What material is the smoothest for air to travel over the wing?

Well first let's dispel the rumor that wings are "pretty smooth" - ideally (in the dreams of aircraft designers and the mathematical perfection of fluid dynamics modeling) they would be, and they certainly are from a distance, but when you get up close and personal most aircraft wings are ugly, bumpy things (as you'll see below). Modern composite wings are a notable exception to this general rule, but there are a few other exceptions in the history of aircraft design.

The material is, for the most part, not relevant: We usually paint aircraft, so the smoothness of the underlying material contributes less to the surface than the paint preparation, clear coat, and wax.

What does matter are the construction techniques used. A few examples (in rough order of decreasing smoothness):

A modern composite wing can have an almost completely smooth surface (with no rivets or seams in the airflow) - for example a 787 wing, or this SR-20 wing:

Some aluminum designs use "bonded construction" (glue) with fewer disruptions of the wing surface. One example are the Grumman AA-1 and AA-5 series aircraft, which has a smooth wing except for the fuel caps and contoured seam lines:

Conventional aluminum wings can be assembled with flush rivets, which once primed and painted give a very smooth surface with only slight irregularities around each rivet:

(Please ignore the blue protective film, and open rivet holes. This is from an RV-14 under construction & was the best photo I could find.)
Fabric wings - one of the oldest wing coverings - are actually pretty smooth. They have "rib stitching" to attach them to the substructure, and are stretched taught over the frame (using heat & dope to shrink the fabric), but the overall result is a very smooth surface between the ribs, with some irregularity over them from the stitches:

Typical aluminum aircraft wing is attached with typical rivets - the head of which protrudes into the airflow slightly. You can see some rivet (and screw) shadows in this image:

Note that I've only considered the TOP surface of the wing (where airflow and smoothness is most critical). The underside of a wing usually has many other things sticking out into the airflow (fuel tank vents, access/inspection panels, hinges & tracks for control surfaces, etc.) which are a much greater disturbance to the airflow than whatever fasteners are attaching the skin to the rest of the structure of the aircraft.


Are there any regulations on who can sit next to emergency exits?

EU No 965/2012 provides some direction.

  CAT.OP.MPA.165 Passenger seating

  The operator shall establish procedures to ensure that passengers are seated where, in the event that an emergency evacuation is required, they are able to assist and not hinder evacuation of the aircraft.

Further clarification can be found from Acceptable Means of Compliance
(AMC) and Guidance Material (GM) to Part-CAT.

  AMC2 CAT.OP.MPA.165 Passenger seating

  ACCESS TO EMERGENCY EXITS

  The following categories of passengers are among those who should not be allocated to, or directed to, seats that permit direct access to emergency exits:

  (a) passengers suffering from obvious physical or mental disability to the extent that they would have difficulty in moving quickly if asked to do so;

  (b) passengers who are either substantially blind or substantially deaf to the extent that they might not readily assimilate printed or verbal instructions given;

  (c) passengers who because of age or sickness are so frail that they have difficulty in moving quickly;

  (d) passengers who are so obese that they would have difficulty in moving quickly or reaching and passing through the adjacent emergency exit;

  (e) children (whether accompanied or not) and infants;

  (f) deportees, inadmissible passengers or persons in custody; and

  (g) passengers with animals.

Whether or not a person can sit in the emergency exit row may also depend on if the specific seat is designated as an emergency exit. For example, on narrow body aircraft, generally all seats in the emergency exit row are considered emergency exit seats and only persons who "able to assist" can sit in those locations. However, on some wide body aircraft, only seats on the window sides are considered emergency exit seats. On an aircraft with a 2-3-2 configuration, the 3 seats in the middle are not considered exit row seats and therefore do not have any further safety requirements.


Is there a tool or site where I can see wind vectors overlaid on a prognostic chart?

Most pilots here in the states get their weather data from NOAA (The national weather service) you can find all of their charts on their site here.

Localized aviation weather is usually reported out of airports and can be found via their METAR's.

For visualization apps like Foreflight and Garmin Pilot allow certain overlaying of data onto a map (these are however paid services).


Could a helicopter perform a forward inversion (front flip)?

Yes.  This video at 0:50 shows a heli climbing into a loop, labeled at the top as 1.4 G and 25 knots, so it's still in forward flight when it reaches inverted flight.  The view from inside the cabin at 0:58 confirms pitching without rolling.
(At 1:26 the heli does what's labeled as a front flip at low G's, but that includes a lot of roll too.)
The pilot is Aaron Fitzgerald, in a Red Bull helicopter
with registration N154EH barely visible at 1:44, identifying it as a
1985 MBB BO105 CBS4, classified "experimental."
Wired magazine describes the crucial "hingeless" rotor head:

The rotor head is milled from a solid block of titanium rather than multiple components, skipping the hinges that typically allow the blades to bounce up and down to absorb aerodynamic forces. Instead, the blades are designed to be more flexible. ... The lack of up and down blade movement at the rotor head limits the “play” in the control stick, giving the pilot more granular control of the helicopter.

The video was published 2019 May 24-25.  It is also available without ads here.
I could not determine the exact date of the flight, but Wired also said it was

a practice session for this Memorial Day weekend’s Bethpage Air Show

so that at least confirms it as shortly before 2019 May 27.


What are the correct procedures for military aircraft interception over international waters?

The F-14 and its AIM-54 Phoenix missile was originally built for a particularly unfriendly intercept of Russian bombers from 100nm away in war time.

In peacetime, the TU-95 Bear bombers still needed to be intercepted.  That practice, at least in the north Atlantic, was usually for one of a pair of F-14s to fly directly toward the intercept point and well above it, while the other was several miles in trail and on the side that would be to the rear of the bomber(s) after intercept.  The first would overfly and make a descending turn to end up about a mile in trail, holding position there while the second did the same thing.  This ensured that (depending on ROE) weapons could always be directed at the bomber by one or the other F-14's throughout the approach.

Sometimes the F-14s were tasked with (really, permitted to) close with the Bear to "gather intelligence".  This resulted in lots of great pictures. You'll note that usually the F-14s in those didn't carry Sparrow or Phoenix missiles so they'd constitute less of a threat while closing (there were exceptions, though).  The Bear is about the size of a B-52, and depending on the day's plan you could come within a couple (Bear) wingspans of one. This in theory was risky (they had a rear gunner who's arc of fire you were to avoid) and took it out of your missile envelope, but you did have a gun...

As the Bear got closer to the carrier, more F-14s would arrive and things would get a little spread out for deconfliction.

But everything was smooth, slow, and initially done from a significant distance. Nothing at all like the Top Gun intercept, which would have permanently grounded all four crew members.


How much lift does the wing attach fitting actually carry?

The answer depends on the elastic deformation of wing and strut. Extreme example: Make the strut a rubber band and all lift needs to be carried by the wing and its fittings. Other extreme: Make the wing spar (or attachment points - this works either way) from rubber - now the strut needs to take all the loads.

In real life, stiffness attracts tension and compression, and in order to know the load distribution between wing spar and strut you need to look at them with a slight deformation from loading. How much resistance does each show (in isolation) against that deformation? This will tell you in what ratio the forces will split between wing and strut. Make sure to use the stiffness of the real structure - the material property called Young's modulus is not what I mean here.

If you want to be safe, you need to consider any single point failure and still have a flyable airplane. Normally, you design your structure with a safety factor (usually 1.5, but higher for fittings). Now assume that in turn each of the structural members is missing and calculate the loads on the remaining structure with a safety factor of 1.0. Dimension each part at least for those loads and you should be pretty sure that the intact structure will work out fine.


What is the 'fuel cost' of a pneumatic braking system vs. a hydraulic one, in terms of weight?

There is an existing triple redundant hydraulic system in those planes required used for the control surfaces. Those are not something you want controlled by pneumatics.

This means the weight of the compressor, buffer tank etc. is already there and using it for brakes means you only need to pull a line from a supply/return line (which would also be near the gear to actuate it anyway) and adding a servo valve.


How to compute thrust to weight ratio of a Cessna 172?

A good estimate for a personal aircraft thrust requirement would be more like 25% of aircraft weight, and remember, the "ton" of Cessna includes fuel and pilot too!

So: 1 ton x 2000lb/ton x 1kg/2.2 lb = 909 kg Cessna

213 kg thrust/909 kg weight = 23.3 % thrust to weight ratio.

But a lot depends what your plane design is.  You can test thrust requirement for level flight by gliding, then multiplying weight x altitude lost/distance flown = thrust.

So it helps a lot to have a good, strong wing too, and more thrust will be needed to climb.  15 kg may not be enough for your plane, but as long as you are on internet, you may wish to study "ultralight aircraft" to get some better information.


Why does a turbine engine compressor ratio affect stagnation pressure?

By stagnation pressure I assume you mean total pressure. Stagnation is not a term commonly used in gas turbine engine performance, it’s more common with aerodynamics. The compressor increases the total pressure because the rotating blades are doing mechanical work on the fluid.

A couple of other comments, to explain in more detail;

First, the flow is not isentropic in a compressor. It only would be if a compressor was 100% efficient. The efficiency is actually calculated by the degree to which it is not isentropic. The efficiency is given by the isentropic temperature rise that would occur for the given total pressure rise, divided by the actual total temperature rise. An efficient compressor obtains the same pressure rise, for a smaller temperature rise. While you might think a higher exit temperature would be good, because it would mean we could burn less fuel, a greater temperature rise across the compressor would require more shaft power to compressor the air, which is taken from the turbine and means the turbine exit gas is now cooler and a lower pressure and now cannot produce the same thrust.

Secondly, the stagnation pressure is not constant (even if it was 100% isentropic). This maybe the case in a fluid flow where no energy exchange is occurring, but in a compressor, the rotating blades are doing work on the fluid. This increases its total pressure. The area at the entrance and exit determine its velocity (along with its density). Different areas, changes in density, and total pressure mean the static pressure isn’t the same at the entrance and exit, either.


What data is displayed on civilian ATC radar screens?

There are a few different ATC Systems and Radar Screens being used throughout the world, so there will be no set standard which applies globally, as vendors and setup differ.

The ATC screen can be adjusted to show what information the controller needs, and some items are universal to all positions being served (Callsign, Speed, Altitude, Assigned Altitude), some items are not required on each position to be displayed on the radar tag (Squawk, Routing, Aircraft Type, Wake Turbulence Category).

Some examples:

Source: www.andreas-milde.de

Source: www.euroscope.hu / Air Traffic Simulation Client

Source: fluglotse.wordpress.com


The top image is a Bellanca Skyrocket.

The second image looks like the Fairchild FC-1, one was built as a prototype, followed by the FC-2 which was powered by a radial engine.

Not sure about the last, found a few similar but nothing exact.


What is the indicated device under the tail of this B-29?

Its a "tail bumper":

Source: Fiddlersgreen.net
Because the B-29 is so long, it helps prevent tail scrapes when taking off/landing.
Here is a close-up picture of the one on "FiFi":

Source: Airport-data.com


What benefits does Automatic Dependent Surveillance bring to continental ATC over Mode S?

ADS-B is more accurate.  SSR calculates the distance to a target based on when it receives a reply from the transponder, which is inherently imprecise, and calculates the azimuth by the sweep, which is also inherently imprecise.  A blip on a radar scope isn't exactly where the plane is but rather the center of an area where the plane is most likely to be.  ADS-B means ATC knows exactly where the plane is, which means they can (eventually) use tighter spacing if needed.

ADS-B is more reliable.  If two aircraft are near each other, their transponder replies may overlap, making both unreadable--and at the time it is most critical for ATC to be able to see both aircraft for separation.  ADS-B messages are transmitted randomly, which does result in occasional errors but means that two aircraft near each other aren't any more likely to step on each other than two far away, which is a substantial reduction in risk.

ADS-B can improve TCAS by not requiring air-to-air interrogations, reducing the total number of mod eS messages being broadcast and therefore the odds of aircraft stepping on each other.

ADS-B updates faster.  SSR relies on a radar slowly sweeping around, which means targets are only updated every 5-10 seconds, and this magnifies the effect of message errors.  This is "solved" in busy terminal areas by having several overlapping SSRs, but that also increases the error rate so it's of limited use.  ADS-B transmits position randomly every second, and even if some overlap, the readable update rate is still far higher than SSR.

ADS-B is cheaper.  You can put simple ADS-B receivers in many places where expensive SSR wouldn't be economically justified, giving ATC much improved coverage, particularly close to the ground and in mountainous areas.  You can also reduce SSR overlap, even if SSR doesn't go away entirely, which also saves money.

ADS-B provides improved situational awareness to pilots.  SSR doesn't provide any traffic data to pilots, and even TCAS isn't all that accurate (which means lots of false alarms) despite being extremely expensive.  ADS-B cheaply shows pilots exactly where the other traffic around them is--even non-participating traffic in an area with TIS-B.

Future ADS-B enhancements will also show aircraft intent.  SSR (and current ADS-B, to be fair) only show a plane's current position, often with a line projecting where it will be in N seconds/minutes if it continues along the same track since the last position.  ADS-B allows an aircraft to indicate what it will do in the (near) future, which is very useful when you have two aircraft near each other and one or both are turning and thus the straight-line projections aren't accurate.

The inaccurate flight paths you see on FR24 et al are due to aircraft not having ADS-B; the jagged tracks are generally from mode S-only aircraft, and the receivers have software that uses multilateration (MLAT) to cooperatively estimate where non-ADSB messages came from.  The FAA has experimented with this tech themselves in mountainous areas, and it's better than having nothing at all, but it's still far less accurate than SSR, much less ADS-B.


What is in the A320 Smoke and Fume checklist?

I'm resuming this old question because no answer was given.
It depends on where the smoke is detected (if automatically detected). The following abnormal procedures exist:

SMOKE FWD(AFT) CARGO SMOKE
SMOKE LAVATORY SMOKE
AVIONICS SMOKE
SMOKE/FUMES/AVNCS SMOKE + REMOVAL OF SMOKE/FUMES

The checklists 1, 2, 3 have the corresponding ECAM message automatically triggered when smoke is detected, while the checklist 4 is a long checklist which guides the pilot in identifying the source of the smoke and taking the necessary actions (and has no corresponding ECAM message).
Checklist 1 instructs the pilots to close the air isolation valve and discharge the agent(s).
Checklist 2 instructs the pilots to punch the guy smoking in the toilette contact the cabin crew.
Checklist 3 instructs the pilots to perform the relevant part of Checklist 4.


Note: Since this answer was first written, updated statistics have been published. The original answer was written against 2015 figures, with the update from 2017 figures.

There is no one simple measure of "busiest" when it comes to airports, there are usually (at least) three.

Busiest by passenger traffic - defined as total passengers emplaned and deplaned, with transit passengers counted once
Busiest by cargo traffic - loaded and unloaded freight and mail measured in metric tonnes
Busiest by traffic movements - total number of landings and takeoffs of all aircraft

The most recent statistics produced by Airports Council International are from 2017.

By passenger traffic the top 3 are

2015

Hartsfield–Jackson Atlanta International Airport,  USA
Beijing Capital International Airport,  China
Dubai International Airport,  UAE

2017

Hartsfield–Jackson Atlanta International Airport,  USA
Beijing Capital International Airport,  China
Dubai International Airport,  UAE

By cargo traffic

2015

Hong Kong International Airport, Hong Kong
Memphis International Airport, USA
Shanghai Pudong International Airport, China

2017

Hong Kong International Airport, Hong Kong
Memphis International Airport, USA
Shanghai Pudong International Airport, China

By traffic movements

2015

Hartsfield-Jackson Atlanta International Airport, USA
O'Hare International Airport, USA
Dallas/Fort Worth International Airport, USA

2017

Hartsfield-Jackson Atlanta International Airport, USA
O'Hare International Airport, USA
Los Angeles International Airport, USA

(Aside: Wow, those Americans like their traffic movements - 8 of the top 10 are USA! | 2017 update: 7/10)

There are a few non-standard claims too. They are interesting, if not winners.

Memphis International is the Home of FedEx, and as such was the highest freight airport for a number of years.
Gatwick Airport is the busiest single-runway airport (There are actually two runways, but only one is ever in use)
Wittman Airport hosts an aviation event which temporarily raises it to one of  the busiest airport in the world for that short period.
The airports of London (Heathrow, Gatwick, City, Luton, Stanstead & Southend) host the most passengers annually for a single city's airports combined.

(Don't get me started on Southend being a "London" airport - it's at least 20 miles from what could sensibly be called London)

References:

ACI: busiest airports in 2015
ACI: busiest airports in 2017
Wikipedia: Busiest airports


What data did the earliest HUDs display (for fighter jets)?

Reflector Sight:

The Me 262 Schwalbe, introduced in 1944 as the world's first operational jet fighter aircraft, did not have a full-blown HUD. Instead, like many fighters of WWII, it had a reflector sight which used lenses and reflecting glass to display a reticle. This sort of thing [all of the bright yellow lines you see in the image are fixed together. Although you only really needed a dot and a circle (like the Spitfire), some pilots liked the extra lines to help line up targets that were not dead-ahead. They were favored by pilots over iron-sights because the pilot was not required to position his head in order to see where the guns would fire.

Simple HUD

The MiG-21, introduced in 1959, used a combination of reflector sight and HUD. Though it didn't display the altitude, speed, heading, or attitude in a way that modern fighter pilots may take for granted, it had some ability to track targets with radar and to display predicted target positions for gun or missile use. Here is a guide on how to aim your guns using its sight. Also, explanations of the displays. The following image was posted on a forum thread related to the MiG-23, which came after the MiG-21, but this image looks much like those from the MiG-21 manual. A different image from another author shows you how simple the display could get. Finally, an F-16 in the sights of a MiG-21. You can tell this is a MiG because of the distinctive pitot tube.

Full HUD

The F-14 first flew in 1970. Its HUD was equipped with an artificial horizon, altitude, speed, heading, gun data, missile data, and much more. This is from the F/A-18, which first flew almost a decade later.


What is (are) the accidental cause(s) most feared by the flight crew?

What crews should be most concerned with is indeed crew error.  In the 1930's and 1940's, more accidents were caused by mechanical failures -- things failed that made the airplane unrecoverable.  Several decades ago, crew errors became the larger source of accidents, where a flyable aircraft (albeit with perhaps some issue, but flyable nevertheless) crashed because the crew did something that made the situation worse.  The hardware these days is pretty darned reliable, and if "you" do what you're supposed to do, chances are really excellent that you can get it on the ground safely.

That said, pilot psychology plays a major role in answering the question, since pilots strongly prefer to be "in control."  Or, less formally, we all tend to be control freaks.  (Not necessarily in every area of our lives, but certainly in the cockpit, we tend to have "take charge" personalities.  If something isn't right, we want to make it right, and a laissez faire "eh, whatever" attitude doesn't tend to be found among pilots at work.)

So the things that most concern us at a more visceral level, I'll suggest, tend to be the things that we can NOT control.  If an engine catches fire, I'm confident I can put it out with the procedures and tools that I have, and I can get the aircraft back on the ground because I'm trained to do that even with one less engine than usual.  But if there is a raging fire someplace that I can't control (electrical wires -- SwissAir Flight 111 or cargo hold -- ValueJet Flight 592), then that bothers me.  Similarly, Terry's scenario of cargo loading done wrong -- outside my control, and the pilots have to trust that somebody else did their job correctly.  And by the nature of that being entirely outside my control, that tends to be more of a troubling scenario than any of the typical list of things that I can control and have been trained for: engine fire, depressurization, electrical issues, etc.


Would a triplane be way more efficient if the wings intersected at the tips to create one wing tip vortex instead of 3?

Well, those nasty wing tip vortices really can't be helped if you are creating lift.  Amazing that airliner designers in this century are still considering biplane vs strutted mono plane vs cantilever mono plane concepts in their proposals.

Bringing 3 wing tips together will create all kinds of air flow issues (remember to model at all possible AOAs), reducing efficiency.

The most efficient way to create lift remains a high aspect mono wing.  I would look to designers actually reducing sweep a little (around 15 degrees for subsonic) and try for as high an aspect wing as possible, just like sailplanes.

However, wing span constraints and support benefits for very large aircraft may yet see the return of the biplane, with very thin, high AR wings.  These could be swept a bit more at the tips, and/or endcapped or wrapped.  Fuel and landing gear could go in a more drag efficient longer fuselage.  Note mounting them in "classic" Tiger Moth style retains the stability benefits of wing sweep, which may be lost in the newer "Prandtl wraparound" proposal.

It seems some designers just can't bring themselves to make a 21st century high AR Jenny.  It might be worth a try.


What is the temperature of the brakes after a typical landing?

Judging by this IATA document, and looking at figure 4 in section 4.2.1, the brake temperature easily exceeds 700°C during landing. They also show some brake temperature history timeline for an airplane without fan cooling.

(Figure 4)


Is the MD-11's third engine slightly nose up?

Yes, there is a slight tilt to the engine. Engines are heavy, so placing them on the tail shifts the center of mass towards the tail, which is not good for stability. To counter this, aircraft with rear engines often tilt the engines slightly, so the thrust they produce can offset their own weight, helping with stability. It's extremely slight though, as large angles can produce major pitch oscillations with power changes (something known as pitch coupling).


What happens when disengaging the electricity generators on a B747?

This is how it works on all aircraft with a Constant Speed Drive (CSD) Generator or an Integrated Drive Generator (IDG) - doesn't matter who the airframe maker is.

When you press the disconnect button (the red arrow), the disconnect circuit is completed and the solenoid pulls the pin out of the pinion shaft (the blue arrow) which then engages the worm gear on the drive shaft (the green arrow) and causes that gear to disengage from the drive mechanism. This causes the generator to stop turning.

To reset the mechanism you have to pull the "RESET HANDLE". This drive mechanism is attached to the gearbox on the engine which means that it can only be done on the ground with the engine off


What are those things under the Concorde’s cockpit windows?

Those are nose (forebody) strakes, from Wikipedia:

On both supersonic and subsonic types, smaller strakes are sometimes applied to the forward fuselage to control the fuselage flow at high angles of attack; for example the Concorde SST has small nose strakes "to get a better directional stability".

You can also find them on an MD-88 (shown below) and the DC-9-50, for example.

Unique to the [DC-9] Series 50 were aerodynamic strakes mounted below the cockpit to assist in lateral stability at low speeds and high angles of attack by stabilizing the vortex pattern (Source: Great Airliners Series).

A 1998 NASA paper on the forebody strakes notes:

Results of this initial, exploratory investigation indicate that the use of strakes on transport aircraft configurations can have a noticeable effect on directional stability. The effectiveness of even very small strakes means that such a concept could be applied with perhaps only minor impacts on drag and performance. The requirement for minimum levels of crossflow, however, could mean that direct application of this strake concept may not be of great benefit in development of a control effector.
Recognizing the ability to alter the fuselage flowfield with relatively small surfaces, whether fixed or actuated, at low angles of attack should hopefully spur greater research toward the understanding of the flowfield behaviors that impact lateral/directional characteristics of transport aircraft. The STRATA program will continue along this course in improving flowfield understanding and in the development of innovative control effectors for transport aircraft configurations.

This is what it is and what it does. As for the how, my basic understanding from the paper is the high angles of attack (such as those experienced by the Concorde in slow flight) increase the crossflow of the fuselage (air flow around the circular cross section of the fuselage). Adding those strakes controls/limits this crossflow and improves the stability by way of vortex generation.
Another mention from a 1976 NASA research:

The use of nose strakes (currently in use on the Concorde) has been investigated. The data indicate large increases in directional stability due to the strakes. For example, at the approach angle of attack of 8°, the strakes approximately double the value of $C_{n_{\beta}}$.

$C_{n_{\beta}}$ being the "static directional stability derivative".


What information on a specific flight can be retrieved?

flightradar24 takes as input mainly ADS-B data, as explained here. It seems to be enough to know scheduled departure and arrival time, departure and arrival airport, registration number and some extra pieces of data you may not need.

For technical failure, you may see the aviation herald website (I don't know how to access ACARS messages)


How much oxygen do commercial airliners carry?

The masks are connected to a chemical oxygen generator by a lanyard.  Pulling the mask pulls the lanyard, which pulls a pin from the generator and starts the reaction.  They typically last betweeen about 10 and 20 minutes, more than enough time to get down to 10,000 feet where additional oxygen is not required.

There is no need for a % of flight time since the crew will descend to a safe altitude then divert to the nearest suitable field.  Therefore, the only requirement is to last during the (emergency) descent.

You cannot "repressurise" since the cabin altitude will be the same as the external altitude.  The only thing to do is to increase the partial pressure of oxygen by descending.

It's worth mentioning that the flight crew each have their own, isolated supply from a bottle which lasts significantly longer.  This is so that they can continue to fly if there are fumes in the cockpit.  Cabin crew often have their own, smaller, portable bottles so that they can freely move about the cabin to assist the "self loading freight".

Many's a morning when I would arrive to work feeling, ahem, a little "under the weather" and nip into the cockpit for a couple of minutes on 100% oxygen.  Works wonders - and don't worry, they are topped up to full as part of the pre-flight service.


Can I get a medical after having had a seizure eight years ago?

This is something only an authorized AME can answer for you and it there is no harm in talking to one or two of them. You can find a little bit of info here and a copy of the seizure questionnaire here but that appears to be something an AME would fill out so its contents are not really useful on its own.

  At the time I was told that I could not obtain a medical again unless
  it was after 6 years being seizure free with 2 off medication. I have
  been off medication for 1 year and have had no problems.

If you were explicitly told this when the FAA pulled your medical then you still have another year to go at which time you can reapply for a medical.

In terms of regulations §67.401 Special issuance of medical certificates allows the FAA to issue medical certificates to airmen who can demonstrate "a Statement of Demonstrated Ability (SODA)" which is at the discretion of the flight surgeon. In short the regulation reads, if you can show that you are fit to fly and we agree we can issue a medical as we see fit.

What has changed quite a bit is the big overhaul that included the Basic Med requirements which do include some notes on special issuance cases that you may be able to operate under.

For you it also depends on what kind of operations you want to do since you are a CFI/Commercial. If you just want to get back in the air it may be a bit easier to do that.

From what I can tell it looks like you can get it back but you will need to talk to an AME.


In the modern aviation context, is the word "supercharger" generally assumed to mean a gear-driven system rather than an exhaust-driven system?

"Turbosupercharger" was General Electric's official term for their system, probably the first mass produced turbocharging system and was used on a range of US fighters and bombers (the system was very sensitive to back pressure in the turbine outlet which could promote stalling, and so they either had the turbine exposed like on the P-38, or if there was an exhaust duct it was very very short).

Anything that compresses the intake charge is a supercharger. Prior to the GE system, they were all mechanically driven and the mechanical drive naturally had horsepower losses associated with that type of drive.  GE added the word turbo to differentiate between the common gear driven or direct driven supercharger and their new and novel system that eliminated most of the energy losses from compressing air.

Move forward into the post war era and the adoption of systems to cars and light aircraft and people get annoyed having to say this pain in the butt 6 syllable word and start to cut out the "super" part, because it doesn't really detract from the meaning, and there you are with "turbocharger" for both cars and airplanes.

Meanwhile, "supercharger" stays as it always was and remains associated with mechanical systems, because the terms, although incomplete technically, don't contradict each other on common usage they continue.


Could the US Air Force ever replace the Thunderbird pilots with drones?

Tight formation flying can be done with stock aircraft and skilled pilots, but drones would need additional sensors and new code in their FCS. Also, you can fly aerobatics even with gliders, but only when a decent power-to-weight ratio is reached, aerobatics becomes a spectator sport. I think it is frivolous for the US Air Force to pay for the development and additional equipment to make drones fly aerobatic displays, but few Air Forces are known for an enlightened budget discipline. I expect, however, that this will be added first by a company producing drones, and for demonstration and marketing purposes, and then the taxpayer will fund this indirectly.

Formation flying was a needed skill for bomber pilots, back then when their bundled defensive weapons provided the best protection against fighter attacks, and aerobatic flying was and still is valuable for fighter pilots. In the days of missiles and UAVs, neither formation flying nor aerobatics are necessary skills anymore, so in a way aerobatic formations are a quaint relic from the last millennium.

To answer the "could" aspect of your question: No, not directly. This would need modifications to existing drones.

To answer the "ever" aspect: Once the services field UCAVs (unmanned combat drones) with a good power-to-weight ratio, having them fly aerobatic displays looks almost unavoidable, but I expect it will not be the Air Force, but the marketing department of a big contractor driving this.


Is there a difference in use of external lights for taxi in/out or takeoff/landing?

The use of beacon, strobe and navigation lights is already covered in this question: When to use beacon, anti-collision, strobe, logo, and navigation lights?

Taxi: Additionally to the navigation and beacon lights, the pilots always turn on the taxi lights during taxi. This is not only to see the taxiway in the dark, but also to signal other aircraft and ground vehicles that this aircraft is currently moving or about to start moving. The use of runway turn-off lights depends on the visibility. In the dark, they are typically turned on, but there is no need for them during daylight. The details may be airline specific as well. There is no difference between taxi out and in.
Takeoff and Landing: In general, all aircraft external lights should be turned on whenever an aircraft is on a runway. This is to increase visibility to other aircraft. There is one exception to this rule: the landing lights are typically only turned on when takeoff clearance has been received (meaning they are left off when receiving a line up and wait clearance). Again, there is no difference between the takeoff and landing roll. Some airlines use the taxi light switch as a reminder for being cleared to land during approach, but it will be on when landing.


Where are the fuel tanks located in an Antonov An-225?

The 225 is derived from the An-124, which has 10 integral fuel tanks in the wings. Comparing the specs, it looks like fuel capacity is the same as the An-124, so the center section of the wing (the only new part of the wing) doesn't contain fuel.
Based on that, I think the tanks are in sections 2-6 and 13-17. I'm assuming the outer wing sections 1 and 18 are not used as tanks. If those were used as tanks you'd have higher loads on the wing during roll maneuvers.


What are the FAA regulations on lighting for ultralight vehicles?

Ultralights are regulated under 14 CFR 103 and there are very few regulations of any kind that apply to them.

The only specific lighting requirement is in 103.11(b):

  §103.11   Daylight operations.

  (a) No person may operate an ultralight vehicle except between the
  hours of sunrise and sunset.

  (b) Notwithstanding paragraph (a) of this section, ultralight vehicles
  may be operated during the twilight periods 30 minutes before official
  sunrise and 30 minutes after official sunset or, in Alaska, during the
  period of civil twilight as defined in the Air Almanac, if:

  (1) The vehicle is equipped with an operating anticollision light
  visible for at least 3 statute miles; and

  (2) All operations are conducted in uncontrolled airspace.

This question and this one have some information about what an anticollision light actually is (a beacon and/or strobe), but since ultralights are so lightly regulated I'd be surprised if anyone cares much about the exact form of lighting. However, you could check with your local EAA chapter or ultralight club to see what people typically use.


Is it OK to move a light aircraft by pushing or pulling the propeller?

A couple of my CFIs have asked me to help them park the airplane (in absence of a tow bar) when I was pushing the airplane by putting one hand on the hub and the other on the propeller near the hub, and them (the CFIs) pushing the tail down and nose wheel elevated. But according to AOPA, it is not a good thing:

  ... never push or pull on the prop blades. Forget what anyone has told
  you about pulling near the hub or the strength of the propeller.
  Aluminum blades can bend, and it doesn’t take much to put the blades
  out of track with one another.

This PDF says the same thing:

  Avoid pulling the airplane around by the prop. Yes, this seems the
  perfect solution to a vexing problem of how to change the airplane’s
  position without having to walk around and get the tow bar, but it’s
  worthwhile to make the extra effort. Neither the engine nor the prop
  particularly benefit from the loads imposed by horsing the whole
  airplane around.


Why is the flight director at 9 degrees nose high when hitting TOGA?

curious to know if other jets set their pitch attitude to a different value.

747-100/200 aircraft didn't have a TOGA button to press, but at the two 747 carriers I flew for in the 1990s, the flight engineer filled out a data card for takeoff and later for landing that listed the pitch attitude target for takeoff and go-arounds, both for 3-engines and 4-engines. He/she looked up the values in tables in the QRH (Quick Reference Handbook), a copy of which each cockpit crewmember had. The card was placed against the instrument panel such that all three cockpit crew members could see it.

The target attitude depended not only upon the number of operating engines, but also engine type, aircraft weight, flap setting, and OAT. I just looked in my old QRH, and the lowest target I found was 9°, the highest was 19°. As I remember, typical actual operational values ran from 10° to 14°. Values higher than 14° were for very light weights and thus would be rarely used.

The 4-engine target pitch was generally 2° higher than the 3-engine pitch except that at very low weights, the difference was 3°.

Adherence to the target attitude was up to the flying pilot as he/she would be hand flying the airplane without flight director guidance.


What's the difference between hover power and maximum continuous power?

As the name implies, hover power is the amount of power required to hover.  If you add people/cargo to the aircraft the hover power increases.  Secondarily, it depends on air density as the rotor is more efficient in denser air - less power is required to lift the same weight.
Maximum continuous power (MCP) is the maximum power the engine/drive system should be exposed to for long periods of time.  This power level may be exceeded for shorter time periods.  For example, there may be 30 second or 2 minute power limits that are substantially higher than MCP (120%+).
I am not sure about takeoff clearances, but as you may already know power decreases substantially in forward flight and hence a helicopter that needs 1.1*MCP to lift off could still cruise around well below MCP.  Also, fuel burned in flight reduces weight and power so that less power is typically needed in the final hover/landing.  This can be upwards of a 10% reduction in weight.


How does exceeding the critical Mach number of an aircraft affect its operation?

At the critical mach number, some part of the aircraft (usually the wing) will have air flowing over it at a speed in excess of mach 1.

If the aircraft is not meant to fly at transonic or supersonic speeds, shock waves will flow over the wing. This can either cause the wing to stall, the control surfaces to become unresponsive, or the plane to go into the mach tuck, which is very dangerous.

The mach tuck is a phenomenon first observed with the P-38 Lightnings and Spitfires in World War II. These planes were so clean that when dive bombing it was possible to exceed their critical mach number. When this happened the center of lift would move back on the wing. This would cause the plane to 'tuck'; the elevators stop functioning, and the plane's dive becomes steeper and steeper until the aircraft is actually partially inverted. Recovery can be attempted by lowering the gear, extending the dive brakes, and lowering the flaps.

In later versions of the P-38 a small 'speed bump' flap was added for diving which caused a more even pressure distribution on the wing, and decreased the chance of entering a mach tuck.


What happens when an airplane stalls and why do pilots practice it?

Stall was an unfortunate choice of words for an engine that suddenly quits since the aerodynamic stall in aviation means something very different and isn't related to the aircraft engine at all1.

To a non-pilot, an aerodynamic stall can best be described as the situation where there is not enough air flowing over the wings to create the amount of lift needed to hold up the airplane.

The main reason that student pilots practice stalls is to learn the telltale signs that occur just before it happens and to make the recovery procedure automatic.  If pilots can recognize an impending stall, they can take corrective action to either avoid the stall altogether or to recover as quickly as possible.

Outside of training, inadvertent stalls typically only occur shortly before landing and after takeoff, when the pilot gets distracted while already at a slow speed.  In both of these situations the airplane is very close to the ground, immediately requiring the correct action from the pilot in order to avoid a crash.  This needs to be instinctive and corrected using muscle memory so that it is accomplished as rapidly as possible.

The next logical question is usually:  How does a pilot fix an airplane that has stalled?

Fortunately, airplanes are designed so that even during a stall the tail is still effective2 and the pilot is able to use it to force the nose down.  This makes the airplane go faster, since it is pointed down towards the ground, and gets more air moving over the wing which allows it to create enough lift for the airplane to start flying again.  During practice it is usually pretty uneventful, but when it happens at a low altitude there may not be enough time to regain flying speed before the airplane crashes.

For more information, AOPA has a great Safety Publication targeting flight instructors called Why we teach slow flight and stalls which is available on their website.

1 However, the sail on a sailboat can also "stall" when there isn't enough wind and since they have been around since 3,000 BC I guess that technically this usage of the word applies to both situations.

2 There are some stalls in particular airplane designs known as deep stalls that can be unrecoverable.  I don't think that this is important when describing it to a layperson though.


A glider and a paper airplane operate on the same principle: Exchanging whatever potential energy (altitude) they have for the kinetic energy (airspeed) required to keep air moving over the wings so they produce lift, giving a stable, controlled descent (glide).
In both cases the airfoil will not stall unless it exceeds its critical angle of attack which is independent of the airspeed. You can continue to fly (with the wing not stalled and producing lift) as long as you still have altitude to trade for that airspeed, and if you do it right you will eventually run out of both altitude and airspeed fairly close to the ground, where you can have a soft landing at a speed where the aircraft is not damaged. In the case of a manned glider hopefully this happens on a runway where you can get another tow plane to take you up again.

Both aircraft can extend their glide time by finding other sources of  lift - thermals, ridge lift, etc. - to carry the vehicle to a higher altitude, providing more potential energy.  Gliders are better at this for one major reason: They have a pilot who can keep the aircraft in an area of rising air longer to gain the most altitude possible.

A paper aircraft can similarly be made to fly for a longer period of time if given an adequate source of lift (equal to or exceeding its minimum sink rate). There's a rather famous video of the "infinity paper plane" which is a paper airplane circling over an electric stovetop, but I'll spoil it for you and tell you that one is a hoax (the general consensus is the plane was on a string).
This one, however, can be replicated fairly easily: The result is more similar to a helicopter in autorotation or an autogyro in a glide than a traditional fixed-wing glider, but it's a good demonstration of the principles involved.


Where can I find an aircraft's year of certification (airworthiness certificate)?

The FAA has a listing of all of the Type Certificate Data Sheets for certified aircraft.

So the first thing you need to do is determine the manufacturer. According to Wikipedia, “The Bombardier CRJ100 and CRJ200 are a family of jet-propelled regional airliners, based upon the design of the Challenger CL-600 business jet.” So look up Bombardier on the FAA site, and then open up the models made by Bombardier.

There are lots of CL-600 variants that all use the TYPE CERTIFICATE DATA SHEET NO. A21EA. The TCDS lists the years for each variant. The CRJ200 PF is a marketing variant of one of these, so you’ll have to do some research to find out which marketing variants match the TCDS but this should get you started.


Is there a system of automated sharing of current (experienced) weather between aircraft in flight?

Aircraft to aircraft, there is not.
Ground or satellite to aircraft exists in the form of FIS-B, and other commercial providers.

However, aircraft to ground in an automated fashion exists.
It's called Aircraft Meteorological Data Relay (AMDAR).

[It's] a program initiated by the World Meteorological Organization. AMDAR is used to collect meteorological data worldwide by using commercial aircraft.
Data is collected by the aircraft navigation systems and the onboard standard temperature and static pressure probes. The data is then preprocessed before linking them down to the ground either via VHF communication (ACARS) or via the [Aircraft to Satellite Data Relay].—Wikipedia

So, if it becomes widespread, FIS-B, et al., would benefit from AMDAR if they share the data. Thus realizing the aircraft to aircraft weather relay, in a sense.


How are "expect" altitudes on STARs used?

My questions are:

  1) When you enter the STAR in the the FMS, will it pre-populate the expected altitude, and does this show up in the FMS exactly the same
  as a mandatory crossing altitude?

This depends on the model of FMS.  Some of them don't even have Vertical Navigation (VNAV), and it really depends on the exact model.  I will say that three of the most common FMS's that I have personally used (Universal, Collins, and Honeywell) all pre-populate the expected altitude and it shows up exactly the same as a mandatory altitude.

In any case, the FMS is advisory only.  Unless the pilot dials in the actual assigned altitude and selects a vertical mode on the autopilot, it isn't going to descend on its own.  So if ATC doesn't assign the crossing restriction, you may see your VNAV pointer come alive and watch as you fly through the vertical profile without capturing it and it would be perfectly normal.  If I am getting close to the point where I would like to descend to make a crossing restriction and haven't been given lower, I will sometimes ask the controller:  "Do you need me to make the crossing restriction at RUGBB today?".  This gives me an idea of what's to come or prompts them to give me the descent clearance.

  2) Are expected altitudes treated as suggestions by pilots or controllers? For example, in the above chart, if you were at JHAWK
  15,000ft landing south, and Kansas City Center or Approach told you to
  "descend at your discretion, maintain 8000", would you (or the FMS)
  make any attempt to cross RUGBB at 12,000 even though it's not
  required?

An "expect" altitude is just that.  It is an altitude to expect, but it is not always actually assigned.  If it isn't, then you don't have to make it and since your example is at pilots discretion, you could descend at whatever rate you want.  You could cross RUGBB higher or lower than 12,000 ft and nobody would care.

In actual practice, they usually only do this in a few situations:

If they have to hold you up higher due to traffic and you can no longer make the crossing restriction, they will just give you a "descend and maintain" altitude, sometimes with a "good rate" tacked on.
It's a particularly slow time (late at night, etc.) and there isn't much other traffic to worry about.
There is an aircraft at, say 13,000 ft. so they tell you to descend and maintain 14,000 ft with the intention of giving you the crossing restriction once you pass the conflicting traffic.

In this last case, I would get down to 13,000 ft. in time to make the crossing restriction if they gave it to me, but it wouldn't be required.

  3) How common is it for ATC to actually issue a "cross [fix] at [altitude]" where the fix and altitude are as expected on the chart?
  And, if it is common, why wouldn't it simply be mandatory?

Again, this depends on the procedure but it is quite common.  That's why they put them there so that you can plan on what is typically done.  There may be operational reasons (like two different procedures that intersect) which prevent them from issuing it every time, so they can't just make it mandatory.

  4) Are expected altitudes part of lost communications procedures?

Surprisingly, no.  Not unless the controller has specifically cleared you to expect or cross it or "descend via" a procedure.

  5) Am I missing anything with regards to the purpose of expected altitudes?

Not on this one!  In some cases, there is a speed restriction which is listed on a separate line from an expect altitude. In these instances, the speed is required whether or not the speed or altitude was verbally assigned, just by being cleared via the arrival. For example, on the SFO HADLY2 arrival, you are required cross EUGEN at 250 knots, whereas 11,000ft is only required if assigned by ATC.


Where can I find current downloadable tower, ground and approach frequencies for USA airports?

I have found something that will work. It is not pretty and I swear I can still smell the punch cards that produced the text files, but here it is:

https://www.faa.gov/air_traffic/flight_info/aeronav/aero_data/NASR_Subscription

It is free, it appears to be updated by the FAA, (I verified it has the current frequency for my local VOR that I know changed 2 months ago) and it is searchable.

Download the current zip file, use the .txt data layout files to determine where in the fixed length record of whatever file your desired data resides in is located.  I did a quick import into Excel and am able to strip the information that I need out based on position in the field.

Not the pretty spreadsheet I was hoping for, but ...

Thanks for the suggestions, everyone. If anyone knows any standard software for the NASR subscription (or what the !@*# NASR stands for), I'd be interested.


Can having too small of a roll or yaw stiffness destabilize the dutch roll mode?

To estimate whether the dutch-roll mode goes unstable, we can assess the real-part of the dutch-roll eigenvalue: negative is stable and positive is unstable. From Etkins, Dynamics of Flight, one illustrative estimate (although not necessarily numerically accurate) is as follows:

$$n_{DR}\approx\frac{1}{2} \left[ \frac{Y_v}{m} + \frac{N_r}{I'_z} + \frac{I'_zL_v}{I'_xN_v}\left(\frac{N_p}{I'_z} - \frac{g}{u_0} \right) \right] $$

where $n_{DR}$ is the real-part of the eigenvalue, $Y_v$ is the dimensional side force sideslip derivative, $N_r$ is the dimensional yaw moment damping, $L_v$ is the dimensional negative roll stiffness (dimensionless form: $C_{l_{\beta}}$), $N_v$ is the dimensional yaw stiffness (dimensionless form: $C_{n_{\beta}}$), $N_p$ is the yaw-roll cross-coupling moment, $u_0$ is the trim airspeed, $g$ is gravitational acceleration, $m$ is aircraft mass, all the $I'$ are inertia terms about the respective axes. Note that all the inertia terms are about the principle axes for simplicity.

The first term ($Y_v$) is always negative, and so is the second term ($N_r$). Ignoring $N_p$ for now, positive roll stiffness requires $L_v$ to be negative, and positive yaw stiffness requires $Y_v$ to be positive; this means that the third term is net positive. Therefore, we can draw the following conclusions:

Dutch-roll damping worsens at lower airspeed
Roll stiffness worsens the dutch-roll damping
Yaw stiffness improves the dutch-roll damping

To answer your question: yes, it's entirely possible for dutch-roll to be unstable due to sufficiently low yaw stiffness.


Why did the L1011's direct lift control help make good landings?

John's fine answer is correct, but there is a bit more to it:
When increasing lift by pulling on the yoke, in most airplanes the elevator moves trailing edge up, decreasing lift initially. To look at the process in detail:

The yoke is pulled, the elevator moves trailing edge up
Downforce on the horizontal tail is increased without any lift change on the wing, so total lift is diminished. The sink rate increases slightly.
The lift imbalance adds a pitching moment, so the nose of the airplane rises.
Now the angle of attack on the wing increases with the pitch angle and lift increases. Only now will the desired reduction of the descent rate kick in.

This effect is especially pronounced in flying wings, but it also is noticeable in regular airplanes. Now compare that with partially deflected spoilers:

The yoke is pulled, the spoilers close.
Lift increases without a change in the elevator angle or the angle of attack. The desired reduction of the descent rate is immediate.

The effectiveness of spoilers is limited, so this technique will not allow you to fly aerobatic maneuvers, but for landing it is perfect. Drag is increased, so the engines will have to produce a bit more thrust than with spoilers fully closed, giving you more immediate engine response, too.


Can resistive fuel senders/transducers be repaired/reconditioned?

There are shops that do this and egid gave you a couple of hints on how to find one, but your local mechanic can probably recondition your fuel sender about as well as any of the specialty shops, as long as they're not squeamish about opening up the unit (and as long as the unit can be opened up - I'm not sure about the TB20 senders).

What's basically involved is cleaning the resistor element and wiper contacts, making sure everything is making good contact through its full range of travel, and verifying that the sender is still within a reasonable calibration range when you're done with the cleaning (you can use your other, working sender to determine what's "reasonable", or verify using your fuel gauge).

The Comanche folks have a nice article on reconditioning a (really beat up) fuel sender, and technologically they're similar to automotive fuel senders, so this article about reconditioning Corvette fuel senders may also be useful to get an idea of what you're in for.


AVTUR stands for AViation TURbine Fuel and is equivalent to JP-1, at least in the UK and in as much as JP-1 no longer exists.  I believe that the US military equivalent is JP8 which is Jet-A1 with additional additives, which differs from commercial Jet-A only by a lower freezing point.

Here is the relevant NATO Def Stan (Defense Standard) for Avtur with is the same defstan as for Jet-A1.

This link to an Exxon document gives a great deal of information for various aviation fuel oils.

[EDIT]

From here:

  JP-8 is the military equivalent of Jet A-1 with the addition of
  corrosion inhibitor and anti-icing additives; it meets the
  requirements of the U.S. Military Specification MIL-T-83188D. It is
  the dominant military jet fuel grade for NATO airforces. The UK also
  have a specification for this grade namely DEF STAN 91-87 AVTUR/FSII
  (formerly DERD 2453). NATO Code F-34.


Are requests for an emergency landing ever refused?

I can imagine a couple of reasons why ATC could tell the pilots to please land somewhere else even if they have an emergency

All runways are closed, e.g. they are repaving the runway surface or when the snow trucks haven't yet cleared a thick layer of snow or the instrument landing system is inop and the visual conditions are not good enough, runway flooded after hurricane,...
Another emergency in progress, e.g. passengers freely running around on the airport after an evacuation, not safe to land
Political reasons with hijacked plane (e.g. Lufthansa Flight 181 Landshut was refused to land even when they declared an emergency with low fuel) https://en.wikipedia.org/wiki/Lufthansa_Flight_181
Presidential no-fly zone when other airports are available close by.
Virus infected people on board to avoid contamination of those on the ground (zombie apocalypse)


Are GA airports typically accessible 24/7?

The general answer is that the airport manager is in charge of ground access (unless the TSA is involved; see below) and individual FBOs can open or not whenever they like. There are no standard federal rules for the same reason that there aren't any for when gas stations should open and close: they're private (or state-owned) businesses.

So before going somewhere new it's always good to call and ask about opening hours, access etc. If there are multiple FBOs at the field, you can call them all: one might be open 24 hours a day even if another one isn't.

One specific point about Salina is that the TSA may be limiting access. The AOPA airport directory says that KSLN is under security directive SD-8G, i.e. the TSA limits access to the apron. That means you might need an authorized escort - most likely someone from the FBO - to and from your aircraft. If the FBO shuts at night there may be no one there, but FBOs in general are usually good at making special arrangements if needed.

And although your question seems to be about ground access, I guess it's worth stating the obvious: airports are accessible 24x7 from the air. Nothing stops you landing at 3am, filling up at the self-service pumps and then taking off again. But watch out for local practices like voluntary noise abatement curfews, e.g. at KPDK:

  Pilots are encouraged not to fly between the hours of 11 p.m. and 6
  a.m. Due to FAA Regulations, PDK cannot implement a mandatory curfew
  at this time.

It's still legal to land or depart there during curfew hours, but you'll really annoy the airport management, FBOs, and local pilots who have to deal with the complaints from local residents.


In reference to airspace, what does the FAA mean by "within the lateral boundaries of"? Is this construed to also imply a vertical limit?

The FAA normally interprets the phrase "within the lateral boundaries of" (x airspace) to mean any airspace whose lat-lon coordinates fall within said boundaries, regardless of altitude, from the earth's surface all the way to outer space, or at least to the upper limits of the airspace which the FAA has any regulatory authority over.

Pilots would be wise to follow this common-sense understanding of the meaning of "within the lateral boundaries of".

However, the FAA is not a monolithic entity, nor is it immune to making the occasional blunder.  On a few occasions, some subset of the FAA has adopted a very different understanding of the meaning of "within the lateral boundaries of".

For example, in the text of a spectacularly misguided Final Rule published on page 51966 of the October 5, 1993 edition of the Federal Register, the FAA implied that the phrase "within the lateral boundaries of the surface areas of ... Class E airspace designated for an airport" would not encompass any Class E airspace higher than the floor of the 700' or 1200' AGL "transition area" that invariably overlies a Class-E-to-surface airspace.

To correct this imaginary problem, the FAA changed the wording of FAR 91.157 from the existing wording

  91.157 Special VFR weather minimums Except as provided in appendix D, section 3 of this part, the following special weather minimums and
  requirements apply to operations conducted to or from an airport in
  controlled airspace:  (a) Operations may be conducted only under an
  ATC clearance-- (1) Within the lateral boundaries of the surface areas
  of Class B, Class C, Class D, or Class E airspace designated for an
  airport; and ...

To the new wording

  91.157  Special VFR weather minimums ( a ) Except as provided in appendix D,
  section 3, of this part, special VFR operations may be conducted under
  the weather minimums and requirements of this section, instead of
  those contained in 91.155, below 10,000' feet MSL within the airspace
  contained by the upward extension of the lateral boundaries of the
  controlled airspace designated to the surface for an airport. (b)
  Special VFR operations may only be conducted--(1) With an ATC
  clearance...

However, the FAA failed to also change the similar wording of FARs 45.22(a)(3)(ii), 91.155(d), 91.303(c), 91.309(a)(4), 93.152, 101.33(a), 103.17, 107.41, 135.205(b), and 137.43(a), thus implying that none of these FARs should be understood to apply to any Class E airspace above 700' AGL in most cases, or above 1200' AGL in the remaining cases.

This blunder has never been officially corrected-- the text published in the October 5, 1993 edition of the Federal Register has never been officially retracted.


What are the reliability statistics for modern jet engines?

What is the actual numerical reliability statistics of the modern, large-aircraft, commercial turbofan engines available today?
e.g. How many running hours can we expect a failure after? Are there empirical or projected MTBF statistics?

Buried in this GE press release is the comment that the GE90 has 'only one engine IFSD  per one million engine flight-hours'.
This ICAO presentation has a lot more info, including these threshholds for ETOPS IFSD rates:

Propulsion system should achieve an in-flight shutdown (IFSD) rate of:

0.05 / 1000 engine hours for EDTO 120 min
0.02 / 1000 engine hours for EDTO 180 min
0.01 / 1000 engine hours for EDTO beyond 180 min
Rate computed based on world fleet data, on a 12-month rolling average

This strongly implies that the reliability targets are empirical, not based on theoretical numbers.

Is there a significant difference in the failure rate between engine models or manufacturers?

Page 56 of the presentation above has some data, but IMHO not enough to draw any conclusions.

How rapidly has engine reliability improved? Do we have a time trend of reliability numbers?

All I can say is it's definitely improved massively, but I'm not sure where to find the info.


Do fuel tank locations on the wing cause a potential for weight imbalance?

YES

If the port and starboard tanks drain at different rates in a gravity fed system (due to a blocked valve or a clog in a fuel line), then eventually a differential in remaining fuel will drive a lateral imbalance in the plane's weight.  Another (and better) way of saying this is that the center of gravity will no longer be aligned with the aircraft centerline.

I can't comment on how this situation might emerge in the P-26 specifically, as I could not find a detailed enough description of its fuel system.

It is worth noting that the same is true with fore/aft center of gravity drift in aircraft where the tanks are located entirely in the fuselage (or under it).  This often has a more dangerous effect if not properly managed (and as a result the Cg drifts too far aft).

It is also worth noting that lateral asymmetry can also be created by non-simultaneous release of stores (like the 200 lb of bombs that the P-26 carried).  However, in the case of the Peashooter, the bombs were carried very close to the centerline, so the asymmetry would be minimal (as compared to that on a P-51 for instance).


There are a few stages where ice prevention or mitigation is relevant. The FAA publishes a nice handbook on it here if you want more info. Very broadly speaking De-Icing activated when airframe ice is noticed. Anti-Ice is activated when a Pilot believes they may enter icing conditions. Ground based De-Ice is applied when icing conditions prevail in the area.

Before Takeoff

Most, if not all commercial airports offer de-ice facilities if geographically relevant. After the crash of Air Florida 90 the FAA took a bit of a harder stance on De-Ice and now stresses the need for mobile De-Ice units to allow planes to be De-Iced without leaving the taxi queue as well as permanent stations as they have always had. A lot of their suggestions are covered in this AC as well as this one. In this case both airline procedure and FAA regulations will dictate the need for De-Ice. Strictly speaking according to FAR 121.629 a dispatcher can hold an aircraft if they feel it is not correctly De-Iced. However by the same law a pilot can hold their own departure for the same reason.

En Route

Once in the air there are a few ways things happen, but generally its ultimately up to the pilot to activate the De-Ice system. On one hand the aircraft POH will more than likely have guidance on when to do this, however, airlines may implement further (and more strict) procedures. Some aircraft are equipped with systems that automatically activate in the presence of ice build up.

Once in route there are effectually two kinds of systems,

Anti Ice: prevents the build up of ice in the first place, heated leading edges etc. These are activated before entering icing conditions.
De-Ice systems: like boots these systems remove ice once its built up. In this case you need to actually enter the conditions and allow the ice to build up first.

Ice can form in a variety of conditions and can be dangerous or potentially fatal in some aircraft. The temperature depends on the cloud type but generally speaking low temperature and higher moisture content will create worse issues.

(source)

Pilots will be alerted to possible icing conditions via an AIRMET ZULU. These are often quite broad area AIRMET's. If a pilot believes they are potentially flying into icing conditions they should keep an eye on the airframe for structural icing build up. Many airplanes have icing lights to help at night with this. A pilot can activate the De-Ice system at any point if they feel it is needed.


Why is a reciprocating engine air intake a reverse bell shape?

It's simply a NACA duct inlet.  On a fully parallel to flow flush surface it has some (but not all) of the effectiveness of a protruding scoop, without the drag.  The curved sides of the ramp act like vortex generators, with the rotation of the vortices on each side pulling air down into the ramp.
On a very clean airplane like one of the RV series homebuilts, that kind of duct can have a measurable benefit.  On a plane like the one pictured, there is a theoretical benefit drag wise, but it would make little detectable difference in that sort of a light plane (with its unfaired nose gear) and is mostly for looks.
In fact since the surface isn't really parallel to the airflow but curves in, the opening is presented more or less directly into the airstream for ram effect and there really isn't a need to create vortices to pull air down the ramp.  A straight sided ramp would work just as well in that particular instance.  Looks cool though, which I suspect is the main reason it's being used there.


Why don't the magnetic compass and direction indicator spin the same direction?

I think I understand your question, and I know what you mean - it's something I have to sometimes think about when setting the DI.
However, I think your premise is slightly flawed. The issue isn't "compass vs DI", it's the difference between viewing a compass from the top down, vs head on.
If you look at a magnetic compass compass which can be used both ways (Such as this one you'll see that sideways on, it looks the same as the aircraft compass as in it increments right to left. But from the top, it's identical to any DI and increments clockwise - however, it reads "upside down" compared to a normal top-down map reading compass.
I'm not even sure if this would work, but I think what you're asking is for the DI to be upside down. This would go against most concepts that "up" is equal to forward.


What is the status of "Notes" in ICAO Annexes?

Yes. But there should not be a contradiction to the standard. Additional material usually serves to guide the user of the standard.


Is the altimeter setting corrected for temperature?

The reported altimeter setting, QNH, is 'somewhat' corrected for temperature, in that it corrects for temperature error at the aerodrome elevation. This is the main difference between the more-meteorologicaly-inclined QFF which does not contain this temperature correction.

You will still get altimeter errors because of the high/low temperature while being above (or below) the aerodrome  (about 40 ft for each 1000ft for each 10 degrees C), but the actual temperature error at aerodrome level will be 0.


On the new A320s when we do a brake check there is no need to call pressure 0 why?

I found an answer here: https://www.pprune.org/tech-log/456530-a320-brake-check.html

The complete fly by wire braking system apparently eliminates the check for residual pressure (check zero) of the older models, probably because the valve that determines which hydraulic pressure reaches the brakes is either no longer present or automatically tested anyway.

The new a320 also has a different PTU design which no longer barks...


How strong someone should be in order to fly without "power steering"?

You can't.  Most of these airplanes are flown with hydraulically powered control surfaces with no mechanical input possible from the cockpit flight controls.  The flight controls just operate servo control valves in the hydraulic actuators, like the bucket on a front end loader but a little fancier.  If it's FBW, the FBW system does the same thing at the actuators using torque motors operated by the FBW computers to drive the servo control valves.

There will be two, or three, hydraulic actuators driving each control surface.  The flight controls in the cockpit just control the extension/retraction of the actuators. Control feel in these airplane comes from spring devices in the control circuit to simulate "air loads".  There is no direct connection between the pilot and the dynamic forces acting on the control surface.  If you lose all of the hydraulic actuators, you lose the control surface.


What to do when moisture forms on the helicopter's canopy in a weather front?

That won't happen "flying through a front" where the temperature of the plexiglass is at at or warmer than the ambient air - you just get drops forming and streaming back.  What has happened to me though, is condensation when climbing into a warm humid inversion on a sunrise clear sky departure where the surface temperature was much cooler than in the inversion.  On my airplane which has a sliding bubble canopy, the outside of the canopy fogged up suddenly at about 200 ft agl as the cool plexiglass hit warmer humid air and it was like the canopy was covered in wax paper.  A bit alarming initially.  I just used the attitude indicator to stay right side up, helped by the opaque blue of the sky above, until it started to stream and clear up on its own after a minute or so.


How slow could the U-2 fly at 50,000 ft?

You can find the official speed envelope in this copy of the flight manual from '68 that was recently declassified, looks like at FL500 you are right around 105 Kts indicated (convert using figure 2). Also note on this chart it is set up for 1535 gallons of fuel at T.O. the plane had various load configurations (covered in the manual) that would more than likely have an impact on the number,

(figure 1)

If you want to do the correction to TAS you can use this chart also from the manual

(figure 2)

Interestingly the copy from '58 that was also declassified (and hosted on the CIA website) is missing most of these charts although it does not look like they were ever in there.

At higher altitudes the margin was much smaller right around its cruise speed of 373 kts as one of the interesting aspects of the U-2 is that due to its design it was always in and around the Coffin Corner at altitude. According to this former pilot of the U-2

  When the littler airplane got up to altitude, the margin between the
  climb speed and the critical Mach number and stall became very, very
  minor, and we were looking at plus or minus two-and-a-half knots at
  one particular point in the climb between the climb schedule and
  critical Mach and stall speed so that’s very very small. When we got
  the bigger airplanes, we got up to plus or minus seven-and-a-half
  knots of margin.

This question may also be of interested to you.

NOTE: The above answer is based on currently declassified information about older variants of the U-2. The plane is still in service and has seen more modern variants which include both aerodynamic and power plant changes to the original designs both factors which could effect the above performance data.


Why is the Inertial Reference System not used to determine true altitude?

IRS will drift over time. Decision altitude is 200ft for ILS CAT I approach.  0.5nm drift is not to much for navigation but it will be huge difference in altitude and you can hit obstacles if your altitude has drifted just couple of feet. Probably it could be used if backed by GPS as EGPWS does or non baro RNAV approaches do. But even GPS precision alone is not enough in this case and you need WAAS.
Radio altimeter can give much better precision.


How does the ground effect affects longitudinal stability?

It depends on general geometry of the aeroplane:

The vertical position of the main wing and the horizontal tail.
If the aeroplane even has a horizontal tail.
The sweep angle.
The angle of incidence in the landing flare.

When a wing enters ground effect, its lift coefficient rises: the wing creates more lift at a given speed and Angle of Attack. A wing is considered to be in ground effect if it is within about half wingspan distance to the ground. Since the main wing has a much larger span than the horizontal tail, it enters ground effect earlier, creating a nose up moment due to more lift on the main wing only.  Low wing aeroplanes have a more pronounced nose-up effect than high-wing aeroplanes do.

 Image source

An increased nose up angle brings the horizontal tail closer to the ground, which will enter ground effect as well at a certain point. Which will the counter the nose-up moment.

A wing with large sweep, at landing angle of incidence, will see the wing tip area enter ground effect earlier, creating a nose down moment.

Concorde enters ground effect with the wing trailing edge first, creating a nose-down moment. In flight this would be called Increased Stability, however in the landing a nose down moment may introduce nose wheel slam.


It's called the Ampaire Tailwind, and as this article explains, it only exists in scale models and renderings at the moment.


What constitute "known icing conditions" and when can you fly VFR while they exist?

The short answer is that it's up to you as PIC to make that determination; the FAA has no clear definition apart from what a "reasonable and prudent" pilot would do.

The FAA issued a legal interpretation on exactly this question in 2009, here's the closest thing to a definition that they give (my emphasis throughout):

  "Known icing conditions" involve instead circumstances where a
  reasonable pilot would expect a substantial likelihood of ice
  formation on the aircraft based upon all information available to that
  pilot. While "known icing conditions" are not defined by regulation,
  the term has been used in legal proceedings involving violations of
  FAA safety regulations that relate to in- flight icing. The National
  Transportation Safety Board (NTSB) has held on a number of occasions
  that known icing conditions exist when a pilot knows or reasonably
  should know about weather reports in which icing conditions are
  reported or forecast

They go on to say that the PIC is responsible for determining the likelihood of icing conditions:

  Any assessment of known icing conditions is necessarily fact-specific.
  Permutations on the type, combination, and strength of meteorological
  elements that signify or negate the presence of known icing conditions
  are too numerous to describe exhaustively in this letter. Whether a
  pilot has operated into known icing conditions contrary to any
  limitation will depend upon the total information available to the
  pilot, and his or her proper analysis of that information in
  evaluating the risk of encountering known icing conditions during a
  particular operation. The pilot should consider factors such as the
  route of flight, flight altitude, and time of flight when making such
  an evaluation

Note that even visible moisture and freezing temps aren't automatically considered to be known icing conditions:

  The FAA does not necessarily consider the mere presence of clouds
  (which may only contain ice crystals) or other forms of visible
  moisture at temperatures at or below freezing to be conducive to the
  formation of known ice or to constitute known icing conditions.

The specific regulations mentioned in the interpretation are 14 CFR 91.9 (compliance with the operating manual), 91.13 (no careless or reckless operation) and 91.103 (become familiar with all information relevant to the flight). Those regulations would be the basis for any hypothetical enforcement action:

  If the composite information indicates to a reasonable and prudent
  pilot that he or she will be operating the aircraft under conditions
  that will cause ice to adhere to the aircraft along the proposed route
  and altitude of flight, then known icing conditions likely exist. If
  the pilot operates the aircraft in known icing conditions contrary to
  the requirements of § 91.9(a), the FAA may take enforcement action.

So the bottom line is: you're PIC and it's your decision whether it's safe to fly or not because there are far too many variables for anyone else to decide. But personally I think it would be difficult for any pilot to say that it was "reasonable and prudent" to fly a non-FIKI aircraft in an area where forecasts, AIRMETs or PIREPS indicated icing.


Did turbofan engine explosions become more frequent in last years in commercial aviation?

May depend on the time period of interest and what you count as an incident, but in general over the time span of decades, turbo fan engines are significantly more reliable now than they were previously. You only have to count the engines to see this trend. Many years ago all jets had 4 engines, then 3, and now virtually all new planes have only 2. The reason of this is the increasing reliability of engines. Decades ago planes had 4 engines because the possibility of 2 engines failing during a single flight, while uncommon, was not unheard of. Now days, planes have only 2 engines because reliability of engines is very good. Failure of 2 engines during the same flight is very very rare (maybe not zero, but very rare)


Where do most fighter jets and combat aircraft mostly get shot? ex: body, wings, engine area etc

It all depends on the types of weapons employed, the aspect of the attacking and defending aircraft and the off-boresight angle between the aircraft in question.

Air to air and surface to air missiles employ proximity fused HE Blast / rod or pellet fragmentation warheads in them.  They are guided to close proximity with the target aircraft and explode like hand grenades, spraying the targets with shrapnel, damaging structure, engines, fuel and hydraulic lines, even the pilot.  Sites of damage depend on the angle of missile impact as well as the proximity of the target within the lethal blast radius of the warhead and thus how concentrated the spread of the shrapnel pattern is.

Air to air gunnery is much more akin to bird hunting with a shotgun and less like modern guided weapons.  The most effective air to air gun systems against fighters tend to be smaller caliber weapons with high rates of fire and high muzzle velocities resulting in flat ballistic trajectories with good range.  The ideal gun kill is maneuvering up on the target's six o'clock and pumping rounds into the aft fuselage and engines.  High angle off kills can also be accomplished by leading on your target, then firing a burst which the target then flies through and gets peppered with rounds, again similar to hunting flying water fowl.  In an off angle shot the burst will be widespread over the dorsal surfaces of the fuselage and wings.


Why are no recent small aircraft designed to be "characteristically incapable of spinning" as the Ercoupe was?

The coupling between the ailerons and rudder are designed such that they avoid uncoordinated turns as you described.  However, this occurred at the expense of control in other flight conditions.

In fact, there are situations where you need to deflect the rudder without roll input, you need to deflect the rudder more than the preset coupling, or in a manner that is opposite to the preset configuration.

For example, if you turn right, the system will add right rudder to keep the airplane coordinated. But if you want to do a forward slip, you may perform a left hand roll, but with rudder all the way to the right. The system would be incapable of performing this maneuver, meaning you can't fly in high winds with the system installed. This is fine if you live in an imaginary place where the winds are always favourable.

As a result, a common modification on the Ercoupe is to disconnect the coupling between the rudder and ailerons...

Edit: I also wanted to add that spins are recoverable, within reason, by a trained pilot. For some planes, you are simply forbidden to intentionally enter a spin as a remedy to its inability to recover from a spin!


Is the entire length of a B747 or A380 wing used as a fuel tank?

Fuel tanks take most of the space in aircraft wings, but not all. There are other things on wings too. They are ailerons, flaps, slats, air brakes. On most airliners, the engines are attached to the wings too, so their assembly takes up space.

On the two aircraft of your interest, here are the pictures:

A380 (its nickname is not jumbo, but superjumbo)

Image Source

747

Image Source


Why did this Cirrus deploy the parachute while ditching over Pacific Ocean?

Once your engine fails the airplane is the property of the insurance company, your only goal at that point should be to survive. Using a whole-airframe chute increases your chances of survival whether over land or sea.

The things that kill people in forced landings of any kind are high-g deceleration and post crash fire. A parachute decreases the chances of both as you have very low lateral speed and much less chance of fuel tank leaks. A parachute also will increase the chance the airplane will remain upright, so escaping the aircraft will be much easier - very important in a water landing!

The only reason for a "normal" ditching procedure is that you have no other choice, using a parachute if you have one will almost always be the right option. The only time I would consider otherwise is if I had enough altitude to glide to a safer emergency landing spot. If pulling the chute would mean landing in water or dangerous terrain but gliding would mean reaching land where a forced landing was reasonable I'd probably opt for gliding.


How many pilots are licensed in Hong Kong?

I reached out to the Hong Kong Civil Aviation Department and asked this question. To my surprise, I got an answer back in less than 12 hours.

As of December 31, 2014, they report:

219 private pilots
951 commercial pilots
4007 ATPL holders
20 MCPL holders

For a total of 5197 pilots licensed in Hong Kong.


OBI, RMI, HSI... What combination do GA aircraft w/o glass typically have?

"two-way radio communication and navigation equipment suitable for the route to be flown", that last requirement being just wonderfully ambiguous regarding what you as a pilot may want or need …

That statement isn't ambiguous at all. You can file and fly IFR with a transponder and a VHF comm radio if you can get controllers to issue you radar vectors for the route -- just be making a visual approach at your destination (or something like an ASR or PAR approach where you get your guidance from a controller).

Of course since your question was not "How do I piss off ATC?" that's neither here nor there - you're asking about typical instrument configurations in GA aircraft (for purposes of this answer I'm going to assume you mean the usual "Light GA / trainer" sort of aircraft - typical Pipers, Cessnas, Beechcraft, Mooneys, etc.)

It's hard to nail down "typical" because it's a rapidly moving target these days. When I started flight training two Nav/Com radios and an ADF was a pretty sweet IFR airplane, even if the ADF was a little sketchy. Now even a six-pack cockpit has a good chunk of glass in the panel in the form of a GPS (Garmin 430 or similar), and people are ripping out ADFs as the FAA decommissions them, but I poked around at some of the rental fleets near me  and it seems to shake out like this as of right now:

Most IFR aircraft have dual OBIs. If there's a GPS they tend to both have glideslope capability (either connected to two GPS Nav/Coms or one to the GPS and one to a traditional Nav/Com radio that has a glideslope receiver).

Older planes with dual Nav/Comm radios often have glideslope capability on the #1 Nav/Com & not the #2 radio, which is why you often see one OBI with a glideslope needle and one without.

Older IFR trainers tend to have ADFs still. Some are placarded as INOP and are basically heavy, drag-producing AM Radios (the Mets won).

Aircraft with a GPS rarely have an ADF, because the GPS can usually display the ADF indications using a "normal" OBI. One less thing for the pilot to have to remember how to operate.

I've never seen a light GA aircraft with an RMI.
They're probably out there but I doubt they're common. Slaving them to the magnetic compass requires equipment which is not cheap, and as ADFs are dying out there's not much benefit to installing one now.
None have HSIs, but I have seen a few planes around with them.
My sense here is it tends to be an owner-installed upgrade because the pilot wants it and they have the money to spend on it. Like you noted they're still pretty expensive, mainly because they're rather complicated bits of equipment combining a vacuum-powered DG, a bunch of sensors, and a VOR/LOC/GS presentation.

Every HSI installation I've seen takes the place of the Nav 1 OBI.
What gets put into the now-vacant hole varies from aircraft to aircraft. This Cessna has an ADF card there (thanks to CFC for the photo)

Very few have DME.
If you're flying on Victor airways you're pretty much always flying toward some VOR (so you have one needle that won't move), and you can easily get a cross-bearing from a VOR that would be roughly perpendicular to your route to find your current position on the chart.
The DME gives you this in Distance/Direction form without needing to tune a second VOR or draw on your chart, and it can do nice things like give you an approximate groundspeed, but that doesn't make it indispensable.

A reason many IFR trainers lack a DME seems to be because on the IFR checkride you can't be tested on equipment that's not installed: If you have no DME you can't be asked to fly a DME arc.
DME is another technology that's being made redundant by GPS: The GPS can give you distance and bearing to any arbitrary point, and that point can easily be a VOR. It can also compute groundspeed.

An ever-increasing number have large chunks of glass somewhere in the panel.
As GPS installations become more common it's increasingly rare to find a plane without a moving map display next to the six pack. The GPS provides the magic "Magenta Line" and also typically feeds an OBI (or HSI).
If the OBI or HSI fails the GPS can usually also display a digital OBI on its display.


Why is the fuselage on an airliner circular-shaped?

If you pressurize any hollow structure, it will try to assume a round shape. If you want to create a lightweight pressure vessel, again a sphere will be the most efficient result, because there the stresses in the skin will be equal at every point. Blow up a party balloon if you are in doubt.

A sphere is not the most efficient shape for aerodynamics, so fuselages are elongated spheres with a nice fairing at the end. If you make them cylindrical in the middle, you can build most bulkheads on the same jig and can interchange sections of the internal fairings. Plus, if you need a longer or shorter fuselage for the next version of the plane, you can easily add or remove sections - the parts will still fit after the modification.

Note that the fuselages of unpressurized aircraft don't follow this logic A Short Skyvan or a Dornier 228 have fuselages with a rectangular cross section, so large cargo can fit in.

Also, some fuselages are combinations of cylinders. The Boeing 377 Stratocruiser used the lower fuselage of the B-29 and had an upper, larger cylinder on top to give the passengers more room.

Boeing 377 cross section (picture source)

For the same reason, rocket stages are cylindrical, too. They also need to be aerodynamic, have to tolerate high internal pressure and need to be lightweight.


How do the European ATC strikes affect us as pilots?

Since these strikes are announced in advance, you will not be caught by surprise half way accross the ocean. If you try to file a flightplan through the soon to be closed airspace, the CFMU will not accept your plan. There will be no IFR traffic in the airspace before they close down the service.

I don't know about VFR.


Is the EASA RT License valid internationally?

The answer saying that "Each country has their own governing rules regarding qualification for Private Pilot Licenses" is of course wrong. The OP has specifically asked about EASA. The privileges of an EASA licence may be exercised by the holder in any EASA member country by virtue of § 11.1 of the Basic Regulation – Regulation (EU) 2018/1139.

if I want to rent an Airplane in another country in Europe (like Hungary), should I get Hungarian RT license? or my Czech RT license is valid for all EASA countries?

The latter.

is the PPL EASA license (with valid RT license) sufficient to rent aircraft in Europe? Or do I have to pass some test for each country?

The former (don't forget about the medical!). Of course, nobody in their right mind are going to let you fly their aircraft without having you checked out first, but that's a club / school / owner policy not something State-mandated.
In any event, ask your flying school in the first instance and the CAA in the second. Only a complete fool would rely on random stuff seen on the internet!


Does the FAA have specific Air Ambulance safety guidelines?

Check out this document published by the FAA which seems to be recent and some notes here on the same topics. The full rules can be found in the FAR at Part 135 Subpart L—Helicopter Air Ambulance Equipment, Operations, and Training Requirements

They are required to do a preflight risk analysis as per §135.617 but this is not really any different than what anyone should be doing before any flight however for them it is very specifically outlined.

  (a) Each certificate holder conducting helicopter air ambulance operations must establish, and document in its operations manual, an
  FAA-approved preflight risk analysis that includes at least the
  following—

  (1) Flight considerations, to include obstacles and terrain along the
  planned route of flight, landing zone conditions, and fuel
  requirements;

  (2) Human factors, such as crew fatigue, life events, and other
  stressors;

  (3) Weather, including departure, en route, destination, and
  forecasted;

  (4) A procedure for determining whether another helicopter air
  ambulance operator has refused or rejected a flight request; and

  (5) Strategies and procedures for mitigating identified risks,
  including procedures for obtaining and documenting approval of the
  certificate holder's management personnel to release a flight when a
  risk exceeds a level predetermined by the certificate holder.

  (b) Each certificate holder must develop a preflight risk analysis
  worksheet to include, at a minimum, the items in paragraph (a) of this
  section.

  (c) Prior to the first leg of each helicopter air ambulance operation,
  the pilot in command must conduct a preflight risk analysis and
  complete the preflight risk analysis worksheet in accordance with the
  certificate holder's FAA-approved procedures. The pilot in command
  must sign the preflight risk analysis worksheet and specify the date
  and time it was completed.

  (d) The certificate holder must retain the original or a copy of each
  completed preflight risk analysis worksheet at a location specified in
  its operations manual for at least 90 days from the date of the
  operation.


From what I can see, the "true" static pressure is the measured static pressure corrected for airspeed & position (Static Source Error Correction).

In my copy of ARINC 429 (May 2004) I don't see a label definition that fits this "true static pressure". Label 171 can be used for manufacturer defined data, so I would see if you can get a better answer from the manufacturer of your data source.


Do propeller coefficients go to zero at the same value of advance ratio?

Do $C_P$, $C_T$, and $\eta$ always go to zero simultaneously at the
    same value of $J$ for all propellers?  Why?

Yes; Talking in dimensional quantities, This speed, at which all coefficients goes to zero is called pitch speed.

At pitch speed thrust goes to zero due to the fact that the incoming airflow drives the apparent angle of attack seen by the blades to zero.

Power = Thrust * velocity , As thrust goes to zero power goes to zero as well.

Efficiency $\eta = \frac{P_{out}}{P_{in}}$, $P_{out}$ goes to zero as shown above hence $\eta$ goes to zero.

HTH


What was the reason for replacing the non-smoking sign with a "no electronics" sign?

I did some searching on this and it's been discussed on some aviation forums (e.g. here). I couldn't find any 'official' sources from airlines or regulators but on the other hand there are a lot of comments and observations that seem to make sense.

A simple summary would be that it's a result of increased public awareness of airline smoking bans combined with a massive increase in the use of portable electronic devices (PEDs). That has made some airlines decide that it's more important to focus on passenger behaviour with PEDs rather than smoking. Wikipedia has an unsupported (citation needed) statement along those lines:

  Due to the ubiquitous prohibition of in-flight smoking and the
  increasingly widespread use of electronic devices, the illuminated
  no-smoking signs have sometimes been re-purposed to inform passengers
  to switch devices off for take-off and landing. Where this is the
  case, the no-smoking sign is permanently printed on the overhead
  panels.

Smoking on aircraft has been banned by most (all?) airlines and regulators for some time now (since 1988 in the US, for example) and the number of people travelling by air has increased significantly over the same period (e.g. UK foreign travel trend here). That means that more and more people know that smoking isn't allowed on aircraft and probably by now that fact has been 'absorbed' at a cultural level, at least in Western countries.

In the last 10+ years the numbers of PEDs in use has increased massively and they were banned too. I guess that at some point some airlines decided that the 'rising' issue of PEDs was more important than the 'declining' issue of smoking, and started adapting their signs, briefings etc. accordingly.

It's interesting that you saw the sign on an Embraer 195, which is used for regional not long-haul flights (as far as I know). Possibly the airline decided that on shorter flights there's less risk of passengers getting desperate for a smoke. But I couldn't find any information on which airlines and aircraft have these signs; that's up to the airline to decide when it orders the aircraft interior.

Of course now the US allows the use of PEDs in all flight phases and that makes it very likely that other regulators will follow. At some point the only sign needed may be the seatbelt one.