Are aircraft transferable between companies with different Air Operator Certificates?

The answer to this will depend on what the two company's Operation Certificates allow and forbid in the Operation Specifications (Ops Specs). All Ops Spec examples provided below represent FAA examples, are examples only, and may differ from those in any specific situations.
Considerations will include:

Aircraft Authorization
Operational Control
Maintenance
Crewmember Requirements

The Ops Specs will specify in A003 which aircraft and configurations are authorized for use, for example:

A003 . Aircraft Authorization
The certificate holder is authorized to conduct operations under the provisions of Title 14 CFR Part 135 using aircraft with the approved configuration and operations described in the following table:
[table omitted]

If the available aircraft is of a type and configuration authorized for use, then it may be possible to use it. This will most likely be the case if the aircraft is of the same type and configuration, and in the same class/category of operation as those aircraft which Company A already operates.
Ops Spec A008 will probably specify that the certificate holder shall not:

Engage in any arrangement with an aircraft owner, lessor or any other person or entity [...] which allows the use of an aircraft for operation under these operations specification without a complete, effective and sustainable transfer of operation control to the certificate holder for all Part 135 operation conducted under these operation specifications.

The lease agreement must provide Company A with complete, effective and sustainable operational control of the aircraft.
Additionally, the aircraft must conform to the extensive maintenance requirements required by Part D of the Ops Specs.
The flight crewmembers must also be trained and approved for the aircraft. However, if the aircraft is of the same type and configuration as those already listed in A003, this requirement may be easily met.


Does a headwind affect the climb gradient?

The gradient of climb is the ratio of the increase of altitude to horizontal distance through the air, not over the ground.
The definition used by the UK CAA in CAP 698 is:

  Climb Gradient

  The ratio, in the same units of measurement, expressed
  as a percentage, as obtained from the formula:
  - $$\text{Gradient} = \frac{\text{Change in Height}}{\text{Horizontal Distance}} \times 100 \% $$

If you have a headwind or a tailwind it makes no difference to your climb gradient because your airplane is moving relative to the air mass.

Climb gradient is not the same as rate of climb, although they are related. Rate of climb is altitude over a period of time, gradient is climb over distance travelled. There is another question which covers the difference in more detail.


What is this strange structure, of a type often seen by pilots in hilly regions?

It's a reflector for microwave links, a passive repeater.

More info here (article in Spanish): http://notascordobesas.blogspot.com/2015/01/el-repetidor-pasivo-de-microondas.html


In this 2nd brace position, should your head lean against the seat in front?

The head should be against the seat in front of you. The reason is that if the plane crashes, your head and upper body will be thrown forwards until they hit something. If you're in a normal sitting position, your head will be moving pretty quickly by the time it smashes into the seat in front of you, leading to serious injury or death. Moreover, as your torso and head are moving forwards in an uncontrolled way, you can get injured by your head essentially flopping around. Since your head is going to end up against the seat in front of you anyway, putting it against that seat before the crash means it doesn't smash into it during the crash, and that it's not flopping around on its way to the seat.


How do wing ribs withstand lateral lift force?

TL;DR: from the ribs perspective nothing changes.

Look at the three figures you posted: the lift is always straight in the middle of the aircraft. Tilt the aircraft, the lift tilts with the aircraft.

From the perspective of the ribs there is no side force, the lift is still perpendicular to the wings (actually, to the incoming airflow, but is a good approximation).

The only case where the wings will see some side force is when the aircraft is in a sideslip, i.e. $\beta \neq 0$.

In such a situation is not the ribs that carry the side load, but the wing beams, that run along the whole wing.


Strut braced or wire braced airplane wings?

Depends on the shape.  A round 1/8" wire would have way less drag than, say, a 1" round lift strut, obviously.  And the same for a streamlined wire vs a streamlined lift strut. So looked at that way, the wires win aerodynamically even with 4 wires per wing vs 2 struts.

However, streamlined wires are crazy expensive and have to be custom made, so they aren't really a practical option and you are stuck with round cable, whereas a streamlined strut is not so hard to do.

So the practical comparison is round wire vs streamline strut.  A teardrop shape has 1/12th the drag of a round shape, so a round shape of 1/8" diameter has the same drag as a 1.5" thick teardrop shape.

In view of that, a streamlined lift strut of say, 1" thickness (frontal area) would still have less drag than a 1/8" cable of the same length, and you only have 2 per wing vs 4 cables per wing, so overall you are ahead with streamlined struts.  Add the benefits of rigidity, ease of assembly, looks, etc, and streamlined lift struts are a no brainer, which is why 99.9% of non-cantilever monoplanes use struts (wire bracing may be somewhat lighter however - or maybe not).

Now, a streamlined aluminum extrusion for an ultralight might also be somewhat expensive to source, though nowhere near as bad as streamlined cables.  So for an ultralight, unless teardrop extrusion is available cheap, the most efficient all round choice would be to design a lift strut made from round aluminum tubing and apply over that a light fairing of .016" aluminum, or formable plastic, or fiberglass, or whatever, to get the teardrop shape.


When a typical commercial airliner flies overhead, what is the actual noise we are hearing?

It depends on the type of operation:

Approach (close to airport):

Much aerodynamic broadband noise from the air-frame
Modern turbofan engines are less noisy than the air frame during approach. But engines emit most of the tonal components in the sound.
Depending on the type of aircraft and angle of descent the pilot might need to use air-brakes to reduce speed. That will cause turbulence and noise.
On some Airbuses you hear a typical high pitch annoying sound that is caused by air flowing across cavities under the wing (Fuel Over Pressure Protector to be exact, not from the engine).

Departure (close to airport):

Pretty much all the noise you hear comes from the engines, such as the buzzsaw noise generated when the tips of the fan blades reach supersonic speeds. Hot high speed gases causes turbulence and that creates low frequency noise, especially behind the aircraft.

Overflight at 35.000-40.000 ft:

What you hear is low-frequency broad band noise that originates from turbulence behind the engines. All the high and medium frequencies are gone because the air between aircraft and ground absorbs much of the sound. The sound will also fluctuate due to differences in wind speed, humidity and temperature, along with the flight path and along the sound propagation path.

Further reading / sources

1. Conference lecture by Prof. Dr. Ing. J. Delfs,
Head of Technical Acoustics, German Aerospace Center

2. ECAC doc 29 (Technical documentation)

3. An Overview of Aircraft Noise
Reduction Technologies


What are these hexagonal things under the Concorde's neck?

(source)

  This is the side loading door. Under this door are the static pressure
  panels that provide data to the Air Data Computers. They have been
  painted over now.

Here is a nice close up image

(source)


Can an increased current rating of a Ground Power Unit damage an aircraft?

I find the easiest way to think about Volts and Amps is that the voltage is "pushed" and the amps are "pulled".

This is the same with pretty much any kind of power supply, whether we're talking mobile phones or planes.

To that end, the voltage requirement always needs to match. If your device is expecting 28Volts in DC then your power supply MUST provide 28Volts in DC - anything else is likely to damage it, could cause a danger and almost certainly won't work.

But current (Amps) is different - your power supply needs to meet or exceed the current demands. So if your device can pull up to 1000 Amps, the power supply MUST be able to provide 1000 Amps or more.

So, to answer your two possible questions. You can increase the Power Supply (GPU) to a 1200 Amp model (or beyond) with no ill effects, but your device (The aircraft) must have a current demand that meets or is less than that.


What does one do when the weather report has a bogus altimeter setting?

We might speculate why the METAR is giving innaccurate data, but the question asks, "What should one do..."
I will take the liberty of inferring the question to be "what should one do if one is unable to obtain an altimeter setting for the airport from which he or she is preparing to depart?" Note that this question could be asked due to an airport with a faulty weather reporting system (as in the question above), an airport without weather reporting at all (quite common, for example: D42 or S68), or an aircraft that is not radio equipped.
I will further take the liberty of answering from what I know: the FAA regulations.
I will point out that it is the pilot's responsibility to be familiar with all available information and this should include a thorough weather briefing whenever possible.
Under the FAA's jurisdiction, the relevant regulation is 14 CFR 91.121 (a) (1):

(a) Each person operating an aircraft shall maintain the cruising altitude or flight level of that aircraft, as the case may be, by reference to an altimeter that is set, when operating—
(1) Below 18,000 feet MSL, to—
(i) The current reported altimeter setting of a station along the route and within 100 nautical miles of the aircraft;
(ii) If there is no station within the area prescribed in paragraph (a)(1)(i) of this section, the current reported altimeter setting of an appropriate available station; or
(iii) In the case of an aircraft not equipped with a radio, the elevation of the departure airport or an appropriate altimeter setting available before departure

(Since all airports and terrain in the US are below 18,000 MSL, this applies to takeoff; the rules governing flight above 18,000—14 CFR 91.121 (a) (2)—do not apply to our question. "Operate" is defined in 14 CFR 1.1.)
We can go through this like a flowchart:
If "the current reported altimeter setting of a station along the route and within 100 nautical miles of the aircraft" is available, use that.
(Note that this could include current reported altimeter settings obtained by radio (ATC, flight service, or a nearby airport), phone call (briefer or AWOS), internet, or any other method that would procure the needed data.)
If no such station is available, then use "the current reported altimeter setting of an appropriate available station."
Now, if the aircraft in question is not equipped with a radio, then (and I would read technically only then) the pilot is permitted to set the altimeter to "the elevation of the departure airport or an appropriate altimeter setting available before departure."
Now, that being said, if a pilot is in the middle of the Idaho backcountry at Wilson Bar (C48), or on the face of an Alaskan glacier, with no cell reception and no real way to acquire a current reported altimeter setting despite being in a radio equipped aircraft, then actual practice will be to set the altimeter to field elevation and get on with it. However, the requirement to use a current reported altimeter setting remains, and should be acquired at the first available opportunity.


How robust are modern parachutes to folding errors, wear, or other problems?

Qualification: I am a master parachute rigger, taught the sport for 10 years and have packed a couple of thousand emergency parachutes.

I can put an apartment-size piece of nylon into a purse in under 5 minutes, and guarantee that it will open. How nicely it opens is a different question. It usually takes about 45 minutes to service an emergency parachute - 20 minutes to inspect it, 10  to fold it up nicely, another 10 to stuff it into the pack, then the paperwork. Double that time if it's a large 2-passenger parachute.

The "fold it up nicely" part is to make it go into the pack without any unsightly bulges, and the emergency packs are never a nice open bag like the main - the canopy has to be shaped around the closing apparatus and the spring-loaded extraction chute has to fit in the middle. Very little of this process has anything to do with ensuring it opens when needed.

A packer would have to be spectacularly incompetent to fold a canopy in a way that would cause it to malfunction. If you feel the fabric used to make main parachutes you will find that it is extremely slippery - good luck keeping that stuff in the proper place when it goes into the bag, but you don't need to. These things sort themselves out quite nicely most of the time.

There are two important tools used in packing emergency packs - one is appropriately called the Death Strap. It is wrapped around the middle of the canopy as you are folding it into the bag, and if you forget to remove it the canopy will not open. The other is a locking pin used to close each part of the pack in stages. Your mistake will probably make the front page of the local newspaper and involve a lot of time with your lawyer, so packers typically only own one of each and all tools are counted after each job.

Going back to the incompetent packer for a moment - the main parachute is usually packed by the owner, and very occasionally you need to open and re-close the pack. If you are lazy or rushed it is very easy to close the main pack in a way that prevents it from opening. Owners (almost) never open their emergency packs, and riggers follow a standard process to prevent these errors from happening.


Where does the 90 seconds limit for plane evacuation come from?

90 seconds comes from a safety aspect, specifically a fire safety aspect

Aviation Safety Study SA9501 Footnote 3 says:

  Internationally, industry accepts 90 seconds as a reasonable estimate of the survivable time in an evacuation where fire is present.

Which means that it is predicted than a burning aircraft is not sustainable for life beyond that period, but interestingly this is not the condition that the aircraft is certified under.

FAA Chapter 77 Section 1.7 says:

  A full-scale emergency evacuation demonstration simulates an aborted takeoff. The operator must show that the aircraft, emergency equipment, and emergency procedures allow the evacuation of the aircraft at full seating capacity, including crewmembers, in 90 seconds or less.

So the 90 second rule comes from a fire safety aspect - as humans are not expected to survive in those conditions for longer than that; but the aircraft is only tested on whether it can evacuate on an aborted takeoff (not specifying that a simulated fire must be the cause of this aborted takeoff).

Sources: https://www.skybrary.aero/bookshelf/books/2699.pdf

http://fsims.faa.gov/WDocs/8300.10%20Airworthiness%20Insp%20Handbk/Volume%202/2_077_00.htm


How can a plane fly far longer than designed?

The design range is fully loaded.  This flight had 35 passengers, no cargo, full fuel and was run as a project and flown by a test pilot.  It was not a commercial flight in the meaning that most people would recognise.

They had to wait for weeks until the winds aloft, especially the jet stream, were at their most advantageous.


What are the ASTERIX CAT010 message types 005 and higher?

Finally, it is solved. It is not about the data issue but some decoding issue. I am using an asterix-decoder in python from https://github.com/CroatiaControlLtd/asterix.
Based on the help of its author, Damir Salantic. "There was a bug in the presentation of hexdata in case when the old format of asterix is used. Old format has several Data Records in Data Block."
Now the issue is fixed and the decoder repository is updated the decoded data is following the format from Eurocontrol.


What is the relation between sweep angle and lift-to-drag ratio?

This is my take on this.
We assume that an infinite-span swept wing is under compressible flow, and that the flow acts on it as in Figure 1 below:

With that, we can now utilize the equation of motion to find the relation between the sweep angle and the coefficient of lift, which in turn, will make the relation with the ratio L/D
From the equation of motion, we have:
$$(1-M^2_{\infty}\cos^2\Lambda)\frac{\partial^2 \phi}{\partial x^2} + \frac{\partial^2 \phi}{\partial y^2}$$
Now, only the perpendicular component acts we have that:
$$(u'_c)_n = \frac{\partial \phi}{\partial x} = \frac{1}{\sqrt{1-M^2_{\infty}\cos^2\Lambda}} \frac{\partial \Phi}{\partial x} = \frac{(u'_i)_n}{\sqrt{1-M^2_{\infty}\cos^2\Lambda}}$$
$$C_{p_c} = -2\frac{\cos\Lambda(u'_c)_n}{U_\infty} = -2\frac{\cos\Lambda(u'_i)_n}{U_\infty\sqrt{1-M^2_{\infty}\cos^2\Lambda}}$$
Now, since:
$$C_L = \frac{1}{c}\oint C_p dx$$
We have that:
$$C_L = \frac{C_{Li} }{\sqrt{1-M^2_{\infty}\cos^2\Lambda}}$$
The above equation shows that the lift coefficient is sweep angle dependent, therefore, the ratio L/D is also sweep angle dependent.
This is a very complex side of aerodynamics and understanding it completely requires some study. I recommend studying Chapter 11 from "Fundamentals of Aerodynamics" by J. Anderson (a classic) and Chapter 8 from "Aerodynamics for Engineering Students" by E.L. Hughton.


Is it illegal for Joe Public to listen to ATC in the UK?

Yes, it is illegal.

The UK has some very strange ideas about Radio, which bear no resemblance to the reality of physics and how radio actually works. Foremost among those ideas is the idea that you are only legally allowed to listen to transmissions intended for "general reception":

  The services that can be listened to under the definition of general reception are:

  licensed broadcasting stations;
  amateur and citizens' band radio transmissions; and
  weather and navigation transmissions

  Radio scanners should not be used to listen to any other radio services, including illegal radio stations (pirates) (by virtue of the fact that they are not licensed radio stations).

Aviation-band transmissions are not on Ofcom's list, so even though they are broadcast entirely "in the clear" and anyone with an appropriately tuned AM receiver could hear them you are legally prohibited from listening to them.

Providing feeds to LiveATC would also appear to be a violation, though it's not clear to me that listening to LiveATC streams would put the listener in violation of the law.

From the same Ofcom site:

  … it is illegal to listen to anything other than general reception transmissions unless you are either a licensed user of the frequencies in question or have been specifically authorised to do so by a designated person.

and

  … it is also illegal to tell a third party what has been heard in a transmission a person has listened to illegally.

So anyone providing UK aviation band transmissions to LiveATC may be in violation of both of those laws, but I'm not certain what that means for LiveATC listeners (that would be a question to ask Ofcom).


What is the behavior of false glideslope signals?

The glideslope system is an analog system, and as such, it's subject to aliasing, resonances, heterodyning, and eight other technical terms I pulled out of my ass.

Maybe a diagram will help:

false glide slopes

In plain English, above the "real" glideslope, there are false glide slopes caused by your equipment locking onto the wrong phase of the signals. If you lock onto the wrong lobe, it will still take you to the runway, but at a much higher rate of descent than you planned for. Maybe steeper than you can manage safely.

Assuming the correct lobe is the bottom-most one in the system (see diagram), you'll be ok as long as you intercept it from below. If you intercept from above, you could lock onto the wrong one, and then you're gonna have a Real Bad Day.


What does "Information " in ATC transmissions mean?

This is a simple versioning system used in ATIS (Automatic Terminal Information Service).
ATIS messages contain information about the weather at the airport, runways in use etc. This information is transmitted on a dedicated radio frequency and repeated in a loop. The ATIS messages are updated frequently as the weather or operations at the airport change. Every time a new ATIS message is generated, the letter is changed.

Example of an ATIS message:

  This is Schiphol arrival information Kilo, main landing runway
  18Right. Transition level 50. Two zero zero degrees, one one knots.
  Visibility 10 kilometres. Few 1300 feet, scattered 1800 feet, broken
  2000 feet. Temperature 15, dewpoint 13. QNH 995 hectopascal. No
  significant change. Contact Approach and Arrival callsign only. End of
  information Kilo.

Now when for example the temperature or pressure at the airport changes, the ATIS information is updated:

  This is Schiphol arrival information Lima, main landing runway
  18Right. Transition level 50. Two zero zero degrees, one two knots.
  Visibility 10 kilometres. Few 1300 feet, scattered 1800 feet, broken
  2000 feet. Temperature 16, dewpoint 13. QNH 994 hectopascal. No
  significant change. Contact Approach and Arrival callsign only. End of
  information Lima.

The flight crew will listen to the ATIS often before they are in contact with the Air Traffic Control of the airport. They note the information in the ATIS, together with the information version letter.

On first contact with the airport's Air Traffic Control they will state what version of the ATIS they have listened to.

  Schiphol approach, this is KLM1234 with information Lima.

The Air Traffic Controller can then determine whether this is the latest version of the ATIS or if there is newer information available that should be passed on to the flight crew.


Do airplanes or helicopters ever fly at night using only white navigation lights?

There are no such things as white navigation lights - nav light, by definition, are red/green/white.

However, we're talking about filming lights at night. And the problem here is that the light source, no matter what colour, is a concentrated source of light in major contrast to the lack of light around it. And so the light will often 'burn in' on a camera and appear to be a lot of light, ie white, where the human eye will pick up the colours.


Why is magnesium not used more often as a structural metal in aircraft?

Magnesium has initially been held back by technical difficulties in the removal of chloride inclusions. These had been solved only after a lot of progress had been made in aluminum alloys. Also, magnesium parts should only be used in a dry environment - when the metal is exposed to water, rapid corrosion must be expected.

The first application of magnesium in aerostructures was in the 1930s (mostly under the trade name Elektron), with a small boom in the 1950s. Lockheed even built one F-80C fully from magnesium. Magnesium was widely used in the former Soviet Union, but eventually phased out in newer designs due to corrosion problems. Flammability, by the way, was never a real concern with magnesium.

With improved protection techniques, magnesium might make a limited come-back. It is already used in castings and extruded parts. Per kilogram, it is twice as expensive than aluminum, but very easy to machine. However, at higher temperature it will lose strength even faster than aluminum.

Parallel to that, aluminum sheet can be made lighter and stiffer by adding up to 2.5% of lithium. These Al-Li alloys have found their way into the newest aircraft designs and will raise the bar for magnesium applications.

Magnesium and water really don't mix well: Trying to extinguish a magnesium fire with water is a memorable experience, as adding water will intensify the reaction. Use iron chips or sand instead to cool down the burning metal and to keep oxygen away. Historically, though, magnesium fires on aircraft have been extremely rare.


What are good resources on causes of private aircraft crashes?

The AOPA's Air Safety Institute has quite a few resources that I like to review from time to time, including some great videos with commentary on exceptional cases.

AOPA ASI Accident Analysis Page
AOPA Accident Case Studies
AOPA Real Pilot Stories

I do exactly what you are doing, during training and still after, but I'd like to also say that you shouldn't narrow yourself to GA crashes, a lot of what happens commercially can be applied to GA, and usually with commercial accidents there is a lot more data and analysis available to work with. In that regard, I like to watch shows on Youtube like "Air Crash Investigation", or on TV like "Why Planes Crash" (some available on Youtube)

AOPA also has a lot of resources to view NTSB reports on individual crashes where you can search by certain criteria like aircraft type, states, type of flight, or even some specific keywords like "Vacuum Failure".

Just don't limit yourself to looking at things like "Pilot Error", pilot error is a broad category of crashes that is usually used to describe the pilot doing something wrong in the air, but a lot of crashes are "pilot error" in that the pilot could have broke the accident chain much earlier in the flight. Read as many as you can, regardless of the cause. For example an accident where the aircraft breaks up in flight may not be attributed to pilot error, but its good to know what lead to the break up and what could have been prevented.


Why do turbofan blade tips exceed the speed of sound while prop tips should not?

Short answer:

Turbofans need supersonic speed at the fan blade tips to create their high thrust.
Turbofans can tolerate supersonic speeds because the intake creates constant flow conditions irrespective of flight speed.
Efficiency for propellers and fan blades is highest at subsonic flow conditions.
Propellers can turn at supersonic speeds, but since flow conditions are less controlled, the penalty for doing so is much higher than the penalty for a fan.

Explanation

It is a bad thing to have supersonic fan blade tips, just like supersonic propeller tips are best avoided. But in turbofans it is a price worth paying, because the faster tip velocity means higher dynamic pressure, and the pressure difference between both sides of the fan blade grows with the square of their velocity. This makes the high thrust levels of modern turbofans possible.

Propeller efficiency over speed (picture source). The plot for fan blades would look not much different. The very thin, uncambered airfoil of a supersonic propeller and the added wave drag lower the maximum efficiency, but hold efficiency up into supersonic air speeds.

Note that the propeller on the XF-84H Thunderscreech did move at supersonic speed. There is nothing inherent in propellers which prevents their tips from moving faster than the speed of sound. On the other hand, the big diameter of a prop requires proportionally more torque to keep the prop rotating against the drag from the supersonic tips. Thus, a fan engine requires less torque per blade to reach supersonic tip speeds on the fan blades.

Also, the shroud of a turbofan engine helps a lot to make the noise from supersonic tips manageable. The XF-84H's noise made people literally sick. But there is more to it: @FreeMan encouraged me with his comment to dive a little deeper.

A supersonic propeller will work well when the direction of flow at every station along the propeller blade is about equal to the local airfoil chord. Since the blade is uncambered, this means that the change in local flow direction at the leading edge can be minimized to the amount which is required to create the desired thrust. But to be able to fulfill this condition you need to match your propeller speed to the flight speed and twist distribution. Also, the angle of attack must be compensated for by sviveling this propeller axis into the direction of flight. It will have no p-factor, but can run at only one speed for a given flight speed.

Contrast this with a turbofan: The intake makes sure that the flow speed and direction at the face of the fan is the same no matter what the flight speed is. This is done by the pressure field in and around the intake which will spill excess air overboard at high speed or suck extra air in from the sides at low speed. In the fan you can indeed match the local angle of incidence to the airspeed so the fan will work well over its design range.

Generally, a fully subsonic fan would be more efficient. But then the diameter would need to be as large as that of big turboprop engines, and the shroud would become impossibly heavy and produce too much drag. The high dynamic pressure on the fan blades is needed to produce the thrust with the relatively small diameter of a turbofan.


What is done to prevent the tail hook from bouncing off the carrier deck?

The tailhook assembly on a modern carrier or terrestrial fighter has a hydraulic damping assembly which forces the hook to stay extended and dampens the impact of the hook into the runway or flight deck.  Without it the hook would bounce off the deck on impact and potentially strike the tail of the aircraft.

This was a major problem during early ship trials of the F-35C airplane the first time it went out to the boat, resulting in an unacceptable 30% boarding rate due to a faulty tailhook design.  The tailhook assembly has since been redesigned and worked well during later sea trials of the jet.

This damping assembly is quite powerful and can injure or kill careless personnel should the uplock accidentally disengage, hence the DANGER TAILHOOK markings on the aft fuselage of some navy aircraft.

The system will handle most landings; on occasion a pilot slams the jet down hard enough that the hook will jump off the deck missing all of the wires.  This is called a hook skip.  It is handled just like any other bolter: Full power at touchdown and go around to enter the bolter pattern for another try.


Is the increased humidity on modern jets artificial?

A Reuters article confirms the humidity just comes from the passengers, on the 787 at anyway:

  (...) the air is dry and moisture comes mostly from passengers.

And this Flight Global article:

  (...) the system does not add moisture through active humidifiers.

This APEX article has no discussion of higher cabin pressure being an influence on humidity.

Lastly, this Business Insider article says Boeing indicates the higher pressure alleviates the feeling of mountain sickness that can come from being at 8,000 ft vs 6,000 ft.

  [S]ince there isn't a perfect one-to-one correlation between altitude and jet lag, Boeing has taken additional measures to mitigate the symptoms. These measures include an increase in cabin humidity as well as a new air-filtration system.

So, it's real humidity, and not really an effect of cabin pressure.


How does flying with flaps differ from flying with airbrakes?

The SF-25 has such a low wing loading that it easily tolerates the small reduction in maximum lift which the airbrakes cause. I have done very few flights in it (I'm too tall to fit comfortably in it's cramped cockpit), but from what I remember the airbrakes are not very big, having little effect on minimum speed. My experience, however, is with the SF-25 B, and you linked to the SF-25 C, so I have to assume that my experience is not fully relevant.

I have more experience with real gliders and composite motorgliders, and here my experience is: Start your approach, stabilize the right approach speed, set the airbrakes such that your glide path looks right and do not play around with them too much. Set your approach such that you need medium airbrake extension, so you have margin for corrections in both directions. Normally, I come in a little high so I am not caught by windshear, and when I am sure I will reach the intended touchdown point, I extend the airbrakes fully to land with the shortest distance possible. However, when touching down, make sure you do not fully extend the airbrakes: This gives you more time for stopping the descent. Especially in gliders with very effective flaps and airbrakes (ASW-20 C, ASH-25) I never made a good landing with fully extended airbrakes. Reduce them to half extension at the most when touching down!

In the ASW gliders the airbrakes are linked to the very effective wheel brake, and touching down with fully deployed airbrakes means that the wheel is braked at touchdown. This is another reason to reduce airbrake extension when touching down.

In high-performance gliders it is easy to float too long, so it is very important to control your approach speed and to continue the descent all the way down to the touchdown point. Don't pull too early! The SF-25 will not float as much, but with its low wing it shows a pronounced ground effect, and exercising strict discipline when landing helps a lot to make the landing better.

I could not find a number for the stall speed change due to airbrakes in the SF-25 manual, but I would guess it is at most a few km/h.


Did large winglets contribute to the spin behavior of the SB 13 tailless glider?

Probably not. Spins usually start from a stall, not a side slip, and yaw stability generally improves spin resistance and recovery.

For model flying wings, removing the tip fins usually makes spins far more likely and much harder to recover from. The usual explanation is that the end plate effect delays the stall at the wing tip.


What route should I fly in this lost comms scenario?

Rule of thumb:  Whenever a clearance has an instruction to proceed from point X to point Y, where the path between those points is at the controller's discretion (such as vectors), and you have declared a comm failure by squawking 7600, you are to use your own judgement to proceed between those points by the most logical and reasonable path.

So if my clearance told me to expect vectors between two fixes and I now had a comm failure, I would just navigate my own way between them using whatever route keeps me clear of obstacles (probably direct), at or above the minimum charted altitude appropriate to the area (vectoring altitudes can be lower - you are expected to climb to the minimum published altitude following 7600 if it happens while on vectors).

On an arrival, if there is a comm failure on an arrival that involves radar vectors to final, you are expected to navigate yourself to the final approach course by the most reasonable and logical path, not lower than the charted altitude for the airspace you are in.

It's similar with the matter of timing; you are expected to start an approach at the last mutually confirmed or flight planned or expected time, so say if you arrive at a clearance limit early following a comm failure, you are expected to hold on your own as necessary so that you can proceed to the approach when you are supposed to.

The objective is that when the controller is notified of your comm failure when you squawked 7600, he/she will expect you to find your own way between any points that are discretionary at charted minimum altitudes, following a logical route and with timings that the controller can anticipate so the controller can route other traffic around you, confident you'll be able to avoid hill tops or tv towers on your own.

Much of the IFR rules structure is designed to ensure that an airplane with no communication capability can complete a trip maintaining its own obstacle clearance and proceeding in such a way that the controllers can anticipate where you are going with reasonable certainty.  The key thing is to maintain  a safe altitude and avoid going off in directions that make no sense to the controller as you find your way around.


When the angle of attack is increased does the air flowing below it slow down

In high alpha flight it is not uncommon to have compression below the wing, which would increase the pressure, and act in concert with the Bernoulli Effect on the top of the wing.  The effect on the underside of the wing could also correctly be called a form of Bernoulli Effect.

There need not be any compression on the underside for there to be lift on the top side of the wing.  However in higher angles of attack there is compression, which supplements the lift.


What regulations apply to changing liveries on private jets in the US?

The only requirement is the height of the registration number, 12" if flying internationally (from the US anyway), 2" I think if staying domestic, and maybe new weight & balance - but usually a layer of paint and primer is taken off, and a new layer is put on, so the weight change is minimal.  Any control surfaces that were removed may need rebalancing.  Colors & schemes are at the whim of the owner(s).


Why should passengers not delay donning emergency oxygen masks after they deploy from the overhead compartments?

The point is not that the oxygen is used up. Even after a depressurization, the air around you still contains so much oxygen that it would take your body (at rest) hours to burn it all. But this oxygen is spread out so thinly that a standard set of lungs will not be up to getting enough of it from the cabin air into your blood at the rate your brain needs. This goes into effect immediately when the pressure drops.

As soon as the oxygen masks fall down, the flight crew will know, and they will make it an immediate priority to get the aircraft down to an altitude where the masks are not needed anymore because the outside pressure is high enough to breathe by. This takes less than the time the oxygen generators last for.

(Usually descending will take much less time than the masks are good for -- the critical design factor for the oxygen mask duration is that if you happen to be over tall mountains when the pressure drops you may need to fly for a bit of time to reach terrain low enough to dispense with the masks. There are a few places, such as over the Tibetan plateau, where airline flights simply don't go because it's too far from sufficiently low terrain for the masks to last).

There is no realistic chance of the oxygen generators running dry while you still need them. If you delay putting your mask on, all you buy is a danger of fainting or otherwise being unable to don it (from low pressure, not depletion of oxygen in the air) before you decide to put it on -- and then you may end up in a low-oxygen state for long enough to risk permanent harm.

There's a reason why the safety briefing always instructs you to put your own mask on before helping others -- because the time it takes to help someone else may well be enough to incapacitate yourself.


Are carbon fiber/composite aircraft at greater risk from lightning?

From Boeing's AERO:

  Areas that have the greatest likelihood of a direct lightning attachment incorporate some type of lightning protection. Boeing performs testing that ensures the adequacy of lightning protection. Composite parts that are in lightning-strike prone areas must have appropriate lightning protection.

  Lightning protection on airplanes may include:

  Wire bundle shields.
  Ground straps.
  Composite structure expanded foils, wire mesh, aluminum flame spray coating, embedded metallic wire, metallic picture frames, diverter strips, metallic foil liners, coated glass fabric, and bonded aluminum foil.

That suggests for composite areas that are vulnerable to lightning strikes, extra measures are taken to enhance the conductivity.


If a Boeing 707 hits turbulence that registers as +5 G on the FDR, would the 787 experience lower G forces due to the flexibility of their wings?

The 787 will not experience lower G-forces, it will experience them later. If the turbulence is of short duration, the 787 might not register much while a 707 is shaken thoroughly. If the updraft persists, both aircraft will eventually feel the same forces.

When an aircraft enters turbulence, the wings experience more lift and start moving upwards. If the wings are heavy (full tanks) and floppy, it takes quite a while before the fuselage experiences any forces. After the wings reached their upper bending limit, the fuselage starts moving upwards together with the wings. In an aircraft with lightweight, stiff wings, the fuselage follows any wing movement immediately.


How to estimate blade interference in a propeller or fan?

For a simple 2D approximation, you can do it in a similar way to how you would analyze the effect of wake on a tailplane or any other body, i.e. by solving the flow field around both at the same time.
Since the movement of the  blades is cyclical and the flow is subsonic, each blade affects both the ones ahead and the ones behind it. Therefore, you would would need to solve for an infinite number of blades simultaneously so that the one in the middle would have a realistic airflow, but since the effect of the N-th blade will tend to nill, a good approximation can be had with just a few blades on either side of the studied one.

The process would look like this:

Choose the spanwise station of the blade you are interested in and the operating point (rpm and forward velocity) you want to study. These will give you the effective angle of attack for the blade station.
Knowing the angular blade spacing around the hub, the spanwise station you selected, the rpm and the forward velocity, find out where the first airfoil will be relative to the second one in a 2D representation.
Solve the flow field for an effectively infinite number of airfoils spaced this way. In practice solving for a relatively small number of blade instances will provide a good approximation of the real flow on the central blades in the series, as the ones on the edges are only used to provide boundary conditions resembling the real world case:


Is flying without sunglasses in daylight doable in a Cessna 172?

Definitely doable. No real protection from the sun just through the windshield but I flew a C172 for many years only using sunglasses occasionally. Just don't make the same mistake I did when I first started flying- paid a lot for a pair of polarised sunglasses then jumped in the cockpit and all the LCD screens went blank! :)


Is there something like an ignition key for planes?

The planes I have trained in (single engined Piper Cherokees/Warriors) do indeed have an ignition key, without which the magneto system (which drives the spark plugs) and the starter cannot be engaged. Without being certain, I would assume the same goes for other small GA aircraft.

When you get to airliners I have no idea whether there are keys for locking the controls - as the controls are much more complex, the keys probably won't be directly connected to ignition systems or starters, and I wouldn't be surprised if the primary security method is keeping doors locked.


The planned cruise speed was Mach 2.7 so I always assumed 2707 was a combination of Mach 2.7 and the then current Boeing 707.


The rules are slightly different in different countries, but common for all is that the "heavy" designation is used for aircraft in the heavy wake turbulence category, that is, aircraft with a maximum takeoff mass of 136 tonnes or more (see Is there a definition of light/medium/heavy aircraft?).

Some countries require aircraft to use the heavy suffix to their callsign in all radio transmissions. Others only require it on initial contact with a new ATS sector, whereas others still will additionally require it to be used at all times in the aerodrome environment, but only on initial call in the en-route environment. The local rules will be listed in the AIP for the country in question.

Also note that in some places, certain aircraft types are considered to be in the heavy category, even though their MTOM is below 136 tonnes. The typical example of this is the Boeing 757, which is put in the heavy category by some countries because it creates significantly more wake turbulence that other aircraft with similar MTOM.


Source: wikimedia.org

I would say an Armstrong Whitworth Whitley.

Somehow the uncommon nose section looks like a special variant, maybe a radar-equipped submarine hunter?


What security regulations apply to US private airstrips?

Private airports have very little security and light aircraft flying within a country typically aren't required to file a flightplan and aren't required to have transponders for secondary radar. You can get in a private aircraft and fly off pretty much as easily as you can get in a car and drive off.

Private aircraft crossing international borders are subject to much stricter requirements. In the case of flights from mexico to the USA they will be required to have a transponder, to file details of the flight with the authorities in advance, to land at the first available airport of entry and to maintain a certain altitude so they remain visible on radar. At the airport of entry CBP (customs and border protection) will gather will check passports/visas, gather customs declarations and may inspect the plane. If you want to know the gory details take a look at http://www.cadds.com/bcpilots/docs/CrossBorderManual.pdf .

There is a section of airspace surrounding the USA and Canada called the North American ADIZ. All aircraft in that zone are required to identify themselves. If an aircraft is spotted in the ADIZ cannot be identified then it may be intercepted by fighter jets.

But a small plane flying low with the transponder turned off is pretty hard to keep track of on radar and if the criminal can slip undetected through the ADIZ he can easily find a quiet private airstrip to land at.


How does the Pratt & Whitney Canada PT6 differ from other turboprop engines?

Split Shaft

Several turboprop engines, including the PT6 turboprop engine, use an epicyclic gearbox only, many other turboprop engines use a multishaft gearbox. The latter usually results in the propeller axis being offset from the turbine axis.

In common with some other engines, the PT6 turbine is also reversed. This facilitates the split-shaft arrangement where the engine and propeller are driven by separate (but in-line) shafts, each connected to their own turbine wheel.

PT6

Image: P&W

Image:12Charlie

A contrasting and common design

Image:12Charlie


Why does the CRJ100/200’s FMS miscalculate temperatures at altitudes in excess of 36k feet?

The reason is that the tropopause is at 11 km (36 089 ft) in the International Standard Atmosphere. At the tropopause, the temperature lapse rate of the atmosphere (how temperature changes with altitude) has an abrupt change: the ISA value is -6.5°C / km (-1.98°C / 1000 ft) below and then suddenly changes to 0°C / km (meaning temperature suddenly stays constant).
The FMS probably converts SAT to ISA deviation based on a fixed lapse rate of -1.98°C / 1000 ft, which means the conversion is wrong above that altitude. Only a Bombardier engineer (or someone involved in the Collins FMS used on the CRJ) could tell you the exact reason why. Based on John K's comment, it seems to have been fixed after the accident.
Note that the actual tropopause altitude can vary (usually between 9 km at the poles and 17 km at the equator).


Does the aerodynamic center always have to lie on the chord line?

No, there is no reason why aerodynamic center (AC) have to lie on the chord line. As the OP correctly pointed out, Thin Airfoil Theory (TAT) result indicates that the AC:

Exists, and
Lies on the chord line 1/4c away from the leading edge.

However, this is only because the TAT makes the fundamental assumptions that the airfoil is thin, the mean deviation of the camberline is small relative to the chord, and small free-stream incidence (AOA). As shown in the diagram below, the vortex sheet is assumed to lie on the chord line instead of the mean camber line. (I should mention, however, that the slope of the mean camber line is accounted for in the theory to construct the tangent boundary condition on the airfoil). And, of course, TAT doesn't account for drag.

(Diagram cited from Anderson, Fundamentals of Aerodynamics.)

The vertical offset is small, however, at least until the drag rise associated with flow separation or when flow incidence becomes large. If there is a large vertical separation between the center of pressure and the chord, then AC will not exist and this manifests as nonlinearity in the Cm curve.

I've included the pitching moment coefficient about 1/4 chord of NACA0010, Clark Y and NLF(1)-0115 analyzed with Airfoil Tools, which were analyzed with xfoil using panel method + boundary layer equations. The plots included Reynolds number of 500,000 and 1,000,000 with Ncrit transition of 5 and 9. Note that AC exists locally where Cm has a constant slope.

For NACA 0010, AC exists up to 10 deg AOA at 1/4c; near stall, the drag rise occurs and the Cm becomes nonlinear. For Clark Y and the NLF, the AC is pretty close to 1/4 for small AOA, then shifts to a point further aft until drag rise.

Therefore, while the concept of AC is useful for theoretical derivation of stability relationships in linear aerodynamics, it's not a good enough for precise modeling. In engineering modeling, we generally measure the pitching moment (from wind tunnel) at 1/4c, and account it as a function of AOA.


What's the name for the structure that helps stop the nose wheel in Boeing 747-400?

They are called Snubbers or scuff plates. Spinning tires rub against them on retraction.


Should I switch the transponder to STBY or not while changing codes?

The FAA started advocating not selecting standby for code changes after it was found that more often than one would expect, the transponder doesn't always come back on after standby.  Seems they uncovered a number of switch failures.

I figure that someone decided that for TCAS it was better to have a transponder squawking any code than not squawking.  But that is my own conjecture.

So for quite a few years the guidance has been to not turn to standby when selecting codes.

I have had the folks at Flight Safety lecture me after sim sessions, with pretty much the same story.

So I now teach students to just switch the codes, and not standby the transponder.  And I suggest caution when dialing through "7xxx" although controllers I have talked to say it's not a big deal.

So the idea is to keep the transponder squawking, even though numbers are being changed.  There is continuity in that they will continue to have returns while you are playing with the knobs. And if you ever have a switch failure, it will likely be on the ground.

Addendum: Also, with ADS-B, one is supposed to keep the transponder on at all times, when on the airport surface in a movement area. So I can see that the philosophy of managing the standby position will continue to change.

Also note that Bob Gardner's book was from the mid-1990's and things change. Both the transponder technology, the technology, such as ADS-B, TCAS (which also relies on transponders, as well as processing algorithms, which decide how to display transitioning codes.


At what point are the pilots allowed to communicate with the ground crew whilst they are still in the cockpit?

no longer under their control

is a strange phrasing, the aircraft has to stop sooner or later, do you define a parked aircraft "not under the pilot's control"?

I'm saying that the ground crew does not generally connect the external "headphones" while the engine is used to power the aircraft, the connector is near the nose gear well and the cable is generally not overly long, to avoid the grond crew from being ingested by the engine, they generally wait until it is safe.


What do the radiation patterns of ADS-B transmissions on large airliners tend to look like?

In airliners, like in most aircraft, the ADS-B transmission come from the ATC radar transponder. The transponders in aircraft with an Maximum Takeoff Mass exceeding 5700kg /12500 lbs are required to have antenna diversity. This means that the aircraft will have a top and a bottom antenna connected to the transponder.

ADS-B transmissions are sent out of either the top or bottom antenna, the selection of which should be random with a 50-50 distribution.

Radar and TCAS replies are sent out the antenna on which the incoming interrogation was strongest.

The antennas are vertically polarised and have an approximately omnidirectional radiation pattern in the horizontal plane. In the vertical plane, most radiation energy will be focused 45 degrees around the horizon. They have a cone of silence.

The aircraft structure blocks and reflects part of the radiated energy. This is causing the far field pattern to be not uniform and varies from aircraft to aircraft. On the lower antenna the main effect is of the fuselage and the engines. On the top antenna the fuselage, the tail and the wings/winglets are the main obstacles.

On small aircraft this is more of a problem, especially when the transponder antenna is between large fixed gear struts.

This study contains an antenna pattern of the top antenna of an aircraft


Why is the circulation around a centrifugal impeller blade tip the opposite to a wing tip?

I think what's confusing you is that the text book is using the term circulation to describe speed relative to the average airflow, not actual circulation around the blade.

There's still a black arrow pointing outwards on the high pressure side of the blade - no air is travelling inwards.

However if you look at the difference between actual speed and the average speed, it's negative on the high pressure side and positive on the low pressure side.

I don't fully understand the theory, but I think you're supposed to imagine the surface of the aerofoil (or an infinitely thin layer of air next to it) to be circulating, and causing the velocity gradients.

Wikipedia says:

Circulation is often used in computational fluid dynamics as an intermediate variable to calculate forces on an airfoil or other body.


What's the inspection/repair procedure following damage from severe hail?

They would have to work from the nose back to ensure there was no other damage but the first thing they would look at is the nose its self. As mentioned that cone is not metal as it houses the aircrafts weather radar behind it. Specifically a Honeywell unit like this one. By the looks of it the element was damaged and most likely needs replacing. From there you would come to the forward pressure bulkhead which, considering the damage would need to be closely inspected. Here is a pic of one from a Boeing for reference.

Degraded or improperly fixed bulkheads have lead to issues in the past. While this is happening they will also work on the windshield and check the struts around it for damage. They would also look over all forward facing surfaces, just a guess but they would check the wings leading edges for damage, engines, leading edges of the horizontal and vertical stabilizer as well as whole airframe for possible damage along its axis'. The question of will the plane ever fly again is more a question of cost than mechanical issues. For what its worth just about anything can be fixed, if and airline will fix it mainly depends on if its cheaper to fix or simply buy a new plane.


When taking passengers, what should I do to prepare them?

I go through the SAFETY checklist with all my passengers.  The FAA recommends this as well.

Seat Belts - This is where they are and how to use them.
Air Vents - Here are the air vents and how to use them
Fire - In case of a fire here is the location of the fire extinguisher and this is how you use it. PASS method.
Exits, Emergencies and Equipment - Here are the exits on the airplane and here is how to open the door.  Know that you are in good hands and that I have been well trained to land safely under most situations.  If for some reason an emergency occurs in flight follow my directions.  If we need to land off the airport, I will ask you to pop open the door just before landing to ensure we can exit the airplane safely.  Here is any safety equipment that you may want to use on this flight. i.e. supplemental oxygen.
Traffic and talking - Please point out an traffic that you see and I will do the same.  Please no talking while I am on the radio.  Once we start taxiing to the runway please remain quiet til we are far enough away from the airport.  I will let you know when it is safe to talk again.  When we come in to land, I will ask that you remain quiet, unless an emergency situation occurs, till after the landing is complete and we are taxiing back to parking.
Your questions - Do you have any questions?  Alright, lets go have some fun!


Is the differential between the forward and aft CG limits indicative of the overall stability of an airplane?

Normally, the aft limit is governed by static stability, while the forward limit is governed by the elevator control capacity (but sometimes, dynamic stability: excessive static stability may cause oscillations).

So, a narrow CG range would rather suggest that the elevator and/or trim capacity is not sufficient to cope with the more forward CG.

However, in practice there may be other reasons for restricting the range. For example, it may simply be impossible to load the aircraft (without exceeding the station load limits) in such a way as to put CG out of the defined range. I think C152 is close to that. Or, say, the stall or spin characteristics are unsatisfactory, so the aft limit may be restricted further than what normal stability dictates.

Needless to say, artificial stability augmentation (including FBW) may broaden the CG range, primarily by affording a more relaxed aft limit.


What are the BUGS and RST buttons on the A320's ISIS for?

The RST button is the attitude reset (note the ATT next to the button) function. The ISIS contains an attitude gyro that has to be re-aligned periodically.

Credit: Smartcockpit.com

The BUGS button enables the BUGS function, which allows the crew to enter speed and altitude bugs on the display. The bugs are a visual identifier to aid the crew in maintaining a speed or altitude.

Credit: Smartcockpit.com


How do I fix a slipping throttle friction lock in my C182?

I suspect there is only one sensible answer to this, and that is to have a qualified mechanic check/replace as necessary.
To continue flying in the meanwhile I would add a check for throttle friction to my FREDA check which you probably already do every 6-10 minutes during cruise.


What is the difference between EPE and HUL on the Satellite Status Page of GNS systems?

EPE is the 1-sigma error level and thus represents the position error circle with a 68% confidence level. Reference: NPS


What happens if the crew do not set a FLT ALT in the cabin pressurization panel and leave it at zero but AUTO is still selected?

Consider a similar scenario: the crew selected 28,000 feet, cruised at 28,000 feet, but then step-climbed to 34,000 feet without selecting the higher altitude for pressurization.
The crew operating manual makes no mention of either scenario, unless you read between the lines. The way I tackled those scenarios is by referring to the controller logic in the manufacturer's patent from 1981 (the same digital controller was optional on the 737 Classic):

When the cruise altitude controller senses that the aircraft altitude change is within selected limits [when approx. 1,000 feet below FLT ALT], the system clamps to a scheduled value of cabin altitude [see second note below] (...)
If the aircraft cruise altitude drifts sufficiently to exceed ±500 feet from the altitude at which cruise control was imposed, the cabin altitude simply unclamps and the cabin climbs or descends at a predetermined rate under the control of central processing unit 54. (...)
Central processing unit 54 computes the differences between the pressure altitude and the value of Hcruise-clamp once per minute. If that difference exceeds the predetermined valve Hcruise-clamp is assigned the value of the pressure altitude.

Based on that, after leaving the ground mode (or lower cruising altitude), the controller will still pressurize the cabin – but not in reference to the DP schedule when cruise is reached (see second note below).
During descent (based on both the crew operating manual and patent), the controller will engage the off-schedule descent mode – landing altitude being the same as the departure airport altitude that was automatically sensed and set in ground mode – the crew will be alerted to that.

Notes:

In newer planes the pressurization controller is simply fed this data from the FMS (CDU or MCP entry).
Unlike other jetliners that maintain a cabin altitude with varying differential pressure (DP) for comfort, the 737 maintains a DP based on altitude blocks (consistent structural loads) when the FLT ALT is set. If you don't have the manual, b737.org.uk covers that part and offers a good system description.


Angle of attack difference between outer wing and inner wing during a descending turn and climbing turn

Here's one way-- not the only way-- to look at the dynamics involved--

Imagine an aircraft in a 45-degree-banked constant-altitude turn.  Now imagine that the pilot gradually adds more and more power and the aircraft gradually enters a steeper and steeper climb until it is climbing almost straight up.  Can you see how to maintain a constant bank angle, the aircraft must actually roll toward the high wingtip?  As the climb angle gets steeper, the maneuver gets closer and closer to resembling a vertical rolling climb, with the direction of roll being toward the wingtip that was originally the high wingtip in the constant-altitude turn.

"Fly" through the maneuver with your hand or with a little hand-held model airplane until you understand this.

(Like this-- https://vimeo.com/128025851#t=157s -- video intentionally starts at 2:37)

Now, can you see how a rolling motion always tends to increase the angle-of-attack of the descending wingtip, and to decrease the angle-of-attack of the rising wingtip?  As the descending wingtip comes down through the airmass, the local relative wind blows "up from below" compared to the local relative wind closer to the aircraft centerline-- this is an increase in angle-of-attack.  Similarly, as the rising wingtip moves up through the airmass, the local relative wind blows "down from above", or at least blows up from below at a shallower angle than the local relative wind closer to the aircraft centerline.  This is a decrease in angle-of-attack. These changes in angle-of-attack create an effect known as "roll damping"-- a resistance to rolling.  This is why the roll rate doesn't just keep getting faster and faster as long as we hold the ailerons in a deflected position.

So that's the answer to your question. In a constant-banked climbing turn, the aircraft is continually rolling toward the high wingtip, so the high wingtip experiences an increase in angle-of-attack and the low wingtip experiences a decrease in angle-of-attack.

Note that while our thought experiment involved a continual increase in climb angle and climb rate, the basic dynamics we're talking about are present even in a climb at constant angle and rate. In a climbing turn, an aircraft must continually roll toward the high wingtip to hold the bank angle constant.  Otherwise the bank angle will increase.  It's not a matter of aerodynamics, but rather of three-dimensional geometry.

In a descending turn, everything is the same except that to keep the bank angle constant, the direction of roll must be toward the LOW wingtip, so the low wingtip experiences an increase in angle-of-attack and the high wingtip experiences a decrease in angle-of-attack.

"Fly" through the descending turn case with your hand or a little hand-held model airplane until you understand that the extreme case of a constant-bank descending turn is a vertical rolling spiral, with the direction of roll being toward the wingtip that was originally the low wingtip when the plane was turning with a constant altitude or with a less-than-vertical dive angle.

(Like this-- https://vimeo.com/128025851#t=128s -- video intentionally starts at 2:08)

As a footnote, you can see how aerodynamic "damping" in roll -- the tendency for the roll rate to decrease-- exerts a destabilizing influence in a climbing turn, tending to make the bank angle increase.  In a descending turn, aerodynamic "damping" in roll tends to make the bank angle decrease.  This is very noticeable in some applications, such as powered hang gliders and trikes.

As another footnote, understand that we are speaking of "ascending" and "descending" relative to the surrounding airmass-- an unpowered glider spiralling up in a thermal updraft is still in a "descending" turn for the purposes of this discussion.

As yet another footnote, we can observe that it is easy to see how the bank angle can change when we pitch up with zero roll rate, in some version of a chandelle or wingover for example. It is harder to see how bank angle can be constant and roll rate can be non-zero in a climbing or diving turn, but it's true, as illustrated in the video links given above.  Again, it's fundamentally a matter of 3-dimensional geometry, not aerodynamics.

In closing, here is a link to a diagram from John S. Dencker's "See How it Flies Website" that illustrates how a rolling motion creates a difference in angle-of-attack between the two wingtips.  The diagram is not dealing specifically with the constant-bank case, and also it is really aimed at explaining "adverse yaw" which is a separate issue, but it still may be helpful-- https://www.av8n.com/how/htm/yaw.html#sec-adverse-yaw


What is "settling with power" and how does it differ from vortex ring state?

I knew that the debate would start :)  This is probably the most contentious question in helicopter operations.  it's right up there with the "equal transit time" theory of lift generation a few years back.  The only agency I am aware of that defines them as different is Transport Canada.  Instructors, pilots, WikiPedia, training videos, books and blogs all get this wrong often. It seems to be very common in the US for people to refer to vortex ring state as "settling with power".

Tom, I know you said you already know what vortex ring state but I think that the "why are they different" explanation is better when both are contrasted together. Please excuse me for repetition.

They are different.

Vortex ring state (VRS).

VRS ring state is a purely aerodynamic condition. In normal flight, whether climbing, descending or cruising, the relative airflow striking the blades is principally from ahead.  In a developed VRS, the helicopter descends into it's own vortex which is "recirculated" as the helicopter descends faster than the vortex descends and results in the recirculated air being drawn up, then almost vertically down into the rotor.

From HelicopterEMS.com

This causes a critical increase in the angle of attack and a corresponding loss of lift causing the helicopter to descend faster and faster up to rates of 6000 feet per minute.

In order for the helicopter to descend into its own vortex, it must meet three conditions at the same time (typical values for most helicopters):

  less than 30 knots airspeed;
  greater than 300 feet per minute descent;
  power applied to the rotor.

Removing anyone of these gets you out of VRS but there's a catch.  If you try to reduce the rate of descent by increasing collective and therefore power, which would be the instinctive reaction of someone not trained to recognise and get out of the state, you increase the strength of the vortex and the recirculation and make the problem worse.

The only way to stop the rate of descent in VRS is to use the ground, which you really don't want to do at up to 6000 feet per minute and will probably spoil your plans for the weekend.  However, you DO have power.  You can use all of it until you hit the limits and still you won't stop that descent.

To recover, remove power by entering auto-rotation or increase airspeed to fly out of the vortex.  Auto-rotating out of VRS can take a long time and use a lot of height in the recovery so the accepted and taught technique is to fly out of it, any direction will do, which takes a second or two to recover.

Settling With Power (SWP)

SWP is not an aerodynamic effect.

At it's simplest, it occurs when you need x amount of power to stop a descent but, for a lot of variable reasons, you have less than x power available.  Increasing power results either in exceeding the engine or power train limits or stalling the rotor as drag increase exponentially and exceeds the power available to drive the rotor.

The slower a helicopter flies, the more power it requires:

From the AOPA blog.

When you get into the low speed regime, you can see that the power required rises rapidly.

Imagine you are coming into a hover.  You are travelling slowly at about 20 knots but have a low rate of descent, not enough to enter VRS.  If you keep going forward, you will be OK.  But, our imaginary pilot makes a mistake and turns into a 15 knot tailwind. The airspeed drops to about 5 knots so the lift produced drops by the square of the speed change and the power required rises rapidly.

The helicopter will very quickly develop a high rate of descent. The pilot increases collective to compensate but finds that the engine cannot produce enough power to maintain lift and power the tail rotor which is also working harder since you increase the torque by increasing power.  It is possible to simply run out of power.  If the pilot is lucky, they will be unconscious and found with the collective lever buried in their armpit.

SWP nearly always happens close to the ground and once in it, there is no recovery (insert suitably large number like 99% of the time).  You have no spare power to reduce the rate of descent or to increase airspeed to increase lift and fly away.

SWP is normally a result of pilot error (as above), mechanical problem leading to unexpected reduction in power available, wind shear causing unexpected reduction in airspeed or other environmental effects reducing lift available (coming into a hot and high hover for example).

Perhaps the easiest distinction to make is that you are already using all of your available power when you enter SWP. There is nothing left to give!


Can radars detect all planes, including military ones?

Some military aircraft reflect little enough radar energy to be effectively undetectable. Note that the actual details are likely classified, but even the modern F-22 still has a radar cross-section of about the size of a steel marble. Still, the B-2, an older stealth aircraft, is claimed to disappear from air traffic radar when in stealth mode.

The same article on the B-2 also notes that it has "deployable radio antennas for navigation in civilian skies". When flying during peacetime and outside of an MOA, military aircraft generally have some level of coordination with ATC. If the pilots of a stealth aircraft don't want to be seen, then presumably they would be responsible for maintaining separation from other aircraft, as they cannot be tracked on radar. Of course, there's also plenty of airspace where aircraft don't need to talk to ATC at all (E and G in the US), and the pilot of each aircraft is responsible for maintaining separation.

That said, there are some things in this article that are unclear:

The Etihad aircraft received a TCAS alert for an aircraft that didn't show up for ATC. TCAS intentionally uses the same frequencies and signalling as ground-based secondary radar, so if an aircraft receives a TCAS response it should also show up for ATC. The article does note that the aircraft were "450 to 480km from Mumbai's coastline", so it's possible that the mystery aircraft just had a weaker TCAS response that wasn't received by a distant ground-based receiver.
The article suggests that fighter aircraft don't fly as high as 36,500 feet. A ground attack aircraft might not be able to fly that high, but most, if not all, air superiority fighters have service ceilings of at least 50,000 feet.


Is it an overkill to request to see airplane maintenance logs at a new flight school?

I'd refer to FAR 91.3(a):

  The pilot in command of an aircraft is directly responsible for and is the final authority as to the operation of that aircraft.

Therefore, I believe you have a duty to determine that the aircraft is properly maintained.   While that doesn't mean disassembling it and checking the work yourself, I do think that its reasonable to verify that the maintenance logs have recent entries, and appear orderly.

At my old flight school, I never got any grief at all (and occasional complements) when I wanted to see the logs for some reason.

If they give you so much as an eye-roll when you ask to see the logs, that should be a cautionary sign.

I think it is also an easy way to meet the maintenance guys, and be introduced to them as a careful, thoughtful pilot.  (The Mx guys likely despise "cowboy" pilots who bring back damaged equipment, and don't report it.)  You'll get to know some people at the new school, and get a reputation right off the bat.


Is it legal for pilots to transport or use marijuana?

Is it legal for pilots to transport marijuana within states that have legalized it?

This I'm not sure about. I can't find any FAA regulation or guideline on it, so I think it would depend more on specific state statutes. The problem would lie in going over state lines, obviously, but intra-state transport is unclear. If you were ramp-checked by an FAA inspector and had marijuana on board, they would probably require you to get a drug test, and if failed (according to the next part of this question) you would lose your license (actually your medical, you would keep the license but be unable to use it). So it may be legal to transport it, but you certainly can't be the one using it.

  Can pilots use marijuana recreationally if their state allows it? Are there implications for medicals?

Negative. AME's have marijuana on the DNF/DNI (do not fly/do not issue) list:

  Controlled Substances (Schedules I - V). An open prescription for chronic or intermittent use of any drug or substance.
  This includes medical marijuana, even if legally allowed or prescribed under state law.

While the guidance just says medical marijuana, I would suppose that it includes legal recreational marijuana as well.

Since you would be using a controlled substance on the DNF list, you would not be eligible for flying under the BasicMed either:

  A diagnosis or medical history of substance dependence is disqualifying unless there is established clinical evidence, satisfactory to the Federal Air Surgeon, of recovery, including sustained total abstinence from the substance(s) for not less than the preceding 2 years. A history of substance abuse within the preceding 2 years is disqualifying. Substance includes alcohol and other drugs (i.e., PCP, sedatives and hypnotics, anxiolytics, marijuana, cocaine, opioids, amphetamines, hallucinogens, and other psychoactive drugs or chemicals)

Another way to look at it: Since pilots licenses are issued by a Federal authority, the Federal rules apply. According to Federal laws, marijuana is illegal and your license (or medical) is not valid even if the state you are in allows it legally. Marijuana is still a Schedule 1 substance (on the same level Federally with Heroin and LSD).


Why don’t aircraft have interlocks to prevent high-lift devices from being retracted when doing so would stall the airplane?

Most modern airliners have some form or other of mechanism that does exactly that, mostly for the slats (which are more important in stall prevention, anyway).

E.g. on modern Airbusses, there is a Slat Alpha Lock function which prevents slat retraction at high angles of attack, on the Boeings there is a Slat Auto-Gap function extending slats from mid to gapped position at high angles of attack.

Military aircraft often have automatic slat deployment to aid with high angle of attack manoeuvres, and even some vintage aircraft did have aerodynamically activated slat-like devices for stall prevention.

Any sensible reference suggestions welcome for any of these... cannot post mine.


What is the fuel/air ratio of the CFM56-5A1 engine (in the A320 model)?

The ratio can be different for different phases of flight. It is easy to calculate for the Takeoff (TO) case because the required numbers are easily available:

TO Thrust: $ 25 \, 000 \, \text{lbs} $ [1]
TO TSFC (thrust specific fuel consumption): $ 0.3316 \, \text{lbs/h} $ per $ 1 \, \text{lbs} $ of thrust [2]
Airflow: $ 852 \, \text{lbs/h} $ [1]
bypass ratio: $ 6.0 : 1.0 $ [1]

The takeoff fuel flow $ \text{FF} $ is then given by

$$ \text{FF} = 25 \, 000 \times 0.3316 \, \text{lbs/h} \approx 8290 \, \text{lbs/h} \approx 2.30 \, \text{lbs/s} \approx 1.04 \, \text{kg/s} $$

and the airflow $ \text{AF} $ through the core is given by

$$ \text{AF} = \frac{1}{6 + 1} \times 852 \, \text{lbs/s} \approx 122 \, \text{lbs/s} \approx 55.2 \, \text{kg/s} $$

This results in a fuel/air ratio of

$$ \frac{\text{FF}}{\text{AF}} \approx \frac{1}{52.9} \approx 0.0189 $$

Sources:

[1]: www.cfm56.com
[2]: Wikipedia CFM56


How do you calculate indicated airspeed on a flight plan?

You do not calculate indicated airspeed: It is an indicated value, you read it from the airspeed indicator. (I suppose you can calculate it if you really want to, but I've got no idea why you would want to do so in the context of flight planning.)

You determine what airspeed to use for flight planning purposes using your aircraft's performance data (from the POH or other manufacturer documents): There will usually be either a chart or a table giving true airspeed as a function of power setting and density altitude.
(True Airspeed is a more useful number for planning purposes as it saves you a calculation.)

When in flight you can calculate your true airspeed based on the indicated airspeed and density altitude. You can then compare this to your planned figures from the performance charts to determine if adjustments are necessary to your flight plan (ETA, Fuel use, etc.)


Why are min and max temperatures (TN TX) not published in TAFs in the United States?

This isn't much of an explanation, but the National Weather Service says:

  The international TAF also contains forecast temperature, icing, and
  turbulence. These three elements are not included in National Weather
  Service (NWS) prepared TAFs. The U.S. has no requirement to forecast
  temperatures in an aerodrome forecast

That sounds to me like "we don't think it's worth it". There are various temperature forecasts on the NWS aviation site (icing level, surface temperatures, graphical area forecast) but personally speaking, I get low/high temperature information from regular, non-aviation forecasts. You can get those forecasts from the NWS site too, if that's what you mean by "official".


Are tail strike landings preferable for an emergency landing on water?

While there probably is an "ideal" attitude to impact water, and it would be nice to crash-land with exactly the correct attitude... it's very much a secondary consideration.

By far the most important thing, when landing on water, is to land slowly. As such, your aim should be to land (/crash) with whatever attitude gives the lowest possible ground speed/descent rate at the point of impact. If that means a "normal" flare, do a normal flare. If that means a harsher flare with a tail strike, do that instead.

The point is that you're in an emergency situation, and your biggest priority is to get the speed right: you likely don't have the luxury of trying to fine-tune your angle of impact and flare. Additionally, you always have the risk of over-flaring and stalling into the water instead, which is a worse end result.

So yes, it may - with some airframes - be beneficial to have a tail strike, but you're far better off just keeping the aircraft under the best control possible and reducing your speed as far as possible


To which airspace does the border of two adjacent airspaces belong to?

You recall correctly. That document is ICAO SARPs Annex 11 § 2.6:

  Where the ATS airspaces adjoin vertically, i.e. one above the other, flights at a common level would comply with requirements of, and be given services applicable to, the less restrictive class of airspace. In applying these criteria, Class B airspace is therefore considered less restrictive than Class A airspace; Class C airspace less restrictive than Class B airspace, etc.

(Emphasis mine.)


What sort of issues related to extreme heat (115°F, 46°C plus) would prevent takeoffs or landings?

Short Answer

Very high temperatures limit how much payload and/or fuel you can load on a plane.

Engines

To help you visualize it, in hot air the air molecules are more energetic, which means the engine will have hard time compressing hot air vs. cool air. Losing thrust.

Wings

Hot air—with the molecules spaced farther apart—has less density, which reduces the lift capability of wings.

Hot and High

Vegas is not only hot, but also high, which means the air pressure is already less than at sea-level.

Each plane has its own performance charts, and on each flight, the flight dispatcher and crew make sure the weather, elevation, etc., would allow a safe take-off and climb.

A plane is configurable for such changing elements. For example using higher thrust setting, or more flaps to augment the lift.

If you have a very heavy plane, hot and high situation, and a short runway, then things become very marginal—

Engine Out

—not just for the take-off run, but also in case of an engine out during take-off, i.e., losing an engine. The plane still has to be able to climb.

That's why in places like Ethiopia, South Africa, Australia, etc., airlines preferred1 quad-jet planes over twin-jet planes. To have bigger margin of safety in hot and/or high operations, i.e., to be allowed to carry heavier loads.

1 When tri/quad-jets were commonly offered alongside ETOPS twin-jets of same class.

Example of Impact

(Map generated using Great Circle Mapper)

A cargo MD-11 plane taking off from Ethiopia en-route to Europe can't take off fully fueled, and has to stop in Cairo for a re-fuel. Note that if Ethiopia were at sea-level or cooler, a direct flight would have been possible.

Landing

For landing in a hot and/or high airport, the landing speed will be higher, so what matters is the runway length available for landing. Again there are performance tables for that.

Rest assured, those things are checked and double checked. And no one can tamper with reported weather, because it is very critical to flight safety.

Also, planes do have their own temperature sensors. Newer planes can even alert the crew if the gross-weight, configuration, runway length, temperature, and elevation combo isn't sufficient.


Can a pilot transition from a localizer approach to an ILS approach?

You can't legally switch from the LOC to ILS approach without ATC approval in this case, since they are different enough and are on different plates. However, if you're outside the FAF you can ask ATC to switch from LOC to ILS, and proceed with the ILS if approved. However, in lost comms, if you got initial approval for the LOC approach but no mentions of ILS, you can't switch to the ILS. Unless you exercise your emergency authority.


What is the available range for DME, and why do we need EFC?

How can DME signal go from the station?

Your aircraft's DME sends a signal (when tuned to an appropriate frequency) to the ground station (suitably equipped with DME, e.g. Vortac, ILS/DME, etc.) and the station sends back an electronic reply. The aircraft's DME will measure how much time it took for the signal to travel to/from the station and translate that into a distance (in slant range).  Here is a good article explaining DME:

If you are asking what the maximum distance between the station (e.g. Vortac/VOR/DME, etc.) and the DME equipped airplane can be for a reliable DME signal, it's 199 NM (slant range).  Of course this depends on aircraft altitude and a few other variables.

See this excerpt from the Aeronautical Information Manual for more information:

DME Article from AVWeb

  why do we need EFC?

This answer pertains to EFC, meaning "Expect Further Clearance" time, route, altitude: (U.S)

If you are flying IFR and are given holding instructions (for example) you will be given an EFC time by ATC.  This is given to you in case of lost communications.  If you loose communications with ATC you are expected to continue with your originally planned, revised, or route/approach you were told to expect by ATC at your EFC  time.

There are other occasions that you may receive an EFC from ATC.  For example, you may be taken off of a previously assigned route, and ATC might say (for example) "N12345 turn right heading 230, vector for traffic, expect direct to Omaha in five miles."  If you lost communications with ATC, then five miles from the point of the vector you should go direct to Omaha.

Or, another example might be if you are told by ATC to "maintain Flight Level 270, expect Flight Level 350 in four minutes."  If you lost communications you would be expected to have maintained Flight Level 270 and, 4 minutes after receiving this instruction, begin your climb to Flight Level 350.

Since your question was not entirely clear regarding EFC, I included 3 different occasions that your might receive an "Expect Further Clearance" from ATC.

As a note, the actual ATC phraseology (generally speaking) where the 3 words "Expect Further Clearance" would be spoken would apply to a routing, or holding clearance (or a short term clearance to a fix/clearance limit other than an airport, with or without holding instructions). But the word "Expect," when used with regard to a route or altitude (such as "Expect Flight Level 350 in four minutes" or "Expect" direct to Omaha in five miles" is implied to be an "Expect Further Clearance." (EFC)

Finally, as noted above, EFC is directly associated with lost communication with ATC.  If you read the Federal Aviation Regulations, (FAR 91.185) you will have a better understanding of how the "Expect Further Clearance" procedures apply.


What is a minimal step angle deflection for flight control surfaces?

There are several phenomena that may affect the asked resolution. The easier one is the static (steady case), and the dynamic case which requires several more analyses.

Statically, the resolution of any surface will determine the moments that that particular surface can generate. Consider the elevator, the resolution will determine which aoa and which speeds the aircraft will be able to fly (with a given weight and a given thrust configuration).

Dynamically, the stability of the plane will derive the required resolution. Consider the elevator, and suppose your resolution is 1 degrees. The inputs will generate short period and long period (phugoid) modes simultaneously and your controller will become a bang-bang controller, because you can only command increments (decrements) of 1.

Hope these give some clues to understand the physics. For more details, control theory will be useful.


Do modern airliners have oxygen sensors in the cabin?

While it would not significantly affect the O₂ percentage one thing that must be tabulated on a cargo aircraft is the amount of dry ice loaded. Dry ice is very common in packaging to keep perishable shipments cool during transport. Since dry ice sublimates into gaseous CO₂ as it warms there is a limit to how much can be loaded into an aircraft. If there is too much there's a possibility that the pilots could be overcome by gas trapped inside the plane. It's a rather insidious threat because you can't smell it so you would only realize something was wrong when you started feeling physiological effects.

An O₂ sensor would not help since pilots would be overcome long before it made any detectable difference in O₂ levels. AFAIK there are no sensors for CO₂ either. The amount of dry ice loaded is carefully tabulated and pilots who fly cargo containing dry ice are aware of the possible hazard and how to recognize symptoms of CO₂ poisoning.


Why is the Antonov 225 (almost) always chocked at the third wheel?

It's a matter of procedure.  Chocking a center wheel provides the greatest defence in the unlikely case the chock is jumped.  Other wheels in the truck must also contend.  If an outside wheel is chocked and that chock is jumped away, all is lost.

No matter tipping or rocking the aircraft in extraordinary winds or loading, the center of a wheel truck is the recommended place to chock.  A chock should be snug against both sides of a single tire to prevent any sway.

Most chocks are paired together by a rope or chain which would prohibit chocking around a large truck of wheels as described in your bonus question.  What's more, chocking at either end of a truck allows more elasticity and movement between the chocks than a single wheel chocked snug.


What are the forces acting on an air particle along curved streamline(wing upper surface)?

In the inertial frame of the free airstream, the pressure force causes the particle to accelerate inwards. Centrifugal and centripetal forces do not play a direct role; there is no space station wall for centrifugal force to be exerted on, nor to exert a reactive centripetal force. The pressure force acts in the role of the centripetal force shown in the astronaut diagrams. The balancing reactive force is instead another pressure force, which acts on the airfoil where it is known as lift.

In the rotating frame of the air particle, inertial centrifugal force does come into play. The particle must by definition remain stationary within its reference frame, so all forces on it must now balance. The pressure force is thus balanced by the inertial centrifugal force. The airfoil lift no longer plays a direct role within this reference frame (having helped to create it).


Why can’t we perform CONFIG 1+F Takeoff in the following conditions as per the MEL?

First of all SFCC1 regulates the engines idle, lo or hi, according to the Flaps/slats configuration, for instance to provide low idle at initial descent

Also SFCC1 uses the blue hydraulic circuit for Slats, in hydraulic emergency case, only blue might be available as being generated by the RAT
  therefore SFCC1 fault is a no go, SO I assume at takeoff SFCC1 is available

SFCC1 uses primary ADIRU1 so if ADIRU1 is also faulty we go into a no go condition

Now if ADIRU2 is faulty, SFCC1 should rely on a single airspeed data, therefore if the speed is incorrect premature automatic retraction of the flaps might occur at takeoff, that is going from 1+F to 1 automatically, so take off with configuration 1+F is prohibited with these faults at takeoff


Why don't planes have a reverse propeller as air brakes?

Planes with a variable pitch propeller can have a pitch range which twists the blades such that they provide reverse thrust. This started to become a common feature on high-performance airplanes in the 1930s.

Not all variable-pitch propellers can produce reverse thrust, however. The constant speed props on small propeller aircraft usually don't, because the energy of the plane after touchdown would be too small to justify the added complexity. On big airplanes which need short landing distances (the C-130, for example), they are a standard feature.

In 1936, Heinkel produced a sleek dive-bomber, complete with retractable landing gear and a reversible pitch propeller which could be used as a dive brake. The He-118 was test-flown by Ernst Udet, who did not pay attention at the briefing and went on to overspeed the airplane in a dive, destroying the prototype in the process. Thus, the clumsy, fixed-gear Ju-87 was chosen to be the "Stuka" and the He-118 would end as an inspiration for Japanese aircraft designers.

The Pilatus PC-6 Turbo Porter is a favorite with skydivers because it can put the propeller into reverse even in flight. This allows for spectacular descents and enables it to be safely back on the ground before the skydivers it dropped a moment before have landed.

As usual, Wikipedia covers the topic well, so here ist the link.


What is the purpose of a USB port in the cockpit?

Some Flight Management System databases are updated via USB stick and require a USB port. Since navigational databases are updated frequently and require a simple way to make an update, USB (or memory card slots) are generally used to allow for rapid and easy updates without having to remove any panels. In some cases the port may be in the avionics bay however that is usually easily accessed as well. It should be noted that a recent change in regulation now allows pilots to update nav data, this question covers it well.

  Was it really intended for charging devices like phones? That seems
  naively insecure.

Generally these ports are not for charging but the basic design of a USB port more or less always allows you to charge from it because of the nature of the port. The security on the ports is more about cockpit security. In most cases the security lies in making it difficult to get into the cockpit in the first place. It is often assumed now that if you are in the cockpit you should be there. There is of course many questions this opens up some of which have been answered here or would be good to ask about.

As iPads become more common in the cockpit for navigation and the such USB ports are becoming more commonplace on panels for charging but this seems to be more common in GA planes currently.


Is it possible to hear a sonic boom when the aircraft is exactly at Mach one?

No, if standard atmospheric conditions apply.

Since speed of sound is proportional to temperature and temperature normally decreases with altitude, the speed of the aircraft at Mach 1 is subsonic in warmer, lower air. This means also that the Mach shock will diffuse and be audible on the ground either as a protracted rumble or not at all, depending on the aircraft's altitude.

Note that I assumed that the listener is located below the flight path of the aircraft. If that would not be the case, the noise of the aircraft diving below the listener altitude would be substantial.


How can I find out if there's an EASA STC for something that has an FAA STC?

Unless I am reading the document incorrectly, EASA and the FAA have a reciprocity agreement since 2011 recognizing each other's findings and approvals. That means an FAA STC approval is good in EASA countries (except the ones that are not EU members) and vice-versa.


Was this an unusual landing sequence for an airliner?

Why do you think the flight "should" take 90 minutes?
You really mean it was listed for 90 minutes on the schedule.
Airlines almost always pad their scheduled times so that their on-time arrivals stats are favorable, and to account for normally expected delays.

Scheduled time is also typically measured "gate-to-gate", while most passengers only observe the flight-time (takeoff-to-landing)

I see the distance is 350 miles, and would probably take a 737 about 60 minutes of actual flight time.  So I don't think your flight was speeding or otherwise behaving abnormally.


How do the uninterrupted and interrupted flaps compare?

The two designs are indeed based on compromises.

Earlier Boeings were designed for high-Mach cruise, which means high sweep and the need for elaborate flaps when flying at approach speeds. The 'thrust gate' reduces the thrust/flap interference and drag, especially in a go-around. It is also a good choice when more powerful engines will be offered as the MTOW increases.

Since the A320, Airbus have used high-lift planform layouts, which allow the continuous single-slotted flaps to work. An A380's approach speed is slower than a 747 or a 737, despite having single-slotted flaps. Owing to its high-lift wing.

When Airbus designed the A330/A340, it helped that they launched the bigger variants first. A targeted (tailored) design is not good when the aircraft would later be stretched, which would require a re-design of the flaps, i.e., if the shorter variant comes first, then 'over-designing' the flaps and having a thrust gate is a good choice.

Interestingly for the A350-1000 (a stretch of the -900), Airbus had to increase the wing area by 4% by modifying the wing trailing edge to maintain the same approach speed (flightglobal.com).

Losing the gap does save weight, complexity, and by extension, maintenance. But the limitations are:

Slower cruise speeds (not a problem since it's by design, flaps follow wing).
Thinner spoilers due to thicker flaps, they have to be made stronger.
Must demonstrate controllability during a go-around.
When stretching a variant, a flap redesign will be needed (ala A350).
Limits the flap span to allow for the innermost aileron to be inboard enough to not cause aileron reversal (lots of wind-tunnel and CFD models help fine tune this).

Own work based on scaled drawings from boeing.com and airbus.com.

Comparing the wings of the A330-200 and 777-200(ER):

The maximum operating Mach numbers (MMO) are 0.86 (A330) and 0.89 (777). Note the higher sweep on the 777.
The MTOW and MLW of the 777-200ER are 55 and 31 tonnes heavier, further evidence to the higher wing loading of the 777, which would indeed need more elaborate flaps.
Keeping in mind in the development cycle, the 777 was stretched, while the A330 was shrunk.

In short:

Boeing tends to prefer higher MMO, higher MTOW, and to offer the base-variant then scale it up. All of which would benefit from the 'thrust gate' and the more elaborate flaps. The overall trend however shows Boeing going for simpler designs:

This answer is based on a publication by an Airbus engineer:

Reckzeh, Daniel. (2017). Aerodynamic Design of Airbus High-Lift Wings in a Multidisciplinary Environment.


Help in understanding this velocity triangle of a propeller

There is an obvious error in this paper. Just look at the final formula, and remember that for small angles $\tan(\phi) \sim \phi$. The formula says that if you increase $\phi$, $v_2$ decreases. Of course, the opposite happens.
By (trigonometric) definition,
$$\tan(\phi) = \frac{v_2}{v_{propeller}}$$
Therefore,
$$v_2 = v_{propeller} \cdot \tan(\phi)$$
The rest follows; the result is similar but you have multiplication instead of the fraction.
P.S. You can get a hint that this is a low quality paper by the fact that they obliviously confuse upper- and lowercase $v$ (on the picture and in the formulae). In math/science, case matters! Sometimes even the script matters.