What is the minimum distance allowed between planes in flight, in Europe?

Separation minima in Europe are pretty much identical to the rest of the world, since almost all countries base their aviation regulations on ICAO recommendations.

To summarize:

The minimum vertical separation is 1000 ft. In theory, above FL290, the minimum is 2000 ft, but since all European countries have implemented reduced vertical separation minima (RVSM), the 1000 ft. rule applies all the way up to FL410.

When horizontal separation is based on surveillance (such as radar), the minimum separation generally is 5 nautical miles (NM). Around larger airports with excellent radar coverage and at lower altitudes (where planes tend to fly slower), the minimum is routinely reduced to 3 NM. On final approach path to some runways, it can be reduced further, typically to 2.5 NM. They can get even closer in case of parallel runway operations, but that's a bit too complex to cover here. Special rules apply to mitigate the risk of wake turbulence. For example, the separation between a light aircraft flying behind a medium aircraft can never be reduced below 5 NM.

Horizontal separation based on position reports (no radar coverage) is pretty rare, but still in use in some areas. Here, the minimum horizontal separation is typically not defined as a distance, but instead can be based on a navigation aid (for example, two aircraft on VOR radials diverging by at least 15 degrees, and one of them is at least 15 NM from the VOR, are separated). Another option is lateral separation, which is basically when aircraft operating in different areas are defined to be separated, regardless of the actual distance between them (for example, an aircraft flying along airway A is separated from an aircraft flying along airway B, since airway A and B never cross). Rules for lateral separation are defined locally.

Finally, in the vicinity of aerodromes, separation can be reduced further (often referred to as "visual separation"). Essentially, if the tower controller has two aircraft in sight, and can determine visually that there is no risk of collision, they are separated (regardless of the actual distance between them).

Remember that all the separation minima above only apply in areas where ATC is required to provide separation. If flying in class D airspace, for example, (used in many control zones and terminal areas) ATC is not required to separate VFR traffic from IFR traffic. Instead, ATC will pass traffic information, allowing the pilots to visually recognise other traffic on their path, and take appropriate action to avoid a risk of collision in accordance with the rules of the air.


How can passengers help in the cockpit in an aviational emergency?

The short answer is to sit down, shut up, and stay the heck out of the way.  That's what I would do.  If you can quietly help the one or two people sitting next to you do the same, you're doing your part.

Seriously, the last thing the flight crew needs in a flight emergency is extra distractions from passengers - especially those without directly relevant experience (e.g., an off duty airline pilot commuting home).

Less seriously, it's a common fantasy/daydream among private pilots that some weird emergency results in them taking over the controls.  Pre-9/11, I had the opportunity to try landing a 747 in one of the airline's full motion sims.  (I have zero relevant experience in flying something that big).  On the first landing, all the big pieces came to a stop on or near airport property.  On the second attempt, I think I got most of the pieces to come to a stop on or near the runway.  I doubt many people would have survived either attempt.

My plan if this would ever happen in real life is to get on the radio & demand that an instructor tell me which buttons on the autopilot to push.  If successful, I'd then go buy a lottery ticket before the crazy luck wears off :-)


Is it possible for an airplane to enter another airplane?

Clearly the plane must enter and exit through the belly of the larger plane

Why so? If you drop this condition, things become much easier, because you could attach the smaller planes externally and avoid folding the wings. And this was indeed tried and even used operationally.
The concept is generally termed as Airborne aircraft carrier. The first (?) and most obvious application of the idea was with airships, where the airplanes could indeed be stored internally.

Wiki
Russians extensively tried the idea in the 1930s with up to 5 fighters attached on or under the wing of a large bomber.

Wiki
Admittedly, this configuration was mostly indended for deployment of the fighters, which would then land normally. This way it was used several times successfully for bombing raids early in the WW2. Recovery of fighters was tried, and some configurations even assembled in the air rather than on the ground. But it was quite difficult and required considerable skills even without any folding wings.
During the tests, on some occasions, there were problems (including at least one fatal incident) you are worried about, namely negative influence of the fighters on the carrier. Mostly they were related to failures, when the attachment broke down or didn't work as expected (sometimes due to incorrect control of the fighter during the process).
However, even pretty much the same idea as yours was explored in the 1970s, with the B747 or C-5 as the carrier and some "microfighters" as the payload. Apparently, the concept was deemed "feasible" but never went to an advanced stage of development. Yet today, the idea may be of some interest again with UAV aircraft.

Wiki


If airliners and commercial planes have turbulence, can helicopters have turbulence?

That 'cloudy stuff' that you say is not 'turbulence', but condensed water vapor, the condensation being due to the sudden cooling caused by the adiabatic expansion of the air due to the aerodynamic disturbance caused by a passing blade (or wing).

That condensation can also be observed as wakes in landing aircraft, and in stationary revving props. It appears when the sudden expansion takes place in humidity conditions close to saturation.


Do any aircraft carry spare parts for making repairs?

South African Airways flights to 'less developed' locations in Africa often carry a mechanic and some spares on board. If there are no suitable repair facilities, supplies or maintenance personnel available at the destination, then their own guy can fix any minor mechanical issues. If there's a major problem then they would have to fly in additional repair supplies and staff (and fly out the stranded passengers).

I found this out on a flight from Johannesberg to Lilongwe (Malawi). A seat was broken in the passenger cabin and SAA's on-board mechanic was able to fix it after a short delay. The captain explained briefly why he was on board.

I assume that other airlines or operators who operate in undeveloped areas would do the same. It's a lot cheaper to carry a mechanic and a few spares than it is to have an aircraft, crew and passengers stranded. If anything on the MEL is broken then an airliner isn't airworthy so even a 'minor' issue can ground it.

I guess that the military might do the same for similar reasons, but I have no idea at all about that.


Do pilots of airliners and jumbos do a walk around preflight check for every flight?

NO, not all airline pilots do a walk-around for every flight.

At my airline, maintenance personnel do a "Pre-Departure Check" (PDC) before each flight from all main bases on all wide body aircraft. (A330, B767, B777, and B787)

The PDC includes:

1) a walk around

2) a check of critical systems

3) a signature in the Journey logbook

As a result pilots very rarely do a walk around on the wide body aircraft.

If we happen to land somewhere without company maintenance, then a walk around would be done by the pilots. If it were an ETOPS flight, we would also have to make an entry in the Journey Log Book stating that the APU oil level was checked by noting the EICAS APU Oil Quantity reading.

In addition to the maintainance walk around, the ramp crew also does a quick walk around inspection just prior to push back.


How do you enter the hold after a missed approach at Riohacha (SKRH)?

The missed approach is a climbing right turn to the VOR and then hold while climbing to 3000 ft.  The purpose of the 360 is probably to gain some altitude before entering the hold (someone with TERPS knowledge can address this).  The MSA where the hold is is 2000' and you start the missed at 390'.  The right turn will be protected starting at 390' wheras the hold is not, so you need to gain altitude before entering it.  Part of the issue here is that you can fly any entry you want, so the protected airspace for a hold (which determines its minimum altitude) is a somewhat large area.

To fly it:

Execute your missed approach items (flaps, gear, etc)
Enter a climbing right turn direct to RHC VOR.
Upon reaching RHC VOR continue to climb and fly the holding entry of your choice
Hold as published.


Are passengers allowed to travel seatless(on the floor)?

Passengers on commercial airliners (US, EU, Canada, most of the world) aren't allowed to sit on the floor because 1) they could block the aisles and emergency exits and 2) they cannot be buckled up, putting their and others lives at risk.

That does not mean it could not have happened, just if it did it was against regulation.

There are cases where commercial passengers may sit on the floor but they are rare, for instance parachuting.

EDIT: In the BBC article cited after the original post says that the passengers were given spare crew flip-up seats for take-off and landing, but had to sit on the floor the rest of the time so the crew could do their service. This is against regs as they would not have been secured against unexpected turbulence. The article says the following which proves my point:

  The Civil Aviation Authority says while passengers are allowed to sit
  in crew seats under certain conditions, they must not be left unseated
  during any stage of the flight.


What is motive flow and why is it used in some aircraft hydraulic systems?

Motive flow is required in design of ejector pumps in fuel system. Ejector pumps (also known as jet pumps or eductor pumps) have no moving parts and therefore represent a highly reliable, low cost means to move fuel in an aircraft. All jet pumps contain the physical characteristics illustrated in below figure.

In this pump, the motive flow comes from a high pressure source such as a primary boost pump, or the returned fuel from the engine. When the high pressure motive flow passes through the throat it creates a suction which sucks fuel from its neighborhood and the total fuel flow are sent to another location. The overall efficiency of an ejector pump is low when compared to electric motor powered pumps but they are frequently used due to their extremely long life, high reliability and low cost.

The ejector pumps generally are used for two functions:

Ejector pumps are often used to provide the primary fuel boost function in smaller transport aircraft applications such as business jets and regional aircraft.
In order to minimize the unusable fuel, scavenge pumps are often employed to suck up fuel from the remote corners of fuel tanks and to discharge this fuel at the inlet to the main feed pump(s). Ejector pumps are used for this purpose and the motive flow for these scavenge devices may be taken from the feed pump outlet if other motive sources are not available.

Note: Most of above material are from: Langton, R. (2009). Aircraft fuel systems. Chichester, U.K Wiley.


In that case, you'll need to increase the power in order to keep your airspeed and stay airborne. The extra power will be spent in fighting the extra drag... Besides, you'll have to reduce AoA in order to keep total lift equal to the weight and thus stay at the same altitude...


What does the phrase “flight attendants: stand by for all call” mean?

"Flight attendants stand by for all call" commands the cabin crew to be ready at their station to report to the  chief purser via intercom.

See the explanation on this and other airline phraseology on
askthepilot.com


Do planes depreciate like cars?

Planes do not really depreciate like cars per say but aircraft engines kind of do!

Planes are a bit different than cars due to the certification process being far more verbose. Year to year changes tend to be non-existent or come down to trim/paint options. As such a well maintained old aircraft with a fresh/low time engine may fetch more than a new aircraft with a run out engine.

There are also a lot more factors that go into the value of an aircraft even from airframe to airframe in the same make and model where cars can have some options the avionics combinations for most light aircraft are nearly endless.

  Is the fuel efficiency worth buying a new Cessna or is it more of a status thing?

A brand new Cessna 172 is no more fuel efficient than a 172 from 30 years ago (more or less) because the design largely has not changed. Unlike cars that get small aerodynamic and engine changes often, it's far more complicated to change aircraft designs and deal with the certification so designs remain largely unchanged short of small and limited improvements.

I'm not really sure its a status thing, thats highly opinionated and a bit off topic here.


Does a Tower controller need to see an aircraft on final to give landing clearance?

The FAA's ATC orders cover this for the US. Note that controllers can use radar instead of visual contact:

  3−10−7. LANDING CLEARANCE WITHOUT VISUAL OBSERVATION

  When an arriving aircraft reports at a position where he/she should be seen
  but has not been visually observed, advise the aircraft as a part of
  the landing clearance that it is not in sight and restate the landing
  runway.

  PHRASEOLOGY−
  NOT IN SIGHT, RUNWAY (number) CLEARED TO LAND.
  NOTE−
  Aircraft observance on the CTRD satisfies the visually observed requirement.

(A CTRD is a Certified Tower Radar Display.)

As others have said, operations in poor weather would be very difficult if controllers needed to see all aircraft before clearing them to land.


Are wings any more efficient at creating lift, versus orienting the engine's thrust downwards?

Interesting question. Purely empirically, it is the lift-to-drag ratio you are looking for. If you take this value as given for any particular aircraft, you have a direct answer for how much more effective wings are. It is the ratio of the lift to the total drag. The engine only needs to overcome the drag.

With L/D equal to unity you would need the same thrust as for the vertical take off. But even quite "bad" fixed wing aircraft would have L/D about 5. Gliders or similar aircraft built with a strong focus on aerodynamics can have an L/D of 50 or more (at least in some narrow range of airspeeds).

So yes, wings are more efficient. About one order of magnitude as a rule of thumb for common aircraft and optimal airspeed.

Why your reasoning with air pushed down is incorrect is more tricky to explain. I'll start with the assumption that, as air passes an airfoil, its speed relative to the airfoil is unaltered, and only the direction changes. (I know air slows down at least because of friction etc., but these are, at least theoretically, avoidable things not related directly to creating the lift. If there is something intrinsically related to lift which makes airflow change not only direction but speed too, then someone will hopefully correct me here.)

See the image. Airmass moving initially towards the airfoil with velocity $\vec{v_0}$ is deflected down by angle $\alpha$. Therefore the change in the velocity is $\vec{\Delta v}$. This change can be divided into horizontal and vertical components. To hold the aircraft in the air, the vertical component has to be equivalent to the aircraft's weight divided by the mass flow rate over the wing. The vertical component is related to the horizontal by
$$
\Delta v_{\rm horiz}=\Delta v_{\rm vert} \cdot \tan{\alpha\over 2}.
$$

So, from this simplistic view, the drag would be $\tan\alpha/2$ times the lift. Higher mass flow rate over the wing (longer wings, higher airspeed) makes it possible to keep the same lift with lower deflection ($\alpha$), thus less drag due to the generated lift.

Additional comment: how is it related to power and energy

The answer above is focused on how wings decrease necessary engine thrust, but original question could be interpreted in terms of energy efficiency too. I'll try to add some comments on this part.

simple example – rocket engine: not too typical for aircraft, but simple one. Rocket consumes same amount of fuel per second in order to generate a unit of thurst regardless of its size and regardless if it is pointing upward (and is static with respect to air) or forward (and moving through the air). You need to burn proportionally more fuel per second to generate higher thrust. So, for the rocket propulsion, you will save fuel in the same ratio as the necessary thrust decreases.
Propeller or jet engines are more complicate as their thrust and fuel consumption depends on engine movement through the air too. As David K pointed out in his answer, we can use momentum and kinetic energy of accelerated air to get power needed for unit of thrust.

With some simplifications, thrust is mass flow rate through the engine/prop multiplied by change of flow speed it causes. $T = \dot m \cdot (v_{\rm out} - v_{\rm in}) = \dot m \Delta v$. Power needed for this is $P = \dot m \cdot {1\over2}(v_{\rm out}^2 - v_{\rm in}^2)=\dot m\Delta v\cdot(v_{\rm in} + {\Delta v\over 2})$. Thus
$$
{P\over T}=v_{\rm in} + {\Delta v\over 2}\,.
$$

For stationary engine holding against gravity, higher thrust compared to flying fixed wing aircraft is needed as shown above. If we do not "cheat" by increasing mass flow rate through engine (like making it helicopter rotor or using multiple engines), $\Delta v$ has to be increased in  order to achieve the necessary thrust. So you not only need more power because of increased thrust but also more power because of increased Watts per unit of thrust. Note that even "helicopter cheat" does not work too well. To match power consumption of engine generating less thrust thanks to the wing's L/D you need to improve P/T too – by decreasing $\Delta v$, thus increasing mass flow (rotor/propeller radius even more than proportionally to increased thrust).

What about decrease of P/T due to the movement through air? Well, it depends on particular engine and its $\Delta v$. It will be typically in similar order of magnitude as airspeed (or even less), so we can not neglect $v_{\rm in}$ in watts-per-thrust equation above. There is a efficiency penalty when engine works on moving aircraft. But it should be still worth of it as the gain provided by lift is greater.

A simplified example: We have an engine capable of producing enough thrust to lift aircraft vertically. It can be throttled by changing $\Delta v$ without any practical problems or change in its internal efficiency. And let's assume that mass flow rate through it is fixed area $S$ multiplied by air density and multiplied by arithmetical average of speeds of entering and exiting air. For hovering aircraft and stationary engine producing thrust equal to aircraft's weight, $w$ it is
$$w=\dot m \Delta v_{\rm hover} = \rho S \Delta v_{\rm hover}^2 / 2\,;\quad \Delta v_{\rm hover}=\sqrt{2 w \over \rho S}$$
and thus
$$P_{\rm hover}=w\cdot \Delta v_{\rm hover}/2=\sqrt{w^3\over 2\rho S}\,.$$

The same aircraft flying on its wings does only need $w\over L/D$ of thrust. Airspeed is $v_{\rm air}$. Equation for the thrust: ${w\over L/D} = \dot m \Delta v_{\rm flight} = \rho S \cdot (v_{\rm air}+{\Delta v_{\rm flight} \over 2}) \cdot \Delta v_{\rm flight}$. Thus
$$\Delta v_{\rm flight}=\sqrt{{2w\over(L/D)\rho S}+v_{\rm air}^2}-v_{\rm air}$$
and
$$
P_{\rm flight}={w\over L/D}\cdot(\sqrt{{w\over 2(L/D)\rho S}+{v_{\rm air}^2\over 4}}+{v_{\rm air}\over 2})\,.
$$

Unfortunately, I do not see any way how to simplify and compare $P_{\rm hover}$ and $P_{\rm flight}$ so some concrete numbers:

Light aircraft, 1 ton, 100 knots, $S = 5\,\rm m^2$, $L/D = 15$: $P_{\rm hover} = 290\,\rm kW$, $P_{\rm flight} = 35\,\rm kW$.
Heavy aircraft, 100 ton, 200 knots, $S = 50\,\rm m^2$, $L/D = 15$: $P_{\rm hover} = 90\,\rm MW$, $P_{\rm flight} = 7\,\rm MW$.

So, based on these simplifications flying with wings with similar kind of engine should be significantly more efficient in energy terms too. And, additionally, you are already moving forward using power $P_{\rm flight}$. For vertical engine extra power would be necessary for overcoming air drag due to the movement.


What is this twin engine propeller aircraft flying for Garuda airlines in Indonesia in 1983?

Looks to be a Shorts Skyvan.  Sometime called the ‘Flying Shoebox’.

https://en.m.wikipedia.org/wiki/Short_SC.7_Skyvan


What technologies exist to find an aircraft position after it crashed out of line of sight?

It depends on the UAV.  Many consumer UAVs eg DJI, etc. track the position of the drone via GPS and log it so you can find the crash site quickly.  Others emit beeping noises so you can locate it by sound.


How does one become an airline pilot in Australia?

I am Australian and I hope I can help.

Firstly, you don't need to fly through a university. There are hundreds of private flight schools here which are of great quality, and very few of them are associated with a university. More and more international airlines are sending cadet pilots to our schools. Most of them offer theory courses in addition to the flying, or you can always self study.

Having said that, the university courses are great and airlines like people with a degree (but it's not mandatory to have one). You'll be paying more though, it's a trade-off.

Your comment about small planes - All flying is initially in light aircraft - even if you got an airline cadetship you start small. No single course in Australia or anywhere will let your first flight be in a jet.

Speaking of airline cadetships - these are definitely the best and quickest way to get into an airline cockpit but the positions are highly competitive (and maybe not open to international students, I don't know). But you can still get an airline job without a cadetship...

The normal progression is this - you can technically get a flying job after 150-200 hours of private training and flying, having achieved your commercial pilot licence (CPL). I say 'technically' because if you only have minimum hours and minimum qualifications you have to look very hard for a job. Most people straight away get an instructor rating, so they can get a job teaching people to fly. Other early jobs include sightseeing flights, parachute flights, and mail flights to remote towns.

Your training will have been in light aircraft, but fortunately Australia has possibly the largest light aircraft industry in the world, so there's lots of jobs in these planes. It's highly unlikely that your first job will be in anything bigger than a 6 seater plane.

If you get extra qualifications (such as multi-engine endorsement, and instrument rating), you can get more jobs, and gradually fly bigger aircraft.

After you have your CPL, the next big step is the Air Transport Pilot Licence (ATPL). Regional airlines here generally require as a minimum, 1000 flying hours in light aircraft, the multi engine rating, the instrument rating, and passes in the ATPL theory exams - note that you don't necessarily need the ATPL licence itself. It will take most people a couple of years until they get this experience.

If you have that much experience flying 6 to 8 seat aircraft, it's not actually a huge leap to the 20 seat planes of the regional airlines, and the airlines will train you for this step. And once you've flown those for long enough any airline can train you to their jet.

Of course if you want to go back home after the training it will be different. But no school here can train anyone to go straight to an airline. You've got to do the small things first. Think of it as character building!

I'm sorry but I'm a bit rushed for time but I hope I've helped a bit. Australia is one of the best places in the world to train in my opinion (but I might be biased!). Please ask if you have any more questions. And good luck.


How is tire rubber removed from the runway?

(wikimedia.org) High pressure water removal.

  Runway rubber removal [requires] high pressure water, abrasives, chemicals and/or other mechanical means.

ICAO Annex 14 notes:

  The surface of a paved runway shall be maintained in a condition so as to provide good friction characteristics and low rolling resistance. Snow, slush, ice, standing water, mud, dust, sand, oil, rubber deposits and other contaminants shall be removed as rapidly and completely as possible to minimize accumulation.

And ICAO Doc 9137 Part 2 Chapter 8 talks about the different methods. Of the methods not mentioned on Wikipedia is hot air blasting. The document notes that high pressure water is only suitable for light deposits. For the chemical they note:

  Chemicals having a base of cresylic acid (a derivative of creosote) and a blend of benzene, with a synthetic detergent for a wetting agent, are used for removal of rubber on concrete runways. For removal of rubber on asphalt runways, alkaline chemicals are applied.

High pressure water and hot air are considered mechanical methods.

(airport-technology.com) Friction tester.

A friction tester is used to determine if a runway needs rubber removal, note the 5th wheel above. A fixed load is applied to that wheel, and any slipping is noted by sensors as the car drives up and down the runway.

Related: Do landing strips suffer from landing wheel tire tracks?


What are these "patches" on an Airbus A321 wing?

I am not familiar with that particular aircraft but I would hazard to guess it is not a patch.  I say this as I have never... in 20 years of aircraft maintenance... seen a patch that incorporated screws.  If this were a patch for a crack in the sheet metal it would be rivets all the way around.

AC 43-13 standard practices is the general reference for skin structural repair although manufacturers will publish their own Structural Repair Manual with their own preferred methods.  And certainly I have seen design Engineers come up with odd things to deal with AD's etc.  But I have never seen screws used as a method for installing a patch.

So... I would say it is likely a designed in strengthening piece. It is also a single piece if you look at it carefully it contains a Joggle which makes it look like two separate pieces.  A Joggle being a step in the metal to account for two different surface heights.


How to read representations of pressure around an airfoil?

The arrows are more for the "gee wiz" factor - while they help to show in which direction which pressure is acting, the regular way of depicting pressures is using the pressure coefficient.

Now to your figures:

This probably tries to illustrate the fact that there is air pressure all around the airfoil, and less on top than on the bottom. But the length of the arrows does not correspond to any real pressure distribution. Please do not use this plot to learn aerodynamics.
This one tries to be more realistic, but gets the pressure distribution around the nose totally wrong. While better than 1, it is still not recommended.
This one is clearly the best of the bunch. Here you have a small but intense overpressure region at and near the stagnation point and suction on both sides, as would be the case at small and medium angle of attack if the airfoil has some thickness. The displacement effect will cause the flow on both sides to accelerate to a speed above flight speed, but camber and angle of attack make this effect much more pronounced on top. At the trailing edge you will find a small overpressure on top and a little suction at the bottom when the flow negotiates around the trailing edge because the boundary layer on the upper surface is much thicker than on the lower surface.
Here you see absolute pressure difference numbers, which is unusual. While the figures look realistic, this plot is also not really helpful because it omits the pressure distribution in the forward part of the airfoil where most of the action takes place. I think this is another special plot to illustrate one specific aspect. The numbers are the pressure difference to ambient pressure.
This one just tries to show how the pressure varies along one streamline. But the streamline has a constant distance from the airfoil, which is wrong, because it would normally come closer to the airfoil surface in proportion to the local speed increase. Also, the stagnation area is stretched out too far backwards.
This is a typical plot from a Euler or Navier-Stokes code where the space around the airfoil is panelled instead of only the surface as is customary for potential flow. The plot looks credible, but without a legend you do not learn much about the pressures around the airfoil. Your assumption about the colours is correct.

Please note that 1 tries to show absolute pressure while the others show the pressure difference to ambient.

To answer your question: Most of the plots suck and it would be a waste of time to "read" them because of their limited truthfulness. Maybe this would improve when you read the accompanying text as well, but it would be even better if all plots were like number 3.

What helps most when reading pressure plots is consistency - here all 6 plots fail. The proper way is to plot the pressure coefficient as explained in the linked answer. Only then can you gain some familiarity with the representation and make meaningful comparisons among different airfoils or flow conditions. Negative values of the pressure coefficient $c_p$ denote suction and positive ones overpressure, all relative to ambient static pressure.


Why do MP and RPM adjustments have to be made in a specific order in constant-speed props?

When setting cruise power, if you were to set the manifold pressure first, it would not remain constant as the RPM is reduced. It would have to be re-adjusted after lowering the RPM.

When adjusting the RPM lever you are actually controlling a governor which maintains a constant RPM. Any change in manifold pressure will not cause a change in RPM.

So adjusting RPM first just makes it a little simpler to set your power.


What happens when an aircraft breaks the sound barrier?

The expression "sound barrier" was created maybe 70 years ago when approaching the speed of sound made aircraft react in unanticipated ways. Actually, there is no fixed barrier, and in reality the transition can be rather smooth, provided the aircraft and its pilot are prepared for it.
The speed of sound is the maximum speed with which small pressure changes will propagate through a medium, so at subsonic speed the air ahead of the aircraft can react to the approaching aircraft. Also, while local air density changes only little at subsonic speed, air density changes become dominant at supersonic speed. To make way for an approaching aircraft, subsonic air will speed up while supersonic air will slow down so that density increases to make way for the supersonic aircraft.
At subsonic speed, pressure and speed will change smoothly while air flows around the aircraft. As a consequence, the center of local pressure changes (its lift force) acts at around one quarter of chord, such that the aircraft is balanced when its center of gravity is at the same location.
At supersonic speeds, the air will be taken by surprise - at one moment all was calm and quiet, and suddenly the air molecules get kicked around by an unknown intruder. Pressure changes suddenly, through a shock, so instead of a smooth transition, at supersonic speed there are regions of similar pressure, separated by sudden drops or jumps. As a consequence, the center of pressure changes shifts backwards to 50% of chord. If the center of gravity remains at a quarter chord, the consequence is a strong pitch-down moment: The aircraft will nosedive.
To make matters worse, a control surface deflection, which could redistribute the lift between wing and tail surface, will not necessarily work in the same way as it would at subsonic speed: the aircraft might become uncontrollable. See this answer for a mode detailed explanation.

The cone you see in the right picture is a Mach cone, which would be caused by a supersonic aircraft. The picture was shamelessly copied from this blog.
The trick is now to give the air some advance warning where it counts, even when the aircraft travels at supersonic speed. This can be achieved with wing sweep, because if the sweep angle is larger than the cone angle in which pressure changes will propagate at supersonic flight speed, the air flowing over the wing will be forewarned, thus reacting similarly to subsonic flow. To correct for the inevitable shift in the center of pressure, the tail surfaces are bigger and full-flying in supersonic aircraft, so they work in trans- and supersonic flow. Also, by pumping fuel, the center of gravity can be shifted backwards, so less trim change is needed.
The sound barrier can be broken at any altitude, if the aircraft has a sufficiently powerful engine and is stiff enough. Normally, to save weight, the designers set a limit for maximum dynamic pressure (= air density times air speed squared, divided by two), so the structural deformation at this maximum dynamic pressure is small enough. Note that the deflection of its ailerons will deform the wing of the Eurofighter at maximum dynamic pressure to an extent that three quarters of aileron effectiveness is lost - the ailerons cause a twisting moment which warps the wing such that it works like the wing warping mechanism in the Wright Flyer, only in opposite direction to the aileron input.
Since density drops with increasing altitude, the same dynamic pressure is reached at higher speed, allowing aircraft to fly faster the higher they fly. The next limit is given by the local heat near the stagnation line. If air is decelerated, its temperature will increase with the square of the speed difference. The maximum continuous speed of the F-22 was reduced from Mach 1.8 to Mach 1.6 to avoid overheating the sensitive composite wing structure.


In what conditions is the APU used in midair?

This answer applies to the AVRO RJ (BAe 146), because this is the aircraft I've flown. Other aircraft may or may not have similar features/issues/restrictions.
Reasons for APU use in mid-air

For takeoff, the APU bleed-air can be used to supply the cabin air pressure system to reduce load on engines. This leads to a significant reduction in runway length required. This is routinely used on short runways.
Similar reason for the landing, where, for the missed approach/go-around phase, a high climb gradient is required. For example in mountainous areas or combined with icing conditions, where use of engine bleed air is limited, the APU bleed air can feed the cabin pressurization.
During flight, when in icing conditions. Similar reason as above. The air-frame anti icing system uses that much bleed-air, there is not much left for cabin pressurization (or the other way round). If the APU bleed-air is used to pressurize the cabin, the (already low) climb gradient is improved.
During flight, in the event of a generator failure. The generator of the APU can replace one failed generator of an engine.
To save engine life. If APU bleed air (- to pressurize cabin) is used for normal takeoff, the peak engine temperatures will be lower during takeoff. This increases engine life as the peak engine temperature is the main factor of engine life. It's significantly cheaper to replace an APU than an engine.

In all of the above cases, there are restrictions on the operation of the APU. It may not light-up above 15'000 ft or operation above 25'000 ft is not allowed or not recommended. General operating rules for the APU (common sense when using turbines) recommend to use bleed air only after couple of minutes warm-up after startup. Likewise, on shutdown, it should be left running without load to cool down for a few minutes before switching off. The exact timings differ greatly between APU models.
Procedures

Before Takeoff, If the APU is not used during climb, the APU is normally shut down during taxi checks. If the pilots decide to use the APU during climb, it is started during normal engine start. In this case the APU bleed air is used to feed the cabin pressurization.
After Takeoff depending on the model of the APU (and following airline procedures), the APU usage is limited to a specified time or altitude. Before reaching this limit, the APU has to be shut down. (cabin air changeover to the engine bleed air, cool-off period of the APU, switching off)
During Flight In case of a technical problem or emergency, the Abnormal Checklist will suggest or dictate the use of the APU for the remainder of the flight. For example: A generator problem, the APU generator replace the failed generator. This may impose limits to flight altitude and duration.
Before Landing Usually after passing 10'000 feet, the APU is started and before the final checks, the cabin pressurization system is switched to the APU.


Currently, there seems to be little official definition, and the term MAV appears is relatively new. The only paper on the topic I could find that specifically approached the area defined it as:

  "small enough to be practical for a single-person transport and use." (Galiński and
  R. Żbikowski, 2007)

Delft University of Technology section on MAV research provide no clear definition in their documents.

I think the definition seems to more subjective to the flying properties to the UAV, which might make the definition more difficult. Since they are not carrying people but sensors, they will be much more varying in weight, especially in with time.

One example, the british army's MAV has a flight time of 25 minutes.  This one is a very small but has a respectable flight time. This will not simplify definition. I think the term coined by Galiński and Żbikowski is the most useful in a practical sense.

Update:
University of Texas page on the DARPA competion says:

  The definition employed in DARPAs program limits these aircraft to a
  size less than 15 centimeters (6 in.) in length, width, or height.
  MAVs must have a weight of 50 grams or less and must be capable of
  staying aloft for 20 to 60 minutes for a distance of 10 kilometers.

The pure source for this this, while not avaliable any longer, I believe I found to be

  The definition employed in DARPA's program limits these craft to a
  size less than 15 cm (about 6 inches) in length, width or height. Source

There are currently no civilian classifications for UAVs from the FAA or EASA, hence the legal problem with these. Most army and air force drones operate under military exceptions if I'm not mistaken.


What is the difference between APV I and APV II?

The difference between APV-I and APV-II "... lie in the signal-in space performance requirements..." (see this presentation, in particular beginning on page 12: ENAV presentation).

This means that APV-I/II refer to navigation signal performance requirements for APV approaches. Note #8 on page 13 of the presentation referenced above is clarifying:

  The terms APV-I and APV-II refer to two levels of GNSS approach and landing operations with vertical guidance (APV) and these terms are not necessarily intended to be used operationally.

Therefore, look at APV-II versus APV-I as providing for lower APV minimums based on signal performance (horizontal and vertical alert limits) at locations where this is possible. Similar in concept, but not in value, as the difference between RNP .3nm and RNP .1nm approaches.


What is the effect of changing the autobrake setting after touchdown?

This answer was difficult to find as both Flight Operation Manuals and Maintenance Manuals did not say. The only guidance was found in the system description provided by the OEM of the BCSU.  I am not mentioning the fleet type because at some point the detailed description might become proprietary.

According to the description I found for a given automatic braking system is that it is armed when the pilot presses one of the three pushbutton switches which set the auto-brake level.

The system will only arm if gear up is not commanded, there is hydraulic pressure as needed, and no existing faults exist that prohibit normal braking, as well as a few other computers available on the associated data bus.

There is nothing that says the system can't be armed after touchdown, however the system will only engage when the spoilers are being activated, or are activated. Or more precisely from the black-box point of view automatic braking is engaged whenever two spoiler signals in three appear once automatic braking has been armed.  In other words, once armed, the automatic braking will only engage if spoilers are sending the signal that they are being activated, or are activated.

It specifically says that the pilot can select another pushbutton switch even after
arming. The BSCU acknowledges this new command and executes
the corresponding task.

Automatic braking is released whenever the braking sequence
is interrupted:

when an arming condition disappears,
when an engaging condition disappears,
when one or both brake pedals are held down beyond the
defined threshold,
when the selected pushbutton is pressed again.

The question, therefore is 'After you have already armed at a given setting and the system is actually engaged, because the spoiler actuation has initiated auto-braking, what happens when you press another setting?'  As long as the arming conditions still exist, which in most cases would, and as long as the engage conditions exist, as would be the case if the spoilers are activated (at least 2 of three spoiler signals being sent to the BSCU), then yes, you may change the setting after touchdown and the BSCU acknowledges this new command and executes the corresponding task.


At what point does an aircraft need a new type certificate vs a STC?

Since this is an aircraft for personal use, is under 19,000lbs gross weight, and less than 19 seats it will fall under Part 23.

If you don't plan on selling "kits" to do these modifications, then an STC is not required. STC's are only for modifications intended for sale to aircraft for installation by an A&P mechanic. STC's are required not for the kit itself, but for each aircraft type (and sometimes variant) that it is to be installed on. This is why the STC process can be very expensive.

You would not need an entirely new type certificate either, again which would be required if you were doing these modifications as a business for sale as another aircraft type, or if the original manufacturer modified the aircraft in some significant way.

What you would need in almost all the cases you described above is an FAA Form 337, which describes "major repair & alterations to airframe or power plant". This document will require you (and your A&P) to make detailed descriptions and drawings of the modification and submit it to an FSDO. The FSDO will review the modifications and approve or disapprove of the changes. It is advisable to work with the FSDO from the beginning, not the end.

  So, which of these alterations would require a new TC of the aircraft vs a STC?

  Lengthening or shortening the fuselage?
  Changing the engine(s) from say piston to turbine or turbine to electric fans?
  Adding extra components to the airframe, like batteries, controllers, etc. to make a hybrid aircraft?
  Changing the wings to newer ones from another certified aircraft (re-winging)?
  Changing the landing gear to a newer model with higher load capabilities?
  Expanding the fuselage diameter by 10%?

None of them require a new TC or STC, however your first question would probably be difficult at best. The second question doesn't make a lot of sense for the Piaggio since it already has turbine engines, and there are no electric fans of the size that would be required. Changing the wing or modifying the landing gear are pretty common things, usually in the form of STOL kits or FOD deflectors. Some of them would require extensive testing from the FAA before issuing the airworthiness paperwork.

The last one though will nearly be impossible. It would be a lot cheaper to just buy an aircraft that fit your needs, like the Pilatus PC-24 than try to make that modification.


What could explain the fact that during 1976-80, I used to hear commercial jets make sonic booms while flying overhead?

Note that 747's and other jumbo jets operating out of Bradley could not have produced sonic booms because they do not fly above the speed of sound (they only do 500 to 550 MPH at high altitude cruise) and, in any case, far slower than that (~250 MPH) when near the ground as for landing and takeoff.
Therefore, whatever it was you heard, it was assuredly not a sonic boom from a passenger plane. The last time these commonly occurred was in the 1950's and '60s when the US Air Force flew mock bombing missions across the United States in supersonic bombers at low altitude, to train the pilots and crews for similar missions against targets in the USSR.
Although sonic booms were essentially outlawed over populated zones in the early 1960's, in your case they apparently did happen during flight tests of the F-22 Raptor in your location, which is very interesting! Thanks for @reirab's  detective work which uncovered this.


How did the service ceiling certification change in the 70s?

I did find a quirk alright. First off the ceiling is either 18,000 or 19,500 feet depending on the source. The video's origin is unclear, but my research hints at the narrator reading an AOPA piece (can be found on superskyrocket.com via web.archive.org):

(...) later T337 and P337 models are only certified to 20,000 feet, whereas the earlier turbo models have no such limitation, a quirk of changes in the certification standards that took place in the 1970s.

The Skymaster's certification falls under Part 23. The relevant amendments I found are 7 and 9, from September 1969 and June 1970, respectively.
Amd 7 (maximum operating altitude):
First limited all Part 23 to 25,000 feet (23.1527). Unless they met a quirky requirement (23.775e). I more than doubled checked it's the right one:

(e) The windshield and side windows forward of the pilot's back when the pilot is seated in the normal flight position must have a luminous transmittance value of not less than 70 percent.

I could not find how the FAA measures the luminous transmittance. But higher pressurization requires stronger windows, it could be as quirky as that. Perhaps the 60s technology couldn't produce clear[er] windows while staying strong.
Amd 9 (oxygen equipment and supply):
Is less quirky, but there is a lot of fine print (23.1447), of which:

(c) If certification for operation above 18,000 feet (MSL) is requested, each oxygen dispensing unit must cover the nose and mouth of the user.

That means proper masks, and for the crew's masks to have built-in microphones connected to the airplane's radio:

(4) If radio equipment is installed, the flightcrew oxygen dispensing units must be designed to allow the use of that equipment and to allow communication with any other required crew member while at their assigned duty station.

That's asking a lot from a light Cessna, and if higher:

(e) If certification for operation above 30,000 feet is requested, the dispensing units for passengers must be automatically presented to each occupant before the cabin pressure altitude exceeds 15,000 feet.

An automatic dispensing system is not something one would find in a Skymaster.

In short, the candidates from the 1970's are the window materials, and the oxygen supply, limiting it first to 25,000, and then to 18,000 feet.


What's the theoretical background of the critical angle of attack?

Both the airfoil shape and inherent properties of the air contribute to the stall angle of attack. You asked for a theoretical background, but I will list the factors that influence stall because there is no simple formula for it.
The most important factor is the suction peak which develops right behind the stagnation point on the upper side of the leading edge. High suction means high speed and that in turn means high friction, so the air loses energy which it needs further downstream to regain its pressure. If too much energy is lost, the flow separates. Enough separation and lift suffers, so here you have the most immediate reason for a stall.
What can be done to shift that point to a higher angle of attack?

Pitch up faster. That way, the flow over the rear part of the wing has a boundary layer from lower angles of attack and will not separate when the leading edge passes through the angle of attack at wich it stalls in normal conditions. This can shift the stall angle of attack up by 50%. But that works only temporarily and the same mechanism will delay recovery once the stall has occurred.
Increase the leading edge radius. This spreads out the suction peak and makes it less pointy. A blunt leading edge is especially helpful with higher wing loadings when Mach effects play into the stall angle of attack mechanics. Once the local suction peak at the nose of an airfoil reaches a local Mach number of slightly less than 1.6, no lift increase could be observed in experiments.
Increase wing camber, either by nose and/or trailing edge flaps or by cambering the airfoil. This helps to reach high lift coefficients already at low angles of attack, and especially nose devices (slats, Krüger flaps) shift the stall angle of attack up as well.
Use a well-designed airfoil with a long laminar run and a Stratford pressure distribution past the turbulent transition point on the upper side. This helps to reduce boundary layer losses and maximizes energy reserves for the steepest possible pressure rise. But you need a clean, smooth and well built wing for that to really happen. And the right Reynolds number range: Gliders use this effect extensively but airliners cannot use it at all.
Increase wing loading. This will shift the stall speed to a higher Reynolds number where friction losses are smaller relative to the inertial energy of the air. Of course this will increase stall speed, but is will also shift the stall angle of attack higher. A bit.
Increase wing chord (while maintaining the same area). This has actually two effects: The smaller one is again from the increase in Reynolds number, but the more powerful is from the reduction of the wing's aspect ratio. At a smaller aspect ratio the lift curve slope is flatter, so the same lift coefficient (and suction peak) is reached at a higher angle of attack.
Increase wing sweep. The pressure changes over the wing are now proportional to the cosine of the sweep angle, so all effects are shifted to higher angles of attack accordingly. But beware of a combination of high sweep and high aspect ratio: Stall will become outright nasty. If you combine 6 and 7, you will at some point arrive at a delta wing which flies well even with fully separated upper side flow (vortex lift). Now your limit angle of attack will be defined either by the vortex bursting or loss of directional stability.
Fly in hotter, less dense air. This also helps to increase the Reynolds number because you need to move faster for the same dynamic pressure. However, much of that advantage is eaten up by the increase of the air's viscosity with temperature.


What is the difference between the NTSB's "Aviation Accident Database" and their "Aviation Accident Reports" list?

The NTSB will investigate every aircraft accident in the US, and any that foreign authorities delegate to them. As you found, there thousands of accidents ever year. Most of these are not fatal. The NTSB will at least gather the factual information and do their best to arrive at a probable cause.

With limited resources, the NTSB must decide which accidents are important enough to do a major investigation. You can see a map and list of the most important current investigations here, along with the following explanation (emphasis mine):

  This listing of investigations includes those open investigations involving accidents or incidents which resulted in significant loss of life, physical damage, involve issues of importance to public safety, or which have generated particular public interest. This represents only a small portion of the investigations conducted by the NTSB, most of which occur at the regional level.

There is no official criteria and not all of the incidents listed will become major investigations that result in full reports. The NTSB will decide based on the situation and factual information whether a full report will be produced. These reports are much more in depth, involve official parties that may submit their own findings and recommendations, and are deliberated on by the board in a public meeting before being officially released along with formal safety recommendations.

The board also periodically releases safety recommendation reports on issues that may not be related to a single major accident, but that are evidenced by multiple accidents that may not have received major reports.


Zenith-Add horsepower, NASA-add drag: to create lift. How is this possible?

Equating rate of climb with more lift is wrong. In order to climb the aircraft needs more thrust but a bit less lift. Therefore, the first statement is wrong: Adding more power does not create more lift. The only case where this happens is at high speed and the maximum sustainable lift coefficient: More power allows to fly at a higher load factor, but depending on the flight envelope, might result in a crash. The explanation does not make that connection, so it is wrong.

The second explanation is special for the X-57 because the concept uses the propeller slipstream to create blown lift. At low speed, the thrust needed to maintain flight speed is low and might not be sufficient to create enough lift on the small wing. Adding some drag allows to fly at higher thrust without climbing away. But only in this special case when most of the wing is in the propeller slipstream. So the second statement is correct but only for a single case.

Artist concept of the NASA X-57 Maxwell (image source).


Why is an outward spinning propeller better in theory on the North American F-82 Twin Mustang?

The theory is actually quite simple and straightforward. It should go like this:

In one-engine flight, the asymmetric prop position will pull the aircraft into a sideslip. The sideslip-induced rolling moment will then proceed to roll the aircraft such that the airplane rolls over the dead engine - something every multi-engine pilot learns to avoid early, because it will be hard to get the airplane back to level flight in this configuration.

If the single operating propeller will give the center wing an increased angle of attack due to the propeller swirl, and the outer wing a lower angle of attack, the prop produces a rolling moment which works against the sideslip-induced rolling moment, and should make it easier to avoid rolling over the dead engine. Engine torque will work against this moment, but the induced rolling moment of the wing is stronger, leaving a net moment which rolls the aircraft over the operating engine.

This should apply to all multi-engined aircraft. My reasoning why it didn't work for the F-82 can be read here.


What is pressure refuelling and how does it work?

With a pressure fueling system, rather than fueling through holes in the tops of the wings, a fuel truck or fuel hydrant is used to push fuel into the airplane through a fitting at about 50 psi. The fuel fitting is generally in the right wing. A fueling control panel allows the fueler to fill the tanks to the amount called out by the flight plan.

These large aircraft still have an overwing fueling port for those times when the pressure fueling system is inoperative.

There is nothing to prevent fuel vapors from escaping to atmosphere.


Are the functions of ailerons and rudder similar?

Short answer:
Rudder and ailerons have different purposes and control rotation about two different axis. However a rotation about one axis induces a usually unwanted rotation on the other one. In order to rotate exclusively about the desired axis, the other control must be used to cancel the secondary rotation. This is called coordination of controls.
Rudder and ailerons are not the only controls requiring coordination, elevators and throttle actions must be coordinated too, to prevent a change in altitude to result in a change in speed and vice-versa.
The rudder is mostly used to:

Limit yaw movements for safety (Dutch roll) and comfort.
To force the aircraft in a crab (heading not aligned with course), while the weather vaning effect tends to orient the aircraft with the airflow (e.g. for a cross-wind landing).
To force the aircraft to face the airflow when performing a turn. We'll talk about this below.

See Understanding the use of rudder for a more comprehensive explanation.
Ailerons are used to turn, but for a non-small turn an unwanted adverse yaw, opposite to the turn, develops and moves the aircraft away from the airflow (crab), the rudder is used to cancel this crab angle and make the aileron-initiated turn effective.
The availability of a yaw damper relieves the pilot from the duty of coordinating rudder with ailerons in a turn. The yaw damper controls the rudder for stability purposes, and at the same time it maintains the aircraft longitudinal axis into the relative wind without pilot action.

Detailed answer
While it is intuitive to think a turn is triggered by yawing the aircraft and keeping the wing horizontal (like a car), this method is actually ineffective with a rudder of the normal size. The rudder forces the aircraft to change its heading (yaw) but the flight continues more or less in the same direction, the aircraft now moving crabbed. This is specially true as speed and altitude increase and rudder aerodynamic force becomes smaller compared to other factors like inertia.
Banking turns the aircraft
An aircraft is turned by rolling (banking) the wing. When the aircraft spins about the roll axis, the direction of the lift is changed (A/B below). Like any force, the lift vector can be broken down into components (B):

The horizontal component of the lift moves the aircraft away from its original path and the aircraft turns around some point. (Note the vertical component, which still opposes the weight, is now smaller, and a non-small turn also requires adding engine power to maintain altitude.)
However something quite undesirable happens (C): To roll the wing, the upper aileron has to create more lift than the lower one. Lift is created by deflecting the airflow, and this action has a cost: The disturbed airflow creates 'induced' drag. This drag is different from the other drags, it's not due to the friction or the shape of the aileron, but to the deflection of the airflow by the aileron, and increases with the amount of lift created.
Like aileron lift, aileron induced drag is larger on the upper wing, that is on the outer side of the turn. As there is a drag differential, the wing is no more balanced and wants to yaw on the right, opposite to what we want. This force is known as the "adverse yaw".
A part of the adverse yaw is balanced by the weather vaning tendency of the aircraft, due to the action of the fuselage and the rudder. However this only compensates partially for the yaw. All these forces makes the aircraft turn a bit, but crabbed, as seen in picture D. This situation where the aircraft is not aligned with the airflow is an "uncoordinated turn", it is very inefficient, slows the aircraft and stresses the airframe.
This is were some action on the rudder is required: The pilot adds some left rudder to completely cancel the adverse yaw created by the ailerons and align the fuselage with the airflow (E). Doing this any slip and skid motion is also minimized. This is known as performing a coordinated turn.
As visible on the figure E, the horizontal component of the lift, the one pulling the aircraft towards the center of the turn, is constantly reoriented in the direction of the center, contrary to the case of the uncoordinated turn (D).
Rolling the wing is a very effective way of turning the aircraft, but needs some rudder correction to account for the induced drag moving the aircraft longitudinal axis away from the airflow direction.
Ailerons deflection reduced in the turn
Note that when the desired bank angle is reached, the pilot reduces the ailerons deflection. The excess of lift and drag on the upper wing decreases too, as does the adverse yaw. The rudder deflection can be reduced too.
Normally the aircraft should maintain its bank and continue to turn with ailerons in neutral position, due to the upper wing flying faster and generating more lift.
However the aircraft in a rolled attitude actually slips into the turn and the dihedral effect tends to decrease the roll angle of the slipping aircraft (roll stability). So some degree of aileron deflection will be maintained.
The ailerons (and the rudder) are used to return the wings to their horizontal position and stop the turn more accurately.

Ailerons-rudder coordination
Coordinating turns is part of the basic training for a student pilot as uncoordinated turns are not only ineffective, they are also unsafe:

Some part of the wing or the controls can be in the shadow of the airflow, meaning they have no useful effect to control the aircraft.
Lateral accelerations develop, the aircraft either slips or skids.

The amount of rudder to apply can be determined using (human senses and) different instruments, including the turn coordinator, aka needle and ball Indicator, which is a sort of level (the ball) usually associated with a bank or rate of turn indicator (the needle). The respective position of the ball and the needle according to different uncoordinated/coordinated situations are like this:

(source)

(source)
When executing a coordinated level turn without wind, at sea level, etc, the radius of the turn and the turn rate depend only on the airspeed and the bank angle:

TAS 150kt, bank 20°: Radius 1,676m, 360° in 2:16.
TAS 300kt, bank 30°: Radius 4,227m, 360° in 3:51.

See this question for additional information.
Yaw damper
In commercial airliners, the yaw control is assisted by one or two yaw damper(s) which function is to increase the yaw stability and prevent the development of the dangerous Dutch roll. Thanks to the yaw dampers, the pilot does not need to use the rudder pedals for coordinated turns.

(source)

Other means of controlling roll/lift
A mean of banking wings directly is required, including when Dutch roll and spin start developing and when flying or rolling with crosswind. But bank control can be obtained by other means than ailerons. While ailerons add lift by changing the camber of the wing,

spoilerons combine spoilers and ailerons, and break lift by disturbing the laminar airflow (B-52),

rudderons combine rudder and ailerons on flying wings (B-2A),

and now bleed air and Coandă effect can bank the aircraft without moving surface (Flaviir project).


Yes, it is correct to use MAYDAY or PAN PAN PAN on the ground.

In recurrent training we are often reminded that in the case of a rejected takeoff in a foreign country it is important to use MAYDAY or PAN PAN PAN on the ground to avoid any confusion due to language difficulties.

It's probably a good idea at any airport as a disabled aircraft on a busy runway could be a major hazard to other aircraft landing and taking off.


Could robots take over pilots' jobs and fly planes - if they can, then how?

It's already in the works.  Fully autonomous unmanned combat air vehicles are no less than 10 years away.  I'd say that the major airlines will follow in 10-15 years, most likely starting with the elimination of the First Officer with fully automated functions.  Similar systems will be introduced, and most likely before the airlines on corporate jets.

It will be fought tooth and nail by the pilot unions, but sooner or later the algorithms these AI pilots use will become increasingly sophisticated to the point that there will be another incident similar to that faced by US Airways 1549 where an AI is under control and makes a decision saving the crew and passengers where 97% of all human pilots who, when faced with an analogous situation, failed resulting in a catastrophic accident.  Thus public confidence will be bolstered in these systems and public opinion will sway in their favor - even demanding these systems will be on board.  All that's required at that point is flights operated by AI are 40% more efficient and 63% more likely to be on time without interruptions of service due to weather, crew fatigue, etc.  At that point the first experimental, totally unmanned commercial flights will happen, probably after the corporate jets lead the way.

Military wise a similar thing is bound to happen as ACM algorithms improve, making super maneuverable drones which are capable of defeating Red Flag instructor pilots 97% of the time and more and more years of confidence built on the AI systems both in peacetime exercises and in conflicts will finally eliminate the manned fighters and bombers.

Perhaps the last vestiges of manned flying will be in general aviation and remote bush flying for commercial reasons (the revenge of GA?), but even these will slowly be eliminated as AI controlled aircraft and infrastructure capable of allowing off field landings and takeoffs, even in the most remote or difficult places come online.


Why is carburetor heat unnecessary at full throttle?

The icing you are talking about is called "throttle ice" and actually just forms around the edges and back side of the throttle butterfly.  It's not really related to the venturi that is upstream; it's from the pressure drop caused by the restriction of the throttle plate (the high vacuum on the back side you might say) along with the presence of vaporizing fuel, which massively boosts the temperature reduction caused by the pressure drop because the evaporating fuel is absorbing a lot of heat from the air stream.

It's the temperature drop from this pressure drop at the butterfly, plus the effect of evaporating fuel, that turns ambient humidity into carb ice.  On a fuel injected airplane you only have the butterfly valve without fuel present, and the temperature drop from that alone isn't sufficient, and therefore you don't need carb heat on injected engines (just an alternate air source in case of impact ice on the air intake).

Anyway, when the throttle is wide open, the pressure drop downstream of the butterfly caused by the throttle restriction is minimal. As a result, the chilling effect of the pressure drop and of evaporating fuel is also minimal. Because of this you won't get ice formation as readily (not impossible, just relatively unlikely) when the passage has say only a 5 or 10% restriction at WOT, vs say, an 80% restriction at a low power setting.  For a given ambient temperature/humidity, carb ice always forms more easily the more the throttle is closed.

One of the worst airplanes for carb ice was the 65 hp J-3 cubs where the carb receives very little conductive or radiant heat from the engine due to the carb mounting and the cowl with the exposed cylinders.  Descending with the engine at or near idle on a 65 deg F high humidity evening was begging for a carb ice related stoppage, and liberal use of carb heat was advised even if there were no signs of icing.  Carb ice at WOT wasn't too much of a problem, but you can never be sure.  Always err a little on the overuse side with carb heat, especially on Continental powered airplanes which are a bit more sensitive to all this due to the way the carb is insulated from the crankcase, at least until you get to know the engine's quirks.


What are reasonable values for the position of an airplane's center of gravity compared to that of its center of lift?

If I understand your question correctly, h is a fraction of mean aerodynamic chord c. That fraction can be >1. It could be that the aircraft is stable with a huge download on the tail.

The mean aerodynamic chord is an aid, to simplify calculations. It is not a hard limit for the equilibrium points. Whether the value is reasonable or not is hard to say without having seen the full problem to be solved.


What is the minimum ceiling and visibility limits in Class E airspace?

VFR cloud clearance requirements are listed in 14 CFR 91.155 and for Class E airspace specifies:

  Class E:
  Less than 10,000 feet MSL.
  Flight Visibility: 3 statute miles
  Distance From Clouds: 500 feet below, 1,000 feet above, 2,000 feet
  horizontal.

  At or above 10,000 feet MSL.
  Flight Visibility: 5 statute miles
  Distance From Clouds: 1,000 feet below, 1,000 feet above, 1 statute
  mile horizontal.

There is also a requirement specific to Class E surface areas that says that the ceiling must be at least 1,000 feet in order to operate in the airspace.  It is also listed in 91.155:

  (c) Except as provided in Sec. 91.157, no person may operate an
  aircraft beneath the ceiling under VFR within the lateral boundaries
  of controlled airspace designated to the surface for an airport when
  the ceiling is less than 1,000 feet.

Note that there are exceptions for both of these that refer to 91.157 Special VFR Weather Minimums if you are instrument rated and the aircraft is instrument equipped.


Is the location of an aircraft spoiler really that vital?

Surfaces sticking out ahead of the Centre of Gravity act in an unstabilising manner: any dissymmetry will want to amplify itself. A dart thrown with the feathers first is in an unstable equilibrium and will very quickly turn around 180º.

Surfaces behind the CoG act as stabilisers, keeping the nose pointing forward. An aeroplane has vertical and horizontal tail surfaces at the back just for this purpose. When spoilers are deployed at low speeds, the aeroplane is in a situation where you don't want any destabilising moments.

Aerodynamic behaviour is stable if a disturbance auto-corrects: a deviation is automatically blown back. Since motion in flight is relative to the Centre of Gravity, it follows that the aerodynamic Centre of Pressure must be behind the CoG.


How can a sUAS operator contact ATC/identify themselves when contacting ATC?

First, you should NOT transmit on air bands as a UAS pilot.  You do not have a ground station license and it would be a violation of both FCC and FAA rules, contact with the tower, when necessary, should be done via the phone.  It is fine (and I'd even encourage) to monitor the air bands relevant to the location you are flying in to be aware of on-going traffic.

How to approach contacting the tower depends on what you are flying your sUAS as.  LAANC (Low Altitude Authorization and Notification Capability) is now active almost everywhere, though some particular airports still do not use it.  LAANC should be used whenever available, however the traditional approach will still need to be used for any particular airports not yet participating in LAANC.

LAANC

If you are flying near an airport where LAANC is available, then you can simply use an app from your mobile phone to request flight authorization/notification.  You simply enter the area or flight plan you will be flying and hit the button to request approval and then wait for the notification it's granted.

This can be done regardless of if you are a part 107 pilot or a recreational pilot.  As long as you are flying below the maximum altitudes defined in the UAS Facilities Maps, you should receive near immediate approval in most cases.  If you are flying above these limits, you will need to be a 107 pilot and go through the traditional waiver process.

You can find a listing of apps that currently support LAANC listed on the FAA's website here.

Traditional Notification/Waiver

If the airport you are flying near does not support LAANC, then if you are flying for purely recreational purposes, you must provide notification to the airport operator and ATC prior to your flight.  You should use the telephone contact information to do this.  As long as they do not specifically deny your flight, you only have to provide notification.

If you are flying under part 107 (FAA certified remote pilot), you will need either an airspace authorization (easier to get and may be requested up to 6 months) or an airspace waiver (harder to get and may be requested for up to 2 years).  You should check the UAS Facilities Maps to find the maximum easily allowable altitude for your flight and submit the airspace authorization request online through DroneZone.

It is currently taking around a week or two for authorizations that fall within the UAS Facility Maps guidelines and longer if additional research is needed to get approval.  Authorizations are ONLY offered for airports not currently supporting LAANC as LAANC is the preferred means of processing.

One of the conditions of getting either a waiver or an airspace authorization is to provide details on how you intend to handle contact with ATC.  Contacting the tower via phone is the most general approach.  Some also monitor ATC frequencies so that ATC can more rapidly get ahold of them if needed.


What are the RVSM Critical Area markings?

Aircraft need to know their altitudes to avoid bumping into each other in the vertical dimension. The default instrument for this is a pressure altimeter. A pressure altimeter needs access to a static port.

RVSM stands for Reduced Vertical Separation Minima. Basically, aircraft above a certain altitude (29,000 ft) used to be kept further apart from each other vertically (2000 ft) since the accuracy of the pressure altimeters degrades with altitude.

Over the years, as traffic density increased there was a need to pack aircraft closer vertically (1000 ft). This is possible if you have a special more accurate altimeter system in all aircraft and these ops are RVSM (late 1990's and early 2000's).

Now, in order to guarantee that this system works as designed several points need to be satisfied one of which is the integrity of that static port I mentioned earlier. Static ports can be sensitive to external air flow and hence any variation / disturbance / abnormality in the area immediately adjacent to them on the fuselage must be avoided whenever you want to use the aircraft for RVSM operations.

And hence the markings to serve as a guide to all involved in aircraft ops about which is the area to worry about. e.g. Any imperfection in that region will have to be dealt with immediately. And worst case the aircraft would not be capable of flying in RVSM operations till any problems are fixed.


Why do METARs report wind relative to true north rather than magnetic?

Metars are used by more groups than just aviation.  In the U.S. it is official weather for the National Weather Service.  It is easier to graph winds in relation to true north than have them in shown in magnetic north.  The graph wouldn't make much sense.

Spoken winds are in magnetic because they are specific to aviation and that is what pilots care about.


Is there an FAA rule or Advisory Circular with regard to blood donation?

An air carrier that I have worked for specifically addresses this issue in their General Operations Manual—which is accepted by the FAA. The manual gives the following requirement:

Flight Restrictions After Blood Donations
Flight personnel shall not participate in any capacity as flightcrew members for a period of 24 hours after donating more than one-half pint of blood.

Note that this portion of this manual is accepted by the FAA, not approved.1
One unit of blood is generally 470-500 mL, or one pint. The one-half pint specified above half of a regular unit of blood.  According the the Red Cross, a typical donation is about one pint, or one unit.

The FAA also publishes the Guide for Aviation Medical Examiners. I am not an AME, nor am I fully familiar with the Guide or how to interpret it. However, I understand that the following table shows that outside the listed time-frames, an applicant for an airman's medical certificate could be considered medically fit for flight duty:

1 The terms Approved and Accepted mean specific things to the FAA. See 8400.10, Vol 3, Ch 15, Sec 1:

Approved: When approved is used to describe a document, manual, or checklist, it means that a regulation requires FAA approval and that the FAA has evaluated and specifically approved the document, manual, or checklist.
Accepted: Accepted is used to describe a document, manual, or checklist that does not have, or is not required to have, FAA approval. Only a portion of an operators manuals are required to have FAA approval. The remaining portions are accepted by the FAA. Operators are required to submit the entire general manual to the FAA for review. If the FAA concludes that an accepted section of the general manual is not in compliance, the FAA must formally notify the operator of the deficiency. Upon notification, the operator must take action to resolve the deficiency.


What kind of insulation is used on commercial aircraft?

This article from Boeing describes fire safety on their planes, and they mention "fire-protective insulation blankets." A quick google search suggests that in non-aviation contexts, these are usually ceramic fiber. So it seems likely that at least one form of fire insulation in modern transport-class aircraft is ceramic fiber fire blankets.


Can bird strikes be dealt with by throttling down engines to idle?

A goose can easily be flying at 40mph and a commercial jet will be landing at about 150mph, giving a closing speed of about 190mph (305km/h). That means that, to spot a goose with 10s warning, you would need to spot it when it's more than half a mile away.

Not only would you have to spot that tiny speck of a goose half a mile away during the busiest phase of the whole flight, but you'd also have to immediately work out whether the tiny speck was even coming towards you. If it was, you'd have to estimate whether it would even hit the plane.

Then, supposing you'd immediately and accurately recognized the danger to your plane from that tiny speck, you'd have to immediately reduce power to the engines, while being very careful not to hit the ground the bad way.

In short, regardless of how much better the outcome of a bird hitting an idling engine would be than one hitting an engine under power, it's just not feasible to try to power down the engines. Once you take into account the false alarms, which would vastly outnumber the actual bird strikes, trying to power down the engines would probably be far more dangerous than just hitting the bird.


Does kerosene have a higher octane value than gasoline?

Octane rating is a measure of how well a fuel resists detonation, which is the premature explosion of fuel in an engine cylinder before the spark is applied. This is relevant for spark ignition engines which use gasoline type fuels like avgas.

Kerosene has a very low octane rating, somewhere around 15, and isn't a good fuel for spark ignition engines as it would detonate on compression. This is why kerosene and diesel are used in diesel cycle engines which rely on the spontaneous detonation of fuel under pressure. Kerosene is not typically used in internal combustion engines, however in aviation there are turbo-diesel piston engines which run on Jet-A1.


I have an FAA ATPL based on a foreign ATPL, can I convert it to an EASA ATPL?

Do you actually have an ATPL or a frozen ATPL?

Essentially, EASA requires you to sit all the ATPLs as well as the individual IR exam and your practical flight tests for the CPL, ME and IR. That is conditional on you having completed an "approved course of training" and whether your FAA stuff counts I don't know; I doubt it as it isn't EASA.
Some stuff (CPL, ME & IR) can be converted depending on experience but from what I understand from a friend, many UK schools are very reluctant to do this at all. I can't speak for other EASA nations.

So essentially, plan on doing your ATPL again.


Was the Airbus A300/A310 ever supplied with a yoke and not a sidestick?

The sidestick was a design that came about along with the new fly-by-wire technology of the A320 in the late 1980's. The physical leverage of a yoke was no longer needed for flight control cables. The older designs of the A300 and A310 series planes from the 70's and 80's have conventional yoke flight controls.

I would not be surprised to see inaccuracies in TV reenactments, but the yoke did happen to be important in that particular case.


Compression and tension members of a biplane wing

It's not a tension member in that sense.  This is a pin jointed truss with flexible tenion-only diagonals.  The lower wing is a non-cantilevered beam, that is, supported at both ends, so it will bow up in the center under load with flight loads, and this applies a modest tension load at the root (as well as pulling the bottom of the interplane strut inboard, to the extent that deformation occurs in the main spar beam).   If the lower wing's spar had perfect rigidity and didn't bend at all, there would be no tension load at all at the wing root; it would be all vertical shear.

If you thought of the lower wing as a sheet of fabric, and imagine that the interplane strut at the outer end was rigid vertically, you'd have basically an upside down hammock, and when you lay in a hammock, the attachments are under tension (of course, the outer interplane struct not being rigid vertically, the hammock would collapse straight up - in the biplane's case the lower "hammock" is a semi-rigid length of lumber that only deflects slightly so the outer interplane strut doesn't have to be vertically fixed).  So the extent of any tension load at the root fitting for the lower wing, it's only to the extent that there is a hammock effect happening as the spar deforms.

To get the lower wing to work in tension as part of rigid truss system with the upper and lower wings integrated into it, the X of diagonal wires have to be replaced with rigid struts that can take compression.  The rigid strut running down from the upper root to lower tip would be in compression, sharing load with the other one in tension, and this would make the lower wing a tension member in the system.  But with tension-only flying wires, that doesn't happen.

Clear as mud?


What provides a higher lift to drag ratio, a thick laminar wing or a thinner wing with a vortex generator

You confuse turbolators with vortex generators. And then you misunderstand the function of vortex generators.

Turbolators trip the boundary layer and change laminar to turbulent flow in order to enable the boundary layer to remain attached over a steep pressure rise. That is definitely required at the Reynolds numbers mentioned (200,000 to 500,000) in order to maximize performance.

Vortex generators work in a fully turbulent boundary layer and re-energize it by mixing more of the outer flow into it.

Both increase the boundary layer drag but help to prevent early separation. Only over the range of that prevented separation they reduce drag.

The answer to your question depends on the Reynolds number. At 1,000,000 and above, the laminar wing should be better and if you add boundary layer tripping at the right chord station, it also wins down to 200,000.


How would an aircraft visually signal "in distress"?

For the US, the FAA's Intercept Procedures list several things a pilot can indicate without radios:

Acknowledge instructions: rock wings, flash nav lights
Unable to land at indicated airport: flash landing lights
Cannot comply: switch all lights on and off at regular intervals
In distress: switch all lights on and off at irregular intervals


Did commercial airliners have microwave ovens in the past?

Generally speaking, airliners do not have microwave ovens for safety reasons. I could not find any reference where commercial airplanes used to have microwaves. Probably some smaller business jets have them.

Some flight attendants mention that they can warm your food, but some say that they will not for legal and health reason.

As also mentioned by sweber in comments to the question, meals are not heated at the airport. Airline catering companies like LSG Sky Chefs prepare the meal near the airport and deliver it to the airplane. Inside the airplane, they use convection ovens to heat it.


What is this hole in the nose of the A330?

It is the avionic compartment access door as described in the Flight Crew Operating Manual!

  An inward-opening, manually operated, hinged door gives access to the avionics compartment. This door is in the lower fuselage, forward of the nose landing gear bay. A ladder is stowed inside the compartment adjacent to this door, which may be either be operated from the interior or the exterior.
  This compartment is also accessible from the cockpit, via a floor hatch located behind the Captains' seat. A fixed ladder in the avionics compartment for access from the cockpit.

Here is a drawing from the outside!

And here a view from the cockpit flight deck for an A340!


Can airliners benefit from vertical take-off and landing?

The closest to what you ask was maybe the Do-31 experimental VTOL transport.

Dornier Do-31 in hover. Picture Source

It was developed to fly supplies to VTOL fighter bases. Makes no sense to have a VTOL fighter fleet if you cannot supply them, right? That was what the Do-31 was for, and the technically successful program folded when NATO abandoned the VTOL strategy in the Sixties.

Compared to regional airliners of its time, the table below shows how much the installation of sufficient thrust has cut performance:

I used the Fokker F-28 for comparison, because it is of similar size and age. As you can see, VTOL easily costs half the payload. 36 fully equipped troops may weigh more than 36 passengers, but they will sit on much lighter seats and have much more frugal accommodations. Note that I used the reduced take-off mass for VTOL flight, but have no information if that mass would have included the full payload. The range is valid only for the higher maximum take-off mass of 24.5 tons, for which a conventional take-off was necessary.

The Do-31 could have fitted the Belgian airline SABENA, which at the time (the Fifties and Sixities of the last century) had the most advanced VTOL strategy of all airlines. They operated regional connections with helicopters, but eventually reverted to regular aircraft well before the Do-31 would had been available. Heli-Air Monaco is still in operation after almost 40 years, but this is more a taxi service than an airline.

Considering not only the increased fuel consumption, but also the increased maintenance cost on more and diverse engines (most VTOL airplanes have dedicated lift engines), the operating cost even at the times of cheap fuel were too high to make the convenience worth it.

I think it is possible to develop a VTOL A320, but it would look very different, would cruise at a lower speed and have a much reduced payload and range. Tickets would be horrendously expensive, though.

EDIT: Thanks to @egid for his suggestion to use mass fractions for comparison. Unfortunately, I found detailed mass data of the F-28 only for a later version, but the expanded table shows the point clearly:

The useful load fraction is the result of dividing the difference between take-off mass and operating mass empty by the take-off mass, showing the sum of payload and fuel as a fraction of take-off mass. Adding lift engines, slow-speed controls and a rear loading ramp clearly reduced what could be carried in VTOL flight.


What would it take to pressurize a cabin with surface pressure?

Not much. The current requirement for 8,000 ft equivalent pressure translates into 8.11 psi at 43,000 ft. Boeing studied the benefits of lower pressure and found that going below 6,000 ft equivalent pressure brought no additional benefits.

The full pressure differential between sea level and 43,000 ft is 12.3 psi or just 52% more than that at 8,000 ft. This would require a heavier fuselage, but would not be impossible to do at all. Statistical methods give a mass factor for the fuselage pressure differential of $(1 + ∆p)^{0.203}$ which yields 1.0933 for 8.11 psi (∆p = 0.552 atm) and 1.1314 for 12.3 psi (∆p = 0.837 atm). Increasing the pressure to its sea level value would increase the mass of a typical airliner fuselage by 3.5%.

If we use the volume of the cabin, we can also calculate how much heavier the air is: The A330-200 has a cabin volume of 372 m³, and with the density of air at 8,000 ft of 0.9633 kg/m³, this computes to 358.35 kg. Compared to the mass of the same volume at sea level (455.7 kg), the difference is roughly equivalent to the mass of a single passenger (not counting the amenities carried along for her/him, too). In other words: The added mass of air for sea level pressure will make no difference if one passenger more misses her/his flight that day.


What are the statistical probabilities of commercial aircraft accidents?

Short answer

The International Air Transport Association (IATA) publishes each year a report about aircraft accidents in the world. The latest one indicates these average figures:

There are 3.3 billion passengers per year.
There are 100,000 flights per day.

Over the last four years the accident rate decreased from 94 to 73 accidents per year.

In 2014, among these 36,500,000 flights:

There has been a total of 73 accidents
12 accidents had fatalities (641 fatalities).

Extracts from IATA 2015 report

(Source: IATA report)

Period 2010-2014

(Source: IATA report)

Type and fatalities:

(Source: IATA report)

Geographical distribution:

(Source: IATA report)


What security clearances does a foreign citizen doing a flying course in the United States have to pass?

You need 2 things before you can start flight training in the U.S.:

An appropriate visa. A tourist visa (B2), business visa (B1) or VWP (Visa Waiver Program) is not accepted
TSA clearance through the Alien Flight Student Program (AFSP)

The complete process is documented at the AOPA website.

In a nutshell, this is what you need to do:

Make sure you have a proper visa or permanent resident card (green card). A visa that allows you to live in the U.S. is fine (you don't need a specific visa for flight training). Examples of appropriate visas: H1B, H4, L1, L2 but there are many others
If you don't have one of the visas mentioned above, you need to apply for a student visa (M-1). You need to contact a flight school that will assist you with the visa application.
Contact a flight school if you haven't already done so in the previous step. They will register your "case" and provide you with information you need when applying for TSA clearance.
Apply for the AFSP program on the TSA website
Wait for approval by the TSA (is a multistep process that could take a while. It includes having your fingerprints scanned, among other things)
Start your training


Direction finders outside of Alaska were decommissioned in 2007 as GPS and and ADS-B, as well as older technologies, have made the DF services obsolete. The DF services in Alaska were decommissioned in 2013.


can I do my PPLA license in spain even if I live in Germany?

Yes, an EASA PPL is valid in all EASA member states


What is the heaviest aircraft fitted with a central control stick?

The biggest I can find is at 585,000 lb the C-17 has a center stick but depending on what you mean by "airbus style" this may be disqualified.

Other contenders:

The SR-71 had a MTOW of 172,000 lb and had a center stick
If you consider the time it spent in the atmosphere as qualifications for "aircraft" at 240,000 lb the Space Shuttle had a center stick


Is flap-asymmetry protection on airliners still active even on the ground?

It is active whenever the flaps are being moved by the hydraulic system on the 737; it isn't available when using the backup (electrical) system.
Allowing asymmetric flap extension before takeoff could have consequences as serious as asymmetric extension in flight. Plus, tying the protection to an air/ground sensor is one more way that the system might fail.
Evacuations are pretty rare events; the chance of having one along with a malfunction as described in the OP is extremely remote. Such an unlikely occurrence doesn't overcome the reasons to keep asymmetry protection available full-time.


For the A320:

Conf 0/1 the rate is 0.3°/s
Conf 1+F/2/3/Full the rate is 0.7°/s

I haven't found any difference for A/P vs Manual flight.

In A319, THS freezes in the following situations:

The pilot enters a manual trim order.
The radio altitude is below 50 ft (100 ft with autopilot engaged).
The load factor goes below 0.5 g.
The aircraft is under high-speed or high-Mach protection.

In A320, THS freezes in the following situations:

The pilot enters a manual trim order.
The radio altitude is below 50 ft (100 ft with autopilot engaged).
The load factor goes below 0.5 g.

There are further conditions under which THS range is limited, let me know if you would like me to expand.

Source: A320 FCOM DSC-27-20