Is Ground Direction Finding commonly used?

Yes, it is commonly used, especially in large complex airspaces.

If two VHF direction finders are installed at sufficient distance from each other, they allow the ATC system to triangulate the position of a VHF transmission. This position is then indicated on the air taffic situation display, which helps the air traffic controller to quickly correlate the transmission to the transmitting aircraft, often before the callsign has been transmitted. The controller still has to crosscheck the callsigns, but it helps to reduces workload.

Example of a VHF direction finder


What ICAO codes are reserved for TIS-B use?

In this answer I'll assume you are analysing ADS-B data on 1090 MHz, which is the defacto global standard. I am less familiar with the ADS-B on UAT (987 MHz) which is used in addition to 1090MHz in the USA, but I assume the same logic applies.

There are no ICAO addresses assigned to TIS-B targets.

If an aircraft has an ICAO-address which is detected by the surveillance sensors (e.g. Mode S radar, multilateration system) and the aircraft is not transmitting ADS-B, then a TIS-B target will be created with the ICAO 24 bit address.

If an aircraft has no ICAO-address, (i.e. it has a Mode A/C transponder / ATCRBS) and is not transmitting ADS-B, then a TIS-B target will be created with a 24 bit address that consists of the Mode A code (first 12 bits) and a unique surveillance system track number (last 12 bits). Primary radar targets are allocated a "Mode A code" of all zeros.

To determine whether you receive an ADS-B message or a TIS-B message you should start looking at the Downlink Format (DF, first 5 bits of the message) if the DF = 17, then it is an ADS-B message. If the DF = 18 then you look at the control field (CF, bits 6-8). CF = 0 and CF = 1 are ADS-B messages. CF = 2,3 & 5 are TIS-B messages. CF = 6 are ADS-R messages. CF = 4 are TIS-B / ADS-R system status messages.

The TIS-B messages contain an ICAO/Mode A Flag (IMF) bit which indicates how to interpret the 24 bit address. The location of this bits varies by message type (e.g. position, velocity) and replaces a bit in the ADS-B format that has no meaning in TIS-B.


How to increase payload capacity of plane?

I'm not sure what you mean by 'payload capacity'.  Airplanes have what's termed a 'useful load' which is the maximum combined weight of the passengers, baggage and cargo, and useable fuel.

If you wanted to increase useful load, you would have to make the airframe and all systems aboard the airplane which constitute useful load lighter.  This does have the adverse effect of making the structure weaker, lighter engines generally are less powerful so you have less thrust, and removal of mission systems reduces aircraft capability.  Manufacturers strive to address these things and improve them over time with more rigid aluminum alloys or composites for increased strength to weight ratio, higher thrust to weight ratio engines with better fuel efficiency and lighter mission systems.

How an increase in weight affects aircraft performance not only depends on how heavy the airplane is but where the center of ends up being located.  On a conventional airplane a forward CG produces better stability but requires more lift from the wings, resulting in decreased performance.  An airplane with a more aft CG offers better performance, but is more unstable, particularly during high alpha operations such as slow flight.   The maximum takeoff weight of the airplane was established during preliminary design studies and verified during flight testing so that it cannot exceed the load limits of the airframe and offer the required performance over a wide range of potential operating conditions.

Aircraft are, on occasion, approved via a Supplemental Type Certificate (STC), to increase their useful load, if the OEM or third party vendor can demonstrate that the mod can still operate safely and fulfill the regulatory requirements.

At any rate, the heavier the airplane is, the more lift it needs to fly, which means more drag, which means more thrust, which means greater fuel burn.  This is why the airlines are so miserly in issuing out the bare minimum gas to meet federal Part 121 and company SOP requirements for their flights.  The fuel saved doing this saves the company millions of dollars annually.


Why are thermal switches connected in parallel to each others?

Thermal switches, here, are indeed connected all in parallel (Fig. 17-1).

Wiring so allows to trigger the response if any of the switches closes in response to high temperature. This should allow to detect small initial fires that trigger only a single switch, or maybe a couple of them.

The switches are a simple computing machine that performs the logical disjunction.

In the same article you can see thermocouples connected sequentially (Fig 17-2). Thermocouples are not switches, they produce voltage in response to heating, and wiring two of them sequentially in the opposite directions produces the signal proportional to the temperature difference between them. The pair alerts when one thermocouple is heated significantly more than another.


Can a IFR flight plan be amended or cancelled whilst in flight?

Yes, an IFR flightplan can be cancelled at any time. The pilot simply tells ATC "cancelling my IFR flight", then it is cancelled. Depending on airspace classification, ATC may need to issue a clearance to continue as a VFR flight.
However, diverting to another destination than originally planned is not the same as cancelling a flightplan. To do so, the pilot will just inform ATC that they are diverting, and then ATC will provide an appropriate route to fly to get to the new destination. The reporting office at the new destination will, when the flight has landed, send a standard message to the original destination, stating that the flight has landed elsewhere.
Most deviations from your filed flightplan does not actually require an update of the flightplan itself. After all, the flightplan is only the plan you intend to follow at time of departure (or really, at time of filing the plan). Very few flights end up actually following their flightplan to the letter. ATC always keeps a local copy of your flight data, which is updated with any clearances given and other requests that might deviate from your original plan. If the deviation, whatever it may be, affects a downstream ATC sector, it can easily be coordinated verbally. However, if, in some rare case, you need to actually amend your flightplan while in the air, just inform ATC. The controller can either make the required changes (and send related AFTN message) directly, or get in touch with a flight data assistant that can take care of it.


What is the relation between IAS and TAS at a constant altitude?

If you divide 114/100 and 126/110 you'll find the common factor is ~1.14.

Which means for that altitude TAS ≈ 1.14 * IAS.

1.14 is the square root of the ratio of standard sea level ISA air density ($\rho_0$) to the air density at that altitude ($\rho$). This is assuming IAS = CAS = EAS (i.e., ignoring positioning, calibration, and compressibility effects).

The formula at low-speed flight is:

$$
\text{TAS}
=
\text{EAS}
\sqrt{
\frac{\rho_0}{\rho}
}
$$

It looks like you got the numbers from this online converter. Note its preset is not a standard ISA, as the altimeter setting reads 28.16 inHg. Instead I recommend this one, which is for standard ISA. For 5,000 ft the values are:

CAS    TAS
100    107.7
110    118.4
120    129.2

With the multiplier at 5,000 feet ISA being ~1.077, and the relation looks like this:


Why did the later versions of AeroVodocody L-39 Albatross find much market success?

It was, although it's not in widespread use.

The L-39 was developed into the L-59 and from that into the L-159 Alca. It's radar-equipped, can carry just over 5,000lb (2,340 kg) of air-to-air and air-to-ground weapons, and is in service with the Czech Air Force. According to Wikipedia, 72 were built between 1997 and 2003.

Given that it's an aircraft designed in the former USSR's influence, it's not unsurprising that it didn't get a lot of customers. Russia prefers to buy Russian; Russia's friends also prefer to buy Russian. America's friends are strongly encouraged not to buy anything that isn't American. And thus a small Czech single-seater is not likely to become very popular.


Is there anywhere I can pick up raw flight data recorder information?

Unlike the AAIB, the NTSB does release FDR data dumps (adjusted for engineering units and culled to the same parameters as the graphs) as part of the docket release for a given accident -- no FOIA pestering needed!

See these examples from the Bedford, MA Gulfstream overrun crash, for instance (they're CSV files).  You'll be able to find more by looking through the dockets associated with recent major NTSB accident reports.


Are there any regulations preventing one from converting an originally cargo aircraft to ferry passengers?

Converting a freighter to an airliner would require lots of work:

you have to install an HVAC system capable of supporting hundreds of passengers, which means installing air ducts from the engines to the cabin, etc. Major surgery to the wing and fuselage.
you have to install a sufficient number of doors and emergency exits (with associated systems). Major surgery to the fuselage.
big changes to the electrical system to support e.g. entertainment for the passengers.

So the conversion would require taking most of the aircraft apart.


Can I get a third-class medical if I have sleep apnea?

The short answer to your question is yes, you can get a third-class medical with sleep apnea in some cases:

  If your OSA is treatable, you can maintain your airman medical
  certificate and continue to enjoy your aviation career.

Everything else in your question is very personal and specific, and the only way to get an answer for your individual case is to consult an AME, preferably one who's handled similar cases before.


Why does the A-4 Skyhawk sit nose-up when on ground?

This was pretty common on naval aircraft from that era which used the launch bridle catapult interface. It gave the aircraft a high angle of attack during launch and helped the aircraft get clear of the bridle at the end of the launch stroke. It's noticeable on a wide variety of aircraft, including the F7U-3, F4D, A-5, F9F, F8, Super Etendard, Buccaneer, F3H, just to name a few.

Even the F-4 did. The nose landing gear oleo strut could be extended to give a nose high squat for cat shots:

(theaviationgeekclub.com)


Can quadcopters still fly with propellers at an angle?

Yes, you can. But it very depend with the angle (as in your drawing). If it is "folded) to make V-shape (that will make divergent thrust), then will reduce the lift compared to if the angle is opposite direction (inverted V-shape), which will make the thrust become convergent, it will produce more thrust. Both will work, but one is better than another. See this Akagi Helicopter. But the angle should not be high enough.

There is research that researching eagle and bird shape. There are two kind of bird or eagle's shapes. The 1st is the wing feathers trailing edge is divergent, which is make it look like V seen from the head. The 2nd is, the wing feathers trailing edge is convergent (closing to the tail, so it look like V seen from the tail, not from the head). From the research, the 2nd is better than the 1st in maneuvering and speed. But in slow move (like surveillance), the 1st is better as the flaps are produce less speed and power for the same amount of flapping (power). Another thing, the power of the flapping of the 1st is divergent, leaving the bird/eagle body, while the power of the flapping of the 2nd eagle is concentrated beneath the body (convergent) that make amount of lifting power.  Unfortunately I can not find the video in Youtube. Maybe later.


How to calculate the amount of thrust of a autogyro during auto rotation?

In auto-rotation, either flying level, or with a constant sink speed, the vertical component of the thrust provided by the rotor is exactly the same as the weight of the gyro...

In Wikipedia  https://en.wikipedia.org/wiki/Disk_loading#Momentum_theory  you can find the derivation of the following expression:

$T = 2v^2· A·  rho$

where T is the thrust of the rotor, v the sink speed in vertical auto-rotation, A the 'disk area' (that swept by the blades) and rho the air density.


Can a 777X legally be ferried with one or both wingtips folded?

As Ron notes in the comments to another answer this is a perfect situation for a Ferry Permit/Special Flight Permit. The FAA via your local FSDO can authorize aircraft to fly for the purpose of being fixed elsewhere via a ferry permit. This question covers whats needed for that.

However in some cases it may be cheaper to fly (or drive) in a maintenance team and fix it on site. Moving an empty 777 even short distances means burning quite a bit of Jet-A. For the cost of the reposition it may just be cheaper to send a team (possibly in car) with the parts and tools they need to get the job done.

On a similar note its likely that the majority of fields big enough for a 777 to touch down have at least some form of maintenance on hand. Again it may be cheaper for an airline to contract the job to a local shop than bother with the ferry logistics and costs.

Boeing also offers these services if you should need them in a pinch as part of the AOG services.

  Our technical experts will provide on-site, comprehensive and
  integrated assistance to recover an airplane. Our goal is to quickly
  and safely return airplanes to service, using methods and procedures
  that avoid costly secondary damage.

From what I can tell they will basically show up with parts and people to get the plane back in the air just about anywhere you can fly it out of.


Is the purpose of variable pitch propellers to maintain an optimal angle of attack?

What you know about variable pitch propellers is generally correct. If you make a slight change, your flight instructor would not have had any reason to object: They keep propeller blades near their optimum angle of attack across a wide speed range.

As the distance from the hub increases, the blade section gains circumferential speed while being in the same forward speed as all other sections. Therefore, the twist of the propeller blade should change linearly from the hub to the tip. If you twist the full blade at its root, you add a constant change to each cross section, so at high speed the root of the blade sees too high an angle of attack and the tip has too little angle of attack. Normally, the section at approximately 75% of propeller span is kept at its ideal angle for the best overall compromise. That is good enough for practical use.

Ideally, the propeller would spin faster with increasing flight speed, but that would require a gearbox and switching gears with the limited speed ranges of combustion engines, would deliver little thrust at the beginning of the take-off run and at high speed you would run into compressibility problems at the tips much sooner - practical high speed propellers spin more slowly than typical low-speed propellers.

If you look at the efficiency chart of a three-bladed variable pitch propeller below, you will see that efficiency peaks for one speed (given as an advance ratio in the plot below) and one pitch angle. This is when the full blade is flown at the optimum angle of attack for each section. This optimum would shift to higher speeds for less twist and lower speeds for more twist. Operating the propeller away from its design point incurs small losses since not all of the blade is exactly at its optimum angle of attack, but if you compare the overall efficiency with that of a single pitch setting, the advantage of variable pitch becomes obvious.

Efficiency chart of a variable pitch propeller. Source: McCormick B.W. Aerodynamics, Aeronautics &Flight Mechanics. John Wiley & Sons, Inc., 1979.


Has a commercial passenger airliner ever had its cockpit fully upgraded?

While many times an upgrade is not economical for older airplanes, sometimes the new features make it worth the cost.

Two examples I found were Southwest upgrading their 737-300 fleet, and Delta upgrading their MD-88 and MD-90 fleet. The second article also mentions American and Icelandair 757 and 767 upgrades. The Southwest and Delta upgrades involve over 100 aircraft in each case, which probably helped to make the upgrades more economical.

In both cases, a major factor mentioned was the ability to perform required navigation performance (RNP) procedures with GPS and other modern features. As the FAA works to implement the NextGen ATC system in the US, these upgrades will offer more benefits for the operators.

Also, I'd like to comment on the following statement:

  Concorde was not properly maintained as its analogue flight deck had never been upgraded.

Proper maintenance and technology upgrades are not always the same thing. Aircraft with older systems can be maintained just as well as newer planes. We have airplanes that are 50 years old or older, like the DC-3, which are still flying. While technology upgrades certainly have benefits, aircraft with analog cockpits are still operating just fine around the world. They may not be the most modern machines out there, but proper maintenance is what has kept them flying this long.


How do you program circular flight plans in GPS?

Custom waypoints would work, but it would not be a smooth circle. And as far as I know looping the set of waypoints is not straight forward. Another way is the CWS (control wheel steering) function of some autopilots such as the King KFC 225 to hold a bank angle and to control the radius with the speed, but as you pointed out in a comment, it would not be perfect due to the wind.

Also a unit such as the Garmin 650/750 available for FAR 23 (small aircraft) has the new radius-to-fix and orbit functions:


What protects the location beacon (pinger) of a flight data recorder?

Is it really a good idea to keep such a vital instrument unprotected? Or is that round metallic thing strong enough to resist impact and fire?

The casing of the ULB is itself designed to be strong enough to withstand the forces expected when an airliner crashes into an ocean, lake or large river (which are the only circumstances where a ULB is useful).

See teardown video starting at around 4:45

Copies of the relevant standards cost $70 each. However, a 1968 report from the early days of ULB development says

As voretaq7 notes in a comment: ULBs need to be external to the FDR/CVR canister because they need to have batteries changed regularly without affecting the integrity of the data recorder canister.


The Competency Based Instrument Rating (CBIR) allows you to gain an IR in less hours than the "full" course, by either crediting previous experience or licenses.

I held a UK issued IR(R) (old IMC rating), which meant that I had approx 60 hours IFR time when starting my IR. A full IR would have meant 45 hours training, whereas the CBIR allowed me to do just 15 hours (in accordance with EASA Part FCL, Appendix 6).

The BIR, as far as I am aware, is effectively going to mirror the UK IR(R) but make it a full EASA rating. That isn't confirmed however, as I haven't yet seen any official documentation from EASA.


Are there regulations about objects/buildings above (across) taxiways?

Bridges over taxiways are not a common airport feature. The FAA does have standards for wingspan clearance on taxiways, but not heights. Airport information will tell pilots if there are wingspan or height limits on certain taxiways, and ATC will know which aircraft are or are not able to take certain routes.

For example, Denver International Airport has a bridge over one taxiway. This provides 42 feet of tail clearance, which leaves 3.5 feet of clearance for the A320 family (except the A318). These are the typical aircraft that use this taxiway. A 737 classic would have 5.5 feet of clearance but the 737 NG and A318 would only have 1 foot of clearance. Since the 42 foot number is only in the center of the taxiway, and accounting for other conditions, 1 foot of clearance does not leave much margin for error. So for regular operations, the A320 and 737 classic are the largest planes that will pass under the bridge.

The bridge at Gatwick Airport provides 22m of clearance, enough for a 747 (19.4m high) but not an A380 (24m high).

This suggests that about 10% margin is enough clearance for taxiway bridges. The FAA requires that taxiways have 20% margin plus 10 feet to objects. While wingtip clearance has many variables that require larger margins, tail height will not change much.


Do pilots have procedures and safeguards against unintended altitude captures?

On the Boeing 737 NG:

ALT ACQ is always armed when flight directors and/or autopilot is engaged in a climb/descent mode (V/S, VNAV, LVL CHG, TO/GA, CWS P), it is however, as you suggest, inhibited in G/S and G/P (glide slope, glide path) modes.

On a typical ILS, I would typically set the missed approach altitude (which would be captured during missed approach in TO/GA mode) on glide slope capture. You could also set the missed approach altitude when ALT HLD is engaged, and you know that you will not need to change altitude again until when intercepting the glide slope. (When changing the selected altitude with ALT HLD engaged, the "held" altitude is maintained, until a new vertical mode is engaged, regardless of selected altitude).

HOWEVER, performing a Non-ILS approach in V/S or VNAV, the set altitude WOULD be captured on descent. To avoid this, the approach MDA is usually set on the altitude selector, and kept there until sufficiently (typically 300 ft) below the missed approach altitude. When passing through this altitude, the missed approach altitude would be set (logic is implemented to make sure the altitude is not captured during the "winding up" of the selected altitude).

Lastly, performing a Non-ILS using IAN (Basically Boeing's solution for performing Non-ILS with ILS display and control laws, using FMC data), the final descent would be performed in G/P mode, which behaves roughly like G/S mode, eliminating the use for initially selecting the MDA.


Why do we undershoot/overshoot with a compass turn?

There is a good video that goes over the topic here ~2:45 into the video. It has to do with the way a magnetic compass responds to turns. When turning north the compass lags when compared to the tun of the physical aircraft so you need to overshoot the heading based on what the compass is showing. When turning south the compass leads the turn and you must roll out early to make your desired heading.

This site offers a nice explanation of why this happens in the compas

  Northerly turning error is due to the mounting of the compass. Since
  the card is balanced in fluid, when the aircraft turns, the card is
  also banked as a result of centrifugal force. While the card is
  banked, the vertical component of the Earth's magnetic field causes
  the north-seeking ends of the compass to dip to the low side of the
  turn. When making a turn from a northerly heading, the compass briefly
  gives an indication of a turn in the opposite direction. When making a
  turn from the south, it gives an indication of a turn in the correct
  direction but at a faster rate.

Similar explanations show up in this thread. Simply put its not the turn that causes the error but the banking of the aircraft. By rolling the compass housing to one side we allow the compass to tilt differently than it would in level flight. Since the pole is generally beneath the aircraft the roll allows the compass to pitch in a slightly different way causing the error we see.


Why do flight schools refuse to tell me the price of a course?

Mostly because what takes one individual 50 hours, will take another 75, and someone else 100.
For that reason, most if not all flight schools will only tell you 2 things

The minimum number of hours required to get the certification you're after (PPL, Night Rating, Instrument Rating etc).
The cost per hour of instruction, and the cost per hour of the various aircraft they use.

While we're on the subject, I should add that you should be wary of putting down a large upfront cost to any school. I have heard too many stories of flight schools going insolvent and students losing their money. Often you will see a discount for "block bookings" - if you can afford it pay just as you go, and if you do decide to upfront a block booking only spend what you could stomach losing.


Why are some airfields not on any sectional chart nor listed in the directory?

There are lots of airfields not listed on the charts or in the directory. For what its worth there is nothing that requires private airstrips to be listed. As mentioned in the comments sometimes its not worth the hassle. As you mention in the original question it is a nice gesture to list them for other pilots in an emergency. That is covered nicely in this question. They may not have listed it because they don't want people doing touch and go's there, or landing there and knocking the door of their house or they did not want to up-keep it etc. etc.


What is the maximum speed for regulation of sonic boom noise?

Business jets are developed to different rules than airliners. The biggest difference is that, indeed, fuel price and fuel efficiency are not an issue when what counts are bragging rights for the fastest plane on the ramp. Their speed has steadily increased and is now at Mach 0.935 for the fastest models. Compare that to Mach 0.78 to 0.85 for regular airliners.
Supersonic business jets were proposed several times in the last decades, but so far nobody has risked to spend the money it needs to bring one design to a type certificate.
Since supersonic flight over land is heavily restricted, the fastest speed would be Mach 0.99. However, since the speed of sound decreases with increasing altitude in parallel with air temperature, what is Mach 1.15 in 40.000 ft becomes only Mach 0.998 on the ground, so the shock will disappear close to the ground. If the goal is to avoid the shock on the ground, flight speed high up can very well be mildly supersonic. However, this will place the airplane close to its drag maximum, giving it exquisitely poor efficiency for a small gain in speed.


How do pilots set the exact amount of thrust needed for a reduced power takeoff?

The EMB-145 used a combination of FADEC settings and the thrust levers to select the desired thrust and to signify the need for additional thrust.

The thrust levers had a detent that selected "100%" thrust for the given mode the FADEC is operating in.  If you pushed the thrust levers past the detent to "max" this would give you extra thrust.  The mode the FADEC is operating in is selected by a button in the cockpit that cycles through the available modes.

For takeoff power the modes were "ALT T/O", "T/O" and "E-T/O" which gave you 90%, 100% and 107% thrust for takeoff when the thrust levers were in the detent.  If advanced past the detent this would put the mode into a reserve mode and depending on model would give you up to 110% or 117% thrust.

Setting the exact amount of thrust needed was up to the engine FADEC units, our job was just to tell it what thrust mode it was in and it scaled the output of the thrust levels to that mode.  Flying a 90% thrust takeoff, a normal rated climb and then reducing to cruise levels only required initially setting the thrust levers into the detent and adjusting the FADEC mode.


What is the trim wheel behavior on the A320 family?

Before takeoff I believe it is set by hand to set the takeoff trim.

Correct. And after landing the trim [wheels] auto-resets.

The trim wheels always have priority over the electrical trim. Moving them in-flight:

Bypasses the flight computers (an override mechanism with micro-switches).
Disconnects the autopilot when moved beyond a certain threshold.
Freezes the automatic trim.

The flight computers for normal stabilizer control (ELACs) remain active though, no change in laws would take place. They remain active to ensure they're synchronized with the manual action. Let go of the trim wheels, use the stick again in pitch, and auto trim will resume.

If you use the stick, while holding tight on the wheels, the flight computers will think the stabilizer is jammed, and the warning STABILIZER JAM will show, with it the associated procedure.

During flight it is not touched unless the aircraft goes into direct law or "worse".

There are two scenarios where you'd need them that are better (not worse) than direct law. That is the aforementioned [actual] stabilizer jam, or F/CTL STABILIZER JAM. The latter is when the flight computers lose contact (electrical signal) with the stabilizer (this scenario leads to alternate law with protections lost).

In both scenarios, if the pilot is able to move the trim wheels, they'll use the elevator position shown on the flight controls display to make trim inputs such that the elevator moves to the neutral position.

Source: A320 FCOM (don't use for flight).


Above is the same SID, but from the official chart (aerocivil.gov.co).

ATS means Air Traffic Services. That climb gradient is what the ATS requires. Versus PDG (procedure design gradients), the minimum to clear obstacles.

From the Colombian AIP GEN 2.2 Abbreviations used in AIS publications:

PDG = Gradiente del procedimiento de diseño
ATS = Servicio de tránsito aéreo


What are technical and aerodynamical limitations to blown wings main propulsion?

In a nutshell, it's the inefficiency of expelling air out a long skinny nozzle which results in massive energy losses due to friction.  In other words, too much duct surface area relative to the amount of total air volume.


A slender delta wing is a delta with low aspect ratio.

The use I have seen is in the study of vortex lift, which is present at high angles of attack.

What is vortex lift?


Can the pilot stop airflow between cockpit and cabin?

fire If there is smoke in the cabin, the pilot would need to prevent
  the smoke from entering the cockpit.

This is a bit more complex as the cockpit door by its own nature will slow the flow of smoke but will not stop it all together. Smoke flow is also dependent on the movement of air within the aircraft. In your example of SR-111 the smoke was not in the cabin but in the overhead section so closing the cabin door would not have accomplished much. While smoke barriers are installed ultimately in a fire situation its only a matter of time before another hole is burned through. This is why early identification and extinguishing is so key. By the nature of cockpits things like wire bundles, cable chases, and at one time in history control cables must come and go so you cant truly seal a cockpit anyway.

  hull breach Does cabin depressurization (due to a hull breach for
  example) directly lead to cockpit depressurization? Or can the pilot
  prevent this by stopping the air outflow from the cockpit to the
  cabin?

  MH370 One working hypothesis in the MH370 mystery is accidental or
  deliberate cabin depressurization. Assuming the latter, is there any
  way the perpetrator in the cockpit could prevent the cockpit
  depressurization ?

You can generally lump these into the more general question of "can the cockpit be pressurized separately from the rest of the aircraft" to which the broad answer is no. Simplly put the cockpit door is not capable of serving as a bulkhead and cant withstand the pressure differential, as far as I know they also lack any sort of sealing, bracketing or joints for such a task. The only aircraft I can really think of that ever had a feature like this was the B29 Super fortress which had independent fore and aft sections that were independently pressurized. This allowed an unpressurized bomb bay in the center. To make this possible both sections had small pressure doors to allow entry.

(source)

The only thing a flight crew could do, is potentially depressurize the whole aircraft and use the pilot and co-pilot 02 system to outlast the cabin 02 masks, then decent below FL100 and breathe normally.


Why do aerobatic aircraft have separate tanks instead of a single acrotank?

A long time ago aerobatic aircraft had just a single tank with a flop tube inside it.

This works "OK", but when you're doing something complicated with a half-empty or mostly-empty tank, it's too easy for the flop tube to ingest air instead of fuel.  This leads to performance problems with both the engine and the pilot.

The solution is to have a very small "acrotank" with a flop tube and an arrangement of fuel line plumbing such that the tank remains 90% full, 90% of the time.

In my Laser, there's a very large tube (2" to 3" diameter) that feeds from the bottom of the main tank to a tube at the top of the acro tank (with that tube extending inside the tank to near the bottom).  There's a small vent/return line.

When I'm right-side-up, the acro tank fills from the main tank in seconds.  When I'm inverted, the tube arrangement prevents most of the fuel from returning to the main tank.  Some returns via the vent/return line, but I still have about 5 minutes of sustained inverted flight fuel.


What is the typical climb angle (versus the ground) of a single engine piston plane?

That depends on wind speed and the aircraft's thrust-to-weight ratio.

Here are some values, all valid for sea level

GA aircraft: 4 m/s climb speed, 36 m/s airspeed. In calm air, this becomes a climb angle of 6.3°. If the wind blows with 36 m/s, the aircraft will climb vertically relative to earth if it flies straight into the wind.
Airliner: 20 m/s climb speed, 120 m/s. In calm air this becomes a climb angle of 9.5°.
Empty airliner: 30 m/s at 100 m/s. In calm air this becomes a climb angle of 16.7°. At airshows this is used to dramatic effect.

Note that the spectacular angles at airshows involve the conversion of airspeed to altitude, so these maneuvers are instationary.

If you want to know more on computing the optimum climb angle, consider reading this answer.

The main influence on climb speed is the thrust-to-weight ratio of the airplane. Since thrust depends on flight speed, ambient temperature and air density, those factors control the attainable climb speed in combination with the aircraft's weight.

For an observer, the next important influence is wind speed, since the aircraft climbs relative to the air mass it is flying through. If this air mass makes the aircraft appear to fly more slowly, a steeper climb angle can be observed.

Climb performance over airspeed and thrust-to-weight ratio for an idealized turbofan engine. The blue lines show thrust (right Y-axis) and the green lines the resulting climb speed. The two black lines show how the optimum flight speed for best climb speed and best climb angle (steepest climb) vary over thrust loadings. They are easy to find graphically: Just measure the angle of a line from the origin to the point on a green line at the desired flight speed and the right thrust loading (thrust-to-weight ratio). If the scales of the two speeds on the X- and Y-axis would be the same, you could directly take the angle from the plot.

With lots of excess thrust, the optimum is limited by the stall speed (the black line bends into a vertical trend), while with no excess thrust both optimum speeds vx and vy converge. This makes sense: If thrust is just sufficient to keep the airplane from descending at one speed, this speed will both give the best flight path angle and the best vertical speed (unfortunately, both will be 0 at this point). It also helps to reduce induced drag, so aircraft with a high aspect ratio wing will climb steepest at a higher lift coefficient (= lower speed).


Why use Mach number for describing the speed of aircraft?

The aerodynamics change with Mach number.

At low Mach numbers (< ~0.3) , air is considered incompressible; it has constant density along the stream line.

At higher Mach numbers, air is no longer incompressible; the density changes as the air passes over the aircraft. The compressing and expanding of air changes the way the air flows, and consequently it changes the performance of the aircraft.

At Mach numbers approaching 1, parts of the flow around the aircraft may breach the sound barrier. This leads to trans-sonic effects such a shock waves which affects the performance of the aircraft even more.

For subsonic aircraft the maximum speed is typically expressed by two numbers: the maximum calibrated airspeed and the maximum Mach number. The first is related to the dynamic pressure the flow of air creates and is typically the limiting factor at lower altitudes. The Mach number is related to trans-sonic effects and is typically the limiting factor at higher altitudes where are is colder and the speed of sound is lower.

For the pilot it thus important to know both the airspeed and the Mach number.


In my experience, 4G is not reliable above 1,000 feet, and is frequently non-existent above 3,000 feet.

Many pilots have suggested the 4G model for two key reasons:

The 4G model has a GPS-chip in it, that the WiFi-only version does not.
Having a cellular connection means you can do on-the-ground operations in places that don't have WiFi. This includes things like: File Flight Plans, Check NOTAMS, and update maps and charts

Personally, my iPad is WiFi only, and I pair with an external GPS receiver for great accuracy.

I use the "regular" iPad (9.7"), but that is a little bulky in the cockpit of a 172.  The Mini may be preferable if space is at a premium.


You have asked several questions. I'll try to answer them in order to clarify.
Is the ferry range specified anywhere?
From the Airbus website, we find for the Engine Alliance GP7000 engine option the ferry range is ~9,600 NM. Let's just say it's 9,500 NM.
A: 9,500 NM. Also, waiting for the right trade winds can increase you range.

Can an A380 fly between any two airports on Earth?
If you place the originating marker over Dubai, UAE, then the A380-800 can fly to any airport on Earth except a region in South Pacific Ocean. This area (a circle of around 6500 km diameter) has many small island states (French Polynesia, Cook Island, American Samoa etc.).
(gcmap.com)
A: Yes, probably over 99% of airports.

Has a flight by an A380 in excess of 15,700 km been performed to date?
None that I could find. The longest flight of A380 (currently) is QF 8 (with duration 16:50 hours).
We know that A380 (October 25, 20071) is much newer than 777 (June 7, 19952) and 747 (January 22, 19703). In future, there can be attempts to fly it in excess of 15,700 km.
A: No record so far.

What is the ferry range of an A380?
This was your original question. Most of the flights mentioned on the Wikipedia article you referred to were either delivery flights or for demonstration purposes. For such flights, you can have:

lesser people on board
lesser equipment (seats etc.) so more space to add extra fuel tanks

With the above two changes, the result would be:

Less people = Less weight. The aircraft will weigh less and its range can increase.
Less seats = Less weight. The aircraft will weigh less and its range can increase.
More space to add fuel tanks. The aircraft's range will increase.

In addition, A380-800 has cargo volume of 6500 cubic feet. If we have a hypothetical rubber tank which fills all this space, we can add 184,000+ L of additional fuel than the original capacity of 323,546 L. This can increase the range over 50%.
This website contains pictures of additional fuel tanks. As you can see, those are inflatable and can adjust to the space available.
A: It depends.

1: Introduction with Singapore Airlines
2: Introduction with United Airlines
3: Introduction with Pan American World Airways


How can I keep the data on a KLN89b GPS up to date?

Thanks Guys. I've contacted the manufacturer and they said that there is an approved cable, only sold by avionics shops, that will connect an old fashioned serial port to the data port on the panel. If I get a USB to serial computer, I may be able to use Windows 10 to install the update. Maybe I'll have to downgrade to Win7.

I asked if there was a published end-of-service date for the unit and they stated that there was not. I also asked if there was a guarantee of future database availability for any period into the future and she said that there was no guarantee, but no plans that she knew of to phase the unit out.


Why is Bombardier selling off all of its airliner series?

It's important to understand that Bombardier Transportation/Aerospace, while ostensibly a company separate from the original Bombardier family (which only retained a minority stake when it was split off from Consumer Products - snowmobiles, watercraft, etc), is still actually controlled by the family due to a bizarre dual class share structure where the family retains its minority stake in the form of class A shares that have many more votes per share (I think it's 9 or 10 votes or something like that) than the single-vote class B common stock.  This gives the family control of the company, and makes it takeover proof (also making it very difficult to raise private capital), even though its equity stake is a small minority one.

But the basic problem is the C series and to a lesser extent the Global 7000, just about broke the company.  So broke they were forced to give the program to Airbus more or less for free.  The CRJ line was neglected due to the commitments for the C with little in the way of proper design updates.  This handed over dominance on the Regional side to Embraer (who's newest Ejet is basically a baby C-series technology wise) and CRJ production is winding down (it is now a Mitubishi product - M's interest wasn't in the Regional Aircraft program, but its support and spares organization, where M was hopelessly lacking).

On the corporate side, the Lear 85 disaster and the Global 7000/7500 development was another money hole, almost as bad as the C.

So in nutshell, since the traditional government money tap the company has traditionally relied on has largely dried up, the family has decided to dump everything (including rail) and just retain the consumer products operation, the separate family controlled company, upon which the whole business was founded, that was spun off some years ago.


What is the difference between IAN and LNAV/VNAV?

A Non Precision Approach (NPA) flown with Integrated Approach Navigation (IAN) is not more precise than the same approach flown with LNAV/VNAV. The advantage of IAN is that the instrumentation and procedures are very similar to ILS (Cat I), which is the most common approach type flown for most airline pilots. Having a common set of indications on the PFD and procedures to follow improves flight safety.
The Boeing 737 Flight Crew Training Manual (FCTM) says:

IAN approach techniques are
similar to ILS approach techniques [...]
All IAN approaches provide the functions,
indications and alerting features similar to an ILS approach. Although non-ILS
approaches using LNAV and VNAV can still be performed, IAN is normally used
in place of LNAV and VNAV because of improved approach displays, alerts and
standardized procedures.

(Boeing 737 NG FCTM 5.60 - Approach and Missed Approach, emphasis mine)
The article about IAN on flaps2approach goes into a bit more detail:

Advantages of Using IAN
There are multiple advantages to an airline using IAN, the foremost
being flight safety. Unstable approaches contribute to many aircraft
accidents, and flight crews strive to always establish a stabilised
approach profile for all instrument and visual approaches.
The Global Position System has enabled stabilized approaches at many
airports and advanced features such as IAN take advantage of this
technology to provide consistent, intuitive displays that support
stabilized approaches.
18 Approaches Types to 1
Through the use of IAN, the number of approach types has been reduced
from 18 to 1, greatly simplifying the approach procedure and
minimizing the amount of time an airline needs to train pilots in
numerous approach types.  Time is money and utilizing advanced
technology such as IAN can increase airline productivity.
Additional Data - Increased Awareness
The distance to runway threshold, approach guidance information, and
vertical and lateral deviation markers are displayed when IAN is in
range of a designated runway.  Whether IAN is used or not, this
information provides additional guidance when executing an approach.
For example, when executing a VOR approach, this information has been
displayed on the Navigation Display (ND) as the distance to the actual
NAVAID (VOR) - which may or may not be aligned with the threshold of
the runway.  IAN will by default, display the lateral and vertical
deviation, and distance to the runway threshold, allowing for greater
precision during a non-automated approach.
These are but a few of the advantages to using the Integrated Approach
Navigation system.

(flaps2approach.com - Integrated Approach Navigation (IAN) - Review and Procedures)


On large aircraft, why do flaperons not run the full length?

This flaperon is actually the high speed aileron. Using the outer ailerons at high speed will twist the wing, which in turn reduces their effectiveness. For every aileron there exists a speed where it becomes ineffective and above that speed its function will even be reversed. See the flexible wing as a flap in its own and the aileron as its Flettner tab of sorts.
By using those high speed ailerons, Boeing can build the wing lighter with less torsional stiffness. In addition, it creates a gap between the Fowler flaps at the spanwise location of the engine exhaust, so the Fowler flaps will not reach into the very turbulent exhaust stream. The 737 uses an exhaust gate for the same purpose.
Using flaps for trim means you need to be able to finely adjust the position of each flap individually. This fine adjustment is better left to the smaller control surfaces or the even smaller trim tabs.


Since P Factor is primarily variation of AOA of a thrust producing blade when its rotation axis is not aligned with the air stream, you should see some P factor in a turbofan engine, to the extent that the inlet flow strikes the front of the fan from an angle.
I say "some" because the cowl inlet is going to align the inflow to be more perpendicular to the fan face than if the fan was in the freestream (where it becomes just a propeller with lots of extra blades), but it's hard to say how much. In any case, the flow is probably not quite 90 degrees to the fan face at higher body AOA, so it's safe to say there is probably a little bit, but since P factor is not accounted for in turbofan installations, what P Factor exists is not enough to matter (maybe if you stuck a turbofan on the nose of a Cessna 172, you might notice some P Factor effect).
On a turbojet there will be no P Factor at all since the thrust is coming form flow accelerating out the burner can, hot section and tailpipe, not from lift producing propeller/fan blades at the front.


"The pilot must know the center of gravity and gross weight to fly" -- True or false?

True. It is the pilot-in-command's responsibility to determine if the aircraft is safe for flight. 14 CFR § 91.3(a) makes the PIC directly responsible for that.

The 2016 FAA Weight and Balance Handbook also states:

4. The pilot in command (PIC) has the responsibility
prior to every flight to know the maximum allowable
weight of the aircraft and its CG limits. This allows
the pilot to determine during the preflight inspection
that the aircraft is loaded so that the CG is within the
allowable limits


What is the difference between Boeing 777-31H and Boeing 777-31H(ER)?

The 777-31H is a standard Boeing 777-300 manufactured for Emirates (customer code 1H).

The 777-31H(ER) is a Boeing 777-300ER (Extended Range) again for Emirates.

Compared to the standard 777-300, the 777-300ER has:

A longer range due to the extra fuel it can carry (145538 kg compared to 135880 kg for the -300 baseline)
A higher Operating Empty Weight (167829 kg compared to 159570 kg for the -300 baseline)
A higher Maximum Take-Off Weight (351535 kg compared to 299370 kg for the -300 baseline)
A higher maximum structural payload weight (69853 kg compared to 64960 kg for the -300 baseline)
A wider wingspan (64.80 compared to 60.93 m)
A different engine delivering more thrust

The Boeing 777-300ER is always equipped with General Electric GE90-115BL1 engines, while the baseline -300 can be ordered with four different engine models from General Electric, Pratt& Whitney or Rolls Royce. The Emirates Boeing 777-300 aircraft have the Rolls Royce RR Trent 892 engines installed. They deliver 415 kN of thrust, almost 100 kN less than the GE90-115BL1 engines.


How is the TCAS negotation information encoded?

TCAS air-to-air messages use the same format and frequencies as "Mode S" surveillance radar. They're defined (in great and overwhelming standardesque detail) by a document called "ICAO Annex 10".

ICAO wants serious money for a copy of it -- and of course if you're producing actual avionics nothing less than the official source will do -- but for satisfying idle curiosity it's often possible to find a draft or bootleg by persistent googling.

The Mode S message format is also used for ADS-B broadcasts, so equipment to receive and decode them is relatively easily available to hobbyists. The lower layers of open-source ADS-B software will also be generally relevant.


How to navigate at night after a complete navigation systems failure?

This is no different then flying during daylight. Your first choice is GPS ( for most people :)). Failing that you fall back on radio navigation ( VOR ). Failing that you fall back on your charts and NavLog. NavLog is essentially pilotage and you rely upon your airplane speed and direction and checking waypoints along the way. If you chose your waypoints carefully ( on the ground when creating your NavLog, I use airports so that I can land of them in case of an emergency) and you know how they look like from air ( I take satellite photos ), assuming that your waypoints are 10-15 minutes apart and you took care of wind speed and direction in your navlog, there is really a minimal chance of getting lost.

Ocean is a different matter. Maybe you will need to look at stars or something. In VFR we are told not to fly over the water, day or night.


Are weather-reporting requirements for an airport in Class D airspace more stringent than for an airport in surface-level Class E airspace?

Your First Question: In the US, are weather-reporting requirements for an airport in Class D airspace more stringent than for an airport in surface-level Class E airspace?
Answer: The "Primary" airport within active Class D airspace requires (Ref: FAA Order JO 7400.2M, paragraphs 17-2-9 and 17-2-10:

That a Control Tower be currently in operation;
That a certified and approved weather observation and reporting system (for the primary airport) be in place and operational; and
Communications capability must exist down to the runway surface area (for the primary airport).

However, a primary airport that is within the surface area of active Class E airspace will not have a Control Tower currently in operation.  (if there are airports with a currently operating Control Tower within the surface area of active Class E airspace, I am unaware of them).
With respect to your specific question above, if the airport in question (within the surface area of active Class E airspace) is meant to accommodate instrument procedures (e.g., instrument approaches, IFR arrival/departure procedures, etc.) then the exact same requirements (Ref: FAA JO 7400.2M, paragraph 18-1-3) for communication and weather observation/reporting must be available as are required for Class D surface airspace. (But there will not be a Control Tower operating)
There are a dwindling few airports that have Control Towers that operate while the airspace is designated as active Class G. But, as I mentioned above, the same is not true for primary airports located within the active surface area of Class E airspace. In that case, the Control Tower, if there is one, is not operational (e.g., closed/not staffed - usually in the later evening as traffic warrants).  If the Control Tower was currently operating the active surface airspace would be Class D.
Your Second Question: Are there other requirements that would cause an airport with an operating control tower to be eligible for surface-level Class E airspace but not for Class D airspace?
Answer: Again, as mentioned above, if the primary airport has a currently operating Control Tower, the active surface airpace would be Class D (or in a few cases Class G), not Class E. Therefore, parsing the eligibility requirements between Class E and Class D airspace, both of which (with respect to your question) might have operating Control Towers, is not possible.
Typically, when/if the Control Tower closes (not staffed/closed for the night) at a primary airport in Class D surface airspace, then that airspace surface area reverts to Class G or Class E.
Lastly, my response above excludes special occasions where a temporary Control Tower may be operating in active surface airspace designated as Class E.  This would be a circumstance where a NOTAM or similar would exist identifying a particular event taking place.


Has the FAA ever granted anybody a license honoris causa?

It's an interesting question, and according to AOPA they did award one to the guy who designed the current FAA license card:

  The FAA awarded Dahlvang his own (honorary) certificate, nicely framed
  with a gold seal.

But it doesn't say what's printed on that certificate and I assume it isn't actually valid for flight. If you give someone a real pilot's license you give them the authority to operate an aircraft and I can't imagine the FAA handing out licenses to unqualified people.

Orville Wright did get an honorary certificate, as did other 'old-timers', but that pre-dates the FAA and again it isn't clear if they were 'real' certificates or not:

Orville Wright
Evan J. Parker

I don't know if that really answers the question, but anyway in practical terms I think it's probably a lot easier for the FAA to come up with a suitably impressive but legally worthless certificate rather than give someone a real one and deal with the legal issues involved in breaking their own rules and possibly federal law.


What has Airbus done to address the dual input issue?

Nothing was changed in the stick design or logic.
The side stick design and logic are not addressed by the final recommendations of both accident reports. Of the issues were the training and lack of crew resource management (CRM). Recommendations toward the manufacturer, for example, are with regard to the barrage of warnings the crew of Indonesia AirAsia had, even though Airbus aircraft already have an EMER CANC button to mute spurious alerts:

The KNKT recommends that Airbus to consider in developing a means for flight crews to effectively manage multiple and repetitive Master Caution alarms to reduce distraction. (PK-AXC accident report)

(There are already buttons to take priority, as well as aural and visual cues as to which seat currently has priority.)
Active sticks
Coupled digital side sticks weren't there when Airbus first introduced the A320, as a technology they became feasible in the early 90s. And were first introduced in c. 2015 on the Gulfstream 500 and 600 business jets.
Imagine panicked, under-trained, and uncommunicative pilots in an active sticks cockpit; they might think their sticks got jammed or the coupling motors are acting up. And seeing how long it took for the active sticks to make it into a business jet already hints at the snail pace (and cost) of aviation hardware certification and approval in general.
As for the captain's / left seat inputs being correct, as others have commented, there have been numerous accidents where the captain was in control and the first officer's recommendations were not heard or they kept silent, again, bad CRM.

Re comments on visually noticing the other yoke (not really a side stick design/logic issue):
That did not help Flash Airlines Flight 604 and Atlas Air Flight 3591. Tunnel vision and/or not speaking up is the main problem. Same with the thrust levers; despite moving automatically on Boeing planes -- showing the current setting -- they did not help Asiana Airlines Flight 214 and Turkish Airlines Flight 1951.


What is this plane flying in overlapping circles pattern doing?

It's acting as a television broadcast relay for the 2020 Tour de Wallonie cycling race, taking place in Belgium from August 16 through August 19.

The flight paths you posted correspond roughly to the race routes for stage 2 (August 17, Frasnes-lez-Anvaing to Wavre) and stage 3 (August 18, Montzen to Visé).

Here you can see a photo of what one of these broadcast planes looks like, with retractable underbelly antenna:


Can I fly in the USA with an FAA ATP, if I don't have a commercial certificate?

Maybe. Your ATP certificate does give you commercial privileges, as per 14 CFR 61.167:

  (a) Privileges. (1) A person who holds an airline transport pilot
  certificate is entitled to the same privileges as a person who holds a
  commercial pilot certificate with an instrument rating.

But, that doesn't authorize you to work in the USA or even to enter the USA, which is an entirely different question about immigration law. As a foreigner, you'll need an appropriate visa or a green card in order to be legally employed and paid. You can ask more about that on another site.


Is it possible to order or purchase a hardcopy of an NTSB report?

I'm not sure that this is on topic, but the short answer seems to be that you need to contact the National Technical Information Service. NTSB reports used to include this text:

Accident reports, safety studies, special investigation reports,
statistical reviews, and safety recommendations may be downloaded from
the NTSB Web site, or printed copies may be purchased from:
National Technical Information Service
5285 Port Royal Road   Springfield, Virginia 22161
(703) 487-4630 (Subscription Orders)   (703) 487-4650 (Single-Copy
Orders)
(Subscription rates apply to certain recurring publications)

The current wording is:

Copies of NTSB publications may be downloaded at no cost from the
National Technical Information Service, at the National Technical
Reports Library search page, using product number PB2020-101001. For
additional assistance, contact—
National Technical Information Service
5301 Shawnee Rd.
Alexandria, VA 22312
(800) 553-6847 or (703) 605-6000

Alternatively, since NTSB reports are in the public domain (with some limited caveats) you could just get them printed at your local print store, presumably much more quickly and cheaply than by going to NTIS.


What is the purpose of the selected altitude/airspeed in ARINC 429?

Both labels are used to transmit the altitude and airspeed that are dialed into the Mode Control Panel of the autopilot. They are not necessarily the current altitude/airspeed, instead they are the target values that the autopilot is steering to.


What is this flying boat being restored at the Udvar Hazy Center?

It is a Sikorsky JRS-1 (Like terry I thought it was a PBY as well at first glance, that center wing joint is fairly unique)

From the smithsonian website you can find all the info on it here

  This amphibious seaplane is the only aircraft in the Museum that was
  at Pearl Harbor, Hawaii, on December 7, 1941. Ten JRS-1s were at the
  U.S. naval base when the Japanese attacked during World War II. The
  Navy immediately sent these unarmed utility craft to search for the
  enemy fleet. The JRS-1 (used 1937-1944) is the military version of the
  Sikorsky S-43 "Baby Clipper." On the day of the attack, the plane wore
  a very colorful paint job: silver overall, black on the bottom, green
  tail surfaces, a red band around the rear of the fuselage, and the
  diamond-shaped squadron insignia behind the cockpit on each side. A
  few days after the attack, ground crew repainted the plane blue, but
  it has weathered and the original paint is peeking through. The
  JRS-1’s current condition is due to many years of storage outside. The
  Museum intends to conserve and restore the plane. Transferred from the
  U.S. Navy, Bureau of Weapons


Compute great-circle track from longitude

@James Turner: considering the date of the question, you've surely moved on. If you found a solution elsewhere, you can post it here and get some bonus points for answering your own question. Anyhow, the Aviation Formulary has the answer to your question: it's not Clairaut's Formula. You can find the latitude of ownship position by entering its longitude and the coordinates of the GC endpoints into the "Latitude of point on GC" formula. Then, knowing lat and long of both current position and destination, you can determine the heading to use leaving that point from the "Course between points" formula.


Does turbulent flow have boundary layer ? Does separated flow have boundary layer?

Yes.
There are boundary layers (BL) in laminar flow, turbulent flow, and the
transition between the two.

"Flow separation occurs when the boundary layer travels far enough against an
adverse pressure gradient that the speed of the boundary layer relative to the
object falls almost to zero. The fluid flow becomes detached from the surface of
the object, and instead takes the forms of eddies and vortices."

From: "Flow Separation"
https://en.wikipedia.org/wiki/Flow_separation

Note that the shear stress at the wing surface drops to zero (or very close to zero) after the BL separates.

It is also possible for BL to re-attach to the wing surface after an initial separation. In that case the shear stress returns to a non-zero value.


Are nearest VOR stations always tuned to?

Your example is a bit confusing because it seems to be a GPS-based route, it may be better to a look at a more 'realistic' one, where you're using only VORs for navigation. The reason to tune a second VOR is to cross-check your position, either by crossing a specific radial or perhaps by using DME (for a VOR/DME or VORTAC). If that's useful to you then you should definitely tune it.

Here's a US example. Let's say I'm flying eastbound on V241 from the SJI VORTAC following the 081 radial outbound. I've tuned the SJI VORTAC on NAV1, but I have no DME or GPS:

ATC tells me to "report LOXLY", which is 29nm from SJI but I have no DME so I can't report based on that. However, LOXLY is at the intersection of the SJI 081 radial, the BFM 052 radial (BROOKLEY VORTAC) and the NUN VOR 305 radial. That means, on NAV2 I can tune either BFM 052 or NUN 305 and when both the NAV1 and NAV2 needles (as it were) are centered, I'm at LOXLY. You might also notice that the PENSI intersection to the east is defined not only by VOR radials but also by the localizer on runway 17 at KPNS.

In this example, two VOR radials are needed to identify the fix (assuming no DME and no GPS) but you could tune a second VOR even if it isn't required for a named fix, to manually check your progress along your route (see chapter 7 of the FAA Instrument Flying Handbook). You can also time how long it takes to cross two radials on the off-airway VOR and use that information to calculate the distance to it, as a sort of 'manual DME'.

Having said all that, if you don't need or want position information from the second VOR there's no reason to tune it. But especially if GPS is your primary navigation method it wouldn't hurt to stay familiar with them as a cross-check and even as a fallback in case GPS becomes unavailable (which is not unusual).

(As Carlo Felicione mentioned, you could use just one NAV radio and switch back and forth between two VOR frequencies, but that's rather awkward and not something that most people would want to do in normal circumstances.)


Are loops or rolls allowed in the "utility" category in any US-certified airplane or glider?

The main difference between Utility and Normal category in FAR 23 is spins and the limitation of bank angles in maneuvers.  Normal category is banks up to 60 deg and no spins.  Utility allows spins if certified for them, and banks up to 90 degrees.

  Limited   acrobatic   operation includes: (1)  Spins  (if  approved  for  the  par-ticular type of airplane); and (2) Lazy eights, chandelles, and steep turns,  or  similar  maneuvers,  in  which  the  angle  of  bank  is  more  than  60  de-grees but not more than 90 degrees.

I would imagine that a Hammerhead, being a chandelle taken to an extreme, would be allowable since done properly the wings don't go beyond 90 deg,  but loops and rolls are definitely out in Utility Category.


You have an extra 2 in the P/N. Check 2024T3 ALCLAD ALUMINUM SHEET on aircraftspruce.com.

Double check the AMM and recontact your suppliers.


When a Tower and the Approach Control closes who takes over the airspace?

All airspace is ultimately owned by some Center (US: ARTCC, ICAO: ACC). Some is delegated to Approach facilities (US: TRACON), and Approach can sub-delegate part of their airspace to a Tower. And Center can delegate airspace directly to Towers without an overlying Approach.
If any facility closes, it’s associated airspace automatically reverts back to whoever had delegated it.


Why does the use of reverse thrust on the DC-8 generate a pitch-up moment rather than a pitch-down moment?

What you're missing from your diagram is @JohnK's drawing (which I'll borrow) from his answer to your related question, Why does the use of reverse thrust in flight on the DC-8 cause areas of separated/reversed airflow over the wing?

The use of reverse thrust increases the wing's angle of attack (AOA) more than it does for the tailplane (as opposed to if the whole plane had pitched up). And not only that, the inboard thicker part of the wing now starts with turbulent air, this reduces the amount of lift at the neutral point (aka aerodynamic center), unlike what happens in a normal AOA increase.

Since the AOA of the tailplane hasn't changed much, it can't contribute to the stability, and with the big reduction in lift, the tailplane wins and the plane pitches up.

Think of it as deploying spoilers, but spoilers that affect the wing from before the leading edge:

  When extended, wing-mounted speed brakes usually produce a nose-up pitching moment (Boeing).


Vintage army Kollsman altimeter - any info?

You should think about selling that altimeter to a museum because you have a piece of history. Kollsman was one of the first people to make barometric altimeters and a Kollsman was used on the first deomonstrated instrument flight by Jimmy Doolittle.
Excerpt from Wikipedia:

Paul Kollsman (February 22, 1900 in Germany – September 26, 1982 in Beverly Hills, California) was a German-American inventor. He invented barometers and instruments for instrument flight in airplanes.
Kollsman studied civil engineering in Stuttgart and Munich (Technische Universität München). In 1923 he emigrated from Germany to the United States. He worked as a truck driver until he found a position at Pioneer Instruments Co. in Brooklyn, New York. In 1928 he founded his own company, Kollsman Instruments Co., with $500 of seed money.
He spent a long time searching for the right opportunity to launch his product, then Jimmy Doolittle flight-tested his instruments. His instruments were later used in the NASA Apollo program. The altimeter setting window of the sensitive aircraft altimeter is named the "Kollsman window" after him.


Does the validation of an ICAO licence allow you to fly internationally?

When doing the validation e.g. in France you will get a validation from an EASA member which enables you to fly an EASA registered plane world-wide.

EASA includes registered planes from

Austria
Belgium
Bulgaria
Croatia
Cyprus
Czech Republic
Denmark
Estonia
Finland
France
Germany
Greece
Hungary
Iceland
Ireland
Italy
Latvia
Liechtenstein
Lithuania
Luxembourg
Malta
Netherlands
Norway
Poland
Portugal
Romania
Slovakia
Slovenia
Spain
Sweden
Switzerland
United Kingdom


What is the geoid undulation used for in aviation?

Earth gravity is not uniform due to the non-uniform distribution of mass/matter. Above is the standard model used to describe the undulation (up/down differences) of the geoid: Earth's sea surface's shape based on gravity and rotation (winds and waves are unaccounted for).

GNSS satellites orbit around Earth's center of gravity (a single point). So there will be differences between what a GNSS measures based on its model of the Earth (based on this single point: ellipsoid), and the actual.

Not all countries adhere to the standard above, hence the difficulty is agreeing to a model. GNSS devices use look-up tables to correct for the difference (the two spheres in your post are the difference between what the satellite sees and what it should see).

Cockpits show neither to the pilots. They use indicated or pressure altitudes/levels that work on the barometric pressure.

For cockpit indications: GNSS systems can't substitute for pitot-static measurements because everyone needs to have the same system and have a reliable refresh rate that is independent of external sources. As the image below shows, a pressure based altitude/level is also undulating due to the non-uniform surface pressure and lapse-rates. Planes fly up and down in level flight but it's hard to notice.

(Source)

For charting the terrain: Whichever system a country uses to mark the terrain on its charts, they will state the source in the AIP, as you've demonstrated. For the geoid, countries may even use different models as I wrote earlier.

The good news is each local station will correct the QNH based on the sea level pressure based on the country they are in.

RE edit:

821 ft is the 'H', which is the above MSL elevation after taking into account the geoid. 'h' is what an uncorrected GNSS receiver measures (982' in that picture), and needs to correct by 'N' (161'). Positive undulation is removed since it's above the 'ellipsoid datum'.

What is it used for?

Not used in the cockpit. It is used for local charting (standards differ from place to place; AIP's mention the source).

RE note:

  If an aircraft is 35,000 ft above Saint Exupéry airport, then this gives two possible horizontal positions, which for aircraft can be very distant.

No. But I have to explain why. There is no diagram online to explain it since it's a no, so I made my own erroneous diagram.

blue is geoid
dashed in ellipsoid
red is uncorrected receiver height (minus the bit travelling through the Earth)
green circle shows the different surface locations based on the normals from the different ellipsoid heights down to the geoid (what is proposed; it is not correct)
(ξ, η) is the deflection of the vertical, the angle stems from the ground, since the topography (different from geoid) is not illustrated above, it stems from where the geoid and ellipsoid meet (a correct sea level for both models)

Deflection of the vertical:

Imagine a table with non-uniform legs, such that two opposite corners are at on the same level, and the other two are not. If I place a ball on that table, it will move toward the lower corner.

If I want to measure this table's level against the ceiling/ground, I will need two vertical angles, one north-south and one east-west. If we had one angle, we wouldn't know the level's direction. That's why two angles are used.

Measuring this deflection is a key element in knowing the undulation (it changes from location to location). That's the angle that is causing this confusion.

x and y:

Now imagine yourself on top of a monument, this monument has x and y ellipsoid coordinates. You then attach yourself to a weather balloon and climb straight up (with reference to gravity). Your handheld GNSS receiver will not show different x and y values for two reasons:

x and y are not derived from z (whether corrected or not)
your ellipsoid (x, y) location has nothing to do with the undulation

The undulation is a correction for the z, it does not shift your [physical and measured] present location regardless of altitude. If the height (red line) is straight up from the monument, then left and right of the red line are different undulations for different locations.

Note that I couldn't draw the erroneous normals on the other side of the red line if I wanted to.

Check this article: How do GNSS-derived heights differ from other height systems? It explains where high accuracy is needed, and the issues that may arise when two countries with different geoid systems decide to build a bridge between them.

As @JanHudec mentioned, EGPWS needs the correction because its model is ellipsoid. So country x needs to have a system by which they measure the geoid, its undulation, and report to the aviation industry the correction. That's why when an airport is not in the database, the pilot gets, "caution, terrain," when they are on a good approach.

Another application is minimizing the drift of the inertial navigation systems, since they inherently indicate the astronomic vertical. It's cheaper to just correct the drift via the GNSS such as on the Boeing 787 (align-in-motion).


How often is the fuel sampled in turbine aircraft?

Water and microbiological contamination are a threat to turbine aircraft even if water mixes with kerosene based fuels:

Industry-wide, the major threat to FQIS [Fuel Quantity Indication System]
availability is microbiological contamination of
the fuel (see FAST 38) and water in the fuel tanks.
Settled water in the fuel tanks may affect FQIS
indications, typically driving FQIS probe readings
out of limits and leading to aircraft delays for tank
draining. Therefore, a regular water drain task
is essential for smooth aircraft operations.

(Airbus FAST 42)
The reason is that both water and microbiological contamination in the fuel lead to a higher dielectric capacitance, which is used for fuel quantity sensing:

The FQIS system is calibrated for
use with jet fuel and the probes
measure from 'unusable' to full
tank capacity. However, the
dielectric of water is approximately eight times higher than the
jet fuel dielectric. Therefore, when
there is water in the proximity of
the probes, the fuel measured capacitance changes. Typically, the
probes will read a higher capacitance level than the actual fuel
level.

(Airbus FAST 42)
If only a small amount of water is suspended in the jet fuel, it can be safely fed to the engines without causing a flameout. However, water collecting at the bottom of the tanks must be drained:

All modern civil
aircraft incorporate water drainage
and/or scavenge systems to help
achieve this. The Airbus wing
design ensures water is maintained
in suspension and fed to the
engines; any remaining water is
then drained at regular intervals
via the water drain valves.

(Airbus FAST 38)
For an Airbus A320, this fuel tank draining must be performed at least once every 36 hours:

The amount of water drained is about 200 ml per week and per tank on an A340 after improvements done in 2007 (Airbus FAST 42).
Airbus recommends to visually inspect the drained water and to perform a fuel analysis at least once a year to detect contamination:

A second key element of prevention is monitoring. Often overlooked is the need to visually
inspect any water resulting from
the MPD water drain task. Drained
water and fuel will separate within
the container with the water
settling to the bottom. Both should
be clear with no particulates
evident to the naked eye. Any
'cloudiness' in either fluid indicates
possible contamination and action
is required.
Currently, Airbus recommends an
annual analysis of fuel from each
aircraft to test for fuel/water contamination, which should be considered a minimum for all operators.

(Airbus FAST 38)
Should the visual inspection show any contamination, or should the pilots notice discrepancies in their fuel analysis (see e.g. here for example calculations), or should the FQIS show fluctuations or degrading (fuel quantity indicates XXX), a detailed analysis should be performed according to this flow chart:

(Airbus FAST 38)


How are VORs oriented near the magnetic poles?

In Canadian Airspace, Northern Domestic Airspace (NDA) is the area of compass unreliability within which runways and NAVAIDs are oriented to true or grid north versus magnetic north.

You should not need to worry about which NAVAID is to true north; simply keep track of whether you're in Southern or Northern Domestic Airspace.


What happens after a clearance or an instruction has been sent by ATC using CPDLC?

Voice communication and CPDLC co-exist as means of ATS communication. CPDLC is considered a supplement to voice communication - even if that may change in the future.

CPDLC is only used for non-time-critical communications. This aspect is very important in the context of your question. A response to a message sent via CPDLC can be up to several minutes, whereas for a message sent via voice radio, a reply can be expected within seconds; pilots and controllers know this, and will only use CPDLC if a relatively long response time is acceptable.

Generally speaking, when communication is initiated via CPDLC, the response should be via CPDLC, and when communication is initiated via voice, the response should be via voice. However, there are situations where it is beneficial to revert to voice communication after a CPDLC message has been sent. One example is when it is necessary to ensure the timely execution of an instruction issued by CPDLC, another is when a system generates a time-out or error. There is no standard time limit for replying to a CPDLC message, but various systems probably have some sort of time limits in them.

Standard phraseology is established for situations where it is required to revert to voice communication. One example is:

  SAS123, disregard CPDLC climb message, break, climb FL330

In this case a CPDLC message to climb sent to SAS123 is no longer valid, and instead the crew should react to the voice instruction to climb to FL330.

If the sender of a CPDLC messages wants to cancel a previous message, this is indeed possible using CPDLC - but most of the time it is probably desirable to do so via voice, to make sure the message is conveyed immediately. The ICAO Standard CPDLC message for cancelling a previous message is UM168:

  DISREGARD

Answer largely based on Introduction to CPDLC Operations (SKYbrary) and PANS-ATM Appendix 5.


What is the difference between ACARS and ADS-B?

One can easily get lost in the alphabet soup that is datalink.

Both ACARS and ADS-B provide datalink applications – which can be broken down in terms of CNS: Communication, Navigation, and Surveillance.

ACARS is used for:

Communication: includes uplinking (ground → aircraft) weather data upon a downlink request to the company/service provider – not a public service
Navigation: if you consider flex-routing
Surveillance: position reports in the North Atlantic for example (CPDLC over ACARS).

ADS-B is used solely for Surveillance; broadcasting (OUT) own location – and can include ownship surveillance by receiving (IN) traffic information.

If this IN setup is via the UAT frequency, then the aircraft can also receive weather information using FIS-B (free service). Its only relation to ADS-B in this particular instance is the UAT frequency, and it is more of a general aviation (and low-flying commercial) service.

Source: https://www.faa.gov/nextgen/programs/adsb/pilot/#fisb


Can pilots use PAN PAN Medical, even if they were not on MedEvac mission?

The UK CAA Radiotelephony Manual (CAP 413) has the following to say about it:

  PAN PAN MEDICAL is not used in the UK but refers to a Geneva
  Convention term associated with medical transportation by parties
  involved in a conflict.

  Use of this term is not appropriate in the UK.

Which seems to be a pretty definitive no. Personally, I'd not heard of the term but assuming the CAA's interpretation of the ICAO's definition (i.e., for use during war) then I can't imagine it ever being appropriate outside of that use.

That said, why would you need to? Using a normal MAYDAY or PAN call and describing the emergency as a medical one is perfectly acceptable and would be fully understood by all parties.


RNAV freed aircraft from the airways that were already in place that may have zig zagged from VOR to VOR, but with the limitations of the ATC system based on human controllers, it is still desirable to keep most aircraft on a "road network" so to speak to make it easy to manage separation, so RNAV airways were created between major centers that provide straighter roads between cities you might say.

Try to imagine thousands of flights going hither and yon all on their own random tracks, instead of being fed along specific airways, without a bank of supercomputers to manage the separation, and you can see the problem that the RNAV airways solved.


Is the highly optimized high subsonic cruise airfoil less safe for higher AOA flight?

The short answer, whales aside, is yes.  Such wings, called "supercritical"  because the critical Mach# is elevated, tend to suffer from leading edge stall that makes the aircraft's natural stall behaviour dangerous.  These airplanes typically require stick pushers (as @Peter Kampf mentions in this answer, the 737, even the later ones that got redesigned wings, doesn't really have a "pure" supercritical wing and I believe that's why they don't require stick pushers).

The Challenger business jets and the CRJ line of Regionals all have supercritical wing  profiles.  The profile promotes a pre-stall flow separation and immediate reattachment at the LE, called a Laminar Bubble, which would form at some AOA prior to stall.

This had an effect similar to having a stall strip or ice shape, with the bubble forming a trip wire so to speak.  It causes the wing to stall at the leading edge instead of advancing from the trailing edge, which meant the entire wing just let go all at once with no buffet or other warning, with a tendency to progress right into a deep stall.  The Challengers and RJs have stick pushers because of this; they must never be allowed to stall naturally, because it is probably going to be unrecoverable.  Bombardier did a lot of testing with various aerodynamic band-aids like vortex generators and vortilons and such, and they didn't help.

The CRJs larger than the 200 have LE slats and are just about unstallable slats out, but they also have the same LE stall slats retracted and still require stick pushers.  Flying with slats extended at high speed is out of the question. The drag they produce is massive, as you discover when you first land one after flying a hard leading edge CRJ200. Incorporating a fixed slot in the leading edge could be done but they are pretty draggy and would negate the benefit you're trying for in the first place, and I'm sure there are other mach related issues with a fixed slot.


Are agricultural pilots allowed to use a highway as a runway?

My answer is colored by having spent a couple of years as an ag applicator.

There is no endorsement needed to use the highway as a runway.

Practically, it is done less now than 30 years ago.  Also more states have codes now which prohibit operating aircraft off public highways.

Locally an operator used a paved road which terminated at an interstate, where all the houses on that road were owned by the same family. In 1978 that operator had to scramble, because the town decided to enforce a code prohibiting aircraft from using town roads for landing and takeoff.  The only other place I have seen it today is in parts of the northern mid-West. I am not familiar with their local codes or state codes.


61 vs 141: What's better for future US ATP?

Either one is fine, though I'd make sure you seek a good instructor for a part 61 and follow a part 141 syllabus (available through ASA, Jeppesen, King Schools, etc.) when you do yours to verify you covered all the bases.

At that stage of your training, future employers really won't care that much whether you did your training as a 61 or 141 student.  They are going to be much more concerned with your professional flying record and later certification and checkrides.


I have worked on large and small aircraft.  You will find a 400hz power bus only on large aircraft. The reason is the greater quantity of poles in the generator and hence weight. Smaller aircraft use a 28v DC system for the avionics.


How can ATC distinguish planes that are stacked up in a holding pattern from each other?

Sometimes we can't.
While having two radar targets presented directly on top of each other is not really an issue (most radar presentation systems lets you move the data label around freely, so you can prevent overlap), the radar system itself can sometimes confuse two targets that are very close. A radar will search for aircraft by sending out a signal and waiting for the aircraft transponder to respond. When two aircraft are very close, they will receive the request from the radar almost at the same time, so their responses will be at the same time as well. The radar will receive the two replies on top of each other, which can result in garbling (see this related question).
In some situations, the radar software can also confuse two close targets, swapping the label between them, so aircraft A is presented to the controller as aircraft B and vice versa. We also sometimes see this close to an airport, where a departing aircraft can "steal" the label from an aircraft on short final, making it look like the departing aircraft is actually the one just about to land.
As a result of these issues, we are not allowed to use normal radar separation to individual aircraft in a holding stack. Instead, radar separation will be provided to a defined holding area, which is a geographical area established around a holding stack, large enough to ensure that anyone holding will remain within. Inside a holding stack, as you correctly noted, only vertical separation is used.
Mind you, most of the time, aircraft in a holding pattern are not flying directly on top of each other. That would require them to enter the holding at exactly the same time, fly at the exact same speed and turn at the exact same rate, which just doesn't happen. So the issues described above are not a problem most of the time, but they are common enough that we have specific procedures to mitigate the risks imposed.


Why does the radome on the AWACS rotate?

Basically, the radar antenna of the AWACS system is just like this (source):

Rotating waveguide antenna (picture source)

The round shape is only an aerodynamic fairing. Proof:

Boeing E-3A AWACS cutaway (picture source)

A surveillance antenna can also be fixed. Electronic beam steering helps to view a sector of approximately ±60°, but in order to get a 360° sweep the airplane needs to fly circles. Beam steering is also used on the rotating antenna to rapidly switch between several targets, so this is not unique to a fixed antenna:

Pakistani AWACS based on EMB-145 (picture source)


When should an Obstacle Departure Procedure (ODP) be used?

According to the definition of the FAA it is a recommended procedure, so there is generally no need to follow it.

  OBSTACLE DEPARTURE PROCEDURE (ODP)- A preplanned instrument flight rule (IFR) departure procedure printed for pilot use in textual or graphic form to provide obstruction clearance via the least onerous route from the terminal area to the appropriate en route structure. ODPs are recommended for obstruction clearance and may be flown without ATC clearance unless an alternate departure procedure (SID or radar vector) has been specifically assigned by ATC. (Source: FAA Pilot/Controller Glossary)

According to FAR 91.175 you are responsible to ensure sufficient obstacle clearance if the airport is IFR (of course also if the airport is VFR).

  (f) Civil airport takeoff minimums. This paragraph applies to persons operating an aircraft under part 121, 125, 129, or 135 of this chapter.
  (1) Unless otherwise authorized by the FAA, no pilot may takeoff from a civil airport under IFR unless the weather conditions at time of takeoff are at or above the weather minimums for IFR takeoff prescribed for that airport under part 97 of this chapter.
  (2) If takeoff weather minimums are not prescribed under part 97 of this chapter for a particular airport, the following weather minimums apply to takeoffs under IFR:
  (i) For aircraft, other than helicopters, having two engines or less--1 statute mile visibility.
  (ii) For aircraft having more than two engines--1/2 statute mile visibility.
  (iii) For helicopters--1/2 statute mile visibility.
  (3) Except as provided in paragraph (f)(4) of this section, no pilot may takeoff under IFR from a civil airport having published obstacle departure procedures (ODPs) under part 97 of this chapter for the takeoff runway to be used, unless the pilot uses such ODPs.
  (4) Notwithstanding the requirements of paragraph (f)(3) of this section, no pilot may takeoff from an airport under IFR unless:
  (i) For part 121 and part 135 operators, the pilot uses a takeoff obstacle clearance or avoidance procedure that ensures compliance with the applicable airplane performance operating limitations requirements under part 121, subpart I or part 135, subpart I for takeoff at that airport; or
  (ii) For part 129 operators, the pilot uses a takeoff obstacle clearance or avoidance procedure that ensures compliance with the airplane performance operating limitations prescribed by the State of the operator for takeoff at that airport.

In this case it seems to be the easiest way to follow the ODP, but it's not binding.

Lnafziger  correctly commented that this is not applicable for part 91 operation. That's why I like to add a part of this Article, which I've found on the AOPA website, to my answer.

  [...] We cannot assume that ATC will assign any special routing or altitude based on the ODP. They expect the pilot to fly the procedure if necessary without further clearance. FAA Order 7110.65R, Air Traffic Control--the controller's handbook--states, "If a published IFR departure is not included in an ATC clearance, compliance with such a procedure is the pilot's prerogative." In other words, you have to decide whether you need to follow a specific route or procedure and fly accordingly. Now, we might think this is wrong, dangerous, and dumb, but it is the way procedures are arranged.[...]

According to all this information ATC would expect you to follow this procedure, at least in IMC. If you like to fly it in VMC and it does not disagree with your ATC clearance you are also welcome to do so. If there is any confusion I tend to ask and clarify the situation.

In most cases an ODP says that you should climb on runway heading at least until passing xxx feet before turning in a direction. I would always comply with it and if there is severe CAVOK and ATC then asks me to turn earlier, I would do it, so everyone is happy and on the safe side.


The categories are actually approach categories that are also used for departures. From the AIM, 5−4−7. Instrument Approach Procedures

  Aircraft approach category means a grouping of aircraft based on a
  speed of VREF, if specified, or if VREF is not specified, 1.3 VSO at
  the maximum certified landing weight. VREF, VSO, and the maximum
  certified landing weight are those values as established for the
  aircraft by the certification authority of the country of registry. A
  pilot must use the minima corresponding to the category determined
  during certification or higher.

  Category A: Speed less than 91 knots.
  Category B: Speed 91 knots or more but less than 121 knots.
  Category C: Speed 121 knots or more but less than 141 knots.
  Category D: Speed 141 knots or more but less than 166 knots.
  Category E: Speed 166 knots or more.

These categories are used to determine visibility and ceiling minimums for an approach and determine the protected area for circling approaches. As you can see in the departure minimums you quoted, they are also used for departures.


Why would a diverted airline flight return to its departure airport rather than land at the nearest one?

It sounds like it was a non-emergency condition where it wasn't feasible to continue to destination but it wasn't imperative to land ASAP. Something like an anti-icing malfunction where you can't continue into icing conditions (all you need is visible moisture and temps close to freezing; clouds of any kind near or above the freezing level constitutes "technical icing conditions" and you may at minimum have to have working cowl anti-ice to fly through them).

The crew will often consult with airline Operations and Maintenance Control over a desired diversion airport.  Having decided not to proceed to destination, the next best choice is to go back to the departure airport, where passengers that originated at the departure airport can simply go home and return for a later flight.

The other major factor is maintenance related.  Maintenance Control will often ask the capt to divert to airport X because the resources are there, so if the departure airport was a maintenance base, that's another plus.


Is Touring Motor Glider included in the term "aeroplanes"?

To my understanding of Part-FCL, yes.
While aeroplanes is a broad term used in the FCL, they use it in some cases to include both, SEP and TMG, e.g.

  FCL.105.A LAPL(A) —Privileges and conditions (a) The privileges of the holder of an LAPL for aeroplanes are to act as PIC on single-engine piston aeroplanes-land or TMG with a maximum certificated take-off mass of 2 000 kg or less, carrying a maximum of 3 passengers, such that there are never more than 4 persons on board of the aircraft.

and hence

  FCL.210.A (b)  Specific requirements for applicants holding an LAPL(A). Applicants for a PPL(A) holding an LAPL(A) shall have completed at least 15 hours of flight time on aeroplanes after the issue of the LAPL(A), of which at least 10 shall be flight instruction completed in a training course at an ATO. This training course shall include at least 4 hours of supervised solo flight time, including at least 2 hours of solo cross-country flight time with at least 1 cross-country flight of at least 270 km (150 NM), during which full stop landings at 2 aerodromes different from the aerodrome of departure shall be made.

Source: https://www.easa.europa.eu/sites/default/files/dfu/Part-FCL.pdf


What does the phrase from the FAA, "clear to maneuver" mean?

That isn't standard FAA phraseology; at least, it isn't anywhere in the ATC orders. The closest thing is in section 9-2-20 on evasive action maneuvers. I know nothing about them, but they seem to be a military training thing:

  PHRASEOLOGY−
  CLEARED TO CONDUCT EVASIVE ACTION MANEUVER FROM (fix) TO
  (fix),
  and
  (number of miles) EITHER SIDE OF CENTERLINE,
  and
  MAINTAIN
  (altitude) THROUGH (altitude),
  and
  COMPLETE MANEUVER AT (fix) AT
  (altitude)

But of course both pilots and controllers use non-standard phraseology all the time, especially for unusual situations. It's certainly possible that a controller somewhere has indeed said "cleared to maneuver as requested" or something similar. Although the 'correct' phraseology would be "approved as requested" (see section 2-1-18 of the orders) for a general request.

Another possibility is that it's military phraseology, not civilian. If you can link to a source or ATC recording then you might get a better answer.


A fused radar track is a track (series of radar detections belonging to the same aircraft) that contains information from detections by multiple radars.

Creating a fused track seems a simple thing to accomplish, however it is not as easy as it may seem.

First of all, lets look at a mono-sensor track. That is a series of detections by a single sensor belonging to the same aircraft. The tracking system has to determine for each detection to which track it belongs to associate the flight data (e.g track label) for that track to the plot (display of the detection on the screen). For primary radar systems (and to lesser extent Mode A/C radar) this can already be difficult when tracks are crossing each other at shallow angles. Especially when you know that the measurements are a bit noisy; an aircraft flying a straight line does typically create a somewhat randomly jagged line.

Now suppose we want to add a second radar to the mix, because the coverage area of a single radar is not big enough. Now we have a situation where there is a common coverage area where the two radars provide overlapping coverage.

In an ideal world, this would show the detections exactly in line with each other. However, each radar has their biases are other measurements error (with various sources, partly external to the radar system). So instead of one track for one aircraft, we end up having two tracks for one aircraft, sometimes a mile apart. This is of course not ideal and can even lead to safety risks.

A simple solution is to have a mosaic system; in such a system there is for each geographical area exactly one radar appointed to provide the surveillance data to the air traffic control's display. The down side of such a solution is that at the edge of the mosaic tiles, when the aircraft moves from one radar area into another, the track may jump because of the differences in measurement errors in both radars. Again not an ideal situation.

That is where radar fusion comes in. In a multi radar tracker, data from multiple radar is combined into a single track. In the process, biases and other measurements errors are greatly reduced, resulting in a track that generally much smoother than a single sensor track. Because of the identification of radar biases, there is no discontinuity (jump) when track move out of coverage of one radar. And due to the higher rate of updates from multiple radars, the update on the radar screen can often be increased as well.

The fused radar track is no longer a depiction of detected positions, but calculated estimate of where the aircraft is based on data from all radar (or other sensors) used in the fusion process. The mathematical process behind the fusion often uses on a form of Kalman Filtering, highly adapted for this task. Outliers are discarded to improve the smoothness of the track.

Trackers like ARTAS or Phoenix do not only fuse radar data into the track, but also include data from ADS-B and Wide-Area Multilateration (WAM). We then speak about a (fused) multi-sensor track instead.


Why do some airports have a non standard traffic pattern altitude?

Airports underneath controlled airspace may need to keep their traffic clear of controlled airspace, which may start from a typical altitude such as 1000Ft.

As is also mentioned in this answer, in April 2013 the standard pattern height was changed from 800 ft to 1000ft, possibly accounting for a number of airports still having the old "standard".