military aircraft have tail numbers beginning with "N"?

The 'N' numbers you're referring to are FAA registration numbers. The FARs (Federal Aviation Regulations) specifically mention registration as not being required for military aircraft:

14 CFR 47.3

  (b) No person may operate an aircraft that is eligible for registration under 49 U.S.C. 44101-44104, unless the aircraft—

  (1) Has been registered by its owner;

  (2) Is carrying aboard the temporary authorization required by §47.31(c); or

  (3) Is an aircraft of the Armed Forces

The FAA issues these registrations in accordance with its responsibilities under the Chicago Convention on International Civil Aviation, which required (in Article 20) that:

  Every aircraft engaged in international air navigation shall bear its appropriate nationality and registration marks.

As per the above-cited 14 CFR 47.3, though, the U.S. specifically requires that all eligible aircraft have registrations unless it's either a military aircraft or it has temporary authorization under 14 CFR 47.31(c).


Unusual Traffic Ene 68 degrees over Dorset United Kingdom - No strobes, green or red just solid white lights

Satellites can look like this shortly after a serial deployment from a single launch vehicle.


Why don’t airports use jetways as an airlock to avoid having to repressurize the plane for every flight?

I believe there are quite a few misconceptions here:

When an aircraft is "pressurised", it means that at higher altitudes, the pressure inside the aircraft is higher than the pressure outside. At lower altitudes, the pressure is exactly the same inside and out.

Originally, aircraft weren't pressurised, and at higher altitudes the low pressure is a problem for the people on board (lack of oxygen, mostly), and for some hardware (due to the pressure differential).

So the pressure is artificially increased inside the aircraft beyond a given altitude (or more precisely, beyond a given outside pressure): when the aircraft takes off, the pressure goes down as the plane reaches higher altitude, until that pressure is reached, and from then on, the pressure outside continues to decrease while the pressure inside is maintained at that safe level.

So there's no reason to pressurise an aircraft on the ground. It has the same pressure inside as outside.
Even if it were useful, when on the ground, there are plenty of openings other than just the passenger door(s). Other doors are opened for catering and technical staff, cargo doors are open, and so on. So it would be impossible to maintain a different pressure in the aircraft and outside without completely breaking down all operations.

Also, having an "air lock" would require doors on each side. One door would be opened, people would enter the air lock, the door would be closed, the pressure would be changed, the other door would be opened, people would exit the airlock. Then the door would be closed again, pressure brought back to the other level, and the first door would be opened again before more people would be able to enter the lock. This would significantly hamper the flow of people embarking or disembarking.

Additionally, people are already annoyed enough by the changes in pressure on board planes which take quite a few minutes. Doing that in a few seconds to ensure relatively quick movement would just be horrible.

Finally, consider that many aircraft do not use jetways but stairs on the tarmac.


In the US, is there a way for a pilot to legally "maneuver at will" in actual IMC?

You don't have to have permission to fly in IMC in uncontrolled, class G, airspace. However, you must have an instrument rating and be in an IFR-certified aircraft. In uncontrolled airspace, you may fly into IMC as you like and perform whatever maneuvers you want. It's a very good idea to get flight following in order to receive traffic warnings from ATC if you decide to fly within IMC in uncontrolled, class G, airspace.

You do need to get permission to fly in controlled airspace (all classes except for G) if you are operating under IFR, regardless of actual meteorological conditions.

Note: Classes A-D require permission under both IFR and VFR; classes E and G do not require permission under VFR.

If you want to practice in IMC within controlled airspace, you must explain your mission to ATC and obtain a clearance to operate under IFR. If ATC has the space and the time, they may give you a clearance for a specific area and perhaps a block altitude if you want to climb and descend. There aren't officially designated areas for practice, but if you ask local instructors, they will tell you where they usually go. Most of the time, the preference is to get out of controlled airspace if possible; it's just easier.


The latest turbofan aircraft feature an exposed exhaust cone, does it come with some benefits?

The « cone exposition » is a result from nacelle engine design, and the choice to mix flows or not. The two main strategies are called:

Mixed exhaust engine resulting to long nacelle hiding exhaust nozzle and plug.

Separate exhaust engine which is shorter and then allows a view of nozzle component.

The reason to choose one type of exhaust is made by considering overall engine performance (mainly efficiency and fuel consumption), noise but also visual pleasing (for business jet for instance).
Exhaust mixer is generally more efficient (secondary flow is slightly accelerate producing more thrust) and less noisy (primary flow is slow down). They might be also an advantage in material resistance in cooling hot primary flow. See this article for details about advantage of mixed exhaust.
Nevertheless, long nacelle has the overcome to increase weight and drag of the engine and this is worst as the engine is bigger. Note that it is related to turbofan by-pass ratio (BPR). More the BPR is high and bigger the engine diameter is. For commercial aircraft, the trends is to increase more and more the BPR parameter because it is directly correlated to propulsive efficiency. Therefore, there is a kind of « BPR limits » where mixed nozzle benefits do not balance its drawback.
That's why, modern turbofan (high BPR and high diameter) have likely to integrate a separate exhaust nacelle.


Is it a common airline practice to base T/O speeds on the actual T/O weight when an assumed temp thrust is used?

You determine the t/o thrust as a function of t/o weight and runway length
Once the t/o thrust is determined you can select the assumed temperature on the thrust limit page on the CDU.

V1 is not the target primary parameter, it is a consequence of the calculation, on modern FMS your calculated value is cross checked with a range calculated by the FMS, that is your calculation could be rejected by the installed FMS unless you may force your value on some models.

A minimum rate of climb is necessary with a speed of V2+10, and at worst V2 with engine failure.

Backward of this Vr is computed.


How realistic was the airplane scene in Terminator Dark Fate?

Completely and utterly ridiculous. Let me count the ways:

First video:
0:22 That collision would have destroyed the bigger plane as well, rendering the entire rest of the scene impossible.
0:35 As you mentioned, the wake turbulence would have knocked the trailing airplane down and away.
0:46 There's no way that collision lasted for that amount of time.
1:11 The autopilot would not have been able to function with that level of damage. It wouldn't have even attempted to activate.
1:19 The front of the plane isn't damaged, so the only wind would be from eddies from the hole in back. Which would be pretty strong, don't get me wrong, but not nearly strong enough to pick up a full-grown woman.
1:33 Gravity doesn't just "go away" when you lose two engines. Not to mention the wind described earlier would still be a factor.

Second video:
1:22 Having one parachute open would have slowed the fall of the Humvee quite a bit. It wouldn't still be in freefall.

Note that I'm only covering the aviation-related ridiculousnesses in that scene. There are quite a few other ways it fails basic physics as well.


What will the 737 MAX 7, 8, and 9 ICAO IDs be?

The new Boeing 737 MAX is based on the Boeing 737 Next Generation family, which it will replace. Also note that 737 MAX is still under development and is scheduled to release in 2017.

Update:

(Source)

The first 7 is omitted and the suffix is now an M for Max, e.g. B37M for the Boeing 737 MAX 7.

Wikipedia has complete list of ICAO codes here.

ICAO Aircraft Type Designators: Search for Boeing and you will find 737 MAX in the list.


How does this RC helicopter keep itself upright?

The rotor is gyro stabilized. The balance bar is the gyro. If the machine rolls right, the balance bar wants to stay in a level plane and generates a correction by influencing the rotor blades to go where the balance bar wants to be.

The Bell 2 blade teetering rotor system used on the '47 and the Huey used a much smaller version of the same thing, to provide a little bit of inherent stability to the rotor disc, without inhibiting pilot control.


How to artificially increase the Reynolds number in a wind tunnel?

Trip strips will approximate a higher Reynolds number in the sense that you get turbulent flow at a lower Reynolds number, but they will not increase the Reynolds number themselves. You will have different pressure and density gradients in the boundary layer, as though you were operating at a higher Reynolds number, but the number itself has no way of accounting for a trip.

The equation for the Reynolds number is $$\frac{\rho v d}{\mu}.$$ These are the only parameters you have to work with if you're going to be using the Reynolds number as your similarity parameter. If you absolutely have to use a wind tunnel, then increasing the model size or increasing the velocity are your only options (theoretically you could pressurize the wind tunnel to increase density if it were sealed, or you could change the temperature of the flow within the tunnel, but these have not been realistic options for any wind tunnel I've worked with). If you don't have to use a wind tunnel, a water tunnel is a viable alternative.

See An Assessment of the Usefulness of Water Tunnels for Aerodynamic Investigations for more details on water tunnels.


How do pilots/controllers deal with overlapping transmissions on the radio?

Well in regard to "How are these situations resolved?" you've already answered your own question in a way: the intended recipient responds with something like "Blocked" or "Calling center, say again." (If they are expecting to hear from a specific aircraft they'll often respond with "N12345, say again.", and if the frequency congestion is really bad controllers may add "All other aircraft standby").
As kevin42 pointed out this is very similar to what digital CSMA/CD systems do - they detect a collision ("Blocked"), wait a while, and try their transmission again.

As a practical matter, two-way voice communication over the radio is possible, but difficult: for example a discrete "uplink" and "downlink" frequency as you have with some radio systems would be impractical in the sort of mesh topology that you have with aviation radio (you could implement it for a single air-to-ground pair trivially, but aviation radios are also used for air-to-air communication, and it's important that pilots hear what's going on as this enables them to build a mental picture of the airspace, as well as ensure that they're not blocking other pilot's transmissions).

Regarding analog-vs-digital, the traditional AM radio used in aircraft has one major advantage over its digital counterparts: when two digital signals overlap the result is garbage -- you can't recover any of the information. When two analog AM signals overlap you get heterodyning (the two signals mix, and your receiver pipes that mix into your ears).
The resulting mixed signal sounds AWFUL, there's an ear-bleeding squeal from the out-of-phase carriers and the voice modulations combine to a garbled mess much of the time, but with experience you can usually pick out one of the communications (particularly if you're close to one of the transmitters, where it will overpower the more distant signal).

The ability to step on a transmission as described above this can be useful: Instructions have been issued over a "stuck mic" before to get other aircraft off the frequency.

In a similar vein, if you have an emergency you probably aren't going to listen before you talk - you're going to key the mic with your mayday and even if the controller misses half of what you're saying under the heterodyne noise they'll know there's an emergency when they hear the other half of your transmission and tell everyone else to standby while they talk to you.

In both of those situations a digital system implementing CSMA/CD would detect that the frequency was in use and not transmit (and if were a digital system and transmitted anyway both digital signals would be garbled and unusable).


How are emergencies handled during In-Seat Rest?

Option 2:

  the pilot flying continues to fly while the pilot not flying
  immediately goes through the engine out checklist, despite the risk of
  sleep inertia.

When waking up to an emergency situation your body will start to produce adrenaline which gets you over the sleep inertia very quickly. If the situation is not clear to the PNF, he will be briefed by the PF.

Besides that, in a checklist flow, both pilots are involved and crosscheck each other's actions.


What fail safe protections exist to prevent non-plug type cabin doors opening in flight?

I am not sure about all aircraft types, but on the 777 cabin pressure is still used to positively lock the door into position in flight. When the door is open, the door is in a slightly raised position. As the door is closed, rollers on the door are lowered into tracks on the door frame. The tracks are curved slightly outwards, so to open the door the it most be moved slightly inward, which is impossible even with a slight amount of cabin pressure. The actual pressure load on the door is carried through the stops, which are inboard on the door and outboard on the frame. Once loaded with the pressure, these stops would also have a tremendous amount of friction preventing the door from sliding upward. Note the vent door near the top of the door in the picture below, this door is attached to the latching mechanism and it opens in the first movement of the handle, again preventing the door from unlatching if the cabin is pressurized.

Refer to this picture of the 777 door, to see the rollers, tracks and stops (Source).

I believe the 777 design is very similar to the Airbus design. There is a very good video showing the operation of Airbus doors on YouTube, here. It shows how the door must be lifted above the stops, before it can open outward. If you watch closely you can see the move slight inboard before lifting. This is a quote from the A340 maintenance manual: The lifting arms of the lifting shaft (which support the passenger door in roller fittings attached to the door frame) move the passenger door a small distance into the cabin and then upwards."

Note, some people (including Airbus and Boeing) still consider these doors plug designs since pressure still loads the door against the stops. For example, Boeing specifically states the 777 doors are plug type doors.


Would it be beneficial for the Boeing 777x to have a biplane wing design?

A major disadvantage to that design would be the aft wing had a disrupted airflow over it as it travels through the fwd wing's wake, so lift is greatly diminished.

As to doing a stacked biplane design typical of small sport biplanes in use over the years, this is probably frowned upon for two reasons:

High Drag - more structure in the relative wind always means more drag anemic this was one of the major advantages to the cantilevered wing developed in the 1930s.
Heavier - more wings means more structure both in terms of the second wing itself plus the mounting structure to mate the wing to the fuselage.

A single cantilevered monoplane is by far the most efficient solution save only a flying wing, but these are not commonly used in commercial travel which has been discussed in previous threads.

Now that's not to say a biplane may not be useful for commercial aircraft.  Researchers at MIT proposed a supersonic biplane design which usea the configuration to dramatically reduce its sonic boom.

Whether this idea survives the CGI proposal and becomes actual hardware is another story; this business is full of concept aircraft and precious little flyable hardware.


What is the difference between Flight Test and Test Flight?

Flight testing is the process (usually involving a number of test flights) by which the capabilities and performance of and aircraft (usually a new one or one which is substantially modified) are established.

Test flight refers to an individual flight which is used for testing purpose. it can be used either as part of flight testing or as a standalone for testing some minor modification.


Stall speed is whatever airspeed you have when the wing reaches the stall angle-of-attack.  When we say  "stall speed", we often mean the 1-G stall speed, but under the right conditions we can place the wing at the stall angle-of-attack at a higher or lower airspeed.

The simulator may have a flaw.  Also, you may not have a good understanding of what angle-of-attack is, and how it relates to pitch attitude.  What exactly makes you think that the wing is not near the stall angle-of-attack whenever the stall buzzer is on?  Just because the nose is below the horizon?  That would be a misconception.  In  a high-drag, low-thrust descent, the flight path can be so steep that the nose can still be below the horizon even when the angle-of-attack is quite high.

In straight-line (unaccelerated) flight, angle-of-attack is much more closely related to airspeed than to climb rate or sink rate.  In wings-level straight-line flight, for shallow to moderate climb or descent angles, the relationship between angle-of-attack and airspeed has essentially nothing to do with whether the aircraft is climbing, descending, or flying level.  In these parts of the flight envelope, to a first approximation, any given airspeed is associated with with one particular angle-of-attack, regardless of the climb rate, sink rate, or pitch attitude.  It sounds like this is what you are seeing on the simulator.  This is normal!

Your question suggests that you may think that a descending flight path is evidence that the wing is producing less lift than in level flight, and therefore should be harder to stall, or should stall at a lower airspeed.  Actually, inadequate lift is not the fundamental cause of a descent, and for shallow to moderate descent angles, the wing is only creating very slightly less lift than it would in level flight, creating an imperceptible change in the unaccelerated stall speed.

To check the functioning of the simulator, try pitching up into a very steep climb that forces the airspeed to decrease.  When the stall buzzer comes on, can you make it go off immediately with a very aggressive forward push on the stick or yoke?  If not, something is probably wrong with the simulator.

If everything is working right, with some practise, you should be able to fly a semi-ballistic arc with the G-load near zero as you go over the top, and with the airspeed dropping well below the normal stall speed as you go over the top, without the stall warning buzzer coming on.  This will be easier to investigate if the simulator includes a G-meter.

If some parts of this answer don't make sense to you and you want to better understand the balance of forces in level, climbing, and descending flight, some of the links given at the end of this answer may help: How does an aircraft descend without its nose pointing down?

For more, see the "See How It Flies" website, especially chapter 2.


Are run-ups required for multiengine piston aircraft?

Yes, From the FAA handbook

  ...be operated from its crossfeed position during the run-up. The
  engines should be checked individually and allowed to run at moderate
  power (1,500 rpm minimum) for at least 1 minute to ensure that fuel
  flow can be established from the crossfeed source. Upon completion of
  the check, each engine should be operated for at least 1 minute at
  moderate power from the main (takeoff) fuel tanks to reconfirm fuel
  flow prior to takeoff.

And also

  Some multiengine airplanes have a ramp weight, which is in excess of
  the maximum takeoff weight. The ramp weight is an allowance for fuel
  that would be burned during taxi and run-up, permitting a takeoff at
  full maximum takeoff weight.

For what its worth a multi-engine piston plane is mechanically double what a single engine plane is, and often carries a similar if not the same engine as a single. The things you are checking in run-up, primarily the ignition system holds true for both single and multi-engine aircraft.


How does NOAA's P3 Orion safely navigate hurricanes?

The National Oceanic and Atmospheric Administration uses three aircraft for carrying out hurricane research- a Gulfstream IV SP and two Lockheed Martin WP-3D Orions, while the USAF 53rd WRS 'Hurricane Hunters' uses the WC-130J for this purpose. Of these only the latter ones are used for penetration purposes.
The Gulfstream is used to fly around and over the hurricane (the 45,000' ceiling helps). From noaa page:

The NOAA G-IV jet usually does NOT penetrate the hurricane eye, but is assigned to fly synoptic scale patterns AROUND the storm, deploying dropsondes along the way, in order to profile the environmental flow that is moving the hurricane.

The other two aircraft- the Orion and Super Hercules are not modified structure-wise (except for extra fuel tanks) for carrying out these missions. From the hurricane Hunters site:

These aircraft are not reinforced in any way in fact the only differences between a WC-130J and a C-130J is the addition of two external fuel tanks ..., a radiometer pod on the left wing and the two addition crew pallets in the cargo bay

The aircraft does have onboard weather radars, one of which is used exclusively for flight safety, with the others used for research:

Each WP-3D aircraft has three radars: nose, lower fuselage and tail. The nose radar (a solid-state C-band radar with a 5° circular beam) is used strictly for flight safety and is not recorded for research purposes.

The aircraft are also fitted with INE and GPS and also satellite communications for transmitting and receiving real time updates. During the flight, the flight crew are in constant communication with the flight director, and make adjustments according to the requirements:

During the most dynamic portion of the flight, Price is in constant communication with the Flight Director, who provides real-time flight guidance based on the radar picture.

As far as flying through storm is concerned, looks like they simply punch through it to get to the center- in the end, the aircraft could handle it. From USAF site:

... airplanes are built to go very fast through the air, and they don't care if the wind is 5 knots (nautical miles per hour) or 150 knots! .... Although there are usually some bumps on the way through, they are nothing that the airplane can't handle..

The NOAA officials say pretty much the same thing in this reddit AMA:

The WP-3D is built like a tough old pickup truck. It can handle a lot of abuse in the storm environment and come back and fly the next day.

Incidentally, according to noaa the aircraft crew are more concerned about the turbulence rather than the actual winds in the eye wall:

... hurricane's rainbands and the eyewall, which can get a bit turbulent. The eyewall is a donut-like ring of thunderstorms that surround the calm eye. The winds within the eyeall can reach as much as 200 mph [325 km/hr] at the flight level, but you can't feel these aboard the plane.
... the turbulent updrafts and downdrafts that one hits. Those flying in the plane definitely feel these wind currents. These vertical winds may reach up to 50 mph either up or down, but are actually much weaker in general than what one would encounter flying through a continental supercell thunderstorm.

Looks like they simply fly through it anyway. Basically, they 'crab' into the hurricane so that they reach the eye of the storm. From the Reddit AMA:

Depending on how strong the winds are you have to point the nose of the aircraft so that your track will lead you into the eye. The difference between heading and track is known as your drift angle. Sometimes you can have as much as 20-25 degrees of drift angle. We sometimes call this “crabbing” into the storm, where we are pointing the aircraft to the left or right to flight straight.

The image below shows the path taken by one of the aircraft during flight into Hurricane Hugo.

Zoomed-in radar image of Hugo's eye, taken during NOAA 42's flight. The flight path of NOAA 42 is shown as the white line (note the loops made within the blue area, the eye of the hurricane). The eyewall (red and pink areas on the radar image) contained violently strong winds. Image credit: wunderground.com; Image from hurricanscience.org


How do you set up your nav instruments and coms during ground operations and takeoff?

I think it is save to say that it is a good practice to do anything you can on the ground rather then doing it in the air.

My setup: I usually end up with a similar set up as you do, though I don't use GPS much, but prefer hopping from one VOR to the next ;) (Well, I'll have to add that I'm not the most experienced pilot around here, for sure!)

Basic principle: I try to follow the rule I mentioned up there: I try to decrease the workload in the air by doing it on the ground already. That's why we make our route up on the ground, not as we go (well, one of the many reasons).

Let's say I have Com1 and Com2, each with a standby frequency as well as two Nav's, also each with a standby frequency: Before taxi, I'd have Com1 Active set up as tower and be listening and talking to Com2 to clearance, having ground in the standby. As soon as I have my clearance, I can put in my initial heading with the heading bug (not flying SIDs), as well as the Dep. frequency in Com1 Standby. This way I have all ground related stuff in Com2, all air related stuff in Com1. As for the Navs and the OBS: If there is a VOR at the airport I'm gonna put it in Nav2 and turn the OBS to initial takeoff heading (mostly runway heading). This is just as a support, "heading" still means pointing your nose to where the controller says, no matter what track the wind makes you actually fly. But then I know where I'm at and can already figure out what the wind is doing on my climb out. Nav1 goes to my first VOR, and depending whether I go direct or join an airway, I center the needle or set the OBS to the airway track respectively. The standby frequencies of the Navs are set to my second waypoint on Nav1, and whatever I think I'll need afterwards on Nav2. After takeoff I use Nav1 primarily to navigate, and Nav2 to verify my position (such a aircraft would usually have DME, so that you don't need to cross bear your position with two VORs, but if there is time to do so, why not).
In the air I usually don't use  the standby freqs much on the Coms, and just swap Com1 and Com2 when changing frequency. Before landing, the same thing counts as before takeoff: Take as much workload off in advance. Thus I'm setting up the coms (I got 3 spare frequencies when talking to approach or center or whatever, the'll all be filled in with usefull frequencies like ATIS, Tower and Ground), the Nav's for the approach (with missed approach in standby if available).

Well that was quite a novel, I hope you didn't fall asleep halfway through. This is what I do, and I get along with it quite well. I am not saying it is the 100% perfect thing to do, and (as Simon points out in his answer) you should do whatever you feel the most comfortable with.

Summing up, I think doing as much as you can in advance is key in flying (especially IFR), as it gives you more time in case you need it for something else to do.


Can spar stresses be calculated using zero (wing) fuel?

In general, combining an empty wing with a full fuselage will give the highest stresses in the wing spar at positive and negative load factors. If the wing tanks held fuel, the weight of the fuel mass would reduce the wing spar bending moment inboard of the tanks at the same load factor.

However, details depend on the particular configuration. Make also sure you look at the most forward c.g. location and at the added load from aileron deflections.

Also, don't assume that the critical load case of one design will also be the critical of another. Please look at cases in all corners of the envelope to make sure you do catch the critical one.


How dangerous are Polar Routes, if an aircraft must land on water or wild land?

Depending on where you are it will take around 4 hours to 3 days, if the location is know. Depending on how remote your location is, and if the SAR team knows your location (Sometimes forgotten by pilots after a emergency landing.). If the location isn't known, the search can take up to 2 weeks, finding you and your passengers dead.
Let's say temperature is -10 degrees Celsius, it will take around 1-3 hours without any clothing or external heat source (like a camp-fire) to start hypothermia. Although the critical point of Hypothermia is 25 degrees Celsius, people survived 14 degrees Celsius. The best thing you can do during this plane crash is stay closely together and if possible start a camp-fire. Drink hot water (just take some ice and put it on the fire) with a lot of sugar (or anything else that gives you energy) and just do anything to keep yourself heated until help arrives.

If possible, keep the navigation lights, strobe lights on of  the plane until battery runs out of fuel. This increases the chance being found in time.


What is the fan tip speed at maximum thrust?

Second question first, the higher the jet engine thrust, the more efficient it is (in terms of thrust for fuel rate, bang for buck).
(Source: Boeing)
On to the Trent 900 and PW6000, the big one and small one. The bigger fan will have slower RPM. From the type certificates the max permissible RPM's are 2818 (takeoff) and 6350 (undefined), respectively.
The fan diameters are 2.95 m and 1.435 m, which translate to 435 and 477 m/s. Speed of sound in dry air at 20°C is 343 m/s.
Here's the caveat, the fan RPM (%N1) at takeoff does depend on the ambient air pressure and temperature (among other operational considerations). But as you can see, the smaller fan can rotate faster—read: max permissible—because it has less mass and the centrifugal forces are more manageable.
And since the 1960's or so, the fan RPM is rarely a limiting factor for the jet engine operation, so the engine manufacturer will have designed for the optimum blade tip speeds.

N1 RPM limit

It might be necessary to limit the engine RPM in order to avoid overloading the fan blades in centrifugal force, and to control the fan blade tip speeds. This is purely an N1 limit and is not a function of altitude.
The N1 limit is rarely more restrictive than the pressure and temperature limits.

(Emphasis mine; Jet Transport Performance Methods)
So much so—as you can see below from a 777 manual—the hotter and higher the airport up to about 40-45°C, the faster the takeoff N1 is to compensate.
(Click to view)
That answers the efficiency part, and the blade tip comparison as requested.

Related: Why does lower atmospheric pressure produce higher EPR (thrust)?


In what order were the runways built at Paris Charles de Gaulle?

Overview

(background image: Wikimedia)

Details

The first runway was finished in 1971 as 09/27 and it corresponds to todays 09R/27L:

  Work on the satellites started in late 1970. Also built were Air France and UTA hangars and a pooled cargo terminal.
  Construction on the first 11.800-foot (3,600-meter) runway, 09/28, and its associated taxiways started on August 1st, 1969.

  The runway was inaugurated by the Ministry of Transport on September 9th, 1971. The earthworks of Runway 2 were started in 1972.

(airporthistory.org)

The second runway was finished in 1976 as 10/28 and corresponds to todays 08L/26R:

  In 1976, Charles de Gaulle handled 7.5 million passengers and opened a second runway. Initially, the second runway was built at a reduced length of
  9.400 feet (2,900 meter) and without a parallel taxiway. It was only used as a backup when the main runway was inoperative or at the instruction of air
  traffic control. The runway could be built out to its full length of 11,800 feet (3,600 meters) and taxiways added when traffic demand required.

(airporthistory.org)

The following ground chart shows the layout in 1977:

(image source: flickr.com by jwhshd)

By 1994, the terminals had been greatly expanded to the south and the new runway was at its full length (I don't know when exactly the expansion happened):

(image source: flickr.com by jwhshd)

The third runway was finished in 1999:

  Expansion of Paris Charles de Gaulle (CDG) Airport has also helped Air France. A third runway at CDG opened in 1999, with a fourth to open in 2002.

(Strategic Management in Aviation: Critical Essays)

Unfortunately, the source does not detail which runway this was. By searching through pictures of CDG from 1999 on airliners.net, I was able to find the following quotes:

  Landing on runway 26L

(airliners.net, May 1999)

  Taxiing out runway 27

(airliners.net, May 1999)

This would suggest that the runway numbering had already changed and the second runway to the south (08R/26L) was built first (in 1999). This would leave runway 09L/27R to be the fourth runway added in the early 2000s.


What kind of airplane is this that has blue cheatlines and a protruding side cover?

Below is the full photo, it's an Ilyushin Il-22PP Porubshchik electronic warfare plane.

  The Il-22PP Porubschik was designed in late 2000s on the basis of the Soviet Il-18 passenger aircraft made in mid 1970s. According to media reports, the aircraft is capable to disable most modern electronic warfare systems installed on foreign planes, air defense systems, as well as unmanned aerial vehicles.

Image and article: https://www.ruaviation.com/news/2017/3/31/8382/


What causes a plane's wing tips to leave a small white vapor trail?

The cause is reduced pressure in the wingtip vortex trailing behind the wing. Reduced pressure causes reduced temperature and if ambient humidity is high enough the result is the  condensation you observe.


How should I refer to a transition through class B or class C airspace?

You'll sometimes get radio phraseology different from what is published on charts either due to some holdover from now-superseded procedures (bad form, but it happens) or because of Letters-Of-Understanding that exist between the local Air Traffic Facility and certain operators or interest groups/associations, etc.

If you're going someplace new and want to use a published VFR Transition through class Bravo, the best way to go about it is to use the nomenclature on the charts in order to reduce confusion. Otherwise, it is also acceptable to simply request a VFR clearance through the airspace in a general direction of travel. Depending on your altitude, position and direction of travel, as well as traffic load and any airports you need to get around, ATC will vector you through or around the class Bravo.

The initial call follows the standard procedures outlined in the AIM and the Pilot/Controller Glossary. For example, starting out NE of Orlando class Bravo and asking for a transition to the SW, could be something like:

"Orlando Approach, Husky 123 Alpha Bravo Charlie, 35 northeast of the ORL VOR at 4500, request VFR transition to the Southwest through class Bravo."

If you're near a local landmark, you could use it as a reference to help the controller find your aircraft more easily:

"Orlando Approach, Husky 123 Alpha Bravo Charlie, 2 northeast of Lake Ashby at 4500, request VFR transition to the Southwest through class Bravo."

Generally speaking, if a VFR Transition or flyway is available, the preference is to have VFR traffic use it in order to lighten the controllers' workload, but if you don't have the charts, or would rather not do that for some reason or the other, you don't have to. Just follow the general procedures for transitioning through class Bravo and they'll do their best to accommodate you.


Why does the Boeing 777X have a flight deck similar to the 787 and not to the previous 777?

The reality is that the 777X is not all that different from the 777 when considering cockpit procedures or 'user interface'. What is different is the hardware platform(s) that are used.

I worked for a supplier to Boeing for the 787. The stated goals for the 787 from Boeing were fairly straightforward. The design shall require a maximum of 5 days transition training for 777 pilot with a goal of 1 day. On the support side, there was a push to greatly reduce maintenance and upgrade costs. These are driven by the hardware and system architecture.

So the big change with the 787 was moving from the Honeywell AIMS and A629 based network to the Collins/GE A651 and A653 based Common Core System and A664 based network. The result of that platform change is why the flight decks look so different and that's what you see in the videos.

I can say with authority that in the 787 design our overriding directive was to make it look and behave like the 777. While a keyboard and a window on a widescreen display looks different from a control and display unit (CDU), the key functions and display behave the same.

So now with the 777X, the hardware is an evolution of what's in the 787. It uses the same basic open architecture and also follows the tenet of minimal changes that will require crew training.

So ultimately, the 777X is operationally similar to both the 777 and 787 while the hardware and software infrastructure follows the 787.

The impact of training is significant.  As explained to me by a United rep, when one senior captain retires it generates 10 to 15 training requirements as crews move up in the system. Every day of training costs them a lot of money.


Is it possible to take off on an elevated short field by "falling"?

Is it theoretically possible? Sure.
Is it realistic or probable? Absolutely not.

If there is not enough space for the airplane to accelerate to takeoff speed it will be effectively stalled when it reaches the end of the ground. That means that as soon as it runs out of ground it effectively becomes a ballistic projectile: it keeps moving forward, but it also starts to fall because of gravity. You can see this in the Goldeneye clip - the plane adopts a nose-down attitude shortly after it leaves the ground.

Eventually, given enough time, the airplane will reach a flyable airspeed (between gravity accelerating it down and its thrust propelling it forward). How far it needs to fall before that happens depends on a number of factors, but if the ground is sloping downward at an angle such that the aircraft's ballistic trajectory does not intersect the ground before it can reach flying speed you could theoretically make such a takeoff.
The obvious downside is that if things don't go perfectly in the attempt you will intersect the ground in uncontrolled flight ("crash").

In the Goldeneye scenario the aircraft is already in a fairly extreme dive when Bond manages to get aboard, so for our intrepid secret agent it's not so much a matter of getting the aircraft to a flying speed (it's probably there already) but rather of recovering from the dive before hitting the ground and without over-stressing the airframe and causing parts to break off.


What do the pilots do if the plane they are operating does not have an anti-ice system?

If an aircraft is not equipped with anti-ice or de-icing systems, than the answer is simple: You don't fly into icing conditions. This is usually listed as an operating limitation in the POH/AFM/FCOM of the respective aircraft. For a Cessna 172, you can e.g. find:

KINDS OF OPERATIONS LIMITS
The Cessna 172S Nav III airplane is approved for day and night, VFR
and IFR operations. Flight into known icing conditions is prohibited.

(C172 POH, Section 2 Operating Limitations)
If you are approaching icing conditions, there are usually two options to avoid flying into icing conditions:

Reduce the altitude: The temperature is higher at lower altitudes. If you can reduce your altitude enough to raise the temperature above 10°C, you are out of icing conditions.

Change course: If you see a cloud ahead and the temperature is below 10°C, you cannot enter the cloud because that would mean you enter icing conditions. You can however deviate from your current course and fly around the cloud.


What is the source for the flight data shown on in-flight entertainment systems?

I work on these panels which get the data (both IFE and cockpit display panels for a big OEM and there are very few in the world :)). This is all Air data systems which are providing all the data. We get this data from various sensors placed inside the cockpit or on aircraft exterior including wings and tail. Their are different kind of data transmission buses like ARINC which transmit that data then the required data is fed to IFE system through a protocol but most crucial data like data coming from Weather Radar etc is kept for Pilot usage and is displayed on the cockpit display panels.

For your question Altitude, elevation. azimuth there are some radars in the aircraft which gives that data and some of these radars measure and send this data using CAN protocol with very high speed varying from 40ms to 100ms.


What is the round thing on the tip of an MD-90 wing?

This is a logo light. The MD90 as originally delivered to Delta didn't have these.

This is the wingtip light arrangement on an airplane without the logo light.


Why did the RAF buy the F-35B model and not the A model

The most probable reason is because of commonality, to reduce costs and support logistics. But, it also increases operational flexibility. The UK MOD want to operate them off the Queen Elizabeth carriers, and they do not have a catapult launch, but a ski jump. Only the B version can get airborne with this setup. So, the RAF had to go with the B version also. As mentioned in this article, having all aircraft as B versions means it is easier to always have the amount needed to fill operational squadrons for the carriers. If you split the buy between A and B versions, A versions cannot fill the place of B versions down for maintenance. Note however, the decision wasn’t “plain sailing” (without debate), as mentioned by J Southwell’s answer.


What is the relation between throttle position and engine thrust for a turbofan?

Check out this Nasa powerpoint it provides a nice overview of some of the basics and how some of the systems are set up.

  Does the auto-throttle send its command directly to the EEC or to the
  mechanical throttle?

This may vary from design to design but the Boeing 777 uses the ARNIC standard bus to send control signals to servos that physically move the throttle levers. You can read up on the ARNIC 429 data bus here.

  Are the throttle levers customized/calibrated for an engine model, or
  are their output standardized (assuming the output is an electric
  signal). Does the electronic engine control apply further adjustment
  to the throttle input?

It seems that Rockwell Collins makes a unit that sends signals to the FADEC system instead of mechanically actuating anything.

With that in mind Im sure there are older designs out there that are closer to or a complete direct linkage from lever to engine.

  Is this correction transmitted back to the throttle lever?

I dont think so, it seems that when say full throttle is applied the throttle control will remain at full and the FADEC unit will take care of spooling it up as need be. Likewise if an engine suddenly cuts out or fuel flow becomes restricted as far as I know the throttles will remain in place. Auto throttle units will however physically actuate the throttles as need be. As per the comments here it seems this is only the case in Boeing aircraft. Airbus throttles must be set to maximum setting auto-throttle is allowed to use.


Is there a standard for the frequency/interval between flashes of anti collision strobe light?

For the FAA, this can be found in 14 CFR Part 25 - AIRWORTHINESS STANDARDS: TRANSPORT CATEGORY AIRPLANES, Subpart F - Equipment, Lights (§§ 25.1381 - 25.1403):

  § 25.1401 Anticollision light system.
  (a) General. The airplane must have an anticollision light system that -

  (1) Consists of one or more approved anticollision lights located so that their light will not impair the crew's vision or detract from the conspicuity of the position lights; and

  (2) Meets the requirements of paragraphs (b) through (f) of this section.

  ...

  (c) Flashing characteristics. The arrangement of the system, that is, the number of light sources, beam width, speed of rotation, and other characteristics, must give an effective flash frequency of not less than 40, nor more than 100 cycles per minute. The effective flash frequency is the frequency at which the airplane's complete anticollision light system is observed from a distance, and applies to each sector of light including any overlaps that exist when the system consists of more than one light source. In overlaps, flash frequencies may exceed 100, but not 180 cycles per minute.

Similar sections can be found for other types of aircraft in other sections; the specified flash rate is identical for all of them.

US military aircraft are not bound by FAA rules, of course, but they tend to voluntarily comply with them anyway unless they have a good reason not to.


Do aircraft manufacturers have the authority to either approve or disapprove the maintenance procedures of its customers?

For N-Registered Planes Under FAA regulations... (this may differ elsewhere in the world)

The short answer is No (although some service bulletins may be legally required), the manufacturer can not legally enforce anything per say, however here's how it plays out.

Most makers are at least in some capacity always testing their aircraft and aircraft procedures (at least the models in service). This may be as simple as inspecting the ones out there and looking at used parts for fatigue and what not. This in turn can lead to the company issuing a Service Bulletin which is basically a document that says: "hey here's something we found, you should look at it". This can apply to a any part of the aircraft as well as inspection and maintenance procedures. However service bulletins are not legally required to be complied with when issued by the company (although many may choose to comply).

On the other hand the Service Bulletins may trigger the FAA to issue an Airworthiness Directive which is a legally enforceable document. In this case the owner/operator of the aircraft is legally required to comply and alter their procedures.

In this case of the accident in question I think this is the AD that was issued as a result. You can find a full list of MD-10 AD's Here.

On to the question of why an airline may not listen. This is most likely a cost related issue. If the airlines insurance does not change and the cost to inspect or possibly replace a part that they don't legally need to replace is simply to high, they wont do so until its legally required. Again since every thing in aviation has two sides, manufactures may have the courtesy to replace the part at no cost to the owner. For example, when Porsche dropped the FAA Type Certification for the 3.2 motor in the Mooney M20PFM leaving all the owners somewhat high and dry, Mooney was kind enough to have the 40 odd aircraft updated with Continental motors (although many were destroyed in a hurricane while under going the change). The crux of it also comes down to the fact that only the government and its various organizations (here in US) can legally impose anything on an individual or company. So while it may be a good idea to heed the advice of the maker you may not be required to do so.

--Edit--

To answer the comment below which is somewhat relevant to the original question. My understanding is that yes the FAR's may require you to refer to the manufacturer procedure but at the same time you only must refer to the procedures required (associated with the current certification of the airframe) for your airframe an SB with out an accompanying AD is a manufacturer procedure but is not legally required. So you may refer to it but you may not have to comply with it. Ill dig into the regulations and see if I can find the letter of the law on it.


Do cockpit panels have an indication that oxygen masks in cabin have been deployed?

Yes, there is an indicator for passenger oxygen status.

(Image Source: www.b737.org.uk)


Upon landing (uncontrolled field), can I exit the runway via a crossing runway?

If you are at an uncontrolled field you are responsible for maintaining situational awareness of other traffic and using UNICOM/CTAF to broadcast your intentions, find out if anyone else is going to be using the crossing runway, look both ways before crossing and then cross.


When should I use "cross" and "pass" on radio telephony?

When related to a significant point, there is no difference between pass and cross. For altitude/FL only pass is used.

The phraselogies used by ATC is described in ICAO Doc 4444 (Air Traffic Management / PANS-ATM), chapter 12, phraseologies. The document explains the meaning for ATC, therefore to be understood and used by pilots.

  12.3.1.2 LEVEL CHANGES, REPORTS AND RATES

  EXPEDITE CLIMB (or DESCENT) [UNTIL PASSING (level)]
  AFTER PASSING (significant point)

  12.3.1.4 TRANSFER OF CONTROL AND / OR FREQUENCY CHANGE

  AT (or OVER) (time or place) [or WHEN] [PASSING/LEAVING/REACHING (level)] CONTACT (unit call sign)
  (frequency)

  12.3.1.10 ADDITIONAL REPORTS

  REPORT PASSING (significant point)
  REPORT PASSING (three digits) RADIAL (name of VOR) VOR

  12.3.2.3 MAINTENANCE OF SPECIFIED LEVELS

  MAINTAIN (level) UNTIL PASSING (significant point)
  MAINTAIN (level) UNTIL (minutes) AFTER PASSING (significant point)

  12.3.2.4 SPECIFICATION OF CRUISING LEVELS

  CROSS (significant point) AT ( or ABOVE, or BELOW)
  CROSS (distance) MILES, (GNSS or DME) [(direction)] OF (name of DME station) OR (distance) [(direction)] OF (significant point) AT (or ABOVE or
  BELOW) (level)

  12.3.2.8 SEPARATION INSTRUCTIONS

  CROSS (significant point) AT (time) [OR LATER (or OR BEFORE)]
  ADVISE IF ABLE TO CROSS (significant point) AT (time or level)

  12.3.3.1 DEPARTURE INSTRUCTIONS

  AFTER REACHING (or PASSING) (level or significant point) ( instructions)

  12.3.4.12 TURN OR CLIMB INSTRUCTIONS AFTER TAKE-OFF

  AFTER PASSING (level) (instructions)

  12.4.2.3 PARALLEL APPROACHES

  YOU HAVE CROSSED THE LOCALIZER (or GBAS/SBAS/MLS FINAL APPROACH COURSE)

If another wording is used in some country, the differences must be explained in the country AIP, at section GEN 1.7. For USA (FAA AIP), Doc 4444 differences are found at GEN 1.7-23. There are none related.


Are there regulations for the minimum amount of toilets per passenger?

(this answer is specific to US laws and regs for domestic flights)

No, there are not. And, in fact, it is perfectly legal to fly with ALL of the toilets broken and unusable. No restrictions on flight time, either. The airline is required to notify all passengers that the flight has no working toilets. (I'm not sure if any compensation is required for passengers electing to not board the flight).

The Department of Transportation does provide the following in their Aviation Consumer Rights rules:

(in the section discussing tarmac delays): While the aircraft remains on the tarmac lavatories must remain operable and medical attention must be available if needed.

Although it's obviously not possible to make the lavatories available during a tarmac delay if the lavatory is broken, there are no rules prohibiting the flight from departing if the lavatory is broken.


Are aircraft separately certified for CAT III ops for +2500 feet elevation?

Yes. In certain jurisdictions.

Such as Europe, if it has not been demonstrated during flight testing.

This is covered in CS-AWOS / Subpart 1 (which covers Automatic Landing Systems).

  In accordance with CS–AWO 132, the effects of aerodrome conditions (e.g. elevation, ambient temperature, runway slope and ground profile under the approach path) are to be investigated and, if necessary, appropriate limitations derived for inclusion in the aeroplane Flight Manual. Guidance is given in paragraph 5.

Paragraph 5:

  Elevation and Temperature. The effects of aerodrome elevation and ambient temperature should be examined where operation is envisaged at aerodromes about 750 m (2 500 ft) or in temperatures greater than ISA + 15°C.

A performance demonstration would then be required (but not additional equipment).


What, exactly, happens when I call 1-800-WXBRIEF?

There is a list of Flight Service Stations in the US Chart Supplement.
The person on the phone is not a meteorologist and does not need to be. Though, just like pilots, they have been trained to be proficient on weather and weather related knowledge.
They provide the weather the same way a pilot can self-brief the weather. They utilize distributed briefings, Area Forecast Discussions, Prog Charts, other tools supplied to them by the NOAA, WPC, NWS, and AWC. Primary though, they use METARs, TAFs, PIREPs, and Winds Aloft reports at your airports of planned use and along your route of flight.
Someone will answer 24/7. Though, the person answering may not be from the closest FSS. It will be routed to the first available representative.
The same goes for inflight contact over VHF radio frequencies,


Why don't El Al 747's stay at the gates at JFK?

Flare (pyrotechnic) type
According to Wikipedia and ynetnews.com, the flare system burns at low temperatures and doesn't pose a danger. Nonetheless Europe in 2006 objected to it and Switzerland threatened to ground El Al if such system was found on board.

"If we catch Israeli planes fitted with this system in our airports, they will be grounded," a spokesman for the Swiss aviation authority told Der Spiegel.

A plane that is deemed unsafe, would be unsafe anywhere at the airport.
El Al defense system
According to ABC News (2014), El Al carries the laser-type.

[The] new system, housed in a pod under the fuselage, employs an infrared missile-tracking camera, an "infrared (IR), ultra-violet (UV), or radar missile-approach warning (MAWS) sensor to detect a missile launch in the very early stages of an attack" and a laser system meant to jam the incoming missile’s "seeker" and "cause it [the missile] to be diverted away from the aircraft."

El Al seen at the gate at JFK and how planes move around

In this JFK time-lapse video, you can watch an Etihad plane being moved from the gate to a remote stand. At the gates is a parked El Al 747 as well. Later a Swiss airplane is towed from a remote stand to where the Etihad was.

(Source) El Al 747 at the gate. A passenger took this photo after deplaning at JFK in 2011.
Long wait
Sitting from 5:10 am to 12:55 pm is most likely the reason for it being moved away from the gate. According to the Port Authority, if the Air Terminal Manager ordered an airplane to be moved and it didn't move within 10 minutes, the airplane is charged extra for each 15-minute delay thereafter.

Related:

How does the Guardian counter-MANPADS system work?
How common are missile defense systems on civil airplanes?


What is the relation between a helicopter's length and rotor diameter?

Important.  I am a helicopter pilot, with no expertise or experience in design so I can give you reasons for this, but not design detail.

Most design decisions are compromises.  Helicopter rotors are definitely compromises.

What is the aim of the rotor design?
To have the smallest possible rotor to achieve the performance requirements of the craft.

What limits the smallest size?
Let's assume that the blades are as efficient at generating lift as you can make them.  There are only 2 ways to increase lift for any given blade at any given angle of attack.  That is to increase the length of the blade or to move it faster through the air, i.e. to make the rotor spin faster.

What limits the speed at which the rotor can rotate?
As the blade tip speed gets faster, drag increases with the square of the speed.  Increased drag means increased power required which means heavier engine and heavier gearbox.  As speed moves to a high percentage of supersonic, turbulence and therefore drag increases enormously.  The longer the blade, the lower the possible rotor RPM since the tip approaches supersonic speed more quickly.

Why not just increase the length?
Because the blade becomes increasingly difficult (and expensive) to manufacture to handle the loads on the blade and the heavier they become requiring more robust and heavier rotors hub assemblies.

The inner part of the rotor also produces little lift since it is moving relatively slowly and since lift decreases with the square of the speed, the lift generated falls away rapidly as you move to the inside portion of the disc.  As you increase the length of the blade, without being able to increase the speed of the disc as above, the area of the disc which is "useless", increases as a proportion of the overall disc size.  Therefore, more power is needed to rotate the increasingly large useless area of the disc.

The lower the disc loading, the more efficient the helicopter is in the hover.
The disc loading is the ratio of the weight of the helicopter and the area the rotor disc describes as it rotates.  The disc loading should be as low as possible to reduce the required strength, and thus weight, of the blades especially as the weight of the helicopter increases under positive G which in turn increases the disc loading.

Non-performance considerations.  Parking; hangar space required; ability to operate in confined areas.

Given these (and other design parameters), the rotor sizes you quote will have been arrived at by factoring each of the variables to find the best compromise, according to the designer, between them to achieve the desired performance goals.

Therefore, I don't believe that there is a relationship between the fuselage length and rotor size, possibly with some influence from the need to park and hangar the resulting craft.

[EDIT]
I've been hoping that some better informed answers would be added.  As there are none, I'll continue with my simple pilot guesswork.

What is the aim of the fuselage design?
To have the smallest possible fuselage to achieve the performance requirements of the craft.

What limits the smallest size?
How many crew?  How many PAX?  Level of comfort (utilitarian - R22, or comfortable - Long Ranger).  Fuel load.  Engine and gearbox size.  Cargo and other payload.  Baggage stowage?

What limits the maximum size?
Weight.  Profile drag.  Cost to manufacture.

Non-performance considerations.  Parking; hangar space required.


Why are some ATP CTP providers not on the FAA's approved list?

The FAA's ATP-CTP Advisory Circular 61-138 does not prohibit a qualified ATP-CTP instructor using an approved training program from delivering the training at any facility that is willing to pay for their services.


Does every control surface need to have a counterweight?

Flutter is an energy storage and release phenomenon.  Surface moves, applies a load to the fixed surface it's attached to, fixed surface bends under the load, stores some of the energy like a spring, then releases it in moving back to its original position, and some of this released energy is transferred to the moving surface attached to it, which is also stored and released back into the fixed surface in a way that adds more total energy than the first time, magnifying the original movement, repeat, and away you go.

For the this to happen the moving surface has to be unbalanced with a fair amount of mass away from the hinge line, the fixed surface has to be flexible (spring like), the whole system has to have a natural frequency that is close to the frequency of the natural oscillation frequency of the moving surface, and there has to be enough energy present in the first place to get the whole thing going.

Generally airplanes that go less than say 80-100 mph don't have the energy to induce flutter if there is reasonable stiffness in fixed surface like the horizontal stab.  Light airplanes with fabric covered wire braced tails have stabilizers that are quite stiff due to the wire bracing, and the combination of high natural frequency resulting from the rigid system and the low input energy at the speeds they fly at means they don't really need a balanced surface (look at a Champ's unbalanced elevator; the C of G of the surface is probably at 30% of chord - no big deal because it simply can't excite sympathetic movement in the stabilizer it's attached to at the energy level present at its operating speed range).

If the fixed surface is not so stiff, the moving surface is really heavy, or you want go faster, then you start having to consider mass balancing.  To really know for sure what the threshold is, you'd have to have someone that knows what they are doing do the analysis. But generally low speed light airplanes have the inherent rigidity to be immune from flutter in their speed range without balancing control surfaces.

You still have to confirm it in the real world though.  When you test fly your creation, you do some rudimentary flutter testing by diving to a speed a bit above your Vne (actually creeping up to it in a series of steps), pull up so you are decelerating, and as you pass the speed of your test point you slap the control stick sharply, trying to induce an oscillation.  By doing it while decelerating, the risks of an oscillation starting and building into full fledged flutter are low. But, if you see an oscillation that starts but then goes away, well you've "tickled the tiger's tail" and you'll need to balance the surface or reduce the airplane's speed range.  You're wearing a parachute while doing this of course (or whomever you're able to talk into doing your test flying).


Are there any aerospace examples of applying a boat tail?

This depends on the mission the plane is built to fit. Some planes need the cargo space so the tail is less tapered but most planes have at least some taper. Diamond Aircraft have very tapered tail sections

(source)

Even the older GA designs like the Piper Seminole have a good deal of tail taper

(source)

Larger planes have some tail taper as well however sometimes there is less as there are often systems in the tail like the APU or there is storage space.

(source)


What lead time is required to change an already submitted flight plan?

The flight plan can be changed by the minute, as long as the two governments and the two airports and the airline agree on this.

As it seems like the government pays the airline to just take off whenever they are allowed to, take the airline out of the equation.
Likewise for the airports, since they are either state-operated or have a concession which states that they have to assist in lawful deportations, emergencies or state affairs.

This keeps two governments in, which have to agree on a time and the who-pays-whom-how-much for the deportation to really take place. In fact, I think this is the only reason why the plane is not yet airborne - because of two governments playing their diplomacy games.


What is this helicopter seen in the Falcon Crest TV series?

Looks to me like a Bell 206 JetRanger/LongRanger


Why require a minimum of 1500 hours to become an airline pilot?

The 1500 hours is requirement for ATPL (airline transport pilot license), which is needed to command a multi-member crew. But in most of the world the CPL (commercial pilot license) with a 250 hour requirement is sufficient to fly as a co-pilot (F/O), and that used to be the case in the USA as well. And those hours include any spent getting the private license and instrument, multi-engine and type ratings.
My understanding of why the USA started requiring ATPL for F/Os as well is that it was only indirectly related to safety and had most to do with job market. At the time it was introduced the large supply of aspiring pilots led to very low wages in the regional airlines, and with that tendency to also overload the pilots and save money across the board, ultimately affecting safety. Raising the requirement aimed to limit this by making pilots more scarce.


confusion between RNAV and RNP approaches and specifiations

RNAV was/is in the older model where each approach was designed around a specific technology, and any detected failure to meet the (assumed) fixed accuracy of that technology means you can't use the approach at all.

RNP is newer ICAO terminology under their Performance Based Navigation model, which essentially means they don't care how you get your navigation data, just how accurate it is.  The better your Actual Navigation Performance is (i.e. lower number), the lower the approach minimums you get to use.

TSO C129/C196 systems cannot be used as the sole navigation equipment because it only has fault detection, not fault exclusion; if the RAIM detects a fault, you have to stop using it and switch to something else.  (If you don't have RAIM, you have to actively cross-check the GPS, so you might as well just use the other system as primary.)  Notice the parallels to the explanation of RNAV above.

TSO C145/C146 do have fault exclusion, so they can be used as the sole means.  They also support SBAS (aka WAAS), which can offer much lower approach minima where available, but they will gracefully degrade to higher minima depending on the signal accuracy--which can vary over both space and time for the same equipment.  Notice the parallels to the explanation of RNP above.


Will creating a strong back pressure within a ducted propeller enable an aircraft to attain a higher altitude?

A very creative thought and project - a centrifugal compressor could be used as a means of propulsion if the exhaust stream is properly nozzled. So what you're basically doing is switching on another engine to produce more thrust, but:

The extra engine is in the way of the propeller, blocking its outlet flow.
Propellers and rotors are very efficient thrust generators on their own.
Creating static pressure is not the most effective way of creating thrust, better to convert it into air flow velocity.

Anything that is in the way of air flow creates back pressure and/or friction. The propeller flow is blocked, and the compressor flow runs into the side wall and does not accelerate any air backwards.

The way the air from the centrifugal compressor is normally deflected is depicted below (from an old uni book).

Air flow needs to flow and be guided gently. If it hits an obstruction, it pushes against it and creates negative thrust, like a person in a sailboat pushing against the mast.

It won't fly, I'm afraid...

Starting an extra engine might help in reaching places that are hard to get to. A simple propeller or turbofan is best - but when the extra propulsion is off, it is dead weight. Best to crank up the engines that are there already.


What DAL level is IFE software certified at?

DAL is specific to a design and installation. It's a flow down from the aircraft system requirements and design and the safety assessment process.

These processes are defined in SAE ARP4754A Guidelines for Development of Civil Aircraft and Systems and ARP4761 Guidelines and Methods for Conducting the Safety Assessment Process on Civil Airborne Systems and Equipment.

ARP4754A is the more relevant to this question. A summary of the process is to start with a Functional Hazard Assessment which identifies hazards associated with failure modes of specific functions. Based on the severity of the failure condition a Functional DAL (FDAL) assignment is made.

The next step is to assess the architecture for functional and item independence. This allows for setting Item FDAL for each of the components of the system.

It can get complicated, but for a simple example: If you have an FDAL B and FDAL E function combined into a single item with no independence, the IDAL of both becomes Level B. If they are functionally independent and also independent items, the IDAL would match the FDAL for each.

Back to the question: An old colleague of mine worked much of the certification effort for the B777 IFE when he was at Boeing. As he explained, the highest criticality function in the IFE is the PA override function which is FDAL C. The rest of the IFE system was set at Level D. (you could argue for Level E based on the argument that losing it has no safety effect, but the Level D is based on the requirement that you show non-interference with any other system.)

The question as posed, is about the software which means we're asking about IDAL. If the IFE SW architecture is a single application or multiple applications that lack independence from the PA override code, the IDAL for the IFE SW will be Level C.

It may be possible to architect the SW with proper hardware or software partitioning to provide independence of the functions and items. In that case, the independent items could be developed at the lower IDAL level.


The NASA X-57 uses 12 electric motors for takeoff. Does it need 12 control levers or just one?

The need for throttles is to provide a linkage to the carburetor/throttle body in the age when everything was mechanical. The throttle in older airplanes directly controlled the air-fuel mixture allowed into the intake manifolds. If electric motors were used, the throttles would have been attached to mechanical rheostats.

In the age of computer controlled engines/motors, this direct linkage is not necessary. You would essentially just tell the computer how fast you would like to go. The system will take care of the rest.

In most cases, the throttle is retained in the cockpit to provide the human pilot with a familiar interface with the computer. Honestly, in an airplane, where throttle settings and changes are more stable and predictable, a knob or a couple of buttons would suffice. FADEC controlled engines/motors are pretty standard now. The method of inputting your desired controls in a fly-by-wire system is arbitrary. It is just a matter of comfort level with the controls. We might even get to the point of a true GUI cockpit one day.

In the case of a multi-engine electric airplane, you would want at least two controls to account for differential thrust when desired. This is not something that you would absolutely need. But, it would be convenient.

Some very complicated aircraft like the V-22 Osprey rely on the pilot not having direct control over the engine-prop systems. It’s absolutely necessary for a computer system to coordinate the two engines during VTOL operation. The same problem would present itself in a quad-copter large enough to carry human passengers.

As an aside, I vividly remember the first throttle-by-wire car our family ever owned. It was a Hyundai Santa Fe. Though, not difficult to drive. The throttle response took some getting used to. Also, modern electric cars with multiple motors have only one throttle.


Can a passenger request to visit the cockpit during a flight?

This stopped after the World Trade Center attacks.

You might be able to get a kid in briefly before the plane takes off.


What is this hatch above the cockpit of a 747?

It's an emergency escape hatch. There are inertial reels in the cockpit ceiling adjacent to the hatch to allow the cockpit crew to exit the airplane. See this link for an account of their use escaping the aircraft during a hijacking.

There were five reels in the 747-100/200 aircraft. The cockpit had five seats: pilot, co-pilot, flight engineer, and two observer seats.

It's also sometimes used in third world countries to send a guy out to clean the cockpit windshield. In Mumbai I once made the mistake of asking the windshield to be cleaned, thinking, of course, they'd do it with a cherry picker. Much to my surprise, bare feet appeared at the top of the windshield followed by this poor fellow who was maneuvering into place to clean the windshield. He had a rope tied around his waist, but had he fallen it would have been bad because the rope was anchored through the hatch, which meant he would have swung badly had he fallen.


What's an "outrigger" for parking aircraft on a carrier?

You can see it a bit better in this picture:

(Source)

  In order to save deck space for operations, the smaller escort
  carriers like HMS Khedive used outriggers. The tail wheel is first
  affixed and locked to the rigger trolley and then the aircraft is
  pushed outwards and the wheels heavily chocked fore and aft of the
  wheels. Here one of Khedive’s Corsairs demonstrates the concept
  perfectly. Note that the Corsair has Type C roundels, indicating it is
  in the European theatre of operations.

They were effectively a simple way to save deck space with out enlarging the deck. There is another decent pic here and some spitfires on outriggers here

Based on the info here they can be found as far back as the late thirties

  It represents an F4B-4 positioned on an experimental outrigger aboard
  the USS Saratoga during the late 1930s. The Saratoga and several other
  aircraft carriers were selected to try out different types of deck
  outriggers for the Navy in the interwar era.


What could be the reason for a feeling of speed oscillation after takeoff in a 747?

There are a whole bunch of possible reasons.

The first thing to note is that, from inside the cabin it can be very difficult to tell the difference between speeding up/slowing down, pitching up/down, and the rise and fall from turbulence (particularly when in a climb). And one I wasn't aware of but as pointed out by Sami, the air conditioning pressure varying because of a malfunction in the engine bleed or pack valve.

So why could it be happening?

Turbulence causing the aircraft to gentle rise/fall, which, in a climb, is fairly akin to small acceleration/decelerations - both to our inner ear, and in terms of what's physically happening to the aircraft
The air conditioning pressure rising and falling more than usual rather than maintaining a constant pressure
Slight pitch up/down manoeuvres, possibly from a relatively inexperienced pilot flying the aircraft
The auto-throttle throwing a hissy fit or, if climbing at 250 knots under 10,000 ft, oscillating slightly in order to stay at/below the 250 knot speed limit
The pilots adjusting thrust manually, possibly for the same reason as above
A gusting head/tailwind. Particularly noticeable near the ground and when in a climb, and can cause a feeling of acceleration/deceleration.
A malfunction in one of the engines causing the power to vary slightly. It's possible this was only noticeable at takeoff/climb thrust levels, and disappeared when throttling back

Typically you'd expect it to be due to either turbulence or a gusting wind, but there are several systems which could develop a small, fairly benign fault and have this symptom.

Edit: As noted by user Jamiec, Storm Katie (a reasonably strong storm) was over the UK at the time, which would certainly back up turbulence/gusting winds being the most likely culprit


To start, the FH timer starts when the aircraft takes off (weight-off-wheels) and stops when the aircraft lands (weight-on-wheels).  This means that whether the engine is in hotel mode or running for taxi, the aircraft (and the DC Gen) are not accumulating FHs.  One thing to consider is the difference between an engine hour (EH) and a flight hour.  Engines have hard time limits based on how many hours the engine was run, not on how many hours it is in flight.  One might think that since the DC Gen is directly driven by the engine, that the wear rate should be based on EH, and I might agree with them. However, since the DC Gen is an accessory component (isn't a PWC part, doesn't come with the PW127 engine), the component is lumped in with the rest of the airframe systems, FHs are accumulated just like any other system outside the engine.

You would be right in saying that some aircraft components have hard time limits, that at a certain number of FHs, they need to be replaced. Good examples would be the engine (for overhaul), landing gear and some structure.  The components and the aircraft as a whole lose its certification if the hard time limits are exceeded.  The DC Gen however, more than likely has a soft time limit.  This means that the DC Gen is certified to be on the aircraft until it malfunctions.  The manufacturer of the DC Gen would likely impose a soft time limit, meaning that if the soft time limit is exceeded, it is out of warranty.

When the engine is in hotel mode, the only difference is that the prop and the turbine powering the prop are arrested.  The LP and HP sections of the engine are running as they normally would during taxi.  This post has some helpful images on what the internals of a turboprop look like (reference the second image, the first one is a PT6 I believe).  Hot exhaust air is still rushing past the arrested turbine that would normally power the prop.  This may cause some back pressure that the Full Authority Digital Engine Controller (FADEC) would need to account for, but in terms of the speeds and torque seen by the HP section, accessory drive and DC Gen, the wear seen on the brushes of the DC Gen would be no more than the wear seen during an engine taxi.


In the B737NG, is the CTR tank fuel the first to be pumped when there is fuel in all tanks?

Because the center pumps effectively put out more pressure, the fuel from that tank will be used first when all pumps are on.


What causes a plane to lose its roll momentum

What you want is the roll constant $\text{T}_R$. This is basically one of the characteristics wich determines the equations of motion of an aircraft. It gives the slope of the roll speed increase over time with full aileron deflection and an ideally stiff wing, and equally the rate of decrease once the ailerons are set to neutral during a rolling maneuver.

With p the dimensionless roll rate, m the aircraft mass, i$_x$ its radius of the momentum of inertia about the roll axis, S its wing surface, b the wing span, v the flight speed, $\rho$ the density of air and $\text{c}_{lp}$ the roll damping coefficient, the formula is

$$T_R = \frac{2\cdot m\cdot\left(\frac{2\cdot i_x}{b}\right)^2}{\rho\cdot v\cdot S\cdot c_{lp}}$$

When the pilot moves the stick, the aircraft will accelerate into the roll but the acceleration will diminish with the square of roll speed until an asymptotic value is reached. This acceleration grows with increasing air density, flight speed, roll damping coefficient and lower wing loading and smaller square of the ratio of roll inertia over wing span. Same in reverse: Stopping will be fastest under the same conditions.

For the roll damping coefficient, use this approximation for wings with an aspect ratio AR larger than 4:

$$c_{lp} = -\frac{1}{4}\cdot\frac{\pi\cdot AR}{\sqrt{\frac{AR^2}{4}+4}+2}$$

Since this is a damping coefficient, it makes sense to be negative.

The asymptotic value is reached when the propelling moment from aileron deflection equals the retarding roll damping:

$$c_{l\xi} \cdot \frac{\xi_l - \xi_r}{2} = -c_{lp} \cdot \frac{\omega_x \cdot b}{2\cdot v_\infty} =  -c_{lp} \cdot p$$

For an explanation of this equation and all the terms used please see this answer.

Please note that this is all only valid for a stiff airframe. Increasing dynamic pressure reduces aileron effectiveness because the wing will warp when ailerons are deflected. Assume a linear decrease with dynamic pressure until only a fraction of the ideal roll acceleration remains at top speed and low level flight.

Now you ask about roll damping torque and that cannot be explained in the comments. Look at the last equation – it is already there, albeit dimensionless. To get from there to an actual torque, multiply by wing area, semispan and dynamic pressure:

$$T=\frac{\rho}{2}\cdot v^2_\infty\cdot S\cdot\frac{b}{2}\cdot c_{lp}\cdot p = \frac{\rho}{8}\cdot v_\infty\cdot S\cdot b^2\cdot c_{lp}\cdot\omega_x$$

with $\omega_x$ the actual angular speed in rad/s. Do the unit check - this is actually a torsion moment [Nm]. Please note that I used the reference length for lateral moments used in Germany; the US uses the full span instead of the semispan. So make sure you check which reference length your sources use!