Why do the Comet's engines point outwards?

The engines were mounted well inboard to reduce the hazard of asymmetric thrust.

Four turbines are placed so close to centerline of plane that even if two on one side cut out, pilot has little trouble maintaining straight, level flight.  [photo caption, p. 101]
...
The Comet's engines are snugged in so closely to the fuselage that there's no need for the customary trim tab on the rudder. [p. 102]

-- Francis, Decon. "I Saw This Jet Liner Fly 500 m.p.h." Popular Science, 156(5), May 1950, pp. 98–104.
Protecting against that hazard also explains the deflection of the engines' exhausts, which places them closer to a line intersecting the airplane's center of mass.
Another reason for the deflection could be to prevent jet blast from overheating or otherwise damaging the fuselage's skin just aft of the exhaust.  The dH Ghost turbojets were built a decade before the first high-bypass engines, so their hot exhaust had no surrounding cooler air.
A third, faint, reason might be to facilitate egress from the over-wing emergency exit windows, sliding aft and down instead of climbing forwards.  But avoiding asymmetric thrust is the reason that is documented in the literature of the time.  (By the way, that entire Pop Sci article is a hoot.)


What is the expected time frame for FAA knowledge test results to show up in IACRA?

I passed back in December 2016.  Took 3 days to get temp license and about 90 days to get my perm license.  Took me a week of study watching Youtube videos on weather and sectionals, in conjunction with UAS107 prep app (https://play.google.com/store/apps/details?id=uas107.openrobotix.labs&hl=en)


How are multiple frequencies monitored at once?

First let's get rid of some misunderstandings:

Many smaller aircraft have just one single radio.
Being told to monitor a frequency does not mean you have to listen to two frequencies at once. See: Being told to monitor a frequency, when are you allowed to transmit on that frequency? Any controlled flight will always be under the control of exactly one controller, never more at the same time.

Now, as for actually listening to multiple radios at once, that is certainly possible, and quite normal on large airliners. In the cockpit of an airliner there will often be up to somewhere around 10 different audio inputs, each with their own volume control. This can include 2-3 VHF radio, an HF radio, NAV radios, communication with ground crew (pushback/handling), as well as audio from the cabin (the PA) and probably a few others. All these audio streams are merged into one, based on the individual volume controls.

Recently having had the opportunity to join a crew on a flight on the jumpseat, I was quite amazed at how good the pilots were at distinguishing between the multiple audio inputs, even when different people spoke at once. But with practise, it's actually not hard to see how it's done. Each audio channel will have a different "topic", using different key phrases and words. An ATC ground unit will be talking about taxiing, whereas the tower will be talking about taking off and landing. And the cabin PA will be explaining how to fasten your seatbelt to a bunch of passengers not paying attention. And of course then there is the fact that people all have different voices. Sometimes it is easy (a female on one frequency and a male on another) and sometimes it is more tricky, but I have never heard two people with the exact same voice.


Why do solar planes have many small propellers instead of fewer large ones?

Because they are very lightweight and fragile. Therefore, thrust and propulsion mass must be distributed over span - a single, large propeller and motor would put too much force into the structure locally. Also, it would require a higher landing gear to give the larger propeller the required clearance.

You are right about the higher losses. However, these airplanes were built to reach record altitudes, and wing loading must be as small as possible to make that possible. Also, boundary layer problems on propellers are less severe than on wings because the rotation will cause the slowed boundary layer to be moved outwards from centrifugal forces. There the blade moves faster which will very effectively suppress flow separation.


How to calculate the shear centre of a wing?

I implemented a program using Matlab for S.C calculus purposes (I'm actually involved in an aircraft project and, fortunately (or not), I'm the structures guy. I have based the code and the theory in a PDF bibliography that is linked w/ the .zip folder. You'll notice two matlab codes:
-One is named "Load_Airfoil_Coordinates_using_MATLAB.m". It loads any .dat file (i.e., if you have your airfoil points, you can plot it using this code);
-Another is named "Matlab_script_for_the_shear_center.m". It calculates, beyond your airfoil's C.G (Xcg,Ycg), the shear center (Xsc,Ysc) - probably you'll need to change some of the inputs to agree with your problem, specifically. Despite I've commented the most part of this code, I recommend you to follow Perini's theory (PDF bibliography) to understand the steps.
To download the .zip folder, please click my OneDrive link: https://1drv.ms/u/s!Aqqj-vTtH2vbomM9cVTInsHp7dbn?e=PMFudZ.
If you're just focusing on the theory, I recommend you some bibliographic references, such as:

T.H.G. Megson - Introduction to Aircraft Structural Analysis

David J. Peery -  Aircraft Structures

B. K. Donaldson- Analysis of Aircraft Structures
Hope I was helpful.

Best regards,
João Cioffi


Are multi-crew operations in a single-pilot aircraft counted towards ATPL requirements?

According to the UK CAA you need:

  500 hours in multi-pilot operations on aeroplanes;

Notice that it does not say anything about the aircraft being multi-pilot/certified for two crew members.

An air carrier can specify in their ops manuals that, for their operations, they require a particular airplane to be operated with two crew members even if it is only type certificated for one crew member.  If their manual is approved, then it is now a "multi-pilot operation" regardless of the type-certification status of the airplane.


What is the EASA equivalent of the FAA's 91.517?

The EASA regulation regarding passenger briefings begins at AMC1 CAT.OP.MPA.170 Passenger briefing.

Here is a link to the document where the above specific reference can be read:
click here


How can I know if North Atlantic Tracks have been amended?

For starters I am not completely knowledgeable with the North Atlantic Tracks but work with some of the other Flex track systems in the world. And they are all very similar.
The Track Messages are a type of NOTAM. They are released everyday and revised NOTAM (Track Message) is released if there are changes. They increment the alphabet character on the end of the TMI so that when a clearance is   issued by Air Traffic Control(ATC) they know which track they are flying including the version and ATC can correct it if the pilot has old information.
Extract from one of the Track Message:

REMARKS.

TMI IS 013 AND OPERATORS ARE REMINDED TO INCLUDE THE TMI NUMBER AS
PART OF THE OCEANIC CLEARANCE READ BACK.

When there is any changes they reissue the entire NOTAM (Track Message). So requesting accessing the message again will tell you straight away what is current. Usually aviation doesn't care about what it was, only what it is and what it will be. The computer systems that the airlines use get the most up to date data when they create the Flight Plans.
The question is what you want to do with the data to how the best way to get the data. But the link you supplied will always have the most recent ones.
Visualization of the these tracks, plus others, can be done on SkyVector. Go to layers to change any settings. The link automatically loads up on an ERC High with North American and Pacific Tracks Selected.


Does ATC clear IFR helicopters for a visual approach if landing at a helipad on a high-rise?

There are no "off-airport helipads" because a helipad is an airport. Actually, anywhere an aircraft lands is an airport as far as the FAA is concerned. It would be just like any other IFR to any other airport with no approach procedure: ATC can clear them for the visual approach if they have reasonable assurance that the weather at the airport is VFR, or the pilot can cancel IFR if they determine the weather is VFR. Public helipads have CTAFs just like any other public airports do. They can be found on helicopter charts, or in the Chart Supplement. In the attached chart snippet, you can see that the CTAFs at East 34th Street and Wall Street are 123.075 and 123.05.

One Police Plaza does not have a published CTAF because it is a private airport. Other helipads in the area are also private and not explicitly depicted.


What are the spikes on Ingenuity's blades?

In the Mars Helicopter Technology Demonstrator paper these are refered as "Chinese weights" and the purpose stated is

Chinese weights provide a restoring force on the blade moments when
under centrifugal loads thereby reducing the torque requirements on
the swashplate actuators.

Searching for the term leads mostly to RC sites, for example this explanation.
Being placed close to axis of rotation (and presumably heavy but small in volume) the aerodynamic effect should be minimal compared to the rest of blade.
My assumption is that this can be quite specific to Ingenuity (and RC models) because limited torque available in electrical actuator servos compared to control system of full-scale helicopter. (But it is my guess only.)
Edit: I have borrowed an image from https://mars.nasa.gov/resources/25043/mars-ingenuity-helicopter-3d-model/ (go there and rotate the model yourself to get a better idea how counterweights are placed) and tried to sketch how the force balance looks like:
Red arrows are centrifugal forces exerted on counterweight or blade's center of mass respectively. These forces are always perpendicular to the mast (rotational axis). Then, each of them can be broken into two orthogonal components -- parallel with blade pitch axis (green) and perpendicular to it (blue). Note that one blue arrow lays above pitch axis and second under, so they produce opposing torque and can cancel each other.


Are there countries where commercial flying can be conducted with a Mexican DGAC private pilot license?

No. If you want to make commercial activities, you need a commercial license.

I remind you the definition of commercial flight


Does Karman line depend on the wing area, and if not, why?

The calculation definitely does depend on wing loading. However, the Kármán line does not, because it is not actually defined by that calculation, it is defined by statement. The calculation, for a “typical” airplane, is just motivation for the value.


How do you calculate trip fuel based on hourly fuel burn rates?

This would typically be solved iteratively. You start with your mass equal to ZFW and calculate how much fuel you need based on the table:

$$ \mathrm{Fuel}_1 = \mathrm{Fuel}(m=\mathrm{ZFW}) $$

Then you add this fuel to your total weight and repeat the calculation:

$$ \mathrm{Fuel}_2 = \mathrm{Fuel}(m=(\mathrm{ZFW} + \mathrm{Fuel}_1)) $$

which will give you slightly larger result. You repeat this process until convergence, meaning

$$ \mathrm{Fuel}_{i + 1} \approx \mathrm{Fuel}_i $$

and this is your final result.


What are the negative associations with Continuous Descent Approach?

From ourairspace.org*:

The FAA wanted to implement Continuous Descent Approach (CDA) at La Guardia as part of the Regional Airspace Redesign to reduce the noise impact when they terminalized a much larger area. In the Draft Environmental Impact Study (DEIS) CDA was included however CDA failed the safety field test in the summer of 2007 and was not included in the Final Impact Study (FEIS).
(...)
The FAA decided to rebrand CDA due to the safety and noise risks discovered overseas and in litigation so they changed the name of the procedure from “Continuous Descent Approach” to “Optimized Profile Descent” (OPD).

Note it says, "... was not included in the Final Impact Study," which to my understanding means the specifics did not make it to the final report (I tried to look for that report, others may have better luck).
They mention failing a safety test, and similar overseas issues. From this paper (atmseminar.org), the one thing that stands out is the need for 4D (time based) traffic management to make it work in high density areas.

This paper has shown that the conflict-free continuous descent approach flown in high density traffic can be achieved based on the 4-D trajectory concept. The proposed scheduling algorithm is proved to be effective in strategically solving the conflicts occurring in the inbound traffic in a full day simulation of terminal airspace operations.

Which means relying only on what each FMS wants is not enough. The ATM systems need to account for all the airborne FMS's, and based on that delays can be introduced for proper management. Not an easy feat.
For comparison, in Europe the CDA and CCD in high density traffic still does not have an IOC (Initial Operational Capability) date. One of the building blocks is expected in 2023.

* [A] volunteer organization of professionals who are committed to addressing and reducing aviation noise and emissions while supporting a safe robust aviation industry.


One of the simplest things you can do is to type in the registration into Google which will normally give you results of the type and history of the aircraft.

Otherwise, many airlines don't operate too many types of aircraft so a quick look on Wikipedia and looking through 'fleet' should show you which types it may be, from which elimination should be pretty quick.

The registration is normally visible on the back of the fuselage and under the wing (D-ABEP on the rear fuselage below), and the last two letters are (often) printed on the aircraft 'forehead' above the cockpit windows, the top of the tail and the nose gear doors (EP on the nose gear doors below).

Aircraft from your photos:

Boeing 737
Airbus A320
RJ85
Airbus A320
Airbus A321
Fokker 100


A flying wing needs an airfoil with an s-bend, so no regular airfoil (none of the ones you mentioned). And you need to incorporate a significant twist towards the wing tips to make it fly stable (incidence is about 10° lower at the tip).

Knowing your turn radius and your desired speed your bank angle is a given, independent of aircraft mass. You can compute it with the centrifugal force and the lift portion that points into the turn...

r = TAS * TAS / ( g * sin( bank ) ), with true airspeed (TAS) in m/s, g = 9.81 m/s/s, r in meters. (if I'm not mistaken)

When you know the mass of the aircraft (roughly) and your airfoil lift coefficient that you want to work with (e.g. 0.5 to 0.8 or so) you can work out how much wing area you'll need to fly that turn without stalling. You could also chose a wing loading and compute the lift coefficient for your turn using the basic lift equations and the force equilibrium...

25 degrees is a good bank angle for passenger aircraft, more makes the passengers scared :) Not applicable here.

I'd start with an existing design of a flying wing and then make alterations to that. A famous aircraft that comes to mind is the Horten H.IV glider. Another example could be the Marske Pioneer 3


Why are traditional knobs not replaced by touchscreens in cockpits?

Adding a pilot's perspective to what others have said:

Look at the switches and knobs in an airplane up close some time. You'll notice that nearly all of them have different textures,heights,sizes or shapes. That's intentional. Pilots train and train and train and train on checklists, especially the emergency ones. Muscle memory is a big part of quickly and correctly executing an emergency checklist.

As an example, flap levers/switches normally have a cap or top that is flat and parallel to the wings. It's easy to identify solely by touch.

Checklist item: "flaps up"
Action: Hand to flap lever (automatic after doing it a hundred times in training), verify feel of lever, move, look to verify

Without the tactile element, every motion would have to be verified by looking before it's made. With the tactile element, the movement can be made and then verified visually while the hand is moving to the next item. In an emergency, every second counts and the savings from tactile + verify matters.

Beyond emergency procedures, they're simply safer. The plane I fly the most has a touch screen display and several non touch devices. In turbulence, the touch screen is basically useless. But, the important devices all have buttons and knobs. I can be banging my head on the ceiling (literally) and still adjust the auto-pilot or radio. In that kind of turbulence, the touch screen device is completely useless.


Why might a Cessna 208 need a FAR Part 23 waiver?

The Cessna 208 is a bit of a confusing model when it comes to seating.

Short version:

Under US legislation, the aircraft may have up to 11 seats and can carry 9 passengers and 2 pilots. Other countries did recertify the aircraft to have up to 14 seats. By doing so they adopt the FAA certification based on part 23 and add text to waive the 9 passenger limitation.

Long version:

Originally the type was approved by the FAA in October 1984 under FAR 23 (up to amendment 28) and given FAA Type certificate number A37CE. The aircraft is certified as 11 Place Closed Land Monoplane (PCLM) and later as 11 Place Closed Sea Monoplane (PCSM).

In 1984 the applicability of Part 23 was described by 23.1 (since amendment 10) as:

  (a) This Part prescribes airworthiness standards for the issue of type
  certificates, and changes to those certificates, for small airplanes
  in the normal, utility, and acrobatic categories that have a passenger
  seating configuration, excluding pilot seats, of nine seats or less.

So this is where the 9 passenger limitation originally comes from. This also implies that if you operate with only one pilot, one of the 11 seats must be unoccupied.

Until 1971 there was no mention of a 9 passengers limitation and since 1987 (amendment 34) a new category of commuter planes is defined allowing for more than 9 passenger (up to 19 passengers) in propeller-driven, multiengine airplanes.

Since the Cessna 208 is a single engine aircraft, the commuter category cannot apply. As a result, when the aircraft is operating under the FAA type certificate, there is a limit of 9 passengers.

When the aircraft is registered and operated outside the USA, the FAA rules do not necessarily apply. Usually a country adopts the Type Certificate of the original certifying country, but changes can be made. This is exactly what happened with the Cessna 208.

Since the aircraft offers space for more seats and the maximum take-off weight allows for extra passengers, Cessna started to offer a 14 seat model for use outside the USA.

For aircraft with more than 11 seats, the flight manual has a supplement stating:

  Limitations

  Utilization of the 13-place, 14-place and Utility seating options
  described in this supplement is limited only to nations where approval
  has been received. The United States does not authorize more than 11
  seats in the airplane. In the 11- seat configuration, the right front
  seat may be occupied by either a second crew member or a passenger,
  However, when the right front seat is occupied by a passenger, only
  eight seats in the aft cabin can be occupied.

Europe (EU)

The EASA Type certificate allows the 11 seat model 208. It also mentions a 14 seat model 208B being approved by the UK CAA. When EASA took over aircraft certification in Europe, the UK CAA approvement for 14 seats was adopted, but only for the 208B model.

In section 2.E (only for 208B):

  A 14 seat place configuration was certified before 28 September 2003
  by CAA UK (see UK TCDS FA54) and subsequently adopt by EASA. Those
  aircraft have to be operated i.a.w. FAA approved AFM 1329-3- 13PHUK
  and AFM Supplement D1340-1-13UK or latest approved revision.

The original UK CAA approval included the text:

  MAXIMUM OCCUPANTS/PASSENGERS: 14 occupants, including pilot. Refer to
  British Aeroplane Flight Manual

Australia

The type certificate for the Cessna 208 mentions:

  Australian registered Cessna 208 aircraft may be configured for
  greater than 9 passenger seats. The requirement of FAR 23 paragraph
  23.1, introduced by amendment 23-10, to limit the passenger seating configuration, excluding pilot seats, to nine seats or less is not
  applicable to Australian aeroplanes certificated under Section 101.22
  of Civil Aviation Orders.

In the type certificate for the Cessna 208B reference is given to the UK CAA approval for more than 11 seats.

New Zealand

New Zealand allows the 208 to be operated with 14 seats.

  In New Zealand the Model 208 Caravan has been approved for operation
  in the fourteen seat configuration in accordance with the provisions
  of the Fourteen Place Seating Supplement to the Model 208 Pilot’s
  Operating handbook. (A similar Supplement is included in the Flight
  Manual for the 208B.) The 208 aircraft was “accepted on the basis of
  compliance with FAR23 excluding the wording of FAR 23.1(a); ‘that have
  a passenger seating configuration, excluding pilot seats, of nine
  seats or less’.”

South Africa

The type certification document from New Zealand mentions that at the time of first approval (1985) Cessna stated:

  Australia, UK, South Africa, Norway, Sweden, Kenya and Columbia had
  all accepted the Cessna 208 with more than nine passenger seats.

Interestingly in February 2014 the CAA of South Africa (SACAA) denied that the 208 was ever approved for operation with more than 11 seats in South Africa. Operators using the Cessna 208 with more than 11 seats found themselves operating the aircraft illegally suddenly.

Quickly a Supplemental Type Certificate (STC) was approved in June 2014 which allows operation with 14 seats again.


(skyvector.com) Chart Supplement for Redding Municipal Airport.

An example of transmit-only frequency would be a VOR frequency used for a remote communications outlet (RCO). From the example above, 108.4T is a transmit-only frequency using the voice channel of the VOR.

How to use: How do I contact Flight Service while in flight?


What is the largest plane ever to have been stolen by a single pilot?

Probably the one you stated in your question.  Though, I should note, that there is some credible evidence that only one person was actually flying the plane and the other may have been forced into coming along.  So you could probably consider it to have been stolen by one person, and that person appears to have not been remotely qualified to fly it.  When it was leaving the plane seemed to meander down the taxiway to the runway, like the pilot had no idea what they were doing, and then it took off.  It hasn't been seen since, and most credible theories think it crashed in the ocean.  But conspiracy theories abound.

A close second would probably be this ATR-42-320(wikipedia plane reference), also stolen in Africa.  This time by an employee of the company who was, unfortunately, suicidal.  He flew the plane around the airport for a few minutes demanding to speak to everyone from his boss, to his significant other to the president of the country.  He eventually crashed it into a couple of other ATR's the company owned.

In reference to the "I'm writing a story" line.  I would suggest that a 727 probably isn't the optimal plane for a single person to steal.  They're older and difficult to manage on your own.  I think a much better option would be a more modern aircraft, like an Airbus A350 or a Boeing 787.  They have avionics that allow for one person to reasonably fly the plane.

Granted, they are very new and may be harder to steal.  Probably the sweet spot between "new enough to be flyable by one person" and "old enough to have one just sitting around to be stolen" would be something like a 737-800 or an Airbus A320.  Both are still quite large, but a skilled pilot could probably operate one on their own if they needed to.  In fact, it has happened before.


How do we use the runway condition assessment matrix?

From the FAA Improves Runway Conditions Reporting article:

  The pilot or dispatcher would then consult the aircraft manufacturer data to determine what kind of stopping performance to expect from the specific airplane they are operating.

The important bit:

  The FAA is advising operators to develop procedures for pilots and dispatchers that address the changes to runway condition reporting procedures.

Here are the corresponding braking coefficients:

From: Takeoff Performance Data for Operations on Contaminated Runways, aimed at manufacturers.


How do I plan TOC/TOD in an IFR flight plan that includes SIDs and STARs?

I'm not sure if there's a standard, 'correct' way to do this, but for planning purposes I'd just assume that your climb and descent aren't affected by the SID and STAR. Calculate them as if it were a VFR flight, in other words, based on the route you have.

The issue here is that you don't know what ATC is going to do. The SID says "maintain 2000 or assigned higher altitude" so it's possible that they just clear you directly to your cruising altitude. Or they might keep you lower for a while for traffic, or have you climb in multiple steps, or whatever. Unless you know the local ATC practices very well you can't plan accurately for that and even if you do know what altitude they assign 99% of the time, your flight might still end up in the 1% that gets other instructions. Ultimately, you have to deal with whatever ATC gives you.

It would be worth asking your instructor about this too. First, he may have a better answer than I do! Second, he may know what the local ATC procedures are in that area. And finally, since you mentioned a checkride he might have some insider knowledge on what the examiner expects or likes to see. However you end up planning it, you should be able to explain to the examiner how ATC's instructions might affect your time/fuel calculations.


Would a lighter aircraft require the same amount of power than a heavier one to fly at the same speed?

You are right. The heavier aircraft needs more power. With one exception.

The power needed to keep an aircraft in the air is the product of flight speed and drag. When flying at the same speed, the drag of both aircraft is crucial to answer the question. Since both share the same geometry, it is safe to assume that both have about the same friction and parasitic drag. But the heavier aircraft needs to fly at a higher lift coefficient in order to carry its higher mass, so it will create more induced drag.

The one exception is when both aircraft have a highly laminar airfoil with a pronounced drag bucket. If the flight speed is picked such that the heavier aircraft will still fly within this drag bucket but the lighter aircraft will fly at a lift coefficient below the lower boundary of that drag bucket, the difference in friction drag could be higher than the difference in induced drag (which is small at high speed). But that exception would need to be made clear in the question.

To fully judge the correctness of the test, please provide all answers. As @David K suggests, your error might have been not to select all correct answers.


What is the minimum altitude over Egmond aan Zee when landing at Schiphol?

Approaches into Schiphol are usually vectored by ATC during the day (see below for night operations). This means the controllers are giving instructions to pilots depending on the current traffic, which makes it hard to say when exactly planes will overfly Egmond aan Zee.

If the Polderbaan (runway 18R/36L) is used for landing from the North (18R), planes will be vectored to the PEVOS waypoint shown on the following chart (source: Jeppesen):

At this waypoint, the aircraft should be at an altitude of 2000 ft (about 600 m):

I marked the approximate position of Egmond aan Zee on the map. There is no given minimum altitude there, so planes could already be at 2000ft, but they are likely still higher (3000 to 4000 ft) see below for update.

During night operations, Schiphol is a lot stricter about where planes can fly and how they can descent. The following night approach chart shows how planes will fly if they land on 18R:

Egmond aan Zee is between EH602 (where planes will be at FL70 or about 2100 m) and EH607, which is on a dashed line indicating a continuous descent path, where planes must fly at idle thrust from FL55 at NIRSI down to the ILS intercept altitude (2000 ft).

I just had a look at flightradar24.com and saw a KLM Boeing 737 flying quite close to Egmond:

According to the ADS-B data, they were between 1800 and 2000 ft when flying just south of Egmond an Zee (I marked the point where they leveled off at 1800 ft). I assume this data is somewhat inaccurate since they should not descent below 2000 ft before intercepting the ILS. Other aircraft were also at similar altitudes around Egmond, so I assume overflights at 2000 ft are quite common.


What materials are used for aircraft windshields?

On light aircraft, acrylic windshields have been the norm.  On higher speed aircraft, glass and laminates are used, particularly with heated windshields. The laminates may use polyvinyl butyral (PVB) is tough and ductile which enhances mechanical properties and impedes shattering of glass layers and the transmission of cracks from one layer to another.

Layered products may have various coatings which affect transmission of light and RF, reduce reflectivity, include elements for heating. While I do not know of an aircraft application, it is common in automotive for layers to include radio antennas.

Glass is an amorphous, non-crystalline material and acrylic plastics and glass have very different properties.  Glass tends to shatter with sufficient impact. However, glass tends to have high resistance to temperatures that subsonic aircraft will normally encounter. Glass also retains good clarity properties over the operational domain of subsonic aircraft. Acrylic tends to be pretty shatter resistant, although I know a turkey vulture which proved otherwise (grin). Acrylic is more suspectable to abrasion and scratches, and therefore requires cleaning and maintenance considerations which glass does not.

It really depends upon the type of aircraft and the design criteria, which include the operations, temperature, heat requirements (ie hot windshield for de ice), weight considerations, EMI considerations (coatings, etc.) and so on.

Both materials have been in use for a long time.

So what kind of aircraft are you talking about?


Do flight attendants have a regulatory responsibility to risk their own lives to save passengers?

In training, flight attendants are given lots of emergency training, but always with the caveat that they are under no obligation to put themselves in danger.  Emergency procedures should proceed up until the time a flight attendant feels they are in danger, then they are to evacuate the airplane themselves as quickly as possible.

There was a long standing joke among flight attendants when I was working, which was the most important emergency instruction you can give:  Follow me!  Funny, but not really.  It keeps things in perspective.  Not commonly known is that any emergency responder today operates under the same conditions.  You are not being paid to put yourself in danger beyond what your training will accommodate.


The pivot wing, also called oblique wing is a type of wing design that tries to minimize the drag over the entire speed range of the aircraft.

At low speeds, the main concern is the induced drag, which can be reduced by increasing the aspect ratio. That is why low speed aircrafts like gliders have very long slender wings.

As the speed increases, the induced drag falls off quickly and the wave drag comes to dominate at supersonic speeds. This is the reason why supersonic aircrafts have highly swept wings with very small aspect ratios.

One way to reduce the drag at high speeds is to sweep the wing. The velocity component perpendicular to the wing is reduced, reducing the drag.

The delta wing is a highly swept wing used in supersonic combat aircrafts. A good example is the Eurofighter Typhoon, which is a tailless delta. The delta wing provides excellent supersonic performance and has a high stall angle. However, the wing 'bleeds' energy rapidly during turns and the requires high takeoff and landing angles.

"Eurofighter Typhoon line drawing" by Inductiveload - Own work. Licensed under Public Domain via Commons.

The trapezoidal wing is a  version of high speed wing with small aspect ratio. The most famous example of the use of trapezoidal wing was the Lockheed F-104 Starfighter, which had excellent high speed performance. However, the aircraft had high takeoff and landing speeds and comparatively less low speed performance.

"Lockheed F-104C Starfighter" by Kaboldy - Own work. Licensed under GFDL via Commons.

Almost all the swept wings in use are swept towards the rear. One disadvantage of this kind of wing is the th airflow is from the root to the tip and as a consequence, the (outboard) ailerons stall before the inboard portion of wing and this results in loss of roll control in high angles of attack. This can be prevented by sweeping the wing forward. However, the bending stress in the wing root is increased due to aeroelastic twisting.

source: NASA

The issue with fixed sweep wings is that what is efficient in one regime will not be so in the other. One way to reduce the drag in all speeds is to change the sweep and aspect ratio of the wing.

The variable sweep wings change the aspect ratio by rotating a part of the wing.

"Three F-111s with different wing configurations" by Jason B from Australia - 3 Configs. Licensed under CC BY 2.0 via Commons.

The pivot wing is an extreme version of the swept wing where the entire wing is rotated. So far, it has only been implemented in one aircraft, the NASA SD-1.

"AD-1 ObliqueWing 60deg 19800701" by NASA - http://www1.dfrc.nasa.gov/Gallery/Photo/AD-1/HTML/ECN-15846.html. Licensed under Public Domain via Commons.

The main aerodynamic advantage of the oblique wing is that by adjusting the sweep progressively, the aircrafts can be optimized for drag reduction over a wide range of Mach numbers. Also, the AD-1 was designed with elliptical wing for minimizing induced drag.

However, on the downside, as the entire wing is rotated, one side of the wing is swept forward, while the other side is swept towards the rear. This means that their stalling characteristics are entirely different. On one side (forward swept side), the inboard region stalls first, while its the opposite on the other side. This makes controlling the aircraft difficult. A follow on project of AD-1, the Northrop Grumman Switchblade was canceled over control difficulties.

The aircraft also exhibited aeroelastic and pitch-roll coupling effects that adversely affected the aircraft's handling qualities at over 45 degrees sweep.
Also, the aircraft exhibited unusual trim requirements and inertial coupling. For instance, it was reported tha the AD-1 required about 10° of bank in order to trim the aircraft with no sideslip at 60° wing sweep.

Though the pivot wing aircraft had excellent aerodynamic characteristics, its poor and unusual control characteristics prevented further development.


What are those things on the B747 engine pylons?

These are latches holding the engine support pylon panel in closed. Behind this panel is the diagonal brace.

This area was modified ~1992 due to the El Al Flight 1862 and China Airlines Flight 358 crashes.

See FAA Lessons Learned (via archive.is).


Why do some airports park the aircraft backwards at the gate?

The airports that feature this parking orientation are of small size, with the apron (or part of it) very close to the runway.
Taking Dortmund Airport as an example:

When an aircraft of a certain size (for example Airbus A319, Boeing 737) reaches one of the parking positions 5-12, it is pushed backwards into its parking position. The engines are switched off. Jets of this size, which are parked forward on their own, would cross the obstacle surfaces, in this case the lateral transition surface, with their stabilizer. This, in turn, would result in an increase in obstacle clearance OCA / H (obstacle clearance altitude / height).
Source: de.wikipedia

In other words, the tall tail fins of certain aircraft when parked nose in would violate the runway's lateral transition surface: an imaginary box around the runway that is meant to be clear of high obstructions, to ensure the safe operation of the runway and any navigational equipment.
For Dortmund Airport, I suspect the aircraft are also "pulled-out" before their engine-start due to the lack of jet blast deflectors (the building, personnel, and vehicles, would be unprotected). For example, the blast from the breakaway (taxi) power of an A320 with CFM56 engines is 20 m/s (72 km/h wind) up to ~60 m behind the plane.
It is also why London City has "caution your blast" holding point signs, so aircraft taxiing onto the runway wouldn't use too much thrust with the apron and its personnel and vehicles close behind.

London City Airport showing tails farthest from the close runway, and highlighted in blue is a jet blast deflector behind one of the parking stands. In this airport the pilots steer into this position without the help of a pushback tug.

Example of how the runway area in Dortmund Airport may affect one apron and not the other (yellow circle).


What's an estimate for the cost of the cockpit technology on a 747 or 777?

Upwards of 30%.

The avionics industry is now a major multi-billion dollar industry world-wide and the avionics equipment on a modern military or civil aircraft can account for around 30% of the total cost of the aircraft. This figure for the avionics content is more like 40% in the case of a maritime patrol/anti-submarine aircraft (or helicopter) and can be over 75% of the total cost in the case of an airborne early warning aircraft such as an AWACS.
— Introduction to Avionics Systems, 2002, p. 1

Boeing promises up-to-date prices (including profit) on their website. The cheapest 777 is listed at USD 283.4 million. For comparison, the engines on the 777 account for 20%.
Moving on to the military side to confirm that 30-40%—as of 2009 the [electronics of the] weapons systems of a single Boeing F/A-18E/F Super Hornet cost some USD 35 million, 44% of the flyaway cost (cost of the aircraft production). Source: navy.mil, PDF page 32.

While expensive, on the long run they're cheaper. Kind of like replacing a good digital watch, compared to repairing an expensive mechanical watch.

The airlines want the advanced technology, despite its higher initial price, because of the lower life-cycle and replacement costs it offers. The cost of maintaining conventional cockpits has soared. Dial-type gauges require watchmaker skills to repair, and skilled people are getting fewer. At the same time digital devices are getting cheaper.
— FLIGHT INTERNATIONAL, 26 April 1986


Why do modern aircraft tend to have angular tails?

The rounded or elliptical design was found to be the cleanest aerodynamically in non-compressible subsonic airflow, which is why it's very common on aircraft of that era.  While the design is very slippery for speeds of Mach < 0.6 or so, it is more difficult to manufacture, which is why, near the end of the war, Spitfires had the 'clipped' wingtips as opposed to the original pure elliptical planforms.

The modern low aspect, sweptback, trapezoidal tail design is a better choice for higher airspeeds and supersonic flight ie Mach > 0.8 and mitigating flight control flutter due to compressibility effects, the same reasons we use sweptback wing.  Note as well that modern fighters use the same kind of planform for their wings and tail planes as they offer a compromise between acceptable supersonic aerodynamics and good trans sonic maneuverability.


Can a 737NG still fly when every single electric run device/system is dead?

TLDR: Yes, the 737 can still fly, the gear can be lowered and one can brake after landing.

A complete failure of every single electrical system is extremely unlikely. The QRH (Quick Reference Handbook) does not even mention this case. Usually, at least the battery remains and can power all emergency systems for at least 30 minutes (60 min, if 2 batteries are installed). See also What happens with the avionics if in midair there is loss of power or fuel flow interrupted?.

Even in the unlikely case of a complete electrical failure, the aircraft is still flyable. As long as hydraulic pressure is still available, the flight controls would function normally. But even without any hydraulic pressure the aircraft can be controlled via manual reversion. This means the mechanical link of the flight controls to the hydraulic actuators at the control surfaces can transmit the forces to the control surfaces (similar to what happens when hydraulic power steering fails in your car). The forces required will be substantially higher than usual, but the aircraft is flyable. Also manual pitch trim via the trim wheel in the cockpit is still possible.

Some things to consider:

A complete electrical failure would include a failure of both EECs (Electronic Engine Control) and therefore both engines would be dead. You would have to sail the aircraft down. As Ralph J pointed out in the comments, the engines could still windmill and might still provide some hydraulic pressure via the engine driven pumps, but far from normal pressure.
Normal flaps extension is powered by hydraulic system B. The FCOM says that the flap lever

  selects position of flap control valve, directing hydraulic pressure for flap
  drive unit
  position of the LE devices is determined by selecting TE flap position

so this might still work with hydraulic pressure. But note that there are electronic components like the flaps/slats electronics unit (FSEU) involved, which would no longer function without electrical power. I am not entirely sure if that would already prevent normal flap operation. See also the flaps and slats control diagram below.

Flaps can also be extended without hydraulic pressure using the alternate flap extension mechanism, but this is electrically powered, so alternate flap extension would be impossible in this case.
Normal gear extension is powered by hydraulic system A. If the pressure is still sufficient to release the up-locks, the gear can then fall down assisted by gravity and the airflow:

  When the LANDING GEAR lever is moved to DN, hydraulic system A pressure
  is used to release the uplocks. The landing gear extends by hydraulic pressure,
  gravity and air loads.

Otherwise, manual gear extension is always possible via three mechanically connected cables in the cockpit using a gravity drop of the gear. It is however not guaranteed that the gear will lock in place.

  If hydraulic system A pressure is lost, the manual extension system provides
  another means of landing gear extension. Manual gear releases on the flight deck
  are used to release uplocks that allow the gear to free–fall to the down and locked
  position. The forces that pull the gear down are gravity and air loads.

Without hydraulic pressure, both normal and alternate braking is unavailable. The brake accumulator will however still have sufficient pressure in it for braking after landing.
Older 737 NGs still have mechanical standby instruments (artificial horizon, airspeed indicator, altimeter). These could still function. Modern NGs have replaced this with an electric standby instrument. Without any instruments, it will be extremely difficult to control the aircraft.
All radios and the transponder would be inoperative, so no airport would even know that you are coming to land there.

Without any hydraulic pressure, the following components are inoperative:

  All flight spoilers inop

  Roll rate will be reduced and speedbrakes will not
  be available in flight.

  Trailing edge flaps normal hydraulic system inop

  The trailing edge flaps can be operated with the
  alternate electrical system. Alternate flap
  extension time to flaps 15 is approximately 2
  minutes.

  Leading edge flaps and slats normal hydraulic system inop

  The leading edge flaps and slats can be extended
  with standby hydraulic pressure. Once extended,
  they can not be retracted.

  Main landing gear normal hydraulic system inop

  Manual gear extension is needed.

  Autobrake inop

  Ground spoilers inop

  Landing distance will be increased.

  Normal and alternate brakes inop

  Inboard and outboard brakes have accumulator
  pressure only. On landing, apply steady brake
  pressure without modulating the brakes.

  Nose wheel steering inop

  Do not attempt to taxi the airplane after stopping.

(Boeing 737 NG QRH 13.12 Manual Reversion)

(Boeing 737 NG FCOM 9.20.24 - Flight Controls - System Description)


Why is it the ATC recording of Ethiopian Airlines Flight 302 is not yet available online?

From LiveATC FAQ:

  LiveATC provides many of the major airport feeds on the network but most of the feeds are provided by volunteers. For this reason we sometimes have only limited control over where (and when) new feeds come online.

The coverage is not global, and in some countries (e.g., UK) it is illegal to broadcast it (that's why you can't find any UK airport on that site).

Officially, CVR/ATC recordings (transcripts are a different matter) of accidents are not made public, unless there is a civil lawsuit (jurisdiction dependent). See: Does the NTSB provide CVR audio recordings alongside transcripts in accident reports?


What type of hydraulic oil is used in the aviation industry?

For the aviation industry, flammability is a major concern, and aviation hydraulic systems require Fluids that cannot burn yet don't create corrosion and still lubricate. Skydrol for instance is a phosphate based ester, a nasty substance that irritates the skin, but at least has some flame resistance.

Old hydraulic motion systems on simulators used the stuff, later ones went to mineral oils like Shell Tellus. If there is an oil leak in a pressure hose, a fine mist of fluid droplets appears, flammable if mineral oil but this could be handled in a ground facility with extinguishers everywhere. Not a good circumstance in an aviation accident though, and that is why in aircraft the esters have to be used.

Vegetable oils are not used for hydraulic systems in the aviation industry at this moment as far as I am aware.


Does the FAA verify or authorize VFR flight plans?

First, one small clarification: ATC doesn't offer any services to an aircraft on a VFR flight plan unless you call and request them.

This short Ask ATC video from AOPA has some useful comments:

Controllers don't know anything about your VFR flight plan
VFR flight plans are for search and rescue purposes only
Even if you call ATC and request flight following, they only enter the destination into their system, not your route (I assume that's because your route could be 'follow that river and then that interstate')

The key point is that VFR flight plans are recorded and managed by FSS, not ATC. So, does FSS accept whatever they're given? I couldn't find a direct answer to that question, but the FAA's procedures for receiving and handling VFR flight plans (see Chapter 6) don't include any steps to "validate" the plan (whatever that would mean anyway). Although there's a lot of detailed, tedious information there so I may have missed something :-)

In fact, this AOPA explanation implies that no one even looks at the route unless it's as part of the SAR process:

  ETA plus one hour

  Within a half-hour of becoming overdue or at ETA plus one hour, the
  search is widened by sending an INREQ (information request) to flight
  service facilities along the route (which is why the route of flight
  is specified on the flight plan). If [the pilot] had been on an IFR flight
  plan, the INREQ would have gone out at ETA plus 30 minutes.

The bottom line seems to be that no one really cares about your VFR flight plan unless it's actually needed to find you. So even if you can enter a nonsense plan, it wouldn't be a very good idea.


Why is the FOV of the Synthetic Vision of the Prodigy Flight Deck asymmetric?

According to the FAA's AC 25-11B, there is no requirement for the asymmetrical SVS field-of-view.

It's not a feature either, as in there is no benefit. Whereas an Enhanced Vision System (EVS) system benefits from an offset overlay to match the sensor's deviation to the different flight deck seat positions.

With that said, here's my guess on why it sees 5° more on the right side.

From the FAA AC linked above:

  The display can depict the scene from the pilot’s view looking through the front window (egocentric) or from outside the aircraft (exocentric). However, if implemented on a primary display, then the display must depict the scene from the pilot’s perspective looking through the front window.

This means the SVS is egocentric, which leads me to conclude* that the left seat is more-or-less aligned with the attitude indicator's centerline. But because of the display's size, the attitude indicator itself is off center, resulting in the bigger angle (5° in this case) to the right.

Which would explain the equal distances shown in white below. They could have been adjusted to allow a centered attitude indicator with the altitude tape being wider than the speed tape.

(Source; added arrows)

* My conclusion is based on the assumption they would want the SVS graphics to share the center of rotation of the attitude indicator. This poses a question with regard to the right seat, because as I can see from this image, the seating position is not accounted for (unlike with EVS).

But since SVS is not meant for barnstorming, I just might be overthinking it. Also, SVS does not need to show everything:

  SV depictions on the PFD have the potential to provide pilots with enhanced terrain and landmark awareness during non-precision and precision approaches. However, the display may not provide depth perception and may not provide a field-of-view for pilots to know what is to the left and right of the display view area.


Why is the Cumulonimbus cloud formation so dangerous?

A cumulonimbus cloud (CB) is dangerous because of the processes occurring in them.  At a minimum you will have an updraft and a downdraft containing rain.  The particular CB you posted in your picture is typical of severe convection.  The anvil is spreading out along the tropopause and there is significant overshooting tops over the anvil.  This indicates the updraft in this cloud is very strong and there is a lot of energy in this storm.  A storm like this likely has hail near the updraft, very strong winds both up and down and severe turbulence within the interface between and around the strong up/down drafts.  There can also be very active in-cloud lightning as well as cloud-to-ground discharges.

Threats near the storm are turbulence, lightning, large hail and significant downdrafts (e.g. microbursts).  Threats within the cloud are severe turbulence, very strong updrafts (some as high as 100 m/s or more) and downdrafts containing torrential rain, hail and lightning.

To better illustrate the magnitude of vertical winds, here is a quick plot from a modeled storm I am working with.

In this plot the reds are updraft and blues are downdraft with the scale on the right in meters/second.  The plot covers 20 km x 20 km area at a height of 5.4 km, which is close to 18,000 ft or 500 mb.  This corresponds to the main updraft in a supercell and you can find areas where less than 5 km cover a vertical wind gradient of 50 m/s.  If you were penetrating this at any decent airspeed you would be in for a very rough ride.
 This storm only had 1800 J/kg CAPE and updrafts can be much faster than this.

CB clouds are (typically) realized from a release of convective available potential energy (CAPE), which is simply a measure of how much warmer a parcel rising from the surface is than its surroundings as it rises.  In an environment that is favorable for convection (CAPE, vertical windshear) where there is ample moisture and a mechanism to force parcels to rise to their level of free convection you can end up with a CB cloud.  A CB is simply a cumulus cloud with rain falling out of it and whether this is a small rainshower or a severe rotating supercell is determined by the environment the storm occurs in.


When is a runway considered to be wet or slippery for 135 or 121 landing performance considerations?

I also could not find a definition for wet or slippery by the FAA, only for a contaminated runway:

CONTAMINATED RUNWAY− A runway is considered contaminated whenever standing water, ice, snow, slush, frost in any form, heavy rubber, or other substances are present. A runway is contaminated with respect to rubber deposits or other friction-degrading substances when the average friction value for any 500-foot segment of the runway within the ALD fails below the recommended minimum friction level and the average friction value in the adjacent 500-foot segments falls below the maintenance planning friction level.

(FAR/AIM Pilot/Controller Glossary, emphasis mine)
My Boeing 737 FCTM does however define:

A slippery surface is any surface where the braking capability is less than
that on a dry surface. Therefore, a surface is considered “slippery” when it
is wet or contaminated with ice, standing water, slush, snow or any other
deposit that results in reduced braking capability.

(Boeing 737 NG FCTM 2.13 Ground Operations, emphasis mine)
This sounds quite similar to the FAA definition of contaminated runways, so I would assume the same definition applies to wet or slippery in §121 and §135 operations as well.
The FCTM further says:

Slippery Runway Landing Performance
Slippery/contaminated runway advisory information is based on an assumption of
uniform conditions over the entire runway. This means a uniform depth for
slush/standing water for a contaminated runway or a fixed braking coefficient for
a slippery runway. The data cannot cover all possible slippery/contaminated
runway combinations and does not consider factors such as rubber deposits or
heavily painted surfaces near the end of most runways. With these caveats in
mind, it is up to the operator to determine operating policies based on the training
and operating experience of their flight crews.

(Boeing 737 NG FCTM A.27 Landing Roll - Factors Affecting Landing distance)
So it seems to be (at least in part) up to the operator to provide clear definitions on when exactly a runway should be considered slippery.

The Flight Safety Foundation has collected some more definitions, although from Europe, not the US:

Dry Runway
The European Join Aviation Authorities (JAA) defines dry runway as "one which is neither wet nor contaminated, and includes those paved runways which have been specially prepared with grooves or porous pavement and maintained to retain 'effectively dry' braking action event when moisture is present."
Damp Runway
JAA says that a runway is considered damp "when the surface is not dry, but when the moisture on it does not give it a shiny appearance."
Wet Runway
JAA says that a runway is considered wet "when the runway surface is covered with water, or equivalent, less than specified [for a contaminated runway] or when there is sufficient moisture on the runway surface to cause it to appear reflective, but without significant areas of standing water."
Contaminated Runway
JAA says that a runway is contaminated "when more than 25 percent of the runway surface are (whether in isolated areas or not) within the required length and width being used is covered by the following:

"Surface water more than 3.0 mm [millimeters] (0125 in [inch]) deep, or by slush or loose snow, equivalent to more than 3.0 mm (0.125 in) of water;

"Snow which has been compressed into a solid mass which resists further compression and will hold together or break into lumps if picked up (compacted snow); or,

"Ice, including wet ice."

(FSF ALAR Briefing Note 8.5 - Wet or Contaminated Runways)


What am I doing wrong in this RBI exercise?

You've got the heading right.
Now rotate the whole view of both instruments to the aircraft orientation, and you see the direction in which the Relative Bearing Indicator (RBI) points. Now it's easy to place it onto the correct position on the card.
The RBI points towards the beacon, but does so relative to the aircraft The dial with the compass in the background is not rotating automatically with the gyro compass, so unless it is manually alligned to the gyro, the top is always north.


Why do we seldom see small unmanned aircraft with gasoline engines?

Because electric is the best propulsion method available for small commercial UAVs and their mission profiles:

-Significantly quieter

-No smells involved

-No flammable liquid involved

-Way easier to operate: properly tuning an RC gas engine is not for everybody

-Much lower vibration and on frequencies easier to filter out

-More controllability, a BLDC (brushless DC) motor has near-instant response to the throttle and thus enables the actual, simple building scheme of quadcopters


Airflow (or any fluid flow) will be zero at the surface of the object it's passing over. Imagine the airflow as layers (or "streamlines"), and remember the surface layer velocity is zero. As you move away from the surface, each layer will be going a little faster than the one beneath it until you finally reach "free stream" velocity. All of these low-energy (lower velocity) layers of air between the aircraft surface and the free-stream air make up the boundary layer.

Here is an illustration from NASA:

(NASA)


What does the PBY Catalina's APU look like?

The link you provided is for a Canadian PBY-5A which were called "Canso" in Canada. I flew these aircraft in water bombing operations during the early 1980's.

In your link it describes the 1955 installation of a 28v Homelite APU. It was installed on the left (port) side of the aircraft in the "living quarters" compartment behind the landing gear. The Homelite APU was powered by a 1 cylinder 2 stroke engine, and were often referred to as a "Putt Putt".  They were only used if the Main batteries were weak or discharged.

This is a photo of a Homelite APU from a B-17. They were also used on B-24s and other large WWII aircraft.  It is nearly identical to the ones we used in the civillian PBYs that I flew.

The original military PBY-5A APU installation looks a little different. It appears to be located on the starboard side in the central compartment near the landing gear. It would have been removed when the water bomb tanks were installed.


Can you be paid to taxi an aircraft if you don't have a commercial license?

Yes, as per 61.113:

  (a) Except as provided in paragraphs (b) through (h) of this section,
  no person who holds a private pilot certificate may act as pilot in
  command of an aircraft that is carrying passengers or property for
  compensation or hire; nor may that person, for compensation or hire,
  act as pilot in command of an aircraft.

A person taxiing an aircraft that is not intended for flight is not acting as PIC under this rule, and therefore can not only be a private pilot, but the person doesn't have to be a pilot at all.

There is no specific FAR that qualifies someone to taxi an aircraft, but aircraft operators and maintenance shops train and authorize mechanics to taxi and run-up engines.

Some individual airports have regulations that specify who may taxi and run-up an engine, such as Palm Springs:

  (a)      Only qualified persons shall start and/or operate an Aircraft
  engine at the Airport and/or taxi an Aircraft on the Airport.
  Qualified persons include a pilot, an airframe and power plant
  mechanic, or a qualified technician licensed by the FAA and qualified
  to start or operate the engine(s) and/or taxi that particular type and
  class of Aircraft.

and Whitman County Airport:

  14.20.130 - Who may taxi aircraft.  No person other than a mechanic, pilot, or properly authorized student pilot, certified by the FAA,
  shall taxi aircraft on any part of the airport.


What are the differences between Cat I, Cat II, and Cat III as concerns aircraft requirements?

The differences are in the demonstrated accuracy of the ILS or RNAV equipment. Not sure if the question can be properly answered without writing a book, but digging into the documents linked by Jonathan Walters I extracted the tables below. The document is very long and full of caveats, exceptions and specifics on testing requirements, etc. and frequently refers to parameters set forth in other documents.

CAT I

Source

CAT II

Source

CAT III

  Landing System Performance.   All types of low  visibility  landings systems, including  automatic flight control, guidance for manual control, and hybrid, shall be demonstrated to achieve  the performance accuracy  with the probabilities prescribed in this section.  The performance values may  vary  where justified by  the characteristics of the airplane.

  The performance criteria and probabilities are as follows:

  (a)  Longitudinal touch down earlier than a point on the runway  200 ft. (60m) from  the threshold to a probability  of 1 x 10-6;
  (b)  Longitudinal touch down beyond 2700 ft.(823m) from  threshold to a probability  of 1 x 10-6;
  (c)  Lateral touch down with the outboard landing  gear more than 70 ft. (21.3m) from  runway  centerline to a probability  of 1 x 10-6.
  (d)  Structural limit load, to a probability  of 1 x 10-6.  An  acceptable means of establishing  that the structural limit load is not exceeded is to show  separately  and independently  that:

  (i)  The limit load that results from  a sink  rate at touch down not greater than 10 f.p.s. or the limit rate of descent used for certification under 14 CFR part 25 subpart C (see section 25.473), whichever is the greater.
  (ii)  The lateral side load does not exceed the limit value determined for the lateral drift landing condition defined in part 25, section 25.479(d)(2).

  (e)  Bank  angle resulting  in hazard to the airplane to a probability  of 1 x 10-7.  A hazard to the airplane is interpreted to mean a bank  angle resulting  in any  part of the wing, high  lift device, or engine nacelle touching  the ground. 6.3.2.  Speed Control Performance.   Airspeed must be controllable to within +/- five  knots of the approach speed*, except for momentary  gusts, up to the point where the throttles are retarded to idle for landing.  For operations flown with manual control of approach speed, the flightcrew must be able to control speed to within +/- five  knots of the approach speed.

Source


Why don't modern heavy bombers have gun turrets?

There are really two reasons. First, fighter tactics have evolved over time, and second, the role of the B-52 has evolved over time.

Fighter tactics

Fighters used to depend (heavily) upon getting fairly close to an enemy, and shooting it down with a machine gun. Over the years, guns have become less and less dominant, and instead fighters tend to use missiles from outside a machine gun's effective range.

Role Change

The B-52 was designed from the beginning to carry nuclear weapons. Nonetheless, it's never been used to actually bomb an enemy with a nuclear weapon.

Early in its life, the B-52 was used to drop conventional bombs on enemies though. During the Vietnam conflict (in particular) B-52s were used to drop thousands of conventional 500 pound bombs on various targets.

The Linebacker II campaign was, perhaps, especially notable. During Linebacker II, 15 B-52s were lost--all of them to surface to air missiles (SAMs) not enemy fighters.

Linebacker II did see some limited success from tail guns as well: two B-52s shot down two MiGs. No B-52 (nor any other aircraft of similar size) has shot down an enemy fighter since.

Now, B-52s act as an aerial platform for launching stand-off weapons. Its normal operation is to fly in low (where it's difficult to detect on radar), and launch from a substantial distance from the target. Since it can be a substantial distance from the target, an enemy would need to defend a much larger perimeter (e.g., a large number of fighters basically blanketing a large area) to stand a decent chance of intercepting it.

Even if we assume an enemy fighter were to intercept the B-52, we get back to the situation with fighter tactics outlined above--they'd be unlikely to get within range of its tail gun anyway.


Is there any plan to create GPS approaches to water areas for seaplanes?

Yes, such plans exist. The Aarhus Harbour Seaport (ICAO code: EKAC) is planning to implement an RNAV approach to allow seaplanes to land in conditions below normal VMC, however, the authorities have yet to approve it.


How is the pitot/static system of a helicopter affected by rotor downwash?

The pitot tube is not much of a problem - it's your typical pitot tube, pointing forward (toward the nose of the helicopter) to measure forward airspeed. Airspeed is somewhat less important to a helicopter pilot than it is to a fixed wing pilot since lift is generated by swinging the rotor around instead of moving the whole vehicle through the air.

The static port requires a little more thought, because it should be located in an area of "undisturbed air", and being in rotor wash is certainly not "undisturbed".
On the R22 the static port is actually located inside the shell per the maintenance manual and is thus shielded from rotor wash:

You could locate the static source in a similar unpressurized-but-shielded compartment in a pressurized helicopter.

On other helicopters the static port is on the fuselage as on most aircraft, for example this one is on an HH-2D Seasprite:

Note that the static port is slightly recessed on the seasprite to keep it out of direct rotor wash.  Multiple static ports may also be used (again, as you'll find on other aircraft) to give an average static pressure and reduce the effects of rotor wash on the static pressure reading.

As with all static systems there will still be some degree of error - no system is measuring truly static air. As long as it's within a reasonable tolerance all the instruments should be able to be calibrated to read correctly though.


What is the technique or procedure to disable/disengage the MCAS on Boeing 737 Max 8 & 9 Aircraft?

MCAS doesn't have its own on/off switch
It is a fly-by-wire feature designed to account for a particular flight regime that would not (or was not expected to be) encountered very often in normal operations, and is intended to account for some of the aerodynamic effects of the LEAP-1B (CFM International) engine installation for this model.  Its activation requires a number of preconditions, but we'll get to that in a moment.
A concise description of the system is found here.  The observation was a follow up to an observation that the MCAS isn't an anti stall feature like a stick shaker, but rather ...

Just about everything you have read in the media is wrong.  MCAS is not stall protection.  MCAS does not counter the additional thrust of the more powerful engines. It is only there because the larger engine nacelles of the B737 MAX cause an aerodynamic pitch up moment at high angles of attack that did not meet FAA longitudinal stability and stick force certification standards.  The easiest fix was to automatically apply a little nose down trim at high angles of attack.

A few things that should disable it (with caveats)

Lower the flaps. It is intended to work only if the flaps are up.

Turn the Stab Trim switches to OFF.  This disables the horizontal stabilizer's trim completely, and reverts to manual trim (there are two guarded stabilizer trim switches in the aisle stand, see Windshear's answer).  This means that the pilots must move/rotate the trim wheels in order to apply pitch trim during flight, though the Max trim wheels being of a smaller diameter raises a training and effectiveness problem1 that deserves its own question and answer.

The manual pitch trim procedure appears to be what a few crews did prior to the LionAir crash in October 2018.  It is unclear how many of the crews knew that it was MCAS that was malfunctioniing, versus any other trim or pitch anomaly.  The previous LionAir crews on the accident aircraft ended up flying to their destination manually. (Original source is the Preliminary Report from that accident).

... pilots encountered problems involving the AoA as well as the pitot tube used to measure airspeed.  In a flight in the same plane the day before, to Jakarta, the pilot experienced many of the same symptoms as the pilots on flight JT610: the stick shaker activated during rotation, an indicated airspeed warning alert appeared, and the aircraft began automatically pushing the aircraft nose down.
The pilot, after determining that his flight display system was malfunctioning, ran a runaway stabilizer non-normal checklist which led to the MCAS being disconnected when the stabilizer trim switches were turned off.  The copilot flew the rest of the flight using manual controls and without autopilot.
That Jakarta flight was using an angle of attack sensor that had been replaced after the previous Lion Air flight to Denpasar experienced problems. {snip} However, it is not clear whether the pilot communicated that he ran a runaway stabilizer non-normal checklist during the flight, which might have alerted the airline’s engineering staff that there was still a problem. (source)

Enable autopilot.  It is supposed to only work if the autopilot is off.  But...CAVEAT

That last part is a little bit complicated: the autopilot may not stay on if it - the autopilot system - keeps getting spurious signals from the AoA sensors, or if the pitot static system is providing bad data to the FCCs.
How do you know that you need to disable MCAS?
A related question is "when do you know that it's time to turn off Stab Trim switches?"
The problem for a given crew is: how do you know what sub-system is giving you trouble?  The AD released in December of 2018 updated the Runaway Stabilizer procedure.  Since there are other malfunctions possible in the trim system for pitch, such as a trim runaway, the same (or similar) symptom may manifest during malfunctions with different causes.  (See the example above).  If additional symptoms are present, such as a stick shaker activating from an erroneous AoA indication or some other fault, which problem do you solve first?
Which problem are you having?
Are you having both problems, or even something else?
That concern, the relationship between different potential failure modes, gets to the heart of

What is in the pilots manuals?

What training the crews do, or do not, get on this sub-system?

The MCAS is only supposed to activate under certain conditions (in theory): high angle-of-attack, flaps-up, flight with autopilot off.  This includes high angle of bank flight in such conditions.

###CAVEAT
Take a look at that last bullet in the lower right of the figure.  It's only partially correct.  When the pilot overrides with yoke trim, MCAS will try again five seconds later (after the pilot has stopped) unless the triggering condition, or signal, goes away.

"In the event of erroneous AOA data, the pitch trim system can trim the stabilizer nose down in increments lasting up to 10 seconds," Boeing explained to operators in a bulletin issued last November, following the JT610 accident. "The nose down stabilizer trim movement can be stopped and reversed with the use of the electric stabilizer trim switches but may restart 5 sec. after the electric stabilizer trim switches are released. Repetitive cycles of uncommanded nose down
stabilizer continue to occur unless the stabilizer trim system is deactivated." (source)

It is this system behavior that is believed to have ultimately overcome the best efforts of the pilots in the LionAir crash.  They were airborne for about six  minutes before they were no longer able to overcome the horizontal stab position with their trim controls.  (Caveat: current as of early 2019.  When the final report comes out this may become a lot clearer, and may need revision).
There is an easy-to-understand video of the relationship between the jack screw and the horizontal stabilizer function here.  Whenever the jack screw is moving the horizontal stab, a cockpit cue that this is occurring is the rotation of the manual trim wheels (seen at about 3:40 in the video).
Why is this activating during takeoff/departure?
That MCAS appears to activate(sometimes) during routine flight regimes is believed to be catching some crews by surprise - and not just the two accident crews.  There is a recent article in *Atlantic* that excerpts some NASA reports by aircrews in the US about some cases of unexpected / odd pitch behavior in this model aircraft.  As of mid 2019, the AoA signal (be it from signal error or a faulty AoA probe) has been identified as a part of the problem in this unexpected activation during takeoff and departure.

1 Note from @user40476, slightly edited:
If you are a bit late to switch off both CUT OFF switches, the deflected angle of the THS will create strong forces on the trim screw, more particularly if simultaneously you hold the yoke to maintain an acceptable pitch.
Critical Flight Safety Issue Follows
In these conditions, it becomes very hard to move the trim wheels manually. This is a major problem; the trim wheel diameter in the 737-MAX is smaller then the trim wheel of the previous models: 737-100, 737-200 etc. This smaller diameter reducing the efficiency of the pilot force on the wheel handle. (Less leverage for the same amount of pilot force applied).
Important Note: this answer is based on information available before the deep dive into the MCAS system that was required to recertify the 737 Max.  It will probably require revision when the final recertification process of the 737 Max is completed.


Can you be cleared to cross a runway *behind* an aircraft on takeoff?

You can cross behind the aircraft on departure roll. This type of operation is done heavily at ATL, on the middle complex during an east flow. Aircraft will depart  runway 9L at M2, and arrivals from either of the south runway will cross behind them the whole time at M1, to get up to the gates.


Can a fighter jet land on a modified airliner?

Technically yes. But I am unaware of any attempt to do this with airliners.

But there were several designs in the past which used a big airplane or a Zeppelin as a mother ship, which took fighters with it for air defense. The B-36 was involved in several such designs.

In all cases the docking was made from below, because this gave the fighter pilot the best field of view and reduced the risk of a tail strike.

While the fighter in the picture above is a Republic F-84, McDonnell even designed one specifically for the purpose of being carried around by a bomber, the XF-85 Goblin. It used a rather complicated trapeze for docking and was then pulled up into the fuselage, as the picture with a B-29 below shows.

Your design proposal with the simple platform on top of the fuselage would carry a high risk of a tail strike if anything goes wrong, so it is unlikely that this will ever be tried for real. But when you change the airliner to a AN-225, the idea looks not totally impossible. The Russians tried to dock a fighter with a mothership as early as the 1930s. The picture below shows a TB-3 docking with a I-Z fighter, the first pair of aircraft in history to dock in flight.

The main reason for docking was the much smaller range of fighters. Today, air refuelling takes care of this deficit, so it is unlikely that anyone will see a benefit strong enough to justify the expense of modifying two aircraft and the risk incurred in the docking process.


An alternative to the Boeing data (if it exists, you might need to call one of their sales reps to find it) is publicly available meteorological data.  One such project is the NCEP/NCAR Reanalysis Project.  There are a few others, as well as archived data.  None of these is exactly the Boeing dataset, but I'd bet that the Boeing dataset is based at least in part upon data like these.  The benefit to the data below is that in most cases it is free and there is a lot of it.

Reanalysis Data

Reanalysis data is constructed from the best available past observations, which are assimilated into a weather model to fill in the gaps between obs and in time.  There are many such projects with various scales (global, regional) and time periods.

The NCEP/NCAR Reanalysis Project

This dataset has 4-times-daily, daily and monthly values between 1948 and present and long term monthly means for 1981-2010.  The data is global. The data is publicly available and you can retrieve files in NetCDF format from the linked website.  The wind data is stored on pressure levels (e.g. 1000 mb, 500 mb, 250 mb) and is stored in its u (east-west) and v (north-south) components separately.

The ERA40

This dataset is a global dataset covering 1957-2002 and has various output resolutions available.  Output from ECMWF is typically in the GRIB format and not all of it is free for non-research use.

The NARR

The North American Regional Reanalysis, as the name suggests, is a regional dataset covering North America.  The data covers 1979 - present.

Observations

Long term past observations are archived at the NCDC and include surface stations, weather balloons and model data, among others.  From the various models available a statistical representation of winds could feasibly be produced.


Which airliners could survive an EMP pulse?

Older airliners use hydraulics and cables attached to the pilot controls. Some RATs power the hydraulics directly as well so limited control is still possible then. The pilots would get a workout but the plane would safely touch down.

However planes with entirely fly-by-wire systems (no current airliner is completely fly-by-wire) will be completely uncontrollable apart from shifting weight and would glide to the ground. They are made stable so they won't just enter a spin and pancake into the ground.


Fuel systems are in general fed by gravity, at least until the fuel leaves the tank, where sometimes (always if the tank is lower than the engine) a pump pushes it toward the engine. This means that fuel is generally extracted from the bottom of the tank (or slightly above the very bottom to avoid having small particles from the bottom of the tank clogging up the fuel filter, incidentally this also introduces the concept of unusable fuel, as the stuff remaining at the bottom of the tank, although there are a lot more factors to this).

Fuel is less dense than water, meaning it'll float on top of the water. Or if you want to think of it the other way around, water is heavier and will sink to the bottom, right where you're trying to get your fuel to feed to the engine. Water doesn't burn very well and the engine will stop. Avgas is generally 0.72 kg/l and Jetfuel around 0.82 kg/l (water being 1 kg/l, see have SI units work well that way?).

A tiny amount of water probably mix with the fuel and simply reduce the power output slightly, whereas anything more will be drained from the tank first, and it'll be very hard to restart the engine. You'd have to pump all the water through the cylinder and out the exhaust, and I don't think this is generally possible in flight, especially right after takeoff which is generally the case when you have water in the fuel (could be right after switching tanks too though).

I don't know much about turbine engines, but I suspect they're less susceptible as the water will not prevent relighting the engine (the pumps will simply push the water out, there's no cylinder that could fill up with water), and you'll generally be using up more fuel on the ground making the problem readily apparent. This is pure speculation though.


Is collaring a circuit breaker considered deactivation by the FAA?

Based on this Advisory Circular, the answer is yes.

  g. Deactivation means to make a piece of equipment or an instrument unusable to the pilot/crew by preventing its operation

Collaring the circuit breaker prevents it from being pushed in, and therefore prevents its operation.


Where can I obtain official German VFR approach charts?

The official German AIP VFR is only distributed via a company called Eisenschmidt. I'm not even sure, there's a digital version of the official charts. But you can buy a 2.35kg heavy print version of the VFR AIP. The only thing that comes close to the charts digitally is something called "VFR eBulletin", a software, where you can enter your route and see that overlaying an ICAO map - but the map is in very bad resolution and low quality.

Sadly, Germany doesn't do it like many other European countries by publishing their AIP VFR online for free.


Did pilots have a separate toilet room for when they needed to relieve themselves?

Given the size and weight of the aircraft, this would be near impossible. There wouldn't even have been margins in the weight budget for toilet paper, let alone a toilet room.
I don't know if there is any official documentation about their bodily fluids.
I did find this quote:

Rutan even brought a small plastic bag with an adhesive, circular opening to answer the question he said he is often asked first—how did you go to the bathroom?

So, the answer seems to be that they glued a plastic bag to their bottoms.

How much room did they have to move around anyways?

Practically none. The aircraft had room for exactly one thing: fuel. If there had been room to move around, that means there was room that wasn't being used for fuel, so they would either have designed away the room or filled it with fuel.
The pilot flying was lying in a lightweight pilot seat, the pilot monitoring sat or lay on the floor next to the pilot flying.

Is there any visual with the interior of aircraft?

Yes, there are quite a number of photos, which you can easily find using your favorite search engine, for example:

Dick Rutan and Jeana Yeager in Cockpit of Voyager
Rutan Voyager Cockpit
Jeana Yeager


What is typical ATC procedure when a non-pilot calls from a commercial flight for help?

There is absolutely nothing "typical" about such a situation, which is also why - as is the case for most abnormal situations and emergencies - there are no detailed and specific standard procedures for dealing with it.
Many ATC units around the world have adopted the general "ASSIST" checklist to deal with abnormal situations. This would likely also be the starting point for handling a situation like the one you describe:

Acknowledge: Let the person making the call know that you understand the situation
Separate: Provide extra separation to other traffic around the aircraft in question
Silence: Stop all unnecessary talk on the radio, switch other aircraft to another frequency, to ensure a good line of communication
Inform: Alert colleagues, supervisors, rescue personnel, the airline/flying club, other aircraft in the area etc. as appropriate. Get more people working on coming up with a solution.
Support: Help the passenger/cabin crew in any way possible. Maybe the controller has flying experience, maybe someone who was contacted in the previous step does and can step in and help guide the passenger/cabin crew.
Time: Try to estimate the possible timeline. Is the aircraft literally falling out of the sky, or is it flying along steadily on autopilot? How much fuel is left? Don't force anyone to make rash decisions if not necessary. Time produces good decisions.

But, again, there is no standard procedure, since such a situation could present itself in countless different ways. There are simply too many variables to come up with a "one size fits all" solution beforehand. Controllers are trained to remain calm under pressure, make good choices and adapt to an ever changing environment. The day we have a set checklist for every single possible emergency situation is the day we can safely retire and let computers take over our jobs.
Further reading on SKYbrary:
Crew Incapacitation: Guidance for Controllers
Guidelines for Dealing with Unusual/Emergency Situations in ATC


Why are 737-200 engines more susceptible to separation?

In general, jet engines are mounted under wings using only a few attachment points- Boeing uses cone pins in 737-100s and 200s (these were changed into fuse pins from 737-300s).

Older 737s with cone pins (the SA 737 is a 200) has a history of failure and almost all the the cases being blamed on the fatigue and manufacturing defect of the aft bolt (which usually resulted in over-stressing and failure of the two front bolts). I've just listed some of the incidents and the probable causes (from NTSB):

Incident: January 03, 1986 involving BOEING 737-2H4, registration: N86SW

  Probable Cause: ...EXAMINATION OF THE CONE BOLT REVEALED THAT IT FAILED AS A RESULT OF FATIGUE, MOST PROBABLY DUE TO IMPROPER INSTALLATION OF THE BOLT, SPECIFICALLY, THAT IT WAS UNDER TORQUED WHEN THE OPERATOR RE-INSTALLED THE ENG.

Incident: December 05, 1987 involving BOEING 737-2B7, registration: N319AU

  Probable Cause:  ... THE AFT MOUNT CONE BOLT FOR THE #2 ENG HAD FAILED FM FATIGUE THRU THE THREAD RELIEF UNDERCUT RADIUS. FATIGUE CRACKS HAD INITIATED ON DIAMETRICALLY OPPOSITE SIDES OF THE RADIUS.

Incident: January 20, 1989 involving BOEING 737-201, registration: N242US

  Probable Cause: PREVIOUS DAMAGE TO THE AFT CONE (ENGINE MOUNTING) BOLT, WHICH RESULTED IN MISMATCHED SURFACES BETWEEN THE BOLT AND ISOLATION MOUNT, LOSS OF TORQUE DURING CYCLIC LOADING OF THE MOUNTING BOLT, AND SUBSEQUENT FATIGUE FAILURE OF THE BOLT

Incident: January 07, 1992 involving BOEING 737-232, registration: N322DL

  Probable Cause: THE FAILURE OF THE AFT CONE BOLT AS RESULT OF PREEXISTING FATIGUE CRACKING DUE TO IMPROPER MAINTENANCE, AND THE FAILURE OF THE SECONDARY SUPPORT STRUCTURE AS A RESULT OF LOADS THAT EXCEEDED THE CAPACITY OF THE ATTACHING HARDWARE AND THE CRUSHABLE HONEYCOMB CORE.

The incident involving the Nationwide 737-230 was also traced back to fatigue of the engine bolt:

  The right-hand engine separated from the aircraft due to the failure of the aft cone bolt as a result of a pre-existing fatigue crack which was most likely caused by incorrect installation of the cone bolt.

No investigation has pointed to any problem with the airflow or associated forces.

In a related note, 747s, which use fuse pins also had a number of incidents/accidents caused due to failure of the pins and Boeing changed the design quite a few times.


When do pilots hold behind ILS Critical area?

In the US (and you're looking at an FAA manual, so that implies US rules), this is covered in JO 7110.65, the FAA order covering air traffic control procedures. Flip to page 135 of that PDF (note that the linked version is not yet the currently effective version) for Section 3-7-5:

  3−7−5.  PRECISION APPROACH CRITICALAREA a.ILS  critical  area
  dimensions  are  described  in FAA  Order  6750.16,  Siting  Criteria
  for  Instrument Landing Systems. Aircraft and vehicle access to the
  ILS  critical  area  must  be  controlled  to  ensure  the integrity
  of ILS course signals whenever the official weather observation is a
  ceiling of less than 800 feet or  visibility  less  than  2  miles.
  Do  not  authorize vehicles/aircraft to operate in or over the
  critical area, except  as  specified  in  subpara  a1,  whenever  an
  arriving aircraft is inside the ILS outer marker (OM)or the fix used
  in lieu of the OM unless the arriving aircraft has reported the runway
  in sight or is circling to land on another runway.

  PHRASEOLOGY−HOLD SHORT OF (runway) ILS CRITICAL AREA

It goes on from there to describe further details, including instructions on when to keep the critical area clear and instructions to warn aircraft conducting autoland approaches if the critical area will not be protected.

In short, pilots hold short of the critical area if they're instructed to do so, and controllers tell pilots to do that by simply saying "HOLD SHORT OF (runway) ILS CRITICAL AREA."


Why 1st and 2nd class but not fast or slow airplanes?

Concorde was built for speed. But it was costly too. People did not like it much. Reality was that they didn't want to get somewhere faster by paying more. People love to pay for luxury though. That is the reason different travel classes were introduced since late 1970s.

Cost of fuel and speed are NOT directly related. As you may know, Boeing 787 has increased fuel efficiency (claimed to be the most fuel-efficient), and still reaching higher speeds.


Can I use actual IMC time for the requirements in 61.109(a)(3)?

Sure can.  FAR 61.109 makes no distinction between flight in hard IMC and simulated in an aircraft using a view limiting device.


What is the front glass in fighter planes called?

It's a Heads Up Display, or HUD.

The HUD can display a number of different pieces of information, including performance data such as airspeed, altitude, and attitude, navigation data such as waypoints or ILS glideslope, or weapons data such as the selected weapon or the targeting reticle you mentioned. Thus, its uses are varied - depending on how sophisticated the system, basic aircraft control may be accomplished using only the HUD. In some modern fighters, there may be additional data on a Helmet Display (or in the case of the F-35, the helmet may have the only display).

It is not just used on fighters - some airliners, cargo planes, and trainers have HUDs:

(C-17)

(T-38)

(Airbus A380)

As for your last question, per fooot's comment, this question and answer has more information.

  The Blackburn Buccaneer was the first production aircraft with a HUD and entered service in 1963.


Why does centre of pressure (drag?) move forward when transitioning from transonic to supersonic?

The center of pressure does not move forward when transitioning into supersonic flight, but back. Let me compare the pressure distribution around a sub- and a supersonic airfoil, and the reason should be obvious:

First subsonic flow, showing an Eppler 502 at a moderate angle of attack (3°):

And here is a rhombic airfoil in supersonic flow, copied from this answer:

While the pressure difference between upper and lower side is highest near the leading edge in subsonic flow and tapers off the more you move backward, the pressure difference between both sides is constant over chord in case of the supersonic airfoil. An uncambered rhombic airfoil is the simplest case: The pressure jumps up when the air passes through a shock and jumps down when it passes trough an expansion fan. In between, pressure is constant because the local inclination of the surface does not change.

As a consequence, the center of pressure is near the quarter point in subsonic flow and at mid-chord in supersonic flow (when tip effects are neglected).

Even in transsonic flight, when the local supersonic flow delays the pressure rise, the center of pressure starts to move back. This is the reason for the pitch-down experienced when accelerating above the critical Mach number which is called Mach tuck.

OK, now I forgot to mention the center of drag so far. It is of minor importance because the drag force is so much smaller than the lift force. The concept is the same: Sum up all drag contributions and find the point where a discrete force applied in the direction of drag has the same effect. While the center of pressure just sums up all pressure (and includes the portions which contribute to drag), the center of drag mixes both shear and pressure effects and looks at the fraction which acts in flow direction.


What are the pros and cons of high service ceilings for fighter jets?

If your question is about advantages and disadvantages of the high ceiling:

Advantages:

-For military aircraft, reaching a high ceiling gives a tactical advantage in air combat and makes it possible to escape from surface-to-air defense . For civil aircraft, it is above all a question of achieving the best efficiency of the engines or of being able to take advantage of the air currents . For both civilian and military helicopters a relatively high ceiling allows intervention in mountainous regions.

-During the Cold War the race for the altitude record was part of the propaganda war between the two blocks. It is however necessary to distinguish the maximum altitude reached during records, not supported, and the operational ceiling of an aircraft, given for standard mission (military) or operating (civil) conditions, and which is the maximum altitude to which the plane can stay in a sustained manner. For example, the absolute altitude record for a conventional jet plane, held by the Ye-266M (one of the prototypes of the MiG-25 ) is 37,650  m , but this same plane has a ceiling of "only" 24 400  m . In the same vein, the Lockheed NF-104A, a demilitarized version of the F-104A Starfighter used by NASA to train the pilots of X-15 , could climb to altitudes higher than 36 600 meters thanks to its additional rocket engine, but its actual ceiling was only about 15,000  m .

Research continues to push the limits reached during this period, with aircraft such as the X-43 and its supersonic ramjet .
Disadvantages:

but nowadays, missiles have evolved and fly faster, higher .... now it's not a race for altitude.
now you have to be stealthy, have good self-protection systems.

it's time for the hypersonic era!

"The first Russian Avangard hypersonic missile regiment, capable of spinning at more than 33,000 km / h and piercing any existing missile shield, has officially entered service."china have same hypersonic missiles


Can you identify this antenna on a Cessna 172N?

Glideslope antennas are those U shaped stubby 3 prong fork things that look like heating elements for a water heater.  That's a 75 Mhz Marker Beacon antenna.  I have revised this post.  I thought it was just a VHF antenna, mainly because almost all Marker Beacon antennas you see out there these days are faired-in blade antennas, but the comment by @Gerry got me to do a bit more rummaging around, and found a couple examples of the same antenna as on that 172 and judging from the apparent length it's likely for Marker Beacon.  That antenna is probably quite old and I'm not even sure you can buy one today, as all the news ones seem to be blade style.


What is this line found above the door on many aircraft?

These are rain gutters.

They are designed to catch rain that runs off the upper surface of the aircraft fuselage and channel it away from the open aircraft door so that the water does not enter the cabin.

This is a close up of the rain gutter over the main cabin door of a Beechcraft King Air B200, showing the channel that would catch and redirect water flow to the side of the door opening:

Source: own work

A jet-bridge may partially deflect rainwater in some cases, but the gutter helps mitigate water exposure for the aircraft interior and passengers. Even gutters cannot completely eliminate such exposure since their size is necessarily limited by aerodynamic constraints. Many operations do not have the luxury of jet-bridges, making the rain gutter especially helpful in reducing the amount of water that might otherwise enter the cabin and pose a hazard to the aircraft or onboard systems.

"Rain Gutters" is the technical name, at least for Boeing aircraft, such as the B777 depicted in the photos in the question.

Here is a Boeing reference to such gutters on the 787:

  Rain gutter: When customers found that water was not being properly deflected
  over a passenger entry door, they requested a change. Boeing relocated the
  gutter to function more efficiently. The solution means happy customers, who had
  fewer water and maintenance issues, and happier and drier passengers. This
  was a significant enough change to process to require certification work with the FAA.


Why would ATC issue a takeoff clearance and also tell the same aircraft to maintain visual separation at the same time?

Yes, the Tower's separation standards are different if the following aircraft accepts the responsibility to maintain separation visually.  If the following aircraft can't (or declines the clearance to) maintain separation visually, the controller has to wait significantly longer between subsequent departures.

Typically, the transmissions from Tower are something along the lines of:

Tower: "Airline 123, line up and wait 25R, confirm A320 on departure roll in sight."
Pilot: Airline 123, line up and wait 25R, Airbus in sight.

After the A320 has rotated:

Tower: Airline 123, 25R cleared for takeoff, maintain visual separation on preceding traffic, they will be turning north.
Pilot: Airline 123, cleared for takeoff 25R, maintain visual separation on the Airbus.

The advisory to the crew about they will be turning north gives them the awareness that they won't be following the other aircraft for miles and miles, just until it reaches the point a few miles from the airport where some traffic turns north and other traffic turns to the south (or proceeds straight-out).  The aircraft will generally be sequenced by Ground Control so that they line up at the runway in a sequence such that the departure directions are staggered.  When this doesn't work, at PHX anyway, that tends to be when there is a break in the flow of departures for a minute or so, and during that time aircraft that have landed on 25L (in this case) and are waiting down-field to cross the departure runway, can cross and then taxi to the terminal.  Tower will often let the "waiting to cross" queue build up to three or four aircraft -- each holding short of 25R at a different taxiway -- while they launch departures rapidly, and then one departing aircraft remains "lined up & waiting" while the arriving aircraft are cleared in rapid sequence across the runway.

And after they're all clear, the departures resume.

All in all, it's a pretty efficient way to "move the metal" & get lots of aircraft into the sky as quickly as possible on clear days -- which PHX has plenty of!


How does an increase in climb rate affect climb gradient?

For small angles, climb gradient can indeed be approximated using ROC/TAS. Easiest if you draw a sketch for things like this!