What is the weight saving of windowless fuselage for cargo aircraft?

Let's take a Boeing 737 as a generic example, and spitball some numbers.
I'll make the post community wiki so someone can come along and plug in more accurate numbers.

Aluminum has a density of 2.7 g/cm3
(For our purposes let's assume the skin alloy is "close enough to pure aluminum" because I'm too lazy to look up the proper alloy density).

Plexiglass (just picking a random variety) has a density of 1.18 g/cm3.

The aluminum skin on a 737 is about 0.038 inches (or 0.1cm) thick.
We know a window on a 737 is thicker than the skin. I couldn't find the number but let's go with 0.25" (0.6cm).

If we have a hypothetical one-foot square window (about 930 cm2), the aluminum skin occupying that area would weigh about 251 grams. The Plexiglass equivalent would weigh about 658 grams (407 grams heavier, little more than 2.5 times as heavy).

Figure there are about 70 side windows on a 737 (quick count from a photo of a Southwest plane, not including exit door windows), so that's 28,490 grams or about 64 pounds, just for the plexiglass.

In addition to the plexiglass there's also supporting structure that needs to be added around the window to hold it in place, sealants to seal it against the skin, etc. - these add additional weight. I've no idea what these components weigh, but let's assume it weighs twice as much as the plexiglass, that's about 1.5 pounds per window of additional structure, or 105 pounds, bringing the total weight savings to just under 170 pounds.

170 pounds is not a lot of weight (in passenger terms it's not even one person), but it is that much more cargo you can carry. Also when combined with the fact that you no longer have to maintain the windows (fix pressure leaks in the seals, replace cracked plexiglass, etc.) the savings can add up over the life of an airframe.

Some more spitballing here... please feel free to correct my numbers:

On the subject of the cost savings: a 737 can carry about 27000 lbs payload, and burns about 5500 lbs of fuel / hour during cruise, and about 3000 lbs for a 15 minute climb. Assuming an average flight of 4 hours you get about 25000 lbs of fuel burnt, or almost 1 per pound of weight. This means that the fuel cost of 170 pounds of weight is about 170 pounds of fuel, which today costs (at around \$4 / gallon, and 6.5 lbs/gallon) around \$100.  Note that the cost of fuel varies a lot with location, so this is very approximate.

Now multiply this by the typical life of the aircraft - three flights per day, 7 days per week, for 30 years? That would be over \$3M of savings. And all because your parcels can't look out of the window.


Why did this aircraft do a ‘spiral’ before landing?

The flight was on the 28th, and before orbiting it was around 12:00 UTC. By using the playback function of FR24, this is the view:

The flight in question was 2383 with call-sign WZZ1161 (FlightAware permalink).

The boxes with numbers and arrows indicate the flight level and either climbing or descending. As you can see, two busy streams were approaching the airport from the north. This orbiting as opposed to a holding track (race track shaped) is common and its phraseology can be:

  for spacing orbit left
  for spacing make a 360 turn left

Fast forward:

And a Ryanair flight did the same before continuing the approach. It was just heavy traffic and it's quite common over Heathrow (live as of writing this):


Why don't all GA aircraft have yaw dampers?

A yaw damper means added cost, weight, complexity, and one more system that has to be maintained. That's the downside. The upside, for most GA aircraft is that they relieve the pilot of having to make a "coordinated" turn. In other words, having to apply appropriate rudder input along with aileron input. Is that convenience worth the downside when the pilot has internalized doing that without having to think about it? That's a matter of opinion. For myself, a yaw damper in any of the, say, single engine Cessnas would be a waste.

There are some GA aircraft that could benefit from a yaw damper in other than banking into a turn or leveling from a turn. For example, in level flight the old V-tail Bonanza would yaw around the vertical axis in turbulence to an objectionable degree in my opinion. Very uncomfortable, especially to passengers in the back seat. It would have been great to have had a yaw damper.


Symbology on standard terminal arrival (STAR) charts: T-ended vs arrow-ended lines?

According to the FAA Chart User's Guide, the arrows are transition routes and the 'T' is "Altitude change at other than Radio Aids." So your original assumption is correct.

Regarding DSERT TWO ARRIVAL and BUSTD. You are correct that the altitude doesn't change at BUSTD when proceeding to YOLOW, but it does change (9000 to 8000) when proceeding to BAYTA. That is why there is a 'T' at BUSTD.


Why doesn't the autobrakes and ground spoilers deploy on the A320 if the speed is below 72 knots?

Not a definite answer: I imagine someone backtracking on a long 4000 m runway might actually taxi at around 71kts?

If armed, MAX braking will occur once the system detects that ground spoilers are deployed.
From the FCOM, ground spoilers:

  If the ground spoilers are armed and the speed exceeds 72 kt, the ground spoilers will automatically extend as soon as both thrust levers are reset to idle.

Because of Airbus SOPs by the time you enter the active rwy, your autobrakes are on MAX and spoilers armed. Once armed&active, they will deploy the second the ADIRS will sense any deceleration. With thr lvl retarded to idle, the plane now thinks you are actually rejecting a take off, not knowing you are slowing down at the end of the runway for the 180deg turn to lineup. All hell will break loose as your plane insta-handbrakes on the spot with the activation of spoilers+max brakes.

Incidentally, my company used to have a 30kts speed limit for backtrack which has been recently removed.


MIL-PRF-5606J, What does "J" means? Does it equal to MIL-PRF-5606?

I don't know this specification, but the letter at the end indicates the revision number of the document. J would be the 10th revision/ 11th edition.
Note that there are often also intermediate publications with minor improvements called 'Amendments'

Version J was published in March 2018.
The version before, H, was published in June 2003 with Amendments in 2003, 2005 and 2006, and an additional notice in 2011.
(source)

Referring to MIL-PRF-5606 can thus mean the first edition of the specification, or it can be a generic reference where the edition is omitted.

It depends on the context, but since the original publication must have been ages ago, my bet is on it being a generic reference.


Why do aircraft manufacturers produce families of aircraft?

There are several advantages, here are a few:

Design costs are lower for a family of aircraft; major parts of the aircraft are the same in the family.
A family of aircraft share the same type certificate. This means it is cheaper for the manufacturer to certify a family of aircraft.
Within a family of aircraft, pilots can operate all aircraft with no
or very little additional training required. This saves the airline a
lot of money.
Maintenance on a family of aircraft is cheaper since the majority of
parts are common to all family members. This means having less spare
parts in stock and less training for maintenance personnel.
For an airline there is often a benefit in having some capacity
diversity in a fleet. A new route often starts at low capacity. When
the volume of passengers rises replacing the flight by a  larger
aircraft from the same family is not disruptive to crew schedules.


Yes, airplanes (all types including jets) can use window tints.

Ultraviolet "A"
Tints for airplanes are with enhanced protection from UVA radiation. UVA exposure can increase the risk of skin cancer and will damage most organic materials. Its intensity increases about 5% with every 1000 feet of altitude. Unlike car tints, airplane tints need to block the additional exposure to UVA.

Solar Energy Control
Tints also block near-infrared radiation which results in lesser interior heat.

LP Aero Plastics (product listing) and PolyOne are the two manufactures I found for aircraft tints.


Why should you not turn in the direction of an inoperative engine?

The AvHerald comment is correct, you generally do not want to turn towards the dead engine. The aircraft will tend to turn (both yaw and bank) towards the dead engine due to asymmetric thrust, allowing it to do so at low speed will make it difficult to end the turn, possibly to the point where you lose control. If you turn away from the dead engine, you'll have a tougher time getting into the turn, but the live engine will help you get out of it. That said, attempting low altitude turns with an engine out seems like a bad idea, you should concentrate on going straight and maintaining optimum airspeed to make sure you get some altitude

There are a couple of mnemonics when dealing with engine failures, like "dead foot, dead engine" (determining which engine failed) and "raise the dead" (keep bank towards the live engine)

I can only speculate as to why they chose to go right, either they wanted to avoid the populated area, or they were already unable to control the turn. The high density altitude would certainly affect the OEI performance as well, perhaps luring them into losing airspeed below Vmc.

Disclaimer: I'm not multi engine rated, and have no first hand experience. This is just what I've read.


Why is Boeing being blamed for the recent 737 Max crashes?

The Ethiopian crash was in a new plane, in good weather, with multiple witnesses describing rattling noises and a smoke trail.

We can rule out weather, and pilot error seems unlikely to cause that.
The plane is so new that maintenance is not likely to be a factor either.

Blaming Boeing may not be fully justified at this point, but caution over the literally hundreds of thousands of passengers who fly on them every day is not inappropriate either.


What are the aileron lengths of commercial and military aircraft?

This is quite difficult to answer as some modern supersonic fighters  don't have just ailerons, but 'elevons', flaperons, tailerons and most of the time combine the movement of several control surfaces by computer to generate a desired effect.

Large civilian aircraft tend to have more than one pair. A relatively smaller set closer to the wing tips for slower speeds and a general large aileron closer to the wing root.

I would suggest you get a top-view of these aircraft. When you find our the length of the aircraft or wingspan you could derive it yourself through approximation.


Why do wind tunnels not have oval turns?

Some closed wind tunnels do have rounded corners, for instance the inner circuit ("thermal test chamber") of the Jules Verne climatic wind tunnel in Nantes.
This plan view is from fig. 1 of "Numerical modeling of the flow conditions in a closed-circuit low-speed wind tunnel" by Moonen et al, J. Wind Eng. & Industrial Aero. 94(10):699-723.

More diagrams of this wind tunnel are in "Benefit of Wind Tunnels with Large Test Sections for Wind Engineering Applications" by Flamand et al, Mathematical Modelling in Civil Engineering 15(2).


What are the lateral limits of Class D airspace in the USA?

JO 7400.2L, Procedures for Handling Airspace Matters, describes how the size of Class D airspace is determined. Per paragraph 17−2−5. DETERMINING CLASS D AREA
SIZE:

The size of a Class D area, and any necessary extensions, is determined
by the use of a 200 feet per NM climb gradient and information obtained
from the person responsible for developing instrument procedures (see
FIG 17−2−1).

The figure lays out the formula for determining the radius and gives an example. In short, it depends on the distance from the airport reference point (ARP) or geographic position (GP) to the end of the outermost runway, and the terrain surrounding the airport. This is why the difference varies at different airports.


When can a tower's callsign differ from the airfield name, and how do I find the proper callsign?

I doubt pilots are expected to have airport diagrams handy for every airfield in the vicinity just for this.

And you're wrong to doubt that.

  If, say, I had to divert to an unfamiliar airfield, how would I find the proper callsign for its tower?

From the chart. Same place you'd get the tower frequency...


Can a jet engine benefit from nitrous oxide boost?

For the combustor, I say the answer is no, because what is limiting the fuel rate, isn't the amount of oxygen (gas turbine combustors run very lean), but the ability of the turbine materials to withstand a higher gas temperature entering the turbine. Hence, to temporarily increase engine thust, water injection into the combustor was used on early jet engines, to increase thrust during takeoff.

This sounds quite counter intuitive, but the explanation is based on thermodynamics. Naturally, the water evaporates into steam, which then gets heated to the temperature of the combustor exit temperature. This evaporation and heating process of the water and then steam, is drawn from the heat of the combustor, and so reduces the combustor temperature (for the same fuel flow). However, the engine does not need to add more fuel to make up for this cooling, at the same level of thrust, because the energy added to the steam is still available in the turbine, to be released as the combustion gas / steam mixture flows through the turbine, expands and cools. As it cools, it gives up this energy, which is effectively used to power the turbine. The remaining energy is then converted to thrust, as the flow expands through the final propelling nozzle. But now, because the turbine temperature is lower for the same thrust level, the fuel flow can be increased until the maximum turbine inlet temperature is reached, and so now providing more thrust.

So, rather than inject N2O into the main combustor, inject water.

For the afterburner (AB) however, the case is quite different, and I believe a performance benefit could well exist. AB combustion runs much closer to an equivalence ratio of 1 (about 0.96), i.e. burning almost 100% of the fuel level that can occur with complete combustion of all the available air. And unlike the main combustor, there are no real material temperature limits (cool bypass air exits along the inside of the AB duct surface). But, the question is, do you really want to do this, operationally? Is it better to use some of the planes tank capacity for some N2O, or just entirely for fuel? I suspect operationally it is better to be able to use the AB for longer, at a slightly lower thrust level, than shorter, for a higher thrust. I don't believe military aircraft use AB to out run missiles, so pure thrust isn't the only aim. But that's another (next) question....


What is the correct use of the verb "to leave," for exiting the runway?

The correct term is to vacate a runway. The term is used several times in the ICAO Manual of Radiotelephony (Doc 9432), including the following example (among many):

  4.9 After landing
  Unless absolutely necessary, controllers should not give taxi instructions to pilots until the landing roll is completed. Unless otherwise advised, pilots should remain on tower frequency until the runway is vacated.

  Pilot: Georgetown Ground Fastair 345 runway vacated
  ATC: Fastair 345 taxi to stand 27 via taxiway alpha

And a relevant note from the same document:

  Note.— The runway is vacated when the entire aircraft is beyond the relevant runway-holding position.


How much pollution is created by an airplane taking off?

To provide more detail, let's look at some actual numbers. Without knowing where you got this information, the term "air pollution" is especially vague. But let's see what we can do. I'll compare CO (carbon monoxide) emissions since I could find that for both cars and jet engines.

The new 747-8 uses the GEnx-2B67 engine. The older 747-400 has a few engine options, one of which is the CF6-80C2B5F. Emissions information about these engines is available from EASA tests, and available for the GEnx and CF6. More info about the tests is here.

Based on that information the two engines have the following CO emissions at takeoff, reported as grams per kg of fuel burned:

CF6: .05 g/kg CO
GEnx: .17 g/kg CO

The fuel burn rates at takeoff for the engines are reported as:

CF6: 2.685 kg/s fuel
GEnx: 2.451 kg/s fuel

To find a value of comparison for cars, the EPA standards are here, in units of g/mi. Let's assume that we are using a recent model year, certified to the ULEV (Ultra-Low Emission Vehicles) standard.

ULEV: 1.7 g/mi CO

Now we need a way to compare these values. Let's use your initial value of 5 miles as the comparison distance. The jet engines will remain at takeoff thrust over these 5 miles, and the cars will meet the ULEV standard.

So how long will it take the 747 to cover those 5 miles? Let's look at the whole takeoff run, from a complete stop. This means that it will take about 40 seconds to cover the first mile down the runway. After that, lets assume it averages 160 knots, or 185 mph, over the next 4 miles. This means it will take 78 seconds to cover the rest of the distance, for a total of 118 seconds.

Computing the emissions for the takeoff:

CF6:

$$\begin{align*}
2.685\,\mathrm{kg/s} \times 0.05\,\mathrm{g/kg} &= 0.13\,\mathrm{g/s}\text{ CO}\\
0.13\,\mathrm{g/s}\times 118\,\mathrm{s} &= 15.84\,\mathrm{g} \text{ CO per engine}\\
15.84\,\mathrm{g}\times 4\text{ engines} &= 63.4\,\mathrm{g}\text{  CO per takeoff.}\end{align*}$$

GEnx:

$$\begin{align*}
2.451\,\mathrm{kg/s} \times 0.17\,\mathrm{g/kg} &= 0.42\,\mathrm{g/s}\text{ CO}\\
0.42\,\mathrm{g/s}\times 118\,\mathrm{s} &= 49.17\,\mathrm{g}\text{ CO per engine}\\
49.17\,\mathrm{g}\times 4\text{ engines} &= 196.7\,\mathrm{g}\text{ CO per takeoff.}\end{align*}$$

The car will be easier to compute:

$$5\,\mathrm{mi}\times 1.7\,\mathrm{g/mi} = 8.5\,\mathrm{g}\text{ CO per car.}$$

The 747-400 holds 416 people, and the 747-8 holds 467 (3-class configuration). Let's assume each car will carry 4 people.

$$\begin{align*}
416/4 &= 104\text{ cars}\\
467/4 &= 116.75\text{ cars.}
\end{align*}$$

We'll split the difference between cramming the three extra people into other cars and adding another car, and just leave it as 116.75 cars. Totaling the emissions from all cars:

$$\begin{align*}
104\text{ cars}\times 8.5\,\mathrm{g/car} &= 884\,\mathrm{g}\text{ CO}\\
116.75\text{ cars}\times 8.5\,\mathrm{g/car} &= 992\,\mathrm{g}\text{ CO.}\end{align*}$$

So comparing the 747 and the cars:

747-400: 63.4 g CO
104 cars: 884 g CO
747-8: 197 g CO
116.75 cars: 992 g CO

So a 747-400 is equivalent to about 7.5 cars, and a 747-8 is equivalent to 23.2 cars, comparing the takeoff run with average vehicle emissions.

I found this pretty surprising. It would be more fair to compare a takeoff with a drag race or a 0-60 test on the cars, which is probably not what the emissions test requires.

If anyone has more info or sees an issue with this please let me know.


Is the term "guinea pig" defined in the Pilot/Controller Glossary?

Being a "guinea pig" means to be the first to try out a (potentially dangerous) situation. There is no mention, past or current of the term "guinea pig" or any derivation of that.

Slang slips through on the radio, this is probably an instance of that. If the pilot or controller used that term the appropriate response would be "unclear, please say again".

There is also no mention of it in the AIM.


Does the large 6-pointed star on a sectional warn of dangerous radar facility?

There are two stars:

The large multi-pointed Star (6 pointed in this case) is described in the Aeronautical Chart User’s Guide as an indicator of High Energy Radiation Areas. The Precision Acquisition Vehicle Entry Phased Array Warning System (radar) may be intense enough to damage avionics. Or, at least cause them to give false readings.
The blue star with the clear circle in its center indicates that the airfield has a rotating light beacon and the beacon’s location relative to the field. The beacon’s location can be used to differentiate one airfield from another while in flight at night.

Reference: Aeronautical Chart User’s Guide


White light illuminating the engine coming on at intervals in flight; Curious what's the protocol?

The answer is in this post at the very bottom.  In the US these wing lights are usually switched on to make the planes more visible during takeoff and landings despite the fact that the lights are designed for ice inspection.  I don't know if China has the same protocols or not but from what you described it sounds like they do.


How would an airplane land if the on-board radio breaks down?

It is important to remember that it is often difficult to diagnose radio malfunction during flight. Therefore it is hard to know whether you have a malfunctioning transmitter, a malfunctioning receiver, or perhaps both. You also have the point-of-failure that is the headset you are using. For this reason it is quite usual to carry a spare headset and the first piece of diagnostics is to swap headsets. Many General aviation aircraft also have a handheld microphone and speakers integrated into the radio stack.
Once you've ascertained that its the actual transmitter and/or receiver that has failed it is common to set the transponder to 7600. For landing, the relevant detail for the procedure to follow is contained within Chapter 4, Section 2-13 of the AIM:
Receiver Inoperative

Remain outside class D airspace until the direction of air traffic can be ascertained
Notify the tower your type, position, altitude, intention to land and request you are controlled with light signals
At 3 -5 miles, advise the tower of your position and join the traffic pattern
Watch the tower for light signals
Continue to advise of position (downwind, turning base, etc)

Transmitter inoperative

Remain outside class D airspace until the direction of air traffic can be ascertained
Monitor the primary local control frequency as depicted on sectional charts for landing or traffic info.
Look out for light signals that may be directed to your aircraft
During hours of daylight, acknowledge tower transmissions or light signals by rocking your wings
At night, acknowledge by blinking landing of navigation lights

Transmitter & Receiver inoperative

Remain outside class D airspace until the direction of air traffic can be ascertained
Maintain visual contact with the tower and acknowledge light signals as above.

The light signals used for an aircraft in flight are as followssource:
Steady green - Cleared to land
Flashing green - Cleared to approach airport, or return to land
Steady red - Continue circling, give way to other aircraft
Flashing red - Airport unsafe, do not land
Alternating red and green - Exercise extreme caution
They can be seen in this video.


Is there a source of deicing holdover time tables?

Here are some holdover charts I have access to.


Why don't we use elevator trim as the primary flight control?

Proper trim control technique involves exerting control pressure to attain the desired attitude then using the trim to alleviate the requirement of holding that pressure. There can be a temptation for pilots to make small adjustments using trim alone. Resist the temptation and use the proper procedure.

We use the proper technique because it's the most precise way to use trim. If adjustments are made with the trim directly we'll end up over-controlling and chasing the correct trim position.

Trim isn't just a convenience. Especially for pilots flying in instrument conditions, alleviating the load of holding control pressure and ensuring that if the pilot lets go of the controls the airplane maintains its attitude are a matter of safety.

The Airplane Flying Handbook explains Trim Control starting on 3-6. It lists the proper technique in greater detail and provides a complete rationale.

There's also the matter of doing things the same way every time. Once we've established the right procedure, we should always use it to enforce the habit. This also benefits the pilot when things get busy. Proficient instrument pilots are experts in using trim effectively.

Predefined trim positions are impractical because they vary based on weight, CG, airspeed and other factors. These factors change the amount of downforce required on the elevator and therefore the trim position. Situations like "level at 8000" or "gliding descent" won't always result in the same trim position. For other control surfaces there are similar factors. We do have predefined trim positions for takeoff, but loading often makes those undesirable and trimming is required immediately.

During flight training, good trimming technique becomes especially important during instrument training. There's a lot of good information about trim and its importance in the Instrument Flying Handbook.


Could the Perlan II glider be used for nearspace tourism?

No, Perlan II can't be used for tourism.  It has only two seats, and every description of it talks about the crew of two, or the two pilots, or the chief pilot and co-pilot.  Someone who gets certified for the type and carries that much responsibility isn't called a tourist.


Is wing sweep needed on supersonic aircraft?

Sweep is not strictly required, but helpful to increase supersonic L/D. Just witness the length to which aircraft manufacturers went to sweep wings for Mach 2+ flight. However, sweep comes with its own set of problems.


When resetting the heading indicator to match the magnetic compass, do I need to use the compass deviation card?

Yes the DG is supposed to be set to the corrected magnetic indication whenever you set it, so you should mentally add or subtract the degree or two or three based on the closest segment on the card as a standard practice.

I agree with Michael however that it's not really that big a deal for VFR flying in the real world, especially in the age of GPS where you can just adjust heading based on GPS ground track on your phone or a tablet to go from A to B and you don't even really need to look at your compass (although, you might suddenly find you need it, so don't neglect it).

If you were doing old fashioned dead reckoning navigation, precision in holding a heading is important.  Or in the IFR world where you have to fly headings in a clearance.  Even there though, the allowable calibration error on a compensated (that is, WITH the deviation accounted for) compass is +/- 10 deg (!), so the little 2 or 3 degree calibration card can be quite a bit off anyway and still be legal.


Can anyone identify the plane in the image shown and/or year of service?

I think it may be a Bréguet 14. Compare it to this photograph:

You can see the same two sets of vertical struts on the wings, which are quite distinctive, and the wing looks like it has the same large flaps, plus the large forward tail section. The fuselage has the same two step holes (at least, I assume that's what they are) seen on this photograph, and the rear seat is also just visible.
The related Bréguet 16 was slightly larger, with three pairs of struts, so it's not one of those; there was also a related Bréguet 17 which seems to have been visually quite similar, but produced in much smaller numbers. I suspect it may be after the war, as it does not seem to have a gun in the rear seat, and the number on the tail doesn't seem to match the wartime style of numbering. They were still knocking around into the late 1920s/early 1930s.
Bréguet 14s were fairly widespread, but I think these look like French markings. However, I don't know enough to be able to speculate on what "N 9732" might indicate in that context.


With flight dynamic equations, how do I return to positive alpha if alpha is always negative with negative w?

I think your problem is in part, that you assume that $w$ is positive if your aircraft is ascending. The opposite is the case. The aircraft coordinate system is defined as a right-handed system with the z-axis pointing downward.

This means a positive $w$ indicates that your aircraft is descending.
Therefore, if your plane keeps a constant velocity $u$, the body-fixed downward velocity $w$ will get positive because of the gravity pulling you down. This in turn results in a positive $\alpha$ providing lift. Eventually if you have implemented your simulation correctly, the $\alpha$-angle (and $w$) will oscillate for a bit at the beginning of your simulation, but after finding the steady-state, it will steadily descend with a positive angle-of-attack and a positive value of $w$.
P.S.: For the calculation of $\alpha$ it is very helpful to use the atan2() function, as it correctly discerns the various sign cases.


What are the triggers of the MD-80's takeoff configuration warnings?

There are 7 conditions, not 5. The two you are missing are:

AUTO BRAKE
This warning is when the auto brake system (ABS) has detected a fault, or the system is not activated.
AUTO SPOILER
This warning is when the spoilers are not armed when the ABS is set to takeoff.

What flap setting triggers the warning?

  Flaps lever position does not agree with selected position in computer window.

Why slats and flaps have separate warnings?

While the flaps/slats handle is the same, there could be a mechanical reason the slats failed to extend properly, or a circuit breaker is pulled. Also historically, the earlier DC-9 from which the MD-80 is developed, had a handle that could be physically separated.

What stabilizer setting triggers the warning?

Same as flaps, when the position disagrees from the selected one in the computer (it varies from flight to flight based on the different conditions).

Source: MD-80 FCOM Section 6 Pages 76–77


In F/A-18, where the servo-loop closure is accomplished?

Ram position feedback is sent back to the relevant channel in one of the two flight control computers via wire carrying an analogue signal. If it is a leading edge flap, aileron or rudder it is done twice. The big surfaces (Trailing Edge Flap and Horizontal Stab) are quad redundant. The signal is processed on a printed circuit board inside the box. There is negative feedback occurring via an operational amplifier type circuit.


Was this a near collision or a normal procedure?

There is only 1000 ft of separation between levels of traffic at the altitudes jets operate in (above 29000 ft) and when you see someone 1000 ft above or below it looks really close.  When you are sitting in the flight deck the first time on a busy airway and oncoming traffic passes above or below, you think they are passing only a few hundred feet away even though they are 1000 ft.  When you first notice an oncoming contrail, it looks like it's coming straight at you until it's a mile or two away.

The Traffic Collision and Avoidance System (TCAS) on each airplane tells the crew the proximity and relative altitude of nearby traffic and the system gives warnings with directions to climb or descend if someone is on a collision path. Plus ATC knows everybody's altitude and the ATC computers provide warnings to controllers if an airplane deviates from an assigned altitude by more than a couple hundred feet.

It takes a lot to go wrong for airplanes to come too close to each other, although nothing is perfect and it can still happen.  The systems in place keep the probability to an acceptably low level.


To what extent (if any) is it possible or desirable for the pilot of a large airliner to "fly by the seat of the pants"?

I can believe that despite its size and weight a large airliner would respond precisely to commands, but does the concept "flying by the seat of the pants" apply to such an aircraft?

The phrase "flying by the seat of the pants" is an imprecise term, and I don't have an answer for that. However, if you allow it to mean operating an aircraft in the absence of instrumentation or other capability that is normally used, or using techniques not normally used, whether you're forced to because of failure(s) or because you prefer not to use them, then here is an observation.

In the early 1990s I was flying 747-100/200 freighters. The carrier had a contract with Japan Air Lines to haul freight between Tokyo Narita and KJFK, with a crew change and refueling at Anchorage. We used a JAL call sign. JAL had their own 747-200 freighters on the route as well, more of them than our small number of aircraft. Many of their flights would have an American flight engineer who would handle the radio going into U.S. airports. Thus, the Anchorage controllers could not tell from the radio communication whether the flight had American or Japanese pilots.

One summer Anchorage took the ILS down for extended maintenance. One severe clear day during this period we were on our descent but still well out when Anchorage approach cleared us for a VOR approach. We immediately called the airport in sight and requested a visual approach, which was granted.

Curious, when we were down I called approach control on a land line and asked why we were first assigned a VOR approach. They explained that, believing our flight probably had Japanese pilots, and having had those pilots always refuse the offer of a visual approach and request a VOR approach (in spite of the additional 10 minutes of flying), approach control had simply assigned the VOR approach.

As part of our contract, we occasionally had a Japanese check captain observe us, and the next time this happened, I brought up the subject with him. He explained that their pilots were never taught to simply look at a runway and land without reference to navigational instruments, and, lacking a robust general aviation segment, their pilots simply never had experience with doing that. He added that from their standpoint, we were a bunch of cowboys. Not the exact "flying by the seat of the pants" wording, but the same sentiment.

  Obviously experience and training will build up a great deal of intuition (visual, vestibular, etc) - what sort of bodily connection does an airline pilot experience with the aircraft? Is it markedly different from that of the pilot of a small plane?

When you're flying the same airplane type day in and day out, you internalize what that aircraft can do and how it will respond. You get used to its noises and even to its vibrations if you will. And regardless of how small or how large it is, it becomes the right size, neither little nor big, especially once you're in the air. When you change airplanes, and especially if it involves a significant change in size, there is a difference.

For example, I spent the last 10 years of my career on 747-100/200 aircraft. Fifteen years after retiring, and not having been in a cockpit during that time, I went out to a local airport to check out in a Cessna 172. I knew I would have trouble with flaring too high, and I warned the instructor. My first landing was a real lesson, actually to both of us. When I said to him, "I think I should flare," he said, "you're way to high." When I said, "I've got to flare,: he said, "still too high." When I said, "I'm flaring," with the sense that if I didn't I would prang the airplane, he said, "you're still a little high, but go ahead." It took me 5 hours to check out in the airplane, most of that time for landings.


How do aircraft rental companies charge while the plane is not flying?

Flying clubs and aircraft renters generally only charge for the time the plane is actually in use. In the U.S. at least, this is commonly measured using the Hobbs time (actual clock time used, triggered by oil pressure or some other indicator that the plane is "in use"), or by Tach time, which is a bit trickier but can very roughly be thought of as the amount of wear you've put on the engine. (Strictly speaking it's a count of the number of engine revolutions, converted to "hours at cruise RPM".)

For overnight or longer trips, it's common to find a minimum hourly usage per day. For example, if you take a plane on a 3-day trip, and your club/owner requires 2 hours/day, you will be paying for 2 x 3 = 6 hours of Tach / Hobbs / whatever time, even if you didn't actually use the plane that much. You'll pay for the higher of your actual usage or your minimum usage per day.

It's extremely rare in the U.S., but not unheard-of, to encounter an extra fixed fee per day for taking the airplane for more than one day. (I've never personally encountered a fixed fee like this.) I'm not sure if things are different in the U.K.

Hourly rates can also either be "wet" (the rate includes fuel: any amount you pay for fuel will be deducted from your rental fee when you return) or "dry" (the rate includes the airplane only and you must pay for fuel). "Dry" rentals may or may not also require you to pay for oil or other consumables used.

(This is general information. Of course, if your question is specifically about Fly ASG's policies and fee scales, your best bet is to contact them directly. I know nothing about them.)


Why do airliners have "pressure bulkheads"?

What part aft of the bulkhead would leak pressure?

That's a partial misunderstanding of what a bulkhead is there for.

You could build the aft cone section to keep the pressure, but it would be a much heavier solution.

The shape of the final aft section is not well suited to resist pressurization stresses: the best shape is a sphere; the cylinder (with spherical terminations) comes a close second. The conical shape would require serious stiffeners to survive pressurization cycles for the whole life of the aircraft; the bulkhead solves this problem by using a shape that is naturally more resistant to stresses - and thus can be built with less material - leading to less weight, and hence fuel savings (in addition to the increased safety).


Is there a penalty for changing the approach procedure after accepting one?

There is no penalty per se, but visual approaches in particular have lower separation requirements, so having to switch you back to a non-visual approach may require ATC to make corrections (e.g. delay vectors, speed control or, in extreme cases, a missed approach), which may feel like a penalty.


What is an FAA Notice? Does it have legal force?

As SSumner pointed out, the FAA produces all kinds of paper - some of which is "regulatory" and/or have legal force, and some of which isn't.  I won't go into all of the specific document categories, but I'll talk about a few that most of us will find interesting.

Handbooks and Manuals
The FAA actually publishes full-length books, if you know where to look!
The FAA has written books on flying an airplane,  flying balloons, risk management, buying & owning an airplane, and a whole bunch of other topics which provide broad information that you can use to familiarize yourself with a topic.
Advisory Circulars
Advisory Circulars (ACs) are the FAA's way of explaining their regulations.
They're broken down into sections which generally match up with the FARs they're interpreting.  Some ACs may rival the lengths of handbooks, but they are much more narrowly focused, generally dealing with a single topic and often much easier to understand than the legislation they're interpreting.
Airworthiness Directives
When an unsafe condition is identified in an aircraft or component which requires action the FAA can issue an Airworthiness Directive (AD), requiring that specific actions be taken.
Often the required action is compliance with a manufacturer's Service Bulletin (or compliance with a service bulletin is also an acceptable method of compliance with an AD).
There are also Special Airworthiness Information Bulletins (SAIBs), which are like "Mini-ADs": The FAA is calling operators' and mechanics' attention to something which may not merit an AD. SAIBs are informational - you don't have to comply with them - but it's certainly a good idea to read them and pay attention to the things they're highlighting.
Orders
An "Order" describes procedures used by the FAA. For example, JO 7110.65U describes various aspects of how ATC works.
Procedures described in Orders may be modified by Notices.
Notices
A "Notice" is just an agency's way of saying "Yo! Pay attention! Something's happening!"
Your question seems generally concerned with internal notices which I linked to in the title. These generally modify Orders, like this one.
The FAA can also issue "Public Notices" about changes that affect airmen and the   general public, or pretty much any other topic they'd like.  Public Notices are published on faa.gov as well, but the easiest place to find those is through the FAA Safety Team's SPANS system which is searchable and has a much nicer interface than digging through the FAA site by region.

As for whether the non-legislative documents have legal force the answer is a very well-qualified "maybe".  Some certainly have the force of regulation – Airworthiness Directives being the most obvious – and for our purposes I think that's what you're really concerned with, because the law says you have to comply with the regulations.
Orders and Notices are similarly "regulatory" for the agency: The FAA has to comply with its own orders, so ATC has to be operated the way JO 7110 says it's to be operated.

For stuff like ACs, Handbooks, etc. we discussed this in chat a while back talking about the answer to FAA Order 8900 and the FSMS - the gist of it is that the non-legislative documents the FAA produces are generally interpretations and guidance, but they are "effectively regulatory" in that if you go against them you need to have an excellent reason for doing so, and be prepared to back it up with appropriate justification and evidence if asked.

As a classic example, alterations to aircraft are expected to be performed in accordance with manufacturer's maintenance procedures, or "other methods, techniques, or practices acceptable to the Administrator" which are described in AC 43.13 (43.13-2B deals with light, non-pressurized aircraft and is an interesting read).

A mechanic doesn't have to comply with the guidance in AC 43.13, but if a mechanic were to modify an aircraft without conforming to that guidance they would need to supply supporting documentation as to why their work is acceptable, such as a statement from a Designated Engineering Representative, otherwise the FAA could deem the work "unacceptable" (and from a liability standpoint, the mechanic could wind up in serious trouble should something go wrong with the aircraft as a result of that work).


Why must some 'dangerous items' be in check-in baggage?

Generally, "dangerous" things that might be used as weapons are required to be kept out of the cabin. For instance, you can have firearms in checked baggage, but not carried in the cabin.

Given what's been learned about terrorist planning, there were plots to bring liquids on board an aircraft that could be combined to form an explosive. To counter that threat, the amounts & types of liquids that can be brought on board have been limited. Since the liquids in isolation are safe, they're allowed in normal quantities in checked luggage.

In the case of Lithium Ion batteries, the concern is less their use as a weapon, and more about a defective battery catching fire. If this were to happen in a cargo hold, the fire would cause other things to start burning as well before the cargo smoke detectors alert the crew to what's going on. So the priority is to keep lithium ion batteries out of the cargo hold. They're allowed in the cabin (with some restrictions) since you're pretty likely to notice your cell phone getting hot & smoking if it's in your pocket, and with that sort of early notice, the fire can be dealt with before it's caught large volumes of material on fire as well.

At least that's the theory. I don't know how many times it's been put to the test. In at least two cases (the Samsung Note 7 phone, and hover boards), devices which are considered to be at high risk of catching fire are simply kept off the aircraft altogether.


What are the rules regarding (HUD) Head-up displays, especially glasses type?

You can read about some guidance from the FAA about HUD design in these two Advisory Circulars:

General electronic displays
Enhanced Flight Vision Systems

This handbook is a bit dated but covers certification.

It really depends on what exactly the HUD is supposed to do. Any pilot can bring a handheld GPS along, with the understanding that it is not an "official" navigation instrument. A HUD could be used in a similar way. There are a couple things to keep in mind:

If the HUD is to be used for real navigation or pilot reference, then certification will be an issue. The handbook above talks about this. The HUD would need to be certified just like any other instruments in the cockpit for that use. If a HUD is used for special situations, like low visibility landing, it must be certified in order to be used in those situations. Otherwise you are not allowed to do anything you could not do without the HUD.

Even if the HUD is not to be used for critical flight data, the HUD needs to comply with the FAR 25 sections 25.773 and 25.775, which talk about the windows in the cockpit. The HUD can't interfere with the normal visibility the pilot should have.


Has this type of "gyrocompass" ever been used in an aircraft?

I think the answer is "no and yes".  Bear with me...  That sort of device as a stand alone heading sensor has never been used in an aircraft and if you parse the Wikipedia article carefully it becomes apparent why, under the paragraph titled "Errors".

  A gyrocompass is subject to certain errors. These include steaming error, where rapid changes in course, speed and latitude cause deviation before the gyro can adjust itself.[12] On most modern ships the GPS or other navigational aids feed data to the gyrocompass allowing a small computer to apply a correction. Alternatively a design based on a strapdown architecture (including a triad of fibre optic gyroscopes, ring laser gyroscopes or hemispherical resonator gyroscopes and a triad of accelerometers) will eliminate these errors, as they do not depend upon mechanical parts to determinate rate of rotation.[13]

To work it requires a very slow moving and stable platform (like a ship). Anything approaching rapid motion, even by ship standards, let alone by aircraft standards, requires external help of some kind.

This rules out aircraft, and small boats for that matter I expect.

"Gyrocompass" in aviation has always referred to a directional gyro that is continuously slaved to an external magnetic north sensor.  The traditional system has some form of directional gyro, either right in the instrument panel or built into an Attitude/Heading Reference System (AHRS) unit that drives the cockpit heading indication, with the actual magnetic field sensor in a remote location, usually out at the wing tip, called a Flux Valve, that provides a continuous magnetic north reference, to which the gyro is aligned.

When not slaved to the Flux Valve, an aircraft gyrocompass becomes just a directional gyro, which must be set manually and corrected for precession manually (on an AHRS system you will have a MAG/DG switch that allows you to select slaved or unslaved indications - in the high arctic where compass indications are useless, you have to operate in DG mode).

Now, I said "stand alone" for a reason. Inertial Reference Systems (or Inertial Navigation) used for aircraft navigation do use this phenomenon for their initialization alignment process.  IRS initialization/alignment is done normally on the ground with the aircraft stationary, but can also be done in flight if heading is held steady during the alignment. The system is told where the aircraft is geographically, by entering lat/long or by GPS/FMS input if equipped, and the IRS senses precession from the earth's rotation to figure out what direction the airplane is pointed relative to true north (because it can sense the west-east axis of the earth's movement and knows the airplane longitudinal axis relative to that).  This is how IRS systems get their directional starting point, from which future indications are derived from inertial changes from the starting point.  If inertial errors build up in the system (you get left right IRS position comparator errors), the system has to be aligned again (which is why there is usually a procedure to do an "IRS Align" in flight where you fly a constant heading, speed and altitude for several minutes while the IRS does its thing).

So the answer is, yes, but limited to IRS systems when starting up, and no as a stand-alone heading device.


What is transmitting this radio signal @~110.515MHz and for what purpose?

Well, the SDR dongle paid off - mystery solved.

It turns out, the signal was actually at 153.2MHz, but was somehow breaking through into 110.515MHz on my handheld scanner.

The signal originates from a high power pager transmitter using the FLEX protocol. As this is plain text, I decoded some of it using an excellent open source application called PDW, and have listed it below for reference and general interest (sensitive information has been redacted!).

  0074162  23:12:31 30-06-15 FLEX-A    ALPHA   3200   31:Jun 30 23:11 Trim Line 2 L359 Error Check 01 Override 010312 30-JUN-2015 23:10:49
  0000002  23:12:56 30-06-15 FLEX-A    ALPHA   3200   THIS IS A TEST PERIODIC PAGE SEQUENTIAL NUMBER  0069
  0121518  23:12:59 30-06-15 FLEX-A    StNUM   3200   31948
  1734139  23:13:01 30-06-15 FLEX-A    ALPHA   3200   61:Jun 30 23:12 Term B  Page-fail test
  1756286  23:13:24 30-06-15 FLEX-A    ALPHA   3200   PIN 6840 PLS CALL DSCC ON 08457 500***
  0118459  23:13:46 30-06-15 FLEX-A    ALPHA   3200   20150630 23:13 boc1web02.servstream.com: conn CRITICAL ALERT
  0000002  23:14:03 30-06-15 FLEX-A    ALPHA   3200   THIS IS A TEST PERIODIC PAGE SEQUENTIAL NUMBER  0070
  1734139  23:14:09 30-06-15 FLEX-A    ALPHA   3200   62:Jun 30 23:13 Term B  Page-fail test
  0076963  23:14:29 30-06-15 FLEX-A    ALPHA   3200   55:Jun 30 23:13 23.13hrs Zone 14 L550 down 15 Mins maint in attendance FROM: GB50-AFENNEL3
  0074162  23:14:46 30-06-15 FLEX-A    ALPHA   3200   32:Jun 30 23:13 Trim Line 2 L359 Error Check 01 Override 010312 30-JUN-2015 23:12:42
  0074179  23:14:48 30-06-15 FLEX-A    ALPHA   3200   19:Jun 30 23:13 Z2A LH Stn 200  Main Call 30-JUN-2015 23:13:22
  0074194  23:14:50 30-06-15 FLEX-A    ALPHA   3200   56:Jun 30 23:13 23.13hrs Zone 14 L550 down 15 Mins maint in attendance FROM: GB50-AFENNEL3 FROM: GB50-AFENNEL3
  0107291  23:14:50 30-06-15 FLEX-A    StNUM   3200   2422085
  0074076  23:14:50 30-06-15 FLEX-A    ALPHA   3200   60:Jun 30 23:13 Fac 1670 More than 20 I/P on conv 30-JUN-2015 23:11:30
  0086317  23:14:52 30-06-15 FLEX-A    ALPHA   3200   36:Jun 30 23:13 Dodo Panel 23 Entry Movement Alarm 000065 30-JUN-2015 23:12:03
  0000002  23:14:56 30-06-15 FLEX-A    ALPHA   3200   THIS IS A TEST PERIODIC PAGE SEQUENTIAL NUMBER  0071
  0067432  23:14:59 30-06-15 FLEX-A    ALPHA   3200   71:Jun 30 23:14 Water Test WATER TEST SUMP LEVEL HIGH 001215 30-JUN-2015 23:14:46
  1754937  23:15:16 30-06-15 FLEX-A    ALPHA   3200   'Adv' 7440298 30/06/2015 23:08:33 tight chest, struggling to breathe, EMAS ETA 11 mn, Priority RED2 Age 59 Incident area - KETTERING ** ****** ** NN16 ***
  0067432  23:15:22 30-06-15 FLEX-A    ALPHA   3200   72:Jun 30 23:14 Skid RETURN PROBLEM CHECK SKID RETURN Tested o.k. 30-JUN-2015 23:12:25
  1734139  23:15:24 30-06-15 FLEX-A    ALPHA   3200   63:Jun 30 23:14 Term B  Page-fail test
  0086317  23:15:44 30-06-15 FLEX-A    ALPHA   3200   39:Jun 30 23:14 Dodo Panel 6 P&F Emergency Stop relay 125KN1 - 400301.08 30-JUN-2015 23:13:32
  1734136  23:15:46 30-06-15 FLEX-A    ALPHA   3200   19:Jun 30 23:14 Term A  Page-fail test
  0067154  23:15:50 30-06-15 FLEX-A    ALPHA   3200   Fr:nocteam Su:Escalate PQV-73575-125 Tx:Auto escalation of ticket (3 hour rule) Ticket: PQV-73575-125 Queue: VelociX Date raised: 2015-06-30 20:11:27 Subject: ANTEL New asset request
  0117556  23:15:54 30-06-15 FLEX-A    ALPHA   3200   PLS CALL DUTY OFFICE
  0000002  23:16:03 30-06-15 FLEX-A    ALPHA   3200   THIS IS A TEST PERIODIC PAGE SEQUENTIAL NUMBER  0072
  0111087  23:16:07 30-06-15 FLEX-A    StNUM   3200   71301
  0118459  23:16:16 30-06-15 FLEX-A    ALPHA   3200   20150630 23:15 boc1backup.siops.net: msgs CRITICAL ALERT
  1734139  23:16:31 30-06-15 FLEX-A    ALPHA   3200   64:Jun 30 23:15 Term B  Page-fail test
  0074208  23:16:37 30-06-15 FLEX-A    ALPHA   3200   69:Jun 30 23:15 Warning : BODY DELIVERY STN 1 OVERCYCLE * BD SKID BD SKID (52)
  1734136  23:16:54 30-06-15 FLEX-A    ALPHA   3200   20:Jun 30 23:16 Term A  Page-fail test
  0074221  23:16:54 30-06-15 FLEX-A    ALPHA   3200   09:Jun 30 23:15 Warning : BODY DELIVERY STN 1 OVERCYCLE * BD SKID BD SKID (53)
  0120075  23:16:56 30-06-15 FLEX-A    ALPHA   3200   PLS CALL 12F ON 42848 2ND CALL
  1734139  23:17:39 30-06-15 FLEX-A    ALPHA   3200   65:Jun 30 23:16 Term B  Page-fail test
  1756806  23:17:41 30-06-15 FLEX-A    ALPHA   3200   PLS CALL ***** ***** - ADDENBROOKES ON 01223 257 ***
  0121619  23:17:42 30-06-15 FLEX-A    ALPHA   3200   P2 TS 3170
  0074162  23:17:46 30-06-15 FLEX-A    ALPHA   3200   34:Jun 30 23:16 Trim Line 2 L359 Error Check 01 Override 010312 30-JUN-2015 23:15:30
  1728604  23:18:05 30-06-15 FLEX-A    ALPHA   3200   41:Jun 30 23:17 ****** ******** 07711 239 ***
  0067432  23:18:07 30-06-15 FLEX-A    ALPHA   3200   73:Jun 30 23:17 Conv 11 Conv 1 Starved Load stn Blocked 30-JUN-2015 23:14:55
  0090980  23:18:07 30-06-15 FLEX-A    ALPHA   3200   30/06/2015 23:15:02 INC 14517765 ETFR Countess of Chester Hospital Chester Cheshire -, THE COUNTESS OF CHESTER HEALTH PARK, CHESTER, CH2 *** Male 25Y ProQA Overrid
  0090980  23:18:09 30-06-15 FLEX-A    ALPHA   3201   [Continued message - Fragment #2]den - Call Escalated GRD 340129 368274
  0067432  23:18:09 30-06-15 FLEX-A    ALPHA   3200   74:Jun 30 23:17 Conv 11 Conv 1 Starved Load stn Blocked 30-JUN-2015 23:14:55
  0067432  23:18:11 30-06-15 FLEX-A    ALPHA   3200   75:Jun 30 23:17 Water Test BOOTH 2 LOW / HI WATER PRES30100230 KU-.2N1u013 (?E4
  0118459  23:18:11 30-06-15 FLEX-A    ALPHA   3200   30 23:17]X[??Xns01.siops.net: dnPyt7xyICAL ALERT
  0114910  23:18:13 30-06-15 FLEX-A    ALPHA   3200   40:Jun 30 23:17 PLS CALL LEAH ON EXT 31505
  0119227  23:18:16 30-06-15 FLEX-A    ALPHA   3200   42:Jun 30 23:17 PLS CALL DUTY NURSE 020 7561 ****
  0120151  23:18:27 30-06-15 FLEX-A    ALPHA   3200   PLS COME TO CAVENDISH UNIT
  0118459  23:18:46 30-06-15 FLEX-A    ALPHA   3200   20150633 27z1b"bocm$n:th4Cp
  1743989  23:18:46 30-06-15 FLEX-A    ALPHA   3201   [Continued message - Fragment #2]
                                                          WN i$*CHER 01226 872 199 REajlFE AT POST OFFICE WONPi OCK AND IS WIDE OPEN*?f
  1756806  23:18:48 30-06-15 FLEX-A    ALPHA   3200   PLS CALL ***** ***** - ADDENBROOKES ON 01223 257 ***
  1734139  23:18:54 30-06-15 FLEX-A    ALPHA   3200   66:Jun 30 23:17 Term B  Page-fail test
  0000002  23:18:56 30-06-15 FLEX-A    ALPHA   3200   THIS IS A TEST PERIODIC PAGE SEQUENTIAL NUMBER  0075
  1734136  23:19:16 30-06-15 FLEX-A    ALPHA   3200   22:Jun 30 23:18 Term A  Page-fail test
  0067432  23:19:22 30-06-15 FLEX-A    ALPHA   3200   76:Jun 30 23:18 Conv 11 Conv 1 Starved Load stn Blocked 30-JUN-2015 23:16:09
  0067432  23:19:24 30-06-15 FLEX-A    ALPHA   3200   77:Jun 30 23:18 Conv 11 Conv 1 Starved Load stn Blocked 30-JUN-2015 23:16:09
  0076517  23:19:26 30-06-15 FLEX-A    ALPHA   3200   38:Jun 30 23:18 Conv 21 Check Zone Start Pulse Count 30-JUN-2015 23:19:15
  0114375  23:19:26 30-06-15 FLEX-A    ALPHA   3200   30:Jun 30 23:18 Conv 21 Check Zone Start Pulse Count 30-JUN-2015 23:19:15
  0076956  23:19:27 30-06-15 FLEX-A    ALPHA   3200   97:Jun 30 23:18 Conv 21 Check Zone Start Pulse Count 30-JUN-2015 23:19:15
  1734139  23:20:01 30-06-15 FLEX-A    ALPHA   3200   67:Jun 30 23:19 Term B  Page-fail test
  0000002  23:20:03 30-06-15 FLEX-A    ALPHA   3200   THIS IS A TEST PERIODIC PAGE SEQUENTIAL NUMBER  0076
  0074162  23:20:09 30-06-15 FLEX-A    ALPHA   3200   36:Jun 30 23:19 Trim Line 2 L359 Error Check 01 Override 010312 30-JUN-2015 23:18:09
  0114910  23:20:13 30-06-15 FLEX-A    ALPHA   3200   41:Jun 30 23:19 PLS CALL **** ****** ON EXT 34335
  1734136  23:20:31 30-06-15 FLEX-A    ALPHA   3200   23:Jun 30 23:19 Term A  Page-fail test
  0102150  23:20:33 30-06-15 FLEX-A    StNUM   3200   0778
  0000002  23:20:56 30-06-15 FLEX-A    ALPHA   3200   THIS IS A TEST PERIODIC PAGE SEQUENTIAL NUMBER  0077
  1734139  23:21:09 30-06-15 FLEX-A    ALPHA   3200   68:Jun 30 23:20 Term B  Page-fail test
  0076517  23:21:14 30-06-15 FLEX-A    ALPHA   3200   39:Jun 30 23:20 Conv 21 Check Zone Start Pulse Count 30-JUN-2015 23:21:02
  0119626  23:21:18 30-06-15 FLEX-A    ALPHA   3200   34:Jun 30 23:20 Conv 21 Check Zone Start Pulse Count 30-JUN-2015 23:21:02
  0102150  23:21:18 30-06-15 FLEX-A    StNUM   3200   0775899******
  0076956  23:21:20 30-06-15 FLEX-A    ALPHA   3200   98:Jun 30 23:20 Conv 21 Check Zone Start Pulse Count 30-JUN-2015 23:21:02
  0200905  23:22:34 30-06-15 POCSAG-3  ALPHA   1200   23:22-98 30/06/2015 23:20:18 INC 14517787 31C02 ************, ELLESMERE PORT, CH65 *** Male 64 Years M PASSING OUT GRD
                                                      340506 375692
  0334410  23:23:50 30-06-15 POCSAG-3  ALPHA    512   23:22-41 C2 Incident Allocated, Locn: *****, GREENACRES CARE CENTRE, TEARN ROAD, PL35JF, , AZ:, CAD:300615005110, ChComp:
  1508907  23:23:51 30-06-15 POCSAG-4  ALPHA    512   CH3A 512
  0273040  23:24:04 30-06-15 POCSAG-4  ALPHA   1200   30/06/2015 CH3A
  0269168  23:24:20 30-06-15 POCSAG-3  ALPHA   1200   23:24-10 30/06/2015 23:22:15 INC 14517792 10D02 ***********, NEWBOLD ROCHDALE ROCHDALE, OL16 *** Female 24 Years
                                                      MIGRAINE - FEELS SICK GRD 390789 412576


What does an owner/operator need to do to legally rent out their aircraft?

As Farhan noted, the rules are essentially the same as if you buy a plane to provide instruction in it.

Inspections and Maintenance

In addition to your required annual inspection you will also be required to complete a 100-hour inspection every 100-hours of operation.

Insurance

You will need a commercial insurance policy which allows you to rent the aircraft.
This policy covers the aircraft, so you will also need (or at least want) general liability insurance and all the other trimmings that come with operating a business.

Everything Else

This is a broad category. There's no way we can cover it all. You will however need to consider:

Maintaining an adequate stock of "service spares" to maintain the aircraft.
Tires, light bulbs, oil, oil filters, 5606 hydraulic fluid, etc. - As an individual owner you may be OK with being down for a week waiting for parts, but as a rental operation that will lose you customers.
Having a relationship with a mechanic to do the maintenance
Owner-Performed Preventive Maintenance goes out the window when the aircraft becomes a rental - you may still be able to assist your mechanic, but you can no longer do & sign-off on things like oil changes.
Vetting your renters
Rental aircraft at an FBO/Flight School live a hard life. If you like your plane and want it to stay in good condition you'll need to vet your renters a bit more thoroughly than "You have a pilot's license and you went around the pattern without hitting anything" - Find the kind of pilots who will police their trash from the cabin, lean the mixture appropriately, etc.


Why does a hydraulic system failure increase the landing distance?

Any hydraulic failure will affect the landing distance as most of aircraft controls are operated by hydraulics.

If the high lift devices (flaps) become inoperative (or become degraded) due to hydraulic failure, the aircraft will have a higher approach speed, which will increase the landing distance.
Hydraulics are also used for operating a number of other systems like brakes, ground spoilers and thrust reversers. Any degradation in their operation will increase landing distance.


How to determine the compressive force in the spars of a strutted wing?

It's very easy. Consider that the point at which the strut is attached does not accelerate, i.e., the forces in all directions exactly even out.

The force in the spanwise direction exerted by the strut is

$$F_{strut}^{spanwise}=\cos\theta\cdot F_{strut}$$

This force must be balanced by the wing in compression, so the above expression is also valid for the amount of compression on the wing.

This assumes the strut only transfers longitudinal forces, while in reality it may have some bending stiffness. Also, I'm not sure where you got your equation for the tension in the strut, but it's not necessarily true (there's a lot more structural members exerting a vertical force on the wing, so the force- and moment balance is not as simple).


What is the Eights on Pylons maneuver intended to demonstrate about a pilot's skillset?

The maneuver tests the ability of the pilot to hold precise altitude and airspeed. You need to make constant small corrections when flying into and away from the wind. In my opinion, it is the most difficult of the Commercial maneuvers.
Garry Wing has a good explanation of the technique.
As Garry Wing explained in the video. If you don’t hold precise altitude and groundspeed the point moves. So as the wind increases upwind it lowers your groundspeed requiring a lower pivotal altitude. Downwind you will increase your groundspeed requiring a higher pivotal altitude. So you need to remain coordinated, constantly vary the altitude, scan for traffic, and maintain situational awareness of your location around the pylons.
Your airspeed will vary a bit as you climb and descend and head into and away from the wind, but if you can’t maintain a consistent groundspeed your pivotal altitude will change and that will throw off the whole maneuver. As you can see in the chart below, if your groundspeed varies by 4 kts from 87 to 92 kts the pivotal altitude changes by 65'. This is the part of the maneuver that requires precise control of airspeed and altitude with coordinated use of the rudder and ailerons.

The FAA explains it well in Airplane Flying Handbook:

Eights-on-Pylons
The eights-on-pylons is the most advanced and
difficult of the ground reference maneuvers. Because of the techniques
involved, the eights-on-pylons are unmatched for developing intuitive
control of the airplane. Similar to eights around pylons except
altitude is varied to maintain a specific visual reference to the
pivot points.
Chapter Summary
At the completion of ground reference maneuvers, the
pilot should not only be able to command the airplane to specific
pitch, roll, and yaw attitudes but, while correcting for the effects
of wind drift, also control the airplane’s orientation in relation to
ground-based references. It should be reinforced that safety is
paramount in all aspects of flying. Ground reference maneuvers require
planning and high levels of vigilance to ensure that the practice and
performance of these maneuvers are executed where the safety to groups
of people, livestock, communities, and the pilot is not compromised.
To master ground reference maneuvers, a pilot must develop
coordination, timing, and division of attention to accurately maneuver
the airplane in reference to flight attitudes and specific ground
references. With these enhanced skills, the pilot significantly
strengthens their competency in everyday flight maneuvers, such as
straight-and-level, turns, climbs, and descents.


Which type of chevrons is applied on the B787?

Strictly speaking, its neither. Chevrons don't resemble either a sawtooth wave or a sine wave in mathematical terms. The closest is that it is a smoothed (modified) saw tooth form.

Image from compositesworld.com
Though the initial research used a serrated nozzle in saw tooth form, the final commercial application differs from it. However, the chevrons are repeatedly noted as having a saw tooth form, by NASA among others:

One of the most recent noise-reducing technologies shepherded through the research process by NASA and now making a difference on commercial jet engines is chevrons.
Chevrons are the sawtooth pattern seen on the trailing edges of some jet engine nozzles.

So, it's a choice between saw tooth and sine wave, its better to go with the former.
GE's patent for the Chevron describes the shape as triangular with qualifications:

... each of said chevrons being triangular in configuration
... said chevrons having a compound concave contour both axially between said bases and apexes and laterally between said trailing edges..

Image from Chevron exhaust nozzle for a gas turbine engine


Do airlines in the US or UK have to pay fuel taxes?

In the US, yes.

Kerosene [for use in aviation] is taxed at $0.244 per gallon unless a reduced rate applies.
These taxes mainly fund airport and Air Traffic Control operations by the Federal Aviation Administration (FAA), of which commercial aviation is the biggest user (Fuel taxes in the United States).

More information from taxfoundation.org.

In the UK, it depends on the user.

Aviation turbine fuel used for private pleasure flying: £0.5795 per litre
Aviation gasoline (Avgas): £0.3770 per litre

Air transport is exempt.
Furthermore:

Article 24 of the [1944 Convention of International Civil Aviation] requires all contracting states not to charge duty on aviation fuel already on board any aircraft that has arrived in their territory from another contracting state. Further to this, the exemption of airlines from national taxes and customs duties on a range of aviation-related goods, including parts, stores and fuel is a standard element of the network of bilateral ‘Air Service Agreements’ (ASAs) between individual countries.


Are the size and location of the registration number regulated?

Under FAA jurisdiction, these items are regulated under 14 CFR 45.

The size of the registration markings must generally be at least 12 inches high:

  §45.29

  (a) Except as provided in paragraph (f) of this section, each operator of an aircraft must display marks on the aircraft meeting the size requirements of this section.

  (b) Height. Except as provided in paragraph (h) of this part, the nationality and registration marks must be of equal height and on—

  (1) Fixed-wing aircraft, must be at least 12 inches high

The markings must be displayed on either the vertical tail surfaces or the sides of the fuselage.

  §45.25

  (a) The operator of a fixed-wing aircraft must display the required marks on either the vertical tail surfaces or the sides of the fuselage, except as provided in §45.29(f).

  (b) The marks required by paragraph (a) of this section must be displayed as follows:

  (1) If displayed on the vertical tail surfaces, horizontally on both surfaces, horizontally on both surfaces of a single vertical tail or on the outer surfaces of a multivertical tail.

  (2) If displayed on the fuselage surfaces, horizontally on both sides of the fuselage between the trailing edge of the wing and the leading edge of the horizontal stabilizer. However, if engine pods or other appurtenances are located in this area and are an integral part of the fuselage side surfaces, the operator may place the marks on those pods or appurtenances.

There are exceptions to these requirements, but these exceptions will not generally apply to the modern airliners referenced in your question.

While the regulations do not prohibit it, I think it would be unusual for the registration to be displayed in more than one location on a given side of the aircraft—for example, on both the tail and the fuselage.

Under ICAO requirements, these items are described under Annex 7.

Annex 7, paragraph 3.3.1 includes the additional requirement for heavier-than-air aircraft that the registration markings should be displayed on the lower surface of the wing structure.

  3.3.1 Wings. On heavier-than-air aircraft the marks shall
  appear once on the lower surface of the wing structure. They
  shall be located on the left half of the lower surface of the
  wing structure unless they extend across the whole of the
  lower surface of the wing structure. So far as is possible the
  marks shall be located equidistant from the leading and trailing
  edges of the wings. The tops of the letters and numbers shall
  be toward the leading edge of the wing.

The FAA has no such requirement, but other jurisdictions do, such as the UK's CAA, which is effectively identical to the ICAO guidance.

The ICAO size requirements for heavier-than-air aircraft are similar to FAA requirements, with the obvious exception of the wing markings. These requirements are found in Annex 7, paragraph 4.2:

  4.2.1 Wings. The height of the marks on the wings of
  heavier-than-air aircraft shall be at least 50 centimetres.

  4.2.2 Fuselage (or equivalent structure) and vertical tail
  surfaces. The height of the marks on the fuselage (or
  equivalent structure) and on the vertical tail surfaces of
  heavier-than-air aircraft shall be at least 30 centimetres.

Note that 30 centimetres is approximately equivelant to 12 inches, and 50 centimetres is approximately equivelant to 20 inches.


How much leverage do commerial pilots have on cruise speed?

There is something called the "Cost Index" - it is basically how you choose between speed and fuel economy. Company dispatchers, after knowing that a flight has been delayed, will calculate this value, and the pilots simply input the updated value into the FMC (Flight Management Computer). That will instruct the autopilot to output more thrust, i.e. fly faster, but less fuel efficient.


Why is not every airplane equipped with 3 angle-of-attack sensors?

Triple redundancy is necessary to detect a fault and exclude it. The system then continues to operate through the fault. Double redundancy is used to detect a fault but cannot exclude it, so the system stops operating. The important fact is that the faults they actually detect are identical.

Stall events are rare and are normally not expected in flight. There is no immediate hazard if handling augmentation or stall warnings are disabled. Therefore, there is no need for triple redundancy.

Simply put, if the system detects an AoA discrepancy, it can simply trip off and stay off until it is repaired on the ground.

If the double redundant system is ideally designed, then only a simultaneous fault will escape detection. Note too that if the same simultaneous fault occurs to two sensors in a triple redundant system, then it will also escape detection because it will outvote the correctly operating sensor. Therefore, both systems share the exact same failure mode.

Double and triple simultaneous faults can and do occur with common causes including environmental factors (AF 447), maintenance errors (XL 888), and birdstrikes (US 1549). It also allows faults in the voting logic (QF 72). Both recent AF and XL fatal accidents are signs of an overreliance of buying 3 of the same box and then calling it "safe".


What is the FAA's source for the type designators they use in IACRA?

Try this.

This is the FAA's Type Certification Data Base, which lists all type certificates issued by the FAA.

Note:  this only covers certified aircraft and not experimental or homebuilts.

http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgMakeModel.nsf/Frameset?OpenPage


What is the purpose of having different ILS categories?

Instrument landing system - ILS - is a very common precision approach system used in airports around the world. An ILS consists of two ground antennas and an airborne received in the aircraft. One of the ground antennas, known as a localiser, transmits a narrow beam along the runway, giving lateral guidance to aircraft approaching the runway. The other antenna, the glide slope, transmits a vertical beam at a specified angle, giving vertical guidance for aircraft approaching. Together, the localiser and glide slope provides aircraft with an exact path to follow toward the runway.

A localiser antenna

The main advantage of ILS is that is allows approaches and landings in poor weather conditions. Pilots do not have to visually see the runway until moments before touchdown, because the ILS can guide the plane down very precisely. However, there are different standards of ILS. These are named CAT I, CAT II and CAT III (CAT III has three additional substandards: CAT IIIa, CAT IIIb and CAT IIIc).

In order to fly a CAT I approach, the cloud based (ceiling) must be no lower than 200 feet and the visibility must be no lower than 550 metres. This is because the pilots must be able to visually identify the runway no later than 200 feet above the ground to be able to land.

For a CAT II approach, the ceiling must not be lower than 100 ft and the visibility not less than 350 metres.

CAT IIIa has a minimum ceiling of 50 ft and a minimum visibility of 200 metres.

CAT IIIb has no minimum ceiling, but there must be at least 50 metres of visibility.

For a CAT IIIc, which has not actually been implemented anywhere, there are no minimum limits for ceiling and visibility.

As you can see, CAT II or III approaches allow pilots to land is extremely bad weather conditions.

So if CAT III is so great, why don't we use it all the time?

In order to use CAT II/III approaches, a number of conditions have to be met:

The ground based ILS equipment must live up to very strict standards, and be very carefully calibrated. As a result, installing and maintaining CAT II/III ILS equipment at an airport is very expensive, so not all airports have it.
In addition to the ILS antennas, there are also strict requirements for other runway equipment such as lighting.
The aircraft must have special equipment that is certified to perform CAT II/III approaches. Again, cost is a significant factor. Equipping aircraft with such fine tuned equipment is very expensive, and if you mostly fly to areas with good weather, it is probably not worth it.
The pilots must be qualified. A normal pilot license is not enough to fly a CAT II/III approach, you need additional training and qualifications to be allowed to perform such approaches.
Air traffic control low visibility procedures result in reduced airport capacity. Because ILS signals are transmitted from antennas on the ground, there are risks of interfering with the ILS signal, resulting in imprecise guidance. The main issue is when an aircraft moves in front of the antennas, partly blocking the signal for other aircraft on approach. Because of this, airports have strict rules for how close aircraft may get to ILS antennas when CAT II/III approaches are in use. Aircraft on the ground must hold further away from the runway than they normally would, to stay clear of so called ILS sensitive areas.

An example of ILS sensitive/critical areas at an airport

Separate runway holding points used when CAT II/III approaches are carried out

We also need additional space between two aircraft approaching the same runway. This is because the first aircraft, once landed and on the runway, can block parts of the localiser signal for the following aircraft. Because of this, the first aircraft must be clear of the runway by the time the second aircraft joins short final. This means we need extra space between aircraft, resulting in a reduced runway capacity.

As you can see, there are a number of factors limiting the use of CAT II/III approaches, which is why they are only used when the weather is so bad that CAT I approaches cannot be carried out.


Currently, FAA's "fusion" software uses discrete squawk codes to merge targets generated by different surveillance systems, i.e. SSR (often several of them) and ADS-B. They plan to upgrade the software so it can merge targets based on Mode S hex code as well, but (as of early 2019) that hasn't been rolled out yet. Once that is in place, ATC will switch to telling Mode S targets to squawk 1000. Mode A/C targets will still need discrete codes, though, including Mode S aircraft in areas that only have Mode C SSR.


What is the difference between ICAO, JAA, FAA, EASA, and CAA?

ICAO is the International Civil Aviation Organization, a specialized agency of United Nations. It was created after the Convention on International Civil Aviation (the Chicago Convention) of 1944 was ratified in 1947. The purpose of ICAO is according to the convention:

  "WHEREAS the future development of international civil aviation can greatly help to create and preserve friendship and understanding among the nations and peoples of the world, yet its abuse can become a threat to the general security; and

  WHEREAS it is desirable to avoid friction and to promote that co-operation between nations and peoples upon which the peace of the world depends;

  THEREFORE, the undersigned governments having agreed on certain principles and arrangements in order that international civil aviation may be developed in a safe and orderly manner and that international air transport services may be established on the basis of equality of opportunity and operated soundly and economically;

  Have accordingly concluded this Convention to that end."

Within ICAO, the 191 Member States and a number of global aviation organizations work together to develop international Standards and Recommended Practices (SARPs). These SARPs are the reference for states developing their national civil aviation regulations which are legally enforcible. This is an important aspect: ICAO SARPs are not legally binding by themselves, they form the basis of national regulations which have legal status.

In this way civil aviation regulations are harmonized all over the world, with slight differences based on the actual implementation in national regulations. These local differences are then reported back to ICAO and published.

CAA is the Civil Aviation Authority. This is a generic term used in many countries, notably the UK and China. A CAA is a national regulatory body responsible for aviation. The CAA implements the ICAO SARPs in national legislation and is responsible for regulatory oversight.

FAA is the Federal Aviation Administration. As the Civil Aviation Authority of the USA, it is responsible for establishing aviation regulations in the US. These are known as FARs (Federal Aviation Regulations).

In addition to its regulatory role, the FAA is also responsible for Airspace and Air Traffic Management, maintenance of Air Navigation Facilities infrastructure and has an active role in Research and Development of aviation related systems and technologies.

JAA were the Joint Aviation Authorities, a co-operation of most European (EU and non-EU) civil aviation regulatory authorities. It was not a regulatory body itself, the member authorities were responsible for the regulation.

Originally started as the Joint Airworthiness Authorities in 1970 its objectives were to produce common certification standards for large aircraft and aircraft engines to facilitate a European aviation manufacturing industry (Airbus). Over time, the scope was extended to included aircraft operations, maintenance, licensing and certification/design standards for all classes of aircraft.

With the creation of EASA (see below) in 2002, the EU members transferred the airworthiness regulations away from the JAA. Over time, EASA became responsible for operations and licensing as well.  In 2009 the JAA system was disbanded. Only the training organisation (JAA-TO) remains, it mainly provides courses for CAA staff of European countries.

EASA is European Aviation Safety Agency. Created in 2002 by the European Commission, EASA took over the functions of the Joint Aviation Authorities of the EU countries.

The responsibilities of EASA include drafting of aviation safety legislation and providing technical advice to the European Commission and to the EU Member States, airworthiness and type certification of aircraft and aircraft parts for aircraft operating in the EU, approval of aircraft design organisations world-wide and of production and maintenance organisations inside and outside of the EU.

Since its creation, the competences of EASA have gradually expanded. This process is still going on.


What are the relative internal noise levels in various aircraft?

Let's start with the items for which hard data is easily available:

This FAA chart gives relatively average noise levels for passenger jets, GA turbine aircraft, and helicopters. In addition, this chart should start to give an idea of how much noise is generated aerodynamically in aircraft:

While this is older ground data and not cabin data, it still serves to show that the contribution of aerodynamic noise to total nose levels is not insignificant.

Based on this, I would say that a likely ranking of these environments, from loudest to quietest, is:

1/2: Helicopters and uninsulated jets. In both cases, the close proximity to large, powerful engines leads to extremely high noise levels.

3: General Aviation piston-engined planes. Again, these generally have little insulation,but smaller engines generating somewhat less sound.

4: Passenger jet cabin. Protective insulation reduces sound, but actual noise levels vary based on seat position.

5: Passenger jet cabin, gliding. As seen in the second chart, aerodynamic noise still contributes to a relatively loud environment.

6: Gliders. Slower speeds and cleaner aerodynamic profiles reduce aerodynamic noise, leading to a much quieter ride.


With similar weapons why does an AH64 Apache require a pilot and gunner when the A10 Warthog only needs a pilot?

Mainly it's because the A10's pilot just has to point his aircraft at the target from a certain height while in forward flight, whereas the helicopter, being able to hover, needs to be able to engage a target while not pointed directly at it, while the pilot is busy flying a machine that takes a lot more attention than a fixed wing aircraft.

Especially when considering the Apache's original tactical function, which was to hover below the tree tops, pop up and engage a Soviet tank, and drop out of sight again.  As the pilot you wouldn't want to be managing the weapon systems AND flying the machine and avoiding obstacles.


Which aircraft maintenance repairs require a test flight?

I've been in aircraft maintenance for over 15 years, and have worked about 10 different types of narrow and wide body aircraft, and have never once seen a maintenance manual direct me to test fly an aircraft.

There is a reason for this, though. Repairs done during routine maintenance are designed by the manufacturer such that the repair itself makes the aircraft airworthy. That is usually part of the manufacturing and STC process, if I'm not mistaken.

That being said, it's not entirely uncommon to have maintenance control or even maintenance management request a test flight. Usually this is done for troubleshooting or for repair verification. This is largely due to the fact that there are some problems that maintenance cannot duplicate on the ground. For example, I recently worked an airplane whose window heat failed at the top of descent about once every ten or eleven flights. I can simulate a lot of things on the ground, but what I can't simulate is the actual descent of the aircraft at about 37,000 feet! The problem had been ongoing for four or five months, but was sporadic enough not to trigger any alarms in the analysts office. It was only when you paid careful attention to the history of the problem that you realized it had major issues.

Due to regulatory requirements, and the way our GMM is written, if the aircraft had another occurrence on the next flight, it'd be "dead" at the next station it landed with no MEL relief. We made a repair, but it was really only a guess because there were no actual signs of wear/fatigue/damage and everything tested normally. Management requested a test flight, and asked the test crew to run it through the wringer, to see if it would fail.

On the other hand, there are certain systems that may require flight crew verification during flight prior to recertification. An auto land system that has had chronic failures may require the flight crew to perform an automatic landing before it can be recertified back to full CAT III landing status. But, this can often be done on a revenue flight, and is often not a dedicated flight meant to specifically test the system.

There is also the rare case in which major structural repairs may require a test flight. I once saw a wide body aircraft that had a tail strike on landing. The damage was so severe, it literally twisted part of the empennage. In order to be repaired, our company required major involvement from the aircraft manufacturer. The manufacturer did provide a repair, but for obvious reasons, the engineers actually mandated several test flights afterward.

However, as far as I know, there is no regulatory requirement which says that a certain repair requires a test flight. From what I've seen, and perhaps this may sound awful, you kind of "know" when an airplane needs a test flight.


How much thrust is applied in a 737 to achieve taxi speeds?

From the 737 (Classic and NG) normal procedures section of the flight manual:

Aircraft response to thrust change is slow, particularly at high gross weights. Idle thrust is adequate for taxiing under most conditions. A slightly higher thrust setting is required to start taxiing. Allow time for aircraft response to each thrust change.
To initiate taxi, release brakes, smoothly increase thrust to minimum required for the aircraft to roll forward and reduce thrust to idle. Under normal conditions, 45% N1 should be considered the maximum N1 for breakaway thrust. Do not start a turn until sufficient forward speed has been attained to carry the aircraft through the turn at idle thrust.

In short, advance the levers a little, achieve breakaway, then back to idle.
Smaller jets with higher thrust-to-weight ratios, such as business jets, often taxi with one of the engines in idle reverse, instead of having to ride the brakes.


What is the up-to-date disposition towards narcolepsy in the U.S.A. for obtaining a pilot license?

In the FAA Guide For Medical Examiners there is only a single direct reference to narcolepsy

Under the Obstructive Sleep Apnea QA section it states

  Does this process involve other sleep disorder conditions? (E.g.
  Period Limb Movement Disorder, narcolepsy, central sleep apnea, etc.)?

  No. This process is for obstructive sleep apnea only. If it is clear
  that the airman suffers from a different sleep disorder, DEFER and
  submit any supporting documentation for FAA decision.

This would indicate that if you suffer from any sleep disorder conditions your medical should be DEFERed

Earlier in the document it states:

  Medical conditions that chronically interfere with sleep are
  disqualifying regardless of whether a sleep aid is used or not.
  Examples may include primary sleep disorders (e.g., insomnia, sleep
  apnea) or psychological disorders (e.g., anxiety, depression). While
  sleep aids may be appropriate and effective for short term symptomatic
  relief, the primary concern should be the diagnosis, treatment, and
  resolution of the underlying condition before clearance for aviation
  duties.

Narcolepsy is a sleep disorder and would potentially fall under this definition and thus prevent your from getting clearance.

In these cases its usually best to get the advice of an FAA AME.


When do pilots disconnect the autopilot on an ILS approach?

The decision to disconnect the autopilot is made by the pilot and can be made at any point as long as the operational limitations of the aircraft are satisfied (according to the type of ILS). The pilot also has to satisfy the applicable regulations and company SOPs (as @Sami already pointed out). Note that this depends on the pilot decision too- the pilot can fly the missed approach in autopilot if he decides so.
Usually, the aircrafts have minimum altitudes below which the autopilot has to be disconnected, which are given in the aircraft operating limitaions. For example, for Airbus A340,

CATEGORY II
If the crew performs an automatic approach without autoland, the autopilot must be disengaged no later than at 80 feet.

For Boeing 777:

Autopilot/Flight Director System
The autopilot must be disengaged before the airplane descends more than 50 feet below the MDA unless it is coupled to an ILS glideslope and localizer or in the go–around mode.
Without LAND 2 or LAND 3 annunciated, the autopilot must be disengaged
below 200 feet AGL.

For Boeing 787:

Autopilot/Flight Director System
Without LAND 2 or LAND 3 annunciated, the autopilot must be disengaged
below 100 feet AGL.

As an example in GA aircraft, for Cessna C172 G1000:

The autopilot must be disengaged below 200 feet AGL during approach operations..

As you can see, there is not much difference.


Many things including bottles containing liquids break when the temperature drops below zero, so the cargo hold is always maintained above freezing; 7°C is typical (source).  This applies to both pure cargo aircraft and mixed passenger/cargo airplanes.

That said, it's harder to control for (say) cargo sitting around on tarmac while waiting to be loaded on the plane.  Your cargo shipper can likely arrange temperature-controlled shipping for you, but at a steep extra cost, and this is usually meant for perishables where the main danger is heat, not cold.  But unless you're shipping something to/from Siberia, you'll likely be fine.


How does a flap load relief system work?

I'm not sure how common flap load relief systems are - I know the Airbus A330 has them and I believe all the Airbus A3xx series do. I've also found at least one post that seems to imply it's common on most "large commercial" aircraft, which I assume encompasses most transport category aircraft.

On the Airbus the system is based on airspeed - When the maximum flap extension speed (VFE) is exceeded by a certain threshold the ship's computer automatically retracts the flaps.
My understanding is the retraction is staged, so if you've got full flaps selected and exceed VFE for that flap setting the system takes out one notch -- presumably it would continue doing so if you're still exceeding the operating limitations of the flap system until it reaches a point where it's convinced you're not going to damage the airframe.

When the overspeed condition is corrected (the speed has reduced to below Vfe by a set threshold) the flaps are returned to the selected position.


Are there any mandatory announcements that a captain has to make?

The US does have specific regulations that require the pilot to ensure that passengers are briefed on certain safety issues, although there's no requirement that the pilot must do it personally.

Here are two regulations from the part 91 (all flights) and part 121 (scheduled airline flights) regulations. There may be others.

14 CFR 91.107(a)(2):

  No pilot may cause to be moved on the surface, take off, or land a
  U.S.-registered civil aircraft [...] unless the pilot in command of
  that aircraft ensures that each person on board has been notified to
  fasten his or her safety belt and, if installed, his or her shoulder
  harness.

14 CFR 121.571:

  Each certificate holder operating a passenger-carrying airplane shall
  insure that all passengers are orally briefed by the appropriate
  crewmember as follows [...]

I guess that other countries have similar regulations, but it would be difficult to list them all, so hopefully this example is helpful for you.


I am no authority on the topic, but I'll at least try to summarise the bits from comments:

MEL can contain additional items not on the MMEL only if:

They concern after-market modifications or additional equipment and the corresponding STC permits it. Typically this includes things like IFE, wifi-routers and similar items for passenger comfort, not necessary for safely conducting the flight.
Sometimes it might be possible to add a normally required item if additional equipment is installed that can work as a backup, subject to overseeing authority approval.

MEL can omit items from the MMEL if:

They concern optional equipment that is not installed on the particular aircraft.
The operator chooses to omit them. This can be done because the associated restrictions would not allow the plane to complete the typical mission profile with that operator anyway or if the operator considers the restrictions to be too much trouble for what they are worth (e.g. would require otherwise unused procedures that would have to be trained).

If all those categories happen to be empty, the MEL will be equal to MMEL.


How can engine positioning affect flutter tendency?

To better understand what flutter is, see the structure as a mass-spring system like a spring pendulum that has a damper attached to it. The aerodynamic forces both make the spring stiffer and dampen the movement. Crucially, they will act with a delay to the motion of the spring pendulum. Since we are dealing with oscillatory phenomena here, this delay causes a phase shift. The amount of damping increases with dynamic pressure and the phase shift angle decreases with flight speed.
Things start to get interesting when the phase shift angle approaches π. Now the damper will not work against the movement of the spring pendulum but will support it. Instead of reducing the amplitude of the movement, it will increase it - damping will become negative*. Flutter happens.
There are several ways to shift that point outside of the flight envelope:

Reduce the mass or inertia of the mass-spring system: Now the eigenfrequency of the system will be higher, so the phase shift will approach π at a higher speed. Moving the engines closer to the fuselage will increase the bending eigenfrequency of the wing, so any flutter that involves wing bending will be shifted to higher speeds. A typical case would be the flutter resulting from the coupling of the fast-period mode with the wing bending mode in swept-back flying wings.

Make the spring stiffer: This again raises the eigenfrequency of the spring, so a stiffer structure will shift the flutter speed up. This is no panacea, however: When the Rockwell Commander 112 was developed, flight test revealed flutter of the horizontal tail. A professor from Kansas recommended stiffening of the tail spar and was so convinced that this would cure the flutter that he joined the next test flight, only to crash with the aircraft. As it turned out, the stiffening shifted the flutter speed up such that the forces involved broke the spar while flutter was non-destructive with the softer spar at a lower speed (like in this video).

Change the Eigenmode of the spring: If the motion of the bending wing will at the same time add a torsion moment which twists the wing, resulting in a lower local angle of attack and, consequently, lower lift on the up-moving part of the cycle and vice versa, the aerodynamic damping can be increased. By shifting the engines forward, the engine mass will introduce such a torsion moment into the wing. Of course, when placed further outboard, the engine mass will cause a larger torsion angle with the same torsion moment, so shifting the engines out towards the wingtips makes this more effective.

Shift the resonance speed below minimum flight speed: This might sound silly, but works sometimes: When flying fast enough, the phase shift can be small enough to turn aerodynamic damping back into the positive region, and the plane will not flutter with that particular flutter mode. But it might still flutter at a harmonic …

Generally, to achieve positive damping, the center of gravity of a part should be ahead of its elastic axis. In the case of control surfaces, their center of gravity should be in or ahead of their hinge line. That is the reason for balancing masses!

* to be precise: As long as damping retards the motion, the damping term is mathematically negative and turns positive when it starts to support it.


When does a Maximum Taxi Weight Restriction happen on a 737-800?

The Maximum Taxi Weight (MTW) is one of the weight limitations in the FCOM:

(Boeing 737-800 FCOMv1 L.10.3 Limitations - Operating Limitations - Weight Limitations)

It can be the limiting factor when the actual takeoff weight including required fuel is very close to the MTOW and adding taxi fuel would get you above this limit. Note that the difference between MTW and MTOW is only 500 lbs (about 2 hours of APU use or 35 minutes of taxi). If the required taxi fuel is higher than that (which can happen at a busy airport), you are limited by MTW.


Is there research suggesting that VFR cruise altitude rules improve safety?

Searching Scopus for (VFR OR 'Visual Flight Rules') AND safety in title/abstract/keywords yields two publications (out of 99 hits) that might contain information (or references to other sources) on the safety performance of the current VFR system with alternatives.

Prinzel et al. (2011) - Flight deck interval management and delegated separation for equivalent visual operations

  An emerging Next Generation Air Transportation System concept Equivalent Visual Operations (EVO) can be achieved using an electronic means to provide sufficient visibility of the external world and other required flight references on flight deck displays that enable the safety, operational tempos, and visual flight rules (VFR)-like procedures for all weather conditions. Synthetic and enhanced flight vision system technologies are critical enabling technologies to EVO. Current research evaluated concepts for flight deck-based interval management (FIM) operations, integrated with Synthetic Vision and Enhanced Vision flight-deck displays and technologies. One concept involves delegated flight deck-based separation, in which the flight crews were paired with another aircraft and responsible for spacing and maintaining separation from the paired aircraft, termed, "equivalent visual separation." The operation required the flight crews to acquire and maintain an "equivalent visual contact" as well as to conduct manual landings in low-visibility conditions. The paper describes results that evaluated the concept of EVO delegated separation, including an off-nominal scenario in which the lead aircraft was not able to conform to the assigned spacing resulting in a loss of separation.

Quinby (1980) - General aviation operating requirements for the 1980's

  This paper presents a review of the use of the airspace and the air traffic control system. Safety, capacity and efficiency of this use under Visual Flight Rules (VFR) are compared with the evolving constraints imposed by operations under Instrument Flight Rules (IFR). The concept of Electronic Flight Rules (EFR) as developed by Topic Group III on Freedom of Airspace in the FAA’s 1978–79 E & D Initiatives Process is reviewed. The potential for conservation of air traffic control manpower and aircraft fuel is further developed. Promising areas for further technical exploration are noted. The paper concludes with some considerations for co-existence of VFR, IFR, and EFR traffic during a transition period.