Why does the moment coefficient for angle of attack = 0° not have to be negative? I know for static stability reasons, the derivative of the moment coefficient of an aircraft has to be negative.

What I do not understand, why the moment of coefficient (cm) at all is allowed to be positive? Because when it is positive the aircraft pitches up.

Is it because when cm>0 I use my tails for trimming ? But is this "static stability" when I actively use my tail ?

I struggle with:
alpha = 0 ° --> e.g. cm=0.3    : the tail is used for trimming so that it counteracts the positive moment of the wing

alpha = 2° -- > e.g. cm=0.4 : now the pilot could also use the tail for trimming the higher moment

Thank you for your hints

An airplane achieves steady flight at a given airspeed only if the total pitching moment about its CG is zero. This is achieved with a particular fixed tail angle/elevator angle/canard angle. If the AOA corresponding to the total lift at this airspeed is 0 AOA, then so be it. It's just that for typical airplanes at operational speeds (away from $V_{FE}$ for example), the AOA is typically larger than zero; this means that, for a typical plane, the pitching moment at 0 AOA must be larger than zero at the tail angle, elevator angle, etc. corresponding to the trim speed for static stability.

Why larger than zero? Static stability means that when perturbed from the trim AOA (at which the pitching moment is zero), the resulting pitching moment will return the aircraft back to its original trim without pilot compensation. Take a look at the graph below; note that the moment is zero at AOA=1.5 (i.e. the trim condition).

If the pitching moment at zero AOA is negative (the orange line), then the airplane will diverge from its trim point when perturbed. That's the opposite of static stability.


Can US pilots fly VFR OTT and/or VFR at night in Canada without additional ratings? In the US, private pilots flying under VFR are implicitly allowed to fly without visual reference to the ground, eg. over an overcast cloud layer, as long as they maintain appropriate VFR weather minimums. The same is true for flying VFR at night.

In Canada, a separate add-on "VFR OTT" rating is required in order to operate "over the top", and there's also an add-on rating for flying VFR at night.

US pilots can operate Canadian-registered aircraft through a Foreign License Validation Certificate, which as far as I can tell confers the privileges of one's native certificate. According to the ICAO, "certificates of competency and licenses issued or rendered valid by the contracting State in which the aircraft is registered, shall be recognized as valid by the other contracting States".

So the question is: do US pilots operating Canadian-registered aircraft via a FLVC need additional ratings to fly VFR over-the-top or at night in Canada, or are the inherent privileges of their US pilot certificate extended to Canada as well?

It looks like if you have a foreign instrument rating you automatically have VFR OTT privileges, but for night VFR you still need a Canadian night rating.

CAR 421.44(7) for VFR OTT:

  An applicant who holds or has held an instrument rating issued by a
  Contracting State shall be considered to have met the Knowledge,
  Experience and Skill requirements specified above

As for night VFR, 421.42 doesn't have any equivalent section that gives credit for foreign qualifications.


Navigate to the final approach course after radio failure under IFR What would ATC expect the pilot to do if, at the position marked below by the red X, the aircraft lost radio communication and was on a radar vector heading 250 degrees at/assigned 3000 msl and the pilot was told to expect the ILS approach to Runway 7 Right? Assume the IFR aircraft did not have DME, RNAV or GPS equipment and the weather was IMC.

First, squawk 7600 to let ATC know you have lost two way radio communications and to clear traffic out of your way.

Then, from the AIM, Section 4. Two-way Radio Communication Failure

Section 6-4-1.c. includes:

  1. General. Unless otherwise authorized by ATC, each pilot who has two-way radio communications failure when operating under IFR must comply with the rules of this section.

and

  2. VFR conditions. If the failure occurs in VFR conditions, or if VFR conditions are encountered after the failure, each pilot must continue the flight under VFR and land as soon as practicable.

This is the preferable solution, but the question said to assume the conditions are IFR. Which leads to (displaying only applicable sections):

  3. IFR conditions. If the failure occurs in IFR conditions, or if subparagraph 2 above cannot be complied with, each pilot must continue the flight according to the following:

  (a) Route.
   ...
  (2) If being radar vectored, by the direct route from the point
  of radio failure to the fix, route, or airway specified in the vector
  clearance;

  (c) Leave clearance limit.

  (1) When the clearance limit is a fix from which an approach begins,
  commence descent or descent and approach as close as possible to the
  expect further clearance time if one has been received, or if one has
  not been received, as close as possible to the Estimated Time of
  Arrival (ETA) as calculated from the filed or amended (with ATC)
  Estimated Time En Route (ETE).

So the expectation of ATC would be that the crew would fly outbound, make a right turn and intercept the localizer and fly the approach.

It would be a challenge to fly it without DME, but not impossible from the starting point. Radar or DME (or GPS) is needed to get to the IAF. If the pilot had a good estimate of his location when comm was lost, it would be to fly outbound for about 1 minute and then a right 180 deg turn to intercept the localizer. Once the glideslope is intercepted, being on GS plus altitude allows to to estimate passage of TIMSE and FUMBL. The rest of the approach can be timed.


Are aircraft sounds publicly available in a repository? Referring to the automated callouts and sounds made by the fwc, tcas, gpws, pws, etc. — are these available to download in one repository at all? For any aircraft, Airbus or Boeing.

Understandably, these may not be freely available, but I'm curious otherwise too (e.g. the likes of Air Crash Investigation must do this).

One place to look is models of the planes for flight simulators. There is generally a "sounds" folder of some sort inside the airplane folder that includes some cockpit sounds.

I'm guessing the original files are proprietary and there is really no reason for the companies to freely share them. Shows like Air Crash Investigation might get access to a simulator that can make all the real sounds.


Is there a resource that lists what's outdated in "Stick and Rudder"? The classic book is awesome but I do know some of the terminology is outdated and perhaps some other things.  Is there a site etc. that keeps track of what's outdated in the book "Stick and Rudder" and what the newest equivalent terms?

I'm not aware of such a list although I would say 99.99% of this book is not outdated.

Maybe some of the terminology is outdated when it talks about the "gaits" of the aeroplane for example which is an horse term apparently.

I wouldn't say anything else is though certainly not the concepts, because the air is the same, the laws of physics are the same and human nature the same as it was 70 years ago. Its a very insightful book that should be every pilots reading.

Maybe it goes on more about tail-wheel aircraft and there are fewer of these aeroplanes around today but this only applies on the ground and is still very interesting even for nose dragger pilots like me.


How can I get more details about information in a NOTAM? In doing some planning for an upcoming flight, I noticed my destination (a towered airport) has a NOTAM about the runway: "FICON PATCHY ICE". That seems rather vague, I'd like more information before departing. Who should I contact to get more details about the runway conditions and how it might affect my flight?

What, you dislike the fact that the NOTAM about patchy ice is patchy in its detail? :)

Generally if you need more information about a NOTAM (in the US) you can check with:

Flight Service
While collecting your briefing ask if they have any more detail -- sometimes they do, sometimes they don't, but it's worth asking.
A local FBO
Particularly for FICON NOTAMs - A local FBO will usually know the condition of the field, and often have other useful info for you (like how much a heated hangar is going to cost you for the night).
Airport Operations
Again, particularly for FICON NOTAMs - These guys will usually have a pretty good picture of the field's condition, since they're generally the poor shmucks responsible for doing the snow/ice clearing.

Failing all of those, you can also call the tower phone number at a towered field (you can get that number from Flight Service too) and ask them for details.
I usually make the tower my last resort call - they're almost certainly going to be willing to give you as much information as they can, but they're also busy doing other stuff like dealing with planes taking off/landing/taxiing around & they'd probably appreciate if we tried the other sources first.
The other folks I mentioned generally have someone sitting around to answer phones and questions.
In the case of Flight Service, that's basically their job :-)


What is the Saint-Venant formula for calculating equivalent air speed (EAS)? I'm studying some ground exams (for a lapsed IR). In the course notes it says that EAS (Equivalent Airspeed, i.e. a compressibility-corrected airspeed) is calculated (e.g. by an aicraft's Air Data Computer) using the "Saint-Venant formula". The course notes don't actually give said formula.

I assume they are talking about this guy who derived a forerunner of the Navier-Stokes equations. However, most of his work seems to be to do with waves in shallow water and not aerodynamics. I think I know how EAS is calculated, and it doesn't seem to involve anything as hairy as Navier-Stokes (although it does require isentropic flow relations.) But I can't figure out how Saint Venant has anything to do with it. From another forum: "In the EASA learning objectives I can find no reference to 'Saint-Venant' so it is probably just something somebody thought up to confuse you." Can anyone shed any light on this?

I found this snippet

from Flight Mechanics of High-Performance Aircraft, by Nguyen here.

I'm not sure if this answer is consistent with the answer given Ugo..


When not cleared straight in for a VOR approach, how is this type of procedure executed? You are flying to the GDM VOR on a 097 heading. The ATC clears you for the approach, but does not specify straight in. The procedure turn is marked by the barb and specifies remaining within 10nm. My assumption is that you would fly a procedure turn style course reversal, using the altitude of 3000 within 10nm, fly the 277 back course, then fly the procedure turn inbound. I would assume most times ATC would just clear you straight in however is there any documentation of this style of double PT/unpublished course reversal procedure?

When talking about approaches, you should limit your terminology to mean the same thing for you as it does for ATC. In other words, for a Category A aircraft:

ATC would not clear you for a Straight-in Approach unless you were inbound from the South for Runway 36 or inbound from the North for Runway 18. There are no Straight-in minimums for this approach, only circling minimums. To use this approach, you are required to fly a modified Traffic Pattern no lower than 1760 feet MSL until you reach a point where you can descend safely to the runway while maintaining cloud clearance. ATC will give you instructions on which direction to circle. In the absence of instructions, circle in the direction prescribed for Traffic Patterns in the US Chart Supplement and Sectional.
There is no Back-Course for a VOR. A Back-Course implies an ILS or Localizer transmitter. VORs transmit their navigation signals differently than ILSs and Localizers. There are Radials for each VOR dependent on your bearing from it. There are To-indications and From-indications for each Radial depending on your location on the extended Radial relative to the VOR. There is normal/direct-sensing and reverse-sensing for each Indication dependent on your Heading.
If you were flying inbound direct to the GDM VOR on the 097° Radial, you are East of the VOR flying Westbound on a heading of 277° Magnetic. The safe altitude at which to remain above is the Minimum Sector Altitude of 3300 feet MSL unless assigned otherwise.
You may request from ATC a Hold at the VOR to buy time to prepare for the approach or to lose altitude. Although, it is not part of the official Instrument Approach Procedure until the Missed Approach Procedure, you may use it to get established inbound to the airport or VOR on the 277° Radial instead with ATC clearance.
If you are not cleared for the hold, or accept clearance for the full procedure, once you pass the VOR, you may descend down to an altitude at or above 3000 feet MSL as long as you remain on the 277° Radial.
You may perform a Procedure Turn (starting with a left turn to a Heading of 232° Magnetic for 1 minute, then a right turn to 052° until reestablished back on the original Radial) anywhere along the 277° Radial as long as your aircraft remains within a 10 Nautical Mile distance from the VOR during the entire procedure. The general convention is to travel at least 2 miles or 2 minutes before starting the Procedure Turn.
Once you are established inbound on the 277° Radial with a Course and Ground Track of 097°, you may descend down to, but no lower than, 2400 feet MSL until you reach the Final Approach Fix which is the GDM VOR. Please be cognizant of the fact that when ATC Radar services are unavailable, other aircraft may be holding at the GDM VOR at or above 3000 feet MSL. It would behoove you to cross GDM inbound below 3000 feet MSL.
Once you have passed the Final Approach Fix, you may descend down to, but no lower than, 1760 feet MSL to start your Circling Approach. The Circling Approach May only be started if you have established visual contact with the runway.
If you never establish or are unable to maintain visual contact with the runway environment during the entire Circling Approach, remain on or return to the 097-From/277-To Radial until you reach the Missed Approach Point of 1.9 miles DME from the VOR (1 minute, 54 seconds at 60 knots ground speed). If you still have not established visual contact, perform the Missed Approach Procedure (a climbing left turn to circle back to the GDM VOR, climbing to hold at GDM at an altitude of 3000 feet MSL).
If, at any time during your descent past the Missed Approach Point, you can not maintain cloud clearance, circle back over the runway to join the Missed Approach Procedure.

—————————————————————————————————
Per the OP’s edit:

Remain at or above the MSA for the inbound heading from which you are coming or your assigned altitude.
Do not descend until you have crossed GDM on an outbound leg.
Once you have crossed GDM, utilize the hold to descend down to but not below 3000 feet MSL.
Notify ATC on whether you will proceed in on the inbound leg directly from the hold, or do the full procedure outbound to the Procedure Turn.
If no altitude loss is necessary, notify ATC of your request to proceed inbound on the procedure. You will have more than 1.9 miles to descend down to 1760 feet MSL (depending on where you get established on the Initial Approach course/leg).
Alternatively, you can intercept the procedure anywhere on the Initial Approach course/leg if cleared by ATC. Provided you do not start your descent to 3000 feet MSL until you are established on the procedure outbound or to 2400 feet MSL until you are established on the procedure inbound. Either inbound or outbound legs must be within 10 NM of GDM.


Why does automatic trim exist only in the pitch axis? Why does automatic trim exist only in the pitch axis? For example, a flight computer can hold the current pitch automatically when engine thrust is applied.

Why automatic trim not lies in roll and yaw axis?

The pitch requires trim because pitch is related to airspeed and engine power. As both of these change quite frequently (except for the cruising phase of a flight), it is convenient to adjust the aircraft's "natural pitch" during climbs or descends, or after changing flaps.

Most aircraft* will not exhibit a tendency to roll / yaw to one side in flight, hence, it is already stable in these axis and trim is not required.

Automatic yaw trim does exist on some multi-engine aircraft. When one engine quits, the flight computer will automatically adjust rudder to compensate the undesirable yaw due to asymmetrical thrust. On an aircraft without such system, the pilot must manually use the rudder pedals, and the amount of rudder has to be adjusted as engine thrust or airspeed changes.

* Small single-engine airplanes do exhibit roll and yaw moments due to the torque and p-factor of the propeller, but these aircrafts are marketed for affordable price and easy handling, so auto-trim is not implemented.


How to measure the aircraft maintenance cost of a operator? How to measure the aircraft maintenance cost of a operator? What tool or mechanism can be used to measure such performance? Or what index can be used to determine the performance?

Maintenance costs are generally expressed as dollars per flight hour for a particular aircraft type.  Chargeable labour hours, parts, overhauls, delay costs, repairs etc., on airplane model X, divided by that airline's total flight hours on that particular type.

This kind of data will be broken down and tracked at the Line Replaceable Unit level as an hourly operating cost of the LRU itself.  Like, say, a hydraulic pump will have all expenses related to maintaining that particular part number, including repairs, overhauls, and chargeable delays/cancellations caused by failures, all added up to a global dollar amount per flight hour for that pump.  This is also tracked by the aircraft manufacturer for the entire fleet.

That number will be used to assess whether the pump is better or worse than the global fleet for that aircraft type, or compared to the same pump used on other aircraft models, to decide whether to pay for improvements, look into changing the maintenance practices, soft timing the pump (overhauling sooner than the legal requirement), and other actions.  There will be some alarm threshold established, say >$1.00 per hour, or 85 cents/hour or whatever, the airline will use to determine whether something should be done or not.

If the pump manufacturer introduces a product reliability improvement, it will be sold to the airline as providing X cents reduction in hourly costs of that LRU, along with X percent improvement in dispatch reliability. The airline will do a business case to decide if the long term saving is worth the up front expense.  They usually go by a payback period, where for example the projected hourly saving from doing an upgrade will pay for the cost of the upgrade within 5 years, or less depending on how cheap the operator is (over the last 10-15 years, a lot of US regionals have been only buying upgrades that pay for themselves in 1 year).


What drives and/or allows the move to higher-bypass turbofans on jetliners? Note: I'm by no means an expert on any of this, I'm just curious.

There seems to be a general trend toward higher and higher bypass ratios in commercial jetliner engines. (I'm thinking here of 737/A320-size and larger aircraft.)

I understand why this is happening (fuel-efficiency & noise). But what has dictated the odd pace of the development?

There was obviously a drive toward higher bypass early on. E.g. P&W JT8D engines introduced in 1962 ran at 0.96:1, while - just a few years later in 1966 - the JT9D ran at 5:1. Quite a leap.

But then it seems to me that it settled around 5-6:1 for 25 years. Next big leap seems to be the GE90 in which runs at 9:1. That was 1992 and then it largely settled again at 9-10:1 for another couple of decades. The latest (smaller) leap appears to be the PW1000G at 12:1.

What has caused such sudden jumps and plateaus? Why hasn't there either been a more linear progression from the 1960s to now? Or a much faster progression toward the ratios we see today? They're obviously desirable.

I can just imagine P&W engineers looking at the JT9D in the mid-1960s, and thinking "well, we went from 1:1 to 5:1 in one go. Let's go for 10:1 next!". But that didn't happen. It seems their next major airliner engine was the PW2000 - fully 20 years later - at 6:1.

Was it due to technical/manufacturing limitations?
Has the emphasis on certain performance characteristics shifted? E.g. settling more permanently on economy over speed.
Is it simply that fleets stabilized around certain aircraft, and no new engines were needed/wanted for a long time?

The last point seems very plausible. Even so, the 747-8, 737-MAX and A320neo, while being comparable to their ancestors in size and role, have made sudden jumps from 5-6:1 to 10-12:1 engines. That feels like something that could conceivably have happened earlier or more gradually.

Of course I know that bypass ratio isn't the only interesting metric for an engine, but it's a noticeable one, even to the untrained eye; engines are simply becoming bigger and bigger. But that's also why I'm asking about the pace of development, since "making the fan bigger" seems like an obvious step to take (I know there's more to it but still). It also seems like something that'd be more likely to happen gradually, rather than in spurts.

Again, I'm no expert, I've just been googling. But I may have missed something basic.

For a clue look at the development in the price of oil:

Historical oil price chart (source)

While the first development into the 5:1 region predates the first oil crisis (1973) and was driven by fuel economy, better range and lower airport noise, the next step was kicked off by the second crisis in the early 1980s. It took one decade to develop the engines and the airplanes which could fit them, so the Boeing 777 - GE90 combination came out in 1995 in a time of falling oil prices.

The next round was only kicked off after the US invasion of Iraq which made oil prices shoot up from 2003 on. Again it took a decade for the engines to become available, but now the increase in diameter is less dramatic and existing designs can be fitted with them (A320neo, 737MAX).

Before the early 1960s the bypass ratio could not grow more because

jet engines were developed for military aircraft, and more emphasis was placed on top speed than on efficiency. Airliners used what was available (note that the Convair 880 was powered by a simplified, non-afterburning version of the J-79, which powered the F-104 Starfighter, the F-4 Phantom II and the B-58 Hustler).
early airliners (De Havilland Comet, Tupolev 104) had their engines in the wing roots, so little space was available for an increased bypass ratio. When Rolls-Royce was developing the first turbofan engine, the Conway, they limited the bypass ratio to 0.25 so it could fit into the Comet and the HP Victor bomber, which also had its engines in the wing roots.

The first oil crisis of 1973 kicked off the development of the unducted propfan (UDF) engine, which has been held back by noise problems. Again, it took about a decade until it could take to the air.

GE36 UDF engine fitted to the MD-81 (picture source)

The development of a new engine takes longer than that of an aircraft, so every time a big push, triggered by a substantial jump in oil prices, was needed to start the development of a new generation with significantly higher bypass ratio. Once the engine technology was ready and certified, it would be quickly incorporated into many models, because the better fuel economy would force everyone to upgrade.


What is the source for the "rule" forbidding configuration changes below 200ft AGL? I keep hearing from countless instructors, and even some DPE's, that in single engine aircraft, no configuration changes are allowed below 200AGL (i.e. flaps).

Some have also stated that this is when a single engine is supposed to be stabilized, despite the 500/1000AGL rule for VMC/IMC approaches respectively.

What's confusing is this is used from instrument approaches to power-off 180's, yet I've heard people use the last notch of flaps to "bump" them to their point.

Does anyone have a source on this 200' rule? Any help is appreciated!

There is no rule.  There is a convention that you should be in a stabilized condition that requires no major control inputs or power changes in the last few hundred feet.  With jets, airlines often have an operational policy that requires a stabilized approach configuration once below 1000 ft to continue with a landing.

The reason is pretty simple.  If I'm well outside a descent rate or speed parameter close to the ground, I'm forced to attempt a much more radical correction, because I don't have much time, than I would farther out.  The radical correction will, unless the pilot is very experienced and proficient on type, invariably result in an over correction, and the result is oscillation about the target parameter just as the moment of truth is approaching, and from there things get entertaining.

So in training it's a mantra that is almost universally taught that you need to be settled in on slope and on speed when getting close to the runway.  On little airplanes, a couple hundred feet, on bigger ones, maybe 500, on transports, a thousand.  The more the mass and inertial involved, the farther out you need to be settled in.

If you are sufficiently skilled and experienced on an airplane type, all this is not quite that critical, but for a newer pilot it's pretty important.

The stuff about using the last bit of flap to stretch a glide doesn't work.  It might theoretically help you make it across a ditch before touching down if you were cutting it that close with an engine failure, but more likely it just steepens the glide angle and makes things worse.


Why are modern regional jet designs shifting towards under wing engines? Historically regional jets (eg, MD-95/B717, CRJ-700/900, ERJ-145, etc) have had their engines mounted near the rear of the fuselage.  But, recently, regional jets are increasingly using an under wing configuration (E-170/175, Sukhoi SJ100, Mitsu MRJ700 to name a few.)

A couple related questions:

Why might this configuration be advantageous for small jets as opposed to the rear mounting configuration commonly used before?
If it's advantageous, I assume technical problems are what stopped it from being implemented before.  So what has changed that allows manufacturers to use this configuration now?

The underwing engine location allows for a lighter airframe.

Placing the engines under/ahead of the wings brings these benefits:

Bending relief: Engine mass is closer to where lift is created, so the structure has less stress to carry around.
Flutter suppression: Placing the engines ahead of the elastic axis of the wing shifts the flutter speed up, so the wing can be built less stiff.
Better evacuation: With wing-mounted engines a rear door is possible to create a second point for emergency egress.
Lower noise level in the rear cabin.
More useable cabin space at the rear.
Easier access to the engines for maintenance.
Shorter piping for fuel and bleed air. Especially in the narrow fuselages of regional jets the air ducts for ventilation take a lot of valuable space.
And don't discount psychology: The underwing engine design looks more like the bigger jets, which can be a big factor for some passengers. The airplane looks safer and more mature.

With modern CFD it is much easier to reduce the interference between the engine nacelles and the wing, so the biggest disadvantage of an underwing engine location can be reduced.

Note that early designs for the Boeing 737 used rear-mounted engines. By relocating them under the wings, the structure could be made 700 kg lighter. Quote from www.b737.co.uk:

  Overall, the wing-mounted layout had a weight saving of 700Kgs over
  the equivalent “T-tail” design and had performance advantages.

The rear-mounted engines were a fad from the late Fifties (started by the Sud Aviation Caravelle) to the mid-sixties and driven by the concern about the higher risk of low-mounted engines ingesting debris and the higher asymmetry in engine-out conditions. With more operational experience and more reliable engines, these concerns proved unfounded. Citing www.b737.co.uk again:

  Initial worries about the low mounted engines ingesting debris proved
  unfounded, this was demonstrated by the Boeing 720B whose inboard
  engines are lower than the 737's and had been in service for four
  years without significant problems.

Small business jets still prefer rear-mounted engines so they can operate from more airfields (on which the runway might not be as clean as those of big airports) and because the weight penalty of rear-mounted engines is less pronounced. Instead of bending and thrust loads, handling loads and manufacturability drive the minimum skin gauges on smaller jets.


When should a pilot use the word "takeoff?" I've been taught before that the word "takeoff" should only be used when reading back a clearance, and that when requesting a clearance pilots should advise "ready" or "ready for departure."

Here's the really critical point to the question. I've always believed that the word "takeoff" should only be used when reading back a clearance for such an action. Not when requesting a clearance for that action.

I've also heard it taught that this is true only for IFR flights but it's okay to ask for a clearance with the word "takeoff" when VFR. I don't see why the difference between VFR or IFR flight would be a factor here.

Has the ICAO, FAA or any other controlling organization released any written guidance on radio communications that covers this procedure?

The word "Takeoff" should only be used when clearing somebody for takeoff, acknowledging your takeoff clearance, or cancelling/acknowledging a cancelled takeoff clearance.

"Departure" should be used in all other circumstances, and as far as I'm aware whoever told you you could use the word Takeoff for VFR was wrong.

Anybody saying the word "takeoff" intends for an aircraft to enter, accelerate along, and then leave a runway in the immediate future: never anything else. Anybody saying otherwise should be immediately directed to the Wikipedia article for the Tenerife 747 disaster.


What are the defining characteristics of aviator glasses? The title pretty much says it all.

It's easy to find pages for resellers of aviator glasses or aviator sunglasses, but what are the defining characteristics of these as compared to ordinary glasses or sunglasses?

If one were to buy from an ordinary optician not specializing in aviator customers, what should one look for or ask for to get "aviator" glasses? Correspondingly, what should be avoided?

Aviators are nothing more than a marketing gimmick developed by Bausch & Lomb back in the 1930s.  The Wikipedia page on them quotes:

  They are characterised by dark, often reflective lenses having an area
  two or three times the area of the eyeball, and very thin metal frames
  with double or triple bridge (so-called ″bullet hole″) and bayonet
  earpieces or flexible cable temples that hook behind the ears. The
  original design featured G-15 tempered glass lenses, transmitting 15%
  of incoming light. The large lenses are not flat but slightly convex.
  The design attempts to cover the entire range of the human eye and
  prevent as much light as possible from entering the eye from any
  angle.

It’s possible that Bausch & Lomb referred to the style of sunglasses as aviators given the popularity of early aviation and barnstorming during the late 20s and early 30s. The brand really acquired notoriety and popularity during World War II when they were used by military personnel and began to get associated with flying. General Douglas MacArthur often wore them.  Postwar, the style became popular with a number of celebrities as well.


Restore air traffic controllers' instructions from aircraft tracks Is it possible to understand what commands had been given to an aircraft if you look at its track containing information about lat, lon, altitude, speed and course? Is there anyone who has already tried to do this thing?

What do you think can be a problem? I suppose it may be ambiguous sometimes. For example, heading command and proceed to a fix command can both result in changing heading.

No - there are just simply far too many permeation's of instructions.

For example - an aircraft climbs 1000ft. This could be because:

It has just received an instruction to do so
It previously received an instruction to do so at a certain point
It is operating within a block clearance and chose to do so
It experienced an emergency or TCAS resolution instruction and did so without instruction
It made a mistake/pilot deviation and incorrectly did so

And that's just one minor change, with one aircraft. You can certainly take a guess on some of them but even ignoring unusual situations the first three possibilities are common and normal practice.

And that's just traffic presumed to be operating IFR within controlled airspace - add in VFR traffic in uncontrolled airspace (And bear in mind that they can be still be receiving instructions and clearances at that point - for example, entry into controlled airspace or landing at an airport in uncontrolled airspace) and you've got, essentially, no chance.


What does aileron droop help to do? Aileron droop helps to:

A - prevent upfloat
B - correct adverse yaw
C - get control feel
D - compensate drag

Please mention the most appropriate choice and only one correct answer. With a brief explanation if possible!

Your choices:

a- prevent upfloat: droop is the reverse of upfloat. Upfloat is useful in reducing adverse yaw.
b- correct adverse yaw: no, upfloat does that.
c- get control feel: yes there might be some increased aeroforce feel gradient around neutral. Around zero deflection it takes a little while before the aerogradient picks up, creating very light forces in an area where good force feedback is important. Droop helps to reduce this, since both ailerons are sticking in the wind already.
d- compensate drag: no, droop creates drag.


Why is the TORA of 27R not the same as the TORA of 09L? 09L and 27R are the same runway but just in opposite directions. I've drawn out a diagram and for some reason the TORA for 27R is 18m less? Where has that 18m disappeared? I've been trying to work out the difference in values using only the information in the table and I still feel that 27R should have a TORA of 3902m (the same as 09L).

These seem to be the numbers of Heathrow / EGLL. When you look at the taxi diagram, you see that on 09L you have a taxiway that places you right at the beginning of the runway whereas on 27R when taxiing on A1 you end up juuust behind the start of the runway – probably 18m behind it.


What does the "remote control" for a QF-4 look like? As I understand it a QF-4 is a Phantom which is converted to a remotely controlled plane for use in weapons testing.

(Apparently in non-destructive runs, a pilot is still on board for safety, convenience etc, but in actual "really shoot down the QF-4" runs, it is flown as a remotely controlled plane.)

I'd be amazed to see what the remote operator station for a QF-4 looks like.

Is it just a ... RC unit?
Is it just an ordinary PC, perhaps? Fly by mouse/keyboard?
I'm wondering is there a video feed from the pilot viewpoint included with the telemetry?
Is it perhaps flown from another chase plane?
Is it "control control" (the remote operator uses something to actually move the control surfaces, i.e. exactly as actually when flying a plane) or is it "concept control" (you just tell it, go to this point, this altitude etc and the software does that).
Can you land it using the remote system?
Do the operators of these get a chance to make any training flights, or is it just too expensive? The only time you get to take off, get shot at, and perhaps land is during actual runs as a target?

Again, I'd love to see a photo of what the control system/bay/iPhone app whatever looks like!

Footnote.  I believe the QF-4 is retired?  Question applies to a QF-4 replacement!

Here's a photo:

Retired Lt. Col. Thomas Mudge, a ground controller for the 82nd Aerial Targets Squadron, remotely pilots a QF-4 during a Combat Archer mission May 12, 2015 at Tyndall Air Force Base, Fla.

QF-4s were retired in 2016. They are now flying the QF-16.


Is a supertransporter considered a different aircraft type than the one it is derived from? By supertransporter I mean the SuperGuppy (derived from the Stratocruiser), the B747LCF dreamlifter, the A300-600ST, the airbus beluga XL, and any other aircraft whose role is to transport so large pieces that its cargo bay is way larger than the fuselage of aircraft it is derived from (I don't even know if my short list is exhaustive).

The answers of the question How are evolution and variants of aircraft considered by certification authorities? highlight that variants of an aircraft are considered as simple modification of the first type. In the case of super transporters, I imagine this is the same but:

aerodynamic obviously differs (may be especially relevant for rudder authority and engine out on take off scenario)
pressurization systems may differ (I guess those aircraft are not pressurized as airliners)
structural strength and command transmission are affected (cockpit shift, cabin floor in which cable may run suppressed, ...)

Those modifications are heavy and can affect all flight phases.

Given the Beluga XL (resp. the B747 LCF) is basically an A330 (resp. a B747) with modifications, does it share the same type certificate?

Such aircraft require separate certification. The Beluga XL has just completed its certification process.

From the Wikipedia articles you linked to:

  The 747 LCF was granted FAA type certification on June 2, 2007.

and

  Following a total of 335 flight hours being performed during the test program, restricted certification of the type was awarded by the European Aviation Safety Agency (EASA) in October 1995, enabling the A300-600ST "Beluga" to enter service shortly thereafter.

and

  The Beluga XL made its first flight on 19 July 2018, and received its type certification on 13 November 2019.


Referring to the B737NG, at what point (height) does a TOGA revert to LVL CHG after the takeoff? If one takes off with HDG SEL armed and no vertical mode (like VNAV) armed, at what height (AGL) will the vertical mode switch from TOGA to LVL CHG, and what will be the IAS applied?
Also, why isn't it possible to arm LVL CHG before takeoff, as it is with VNAV?
Depending on the entered plan, there are instances when VNAV cannot be armed, even if one wanted to.

LNAV & VNAV can be armed before takeoff; HDG SEL cannot be similarly armed.
If VNAV is armed & LNAV is not, then when VNAV engages at 400', the lateral mode switches to HDG SEL. But that's because the pilots had armed VNAV.
Taking off in TO/GA, the system won't revert on its own to LVL CHG. You can climb into the flight levels still in TOGA, although it's hard to think of a good reason to do do. If TOGA is active when the autopilot is engaged, the vertical mode will change at that point to LVL CHG, with V2 + 20 as the commanded airspeed.
As to why there is no option to arm LVL CHG on the ground, there is no need to. TOGA gives you speed guidance to bugged speeds (starting with V2 + 20) anyway, and VNAV gives you guidance to the profile speeds. Why offer another mode change that adds nothing to what you already have?


How is a flight routed from the last waypoint of a STAR to final? If you look at a flight plan on FlightAware, the last code will be a STAR. Take a flight into JFK, for example, that uses LENDY6: the last waypoint of LENDY6 is the LGA VOR/DME at FL190. If the plane then lands on 04R, how does it get routed to final? Are there any documents that show this routing?

Look more carefully; says it right at the bottom. At the STAR's termination waypoint, LGA, expect radar vectors to final.

If you had comm failure, and couldn't talk to ATC, you would fly the STAR in your clearance and if it is an open STAR like that, at the termination waypoint you would find your own way to the ILS/LOC and shoot the approach, taking the most logical path to get there and avoiding any unusual maneuvers or turns.

A lot of the procedures you see in SIDs and STARs are not followed exactly as depicted when ATC is giving instructions (the controller may put you on vectors long before you reach the termination waypoint for example), but are there in case of a communications failure, to ensure that an arriving or departing aircraft has obstacle clearance and so that ATC can predict with reasonable certainty where you are going to go as you arrive with no way to talk to them.


Has anyone ever been penalised for buzzing a control tower? Has there ever been a pilot who was caught and penalised for performing a "circus stunt fly-by" next to a control tower?

To clarify the question:

I mean legal actions took place; for example arrested, license revoked, attended a court martial (if the person is in military service)
the action must have been unapproved, possibly illegal. Pre-arranged fly-bys, such as air-shows, or the ones used to film Top Gun, do not count.

Well, there's always someone.In January 1954, American TV and Radio personality Arthur Godfrey buzzed the Teterboro control tower with his Douglas DC-3, resulting in the suspension of his license:

In the mid 1950’s, Arthur Godfrey was preparing to take off from Teterboro Airport in his private DC-3. He requested a take off on a runway which was into the wind.  The tower refused his request and instructed him to use a runway which had a sizeable crosswind. He complied, but he buzzed the tower, almost running into it. The tower personnel dove for cover and reported him. After a long hassle, Godfrey had his license suspended for six months.

And he wrote a song about it.
Back then, you lost your license. If you try that stunt now, your chances of ending up in a black site are frighteningly real, as Shaun Lees, an amateur pilot found out:

... (Lees) chartered the helicopter from another airport, landed at Coventry, where his actions effectively closed it down, then flew toward the control tower.
Hovering close to it, he announced over the radio, "you are going to see the very worst of my flying", then started to circle.

He got sent to the jail for three years, with

... Judge Marten Coates told Shaun Lees, a 41-year-old electrician, what he had done was "practically an act of terrorism".


How does the safety record of the twin piston Diamond DA-42 compare to the single piston DA-40? Its fairly well known that the Diamond DA-40 has one of the smallest fatality rates of any GA plane. The Diamond DA-42 is a twin engine aircraft with a very similar design to the DA-40.

Now, it has been shown that, in general, twin aircraft are not that much safer than single because the added complexity of operation removes the added safety from engine failure. However, the DA-42 is much easier to fly with FADEC control of the engines and a lot of automation.

Is the DA-42 safer than the DA-40?

So it appears that Diamond answered this question for me.

See this page:
http://www.diamondaircraft.com/about-diamond/safety-features/

From this chart, it would appear that the DA42 has a slightly higher accident rate, and of those accidents, even more are fatal (which makes sense due to the higher speeds). Still loads safer that the SR22 though, and I'd personally prefer the 42 over water as well.


Is an EASA STC valid if it mentions issue 1 of a Master Drawing List that was later revised? EASA STC certificate mentions the original issue of the Master Drawing List of the STC as "Associated Technical Documentation". But the STC provider delivered a revised version of the MDL. Is the certificate which refers to the original issue still valid or shall I request a revised certificate for the STC? Can anyone advise me on this?

Thank you in advance.

This sounds like a case where I would contact the STC holder and ask them what's up.
In the USA I'm used to seeing STCs with the magic words or later approved revisions (which means that the manufacturer can revise the document and get it re-approved without needing a new STC), but if a specific revision is called out and those magic words aren't present then later revisions are no longer "approved data" (or whatever the EASA equivalent term is) and technically can't be used.

In all likelihood the two revisions are materially identical and this is just a "paperwork problem", but you're better off being sure (and either getting a STC with the "later approved revisions" wording or getting the original issue of the drawing list so you have it in hand and comply with the STC you have) rather than having your local regulatory authority decide your installation is illegal because you didn't use approved data.

  If there is a changelog on the document in question your mechanic could theoretically make the determination themselves - Added drawing #123 has no material effect if your installation doesn't reference that drawing. At that point it depends on how picky the folks approving your installation are though - again, they could say since it's a later revision it's not the approved revision.


Why are liquids deemed hazardous in airport security? Airports seem to have strict rules for the amount of liquids the passengers are allowed to take on a plane.

Why is that so?

It is in part due to the 2006 transatlantic aircraft plot, a plan to use explosives disguised as soft drinks to bring down a series of airplanes. As for how they chose the 3 oz. 1 Liter bag rule:

  In an interview, Mr. Hawley explained that security officials in the
  United States, Britain and elsewhere quickly determined that the
  liquids explosion plot was “chillingly real.”

  In August 2006, the thwarted terrorists were planning to use “a
  formulation that was specifically put together to get around our
  screening measures,”

  ...

  Tests showed that a container of a certain size is needed for an
  effective explosion. Separate three-ounce containers limited in number
  to what will fit inside a single one-quart bag do not have “enough
  critical diameter” to blow up an aircraft, he said.

This is similar to why you also now need to put your shoes through the X-Ray Machine.


At a non-towered airport in the US, what should I do if I hear a medevac flight waiting to take off while I'm turning base? I'm in the left downwind at my favorite non-towered airport. Just while I'm making the turn to base, I hear a radio call on CTAF: "Such-and-such Traffic, Medevac 123, holding short runway 31." They don't make any requests or say anything else; they merely announce that they're there, waiting for me to land and get clear.

Since they're a medevac flight, should I abort my approach and let them take off immediately, or is it fine if I simply land and vacate the runway as soon as practical?

If I abort the approach, what's the best way to do that, given that I'm on the base leg now? Continue past the runway and make an upwind leg? Just turn right and exit the pattern completely, and then come back once the medevac flight is out of the way?

And whatever the right thing to do is, what radio call should I make? I assume that there's something more standard than "Medevac 123, Diamond 456, I'm just gonna continue past the runway and make an upwind leg so that you can take off right away."

(This happened in a 2-seater I was riding in today. In this case, the pilot decided to simply land and get clear of the runway quickly.)

The most obvious thing to me would be to just talk to them:

  Medevac 123, this is the Diamond on base for 31, do you need to expedite your departure?

If they say no, then just continue and land as normal. If they say yes, then I'd get out of their way:

  Medevac 123, roger, we'll extend our base and fly a wide upwind to let you  out

I wouldn't worry about standard phraseology too much, the critical point is to make sure you both understand each other and if there's no well-established phrase for what you need then just say whatever seems clearest.

Extending base to upwind has the advantage that it keeps you in the pattern so you can see what's going on as the medevac flight departs and you don't waste too much time going around the pattern again. (Although unless I have an emergency of my own I'm more than happy to make whatever detour is necessary to help out a medevac flight.)

Turning out right puts the pattern behind you and if you turn too early then you're potentially turning into other traffic on a long final, so it wouldn't be my first choice. But I don't think there's any standard way to break off from base and there are lots of possible variables (terrain, traffic, airspace etc.) so it's up to the pilot to decide what's safest at that particular moment.


What is the strongest jetstream ever encountered in commercial flight? Jet-streams are high-altitude winds which flow from west to east. They can be provide a very strong tailwind or headwind depending on which direction the aircraft is going.

What is the historic record of the strongest jet-stream ever countered by commercial aircraft? I'd expect the result to be either a very short east-going flight (much shorter than the expected time of travel), or a very long west-going flight.

Jetstreams generally don't stay perfectly straight. They tend to follow a meandering, curved path so it would be rare for a flight to stay in the max tailwind for very long.

Dispatchers will often take advantage of jetstreams and plan the routing to follow part of the jetstream core.

There is a website called Ground Speed Records where pilots can post photos of high groundspeeds for an "Unofficial" record.

Here is an example from that website giving a groundspeed of 736 knots from a 240 knot jetstream tailwind. That is probably about the highest jetstream speed you will see:  B747-400 Ground Speed Records


Why don't commercial passenger safety videos ever explain policy instead of merely dictating it? British Airways announced and published their new in-flight passenger safety video:

I'd like to draw your attention to two pieces of instruction given in the video, but also stated in every passenger safety video I've ever seen on every airline I've flown:

Never inflate the life-vest inside the aircraft.
Always put on your own air-supply mask before assisting others.

These instructions are always given in a dogmatic or dictatorial, way - the airlines expect passengers to comply with these instructions despite never giving any the reason for these policies - and I'm concerned certain passengers would disregard the instructions because they think they know better (and I included myself in that category until I found out why these policies exist).

I understand the reasons, respectively, are:

While being inflated makes it harder to move around the plane when your torso just doubled in volume - more crucially: if the plane does take-on water it means you'll be trapped inside the plane because you won't be able to submerge yourself to access an underwater door or exit.
Useful consciousness at altitude is measured in seconds, not minutes, and you will likely be unconscious and suffering hypoxia if you get distracted - it will take you a good 10-15 seconds to put your own mask on, let alone someone else's. It's entirely possible you'll die or suffer serious brain damage in your selfless attempt to assist your child.

Before I was aware of these facts I simply assumed the reasons were more mundane: inflating your life-jacket would simply make things slightly harder for yourself, and you should don your own mask first simply because it's easier - and I thought that inflating my own jacket inside the plane would actually save me time, and that I believed I was perfectly capable of assisting family members with their masks before my own if I held my breath. While laughable when informed, I genuinely believed these facts about myself until fairly recently. It would not surprise me if many passengers today feel the same way about themselves.

I understand the the real reasons for the policies make for grim reading and putting those kinds of visceral descriptions in the videos would spook passengers - but I assumed that because the videos never give any dire warnings, and are always said with a cheerful tone of voice, that the instructions weren't all that important, so it would somehow be tolerable if I did my own thing and disregarded the rules because I thought I was acting in my own best interest.

So why don't they at least add some transparency and explanation, for example they could say:

Never inflate your life-jacket inside the aircraft so you can fit through smaller openings and to avoid being trapped if the aircraft takes on water.
Always put on your own air-supply mask first before assisting others because seconds matter in low-oxygen situations.

While the sample explanations I gave don't go into too much detail, they still make it clear to passengers that the consequences of noncompliance are serious, if not fatal - and could still be read with a cheery tone of vocie :)

I compare this to the problem with "Danger: Confined Space" warning signs: the layperson thinks a confined space is dangerous because they might casually bang their head on a low ceiling - no thought is paid towards the common, very real risks and dangers of dangerous gasses pooling in a narrow shaft - yet it isn't too much trouble to add a short message to the sign saying "Because of trapped carbon-monoxide and other gasses", for example. It's odd because we already have other explanatory danger signs like "High voltage" (don't touch it without gloves), "Moving parts" (don't touch it, period) and "Falling objects" (so wear a hard-hat) - so why not airline safety instructions?

There is no time. You need to convey the information in as little time as possible or people (those few that watch at all) lose interest and start doing other things.
Reasoning tends to invite arguments, there's always someone who thinks he knows better. You don't want that.
Simplicity. Make things as easy to understand as possible using simple words. That way less intelligent people and people who have trouble with your language are more likely to understand what's expected of them.

There might be other reasons, but those are the ones that come to mind.


How do police/ambulance helicopters communicate with ATC? I was watching some police programme on TV the other day, with an air chase that had the police helicopter crew on their toes; having to perform a lot of sudden maneuvers.

How do police, or HEMS (medical), helicopters communicate with ATC? I presume they get priority, but do ATC clear other traffic out of the way? Is there a comms person/navigator on-board? Do they simply "see and avoid"?

The exact procedures will vary locally but typically ATC will give priority to police and ambulance helicopters that operate emergency services.

If these helicopters are operating in controlled airspace, communication with ATC will be done by normal VHF radio. There is no need for a dedicated communications person, the pilot will be in contact with ATC.

Sudden manoeuvring of these flights is rarely a problem for ATC since these aircraft are operating under Visual Flight Rules.

When chasing a car, the pilot remains responsible for keeping clear of obstacles and other traffic, therefore this requires a second person to keep a look out (either on the car or the surroundings)


How does the F-16 side stick convert pilot input to an electrical signal? In What is the motivation behind designing a control stick that does not move?
the F-16's control stick is discussed. What is the method that is used to sense the pilot's input to the stick and convert this to an electrical signal?

The stick measures force by using strain gauges. These work by measuring the change in electrical resistance caused by stretching or compressing the thin metallic foil, which is bonded onto the stick shaft.

An accurate setup requires two strain gauges at opposite sides, which are measured using a Wheatstone bridge: the difference in resistance of the two gauges is used for the force signal.

There are other ways of measuring input force, but none are more accurate than the strain gauge/ Wheatstone bridge setup which can measure force in both directions and has little to no hysteresis.


Why do aircraft piston engines require priming? Aircraft piston engines generally require priming, but automobile engines don't seem to need it. Why doesn't cranking the engine with the starter pull in fuel mixture that would ignite without help of the priming?

Modern car engines are really very sophisticated compared to most airplane piston engines, which are 70 year old technology.

Modern cars typically have an electric fuel pump in the tank which is often started by opening the drivers side door, by the time your butt is in the seat the fuel system is pressurized. When the ignition system is activated the ECU (engine computer) looks at engine coolant temperature and outside air temperature and directs the electronic fuel injectors to meter the exact amount of fuel which is correct for the conditions, directly into the inlet valves. A cold engine needs a much higher ratio of fuel to air when starting (2-3 times when hot), which reduces as it heats. When it starts running the ECU also takes into account the mass of the air flow and oxygen content of the exhaust to maintain the ideal fuel-air balance for the smooth and efficient running of the engine.

This technology does exist for airplane engines, it's just expensive to fit so very few airplanes have it. Most light airplanes have very simple, completely manual systems. You shut down the engine by cutting off the fuel supply (closing the mixture), this ensures that the engine is completely dry of fuel so that if the prop is spun there's nothing in the cylinders which could go foom and spin the prop, potentially maiming someone.

Piston engines create a lot of suction as they operate, and rely heavily on vacuum suction to operate. The low pressure in the carburetor atomizes fuel, which then gets pulled into the cylinder, explodes which in turn pulls more fuel and air in. However, because the mixture was cut off the engine and carb are all dry (any fuel left in the carb bowl will evaporate over time), which produces little suction. No suction, no atomization of fuel, no foom. The primer pumps a very rich atomized mist of fuel into the intake for each cylinder, giving the engine something to foom, creating suction to pull fuel through the carb and sustain the engine. This is why you feel resistance when using the primer, you are forcing it through a bunch of atomizing nozzles. This is why you need to start right after priming, if you wait too long you lose atomization.

Note that many airplane piston engine carbs have accelerator pumps which jet raw fuel into the carb on quick throttle advances, this is to prevent a lean cut-off. Some people think it's the same as using the primer, but it isn't at all. Because there's no suction when you pump the throttle forward all you are doing is jetting liquid fuel into the carb, there's no vacuum to atomize it, so all you are doing is filling cylinders with raw fuel and they won't go bang. A single jet is good because having fuel in the carb bowl gives something to atomize once it catches, but too much will just flood the engine.

A hot start is very different from a cold start, the engine doesn't need as rich a mixture and the carb bowl still has fuel in it, so when you crank it you don't need to prime in most cases.


Where can I go to sit in the cockpit of a Boeing? This might sound like a silly question to some, but is it possible to go and sit in the cockpit of a Boeing 737, somewhere in the UK? (Otherwise in Europe, or beyond).

Maybe at a museum or something? I'm building a [currently tiny] home cockpit based on a 737, and I'd like to see how the real thing looks and feels.

I tried searching online, but I couldn't find anything.

Hope this isn't too dumb of a question, i.e. "not possible Jim!"

There is a company called Flight Experience which builds 737 simulators and offers their use to the public. These are fully certified simulators and are frequently used by commercial pilots for currency training.

Their closest location to London appears to be in Paris.

I had an opportunity to fly one of their simulators a few years ago, and it was a lot of fun. We spent some time doing landings at the old Kai Tak airport in Hong Kong.


What are the elements of an approach briefing? I've heard that before landing an airliner, the pilots perform a mini-briefing to agree on what they will do and what they can do if something goes wrong during the approach and landing.

Is this true?
What is it called? (my best guess would be "approach briefing")
What elements does the briefing contain?

Yes, it's true.  Usually called approach or arrival briefing

Details will vary according to aircraft and operator but a typical list is NATS:

  NOTAMs1

  ATIS2 notes, chart briefing point by point, date, frequencies, courses, minimums and missed approach procedures.

  Terrain, minimum safety altitude, which route

  Special notes for arrival, taxiing, likely gate for arrival?

I noticed that you specifically asked about something going wrong.  The following assumes a serviceable aircraft.

According to operator, if the aircraft is not on a stabilised approach by 1,000 feet, a go around will be performed and the missed approach procedure (MAP) followed.  The MAP is printed on the approach chart.  The initial action is:

to get the aircraft safely climbing away (aviate)
to the altitude and heading defined in the MAP (navigate)
then call ATC to let them know (communicate).

Aviate, navigate, communicate, always in that order.

A stabilised approach might differ between operators but is essentially.

  The flight path is correct with only minor changes in pitch and
  heading needed to stay on it.

  No more than 20 kts above the approach reference speed briefed as above.

  Correctly configured for landing (flaps, slats, gear, spoilers armed, autobrake set etc)

  Checklists completed

  Rate of descent <= 1,000 fpm

  Power setting is appropriate

  There may be other special checks for some types of approaches which must have been briefed as above).

The MAP might be something like:

Maintain runway heading and climb to 1500' until reaching 4 DME.  Turn right heading 250 degrees and climb to 5000' to join the hold at DISNEY

The MAP is unique for each approach so must be briefed in advance.

1
Notice to Airmen: Warn of recent changes, temporary restrictions, equipment malfunctions etc.

2
Automated Terminal Information Service: A continuous broadcast of airfield information such as weather, special precautions, runways in use etc.


What aircraft had the first pilot-assisted controls? This question about regulations regarding hydraulic flight controls got me thinking about the history of hydraulic or pilot-assisted controls. As aircraft get larger the control surfaces must grow proportionally but it seems that the forces required to move those surfaces may grow at a non-proportional rate. That means at some point they had to switch from a pure cable/pulley system to an assisted system.

What is the first aircraft to use an electrical/mechanical/hydraulic system to assist the pilot with the control surfaces? I'm mostly interested in an answer from a commercial aircraft standpoint.

It was the Lockheed Constellation and the P-80, both introduced in 1943. The DC-3 had hydraulic flaps, but the Connie was the first to have hydraulic flight controls.

  The DC‐3 had wings flaps powered by hydraulics (1934). But it wasn’t until the early 1940s that hydraulics were used to power the primary flight control surfaces on the Lockheed Constellation and P‐80 (first US Jet Aircraft).

Source: A History of Aviation Actuation, Control and Fluid Power (PDF)

Also in 1943, the Lockheed P-38J-25-LO version of the WWII fighter aircraft was fitted with hydraulic boosted ailerons.

Source: Lockheed P-38J Lightning, Joe Baugher


Is there any FAR defining an "introductory" or "familiarization" flight? I have given a number of young people their first inspirational flight. I am a CFI, but I do not issue any endorsement for these flights, and do not charge for my time or the aircraft. Is there any FAR defining "introductory" or "familiarization" flight, or addressing how many times a non-flight-student (no student pilot medical certificate and no student pilot log book) can receive an introductory or familiarization flight?

There's no formal definition or regulation that I could find; introductory flights aren't defined in 14 CFR 1.1, for example. I'm not sure why the FAA would care how often you fly with someone, or what the difference is between an introductory flight and any other flight with a non-paying, 'non-logging' passenger.

The only other people who might care about it are the TSA but if you aren't providing instruction during the flight then that shouldn't matter either. Introductory flights are usually understood to be a "demonstration flight for marketing purposes" (49 CFR 1552.1) and therefore exempt from TSA requirements, but there doesn't seem to be any rule about how many demo flights you can make with an individual.


Relationship Between Aircraft Thrust and Jet Exhaust Velocity? What is the relationship between aircraft thrust and jet exhaust velocity & thrust and mass flow.

Actually, my question is how to reduce or decrease jet noise without decreasing the thrust ?

The thrust produced is propotional to the exhaust velocity and mass flow, in simple terms. The thrust equation can be written as,

$T$ = $\dot{m}_{e} v_{e} - \dot{m}_{o} v_{o} - (P_{e} - P_{o}) A_{e}$

where, $\dot{m}$ is the mass flow rate $v$ is the velocity, $P$ is the pressure and $A$ is the (exhaust) area. The subscripts 'o' and 'e' denote the freestream and exhaust values respectively.

There are multiple ways to go about noise reduction in aicraft engines, all with some kind of penalty- the Boeing method is to use chevron shaped exhausts (Interestingly, the type chosen is the one with lesser thrust penalty, not the most effective in noise reduction). However, Airbus has cited higher fuel consumption as the main reason for them not using it. Airbus uses acoustic liners in the engine to reduce noise:

  The thrust reverser structure was acoustically treated along approximately
  half of its internal surface. It was clear that increasing this acoustic area would increase the acoustic sound absorption and hence decrease the overall measurable exhaust noise.


What are the Radarless approach control services in the United States? I was recently in Twin Falls, ID at KTWF. There is no radar for approach control services. All instrument approaches are full procedures and aircraft must report all requested fixes.
There is Salt Lake Center radar services at altitudes well above the usual approach and landing phase of flight for KTWF.
When I remarked to tower that is old school, they stated "last of two in the country."
What is the other?

Twin Falls, ID
Helena, MT

The Chart Supplement shows if a facility has radar or not. The entries for KTWF and KHLN show that there's no radar at the local TRACONs.


Book recommendations for learning how to fly? With the success of this question, which asks about good books on aerodynamics, I thought I'd ask another general question regarding books that we can turn into a community wiki.

What are good books to use to learn how to fly?  And yes, I know that, in the end, you'll just need a good instructor.  But there are several books that suppliment a good instructor, or can be used by people who are interested in learning to fly, but perhaps are unable to get an instructor just yet.

Note: I am well aware this is a very general question.  But I would like to have a centralized resource, vetted by users of this stack, that we can point to when someone asks for text resources on learning how to fly.

As you pointed out in your question, no book is a substitute for actual instruction in an aircraft with a flight instructor. That being said, doing your homework and knowing what your instructor is going to expect goes a long way toward completing your training in a timely manner.
The books here are all great reference texts to be combined with a flight instruction curriculum.

FAA Publications / Books for initial training

A surprising number of new student pilots are not aware of the wealth of information the FAA has compiled and published to help people learn to fly. There is a whole series of FAA Handbooks and Manuals that you can take advantage of which are available from the FAA as well as from a variety of publishers like ASA. While all of the regulatory information is geared toward US/FAA regulations much of the technique information, signs & markings, etc. will be universal, in conformance with ICAO rules.
I list a whole bunch of them here, but you can find a wealth of information by googling what you want to do and the words "FAA Handbook".

Books on Flying the aircraft - maneuvers, etc.
Quite simply if it flies the FAA probably has a book about how you should fly it.  These books cover basic flying technique and the maneuvers the FAA expects pilots to be able to demonstrate.
The popular ones include:
The Airplane Flying Handbook (FAA-H-8083-3A)
The Helicopter Flying Handbook (FAA-H-8083-21A)
The Glider Flying Handbook (FAA-H-8083-13A)
The Balloon Flying Handbook (FAA-H-8083-11A)
Books on "essential aviation knowledge" - Airport signs & markings, "rules of the air", etc.
The Pilot's Handbook of Aeronautical Knowledge (FAA-H-8083-25A) is the starting point here.
The Aeronautical Information Manual (AIM) is another key resource (you will often find this as a combined "FAR/AIM" printed publication).
Books for the more advanced stuff - Instrument ratings and beyond
The Instrument Flying Handbook (FAA-H-8083-15B) and Instrument Procedures Handbook (FAA-H-8083-16) are excellent references for pilots pursuing an instrument rating.


Is the aft position the ideal place to fly a large aircraft from? Cockpits are at the front of the airplane, and they have pretty limited visibility. Pilot windows can actually open to help with some of this. We know that there are a ton of tricks that are done to assist pilots in navigating their aircraft with the limited visibility that the cockpit provides. The A380 has multiple cameras to assist in visibility. On the ground, there are people to assist in taxing the aircraft.

Has there ever been any research into a flight engineer, or pilot flying an airplane with a VR headset?

The only direction a (fixed wing) aircraft can move using the flight controls  is forward. So, it is the forward visibility that is important. The front of the aircraft is the best place for this purpose. The limited visibility in other cases are reasonably over come by using extra cameras or marshalers and markings in the ground.

The Airbus A80, for example, has three cameras, one each in the nose, belly and the tail,which can be viewed in the screen by the pilot.

Source: onemileatatime.boardingarea.com

The closest any aircraft has come to be flown using a VR headset is the  AN/AAQ-37 electro-optical Distributed Aperture System (DAS) which is being used in the Lockheed Martin F-35 Lightning II.

The EO/DAS consists of six high resolution Infrared sensors  flush-mounted around the aircraft to afford 360-degree, spherical (4$\pi$ steradian) coverage, basically allowing the pilot to see through the airframe.

Source: alternathistory.org.ua

Each of these sensors collect data in different directions and the on-board computer 'stitches together' these images (and data from EOTS and Radar) and projects them onto the pilot's Helmet Mounted Display System (HMDS), making it the only modern combat aircraft without a HUD.

Source: brucesterling.tumblr.com

However, there are issues with using these in a commercial airliner:

They are costly- around $400,000 (some reports say ~700,000) apiece and non-interchangeable; while this (situation awareness) could be priceless in combat scenarios, I don't see commercial airliners shelling out this amount of money to replace a system that works pretty well.
The amount of computing power required is enormous. Reportedly, the DAS system collects about a terabyte of data per hour. For aircraft which fly most of their time in a predetermined altitude and heading, this amount of data flow and computing power is not required.
Note that the system is not yet fully operational. There are issues with the helmet like latency, 'green' glow, jittery image, resolution issues etc.- reportedly solved, though some pilots say they don't use this system very often.


Is flight data recorder erased after every flight? Flight data recorders store massive amounts of data per flight and despite improvements year on year with data storage as with Moore's law, carrying larger and larger amounts of data can become expensive, through larger hard drives and the extra weight.

So, is a flight data recorder erased after every flight? If so, after how long and by whom, is it automatic on landing, engine shutdown or it's one of the pilots procedures on landing?

Flight data recorders have changed over the years and evolved to what they are today. Modern recorders are recording up to 88 parameters. The storage of the recorder is dependent on the range of the aircraft. Early recorders were using a circular tape that ran through the recorder. E.g. loop recording all the data and automatically overwriting the oldest data on the tape.
The recorder of a Boeing 777 is based around modern solid state storage, capable of recording up to 25 hours continuously. Modern flight recorders are still recording continuously, so after the initial 25 hours, the storage is full. It will then start overwriting the oldest datablock stored. This ensures that you will always have the last 25 hours of data before a crash available for research.
The following quote comes from AERO Magazine Issue 02 - Spring 1998:

Flight data recorders were first introduced in the 1950s. Many first-generation FDRs used metal foil as the recording medium, with each single strip of foil capable of recording 200 to 400 hr of data. This metal foil was housed in a crash- survivable box installed in the aft end of an airplane. Beginning in 1965, FDRs (commonly known as "black boxes") were required to be painted bright orange or bright yellow, making them easier to locate at a crash site.
Second-generation FDRs were introduced in the 1970s as the requirement to record more data increased, but they were unable to process the larger amounts of incoming sensor data. The solution was development of the flight data acquisition unit (FDAU).
As shown in figure 2, the FDAU processes sensor data, then digitizes and formats it for transmission to the FDR. The second-generation digital FDR (DFDR) uses tape similar to audio recording tape. The tape is 300 to 500 ft long and can record up to 25 hr of data. It is stored in a cassette device mounted in a crash-protected enclosure.
FAA rule changes in the late 1980s required the first-generation FDRs to be replaced with digital recorders. Many of the older FDRs were replaced with second-generation magnetic tape recorders that can process incoming data without an FDAU. Most of these DFDRs can process up to 18 input parameters (signals). This requirement was based upon an airplane with four engines and a requirement to record 11 operational parameters for up to 25 hours (see "Parameters Explained" below).
Another FAA rule change that took effect October 11, 1991, led to the installation of digital FDAUs (DFDAUs) and DFDRs with solid-state memory on all Boeing airplanes before delivery. This FDR system was required to record a minimum of 34 parameter groups. The DFDAU processes approximately 100 different sensor signals per second for transmission to the DFDR, which uses electronics to accommodate data for a 25-hr period.
Today all Boeing current-production models use DFDR systems, which will store 64 12-bit words per second (wps) over a 25-hr period in electronic memory. At the end of the 25 hours, the DFDR will begin recording the most recent data over the oldest data. No tape removal is required with these systems. Each of these systems on every Boeing model (except the 777) have at least two data frames that are transmitted from the DFDAU to the DFDR (see "What Is a Data Frame?" below).
These separate data frames accommodate the different regulatory agency requirements. A 128-wps DFDR was available for the Boeing 777 and MD-90, allowing the development of one data frame that incorporated all regulatory agency requirements and that required operators to develop only one data frame decode algorithm. "How a FAA Rule Is Changed", below, explains the basis on which the FAA may propose rule changes.

Source


How is the air traffic managed at a field with many privately owned aircraft? As example "Spruce Creek". Many residents own private aircraft and can fly anytime they want. Do they have an separate air traffic controller? How is this high amount of air traffic managed?

How is this high amount of air traffic managed?

Air traffic is managed at many levels by many people and is heavily dependent on the airports specifics when it comes to GA. First off not every airplane in the sky is talking to or under control of ATC, for that mater in some airspaces you don't even need a radio on board. The following is pursuant to US FAA regulations, other countries may handle air traffic differently.

The first level of traffic management is the pilot, its the job of every pilot to "see and avoid" other traffic, this goes for both commercial and general aviation traffic. Even if issued a command by ATC you can deviate to avoid an emergency (i.e. hitting another plane).

The next level of traffic management is the various FAA regulations on both ground and air flight operations. These regulations (like traffic rules) are laws and must be followed. They are designed to mitigate traffic in certain areas and will also force you in some areas to at least be on the radio with ATC (e.g. class B airspace). You can read up on the full regs here and you will find most of what you are looking for under "flight rules". Much of the country (below 18,000Ft and above 1200ft generally) is actually class E airspace which does not require ATC communications. This is where most GA traffic lives although small turbo props and the boldest of piston singles can now make it into the levels, most GA planes cant. There are also pre set cruising altitude intervals for VFR and IFR traffic to help keep separation.

Above that you will have ATC who is controlling all IFR traffic, traffic in Class A, B, C, and D airspace and will provide limited radar services to VFR traffic when load permits. When flying under VFR (depending on where you are) you may not need to ever talk to ATC. It is possible to depart an un-towered airport in class G or E airspace, fly around and return with out ever having contacted an ATC facility.

On the ground control depends on the airport. At an uncontrolled field (lots of smaller general aviation airports) the pilots decide. Taxing around is much like driving a car and there are pre determined radio calls to enter the traffic pattern and use the active runway. At a towered airport ground control will monitor and control the flow of traffic on the ramp and the tower will control the traffic from the runway thresholds until the plane departs its airspace.

The only exceptions to the rules here in the US are 5 airports (LaGuardia, Newark,  O'Hare, Ronald Reagan National, and John F. Kennedy) which are subject to the FAA's high density airport rules (specific to the airports) generally speaking the operations are the same in terms of how ATC will handle a given aircraft but departures and arrivals are limited and must be reserved ahead of time.

Another note on IFR operations, ATC will treat all planes the same and will only give priority to a plane in an emergency. Your little Cessna 172 on an IFR flight will receive the same services as a 747 30,000ft above you.

  Do they have an separate air traffic controller?

No. See above but for what its worth the big planes contact the same ATC facilities as the little guys.

Spruce Creek

For what its worth Spruce Creek sits under a Class C shelf as you can see on the sectional here.

Departing from RW 5 and staying below 1200 puts you right between the Daytona Class C and New Smyrna Beach Class D so you may find your self contacting ATC on departure depending on your route you are somewhat boxed in there. Even departing from 23 you may find your self contacting Daytona approach to punch into the Class C there. Technically you can get out of there with out contacting ATC but you may find your self needing to depending on the situation.


What is the difference between "Standard Metric Level" and "Altitude" in ICAO flight plans? What is the difference between "S" and "M" in flight plan altitudes?

The FAA's ICAO flight plan documentation says:

  Standard Metric Level in tens of meters, expressed as S followed by 4
  figures (for example, S1130), or

  [...]

  Altitude in tens of meters, expressed as M followed by 4 figures (for
  example, M0840)

I don't know what "Standard Metric Level in tens of meters" means exactly? How is that different from "Altitude"?

Standard Metric Level is the metric equivalent of the foot-based Flight Level. It is what you get when the altimeter is set to QNE, i.e. above the Transition Level, and read in meters.

Metric Altitude is the metric equivalent to the foot-based Altitude. It is what you get when the altimeter is set to QNH, i.e. below the Transition Altitude, and read in meters.

These are actually the official ICAO systems, with the foot-based systems declared a "temporary" alternative.


Was the Space Shuttle aerodynamically neutral while piggybacking, or did the combination act like a giant biplane? Trying to investigate this question, I see that 'Ask the Captain' says:

  The weight of the shuttle is calculated like any payload. The 747
  produces enough lift to fly and to carry the weight of the shuttle. In
  this respect it is no different than cargo carried inside the
  airplane. source

But of course it is different, since cargo is generally carried inside an aircraft.

There was a fairing for the Shuttle's engines for drag reduction, but I'm wondering if the wings of the Shuttle had some aerodynamic contribution to the lifting body, or whether that was all down to the 747's wings.

 source

This podcast with one of the pilots answers just about every question on the shuttle carrier you could have and it's worth a full listen. But to cover the flight dynamics, I would skip to 50:33 minutes, where the pilot states (please note there is no official transcript of the podcast and I typed this as I listened to it, please see the official podcast for the actual verbiage, but this is close):

  Markus Voelter (Interviewer): Let's talk a bit about the flying characteristics, did the wings of the shuttle add some extra lift or
  was it mounted with essentially 0 angle of attack?

  Arthur C. “Ace” Beall (Pilot): It was mounted with some angle of attack, you can see that as it's sitting. At the speed we were flying,
  the carrier itself was about 5 degrees nose high. The shuttle was creating lift, but
  how that affected it aerodynamically is hard to say, it was always
  mounted the same way so we had no basis of comparison. It did, however,
  create a lot of drag and made the aircraft very top heavy so bank
  angles were limited.

So some lift was generated but at the speeds they were flying, other limitations came into play that were more of a concern. It's also worth noting that when in transport no one was in the space shuttle and the control surfaces were not used in any way.


What causes spiral mode instability and how do you minimize it instead of trying to dampen it? What causes spiral mode instability in a GA plane and how do you minimize it in the first place, instead of trying to dampen it with dihedral (which is reducing efficiency by reducing vertical lift)?

One of the primary causes of spiral instability is the fact that once a turn begins, the outboard wingtip is moving along a larger circumference and therefore moving faster, and tending to produce more lift, than the inboard wingtip.  So the bank angle tends to increase.  Keeping the wingspan small will minimize this effect.  Obviously, this is a trade-off and other desirable qualities are sacrificed.

Re dihedral-- the inefficiency due to more wing area being needed to get the same amount of vertical lift component is rather minimal.  The more significant negative effects of dihedral include a excessive slip-roll coupling that creates excessive roll torque during an intentional slip (eg crosswind landing), bad effects in gusty crosswinds, poor roll response to aileron-only roll inputs, and a tendency toward "Dutch roll" yaw-roll oscillations.

Keeping the vertical fin small will help allow enough sideslip to allow whatever dihedral is present work as effectively as possible to  help minimize spiral instability, but obviously this is a trade-off as well.

For more on the relationship between sideslip and dihedral see the related answers in Is this paragraph about the dihedral effect in the FAA's Glider Flying Handbook correct? or How does the dihedral angle work? .


After a crash, does the information stored on flight recorders have expiration dates? After the recent announcement of the recovery of the flight recorders of AirAsia flight were recovered, I was wondering if black boxes deteriorate after a set amount of time.

As of now, nothing of the plane MH370 has been recovered, including either of the flight recorders. In another downed flight in the past, it took over two years for the for the black boxes to be recovered from the ocean, and even then the information in the black boxes were intact.

So do these black boxes ever expire? Or do they always keep the information intact throughout the years?

Everything will expire one day, including our Sun. Flight recorders are no exception.

Older flight recorders used magnetic tapes. They used to work like any other tape recorder. At present, solid-state memory boards are used. These are considered much more reliable than magnetic tapes, because no moving parts are involved like magnetic tapes.

Data from both recorders is stored on stacked memory boards inside the crash-survivable memory unit (CSMU). A CSMU is:

  ... is collectively the solid-state memory chips and a hardened metal
  container filled with specially designed heat insulating material. It
  is this container that provides the survivability, for it is able to
  withstand massive crushing loads, intense heat, and exceptionally high
  G forces, all of which is proven by crash survivability testing.

Image Source

You can see that the memory boards are inside stainless steel shell, which is designed to withstand the crash. Although there is a limit of writes on solid state memory, after a crash there are no more writes.

When the FDRs/CVRs are recovered from a crash scene, there are various methods to retrieve data, depending on the condition of flight recorders. This process can take weeks or months to complete.

Further reading: How Black Boxes Work


Question about congestion of the 1090MHz frequency I'm no expert so there's likely to be a lot of mistakes in this post.
ADS-B - Automatic Dependent Surveillance - Broadcast, (out) transmits (in) receives position data from/to other aircraft and to ATC.
I've been trying to find out more about how congestion of the 1090MHz frequency will be addressed. It seems that ADS-B out is becoming fairly ubiquitous. Additionally, there will be more aircraft interrogating (on 1030MHz) and responding to interrogations on 1090MHz for transponder based systems (TCAS, SSR). From this post, it sounds like things are already congested in some areas.
Here are some of the things that I'm unable to google for so far:

On the wikipedia page for TCAS, there is mention of a bandwidth limitations of 1 megabit/second. What does this mean?:

a) Within an airspace only 1 megabit/second of data can be transmitted cumulatively.
b) Air traffic control can only receive 1 megabit/second.
c) Individual aircraft can only transmit 1 megabit/second.
d) The receiving equivalent of c.
e) Other

What is physically limiting bandwidth? Will there eventually just be too much interference between signals whilst using this frequency, or is it a hardware issue? I couldn't seem to google this issue, maybe I need some keywords.

Are the solutions to increasing capacity about being more clever with how the packets are sent (more efficient packet sizes, fewer packets, better/cleaner transmission), improving ground or air hardware, or is there a "add more lanes to the highway" solution? It seems 978MHz is equivalent to adding more lanes.

What is the consequence of congestion? Are packets corrupted as noise rises? What keywords should I google?

Also, thanks for all the useful info on this site, aced a Masters assignment recently because of the aircraft designers on here.

Additionally, there will be more aircraft interrogating (on 1030MHz) and responding to interrogations on 1090MHz for transponder based systems (TCAS, SSR).

Actually, no. More Mode S (vs Mode A/C) aircraft means TCAS can use Selective interrogation instead of All-Call interrogation, which will reduce congestion from unnecessary replies.
Also, newer TCAS systems are ADSB-aware and will reduce (not stop, for safety reasons) even their selective interrogation rate for ADSB targets, further reducing congestion.
Also also, part of the goal of ADSB is to reduce the need for SSR overlap, which will greatly reduce congestion as well.

... bandwidth limitations of 1 megabit/second. What does this mean?

Remember that this is a spatially distributed system, so congestion observed varies for each receiver based on which subset of transmitters they can hear. How far you can hear depends mostly on how high your antenna is.
The bandwidth number is a theoretical maximum data rate based on the bits per message and number of messages per second, assuming no overlap and no gaps. It will never happen in practice; it’s only useful as a yardstick for the current data rate.

What is physically limiting bandwidth? Will there eventually just be too much interference between signals whilst using this frequency,

Yes, see above.

Are the solutions to increasing capacity about being more clever with how the packets are sent (more efficient packet sizes, fewer packets, better/cleaner transmission),

The protocol is already as clean and efficient as it can be while remaining compatible with older Mode S equipment.
Most of the congestion comes from frequently sending redundant data as a crude form of FEC. Turn that off and congestion would go away, but so would the ability to gracefully degrade.

improving ground or air hardware,

One vendor (Airspy) claims to be able to decode overlapping messages, which if true would drastically reduce data loss and raise the practical bandwidth above the theoretical maximum. But I don’t know how well it works in practice or whether anyone is pursuing this for certified hardware.

or is there a "add more lanes to the highway" solution? It seems 978MHz is equivalent to adding more lanes.

That is allegedly why the FAA pushed UAT978 for light GA aircraft in the US.

What is the consequence of congestion? Are packets corrupted as noise rises?

The only real problem is collisions, not noise. Unless you define unreadable-due-to-collision messages as noise, of course.
The consequence is simply that you miss any data whose message was unreadable. However, the protocol was specifically designed to be highly redundant to minimize the impact of low to moderate levels of loss. Exactly how much loss it can tolerate is not clear, but so far it doesn’t seem to be a problem in practice.


Does a strobe light shield act like a wingtip fence [or better sort of vortex generator]? I was told it is a shield to avoid to blind the pilot during night flights when the strobes are on. Now, knowing the primary reason is, as far as I know, the above mentioned:

Does anyone know any official document where the definition of this device is mentioned?
Does anyone know any reference where the effect on the wing tip aerodynamic is studied? Considering different speed regimes?
Does anyone know if there are any regulations on this small device?

As far as I know, this device can be founds on the following aircraft:

King Air
T-6 Texan
Embraer Legacy 600

As can be seen, it can be found on models with and without wing tip devices.
One thing that should be mentioned on aircraft fitted with winglet (not wing fence at the tip as those found on the A380), is that during the pull up manoeuvre, at take off, a mild/severe separation is generally observed on the inboard part of the winglet. Could the strobe shield fitted in the Embraer Legacy 600 mitigates this by re-energising  the boundary layer. It would be easy considering the amount of cross flow at the tip.
Any official paper or informal discussion anywhere in the web would be very useful.
More pictures can be found on these links:
http://79ft.net/tag/mechanicing.html

It is a long structured question, I will try to keep up with the answer. As first I would like to cite some sources.

I compared both CS23 and CS25 looking for the certification requirements on the lights. They are almost identical. If you want to check them yourself the keyword you want to use is "Lights". The paragraphs of main interest are from 1285, to 1401, three pages in total. That said.

  I was told it is a shield to avoid to blind the pilot during night flights when the strobes are on.

The light on the wingtip in this case are both position lights and anti-collision lights, the strobing light you refer to.

The Position lights: are described in paragraph from 1285 to 1391. There are requirements on the shielding of them and the intensity of the lights from different radians as well as the colors of them, but none from an aerodynamic point of view.

From a design point of view the shield should define some dihedral angles:

  (b) Dihedral angle L (left) is formed by two
  intersecting vertical planes, the first parallel to the
  longitudinal axis of the aeroplane, and the other at110º to the left of the first, as viewed when looking
  forward along the longitudinal axis.

  (c) Dihedral angle R (right) is formed by two
  intersecting vertical planes, the first parallel to the
  longitudinal axis of the aeroplane, and the other at
  110º to the right of the first, as viewed when looking
  forward along the longitudinal axis.

  (d) Dihedral angle A (aft) is formed by two
  intersecting vertical planes making angles of 70º to
  the right and to the left, respectively, to a vertical
  plane passing through the longitudinal axis, as
  viewed when looking aft along the longitudinal axis.

For the anti collision lights:

  The aeroplane must have an anticollision
  light system that

  (1) Consists of one or more approved
  anti-collision lights located so that their light will
  not impair the crew’s vision or detract from the
  conspicuity of the position lights

  (b) Field of coverage. The system must consist
  of enough light to illuminate the vital areas around
  the aeroplane considering the physical configuration
  and flight characteristics of the aeroplane. The field
  of coverage must extend in each direction within at
  least 75º above and 75º below the horizontal plane of
  the aeroplane, except that a solid angle or angles of
  obstructed visibility totalling not more than 0·03
  steradians is allowable within a solid angle equal to
  0·15 steradians centred about the longitudinal axis in
  the rearward direction.

On the aerodynamics effect of vortex generator at the wingtip, I found a paper: Modification of a wing tip vortex by vortex generators. It is an experimental study without a wingtip device though. Citing from the conclusion paragraph:

  The results show that substantial redistribution of wake circulation can
  be achieved by the merger of the tip vortex with a co-rotating
  vortex from the VG with the core radius of the merged vortex increased by a factor of up to five relative to the undisturbed
  tip vortex.

The VG was though positioned at a $\eta =\frac{y}{b} = 0.2$ inboard of the wingboard.

Summing up the comments above, and merging this interesting explanation from @Peter Kämpf on winglets, what I think (yes, it is an "opinion", but otherwise I would need to run some 3D CFD and/or a wind-tunnel test) is that:

There would be a vortex generated in certain conditions for sure.
To design this device in order to avoid winglet stall separation would be quite a challenging task. The device its positioned very outboard which would make it be more or less aligned with the winglet. I think that the close span-wise coupling between he device and the winglet would make it hard for the vortex to develop in such a way to re-attach the flow on the winglet.