Can a sonic boom produced at 60,000' be heard on the ground?

Yes, a sonic boom produced at 60,000' can be heard on the ground.

First of all, a sonic boom consist in a steep increase of air pressure, followed by a slow, linear decrease below the nominal ambient pressure, and again a steep increase back to the nominal pressure. It is therefore called N-shaped wave or just N-wave. Here is a graph with several sonic booms, measures by NASA and found on Wikipedia:

The same wiki page cites a document from NASA

Aircraft        speed   altitude        pressure
               [mach]   [ft (m)]        [lb/ft² (Pa)]

SR-71           3      80,000 (24,000)  0.9  (43)
Concorde SST    2      52,000 (16,000)  1.94 (93)
F-104           1.93   48,000 (15,000)  0.8  (38)
Space Shuttle   1.5    60,000 (18,000)  1.25 (60)

These measurements are from aircraft with different altitude. As sound pressure depends from distance like  $p\sim\frac{1}{r}$, one may calculate the pressure for a certain altitude as in the following table. However, this assumes that the aircraft causes the same "boom intensity" at that altitude, which you should doubt at least for the SR-71.

Aircraft        speed   altitude        pressure
               [mach]   [ft (m)]        [lb/ft² (Pa)]

SR-71           3      48,000 (15,000)  1.44 (69)
Concorde SST    2      48,000 (15,000)  2.07 (99)
F-104           1.93   48,000 (15,000)  0.8  (38)
Space Shuttle   1.5    48,000 (15,000)  1.5  (72)

As you can see, the Concorde is the loudest aircraft, the most comparable F-104 (speed, altitude) produces just 40% of its sound pressure. But the F-104 is also much much smaller than the Concorde.

The Space Shuttle is very loud for its low speed. However, it looks more like a flying brick than an elegant, streamlined aircraft, so no wonder that it creates strong shock waves.

The SR71 seems to be very quiet for its speed, but as said, I don't think you can pull it down to 48000ft and expect the same behaviour. However, a sonic boom starts to disperse in some (larger) distance, may be this already happened for the SR-71. (Also, it's a spy plane with a very special shape - may be, this reduces the boom, too).

It has to be said that it is hard to translate the numbers into a comparable sound level, because what makes up the loudness is not only the maximum pressure, but also the rise time.
As counter-example, the air pressure changes by 130Pa every meter of altitude (at ground), and you don't hear the change of pressure when standing up from your chair (~100kPa)

Also, a sudden noise appears to be much louder than a noise slowly increasing to the same level - and the bang has the most sudden wave form possible. (Listen loud music with earphones - when the player clips a second, the first moment after really hurts)

However, there is a long table on Wikipedia listing noise sources and their levels. For example:

Trumpet at 0.5m:                63Pa
Jack hammer at 1m:               2Pa  (I'd say: a little quite...)
Loudest human voice at 1 inch: 110Pa

These levels are effective sound pressure. To translate a perfect N-wave with given maximum pressure to effective pressure, you have to multiply the value by $\frac{1}{\sqrt{3}}\approx0.577$.

Thus, the sonic boom of the Concorde has an effective value of 57Pa, which is comparable to the trumpet in 0.5m distance.

(As said, there is still a difference, because the boom is a sharp, short noise, but it gives an idea.)

By the way, I just stumbled on another document, about primary and secondary sonic booms.

It states that you hear a primary sonic boom coming from the aircraft within a lateral distance of ~20nm (solid lines) as well as a secondary boom within a distance of 60-85nm (dashed lines). This secondary waves are a reflection of the upwards travelling shockwaves from the aircraft at the atmosphere.
The secondary boom is not a short, loud bang, but a longer and less intense rumbling, making it difficult to identify the source.


Why couldn't the CRJ100/200 be equipped with triple-string autoland?

I have experience on that program and can tell you that:
A:  While anything is possible, this would cost a fortune to implement, requiring a complete avionics overhaul.  For a single potential customer?  Snowball's chance in heck.  The customer would have had to commit to paying the development costs, many zillions, which would also have a snowball's chance in heck of happening.
B: By the mid 2000s, no development money was being allocated for that sort of product improvement on the 200. By then the program funding was generally only to deal with airworthiness issues and upgrades to deal with avionics obsolescence, as development money focused on the 700/900.
C: British Airways aside, there was no demand to speak of from the industry for that kind of capability, that anybody would be willing to pay for. Adding HUGs on the 700/900 to get Cat IIIa cert was more than sufficient.  On the 200, even to do that would have required an avionics suite upgrade that no regional operator would be willing to pay for (again, Snowball's chance in...).  Regional operators run on very thin margins.
In the US, by the late 2000s, Regionals would not even implement optional Service Bulletins unless there was a financial payback of ONE YEAR or less.  That meant that only SBs mandated by Airworthiness Directive were being incorporated.


What does 'in-trim speed' mean with respect to Boeing 737 mis-trimming correction?

"In-trim" speed means whatever speed the airplane will naturally seek if you let go of the controls.  If you set the stab to position X, the airplane will naturally seek speed Y, for a given weight, thrust, flaps, and C of G condition.

So say the stab is at position X and this makes the airplane want to pitch to 240kt.  It will seek and maintain that speed if you don't touch the controls.  If you want to fly slower, you can add up elevator by pulling the column back, increasing the tail's downforce and pitching the nose up, until it slows to a speed where the forces are back in balance with the elevator held fixed at that position.  Say it's 200kt.

You are now 40 kt below trim speed, and having to hold the elevator displaced to keep it there.  If you want to be able to let it fly hands off at 200kt, you have to move the stab itself so that the tail's downforce with the elevator at neutral is the same as when the elevator was being displaced.  So you trim out the elevator displacement (by applying trim and easing the column back to neutral in little trial and error inputs) and now you're in trim at 200kt, hands off.

The 737 has a stab screw jack with a manual operation feature with a cable circuit between the screw jack and the trim wheels in the cockpit that let the crew turn the jack directly with the trim wheel, with no electric input, when in manual trim mode.

If you are way out of trim, that is, holding a lot of elevator to make the airplane fly slower or faster than its trim speed, it puts a large rotational moment within the horizontal tail which increases the up or down load on the screw jack itself.  These jacks are usually acme screws with dual load path threads that have a fair bit of internal friction under load, and the effort to drive the screw when it's highly loaded can be more than you can apply with your hand on the little wheel on the sides of the center console.

So say you're in manual trim and the airplane is trimmed to 280 kt and you want to slow to 200kt, and pull the nose up with elevator to slow down and you don't retrim as you're slowing down.  At some point, if the out of trim condition and resulting the load on the screwjack is high enough, you can't move the trim wheel because you can't apply enough force to turn the jackscrew.  To avoid this, you should be retrimming the stab as you slow down.

Their procedure is to try to offload some of the out of trim load on the stab jack by moving the elevators back toward the original trim speed.  If you were holding the column way back to slow to 200kt while the airplane was still trimmed for 280kt, you'd release some of the pull, letting the airplane pitch over a bit and accelerate, while trying to move the trim wheel.  At some point you'll have unloaded the stab screw jack enough to make the wheel move.  You don't want to pitch over any more than you have to so you just relieve the elevator enough to get the wheel to move, and keep working it along until it works normally.

In this context, "extreme cases" refers to the case of a large difference between existing speed created by elevator input and existing trim speed.


Airplane longitudinal control: pitch or power?

I was wondering how long that it would take for this question to come up.

It is the old "pitch -vs- power" airspeed control technique debate that rages throughout the aviation world.  There are strong proponents of both techniques (and they seem to view it almost as a religious debate in that the other side can never be right, no matter what), and both sides have good reasons for it!

Instead of saying that one is better than the other, let's just say that they are both techniques for managing the potential energy of the airplane (the airspeed that can be traded for altitude and vice-versa).  In fact, this is how I like to think about it (and don't pick a side):

If you change the pitch of the aircraft without changing power, the airspeed will stabilize out at a new value.

Pitch up and you lower the airspeed.
Pitch down and you raise the airspeed.

If you change the power setting of the aircraft without changing the pitch, the airspeed will stabilize out at a new value.

Add power and you raise the airspeed.
Reduce power and you lower the airspeed.

You can change both at the same time and get various results.

You can end up with the same airspeed that you had before.
You can end up with a lot more airspeed.
You can end up with a lot less airspeed.

Most often you need to change both at the same time in order to properly manage your airspeed.

So basically it comes down to what you want to accomplish.  If you need to change the airspeed you have two ways to do it, but used individually each comes with a side-effect.  In some situations this may be okay or even desirable, but you need to be aware of what your actions are going to accomplish.

Let's look at a specific example:

Sometimes, especially on an instrument approach, you want to maintain your current airspeed while changing your vertical speed.

Let's say that you are a little high on the glideslope.

If you simply pitch down to recapture the glideslope, you will gain airspeed but will recapture it quickly.
If you simply reduce the power to recapture the glideslope, you will lose airspeed but it will take longer than using pitch.
If you want to maintain your airspeed while recapturing the glideslope (typical on an instrument approach) then you would pitch down and reduce power at the same time, and when you recapture the glideslope you will pitch back up to maintain it and add power to maintain your current airspeed.


Can the VNAV Path angle be modified in a Boeing 737 NG?

In the 737 NG, the descent angle is never entered by the pilot into the FMC. One enters a Cost Index, or alternatively a descent speed that's desired, and the FMC, considering forecast winds, computes the Top of Descent point and the angles that it expects to fly in order to achieve that speed.

But, it never tells the pilot what descent angle it's planning to use (although you can see the present vertical angle to a specified waypoint/altitude). Whatever the angle it's planning, you can steepen it or shallow it by increasing or decreasing (respectively) the planned descent speed or Cost Index.

But, unlike some other FMC's, the 737's never explicitly tells you the planned descent angle for enroute operations.

(On an approach, it's a different story; there your gradient path is coded with the waypoints, and it is displayed on the LEGS page. But the user can't change values in the database like that. Speeds, yes; GP angles, no. A pure visual approach, with only a runway-end waypoint is the ONLY time you can specify whatever angle you wish... but that's only to the runway itself, and not at all usable on any other leg.)


Engine failure is not that common. For a gas turbine engine, a press release by GE gives some data as a reference point. In 1995 they quoted various engines as having a dispatch rate of between 99.99% and 99.89%. That is only 0.01 to 0.11 % of flights could not depart due to an engine issue. However, that doesn't identify in flight failures, best captured by the inflight shut down (IFSD) rate. Data on this is difficult to get for specific engines, as the OEMs consider it competitive information, so the best guide is probably as mentioned the ETOPS rating. The ETOPs fleet is reported as achieving a shut down rate of less than 0.01 per 1000 engine hours. Another way of defining reliability is the (repair) shop visit rate (SVR). Figures given for this (by GE in the same link as above) were between 0.085 and 0.231 visits per 1000 flight hours. However, this covers both scheduled and unscheduled maintenance (i.e. failures), so perhaps doesn't identify what you want.

For piston engines, the answer to this  question probably has some useful data. In addition, Continental claimed in 2014 that they had an IFSD rate of 0.0061 per 1000 flight hours, which they claim is the most reliable piston engine in general aviation. This compares with "less than" 0.01 for gas turbines, so, it seems very similar.

It maybe possible to find a better value for the IFSD rate for gas turbines. Given the rate is so low, it really needs to be quoted to more than 2 decimal places, or given per 100,000 flight hours. Ultimately, I would expect the IFSD rate for gas turbines to be lower than for piston engines, due to the huge economic incentive gas turbine manufacturers and the commercial airline industry has increasing reliability for turbofan engines, that does not exist to the same extent, for general aviation piston engines.


How were fighter jets built in the 1950's?

Building an airframe did not change all that much in the jet age. Assuming you are talking about all aluminum aircraft the power plant is somewhat abstracted from the equation in terms of a production line.

Here is the assembly line that Lockheed had for the early P-80 Jets (not all that different than their propellor counter parts). This picture would make it seem as though the airframe was all built in one place as you can see it in various stages in this image alone.

(source)

This is a pretty interesting article about the history of the plane and the role Kelly Johnson played in it.

Like anything in the world of production the assembly line does not change nearly as much as the tooling does. One of main costs in bringing anything to production is cutting and preparing the tooling. Assembling a jet airframe was not all to different than assembling a high performance prop plane of the era.

Things got more complex as they moved to more complicated materials (this came a bit later than your question references but none the less). By all accounts an enormous portion of the SR-71 Blackbird budget was spent developing tooling that could work with titanium.

The engine companies (Like GE/P&W etc) saw much bigger changes as they were now making and testing a completely different product. The P-80 above housed a GE/Allison J33. This would have fallen on to GE to build and like many engines prior would have simply been bought by Lockheed for the plane.

I will try and find some hard production numbers/times for this era of planes.


What is the most critical data to measure for a predictive maintenance model for a drone?

Predictive Maintenance (PM) typically relies on a triad of vibration, thermal and oil analysis, or any combination thereof. Probably vib and thermal would apply. Cheapest option would be to physically hold the drone while running (if possible) and acquire vib and thermal, using handheld instruments. All-in option would be a hardwired system, permanently installed. With a hardwired system, you'll need a vib and a thermal transducer installed on each power/rotor module. Hope this helps.


Why are the affected engine's bleed and pack switched off when there is an engine bleed under MEL?

It's not unique to the neo and the PW engine option.
Yes a single engine can supply both packs, but it's a big load on the remaining bleed system that can lead to its loss when used for a long duration.
An example from 2013 is Swiss A320 near Marseille on Sep 12th 2013, loss of cabin pressure (avherald.com). The plane was dispatched with 1 pneumatic system, the operator did not have the revised MEL procedure, and the working pneumatic system failed.
An explanation given in an Operations Engineering Bulletin for the AIR ENG 1(2) BLEED FAULT is:

(...) due to undetected failure, the remaining bleed may not succeed in sustaining this increase in air demand. In that case, it can result in an overheat of the remaining engine bleed and subsequent loss of the entire engine bleed system, leading to possible emergency descents. (...)

There is also the Airbus publication, Avoiding Dual Bleed Loss (airbus.com; PDF), from which:

Over the past years, the A320 family fleet experienced a significant number of dual air engine bleed losses. The consequences of these losses ranged from in-flight turn backs shortly after take-off, to full blown cabin depressurization events and flight diversions. (...)
The dual bleed loss events usually happen when one bleed fails, resulting in the remaining bleed on the other engine to compensate for it. (...)
In case of one engine bleed loss, the remaining bleed fails when the Fan Air Valve (FAV) does not let enough cold air reach the Precooler (PCE).

What's unique to the PW engine from my discussion with you, is that the one engine taxi procedure calls for crossbleed to AUTO, because the higher-idle of ON (used with CFM/IAE) would negate the fuel savings. For the ceo engines, one engine taxi is not a long duration, and the denser air on ground helps the precooler.
The MEL item being asked about is still as outlined by Airbus above.


Does EASA approve the use of localizer back course?

Depends what you mean. If you mean "are they approved at EASA airports?" I can't help except to say that I have never seen a plate for one, flying into most EASA countries into a wide variety of airports.

If you mean "are EASA aircraft and pilots allowed to fly them in countries that do allow them?", I can tell you that in the Radio Navigation syllabus for the EASA ATPL exams there is a learning objective that the student must know what to set on an OBS or HSI to fly a back-beam localiser approach (if you want to check it's LO 062.02.05.02.08 in the new syllabus, 062.02.05.02.13 in the old one which is just about to go out but more widely available at the moment). This implies that flying one in an EASA-registered aircraft with an EASA licence and IR is not prohibited.


What would happen if a hot air ballooon was punctured in mid-air?

Hot-air Balloons are already made with large holes in them. They are called vents. They can be located in the balloon’s top or sides. They tend to be much much larger than the 4-inch diameter you described in your question. But, their opening and closing are controlled by the pilots. Research the FAA Balloon Flying Handbook. It will give you much more insight than I can.


What is the lightest jetliner out there?

I assume that you want to only compare turbofan-powered aircraft, and exclude aircraft designed to be used as private jets.

In that case, the lightest would be Dornier 328 Jet with a basic operating empty weight of 9200kg, and the next would be Embraer 135 measuring 11402 kg.


Is a winglet better than an equal span extension?

Here is what I think you need to come to your own conclusion. First I will give a very general overview over lift creation, and then I will look at three wings:

An unmodified wing
This wing plus a winglet
This wing plus the winglet, but this time folded down into the plane of the wing.

For each I will plot the lift and bending moment distribution. I will assume an elliptic circulation, fully knowing that this is not what most aircraft use. But I have to pick a distribution to make all three cases comparable, and the elliptic one makes things easier. The conclusions can be generalized for other distributions.

This will be a lengthy post (you should know me by now), so thanks to all who persevere through all of it.

Lift creation and induced drag

This topic had been covered before, and I mention it again to show a very simple and elegant way to explain induced drag that does not need vortices. I want to dispel the myth that induced drag is caused by air flowing around the wingtip, and winglets somehow magically can suppress this flow.

Consider a wing with elliptic circulation over span (think of circulation as the product of the local lift coefficient $c_l$ and local chord; it is basically the lift per spanwise increment). The wing bends the air through which it flows slightly downwards, and creates an opposite upwards force, namely lift (Newton's second law). I choose an elliptic distribution because then the downwash is constant over span, which makes the following calculations easier.

The sheet of air coming off behind the wing looks trough-shaped and moves downwards, thereby pressing other air below out of the way and allowing air above to flow inwards and to fill up the vacated volume. That is how the free vortex is created, and air flowing around the wingtips has only a small part in this.

Induced drag is the consequence of the wing bending the airflow downwards. To simplify things, let's assume the wing is just acting on the air with the density $\rho$ flowing with the speed $v$ through a circle with a diameter equal to the span $b$ of the wing. If we just look at this stream tube, the mass flow is $$\frac{dm}{dt} = \frac{b^2}{4}\cdot\pi\cdot\rho\cdot v$$

Lift $L$ is then the impulse change which is caused by the wing. With the downward air speed $v_z$ imparted by the wing, lift is: $$L = \frac{b^2}{4}\cdot\pi\cdot\rho\cdot v\cdot v_z = S\cdot c_L\cdot\frac{v^2}{2}\cdot\rho$$

$S$ is the wing area and $c_L$ the overall lift coefficient. If we now solve for the vertical air speed, we get $$v_z = \frac{S\cdot c_L\cdot\frac{v^2}{2}\cdot\rho}{\frac{b^2}{4}\cdot\pi\cdot\rho\cdot v} = \frac{2\cdot c_L\cdot v}{\pi\cdot AR}$$
with $AR = \frac{b^2}{S}$ the aspect ratio of the wing. Now we can divide the vertical speed by the air speed to calculate the angle by which the air has been deflected by the wing. Let's call it $\alpha_w$: $$\alpha_w = arctan\left(\frac{v_z}{v}\right) = arctan \left(\frac{2\cdot c_L}{\pi\cdot AR}\right)$$

The deflection happens gradually along the wing chord, so the mean local flow angle along the chord is just $\alpha_w / 2$. Lift acts perpendicularly to this local flow, thus is tilted backwards by $\alpha_w / 2$. In coefficients, lift is $c_L$, and the backwards component is $\alpha_w / 2 \cdot c_L$. Let's call this component $c_{Di}$: $$c_{Di} = arctan \left(\frac{c_L}{\pi\cdot AR}\right)\cdot c_L$$

For small $\alpha_w$s the arcus tangens can be neglected, and we get this familiar looking equation for the backwards-pointing component of the reaction force: $$c_{Di} = \frac{c_L^2}{\pi\cdot AR}$$

If the circulation over span has an elliptic distribution, the local change in circulation times the local amount of circulation is constant, and the induced drag $c_{Di}$ is at its minimum. If this would be different, a higher local $v_z$ causes a quadratic increase in local induced drag, so the whole wing will create its lift less efficiently.

Now we know we can calculate induced drag and we understand why the vortex sheet behind the wing rolls up, producing two counter-rotating vortices, all without looking at the details of the wingtip. What counts is that the wing is of finite span, so the stream tube which is influenced by the wing is of finite diameter as well. Of course, in reality there is no clear boundary between air which is affected by the wing and other air which is not. There is a diffuse transition the more one moves away from the wing.

Comparison of wingtips

First the geometries: Here are three wingtips in top and front views for comparison:

Now let's look at the circulation distribution of the simple wing tip:

Again, I choose the elliptic distribution for simplicity. The corresponding bending moment looks like that:

No surprises so far. Now we add a winglet and make it work as best as possible. This means we have to give it an angle of attack where it carries the circulation from the wing over on the winglet and completes the elliptic tapering of circulation down to 0 at the tip:

The grey dashed line is the circulation of the original wing. I adjusted the circulation such that both wings produce the same lift. $b_{WL}$ is the span at the winglet tip, and for the bending moment plot I have folded the spanwise coordinate down on the y axis:

Now the bending moment starts at the wingtip with a nonzero value. Since the sideways force of the winglet is parallel to the wing spar, this bending moment contribution is constant over span. But there is more: Now also circulation at the old wingtip location is nonzero, and we get a substantial lift increase at the outer wing stations. This effect is what causes the additional lift and gives the better aileron response that winglets make possible. But it also increases the root bending moment, because this additional lift acts with the lever arm of the outer wing.

How can we compare the induced drag of the wing with winglets to the original wing? The circulation gradient is lower, that helps. Also the diameter of that stream tube is larger, but it is hard to say by how much. The sideways force on the winglet is created by pushing the vortex sheet aft of the winglet sideways out, so the trough-shaped area should become wider. Empirical evidence hints at an increase in diameter of 45% of the winglet span (see chapter 6 for a discussion of several papers on the topic).

Just for the heck of it, let's assume that the diameter really increases in line with winglet span. Then let's compare that to the straight wing extension, where the same diameter can be assumed with much more certainty:

Now also the lift on the folded-down winglet acts upwards, so the circulation at the center of the wing can be reduced even further. However, now it adds a linearly increasing part to the bending moment, and the outer wing section creates more lift, as before with the wing with winglet:

Here, the root bending moment is higher than in the winglet case. This is a second advantage of winglets: They allow to increase maximum lift with less bending moment increase than a wing extension. But the wing extension puts all parts towards the creation of lift, and not some to the useless creation of side force. Both the extended and the winglet-wing have the same surface friction and (when we assume the same diameter of the hypothetical stream tube) the same induced drag. But since the winglet creates some side force, the remaining wing needs to fly at a higher lift coefficient. Also, the intersection of wing and winglet might be as well rounded as possible, this is where early separation starts at higher angles of attack. None of this affects the straight wing extension.

Most evidence shows that winglets improve L/D over the original wing, but folding the winglet down will more than double its effectiveness in lowering drag. Even if we assume that the winglet is just as good as an equal span extension, still the span extension comes out ahead in L/D improvement because all its lift contributes to overall lift, whereas the winglet produces a side force instead. If no separation occurs at the wing-winglet intersection, both will create the same induced and profile drag (pressure and friction), because both have the same wetted surface and the same local circulation. Again, this gives winglets the benefit of equally low induced drag, which is not supported by most measurements.

The extended wingtip in the example above has interesting characteristics. It is a sweptback (raked) wingtip, which causes the local lift curve slope to be lower than that of the straight wing. This increases its maximum angle of attack and  - assuming that the local area is bigger than what an elliptic wing shape would dictate - makes it possible to keep a nearly elliptic circulation distribution over a wider angle of attack range. The bigger local area is a sensible precaution against the wing tip stalling first, so a raked wing tip will combine benign stall characteristics and very low induced drag.

Compare this to the winglet, which has to be tailored for one polar point: Since changes in wing angle of attack will not change the incidence of the winglet, it cannot adapt as well to different flow conditions as can the extended wing. In sideslip the winglet will mess up the circulation distribution on the wingtip and will act like a deflected spoiler.

Conclusion

Comparing equal winglets and wing extensions gives these basic characteristics:

Both have the same viscous drag at low angle of attack.
Both can create more maximum lift, and both lower induced drag.
The wing extension can create most lift for the given increase in wetted surface.
The wing extension is more than twice as effective in lowering induced drag.
The wing extension gives a better circulation distribution at off-design angle of attack.
The wing extension produces the highest root bending moment for a given amount of lift.

How much the bending moment increase will drive up structural mass depends on the aspect ratio of the original wing. Low aspect ratio wings will not suffer much, but stretching high aspect ratio wings will drive up spar mass considerably. But please note that the winglet also causes higher root bending moments, and it creates less bending moment than the wing extension because it creates some side force instead of pure, useful lift.


How does a jet's throttle actually work?

The throttle (or thrust lever) in a gas turbine engine adjusts the thrust produced by controlling the fuel flow to the combustion chamber.

Most of the modern engines are actually controlled by the Full Authority Digital Engine (or electronics) Control, FADEC (or Engine Control unit)- so the signals from the throttle are sent to the computer, which regulates the fuel flow based on various parameters (including engine safety) thereby adjusting thrust. The computer handles the additional components of the engines like the thrust reversers and afterburners.

The image below shows the throttle controlling the fuel system through the engine control in the Pratt & Whitney F100 engine that powers F-15 and F-16.

Image from kaskus.co.id


What is the encoding difference between ARINC 429 BNR and BCD formats?

Your basic decoding strategy looks correct -I didn't double-check the values, but the logic is sound. Note, however, that the difference of BCD vs two's-complement is not the only difference between BNR and BCD (and Discrete labels, which are also common). Binary-coded decimal (BCD) and binary (BNR) labels generally do decode as you have shown, but the Sign-Status Matrix (SSM) plays a large part in interpreting that data and using it is not optional.

For BCD labels, the SSM informs whether the data is positive or negative (or what direction is points), hence "Plus, North, East, Right, To, Above" vs "Minus, South, West, From, Below". It also informs if the data is invalid ("No Computed Data"). BNR labels include sign information already in the two's-complement encoding, so duplicating that information into the SSM would waste valuable bandwidth. The SSM still informs you of invalid data, but can also inform of (non-)operation in reversionary mode ("Failure Warning") or correct behavior ("Normal Operation").

What that of that means for a given LRU (line-replacable unit)1 can be completely different from any other LRU. To have any confidence in your interpretation of a label, you must obtain a hardware integration guide for the specific LRU in question to determine what format data is or must be provided in and what the SSM values imply. This integration guide is a separate document from any user or maintenance manual you may have received with an LRU for installation into an aircraft. It is usually only provided to original equipment manufacturers of other LRUs.

For example, a BNR label might still contain a readable value when the SSM is set to "Failure Warning", but whether or not you can still use that data depends on what the failure implies for the particular LRU. I once encountered an LRU that provided a label for barometric altitude that reverted to GPS height above ellipsoid when failure mode was set. This change in represented value was not appreciated at the time, but did teach me to always inspect the SSM first before believing any particular value. Furthermore, many BNR labels are also scaled by some arbitrary factor to provide a wider range of representable values. The scale factor is provided in the integration guide, and is usually a fixed value, but I have encountered some labels with values scaled by values from other labels.

The format for Discrete labels is always specific to the LRU. To know what this encoding is, you must have the integration guide.

Ultimately the difference between each particular ARINC429 label will depend on the specific equipment to which you are interfacing. The standard data types (BNR/BCD/Discrete) provide a rough idea of how the data is packaged, but the integration guide is the authoritative source for data encoding.

1: I use LRU as shorthand to mean any ARINC429 node. In practice, many ARINC429-compatible devices are not necessarily line-replacable.


Could an AN/APG-79 AESA radar "lock-on" a single bird?

Depending on the radar, the accuracy fallow might be too big for a smaller object as radar resolution and accuracy matter a great deal in detecting and hitting a small target, that is why usually birds do not show up on radar or are actually filtered out as they could not hit targets that small anyway…
Resolution refers to the size, meaning electromagnetic size or radar cross section (RCS), of the objects a radar can detect. The smaller the minimum detectable RCS of a radar system, the better its resolution. A radar with poor resolution might see a supertanker sailing past but not a tugboat, for example.
Accuracy is referring to the degree of uncertainty in the radar’s calculation of the target’s location. A very accurate radar, for example, might tell you that it’s detected a target at a distance (range) of 87.118km ±10cm from the radar antenna. A much less accurate radar seeing the same target might report its range as 90km ±100m.


The short answer to "Can I smoke in my own private aircraft?" is "Yes, usually".

As Promised, I looked up the relevant FAR (23.853 - Passenger & Crew Compartment Interiors).

The actual rule is long and verbose, but pretty common sense. The important regulatory bits for most personal aircraft are just two points though. You must:

Have "an adequate number" of self-contained ash trays
You don't want flicked ash or a snubbed cigarette to start an in-flight fire.
Have "No Smoking" signs you can illuminate, if the passenger/crew compartments are separated
This doesn't apply to most of us since our "personal" airplanes are light singles, but if you've got a fancy twin with a curtain or door between you and the passengers you'll need those signs.

For "commuter category" aircraft there are even more requirements. Those requirements don't apply to most "personal" planes, so even though it's probably a good idea to meet some of those requirements if you're going to allow smoking in your personal aircraft they're not legally required.

All that said, while it's likely legal (unless you've removed your ashtrays or your plane didn't come with them) common sense generally dictates you don't want to smoke in your plane - It's bad for the vacuum-driven instruments' filters, will require even more attention to cleaning the inside of your windows, and a loose cigarette in turbulence or a bunch of ashes blown about by an open air vent can be a pretty substantial distraction.


The Info button (top right) takes you to an explanation site, which in turn links you to

https://www.AviationWeather.gov/metar/symbol

Which explains the Symbol (under the section Fog or special weather) as Thunderstorm


Why can't an Airbus A330 dump fuel in an emergency?

To supplement Jimmy's answer, if they had to land right away, they could have; it just would've resulted in an overweight landing being recorded, and which on most airliners triggers a special inspection of the landing gear and its attaching structure, and if nothing is permanently bent or cracked or broken, you are good to go.

An overweight landing in itself shouldn't result in damage unless the landing was hard, the overweight condition using up some of the structural safety margin, and if you know you are landing overweight you will take extra care to land smoothly.

Depending on the airplane, an overweight landing may apply a "penalty" so to speak, accelerating some inspection interval, or advancing a life limit on a structural component in the gear, or some other negative impact maintenance cost wise.  So there may be a significant incentive to avoid it from a long term cost perspective even if it means wasting 5 hours of fuel going round and round in a hold.

In the case mentioned, the crew would have consulted with the airline's Maintenance Control organization on the private company radio frequency to discuss whether to land overweight or not, and if there wasn't an urgent need to land, the Capt would have agreed with Maint Control and burn off the fuel to avoid the overweight landing and its ramifications.


How many African countries currently deploy Cat 3 ILS?

This answer has a list of all airports with a Cat III ILS system.

Africa was assigned ICAO region codes D, F, G and H, so you can just look for ICAO airport codes on the list starting with those letters. The only one I see is "GMMN (MOHAMMED V INTL) on runways: 35L, 35R". That name wan't familiar to me, but a quick Google search says that GMMN is Casablanca, Morocco.


What does this plus (cross) sign on this electrical panel mean?

(airliners.net)

Above I marked five similar plus signs on the 737 (there are more). Beneath the +'s are the contacts for the backlighting of each panel. If it acts up then pressing on the sign will ground/secure the connection and may solve the issue.

The electroluminescent light-panels are flexible and the ride can be too bumpy sometimes. Better push the right spot than wait for a specialized someone on the ground who knows where each contact is.

Composite based on images from b737.org.uk.


Why do reciprocating aircraft engines have more than one spark plug?

Bold Method has a great post today about why aircraft engines have more than one spark plug per cylinder. There are a few basic reasons.

Reliability

Having two sparks plugs is more reliable. If one spark plug becomes inoperative for some reason, there's a second to provide the spark for the power stroke.

It should also be noted that the spark plugs are usually powered by dual, independent magnetos or, in some cases, an electronic capacitor discharge ignition. The redundancy of the ignition system adds to the reliability.

More Power

Having two spark plugs means the flame ignites from two points leading to more power per power stroke. This point is demonstrated during run-up. When the magneto check is done the engine RPMs drop when running on a single mag and set of spark plugs.

Even Combustion

Two sparks plugs and a two flame front leads to a more even burn of the fuel air mixture for a smoother running engine.

Prevent Fouling

Aircraft engines burn leaded fuel which can lead to getting lead deposits on the spark plugs. Having dual plugs leads to a more complete burn which can prevent the deposits from forming.


Where can I find nice animations of flutter?

YouTube is really your best bet - is there any reason you wouldn't be able to use one of the many NASA videos?

If you need a release for legal reasons NASA is famously liberal about granting rights to their research/educational videos - just contact then and you'll almost certainly get an official "Sure, you can use it!"


How to calculate best glide speed at a 30 degree bank?

During a turn the load factor increases. This increases the apparent weight. Thus, during a turn, the best glide speed is selected according to the weight times the load factor.
The load factor at 30 degrees bank is $$n=\frac{1}{\cos{\theta}} \approx 1.2$$
The best glide speed is thus the best glide speed for a weight that is 1.2 times your actual weight. This will be proportional to the square root of the load factor.
$$V_{opt,\theta}= \sqrt{\frac{1}{\cos{\theta}}} V_{opt,0^\circ}$$


What is this plane seen in Mobile, Alabama?

(Source)
B-52D Stratofortress "Calamity Jane".
It is a long-range, subsonic, strategic bomber operated by the US Air Force (not the Navy) since 1955.

The aircraft you see here was amoung 170 B-52Ds manufactured by Boeing Airplane Company, and was equipped exclusively for long-range bombing missions. "Calamity Jane", as she is called, has been demilitarized, but remains in the high camouflage used during Vietnam operations. (Source)


Is there a general radio frequency in Class G for broadcasting intentions?

I'm not aware of any regulation or AIM entry that specifies what frequency to be on.

I use the UNICOM frequency of the nearest airport when I'm out looping because I consider it to be the frequency most likely to be used by traffic near me.

It also has a mild safety benefit -- if something on my plane were to break, I'd already be on the right frequency for the airport I'm about to inhabit.


Could an airliner exceed Mach 1 in a zero-G power dive and safely recover?

There is actually some data (albeit limited) on this scenario:
On August 21st 1961 this test was performed in a DC-8. When this test was performed they were supersonic for about 16 seconds which took a lot of planning to pull off. You first need to climb higher than the plane typically does to have enough altitude to pull this off, then make sure you understand how the control surfaces are loaded in the dive. You get out in once piece by planning for it and understanding exactly what's going on:

We took it up to 10 miles up, 52,000 feet—that’s a record—and put it
in a half-a-G pushover. Bill maintained about 50 pounds of push. He
didn’t trim it for the dive so that it would want to pull out by
itself. In the dive, at about 45,000 feet, it went to Mach 1.01 for
maybe 16 seconds, then he recovered. But the recovery was a little
scary. When he pulled back, the elevator was ineffective; it didn’t do
anything, so he said, “Well, I’ll use the stabilizer,” and the
stabilizer wouldn’t run. It stalled, because of the load. What he did,
because he was smart, is something that no other pilot would do: He
pushed over into the dive more, which relieved the load on the
stabilizer. He was able to run the [stabilizer] motor, with the
relieved load, and he recovered at about 35,000 feet.

Remember you're diving fast, really fast, so you likely can't go much faster as you will ultimately run out of time to accelerate:

The Mach number itself isn’t used in a dive as a target because it’s
much more accurate to use airspeed. So every thousand feet I would
read off to Bill the airspeed [he needed] at the next altitude. As we
were coming down, I was talking almost all the time because at a
descent rate of 500 feet per second, every two seconds we were 1,000
feet lower. Looking out the window—which I stopped doing—it looked
like it was straight down.

The trick is to not over stress the airframe.


What do airline pilots eat on a flight, and when?

1: Do pilots eat during flight or they wait until they are back on the ground?

As pilots happen to be humans, their metabolism works in a similar fashion as yours or mine work. So they eat when they are hungry. On a long flight, they can eat during the flight, but on short flights (e.g. 30 minutes - 2 hours), they might not get enough free time to have a meal.

On busy days, pilots may not get enough time to have proper meals, so they try to eat small meals containing more nutrition. This is detailed in an article on Airline Pilot Central. They also avoid heavy meals before a flight.

2: Do they get the same food that is served to the passengers or do they bring their own meal?

Most of the time, food served to the passengers is the same which is served to the pilots, although they don't eat the exact same food. An airline pilot revealed that:

  ... the pilot gets the first class meal and the copilot the business
  class meal.


Is there a "Quid Pro Quo" of flight following?

There is indeed a Quid Pro Quo with flight following: you're adding to the controller's workload, and they may ask you to do things to help alleviate that workload (like not flying through a busy approach/departure corridor).
Some controllers will also vector you around a hot MOA (even though you can fly through it VFR their normal operating mode is for IFR traffic) while others will simply alert you that the MOA is hot and leave it up to you to decide how to handle that.

Because there's no language in the ATC manual for "Hey could you please fly around this area so you don't make my job harder?" when controllers want to ask you to do something they use the language they do have, which takes the form of instructions (vectors).

As a pilot you should remember that vectors are the opening round in a negotiation: If a controller gives you a vector you don't like you can always ask them why, and often you can negotiate for something better.
This is true for IFR flights as well - The only exception is when a controller uses the word "Immediate" or any variation thereof (then you do what they say and ask your questions later).

If you know you'll be flying through an arrival or departure path you can offer to change your altitude to stay out of the way. Your handy VFR Sectional or Terminal Area Chart shows some of the arrival and departure paths for busier airports:

If you offer a climb or descent controllers will usually tell you what altitude they need you at so you aren't in the way, and if they're not forthcoming you can ask ("What am I being vectored around? Can I go through at a different altitude?").

Finally remember that as a VFR flight you are under no obligation to accept their vectors in Class E airspace: If you don't like what the controller is asking you to do and can't negotiate something better simply say We'd like to cancel flight following at this time and continue on your own navigation (keep listening to the frequency to see what they do and maybe you'll come up with better alternatives for your next flight).

The controllers may grumble about it, particularly if they just put you into the system and you immediately cancel services, but that isn't your problem.


How can you identify the upwind side of a thunderstorm, and why should you fly there?

The "anvil" of a Thunderstorm is always on the downwind side. Airline pilots routinely deviate around the upwind side in hopes of a smoother ride.

photo source: CRAZY CLOUDS: The Thunderstorm Anvil


Does the parking brake provide additional deceleration in an abnormal situation?

This is probably aircraft dependant, but I can give some examples for the airplanes that I have flown and will be generally applicable to transport category aircraft.  Understand that it won't cover every airplane as an absolute rule though.

In general, these types of airplanes have an antiskid system which keeps the wheels from locking up during heavy braking.  If they were to lock completely up, the tires would likely blow, greatly decreasing deceleration and making it more likely to run off the runway (either at the end or off a side).

Parking brakes often have multiple settings because of this.  One setting will be one which can be used when the normal brakes have failed, and have a relatively low brake pressure / stopping capability compared to the normal brakes in order to protect the tires.  Using this setting will stop the airplane eventually, but you are better off with the normal brakes which have a higher brake pressure with antiskid, and better deceleration.

Another setting would have a much higher pressure, intended to keep the wheels from turning (while it is parked), and this would be undesirable while attempting an abort.

In the end, I will say what I usually say:  Follow the guidance in the AFM.  If it says to use the emergency brake when you abort, then do it.  Most likely it will not (because of the above reasons), and you should not do it.  If you take it upon yourself to go against their guidance, you become a test pilot and are either trying something that hasn't been done before, or worse yet, something that has been tried and has had an undesirable result.


Is it required to report climbs and descents within a block altitude assignment?

When given a CRUISE clearance [...] where does it say you don't have to report altitude changes.

In my opinion, it say that by implication in the text you quoted, emphasis mine:

The pilot may level off at any intermediate altitude within this block of airspace. Climb/descent within the block is to be made at the discretion of the pilot. However, once the pilot starts descent and verbally reports leaving an altitude in the block, the pilot may not return to that altitude without additional ATC clearance.

I read that to mean, and as a controller I was taught that that means, you can climb and descend to your heart's content while operating on a cruise clearance. Only once you report leaving an altitude are you required to remain below that altitude; therefore by implication you are allowed to return to that altitude so long as you don't report leaving it, and therefore by further implication you are not required to so report in the first place.
The AIM references the Pilot/Controller Glossary term "cruise" which contains the same exact verbiage.
The 7110.65 contains instructions to controllers that further this interpretation, particularly 6–6–2c under the Non-Radar section and 5–6–6a under the Radar section, which say that controllers cannot use Mode C altitudes to guarantee vertical separation if one of the aircraft involved is on a cruise clearance—because the aircraft is allowed to climb or descend without notice.


What are the advantages and disadvantages of ruddervators?

More induced drag

A disadvantage (especially critical during landing) is that there is more induced drag to make certain movements.
The image below helps to understand this:

Source

To yaw, you have to use both ruddervators (contrary to just a single rudder movement for a normal tail). This is done in order to compensate the unwanted vertical component. This leads to increased induced drag, which is a big problem during take-off.

Less interference drag

The number of intersections goes down. In the case of a conventional tail you have three intersections (fuselage - left elevator, fuselage - rudder, fuselage - right elevator), whereas for a V-tail you only have two (fuselage - left ruddervator, fuselage - right ruddervator). This reduces the interference drag.


Is the Batjet Design Physically Feasible?

Yes, rounded wings have been tested in the past. Probably the most famous example is the Vought XF5U "Flying Flapjack". They work perfectly fine. However, the design as pictured does have some flaws.
Efficiency
The lower the aspect ratio (i.e. wider front-to-back in comparison to their length left-to-right), the more inefficient the wing. This is due to there being a lot of area available for the high pressure under the wing to wrap around to the low pressure on top, creating large wingtip vortices. For the Batwing, this would be doubly true, as a large part of the wings have edges on the inside, almost doubling the effect.
Stability
It appears that the engine is either directly behind or directly below the cockpit, putting the center of gravity way too far back compared to the center of lift. This creates an unstable situation, especially at low speed. As the elevator loses effectiveness, the nose of the aircraft will tend to rise, further exacerbating the loss of speed and leading to a stall. Such a stall would be almost guaranteed to be unrecoverable using normal means.
(I say "normal means" because, in the show, the Batwing was shown to have VTOL capability, meaning it has vents in the bottom to redirect thrust down and hover. So, it would be theoretically possible to use engine thrust to rotate the plane nose-down and recover from the stall. If the engine fails, though, this airplane becomes an absolute deathtrap.)
Control Surface Effectiveness
Unfortunately, the animators of the show never animated the control surfaces, so we're left to guess where they are and how big they are. If they're in the standard position in back, that puts them close to the axis of rotation (which goes through the center of gravity, see above), limiting their effectiveness.
The elevators could be moved to the leading edge, but the slipstream on them would cause issues with flutter, and it would take a huge amount of control force to keep them from being pinned at their limits. This also wouldn't help the ailerons (because they'd still be close to their axis of rotation) or the rudder (because there's nowhere to put it other than that big mohawk structure coming off the top of the cockpit).

So, in short, it's possible, but not in any way practical.


How many active large commercial airplanes are there?

As mentioned this question is hard to answer very accurately without better access to data. It also depends on your definition of "large, commercial aircraft." Including all wide-body aircraft would be a large number of planes, and the totals are constantly changing as aircraft are delivered and retired.

This site will probably be the best resource for this kind of question. The data is probably not 100% accurate but it seems to be close. Other information is also available here.

I looked at the widebody models on the first linked site, sorting by status to find how many are in "Active" service. This does not include "Stored" aircraft which will be either put into service or not.

The models below total: 1026 cargo, 3825 passenger. This means about 21% of the 4851 widebodies are cargo aircraft, and widebodies constitute about 24% of the worldwide commercial aircraft fleet of 20000 aircraft.

747

There are 652 aircraft in service of 1500 delivered to date. Of these, about 289 are cargo aircraft. Excluding 28 aircraft operated by militaries or other organizations, this leaves about 335 passenger aircraft.

DC-10

There are 69 aircraft in service of 446 delivered. This does not include aircraft in military or firefighting services, or the aircraft used by Orbis.

A300

There are 255 active of 561 delivered. Excluding 6 in military or other service, this leaves 178 in cargo service and 71 in passenger service.

767

There are about 821 767 aircraft in service of 1062 delivered. About 165 are cargo versions, and excluding 16 in military or other service, this leaves 640 in passenger service.

A310

There are 105 active of 255 delivered. Excluding 17 in military or other service, this leaves 14 in cargo service and 74 in passenger service.

MD-11

There are 153 aircraft in service of 200 delivered. Only 3 of these are passenger aircraft. These are operated by KLM, and the last scheduled flight is October 25, 2014.

A330

There are 1069 active of 1112 delivered. Excluding 22 in military or other service, this leaves 27 in cargo service and 1020 in passenger service.

A340

There are 289 active of 377 delivered. Excluding 11 in military or other service, this leaves 278 aircraft in passenger service. If there are any versions used only for cargo, there aren't many.

777

There are about 1216 777 aircraft in service of 1230 delivered. About 134 are cargo versions, leaving about 1082 in passenger service.

A380

There are 139 delivered. There are no cargo variants and none out of service.

787

There are 183 delivered. There are no cargo variants and none out of service.


What is the mathematical relation between CLmax and Reynolds number?

The Reynolds number is the ratio of inertial to viscous forces, so viscous effects become smaller with a growing Reynolds number. Viscous effects cause flow separation, so a higher Reynolds number helps to delay stall.

Details depend on the particular airfoil shape, so a general formula does not exist. However, there are many plots of how maximum lift varies over their Reynolds number for groups of similar airfoils.

Below you see Figure 18 from chapter 4 of S. Hoerner's "Fluid Dynamic Lift", giving the maximum lift coefficients of some airfoils of 12% thickness. Besides the Reynolds number, nose shape and camber also influence the maximum lift coefficient, so no simple formula is possible.

Note that the Reynolds number has a logarithmic scale and shows a linear dependency with lift coefficient above Re = 10⁷. So for large Reynolds numbers you might approximate the maximum lift as something like $$c_{L_{max}} = 0.3\cdot log(Re) - 0.5$$
but there is rather little experimental data to support or refine this approximation.


What is the difference between buffeting and fluttering?

The vernacular meaning is...

1) Flutter is un-commanded self perpetuating (positive feedback) destructive & adverse cyclic movement of any part of an aircraft. It most commonly occurs on a control surface but may be an entire wing, tail surface, or more rarely fuselage or other part or device. Flutter may be induced either mechanically or aerodynamically and may be sustained mechanically (i.e. engine or prop, landing gear or ground resonance of a helicopter skid) or aerodynamically by self perpetuating (positive feedback) force. Mechanical inception can be (but not limited to) brisk or pilot induced oscillation, weak, unsupported, or flimsy structures. Aerodynamic inception can be (but not limited to) undesirable cg, or aerodynamic forces on parts. Flutter is always undesirable, dangerous and a destructive force.

2) Buffeting is a turbulent stream of air striking any part of the airframe. The turbulent air may be completely external (weather) or created by the aircraft it self (prop, wing,etc). The most common form of buffeting is turbulent airflow over a wing (i.e. during a stall or wind gusts) striking the wing or horizontal tail. Buffeting is not usually considered self perpetuating with positive feedback, nor is it considered to be precisely cyclic or harmonic - though it may be repetitive. Buffeting is usually considered undesirable but benign and not a destructive force.


Some aircraft may have a special "ETOPS APU" that can be purchased, but many aircraft simply have THE APU that they come with. It is maintained to the standards required in the approved ETOPS program, and is either run during the ETOPS portion of the flight, or else has some means to ensure that it will reliably start even when cold-soaked. (For instance, at least one ETOPS program requires that the APU be started shortly before the top-of-descent on enough flights to "prove" that it does, in fact, start up reliably even in a worst-case cold-soaked scenario.)

Most (perhaps all) APU's in aircraft currently in production have the general capability of being started in flight, so that particular aspect of things isn't unique to the ETOPS world.  Documenting the reliability of the APU is a uniquely ETOPS thing, but so much of ETOPS is about exactly that: demonstrating and documenting just how reliable the hardware is.

It often isn't different hardware, but the same equipment as in a non-ETOPS aircraft, but maintained & tracked to higher standards.


Can a small GA plane maintain level flight with a significant nose-down attitude?

I may have misunderstood the question but I think the answer may be... flaps. Wing flaps will increase the lifting ability of the wing and at a constant airspeed the nose will need to be lowered to maintain a particular altitude.


How does the energy and weight efficiency compare between a battery/electrical propulsion and combustion engine?

Poorly. That is a reason why we don't see battery powered aircraft beyond some experiments. The specific power is still much worse for batteries.
Energy storage:

Jet fuel has specific energy around 43 MJ/kg and energy density around 35 GJ/m³[1].
The best mass-produced rechargeable batteries to this day, Lithium-ion polymer, the best kind has specific energy 0.95 MJ/kg and energy density at most 2.6 GJ/m³[2].

That is more than an order of magnitude difference in favour of hydrocarbon fuel (almost 2 orders by weight, one by volume). Even taking into account the 2-3 times higher efficiency of electric engines (which do not suffer the theoretical efficiency limits associated with heat engines) hydrocarbon fuel is an order of magnitude better by weight.
Engines:

According to [3], the power-to-weight ratios for electric engines and gas turbines are comparable (in the range of 5-10 kW/kg).

Electric engine won't give any advantage to electricity.
Well, the difference in energy density is so huge that even large difference in engine weight wouldn't help much anyway. For models, electricity is OK as due to the square-cube law they have a lot of power and lift and small-scale heat engines are difficult. But for aircraft carrying humans, batteries are very far from usable.


How can I figure out the take-off minimum when multiple minimums are listed in the TPP?

(this answer is specific to the USA and FAA rules. Other countries may be the same, or similar, but I'm not familiar enough with them to guaruntee that this answer can apply outside of the USA)

To answer your question, we must first define what a "Standard Takeoff Minimum" is. Part 91.175 defines the standard wx conditions required for takeoff for commercial operators on an IFR flight plan:

  §91.175 Takeoff and landing under IFR. (f) (2) (i) For aircraft, other than helicopters, having two engines or less—1 statute mile visibility. (ii) For aircraft having more than two engines— 1⁄2 statute mile visibility.

Notice that there are no cieling requirements, only visibility. One- and two-engine airplanes must have 1 mile of visibility, and airplanes with 3 or more engines require 1/2 mile visibility.

Non-Standard - Some runways have obstacles in the distance or, for other reasons, require the weather to be higher than "standard" in order to use that runway during low visibility operations. These non-standard" minimums are published in the TPP. These minimums might be visibility-limiting only, or they might require both a minimum visibility as well as a minimum ceiling.

Ok, so that gets us to your question, in which you have provided specific examples.

  Question: If take-off minimum depicts "Standard with minimum climb of 565' per NM to 2800, or 1000-3 with minimum climb of 370' per NM to 2800, or 1500-3 for climb in visual conditions."

Standard with minimum climb of 565' per nm to 2800. This means that if your aircraft has the capability to climb at a rate of 565 feet per nm all the way to 2800 feet MSL, then you can use "standard takeoff minimums", which is 1 mile viz for 2 engines or less, or 1/2 mile for 3 engines or more, as long as you maintain that climb rate all the way to 2800'.
or 1000-3 with minimum climb of 370' per NM to 2800. If your aircraft cannot maintain the climb performance listed in #1, but you CAN maintain a 370'/nm rate of climb, then you can takeoff when the weather conditions are 1000-3.
or 1500-3 for climb in visual conditions. If you cannot maintain either of the two previous climb-out requirements, then you must takeoff in visual conditions and the weather observation must be a minimum of 1500-3

  Question: If the airport has 1200-6, what take-off minimum can be used?

In this case, you have a visibility of 6 miles, which is higher than the minimum visibility requirements for all 3 items listed above.  But you also have a ceiling of 1200 feet, which would prevent you from using Item #3 (due to the minimum ceiling requirement of 1500).

If your aircraft has the performance capability to meet either Item #1 or #2, then you have legally met the minimums and can depart.

  IMPORTANT Follow-On

The above information is only applicable to commercial flights operating under Parts 121, 125, 129, and 135 rules.  "Takeoff Minimums" do not apply to flights operating under Part 91 rules.  A part 91 flight can legally depart under 0-0 wx conditions. (although it is generally considered unsafe to do so, and several arguments have been made that it might be a violation of the rules to "operate safely"


Are en-route ATC callsigns standardized?

The 'Center' suffix is indeed more common in the US for the en-route call-signs under radar control. There is also New York Radio, for example, for the non-radar service over the Atlantic. Another example is the 'Director' suffix that is not common in the US, but is common elsewhere for the final approach controller.

In this case we need a referee, enter ICAO Annex 10 Volume II Communication Procedures:

  5.2.1.7.1.2 The unit or service shall be identified in
  accordance with the table below except that the name of the
  location or the unit/service may be omitted provided
  satisfactory communication has been established.

Unit/service available                Call sign suffix

area control centre                   CONTROL
approach control                      APPROACH
approach control radar arrivals       ARRIVAL
approach control radar departures     DEPARTURE
aerodrome control                     TOWER
surface movement control              GROUND
radar (in general)                    RADAR
precision approach radar              PRECISION
direction-finding station             HOMER
flight information service            INFORMATION
clearance delivery                    DELIVERY
apron control                         APRON
company dispatch                      DISPATCH
aeronautical station                  RADIO

Above are the standards, but nations are free to deviate. Below is from the UK AIP listing the differences:

And from the US AIP:

Facility                                         Call Sign

Airport UNICOM                                   Shannon UNICOM
FAA Flight Service Station                       Chicago Radio
Airport Traffic Control Tower                    Augusta Tower
Clearance Delivery Position (IFR)                Dallas Clearance Delivery
Ground Control Position in Tower                 Miami Ground
Radar or Nonradar Approach Control Position      Oklahoma City Approach
Radar Departure Control Position                 St. Louis Departure
FAA Air Route Traffic Control Center             Washington Center

  The U.S. does not use the term "area control service" to indicate controlled flight in controlled areas. The U.S. equivalent facility for an Area Control Centre (ACC) is an Air Route Traffic Control Center (ARTCC).

Related: Where to find the callsigns of the en route controllers?


Are some airline's flights more noisy than others for security reasons?

Being familiar with neither El Al nor LHR, what follows is entirely in the category of "educated guesses".

There are two broad ranges where noise levels can be affected by operations, those being on approach and on departure.  The things that tend to make aircraft noisy on approach would be configuring early and flying down final with lots of drag (i.e. full flaps) and lots of power (i.e. lots of engine noise).  On departure, using maximum thrust instead of a reduced thrust takeoff tends to be more noise close-in to the airport, but it results in a steeper climbout, which makes for less noise farther away.

Would "standard operating procedures" for a "high risk" airline tend to require either of these?  Hard to say.  As far as survivability, configuring early means that if you take a missile close in, you're already in a landing configuration, so losing a hydraulic system or two doesn't affect your ability to get configured for landing.  On the other hand, being at full flaps makes performance on a go-around worse if you take the missile and can't change configuration (but need to go around rather than land).  Plus, engines running at the higher power setting would tend to be more of a target for an IR (heat-seeking) missile.  If you thought you were coming in to a high-threat airfield, you'd probably want a steep approach, meaning lots of drag but a LOW power setting.  I have a hard time envisioning a 747 doing this coming into LHR, but maybe they do, spooling the power WAY up to arrest the steep descent at some point close-in.  Maybe.

On departure, the max-thrust takeoff DOES get you out of some threat envelopes more quickly than the reduced thrust takeoff, so that's fairly believable.  Get as high as you can before you depart the airport perimeter (which is presumably more secure than the areas outside the airport fence).  If "always fly a max thrust takeoff" is part of the El Al S.O.P., then it wouldn't be surprising that this would result in higher noise levels close in.

Still in the "educated guess" category, I would wonder if some element of the noise ratings may have to do with how they're calculated.  If the rating for British Airways averages out the 747's departing at heavy weights to destinations far away (four engines at very high power settings putting out lots of noise) with smaller, lighter airplanes departing to closer destinations (two engines at reduced thrust, putting out less noise), then their average would be lower than a carrier which is always flying heavy 4-engine jets to a fairly distant destination.  Not that El Al would be the only airline in this situation, I'd suspect, but not having smaller & less noisy aircraft to reduce the average may be at least one factor in the ratings.

Without seeing the actual ratings and at least some of the methodology as to how they're calculated (near/far, approach/departure/both, weighted by time of day, whatever else), it's very hard to know what's really going on there.  Plus, taking a look at the procedures into LHR & seeing if there is any difference in how El Al flies them and how "everybody else" does.  A lot of questions there in order to get a true high-quality answer to what's really driving those results.


Why are there different number of propeller blades on the inboard and outboard engines?

The inboard engines were of a different type, and more powerful than the outboard engines. Hence, the props had to absorb different power, so they were four-bladed for the inboard and two-bladed for the outboard engines.

Yo can see the specs of the airplane here
https://en.wikipedia.org/wiki/Junkers_G.38#Specifications_(G.38_1929)


How were the graveyard spiral and other sensory illusions discovered?

This paper from the website of the Department of Behavioral Sciences and Leadership at the US Air Force Academy reviewed cases dating back to 1913 (note though it doesn't assert that the reports in 1913 suspected Spatial Disorientation (SD)). In the linked paper the author references a previous paper which I can't seem to find: Gibb RW . Historical assessment of visual spatial disorientation
[abstract] . Aviat Space Environ Med 2010 ; 81 : 318 .

  In 2010, the lead author presented an assessment of visual spatial
  disorientation at the annual Aerospace Medical Association conference
  and cited 25 studies dating from 1947 to the present declaring SD’s
  role in mishaps as well as surveys of pilots anonymously sharing their
  SD experiences

The earliest research they reference is a Navy survey from 1947. Quoted from the linked paper

  1947: U.S. Naval aviators, 67 total, reported on their illusionary
  experiences and categorized them into visual, non-visual, conflicting
  sensory cues, dissociative, and emotional ( 48 ). Of note within
  visual illusions categories were confusion with lights, depth
  perception, “ black night, ” and judging height above the
  ground/water. Experienced pilots were still prone to illusions
  regardless of total flight time.

  ( 48 )Vinacke WE . Illusions experienced by aircraft pilots while
  flying .J Aviat Med 1947 ; 18 : 308 – 25 .

The linked article suggests that the aviation community has known about these issues since the early days of flight but the issue was (and they assert still is) an underrated and underreported flight risk which may skew reporting which causes underfunding. Thus the published research may lag the time in which the community started noticing SD.


How is it safe for helicopters and Ospreys to refuel in mid-air?

That photograph distorts the perspective.  Just Google for "helicopter air-to-air refueling" and look at the image results.  Many show other perspectives from which you can see that it is not possible for the blades to contact the hose or basket - the probe is longer than those on a fixed-wing craft for exactly that reason.

This video shows a CH-53E Super Stallion chopping off it's own probe through over-controlling the cyclic, but that particular mishap would be possible in other flight phases too.


What could I do to a give a plane an emergency boost of power for takeoff?

That really depends how safely you want to get off the ground.
If you are looking to get in and out of tight airfields using STC'ed parts you may want to consider a STOL kit which can modify the plane such that you can utilize a shorter runway.
There are some airframes that do have horsepower increase modifications available but that takes actual mechanic work and wont really be feasible in your "pinch" scenario.
There are a few aircraft that can be operated with JATO rockets and it looks like it was done at least once on an ercoupe during testing
You could add Nos but then again most pilots prefer their engine to run for the duration of the flight... You would also have to contend with the fact that adding NOS may very well require a direct port bore, which is no small job.
Afterburners don't really apply to internal combustion engines, at least not ones that generate meaningful thrust...


Why is the flow ahead of a shock wave chaotic?

The wind tunnel design is not providing clean smooth airflow. Turbulence at supersonic speed does not travel upstream so the turbulence must be created by the wind tunnel design.


Is there a procedure to safely handle a PED battery problem on a commercial flight?

FAA Advisory Circular 120-80A contains recommended crew member procedures and training for combating in-flight fires. It has information about causes, indications and procedures of in-flight fire fighting. According to the AC,

  Upon discovering a fire, the initial focus should be on aggressively
  extinguishing the fire with a readily available extinguisher (which will likely be halon), but do not use water if it is believed the fire is of aircraft electrical system origin. Generally, you should consider using the first available extinguisher rather than delaying your firefighting efforts while you locate a particular extinguishing agent for a class A, B, or C fire.

Airbus Flight Operations Briefing Notes- Managing In-Flight Fires also says pretty much the same thing:

  Any fire, no matter how small, may rapidly become out of control, if not  dealt with quickly.The first priority will always be to put it out.

Coming to the Galaxy Note 7 issue, the AC says,

  h. What are the Recommended Procedures for Fighting a Lithium Battery Fire? The following procedures are recommended for fighting a fire in a lithium-type-battery-powered PED. The procedures consist of two phases: extinguishing the fire, and cooling the remaining cells to stop thermal runaway.

  (1) Utilize a halon, halon replacement, or water extinguisher to extinguish the fire and prevent its spread to additional flammable materials.

  (2) After extinguishing the fire, douse the device with water, an aqueous-based extinguishing agent, or other nonalcoholic liquids to cool the device and prevent additional battery cells from reaching thermal runaway.

Though the standard procedures in case of a fire has to be decided by the company, the FAA recommends some procedures to be followed, like:

  • Be aggressive; if flames are visible, fight the fire immediately.

  • Someone must immediately notify the flight crew to describe the fire, smoke, smells, action being taken,  etc.

  • If flames are not visible, find the base or source of the smoke.

  • Pull circuit breakers, in applicable area.

  • Do not reset circuit breakers, unless instructed by flight crew.

  • Relocate passengers as necessary.

  • Locate hot spots using the back of your hand.

  • Don PBE (not necessarily in this order).

The flight crew (who are supposed to don their oxygen masks on indication of smoke/fire) are supposed to inform the ATC and plan for an emergency landing, if necessary.


What would the reason be for this helicopter maneuver?

Ex-Royal Air Force helicopter force here, spent a lot of time around Chinooks.

I think the main answer is "because I can", but I can think of a legitimate combat use.

You are heavy, and forced to land downwind into a narrow strip because there is a hazard on the upwind side of the landing zone.  There is not enough room to turn around.  You could hover taxi backwards like this to pick up some inflow into the rotors from the relative airflow (and therefore increased lift), then climb away backwards until you do have enough room to transition into normal forward flight, more or less as shown in the video.

This is where team work kicks in - you've really got to trust your load master who is telling you exactly where you are.

Never seen it done though.


How to estimate the altitude of an aircraft at a given distance from a runway?

Straight in, on glidepath, about 6000' above the runway. Straight-in & fast, below glidepath at 3000 to 4000 feet above the runway.

That's based on about 3 miles per thousand feet is a standard glidepath, and it takes in the ballpark of 5 miles at idle power & level flight to slow from 250 knots to a configuration for starting down the glideslope.

Those are ballpark numbers; a heavy aircraft slows less rapidly than a lightweight one does, headwinds can shorten those distances, while a tailwind at altitude can extend them. And there are techniques to slow a little faster than that, and you can leave the power in & slow down over a (much) longer distance if desired.

But for ballpark values, those are good approximations.


What is a good flight simulator for a beginner?

Most commercially available flight simulators (MS FSX, X-Plane, Prepar3d) can make excellent training tools for a budding pilot.  But do take this caution to heart.

The cup has to be empty before it can be filled.

Applied to flight training, do not attempt to instruct yourself how to fly.  At best, you will develop a lot of bad habits which a CFI will have to root out and correct prior to being able to teach you correct airmanship techniques.

On the other hand these kinds of games, when set to use realistic flight models, can be excellent tools for practicing skills you learned when you flew with a CFI in the real thing.  Using a realistic simulator game in parallel with real world flight training can save you a lot of time and money in your training.  These sim games are also excellent for instrument training as much of the required instrument skillset is easily modeled by the computer.  While not approved as an official Flight Training Device for logging official flight time, these sims are extremely realistic - so much so that the same mistakes I make in FSX I will make in the real thing!

One cautionary note:  sims like FSX do model a number of details correctly whereas other ones like dangerous weather, flying at the extreme edges of the envelope, etc are not.  There are a number of scenarios (eg flying into thunderstorms) you can do in FSX which will get you killed in the real world.  Approach learning to fly in a game with caution and any instruction you receive from a CFI should supplant game derived knowledge.


Why were the cabin lights turned on during the flight?

Most likely to keep the passengers awake and alert in the even to severe air turbulence, unusual attitudes, or even a mishap which might be encountered during the passage through those areas of storms.  Awake and alert passengers can better react and avoid injuring themselves and/or others.

It's the nice form of the captain coming on the intercom and saying:

"Good evening ladies and gentlemen.  We are about to pass through an area containing several red cells, possibly hail, and severe turbulence.  If you don't feel like having your head put through an overhead bin, wake up and get those seat belts fastened - NOW!"


Are the cockpit and crew rest area considered part of the cabin?

Speaking as an ex cabin crew with one of the world's largest airline. I can definitely say that the CRC is part of the cabin, as safety and security checks are completed by the crew as part of cabin checks.

Flight deck if I'm not mistaken is not considered part of the cabin. However smoking is usually not allowed according to general aviation rules everywhere. Not even e-cigarettes are allowed. Why are e-cigs not allowed if they have no smoke you may ask?

Reason is that many people might see someone using an e-cig and think that it's ok to smoke, hence lighting up a real one. This has happened before.

I've even had faulty no smoking lights on flights and passengers thinking that smoking in that specific area of the plane where the light is faulty is fine.

When travelling people tend to pack so much stuff for their trips but leave the most vital thing behind - their brains!


Do pilots eat the same food as passengers?

Yes, commercial pilots eat the same meals that the passengers do. They may have extra snacks and such that the passengers don't, but that's it.

It's actually quite easy to find time to eat, since the majority of the actual control manipulation is handled by the autopilot. If the autopilot isn't available for whatever reason, one person can fly while the other eats.

Fun fact: Most airlines have a policy that the pilots must eat different meals, so that if there was a bad batch of chicken that gave everyone who ate it food poisoning, then the pilot that had the fish can still fly and land the plane.


How does the B737's 'throttle offline' setting work?

That article is about somebody's simulation. In the real aircraft, the pilots can always override the A/T and can always turn it off entirely. The A/T will push the throttles toward the target position, but not so hard you can't move them easily yourself. (You may need to turn them off to get them to stop trying to push the power up, but for an action like pulling them to idle for an aborted takeoff before THR HOLD engages at 84 knots, the pilot can easily override them.)
Also, the terms "online" or "offline" aren't used with reference to the authrottles in any Boeing documentation that I've seen.  They may be off, or they can be on -- in which case the mode may be "armed" or any of various other modes. But not on/off line.
Mostly the info in that article is okay, but the table referenced seems to reflect some misunderstanding about what the pilots can/can't do with the thrust levers... at least, with regard to the actual aircraft. That info may be spot-on with regard to the simulation the author is writing about.


What is the history and process of designing new waypoints and airways?

In systems theory, emergence is the "phenomenon whereby larger entities arise through interactions among smaller or simpler entities such that the larger entities exhibit properties the smaller/simpler entities do not exhibit."
I think this best describes how the airspace design came to be from nothing.
In the beginning...
There was air mail. The pilots had hard time finding their way despite the US Postal Service installing lighted beacons connecting the major routes.
Then came a 20-something year old chap by the name of Elrey Borge Jeppesen. He made a cheat sheet that everyone wanted. The aeronautical charts and the AIM's precursor was born. He even included farmers' telephone numbers for weather reports.
The Department of Commerce then funded a better airway system. First there was the four-course radio range, which gave way to VOR and NDB. NDB is now extinct in the wild, and VOR is vulnerable. GPS gave birth to the free route airspace.
(SkyVector) Airways black hole in Europe (Free Route implementation).
Who draws the map?
Everyone. Each country designs its airspace, but since airspaces share borders (even over water), countries also work together. Article 68 of the 1944 Convention on International Civil Aviation says:

Each contracting State may, subject to the provisions of this Convention, designate the route to be followed within its territory by any international air service and the airports which any such service may use.

Or, as the Australian Department of Infrastructure and Regional Development puts it:

Before an airline can operate international services to another country, the government must first negotiate a treaty level agreement with the destination country's government. These treaties are known as bilateral air services agreements.
The result is that international aviation is regulated by a complex web of over 3000 interlocking bilateral air services agreements.

Map of bilateral air services agreements.
International waters
(Source)
In civil aviation, the Flight Information Regions (born c. 1947) share borders. They are not limited to 12 NM offshore like territorial waters. In the Mediterranean Sea for example, Egypt and Greece share a border. So does Scotland and Norway across the North Sea. Along the shared border are waypoints shared by both countries, they form the entry/exit points to/from each county's national air system.
Airways that cross borders form regional networks, they have different prefixes from airways that never leave an FIR. See: ICAO Annex 11.
Really, who draws the map?
The air navigation service provider (ANSP) of each country, by working with the national aviation authority (NAA), other countries, airlines, ICAO, IATA, etc.
An example would be the FAA redrawing the map for the NY/NJ/PHL airspace.
Each ANSP or NAA will have an airspace design unit responsible for the analysis, design, and simulation of the airspace system, among other tasks. Guidelines and regulations exist on the local and international levels for every aspect of the route and sector design. An example would be ICAO Annex 11.
A typical team and process (via icao.int):

This process takes 280 days to complete.
The bigger the scale, the more cooperative the process becomes, for example check this airspace design webpage for the EU.
(Source) Software for airspace design.
Demand and technology
It's supply following demand. You don't see many airways above the Tibetan Plateau for example. And of course the technological advances are a huge driving force. A bend in an airway due to a mountain range shielding a VOR can now go away thanks to GPS, RNAV, RNP, etc.


Can lift occur if air is flowing over an object, but not under it?

Yes.  This jar of paint weighs 34.8 g, but only 32.6 g to 33.4 g when a fan blows at it.  The reduction of weight persisted when I repeated the experiment with a hodgepodge of baffles made from CD jewel cases and Post-Its to prevent any air leakage under the scale's sensor plate.  Others can easily replicate these results.
Per FlanMan's comment, without the fan, I also tried pushing the jar horizontally with a very sharp pencil, like a pool cue to avoid imparting vertical force.
No matter where I put the jar on the scale,
no matter which way I pushed relative to the scale,
no matter how high the pencil tip touched the jar,
by the time the jar moved, the scale's report changed no more than -0.1 g to +0.2 g, and usually increased: it "got heavier" instead of "producing lift."
(The fan wasn't nearly strong enough to move the jar.  High volume, low pressure, in paint sprayer parlance.)
So the horizontal component of the fan's force accounts for at most 1/7 to 1/10 of the effect.  One could throw some statistics at this, or a milligram-accurate jeweler's scale, but more confidence would come from trying this in a proper wind tunnel whose load cell is quite independent of the air flow.
With baffles, with fan, without jar, the scale reported -0.5 g to +0.5 g, tending towards the negative (i.e., lift), depending on how I placed the baffles and the fan.  However one might label that effect, at least some of the time this flat plate also counted as an example that answers yes to the question.
The scale is a DigiWeigh DW-500BS, unsurprisingly out of production, capacity 500 g, claimed repeatability 0.1 g which I've confirmed every few months with the calibration weights from a triple beam balance.


Why was the engine of the Ju-87 Stuka not replaced with a more powerful one?

The Ju-87 Stuka did undergo engine change during its life.

The initial Ju-87A version used the Junkers Jumo 210 A engine, which produced 602 hp. This was almost immediately replaced with Jumo 210D, which produced around 661 hp.

The first production version, the Junkers Ju-87 B-1 used a Junkers Jumo 211D generating 1,184 hp. Note this version had the fuselage and landing gear redesigned from 87A.

The next major version, the Ju-87D, used a Jumo 211J delivering 1,401 hp, after briefly dabbling with Daimler-Benz DB 603 engines.

The final operational version of Stuka, the Ju-87G, used the Jumo 211J engine.

This is more or less the same path followed by other combat aircraft of the era. For example the Hawker Hurricane MkI used a Merlin III engine producing 1,310 hp, while the last major version, the MkIV used the Merlin 24 (or 27) engines, producing 1,620 hp.

However, the main thrust in engine change in Ju-87 was increasing the payload, rather than increased speed or maneuverability like the Hurricanes. For example, Bomb carrying ability was nearly quadrupled from 500 kg in the B-version to 1,800 kg (max load) in the D-version.

Another reason was the aircraft design itself. It was designed to be a rigged dive bomber, and increase in speed would've done it no good (it is to be noted that the fixed landing gear added a lot of drag, though it was study enough to mount a cannon) and it had limited maneuverability at the best of times when loaded (though it had good turn performance at low altitudes). The airframe had reached its limit.

The only reason the Stuka served till the end of the war though its limitations had become apparent by the Battle of Britan was simply because no better replacements were avilable (though the process started in early 1940's), though the Focke Wulf 190 took over some of the duties of Ju-87.


What is Class F airspace, and why is it not used in the US?

ICAO Class F airspace is a bit of an odd duck (and the US FAA is apparently not the only agency that thinks so - from a quick check on Wikipedia it seems more jurisdictions ignore class F than implement it. They only mention Class F as being in use in Germany and the UK).

From a functional/regulatory standpoint Class F is a sort of hybrid between "Class E" controlled airspace and "Class G" (fully) uncontrolled airspace:
Class F airspace is designated as "uncontrolled", but you can get ATC clearances in Class F airspace just like in controlled airspace. The catch is they're "advisory only" (so you don't have to comply with them, and all the weight is on the pilot's shoulders ). Similarly ATC will provide separation services to IFR flights in Class F airspace, but they do so "where possible", which means they might tell you they can't provide that service and you're on your own with see-and-avoid.

The general use case for Class F airspace seems to be allowing IFR flights to operate in "uncontrolled airspace".

As a US pilot (and thus having no experience with Class F Airspace), it sounds like the services provided in Class F airspace are effectively the equivalent of VFR Traffic Advisories ("Flight Following"): Controllers can give you advisories and make suggestions, but all responsibility is ultimately still on the pilot's shoulders, and you can politely tell the controller to get stuffed if you don't like their suggestions (without needing to declare an emergency to vest yourself with that authority).

In the US we already have the Flight Following system and culture set up for VFR folks (and generally speaking it's available nationwide, irrespective of airspace class, as long as the controller can get you on radar and isn't overworked). We also have a pretty robust Class E airspace nationwide.
Because of this the FAA probably sees no need to designate specific "Class F" regions where IFR flights can get the equivalent of "Flight Following": If you're VFR you can usually get flight following if you want it, and if you're IFR you should have no trouble staying in controlled airspace (Class A, B, C, D, or E) for your entire route of flight.


Are the number of unique passengers per airport counted?

Short answer is no, mostly they are not counted. Even if they have this data it is very unlikely that they publish it.

Assuming that you are not a transfer/transit passenger; meaning you have arrived to airport by ground transportation for your departure and you have left the airport via ground transportation when you have arrived; you will be counted as 42 times in the statistics (21 departure + 21 arrival). This is standard counting method.

If you arrive to the airport by a plane, you stay inside the plane and you leave the airport with the same plane; then you are a transit passenger which is counted 1 time.
(You are not a departure or arrival passenger, you are a transit passenger)

If you arrive to the airport by a plane, you leave the plane and you leave the airport with the another plane; then you are a transfer passenger which is counted 1 time.
(You are not a departure or arrival passenger, you are a transfer passenger in this case)

So passengers of an airport are basically; departure + arrival + transit + transfer
(Note: Exact definitions of transit and transfer might change from airport to airport)

Most of the time, especially in smaller airports, airport management does not record passengers on a unique person basis. They simply don't have the unique identifier for each passenger, such as a passport ID number. So they cannot know if a person is travelling first time or fifth time.

However, there are exceptions of course:

There are (very expensive) software that allows airport management to record, filter, manage each passenger data with extreme detail. Its work logic is that it records a special text message that airplane sends to airport before arrival.
For "international" departing/arriving/transfer passengers, this unique traveler information can be obtained from the system of the passport police since they record ID numbers of passports.
Airlines might have this data separately; however this is not a feasible approach since airlines mostly do not share this info.


Why are commercial airplanes painted at all?

I remembered hearing that paint actually reduces the drag of the plane. Searching a bit I found this Boeing document  describing it.

So the painting reduces the fuel costs, instead of increasing them. Another interesting thing is, that planes are regularly repainted to keep the drag low. Of course there is the billboard effect too.

From the report:

  In response to numerous questions raised by
  Boeing customers regarding the efficacy of
  surface coatings to reduce drag, Boeing has
  investigated some possible airflow physics
  explanations. Possible explanations postulated by Boeing aerodynamicists include:

  Increased regions of laminar flow due to reduced surface roughness.
  Reduction in surface roughness resulting in lower skin friction drag, when flow is turbulent.
  Reduction in dirt and/or insect adhesion resulting in reduced roughness and hence reduced skin friction drag.