Due to the corrective calculations being ground-based, does the reliability of WAAS degrade with increases in altitude?

Yes, but it is a fairly small error.
Some of the major sources of GPS error are able to be "corrected" by WAAS.  The WAAS stations are used to build a model to make these corrections.  These corrections are most accurate near each station, and less so the further away from each station.
A couple of the largest errors are due to Satellite clock error and ionosphere delay.  Satellite clock error is "correctable" by WAAS and will only depend on the specific satellite so would not change with receiver location.  (ie when using Satellite number 1, add 1 microsecond...).  On the other hand the ionospheric delay is somewhat location specific (when receiving satellite number 1, while standing at position X, the atmosphere is delaying the signal by Y microseconds). For locations that are not at one of the WAAS ground stations an approximation for the the ionosphere delay must be used.
However, being at altitude is probably not going to change the error by much.  I don't have data on how it scales.


Is an area of localized reduced visibility considered to be a cloud?

This might be an answer that works: In meteorology, the definition of fog is less than 1000 m visiblity and mist/haze more than 1000 m visibility.  I think you could reasonably infer the same definition to apply to higher cloud as well.  To the extent you are looking for a go/no/go definition, I think that might be all there is.


The shed bus powers non-essential aircraft systems. In the case of the phenom 100 this is things like the air conditioning, passenger power sockets and entertainment systems, the toilet and some lighting.

The shed bus is the first thing to lose power (be shed) should the aircraft not be generating enough electricity through, for example, a generator dropping offline.


How easy is it to make a connection to the aircraft pitot-static system?

It's very easy to connect a component to the pitot and static systems: It's literally just basic plumbing (install a T fitting and connect the lines). For IFR certified aircraft a static system test will also be required (and a pitot pressure leakdown test would be advisable if the pitot system is opened).

The regulatory issues surrounding the installation are more complex regarding what kinds of devices may be installed on a certificated airframe and under what conditions they such devices could be used as a primary or standby reference for flying the aircraft, as Ron alluded to.


What causes the "growl" of some large turbofans at takeoff thrust?

There is a wide range of harmonics generated by the fan, descending all the way into the lower sound spectrum. This article is about sound insulation of a turbofan shroud, and contains sound measurements of an actual turbofan in a ground installation at full TO power:

The article seems to be Google translated into English from Russian, but the observations made are very valid:

  At power regimes with Mach number M>1 at the periphery of blade wheel there is a well- observed shock wave noise appeared on harmonics of rotor frequency that could be seen at fre- quency range between the first rotor frequency and fan BPF. Shock wave noise has a high sound power level due to the used lemniscate inlet duct without lining and waisting.

We presume that "waisting" is meant as in: application of a varying cross-sectional shape (waist). The blue lines in the plot are the harmonics of the rotor frequency. There are 16 of them in the first 1200 Hz, in a linear scale this implies that the distance between blue lines is 75 Hz.

Significant sound peaks can be found at intervals of 75 Hz, immediately starting at the first harmonic line of 75 Hz. Note that the fan Blade Passing Frequency is at around 2,500 Hz, but that the frequency spectrum below the fan BPF is quite densely populated. The dominant sound that is observed on ground from an aircraft turbofan is of course dependent upon the position, distance, inlet shape, acoustic insulation measures etc etc. It makes a lot of sense if most sound insulation efforts are invested in the loudest spectrum, and that the low buzz sounds are regarded as a low priority for suppression since they are not very disturbing.


If I buy my own aircraft in which to earn my PPL, does my instructor need to be certified to fly the type of aircraft I own/am training in?

You are sort of correct. For the ground instruction for your basic Private Pilot Certificate, it would not really matter. For the actual flight instruction, the CFI has to be certificated for the category and class of aircraft in which you are being trained by them. If the aircraft is a taildragger, high performance, and/or complex aircraft, the CFI will need an endorsement in their logbook from another CFI showing that they have been trained for that scenario. If the aircraft requires a type rating (which almost no trainer aircraft does), the CFI will need a type rating on their certificate in that aircraft as well. Those aircraft requiring a type rating are generally defined by the FAA as:

(7) Aircraft type ratings—
(i) Large aircraft other than lighter-than-air.
(ii) Turbojet-powered airplanes.
(iii) Other aircraft type ratings specified by the Administrator through the aircraft type certification procedures.

Remember, the above explanation applies to the instructor’s Pilot Certificate for them to have the privileges to act as PIC while flying. The instructor’s CFI certificate is a separate certificate allowing them the basic privileges of instructing. The categories and classes listed on a CFI certificate are a little more general than those listed on a Pilot Certificate. An instructor will need both certificates to give the actual flight instruction in flight in the air. Ground instruction is different.
Most people learn to fly in something along the likes of a Cessna 150, 152, 172, 177, or (in some rare cases) 182. The Piper Cherokee line is another popular trainer. Even Cirrus has a line of aircraft that are very suitable as trainers. Any aircraft around that size or smaller is a great start.
As long as the CFI has an ASEL (Aircraft Single Engine Land) class rating on their Pilot Certificate and an ASE (Aircraft Single Engine) rating on their CFI certificate, they can instruct you in almost all aircraft typically used as trainers. If the aircraft in which you want to train is a float plane, the instructor will need an ASES (Aircraft Single Engine Sea) class rating on their Pilot Certificate. If the aircraft is a multi-engine, the CFI will need a multi-engine class rating (AMEL or AMES) as well as have a Multi-Engine Instructor certificate. If the aircraft is a rotorcraft, that falls into a different category than the above aircraft. Gliders also fall into a totally different category. So do balloons.
One caveat is that some CFIs are limited to training students for the Sports Pilot Certificate, only. While a regular CFI can train students for the Sport Pilot Certificate, a Sport Pilot CFI can not train students for the Private Pilot Certificate. Although the hours acquired in one can apply to the other in the same category and class, the Sport Pilot CFI can only endorse students for that specific test and checkride.
For a more in depth description of aircraft category, class, and type ratings as they apply to pilot certificates, please see Title 14 of the Code of Federal Regulations (14 CFR a.k.a. the FAR/AIM) Part 61.5. Especially pay attention to Subpart (c) pasted below.

(c) The following ratings are placed on a flight instructor certificate when an applicant satisfactorily accomplishes the training and certification requirements for the rating sought:
(1) Aircraft category ratings—
(i) Airplane.
(ii) Rotorcraft.
(iii) Glider.
(iv) Powered-lift.
(2) Airplane class ratings—
(i) Single-engine.
(ii) Multiengine.
(3) Rotorcraft class ratings—
(i) Helicopter.
(ii) Gyroplane.
(4) Instrument ratings—
(i) Instrument—Airplane.
(ii) Instrument—Helicopter.
(iii) Instrument—Powered-lift.
(5) Sport pilot rating.


How does the Coanda effect help some aircraft produce more lift?

According to Wikipedia, the Coandă effect causes the airflow over the top of the wing to "stick" to the upper surface of the wing and continue to hug the wing surface even as said surface curves downwards.  In normal flight, the airflow remains attached to the wing surface all the way to the trailing edge of the wing; as the upper surface of the wing's trailing edge (and, for that matter, generally the lower surface as well) is angled downward, the airflow over the wing is travelling downwards when it leaves the trailing edge, which, as per Newton's third law, produces an upwards force on the wing (and, thus, the aircraft), which we know as lift.  The An-72's overwing engine placement increases lift at low airspeeds because it causes the engine exhausts to blow over the top of the wing; the high-speed exhaust sticks to the upper surface of the wing thanx to the Coandă effect, and is thereby ultimately deflected downwards by the downwards curvature of the rear portion wing's upper surface, producing good lift even at low airspeeds.

A simple way to think about it would be that the An-72's engines blow air and hot gas downwards as well as backwards, but, instead of doing so via traditional ducting, they blow air downwards by blowing it over the top of the wing and allowing it to stick to the upper surface of the wing and follow said surface down.

Note that this is not the only, or even necessarily the primary, mechanism by which aircraft generate lift; it just happens to be the mechanism that is enhanced by the An-72's engine placement.


Where do I land if I fly from KLAX with a constant east heading, crossing the US and the Atlantic ocean?

If an aircraft is following a magnetic course changes in magnetic declination as the aircraft moves along its route of flight will affect the true course, and on a long flight such as the hypothetical trip posed here we need to take that into account.

Magnetic declination is empirical data, i.e. there are tables of it, and while formulas exist to approximate it you would normally use the reference tables. There are several sources of data for the worldwide declination of the magnetic field, for example here.
  Following the link "Magnetic Model maps and grids" I took D_map_mf_2010.zip which contains a simple lat/lon/declination table (0.5° steps) and wrote a small simulation which moves the aircraft 10 km along the heading, calculates & records the new angular coordinates, moves again and so on. The result is this figure:

The green arrows show the direction of north as displayed by a compass, the blue shows the direction of east.
The black line was generated by the simulation shows the true course of an aircraft with a constant magnetic heading of 90°. While it will fly over north Florida, it deviates markedly to the north over the ocean and just touches the north coast of Spain.

Note that this only accounts for the magnetic declination, since your question assumed no wind.
During a real flight the aircraft may experience unknown crosswinds, so the actual position has to be determined from time to time, and a look into the table / map shows the correct heading at the current position leading to your destination. (If the aircraft only has this map, a compass and a sextant aboard.)

So, if you have this data, you can correct the compass headings such that you fly the true course you want. However, I don't know how it's actually done in aviation.

EDIT:

Here is the code. It is written in python and gnuplot, and you will not need any programming skills to use it.

Have fun!

To answer one question from the comments:

  If you carried on around the world, would you return to your starting point? I'm guessing yes as we would be following a contour of equal magnetic potential?

From the physics side, magnetic fields are not conservative and so do not have a potential. However, I think it's clear what you mean.

As long as the heading is +90° or -90°, you will end up where you started. The following figure again shows a travel from KLAX heading 90°, but with a total lengh of 40mio km (i.e. 1000 times the circumfence of the earth and a little more turns for the track as it's not at the equator)
As you can see, there is just a single black track, no deviation.

And if you want to fly to Casablanca, you will need a constant heading of 93,6°. And if you don't land there and have enough fuel, strange things happen:

I would also like to emphasize Bob Jarvis' comment, about how it's done in the real world:

  Long distance journeys, whether by air or sea, will generally use a "great circle" where the heading steered is not constant. In practice the continuously changing great circle course is broken up in to a series of segments of constant heading. Reference here.


Are there areas to avoid while flying formation with a larger aircraft?

In higher altitude the wake turbulence moves downward behind the aircraft. So as the pilot of the lighter aircraft behind the bigger you should keep the same level at least.

photo by: Steve Morris, image source

  I suppose the wake turbulence only becomes dangerous at some distance, when the downwash forms vortices. – Sanchises

No.
The wake turbulence starts forming at about 2/3 of the wing span (measured from body). It starts as a real narrow but powerful vortex. Then it raises its diameter losing power (slowly).

photo by: Josef  Willems, image source

As you can see near the aircraft the  wake turbulence has a sharp profile and is quite predictable. Therefore there is a safe area directly behind the tanker.

related post: How does an aircraft form wake turbulence?


What aircraft model is this that crashed?

That was a Cirrus SR22T, registered in Guernsey as 2-RORO.

The registrar published a statement including the following information:

  The Guernsey Director of Civil Aviation (DCA) and SGI Guernsey Ltd.
  (2-REG) confirm that an accident involving a Cirrus SR22T aircraft,
  registration 2-RORO, occurred on May 12, 2019 between Raglan and
  Abergavenny, Monmouthshire, Wales, United Kingdom. The accident
  aircraft had been registered in Guernsey since August 1, 2018. The
  three occupants of the aircraft were reportedly taken to hospital with
  minor injuries. No further casualties have been reported.

According to the Aviation Safety Network, 2-RORO was owned by Transport Safety Resolutions Ltd. On May 12th, 2019 it departed from Denham (EGLD) and crashed at the A40 in Monmouthshire, Wales, UK:

  The aircraft hit some overhead trainwiring during a forced landing and
  impacting a main road between Raglan and Abergavenny, Monmouthshire,
  Wales. It was consumed by the post-impact fire.

Image of better times by Andrew Goldsmith on Flickr, 09-05-2019

There was already an (only seemingly similar) event on the A40 between Raglan and Abergavenny in June 25th, 2016. A Piper PA-28 (G-SVEA) tried to depart from Abergavenny airfield - a gras strip just next to the A40. It stroke some trees, veered onto the highway and crashed into the central lane separation.


How do I determine the maximum thrust that a Tesla powertrain (P100D for example) could produce if attached to a single propeller?

For a propeller/rotor, net consumed power = torque * rpm. For an electric drivetrain, net power delivered = current * voltage, with current equating to torque and voltage to rpm. Tesla should have really good data analyses on the power delivery as a function of demand over time, with wheel torque and wheel rpm as parameters.

Then you only have to replace the propellant medium: slippery air instead of the stony fixed world. Torque is a measure of drag of the rotor blade, thrust is a measure of lift. Both are a function of rpm as well, usually the rpm is limited by the tip speed approaching the speed os sound and is chosen to be as close as possible to it.

So a design process might be:

Determine payload.
Determine approximate disk load by comparing with existing designs, resulting in the disk area and the blade radius.
Compute rpm so that tip speed is about Mach 0.8
Compute power, torque and thrust from data available for comparable comfigurations.

Two books that contain chapters on pre-design of helicopters are Helicopter Performance, Stability and Control by Raymond Prouty, and Helicopter Aerodynamics by J. Gordon Leishman.

But the area that will give you most headache won't be computing the thrust etc, it will be figuring out how to control the flight path. Do you plan to use a swash plate?


How to interpret the published altitudes for each of US STAR procedures?

Some STAR procedures provide altitude limits on them, so ATC would say:

  Descend via the X arrival

All of the needed restrictions are published on the chart. Since the CAMRN4 does not provide hard limits (just "expect" altitudes), ATC will provide pilots with altitude restrictions per other traffic and their SOP, such as:

  Cross HOGGS at FL180

For most arrival procedures, it wouldn't be critical to restrict altitude at every fix along the route. Any important restrictions would be included. If a fix doesn't list altitude restrictions, then no special restrictions apply. It's up to ATC to provide additional restrictions as required. Once an aircraft gets to the approach phase, altitude becomes more critical, and there will be more restrictions noted.

If you imagine a flight path through space, only two points are required to define a line. You could even consider the top of descent as one of the points, determined by the aircraft's rate of descent. Altitudes at the other points can be determined by that path. A modern Flight Management Computer is able to provide Vertical Navigation guidance, so that an airplane will basically follow that path to cross fixes at the required altitudes. Without this system, pilots would be expected to either manually adjust rate of descent to follow the restrictions, to perform an idle descent to the next restriction. On the CAMRN4, it would be fine by the chart to dive to 11000 after HOGGS, but this would not be expected or efficient. Some arrival procedures may be steeper or shallower than an open descent.

Note that the CAMRN4 says it is applicable to turbojet aircraft only, and pilots should expect FL180 at HOGGS and 11000 at CAMRN.  Pretty much any aircraft on this STAR will be well above that 6000 MEA. If they do happen to be that low, the MEA should keep them clear of the Atlantic City class C that extends up to 4100 ft. Other than that the general minimum altitudes in the area would apply.


Can Instrument Approaches be carried out when RVR is not given for the full runway length? (Approach Ban)

To perform an ILS CAT I approach, at least the touchdown zone RVR sensor must be operational. For CAT II, you need the touchdown zone and midfield sensors, and for CAT III you need all three. As per your NOTAM, if only the stopend RVR sensor is out of service, it should be possible to perform CAT I and CAT II approaches (assuming those are available for that runway in the first place).
There are procedures which allow aircrews to perform a CAT I ILS based on meteorological visiblity alone, using a special conversion table to estimate RVR values based on visiblity, but I believe those are company specific.
RVR can also be measured manually, but I am not sure this is actually allowed anymore. It would require someone to physically go to the end of the runway, and then count the number of runway lights visible from the end. Given there is a fixed distance between runway lights, you could then multiply the number of visible lights with the distance between them to get the RVR.
Not sure what the rules are for RNP approaches, but I would imagine they are similar to those regarding ILS.


Do airports charge airlines for extra time spent on ground due to weather conditions?

The correct answer may differ for each pair (airline, airport) and can be found in the contract that they mutually agreed upon. Such contracts are mostly seen as a business secret, and most of their contents are not known to the general public.

As far as I know, both parties agree to do their best to keep everything working during every weather. Which means that there has to be enough equipment to clear a runway really quick, such that these "penalties" are "background noise" in the overall bill, even compared to the penalties caused by other reasons. The airport may decide not to bill the airline most of these penalties, as long as the airline won't try to bill every loss caused by the airport's fault. As a rule of thumb, you don't upset your business partners like that over peanuts, more so if claims go both ways. They may even have agreed on how many minutes delay won't be billed.

Yet, this partnership may be put to the test when one of the partners is seen as cutting cost at the expense of the other, or when one really unexpected condition occurs (like that volcano on Iceland, which disrupted air traffic in central Europe for two weeks or more).


What suits best for lateral controllability at high Angle of Attacks- a vortex generator or wing slots?

Vortex generators can be used at the leading edge to energize flow and delay separation.  They are widely used as an add-on device to improve low speed behaviour of a range of light aircraft, and in that usage they have a similar effect to a slot or slat in that they both increase stalling AOA and improve aileron response in the stall. I call them "poor man's slats".
However, slats are able to energize the boundary layer to significantly higher angles than leading edge vortex generators.  As an add-on, VGs are great, but if your objective was to maximize AOA at stall, you would go with a slot or slat.  A VG might raise stalling AOA from 15 to 19 or 20 degrees, whereas a slat/slot is good to the mid 20s.  Similarly, a VG can increase a wing's Clmax by maybe .3 to .5, whereas a slat/slot adds about 1.
To answer the question specifically, for maximum benefit for lateral controllabilty at the highest AOA possible, you would use a slot/slat. VGs would be a second choice, unless your objectives were more modest, in which case if they do the job, they would be a much cheaper and simpler solution.
There was a period back in the 40s when leading edge slots in front of the ailerons were popular as a way to maintain aileron authority through the stall (Globe Swift, Stinson, etc). Later, designers just included sufficient wing washout to achieve the same goal without the manufacturing hassle and drag, and fixed slots disappeared.
Modern transport airplanes and specialty STOL airplanes will use slats across the full span to increase stalling AOA and maximum lift the wing can make, as opposed to just improving aileron control.  Same with leading edge VGs, although the benefit is only about half.  On light twin engine airplanes, VGs have miraculous benefits for single engine performance.


What is the difference between published and unpublished waypoints?

Published waypoints are waypoints that appear on the charts and in the published navigation databases used by GPS navigators or FMSes.  They are referenced using the published identifier for the waypoint. Examples: TPA, ITAWT.

Unpublished waypoints are waypoints created by the pilot.  FMS allow for the creation/entry of a waypoint by the pilot.  The waypoint is defined by one of the following:

Latitude/Longitude
Place/Bearing/Distance
Place-Bearing/Place-Bearing

The pilot-defined waypoint can then be added to the flight plan.

Here's a snip of how a waypoint is defined in an A320:

As to when you would use it, the short answer is when you need to or want to.  A common example would be to deviate a short distance off an airway (maybe 5 or 10 nm) to avoid a temporary flight restriction.  You would just want to avoid the restricted airspace and using a published waypoint or waypoints would take you farther off your route than necessary.


What is primary cause of shock induced separation (shock stall)?

The simplest answer is that a shock wave for a boundary layer means a sharp adverse pressure gradient. You probably know already that adverse pressure gradient will thicken a boundary layer and thick boundary layers are more prone to separation. Also, if the adverse pressure grad. is so strong, it can immediately produce a detachment of the flow from the wall.

Add to this that a separation bubble forms in the near region and this interacts with the shock. All these phenomena are quite complicated and to explore their underlying physics Large-Eddy Simulations (LES) are used for the Navier-Stokes equations. This is a topic of Ph.D level research. If you want an introduction you can check this source and discover further on your own.


Why will the 777X be tested for crosswind handling with wingtips raised?

If you read the details in the Federal Register, you can see that this refers to crosswind handling on the ground, not in the air:

The folding wingtips and their operating mechanism must be designed
for 65 knot, horizontal, ground-gust conditions in any direction as
specified in § 25.415(a). Relevant design conditions must be defined
using combinations of steady wind and taxi speeds determined by
rational analysis utilizing airport wind data.

And:

The airplane must demonstrate acceptable handling qualities during
rollout in a crosswind environment, as wingtips transition from the
flight-deployed to folded position, as well as during the unlikely
event of asymmetric wingtip folding.


What is the difference between a forward, aft, high and low center of gravity?

I'm not sure I'm understanding what you're trying to get at, but let me try to answer the sentence:

  most importantly when is the CG is AFT or Forward?, and when is the CG Low or High?

Whether the CG is aft or forward refers to its position along the longitudinal axis of the airplane, that axis that runs from the aircraft nose to the tail. Usually if people refer to just "the CG" they're typically referring to the longitudinal position of the CG as that is generally the most critical. Boeing refers to the longitudinal axis measurement as the BA, balance arm, although the longitudinal CG is usually spoken of in terms of the percent of the mean aerodynamic chord.

Let's say you have a freighter with a single 10,000 lb pallet in it. If that pallet is in the forward most position capable of handling it, the longitudinal CG would be considerably more forward than if the pallet were in the aft most position. Very possibly in either instance the respective forward and aft CG limits would be exceeded. If a loadmaster said only, "I've got a forward CG," he might mean that the load is forward of the forward limit, or he might simply mean that the load is within the limit but more forward than he likes.

Now let's say that we split the 10,000 lb pallet into two 5,000 lb pallets, and we put one of them in that most forward position on the main deck and the other in the same longitudinal position on the lower deck. That wouldn't change the longitudinal CG because both pallets are at the same longitudinal position. However, it would change the vertical CG as measured along the vertical axis. Loadmasters on 747s don't have to worry about the vertical CG because there are no defined limits for it in 747 weight and balance manuals. Loadmasters on 767s, however, do as there are defined limits. If a 767 loadmaster says he has a high CG, he can mean that the maindeck load is too great given how much is in the lower deck. He also might mean that the vertical CG of the maindeck load itself is greater than 42" above the maindeck floor. Boeing refers to the vertical axis measurement as the WL, water line.

Though you didn't ask about it, there is a third axis, the lateral axis, extending from wing tip to wing tip so to speak. Boeing refers to the position along this axis as the BBL, body buttock line, and there are typically limits as to how far from the aircraft centerline the lateral CG can be.


Why disable stall warning based only on low airspeed, rather than multiple criteria?

A review of the stall warning system was recommended in the final report:

EASA require a review of the conditions for the functioning of the stall warning in flight when speed measurements are very low.

Here is the outcome of reviewing the "conditions" (plural):

EASA has reviewed the conditions for the functioning of the stall warning in flight when speed measurements are very low. The stall warning is designed to be efficient in a realistic and recoverable flight domain. It is also designed to avoid spurious triggering, hence the 60 knots stall warning inhibition threshold implemented on a large number of large aeroplanes. At very low speed (below 60 kts), corresponding to exceptionally high angle of attack, the aircraft flight characteristics are unknown. Flying below 60 knots is out of the flight envelope. Certification requirements are not established to ensure safe flight outside the aeroplane flight envelope.
Status: Closed — Category: Disagreement

While yes there are multiple factors in any one accident, the stall warning design was not one of the listed contributing causes. The biggest factor is that the plane was stalled by the crew. Tragic as it is.
Adding criteria to a system adds more points of failure to that system. As an example, if one RA (radio altimeter) is inoperative, the crew will have an erroneous stall warning on ground that they can't silence. The solution will be to pull a circuit breaker, but this might lead to a flight conducted with no stall warning.


Do modern flights and pilots have reservations about flying over the Bermuda Triangle?

A quick check of a site like Flightradar24 will show that the area is not overly avoided. The triangle between the southern tip of Florida, Bermuda, and Puerto Rico has quite a bit of traffic.

The southern part is a busy route from Florida to Puerto Rico and other areas in the Caribbean. The rest is also part of routes from the east coast to the Caribbean and South America.

While the idea of an area causing mysterious disappearances is understandably popular, evidence suggests that the area has not been significantly more dangerous than other areas in the world. As noted, it's an important route between Florida and the Caribbean, and one would expect lots of traffic in this area, and therefore lots of incidents.

While navigation issues were once a not-infrequent cause of air incidents, modern technology has made this sort of thing much more rare. Airline flights are monitored by ATC. Anomalies in either magnetic bearings or radio aids such as VOR or GPS are routinely surveyed and listed on navigation charts. I took a quick look and nothing seemed to stand out here. Weather forecasting has also become much more helpful with the usage of long range weather radar and weather satellites.

A look at incidents in this area shows most incidents were in the 1960s or earlier. The few recent air incidents seem to be nothing out of the ordinary. General aviation accidents are fairly common (flying into a level 6 thunderstorm also not advised), and airliners divert due to technical issues fairly frequently.

While some people may have apprehensions about the area, this concern doesn't seem to be supported by a higher than normal rate of incidents and the area is routinely traveled by both ships and aircraft.

From Flightradar24.com

Don't worry about that question mark, I'm sure it's totally routine, nothing to see here


Do jet aircraft have an emergency propeller?

I think you might have heard about the Ram Air Turbine, which is deployed in case of some aircraft in case of loss of main electrical power supply. From A320 Systems briefing:

  In case of total loss of all main generators, the RAT is automatically extended and drives the emergency generator via a hydraulic motor.

The location of the ram air turbine varies with different aircraft and some of them (like the popular A320) have them near the landing gear. The following image is from @mins' excellent answer to another question.

Location of Ram Air Turbines in different aircraft, image from aviation.stackexchange.com

Bombardier BD700-1A11 Global 5000 (source)
Airbus A320 Flight test (source)
Bombardier CRJ700 (source)
US Navy T-45A (source)
Airbus A330 (source)
Boeing B747-8 (picture by Gregor Schläger, source)
Boeing B777, RAT extension switch (source)


Where to find a waypoints/fixed points, navaids and airports database?

Nice question. There are several ways how to get these information.

http://www.fallingrain.com/: free to use, no registration needed. World database of the airports and waypoints. From these information you could easily make DB for waypoints.
EUROCONTROL EAD (https://www.ead.eurocontrol.int/eadcms/eadsite/index.php.html): free to use, registration needed. Big advantage - real and up to date information for all ECTL countries. But a bit difficult navigation.
JeppView (http://ww1.jeppesen.com/): very expensive SW, but the best in this time. You will find there all information which pilot needs. But it is not real database.
Garmin for pilots (http://www.garmin.com/en-US/explore/intheair/): another not free SW, very similair to JeppView but lightweighted.
NAVIGRAPH (http://www.navigraph.com): Great DB of all things which you need in FMC. But I guess that they have it just for flight simulator.
OpenFlights (http://openflights.org/data.html): free DB of airports, airlines and routes. You could downlod all data in one file :-)


Can I fly under a solar eclipse to lengthen its effect?

The speed at which the shadow of the Moon crosses the Earth varies according to time of day and latitude. However, 1500mph is a good starting point.

The only supersonic commercial aircraft to enter service was Concorde, top speed around 1350mph. And, of course, Concorde is now out of service.

Flying something subsonic along the path of totality will give a longer view, but most airliners top out at around 600mph.

You've really no chance of keeping up with it. You're probably better off finding a spot with a good view and enjoying your 2.5 minutes!

Nasa have a range of materials dedicated to this. If you fancy a little mental gymnastics  take a look at https://eclipse2017.nasa.gov/challenge-5-%E2%80%93-estimating-speed-lunar-shadow. In particular, download the PDF worksheet and do the maths!


Where is RC aircraft flying allowed in the US?

Update

Everything in the second section (my original answer) used to be true (well, except for the first statement), but doesn't consider that the FAA Modernization and Reform Act of 2012 made this regulatory.

The FAA has a webpage that discuss it in more detail , but here is an image that covers the basics:

There is also a much more detailed letter of interpretation from the FAA which discusses their ability to enforce the regulation and many other parts of 14 CFR 91 if a model aircraft endangers another aircraft, flies within 5 miles of an airport without receiving a clearance, flies into a restricted area, etc.

The short version is that it isn't regulated (yet).  For more details, read on.

FAA has an Unmanned Aircraft (UAS) Questions and Answers page on their website which addresses this:

  Do I need permission from the FAA to fly a UAS for recreation or as a hobby?

  There are two ways for recreational or hobby UAS fliers to operate in the National Airspace System in accordance with the law and/or FAA regulations.

  ...

  Option #1. Fly in accordance with the Special Rule for Model Aircraft (Public Law 112-95 Section 336). Under this rule, operators must:

  Fly for hobby or recreational purposes only

  Follow a community-based set of safety guidelines

  Fly the UAS within visual line-of-sight

  Give way to manned aircraft

  Provide prior notification to the airport and air traffic control tower, if one is present, when flying within 5 miles of an airport

  Fly UAS that weigh no more than 55 lbs. unless certified by a community-based organization

  Register the aircraft (UAS over 0.55 lbs. and less than 55 lbs. can be registered online at registermyuas.faa.gov; UAS 55 lbs. or greater must be registered through the FAA's paper-based process)

The other option is to obtain a pilot certificate and comply with part 107 UAS regulations.

The FAA has also published an Advisory Circular Model Aircraft Operating Standards, which states:

  1 - PURPOSE. This advisory circular (AC) provides guidance to persons operating Unmanned Aircraft (UA) for hobby or recreation purposes meeting the statutory definition of “model aircraft” contained in Section 336 of Public Law 112-95, the FAA Modernization and Reform Act of 2012. This AC describes means by which model aircraft may be operated safely in the National Airspace System (NAS). Nothing in this AC changes the requirement to comply with the statute or any applicable regulations.

  ...

  6 - MODEL AIRCRAFT OPERATIONS.

  ...

  b. Model Aircraft Hazards in the NAS. While aero-modelers generally are concerned about safety and exercise good judgment when flying model aircraft for the hobby and recreational purposes for which they are intended, they may share the airspace in which manned aircraft are operating. Unmanned aircraft, including model aircraft, may pose a hazard to manned aircraft in flight and to persons and property on the surface if not operated safely. Model aircraft operations that endanger the safety of the National Airspace System, particularly careless or reckless operations or those that interfere with or fail to give way to any manned aircraft may be subject to FAA enforcement action.

  c. Determination of “Model Aircraft” Status. Whether a given unmanned aircraft operation may be considered a “model aircraft operation” is determined with reference to section 336 of Public Law 112-95:

  (1) The aircraft is flown strictly for hobby or recreational use;

  (2) The aircraft operates in accordance with a community-based set of safety guidelines and within the programming of a nationwide community-based organization (CBO);

  (3) The aircraft is limited to not more than 55 pounds, unless otherwise certified through a design, construction, inspection, flight test, and operational safety program administered by a CBO;

  (4) The aircraft operates in a manner that does not interfere with, and gives way to, any manned aircraft; and

  (5) When flown within 5 miles of an airport, the operator of the model aircraft provides the airport operator and the airport air traffic control tower (when an air traffic facility is located at the airport) with prior notice of the operation. Model aircraft operators flying from a permanent location within 5 miles of an airport should establish a mutually agreed upon operating procedure with the airport operator and the airport air traffic control tower (when an air traffic facility is located at the
  airport).

  d. Public Law 112-95 recognizes the authority of the Administrator to pursue enforcement action against persons operating model aircraft who endanger the safety of the National Airspace System. Accordingly, model aircraft operators must comply with any Temporary Flight Restrictions (TFR).

  ...

  Model aircraft must not operate in Prohibited Areas, Special Flight Rule Areas or, the Washington National Capital Region Flight Restricted Zone, without specific authorization.

  e. Model aircraft operators should follow best practices including limiting operations to 400 feet above ground level (AGL).

  f. All other operators and for additional information on Unmanned Aircraft Systems please visit: http://www.faa.gov/uas/ .

Note that this is "guidance" and recommended procedures that the FAA "encourages voluntary compliance with" in order to "reduce the potential for hazards and create a good neighbor environment with affected communities and airspace users."

That being said, any city/county/state could have rules on their books, but there is not national guidance for this.


When a helicopter engine fails, the pilot lets the rotor blade rotate freely pushed by the wind as the helicopter is falling out of the sky. This is called auto-rotation.

Normal rotation is with the engine powering the rotor.

The most important goal of auto-rotation is to get enough lift right before touch down by flaring so the landing is not a crash.

You would also enter into autorotation when the tail rotor becomes ineffective and you can't recover it otherwise.  Once the tail rotor is back into action you can drive the rotor again.


Which moments are acting on a flying airplane?

The airfoil, on its own, also has an aerodynamic moment (positive) which would make the wing rotate nose-up about the CG of the wing itself if the wing was placed free in the wind stream.

Well, that depends entirely on the location of the wing's cg. The airfoil camber determines its moment, which is negative around its aerodynamic center or neutral point for positive camber. The first derivative of that moment with respect to the angle of attack is positive, so the cambered airfoil is unstable in pitch.

  the aerodynamic moment about the aerodynamic center is constant negative

Yes. That is correct. When hinged at its quarter point, the wing will pitch down, and that moment is independent of the angle of attack if the aspect ratio of that wing is large enough.

  The physical effect is the nose up intrinsic moment of the cambered wing due to the fact that the force on the bottom and the force on the top of the wing do not act along the same line of action.

No, not really. Aerodynamic forces are pressures acting on an area, and the force is the result of the pressure difference between both sides of the wing. There is not an isolated lower and upper side force. Again, which sign the moment of the wing has depends on your choice of reference point. You only will get a nose-up moment if your reference point is aft of the center of pressure.

  For longitudinal stability, are the participating moments the moment due to Weight, the moment due to the wing lift and the moment due to the horizontal stabilizer that need to add to a zero resultant moment?

Longitudinal stability is achieved by a negative gradient of the sum of all pitching moments over angle of attack. If you balance the moments, you trim the aircraft, but that does not say anything about stability. To simplify this task, I recommend to place your point of reference into the point in which one of the forces attacks, so you can neglect this force's moment contribution. The two preferred points are the center of gravity and the neutral point of the whole aircraft, because both don't move in flight.

  Can the positive aerodynamic torque of the wing be ignored because [it is] much smaller in magnitude than the other torques?

Yes, in a first-order approximation. The tail moment is an order of magnitude bigger and dominates the pitching moments. If, however, you need to calculate the required tail size in order to trim the aircraft at all speeds, flap settings and center of gravity locations, of course you need to include the wing moment into the calculation.

  How far behind [the] CG should the wing AC be placed?

It is much easier to shift the cg than to shift the aerodynamic center around - that one comes with the wing planform. Also, for stability you should look at the distance between the whole aircraft aerodynamic center and the cg - it just happens that a cg near the wing's aerodynamic center provides the aircraft with decent stability. But the cg can very well be a bit behind the wing's aerodynamic center.

  I realized that some big airplanes have the CG behind the wing AC. In that case, the lift from the tail is force always directed upward and not downward like when the CG is in front of the wing AC.

Now you mix up center of pressure and aerodynamic center. That is one reason why I prefer to call the aerodynamic center "neutral point". The tail lift is only upwards for a rear cg location and high angle of attack, which is quite different from "always".


Is this BA15X flight a logistic flight for British Airways?

The Wednesday flight was indeed delayed for a full day as was suggested in a comment.


When flying in uncontrolled airspace, which ATC frequency should I contact if I have an emergency?

The safest approach is to use 121.5 until someone instructs you to try another frequency.  ATC will monitor 121.5 at all locations it has antennas at. Additionally, military, some airlines, some medvac, and other operations will monitor 121.5  So your coverage will be greatest if you just use 121.5, unless you are already talking to ATC.

Addendum: Really in uncontrolled airspace?    If you are really in uncontrolled airspace, in the CONUS, you are likely flying rather low.  121.5 will be your best best in that case as well.  With enough time, you might work out a relay with higher traffic, perhaps on a center frequency.  But 121.5 remains the go to frequency.


Which specific version of English are international pilots and ATC required/recommended to learn?

The FAA bases English proficiency on the ICAO Level 4 English Language Proficiency Criteria, which don't mention any particular dialect or variant of English. Instead, they focus on the speaker's ability to communicate and they explicitly accept that the speaker may make mistakes (emphasis mine):

  Pronunciation, stress, rhythm, and intonation are influenced by the
  applicant’s first language, but only sometimes interfere with ease
  of understanding.
  [...]
  Basic grammatical structures and sentence patterns are used creatively
  and are usually well controlled by the applicant. Errors may
  occur, particularly in unusual or unexpected circumstances, but
  rarely interfere with meaning.
  [...]
  There may be occasional loss of fluency [...] but this does not
  prevent effective communication

It's clear that ICAO doesn't expect non-native speakers to be fully fluent, and once you accept that then there's no benefit at all in trying to enforce a particular dialect. Using standard vocabulary and phrases is the real key to effective technical communication, and you can see that in many other professional contexts too.

I've met plenty of non-English speakers who can speak effectively but not fluently about a specific technical domain, but they still don't have the vocabulary to talk about their holiday plans or other 'trivial' topics. Asking what dialect of English those people speak is fairly meaningless, but Globish might be the best answer :-)


Does a Mach 1 plane hear a sonic boom from a Mach 3 plane overtaking him?

To answer the question:

Yes, and even more, both would be able to notice the sonic boom of the other aircraft.

Why

To understand why, you have to understand how sonic booms are created.

Sound is nothing more than waves of different air pressure travelling through the air. Once released by an aircraft or other object, they start to propagate in all directions with the speed of sound in the resting air. (This means the waves do not travel faster than sound, even when the aircraft does!) If we mark e.g. the regions of high pressure, we get growing circles, the center of each being the point where it was created by the aircraft.

If the aircraft is moving, the circles will not be concentric, like in this animation for an object traveling at half the speed of sound:

If the aircraft is moving with the speed of sound, the circles start to touch each other on a line perpendicular to the track of the aircraft, just where the aircraft is. This is not so clear on the next animation, as there are simply not (big) enough circles.
However, on this line, all the regions of high pressure sum up to a region of 'very high' pressure. This is the shock wave, which is often referred to as sound barrier. (The term also describes just the insurmountable speed limit encountered by non-supersonic aircraft.) If this shock wave passes an observer on the ground, he will hear a sonic boom.

As the aircraft accelerates more, the shock wave isn't perpendicular any more, instead, you get two lines. In reality (3D), you get a cone with the aircraft at the tip, and the opening angle is defined by the speed of the aircraft.

Now, to answer your question: As the tip of the cone is where the aircraft is, this cone travels with the aircraft, and with its speed.

So, if an aircraft is overtaken by a supersonic aircraft, it will be overtaken by the cone-shaped shock wave of that aircraft a little bit later, too. Also, the faster aircraft will pass the shock wave of the slower aircraft.

Remarks

An aircraft itself is very loud, but also dampens every noise from outside, and headsets and helmets may contribute to the dampening, too. So, I don't know if a pilot would hear something from the boom. Maybe he does not, but the aircraft definitely crosses the shock wave.
My explanation does not describe where the sound comes from. While the sound of a subsonic aircraft mostly comes from the engines, it comes from the compression of air at the surfaces of supersonic aircraft.
This cone sometimes is visible, as on the following picture of an F18, stolen from air-attack.com. This is because the high pressure region is followed by a low pressure region, where air expands and moisture may condensate. The picture also shows that there are usually two shock waves, each where the cross section of the aircraft changes significantly.  One is generated near the canopy and one near the wings. EDIT: As commented by @PeterKämpf, this picture does NOT show an F18 at supersonic speed. It is at transsonic speed, which is close to, but still below mach 1. The fog forms due to other effects.

However, here is an other picture of a Northrop T-38 at mach 1.1, showing the shock waves, from wiki commons:


What are these little things on the evacuation slide?

@ratchet freak is correct. The protrusions are canopy poles, where the canopy in the evacuation slide/raft is propped up. The image below shows a canopy propped on them.

Image from tulmar.com

From the document:

  The canopy is supported in the center in 4 places by inflatable yellow “CANOPY END SUPPORTS” and “CANOPY CENTER SUPPORTS”, and supported along the sides by 14 numbered supports on the top of the slides inflatable structure.

Here's a closeup of the support from the same document.


For a flying wing airfoil, which AOA is to consider when selecting Cl?

Do not look at the angle of attack. Instead, focus on ratios like best lift-to-drag ratio. The angle of attack will be a consequence and not a design parameter.

First you need to determine what your flying wing will be good at. Next, determine which propulsion (jet or propeller) it will use. Then you can work on the layout (aspect ratio, wing sweep) and when that is decided, only then you are able to determine the optimum lift coefficient.

The process to determine the optimum lift coefficient is discussed here, here and here.


Is it acceptable to use VNAV data in lieu of localizer recommended altitudes?

If your company uses CANPA (continuous descent) approaches, the whole point is using artificial VNAV on non-precision approaches where no vertical navigation is part of the approach. This involves determining a DDA, or derived decision altitude, based on the published minimums and some other criteria. Arrival at the DDA requires a go-around just like if you were arriving at a DA on a precision approach.

In defense of your point, if you aren't using any form of vertical navigation, one might argue that it's no longer a CANPA approach at all. How can be maintain a constant angle without vertical nav?

Then again, if you are flying the CRJ a localizer approach would involve having the Proline 4 in "green needles." Advisory VNAV only works in "white needles," so if they're saying you shouldn't use advisory VNAV on a localizer only approach that might be the reason. You can't.

In reference to the main question in the title, you can't use advisory VNAV "in lieu" of the published minimums or minimums derived from your company regulations, but if you want to use advisory VNAV to plan your descent to the appropriate minimums, that's okay unless specific language in the company manuals forbids it.


What is the difference between en-route delays and airport delays?

The delays you mentioned are imposed by Eurocontrol to manage traffic flow all over Europe:

  Even when an aircraft is ready to depart, it may still be delayed by ‘flow management’ (ATFM). You may well hear that your flight is ‘waiting for its Air Traffic Control slot’ and this is explained in another article. In short, if there is a problem that will delay an aircraft either en-route or on the approach to the destination airport, then it’s safer and cheaper to hold the aircraft on the ground, not burning fuel, and give it a delayed take-off time.

  EUROCONTROL as Network Manager looks at all the flight plans and identifies where and when there are too many flights/too little capacity. This might be as a result of a peak in demand (aviation has rush hours too!), weather problems, limited capacity at the destination airport or many other possibilities. In total, flow management delays account for about 16% of total delays (in 2017), mostly relating to issues at the destination airport.

(Eurocontrol)

  ATFM departure slots are allocated centrally by the European Network Manager upon the request of the local Flow Management Position (FMP), when an imbalance between demand and capacity is foreseen at airports and/or en-route. The purpose of such regulation is to hold aircraft on the ground.

(Eurocontrol ATFM Slot Adherence)

To the pilots, this comes as a so called CTOT (Calculated Take-Off Time):

  A time calculated and issued by the Central Flow Management unit, as a result of tactical slot allocation, at which a flight is expected to become airborne.
  An Air Traffic Flow & Capacity Management (ATFCM) departure slot, forming part of an Air Traffic Control (ATC) clearance, which is issued to a flight affected by Network Management regulations. It is defined by a time and tolerance (-5 to +10 minutes) during which period the flight is expected to take-off.

(Eurocontrol ATM Lexicon)

For each of these delays, there is an associated Reference Location where the reason for the delay is located. This defines, which delay category applies:

En-route delay:

  Delay caused by regulation based on traffic volume which has a reference location classified as AS (Airspace) or SP (Special Point).
  ATFM delay caused by regulations applied by the CFMU at the request of the FMP to protect en-route ATC sectors from overload.

(Eurocontrol ATM Lexicon)
Airport Delay:

  Delay caused by regulation based on traffic volume which has a reference location classified as AZ (Aerodrome Zone) or AD (Aerodrome)

(Eurocontrol ATM Lexicon)

Examples for delaying a departure could be:

enroute weather does not allow to fly the filed route at the moment (En-route delay)
weather at destination is not expected to be good enough to land at the estimated arrival time (Airport delay)
there will be too many aircraft in one air traffic control sector (En-route delay)
there will be too many aircraft arriving at the destination airport at the same time (Airport delay)


What happens to the transponder, FDR and CVR in case of an explosion?

As ratchetfreak noted, the recorders don't transmit data, attached to them is a location beacon that operates for up to 30 days.
This location beacon isn't always successful in enabling searchers to find the recorders. In the case of AF447, it took two years before a search located the aircraft debris field on the sea floor and recovered it's recorders.
As for withstanding the stresses of an explosion, it obviously depends on the strength of the explosion and it's location in the aircraft. In the case of Pan Am 103, destroyed in flight by explosives, the recorders were recovered and data extracted.

A DFDR must obviously have a high degree of ‘crashworthiness.’ The first units were required to withstand a momentary shock force of 1,000gs, the latest test standards now call for a test to 3,400gs for a duration of 6.5 milliseconds. The units also have to withstand a static crushing force at all of its six axis points of an applied load force of 5,000lbs for 5 minutes on each axis. Third, it must withstand a 500lbs piercing force test conducted by dropping it onto a ¼ inch steel pin from 10 feet. Lastly it must withstand a 1,100°C fire test for 60 minutes, and a 260°C oven test for 10 hours.
It is also required that these units are mounted within the tail area of an aircraft, away from the potential crushing force of any engines mounted nearby. The DFDR must be watertight to a depth of 20,000 feet in sea water, and survive at this depth for 30 days - and it must be fitted with an underwater locator beacon which will act like a sonar transmitter, by ‘pinging’ a signal through the medium of water that it might be laying in.

From http://www.avbuyer.com/articles/detail.asp?id=1858

1G is the force you feel on your feet standing up.
12G is the most a fighter-jet pilot normally experiences in combat.
16G sustained for 1 minute will kill you.
25G for an less than a second will hospitalize a fit racing car driver

350G results in total body fragmentation

In a 727 crash landing

Impact forces at the front of the plane peaked at 12 G (12 times the force of gravity), in the centre the force was less, 8 G, at the rear it was 6 G, half that at the front and no greater than being hit in a fairground bumper car.

In a 720 crash,
the maximum force was 14 G vertically for 0.8 seconds

This F4 phantom striking a concrete block at 480 MPH produced average peak forces of less than 60 G (see fig 7). The most solid elements (the engines) experienced forces of up to 700 G (fig 11).

3400G is therefore a lot.


How accurate is the barometric altimeter in the Tu-154?

A barometric altimeter is required to meet certain operational standards for use in an aircraft under instrument flight rules. We talked a little about this in another question with references to the relevant FAA requirements for the instrument.
I'm certain there's an equivalent in the Polish regulations, and while I don't know where you'd find it I would bet it's broadly similar in its requirements.

A radio/RADAR altimeter is typically accurate to within 20 feet within its operating range (typically <= 2,500 feet AGL). There are varying TSOs for radio altimeters, so you'd have to look up the standard a specific unit was built to in order to get exact numbers.

One of the core issues underlying this accident which you highlighted in your question is that a barometric altimeter and a radio altimeter are two different devices, measuring two different things, so it's not really reasonable to compare them.

Barometric altimeters measure altitude above a standard reference (usually sea level) by using a known/standard pressure lapse rate (~1 in.Hg per 1,000 feet) and measuring the difference in pressure at the instrument.

The readings given by a barometric altimeter are affected by weather conditions (mainly temperature), so the displayed altitude may be 'incorrect' (relative to say GPS altitude above mean sea level).
The readings given by a barometric altimeter are not affected by the local terrain, so peaks, valleys, and tall buildings won't change what it shows.

Radio altimeters measure the distance to whatever radio-wave-reflecting object is below the unit (typically "the ground" - whatever terrain happens to be under you) by detecting how long it takes a radio pulse to be reflected back.

The radio altimeter reading is not affected by weather conditions (temperature) as these don't affect the pulse reflection time.
The radio altimeter is affected by local terrain (peaks, valleys, etc.) as this changes the distance the radio pulse has to travel.
The radio altimeter reading is affected by any object that reflects radio waves (buildings, other aircraft passing below you).
The radio altimeter reading may be affected by "slant range error" just like DME, (in practical terms this is less of an issue for radio altimeters: The radio altimeter points "straight down" so the slant range error is generally small unless the aircraft's pitch or roll attitude is extreme).

So to directly answer your question, barometric and radio altimeters aren't comparable in the way you're asking: Because they measure two different things it's not possible to say one is "superior" to the other. They are different tools, serving different purposes: It's incumbent on the pilot to be aware of the limitations of whichever tool they happen to be using at the time (and to ensure that they've selected the correct tool for the task at hand).


If your radio has DME installed, then it is shown on the instruments


Is vertical separation based on geometric difference or altimeter difference?

The short answer: "Altimeter difference"

The long answer:

From a pilot perspective, when issued an altitude to maintain by ATC, he/she will fly the altitude in reference to his/her altimeter, whether or not it's a "Flight Level" assignment (usually FL180 and above in North America), or "altitude" assignment (below FL 180).

For example, when the temperature is colder than ISA and one aircraft is assigned FL250 and another is assigned FL260 , the  actual (geometric/true) vertical separation between the aircraft would be marginally/somewhere less than 1000 ft. There is no ATC correction (in the U.S.) for actual "true" altitude being (probably slightly) less than 1000 ft. in this scenario.

Since there is not an automatic correction for colder than ISA (or warmer than ISA) internal to the altimeter, true altitude is different than what is being displayed to the pilot on his/her altimeter and being displayed to the controller on ATC radar.

This is only with respect to separation between aircraft.  Separation from terrain is considered both by the pilot and ATC, as necessary.  For example, at some locations during very cold temperatures, MVA (minimum vectoring altitude) for a specific area may be raised so that aircraft always have the necessary "true" altitude separation from the terrain while being vectored by the controller.

The pilot, while conducting instrument approach procedures at specifically designated airports, will make altitude adjustments for the IAF/IF/FAF/MDA/DA/missed approach holding, based on a correction value obtained either automatically from the onboard equipment, or manually from a cold temperature altitude correction table/chart.

On these occasions, the pilot has the obligation to notify ATC of the altitude adjustments being made. These adjustments will be made to the indicated altitude being flown for the purpose of obstacle/terrain clearance and the indicated altitude on the altimeter will be higher than published on the chart.


Could a Personal Locator Beacon or EPIRB carried by a passenger aid in locating a downed airliner?

Relatively short answer

Cospas-Sarsat: Feasible but...

It's possible, but there are many individual elements involved. It's a matter of probability that most of the time there will be a combination preventing the link to work. If you know what to do and take care of ensuring a good direct line of sight (LOS) you may be able to avoid some of these combinations. It cannot work underwater.

Parameters that can attenuate the signal reaching the satellite receiver are of different origins:

The aircraft design itself (composite materials or aluminum, number of windows, ...)
The location of the accident (canyon, trees, ...)
The transmitter use (position, window proximity, metallic surface or debris interference, body proximity, ...)

I'm not aware of experiment results for using a PLB within a metallic container like a commercial aircraft cabin. It's still possible to evaluate the RF channel loss in different configuration and see if the signal can reach the receiver with the minimum required level.

As explained in the next sections about the Sarsat satellites of the international SAR service on 406 MHz:

The threshold for signal reception by the receiver is 161 dBW.
With an initial power of 7 dBW (5 W), the attenuation must be at most 168 dB
In good conditions we can expect an attenuation of "only" 148.1 dB. Such signal 12.9 dB stronger that the threshold can be detected easily.
In degraded conditions we may experiment an attenuation of 177.5 dB. Being 9.5 dB below the threshold, this signal is not detected.

Indoor transmission put the system at its limits of detection capability (a S-meter unit is 6 dB).

Weak signal on a S-meter, S-unit is 6 dB (source)

Many small attenuation causes that, when summed, can prevent the link to work must be taken into account, hence this answer is a long one.

SPOT LLC

SPOT LLC solution you mention is a commercial messaging initiative working on 1.6 GHz, out of the Cospas-Sarsat system. Higher frequency means higher attenuation. The limited 0.4 W RF output also makes the signal weaker. It's very unlikely that SPOT could work within the cabin.

Details

Introduction: PLB principles

Emergency PLB operate on 406 MHz. The previous 121.5 MHz civil frequency is not monitored anymore by SAR satellites, but can be used (in addition of the actual signal at 406 MHz) as a homing guide for the SAR team. They are informed about whether this homing feature is active or not by the message sent by the PLB.

PLB output power is 5 W (equivalences: 7 dBW 37 dBm) at 406 MHz, in vertical polarization.
From C/S T.004, the performance of the satellite system is:

A "probability better than 95% to provide a valid solution (15 hexa identification provided) for a beacon transmitting with a 37 dBm output power (with a whip  antenna) and for satellites passes with elevation above 5°)"
A "probability better than 95% to provide a Doppler location with an accuracy better than 5 km"

There are no satellites entirely dedicated to the SAR service, rather distress signal receivers are carried as one of the payloads aboard satellites. The system is made of two constellations:

GEOSAR constellation, Geostationary Earth Orbit SAR. These satellites are at fixed positions, 36,000 km above the equator, and are covering the globe except the polar regions.
LEOSAR, Low Earth Orbit SAR. Satellites in near-polar (about 85°). LEOSAR is made of two sub-constellations: Sarsat satellites orbiting at 850 km, and Cospas satellites orbiting at 1,000 km.

(Source)

A third constellation is planned to operate at a higher altitude than LEOSAR (MEOSAR, currently not fully deployed).
While GEOSAR are likely to be first to detect the PLB activation due to their permanent LOS, LEOSAR will provide the best detection due to the shorter distance to the device.

I'll focus on LEOSAR / Sarsat payload which provides the best chances for the detection of a PLB signal partially blocked by RF impermeable obstacles.

Sarsat payloads

Satellites carrying a LEOSAR Sarsat payload are NOAA 15 (Sarsat 7), NOAA 18 (Sarsat 10), NOAA 19 (Sarsat 12). Other are scheduled to be active in the future (some may be already, I haven't checked). They are fitted with a SAR receiver (search and rescue processor, SARP). Sarsat satellites can be tracked on N2YO.com.

According to Cospas-Sarsat LEOSAR Space Segment Commissioning Standard - C/S T.004, a SARP-2 has a sensitivity of -161 dBW, and SARP-3 -164 dBW (that's about 60 attowatts to be compared with a cellular phone cell: -134 dBW, 1,000 times less sensitive).

Can this small quantity be delivered to the SARP from the inside of a cabin?.. This is a matter of knowing the initial power, and determining the loss along the wave path until the signal reaches the receiver.

The power generated by the transmitter amplifier is 5 W, or 7 dBW. 161 dBW on the receiver means receiving a 1 W signal that has been attenuated by 161 dB. If we have already 7 dBW at the source, we can bear a maximum attenuation of 168 dB.

Main loss inventory

Propagation loss in direct view

The most important part of the signal will be lost in the atmosphere between the antenna of the PLB and the antenna of the SARP.

Loss due to distance

Loss is dependent on two factors: distance and wavelength. Both factors limit the area of the receiving antenna compared to the whole sphere of the wave front, and in consequence the portion of energy received is smaller too.

Using the propagation model ITU-R P.525 (free-space propagation).
Distance = 850 km, f = 406 MHz.
Assuming isotropic antennas for the time being.
According to the model, the loss (dB) is:
Lbf = 20 log(4πd/λ)
.   = 32.4 + 20 log(f) + 20 log(d)
.   = 32.4 + 20 log(406) + 20 log(850)
.   = 143 dB

The signal that left the PLB antenna reaches the SARP antenna -143 dB weaker, assuming the best antenna alignment. But this is never the case, because when in a polar orbit, the satellite is unlikely to be exactly above the beacon.

Misalignment of the receiving antenna

There will be an angle between the nadir of the SARP and the beacon. This off-nadir angle, depends on the actual track of the satellite for the current orbit:

Target off-nadir

The gain of the antenna varies according to this angle. Sarsat-TIROS SARP Receive Antenna (UDA) Gain Pattern:

UDA antenna gain at different off-nadir angles (source)

Assuming the polarization is favorable (RHCP), the gain may varies between +2 dB and -10 dB. Note that:

The gain is better when the off-nadir angle is large. This is likely to compensate the higher distance to the beacon.
I'll assume a link length f 850 km, but the actual length is larger when the beacon is not directly at the satellite's nadir.

We should now work with the probability distribution of the misalignment for the LEOSAR antennas to have the full range of possibilities and their likelihood (e.g. Monte-Carlo simulation). To simplify, let's just use a bad case: -4.4 dB (this is not the worst possible). Loss so far: -147.4 dB (-143 - 4.4).

Attenuation due to feeder and duplexer

On the satellite, the SARP is connected to an antenna via a duplexer to isolate the SARP uplink antenna from the SARR downlink signal (SAR repeater used on local mode, not detailed here):

Hardware on the Sarsat satellite (source)

The duplexer + feeder loss is -1.6 dB. Loss so far: -149 dB (-147.4 - 1.6).

Loss margin left

We had a budget for -168 dB loss, we have used -149 dB. The margin until the PLB signal is lost by the SARP is 19 dB, assuming we are in this configuration:

PLB is outdoor.
The LOS is completely clear, no foliage, no roof, etc.
PLB antenna has no gain/loss (0 dB gain).
PLB antenna is vertical, this is the normal use of the SAR device.
PLB antenna and RF output stage impedances match (no SWR).
There is no atmospheric loss (free space)

Additional losses

It's time to re-look at the assumption made until here, and take into account the additional effects encountered when the PLB is used from the cabin of a crashed aircraft.

PLB is outdoor.

Actually the PLB is behind a cabin window.
From Arkema:
"Most formulations of colorless Plexiglas sheet readily transmit standard broadcast, television and most radar waves of the electromagnetic spectrum". It can been assumed that windows (including the internal protection sheet) don't block the PLB signal. Loss = 0 dB.
In the cabin, numerous reflections will occur on the wall, and due to the closed space with only small windows, it's likely the reflected signals will globally interfere in a destructive way (phase mismatch) with the original signal.
If the PLB is displaced, even by a small amount, the reflections are changed. The RF energy actually vary continuously, creating a fading effect. Reflections has been studied in somehow comparable environments, for UHF frequencies. While the frequency was a bit higher, and the environment was a simple one, we can use the results for a rough order of magnitude:

RFID signal (915 MHz) loss due to reflections (source)
The spatial fading is visible, at some distances reflected signals add, at other they subtract. This loss is also known as multipath effect. The signal may be attenuated by 10 dB or more compared to free space.
Each reflection has also the potential to change the polarization. See next point.

PLB antenna is vertical, this is the normal use of the SAR device.

The transmitter and receiver antenna polarization must match or an attenuation occurs. The polarization of an antenna describes the plane in which the electric field is transmitted. For a simple antenna, made of a single active element, the electric field is sent in the plane of the element:

Vertically and horizontally polarized waves (source)
Vertical polarization creates less reflection on the ground, which is usually what is desired, so a PLB creates a vertical polarization, but only if the antenna is kept vertical, else the polarization will follow the antenna orientation.
To cop with both linear vertical and horizontal polarizations, and everything in between, the SARP antenna is designed to be circularly polarized, and is able to receive both in good conditions, but not optimal conditions:

  linearly polarized antennas will work with circularly polarized
  antennas and vice versa. However, there will be up to a 3 dB loss in
  signal strength. In weak signal situations, this loss of signal may
  impair communications (source).

The antenna on the satellite should be like this:

Helical, circularly polarized, antenna (source)

The LOS is completely clear, no foliage, no roof, etc.

Indeed, if there is a metallic obstacle in the LOS and there is no possibility for reflections (no hole in the metallic cabin), no signal is transmitted. This could happen if the PLB were surrounded by metallic debris from the airplane wreckage.
Else there is a volume (the Fresnel zone) between the transmitter and the receiver that must be free of obstacles. This zone is an ellipsoid around the LOS. If obstacles are present there will be diffraction and reflection. Diffraction scatters the signal (no need to have knife-edge corners), and reflection deviates it, which could be a positive effect when there is no clear LOS.
Dense vegetation or heavy foliage on the LOS: There is water in plants, a loss occurs, typically larger than 0.1 dB/m at 406 MHz. We can use models to evaluate the attenuation:

(Source, page 155)
Example: The aircraft crashed in a forest. The aircraft is surrounded by 25 m trees, except in the direction from which it came.
Satellites low on the horizon will not be accessible: GEOSAR satellites over the equator are usually low on the horizon when viewed for medium latitudes, and some orbits of LEOSAR will be hidden by the trees due to the loss exceeding -15 dB as soon as the depth of foliage is 50 m (slant depth). This depth can be quickly encountered, leaving a small free field of view from a window (it would be larger for the windshield though):

Tree trench created by crash-landing in a forest

PLB antenna has no gain/loss (0 dB gain).

This is likely the case for many PLB. PLB antenna seems to be a shortened 1/4 λ whip. Antennas are measured against an hypothetical perfect antenna (isotropic antenna), and the ratio of amplification is expressed in dBi (dB comparing to isotropic). dBi and dB are equivalent in the current discussion as the isotropic antenna has a gain of 0 dB.

PLB antenna and RF output stage impedances match (no SWR).

In order for the current out of the PLB RF amplifier to be radiated entirely by the antenna, PLB output impedance and antenna impedance must be equal. As soon as there is a mismatch, a part of the RF current is not converted into an electromagnetic wave and returns to the amplifier, mixing with the current flowing in the other direction. The result is the appearance of standing waves in the PLB device. The ratio of SW is smartly named SW ratio (SWR). PLB are stated having a SWR less than 1.5 or 2 in their specifications. The corresponding loss is 0.2 and 0.5 dB. Not so much.
The impedance of the antenna varies greatly as soon as the antenna is not in a free space. A common cause is that a part of the body (containing water) is close to the antenna, or touching it. This could easily lead to a loss of 10 dB. The radiative efficiency of the antenna (gain) also suffers: Touching the antenna is like deforming it. Its characteristics are changed. For example is is no more optimized for the signal frequency to radiate. So in addition of SW appearance, the current that reaches the radiator is also poorly converted into waves. In your scenario it is important to use the PLB as intended, the antenna being unobstructed.

There is no atmospheric loss (free space).

This is another effect difficult to estimate, as it varies with time of the day, weather aspects and Sun activity.
Oxygen and water vapor play an important role. From ITU-R P.676-10:

Attenuation in dB per km (source)
It seems for UHF the absorption is rather limited, so let's ignore it.
Other losses are due to sporadic electrical activities in the ionosphere. They are more difficult to estimate, and they translate into noise rather than attenuating the signal received by the SARP. Other elements like the capability of the SARP to reject noise would also need to be considered.
Ionosphere anomalies could potentially introduce errors in the Doppler localization.

Bottom line

Let's recapitulate the losses we have discussed:

 - Impedance mismatch / SWR:                 -0.5 dB
 - Transmitter antenna gain:                 +0 dB
 - Reflection in the cabin:                  -0 to -10 dB (center).
 - Cabin window:                             -0 dB
 - Fresnel obstruction and trees:            -0 to -15 dB
 - Free space loss:                          -143 dB
 - Absorption by atmosphere gases            -0 dB
 - Other propagation losses:                 Not evaluated.
 - Off-nadir angle:                          -0 to -4.4 dB
 - Linear to circular polarization mismatch: -3 dB
 - Satellite duplexer:                       -1.6 dB

                               Acceptable:   -168   dB
                               Best case:    -148.1 dB
                               Worst case:   -177.5 dB

The worst case is encountered when:

The PLB experiments the higher level of reflected waves. This can be eliminated by being very close to the window, and shielding the rest of the cabin with something metallic, but not too close.
The Fresnel ellipsoid is blocked by trees. Not much freedom here. LEOSAT will hopefully have orbits with sufficient high elevation to be out of the obstacles. If the aircraft is really covered by deep foliage, there is no much chance for a successful link.
The aircraft is at the nadir of the satellite. The SARP antenna is optimized for off-nadir locations (no sure off-nadir locations will be better served, due to the increased slant distance, that would need to be checked). Too bad if the aircraft is in a forest.

Note that carrying a personal locator doesn't cause a safety problem, as it doesn't transmit before being activated. Activation will be either manual (usually for PLB) or by sensing a large acceleration (seems limited to ELT). I don't know if the security guys at the airport will let you board with a transmitter. It should be easier to persuade the pilots.

Case of a SPOT device

Compared to the numerous documents that describe governments-financed SAR service on 406 MHz, SPOT is a more confusing solution.

This is not related to SPOT, the observation satellite family built by Astrium. GEOS IERCC (International Emergency Response Coordination Center) has no link with the GEOS satellites family launch by Nasa some decades ago. It is not either GOES, the geostationary satellites that support GEOSAR.

Globalstar is a large satellite phone company owning satellites. SPOT LLC is a subsidiary of Globalstar providing satellite data links and related sets for messaging and voice communications. GEOS-Alliance has launched a privately-owned assistance service based on SPOT capabilities. GEOS-Alliance services are sold online, and by retaillers.

From SPOT website:

  SPOT Gen3 provides location-based messaging and emergency notification
  technology that allows you to communicate from remote locations around
  the globe. It offers custom tracking interval options,
  motion-activated tracking, long-life battery and more.

In short:

Instead of buying a SAR transmitter and then having the service for free, the GEOS-Alliance subscriber receives a transmitter and pays an annual fee.
Instead of having the SAR device connected to the SAR organizations worldwide through the LUTs and MCCs/RCCs, the subscriber is connected to GEOS which calls the local emergency services on your behalf.

The technology behind:

SPOT/Globalstar seems to use LEO spacecraft at 1,414 km instead of 850 km for Sarsat, with a 52° inclination instead of 85°, meaning their coverage could be reduced.
SPOT messengers are limited to 0.4 W instead of 5 W for Sarsat, maybe because of regulations, as they can be used without actually signaling a distress situation.
Globalstar frequency used is 1.6 GHz, instead of 406 MHz for Sarsat.

It seems that these three technical differences are not going to make SPOT devices as efficient as Sarsat:

Using the same ITU-R P.525: Lbf = 20 log(4πd/λ) gives a free space loss of 159 dB upfront, to be compared to the 143 dB for Sarsat (difference: -16 dB).
0.4 W = -4 dBW instead of 7 dBW for Sarsat (difference: -11 dB).
We may add a loss of 1 dB for the atmosphere absorption at this frequency.

If I'm not wrong, that's already a difference of -28 dB at the receiver. It must be very sensitive, or be liked to hi-gain antennas to compete with the governments-operated SAR. That's not going to make it from within the cabin of an aircraft with a limited LOS, and sometimes this seems to even not work well in the open space.

Reference documents

C/S A.003: Cospas-Sarsat System Monitoring and Reporting
C/S G.003: Introduction to the Cospas-Sarsat System
C/S G.004: Cospas-Sarsat Glossary
C/S G.006: Cospas-Sarsat System Assessment
C/S G.008: Operational Requirements For Cospas-Sarsat Second Generation. 406 Mhz Beacons
C/S T.001: Specification for Cospas-Sarsat 406 MHz Distress Beacons
C/S T.003: Description of the Payloads Used in the Cospas-Sarsat LEOSAR System
C/S T.004: Cospas-Sarsat LEOSAR Space Segment Commissioning Standard
C/S T.011: Description of the 406 Mhz Payloads Used in the Cospas-Sarsat GEOSAR System

More Sarsat documentation: Cospas-Sarsat site


Could a single engine pilot land a passenger jet? (from Airplane)

I can relate to you the true story of my uncle who successfully landed a large WWII aircraft with no flight training.

He was the flight surgeon on board a large aircraft that got heavily shot up.  Hostile fire killed or severely injured every crew member.

He moved the pilot out of his seat, and contacted a control tower.  With the expert help of the control tower operators, he successfully landed the aircraft.

After the war, he had a private practice in his home where he saw patients.  For patients too ill to come to him, he performed house calls.  He continued to perform house calls until a short time before he passed.

I have always thought his life story would form a compelling foundation for an inspiring movie.


What does feathering mean and how does it work technically?

Feathering is only possible with variable pitch propellers and means that the blades are turned such that their mid-to-outer section is aligned with airflow and they create minimal air resistance. This is done when the engine is shut down and the propeller should create minimal drag. This means also that all accessories on this engine will not be powered anymore.

Due to the normal twist of a propeller blade, some sections are still not completely aligned with airflow and produce more normal force and drag than they would if all sections could be aligned with airflow at the same time, but in total those forces will cancel out, and the propeller stops windmilling.

This picture of a C-130 engine with feathered prop should help to illustrate the concept.

On pure jets no equivalent setting is possible (we have to wait for variable-pitch fans to add this in the future).


Do modern aircraft automatically manage the deceleration to Vref?

This depends on the aircraft.

Airbus aircraft have a managed speed mode in the FCU (flight control unit), where the speed is completely controlled by the FMGS (flight management and guidance system). This includes slowing the aircraft down when the appropriate flaps are selected by the crew. No manual action is necessary to reduce airspeed for landing until you hear "RETARD, RETARD" during the flare and pull the thrust levers to idle. See here for some details.

Boeing aircraft can also manage speed automatically in VNAV mode, but not all of them slow to reference speed automatically, only to the flap maneuvering speeds when flaps are selected by the crew. When using other modes than VNAV for the approach (like APPR for an ILS approach), speed must always be set manually in the MCP (mode control panel). For an RNAV approach, this may be possible, see e.g. from the 737 NG FCTM (5.46 Approach and Missed Approach):

  When on final approach, VNAV may be used with speed intervention active (as
  installed) to reduce workload. Adding speed constraints to the final approach
  waypoints is normally not needed and causes extra workload without providing
  any safety benefit. This also reduces the ability to make last minute approach
  changes. However, if needed speed constraints may be changed if the default
  value is not suitable.


Is there any way to determine or estimate where the cloud tops are?

https://www.aviationweather.gov/obs/radar/ provides cloud tops for weather with precipitation.

Cloud tops with no precip can be discerned from data provided in the Skew-t log℗ charts that are part of this app http://www.skewtlogpro.com/about-skew-t-log-p-charts/

Where the temperature and dew point on the skew-t charts are converged you can expect clouds. If the convergence extends into the freezing level indicated on the chart you can expect icing.


Can the fluid from one hydraulic circuit go to another one (voluntarily or not) in flight?

This depends on how the systems are plumbed, and while this is likely an exception, for some airplanes like the EMB-145, the answer is yes.

The EMB-145 has 2 hydraulic systems.  System #1 serviced the outboard brakes and system #2 serviced the inboard brakes and the parking brake.  The parking brake actuated all of the brakes and this let you transfer fluid between the systems through the outboard brakes.  This isn't a normal procedure, but one maintenance would walk you through if you had low fluid in one system and more than you needed in the other to balance the systems if you were out somewhere without the ability to service the hydraulic fluid.

The procedure was either

Depress and hold toe brakes
Set parking brake
Release toe brakes
Release parking brake

or the opposite, depending on which way you wanted to transfer fluid.

This works in flight or on the ground (don't do this in flight lest you get distracted and end up landing with the parking brake set)


With helicopters, is normal landing or auto-rotation landing any different when landing on water?

As a helicopter pilot, I've never made a water based landing, so I'm not speaking directly from experience, only from my training, but there are a couple things that are missed in the discussion here that I would certainly worry about.

If I had a real engine failure, and was forced to perform an auto-rotation, in all likelihood, I would not end the auto-rotation with zero forward velocity, I would probably perform a running landing (where you slide on your skids). This, of course, is assuming I'm landing on a flat surface where I'm not likely to roll over (such as a street, parking lot, or runway). Holding the flare to bring the helicopter to a complete standstill has a few risks for me, the biggest one being that if I flare and stop my descent while I still have forward velocity, holding the flare will start to increase my altitude again. Higher inertia (heavier) rotors in small helicopters will suffer from this problem, for example, in training, a Robinson R-22 will generally not have this issue, but an R-44 has much heavier rotors, and we get trained to anticipate a flare at the end of the auto-rotation. Depending on the helicopter, weather, and how I've performed my auto-rotation, if I'm in a real emergency, I would rather put the helicopter down on the ground and slide a little bit than suffer a rotor stall at 50 feet, but a running landing is clearly not an option in a water based landing.

Once I've performed an auto, and the helicopter is on the ground, I'd apply the rotor brake to get the rotors to stop moving before I exited the aircraft, and generally speaking, won't have to worry about the rotors any longer at that point.

If I am performing a water based auto-rotation, there is quite a bit more to worry about. The first thing I have to worry about is that I won't be able to perform a running landing. This means that I'll have less margin for error in my auto-rotation. The second problem is that as soon as I set the helicopter down into the water, it's going to start sinking, and I'll still be strapped in. If I jump out, I'll have to worry about hitting the rotors (or the rotors hitting me) as the helicopter sinks. This means that as soon as I hit the water, I have to remain in the aircraft, and I'll pitch the cyclic over in the opposite direction from the side I'm sitting on, so that I can stop the rotors and still exit the aircraft on the surface side rather than underneath the sinking helicopter. This gets more complicated in the case of passengers, I would encourage them to jump out before the helicopter hits the water, but after my flare, so that they can clear the aircraft and I don't have to worry about them. I only mention it as an additional complication I'd potentially have to deal with.

All of this complexity is a large reason why most of the helicopter pilots I know really do not like flying very far over water. When I'm flying over the water, I tend to stick to an area near the coastline specifically for this reason.


Why aren't "fuel polishing" systems removing water & ice from fuel in aircraft, like in cruising yachts?

The simple answer is weight/risk/added complexity: the systems are heavier than they are worth for the problems they avoid in aircraft.
While ice blockage has been an issue for aircraft in the past, planes that fly high enough to warrant it have fuel heating systems to avoid this very issue.
The reality is that the chances of water getting into marine fuel are MUCH higher than water getting into AvGas. Water finds its way into airplanes in mainly one way: warm moist air that fills the space in fuel tanks condenses in the cold and the water precipitates out. This often happens over night when planes are not re-fueled after their last flight and left out in the cold. As such its extra important to sump the tanks for the first flight of the day. You can also mitigate this by filling the tanks every night if possible. Pilots are also taught to diligently sump tanks to avoid the issue in the first place.
In my experience, flying in the north east of the US where the air can get humid and the nights can be cool, I've never pulled more than a few bead size drops of water out of the tanks of my archer in the morning. I know of others that have pulled more but not significantly more.
There have been occurrences of a fair bit (hundreds of gallons of water) getting into aircraft tanks but these have generally been caught and handled. On the bright side we have a few nice things in aircraft that make water easy to deal with.

Water is heavier than AvGas so it will pool at the lowest point of the tank which is generally where the outlet/fuel line is connected.
The lowest point of a fuel tank on an aircraft is fairly easy to get to so pulling a test sump of fuel is no problem during pre-flight
It's fairly easy to deal with the fuel once it's in the sump cup on the ramp, chances are you wont anger the EPA all to much.

On the contrary, with marine fuel tanks it can be hard, if not impossible, to access the sump in any reasonable way and once you drain it you run the risk of it getting in the bilge and ending up getting pumped overboard which the EPA will have an issue with.
On a boat you have lots of options for water to get into the tank since there is generally water all around. Maybe it splashed in some gas cans you had on deck, maybe it splashed in during a mid trip re-fuel, maybe it splashed in refueling at a dock, maybe it was raining one of these times or all of these times, maybe the dock kid put the fresh water hose in the fuel inlet in a haste etc. etc. As such fuel/water separators are far more critical on a boat where there is often space and weight to spare and the chance of water getting into the fuel is high.