Could a high absolute difference between heading and course give a hint about weather conditions? I am developing an application that tries to predict the future track of an airplane. At the moment I don't have access to weather data and I am trying to find a metric that could substitute that.
If I am not wrong, a pilot should change his heading according to wind's direction in order to maintain the airplane's course to the target airport. So If the wind benefits the airplane's movement, the absolute difference between heading and course should be zero most of the time. Is that true? If not is any another way in order to get a hint about weather conditions from heading/course information?

Thinking through the possibilities, if you knew the pressure conditions, and the change of those conditions as plane moves, and you knew the wind direction and speed and its changes as the plane moves, you might be able to have some kind of AI software estimate the location of the pressure centers in the airmass you're flying in, and from that calculate the pressure gradients and wind direction/velocities for some distance around the plane's location.  This might be able to produce a "better than nothing" educated guess as to the wind speed and direction ahead based only on the data being received in real time.
To do this, besides an extremely powerful computer (weather forecasting agencies use multiple Cray supercomputers to predict circulation flows, but maybe you don't need that much power) you would need the normal air data inputs like ambient and dynamic pressure (indicated airspeed), and you'd need to know the airplane's true altitude and true position, which can be provided by a GPS interface.
If the software knew the precise height above the earth so it could measure ambient pressure and continuously calculate barometric pressure and measure pressure changes, and it knew the precise location, track, heading, groundspeed, and true airspeed of the airplane so it can continuously calculate wind velocity and direction (FMS systems on jets do that already), it might be able to create its own pressure pattern map of the immediate area, and from that generate a prediction of wind conditions some distance ahead.


What is the maximum distance for class C service? Sectionals say to contact the approach center of a class C airspace within 20 miles. Is this a suggestion or a rule?

What is the maximum distance to contact them via radio, other than signal limitations, if one exists?

What is the maximum distance to receive radar service from class C?

Note that class C radar service and flight following from an ATC center are not the same thing as it pertains to my question.

There is no such thing as "Class C radar service".  "Class C airspace" and "radar service" are mostly orthogonal.  "Flight Following" is just shorthand for getting radar service when you're not required to.

Terminal areas around a Class C airport generally comprise a 5-mile "inner ring", 10-mile "outer ring" and 20-mile "outer area".  Approach is guaranteed to control (at least) that much airspace, regardless of class.  Within the airspace they control, they provide (roughly) the same radar services regardless of whether you're in Class C or Class E at any given moment.  The only practical difference is that in Class E, you're not required to talk to them, whereas in Class C, you are.

The reason the box says "CTC KNOXVILLE APP WITHIN 20NM" is that 20 miles guarantees you're within the "outer area" and thus Approach's airspace.  If you contacted them at 30 miles out, you may be Center's airspace, in which case Approach would need to redirect you to Center, and then Center would hand you back to Approach a few minutes later.  That's a waste of both your time and the controllers' time, so the chart reminds you of the minimum range to help you avoid that.

There is no theoretical maximum, and many Approach facilities do in fact control more (sometimes far more) airspace than the minimum.  However, the FAA does not publish the actual sector boundaries, so the best practice is to assume no more than the minimums—or get Flight Following for your entire trip, in which case you don't have to worry about it at all.


What are the "channels" on the A320 Rudder Travel Limit Unit? The KNKT's final report on last year's Air Indonesia QZ-8501 crash repeatedly mentions that the faulty solder joint on the Flight Augmentation Computer (FAC) caused an open circuit on "both channel A and B", leading to the repeated failure of the Rudder Travel Limiter Unit (RTLU). (Page 66 of the report has a photo of the offending solder joint and of the whole module.)
What are these "channels"? The only relevant mention I can find in the report is on p37, an extract from the Flight Crew Operation Manual, as follows (ellipsis mine):

In performing these functions the FAC uses independent channels:

Yaw damper
Rudder trim
Rudder travel limit
Flight envelope

...
If  a  failure  is  detected  on  any  channel  of  FAC1,  FAC2  takes
over the corresponding channel.

Are the "channels A and B" two of the output "channels" mentioned here? The last quoted line suggests that each channel is redundant between the two computers, in which case why would both RTLUs fail together?

The problem is that you're using the Flight Operations Manual, and not the Schematic Manuals. Quite frankly, FOM's pretty much suck in terms of technical details, but that's not their purpose either.

In regards to your question about what the channels are:

Channels are really just a euphemism for system redundancy. The FAC's are two completely separate entities (with crosstalk capabilities) - kind of like flight crews. The PIC (pilot-in-command) has primary control of the aircraft, while the SIC (second-in-command) has the same independent authority. The PIC and SIC can talk to one another, and monitor what each is doing. If the PIC falls ill, becomes incapacitated, etc.. the SIC can take over the functions of the PIC.

The FAC's work the same way. They both receive the same information, and have full capability of performing the work of one another. Take note of this schematic, courtesy of Airbus (found on the web), and which I took the liberty of highlighting:

Basically, what this schematic is saying is that the ELAC's, under normal law, provide turn coordination and dutch roll damping to the FAC's. They do this by receiving inputs from the rudder pedals, sidesticks, FMGC's, ADIRU's, SFCC, LGCIU's, and hyd pressure. Based on those inputs, it computes the proper yaw commands and sends that to the FAC's. It should be noted that both FAC's receive the same information on, you guessed it, separate channels. What does that mean? The data from ELAC 1 is sent to BOTH FAC's on separate sets of wires. Inside the FAC's, those data paths are split as well (Channel A & Channel B) and a separate processor computes the data on Channel A & the data on Channel B. Never the two shall meet. Likewise, the data from ELAC 2 is sent to BOTH FAC's on separate sets of wires, and again, those two data paths shall never meet.

At the same time, both FAC's are receiving the same FMGC, ADIRU, SFCC, LGCIU data that the ELAC is. Again... Separate wires, separate outputs, and computed with two different processors inside the boxes. The FAC's are also receiving hydraulic pressure, commanded rudder trim position, and SEC fault data. Guess what? All on different channels.

Now, take note of the highlighted portion in red. Ordinarily, FAC 1 is in control of the servo loop for the RTL Motors. This essentially means that based on ALL of the inputs received from the ELAC's and other independent systems, the FAC 1 sends a signal to the rudder travel motor and says "Move here." The motor moves, and a feedback signal from the RTLU circuitry is sent to the FAC saying "Here I am." When the commanded position of the surface position minus the actual position of the surface is approximately ~0, the surface is nulled. This is a basic feedback loop/servoloop.

The FAC 2 has the exact same capabilities as FAC 1. The two are in constant communication, making sure that neither has failed. If FAC 1 reports a self-failure, or FAC 2 detects a problem with FAC 1 and/or its servo loop, FAC 2 can immediately take over.

Notice that FAC 2 is responsible for the M2 (second motor) of the rudder travel limit system, and FAC 1 is responsible for the M1 (primary motor) of the rudder travel limit system. The wiring for the motors and its associated servo loop are completely separate. Again, the idea is complete system isolation. As such, any one failure cannot take out the entirety of a system.

All of the above is under the presumption of NORMAL LAW. It appears that cracked solder joints, emphases on the plural form, caused failures of Channel A & Channel B of the RTLU (see page 66 of accident report). Basically, like I mentioned previously, FAC 2 was monitoring FAC 1 for faults with it or its associated servo loop. When RTL channel A failed (the servo loop feeding data back to FAC 1; associated with Motor 1), the FAC 2 picked up on it, and took over on its own separate channel. A cracked solder joint on RTL channel B caused FAC 2 to trigger a failure. At some point during these failures, the flight crew pulled the circuit breakers, presumably to reset the faults. The loss of both FAC's put the aircraft into alternate law.

Once the aircraft was in alternate law, it seemed that there was a lot of confusion as to what was happening. From there, things went from bad to disastrous.


Are there any helicopter blades that fold in the middle? Let's assume that, for some arbitrary reason, helicopter blades are too long for transport or storage. Folding them at the rotor hub, as is done with conventional folding helicopter blades, would still be too long and there is a need to fold them further. So, they are folded somewhere in the middle of the blade instead (or as well).

Do such folding helicopter blades exist? If not, has there been theoretical studies on how it could be done? What would be the impact on blade performance?

This is a question about the theoretical feasibility and difficulty of using such folding blades, and whether there have been existing studies or designs for it. As such, the practical applications and whether it would be worth it, or whether there would actually be a real-life scenario where this would be useful, should mostly be ignored.

(Bonus point if it is possible to deploy the folded blades simply by starting the engine, but this is probably too outrageously complicated to pull off anyway.)

Bending a helicopter blade in the middle is of course possible, but poses many serious problems and risks. The designers would look for different solutions first, like they did for the UH-60.

The blade loads are lift, centrifugal force, and twist. Manufacture the blade with modern composite technology, mount it with the fully articulated hinges that are usually a requirement anyway, and trust the blades with your life because a breakage would be catastrophic.

Any repeated action poses additional risk. Mounting a hinge and lock that operates every time, is not open to human error, and never fails - that is would be the quest for the folding blade designer.

Of course a folding blade can be designed, like the folding wings on navy fighter aircraft. But not for some arbitrary reason. Only for a vital reason that cannot be solved in any other way.


Is Flight Following in the USA directly equivalent to Basic Service in the UK? This is partially a question on terminology, I have flown in the USA and used a service which is commonly referred to as "Flight Following".

I have read this question: Is there a European equivalent of VFR Flight Following?

And I am interested in whether requesting a "Basic Service" which I use in the UK is a direct equivalent? If not, what are the major differences?

Based on the UK Flight Information Services document that Dan helpfully provided in chat, it looks like they're different:

Basic Service

Available to IFR flights in class G
Available to VFR flights in class E and G
Provides information on "airspace activity that may affect your flight"
Pilot is free to manoeuvre as needed, unless otherwise "agreed" with ATC
Provided workload permitting

Flight Following

Not available to IFR flights
Available to VFR flights in any airspace where ATC has radar coverage
Provides information on airspace, traffic and weather
Pilot is free to maneuver as needed, unless otherwise instructed by ATC
Provided workload permitting

So the major differences seem to be:

Basic Service is available to IFR flights; Flight Following is not (it wouldn't make sense anyway)
Basic Service provides airspace information only, not traffic information; Flight Following provides both

The whole traffic vs airspace information thing is very confusing in the CAA doc. Read literally, there's no VFR service that offers both airspace and traffic advisories, but that makes no sense at all. I'm probably missing something, but reading that document makes me glad the US has kept it simple...


Why are adjustable area jet engine nozzles mostly limited to military use? It seems that only jet engines with afterburners use adjustable area nozzles (this means adjusting the area of the nozzle but not necessarily the direction). This includes most fighter jets, as well as bombers like the B-1B and Tu-160. Outside of the military or afterburning engines, they don't seem to be used, even for smaller engines.

What is the reason for this? Is the Variable Area Fan Nozzle (VAFN) concept related?

Wikipedia explains that it is related to supersonic operation; I'm looking for a more detailed explanation about the reasons for this.

A variable area nozzle helps to adjust the exit pressure of the combustion gases to ambient pressure. When they leave the turbine, the combustion gases have still some remaining pressure which is converted into speed by a convergent contour of the nozzle.

If the combustion gases have enough pressure to be accelerated to supersonic speed, the nozzle is actually first convergent and then divergent to achieve the best acceleration of the flow. The convergent, subsonic flow accelerates until in the section with the smallest area, called the throat, the speed of sound is reached, and the following divergent section accelerates the now supersonic flow further until its pressure drops to ambient pressure. This con-di-nozzle needs to adjust both the cross section of the throat and the cross section of the exit area. Failure to get especially the throat area right will mean substantial thrust loss in operation.

Afterburning engines need adaptable nozzles due to the different operating conditions in dry and wet mode, so they profit the most from adjustable nozzles. Reheating the exhaust gas means to increase its volume, so the nozzle needs to become wider to be properly matched. In general, if the exit speed of the combustion gases is supersonic, an adjustable nozzle is required. Even some early jets without afterburners had an adjustable nozzle: The central cone of the Jumo-004 nozzle could be moved fore and aft, which changed the location of the bulbous aft section, helping to get the throat area right. Note in the picture below that the cross section widens again in the last part of the nozzle, which shows that the exhaust stream of the Jumo engine was mildly supersonic.

Airliner engines would only gain little from an adjustable nozzle, and considering the mass increase of a fully adjustable nozzle, would in total have lower efficiency. Short-range aircraft usually have nozzle geometries optimized for field performance while long-range aircraft prefer to optimize for best cruise efficiency. Their core flow exit speed is still subsonic or only mildly supersonic - please note that the speed of sound in the heated combustion gas is much higher. At 500°C the speed of sound is almost 560 m/s.

The variable area fan nozzle tries to do for the fan flow what the regular nozzle does for the core flow of a jet. So this is indeed a related concept and helps to optimize performance both at low and high speed. The picture below is copied from the US patent 2011/0302907A1 and shows an adjustable end part of the cowling (crosshatched, 54). The exit speed of the fan flow is subsonic at take-off and mildly supersonic in cruise, and since its mass flow is much higher than that of the core in airliner engines, making the nozzle variable pays off earlier. By adjusting the exit pressure by varying the exit area it can squeeze out some performance gains.


Is there a procedure to safely handle a PED battery problem on a commercial flight? On a recent flight, I heard a (somewhat unsettling announcement) from the flight attendant (paraphrasing from memory):

  Dear passengers, if you currently have a Samsung Galaxy Note 7 device in your possesion, we kindly ask that you turn your device off completely and make no attempt to charge your device while in flight. If you see or smell smoke or hear unusual noise coming out of your device, alert a member of our staff immediately.

(at the time, I had no idea what this is about, but apparently the device was recalled due to a faulty battery)

I'm curious at this point, in the unlikely event of a (normally-safe) device like this displaying symptoms of imminent fire or explosion hazard, how would the staff react after being alerted of it? Is there a standard procedure for something like this?

FAA Advisory Circular 120-80A contains recommended crew member procedures and training for combating in-flight fires. It has information about causes, indications and procedures of in-flight fire fighting. According to the AC,

  Upon discovering a fire, the initial focus should be on aggressively
  extinguishing the fire with a readily available extinguisher (which will likely be halon), but do not use water if it is believed the fire is of aircraft electrical system origin. Generally, you should consider using the first available extinguisher rather than delaying your firefighting efforts while you locate a particular extinguishing agent for a class A, B, or C fire.

Airbus Flight Operations Briefing Notes- Managing In-Flight Fires also says pretty much the same thing:

  Any fire, no matter how small, may rapidly become out of control, if not  dealt with quickly.The first priority will always be to put it out.

Coming to the Galaxy Note 7 issue, the AC says,

  h. What are the Recommended Procedures for Fighting a Lithium Battery Fire? The following procedures are recommended for fighting a fire in a lithium-type-battery-powered PED. The procedures consist of two phases: extinguishing the fire, and cooling the remaining cells to stop thermal runaway.

  (1) Utilize a halon, halon replacement, or water extinguisher to extinguish the fire and prevent its spread to additional flammable materials.

  (2) After extinguishing the fire, douse the device with water, an aqueous-based extinguishing agent, or other nonalcoholic liquids to cool the device and prevent additional battery cells from reaching thermal runaway.

Though the standard procedures in case of a fire has to be decided by the company, the FAA recommends some procedures to be followed, like:

  • Be aggressive; if flames are visible, fight the fire immediately.

  • Someone must immediately notify the flight crew to describe the fire, smoke, smells, action being taken,  etc.

  • If flames are not visible, find the base or source of the smoke.

  • Pull circuit breakers, in applicable area.

  • Do not reset circuit breakers, unless instructed by flight crew.

  • Relocate passengers as necessary.

  • Locate hot spots using the back of your hand.

  • Don PBE (not necessarily in this order).

The flight crew (who are supposed to don their oxygen masks on indication of smoke/fire) are supposed to inform the ATC and plan for an emergency landing, if necessary.


Why did early 747s have only two or three windows on the upper deck on each side? All 747-100s and some 747-200s were built with just three windows on each side of the upper deck.[1] I'm wondering why so few?

Some of the 100s were retro-fitted with ten windows on each side, so clearly the reason isn't structural; nor do I imagine the cost difference would be relatively very much. It seems connected with the original use of the upper deck as a 'lounge' area, but it seems surprising that you'd want a premium area with very little natural light. On occasion Pan Am seems to have been content with just two windows each side.

Was the three-window configuration purely driven by aesthetics, or were there other considerations by Boeing or the airlines?

3-window Pan Am 747-100 upper deck source

10-window Quantas 747-200 upper deck, 1971 source

 source
Pan Am 747s 1969

Early on in the design and development of the aircraft the function of the upper deck changed throughout the early life. Windows are high stress areas and if they can be avoided they typically are. Juan Trippe was a major figure in pushing the 747 into production but during the SST race it was his view that the 747 would largely be a freighter holding the crew on the upper deck. Generally freight aircraft do carry small crews and were likely the original reason for the windows.

  Boeing was competing for a supersonic transport contract in 1965, at
  about the same time the 747 was conceived, and Pan Am founder and
  chairman Juan Trippe believed that the big subsonic jets would end up
  as freighters and that the SST would replace the 747 on passenger
  routes. Trippe was one of Boeing’s best customers and usually the
  first to order new models, so Boeing put the flight deck of the 747
  above the passenger cabin to give the aircraft a hinged nose for a
  front-loading cargo door.

The original bubble deck was much smaller but created too much drag and was ultimately elongated. This left dead space that Trippe and his team drove Boeing to turn into a lounge/bar akin to the 377 Stratocruiser's area. Bar's rarely have windows on the ground so why have them in the air...

  The first design for the cockpit enclosure was a hemispherical hump
  atop the fuselage. This produced too much drag, so Boeing extended the
  aft portion of the hump to form a teardrop. Then, in a deliberate echo
  of the below-deck lounge on the model 377 Stratocruiser, Boeing’s
  1940s flagship, Trippe and his colleagues persuaded Boeing to turn the
  extra space behind the cockpit into a bar and lounge.

It was not until almost a decade after its introduction during the '73 fuel crisis that airliners started using the upper deck for full passenger seating. This likely lead to the later models having full window treatment of the upper level.

  The party days ended with the 1973 fuel crisis, when virtually every
  747 operator got rid of the lounge and replaced it with more seats for
  paying passengers. In announcing the change, a British Airways press
  release noted that the upstairs area was “currently used for a
  first-class lunge”—the spelling was probably appropriate more often
  than not


What are the advantages of centerline armament? In the ME 109, Messerschmidt went through a lot of effort to squeeze a cannon into the fuselage firing between the piston banks of the DB engine, exiting the spinner. Why not just put the cannons in the wings? Is it because the trajectory of a center-line shot doesn’t need to converge (as wing-mounted guns do) and therefore has a longer range of sight?

Yes it's because of dispersion.  With wing mounted guns you normally "harmonize" them to converge at a point, say 300 yards or 600 yards to have a sweet spot where most of the projectiles are passing through a small area to maximize the fire concentration.

But at ranges closer and farther, the streams of projectiles are more dispersed and their effects are reduced.  Watch gun camera footage of strafing runs in something like a P-51, and you can see the bullet strikes widely dispersed and coming together into a tighter cluster as the range closes in.

Putting the armament in the nose eliminates the range issue and you have maximum concentration at any range.  The later versions of the 109 with the Mk108 30mm cannon were just about ideal for this because the cannon was very compact and had a really high rate of fire for its caliber (about 4-600 rpm), so a single cannon + two MGs was plenty of firepower and was probably the ideal configuration for the 109.

The ME262 jet had 4 Mk108s in the nose, providing close to the concentrated firepower of the A-10's 30mm 3000 rpm gattling gun.  A very short burst would bring down any fighter if it scored hits.


What are these things on strings after the loss of cabin pressure? I saw a picture on Twitter after the loss of cabin pressure. I've seen these images many times before, but in this picture, there are some things on strings that I cannot identify.

They are the holders for the oxygen masks, they are packed into the plastic retainers and stored in the overhead, when the masks drop, they fall out of the containers. Not all systems have these retention pieces that I can find, but some do.

The "black" tubes (actually clear, but look black in the picture) you see are the oxygen mask tubes and the mask itself is dangling from the end of the tube, you can see they have green/red labels on them that signify they are oxygen. The oxygen generator for that group of seats/masks is under the label in the top "HOT HOT", oxygen systems get very hot when generating oxygen (just ask ValuJet).


Are CO2 cartridges not considered explosive? I've recently starting riding a push bike to work and got myself a CO2 pump and some cartridges (like this), which I promptly forgot about. As a result, when going on work trips and holidays, I had a cartridge in my bag when going through airline security.

I estimate roughly 15 airports (some duplicates) either didn't detect the cartridge or just ignored it. Perth International is my main airport, but I also visited Singapore 3 times (so bare minimum of 6 security checks there. Is this normal behavior/protocol? I would have thought that while CO2 cartridges are single use, they probably present more danger than other prohibited items, such as nail clippers.

I had a cartridge in my bag when going through airline security.

These are not uncommon. They are also used in for instance:

Life Vests
Ski Airbags
Soft air guns

In other words, it's not an unusual object, especially for holidays which I guess both your two mentioned destinations might be for many travellers. I've checked in my bag with an automatic self-inflating life vests a few times and while it went in the  hold never had any problems or found it removed. I believe there may be some limitations though on the number you can pass through, and they might start asking questions if you have more than two.

  I estimate roughly 15 airports (some duplicates) either didn't detect the cartridge or just ignored it.

It's not unjustified not checking them in. Onboard pressure changes, the cargo hold is cold and will shake during turbulence which just might trigger it to deploy if left screwed onto a life vest of similar.

  probably present more danger than other prohibited items, such as nail clippers

I can't see any real threat posed by these, except for the gun application, which of course requires a gun and not only a cartridge. Btw, TSA allows nail clippers.

Ryanair, the World’s favourite airline ;) states the following:

  Carriage of Self Inflating Lifejacket

  A self inflating lifejacket with 2 carbon dioxide cylinders (plus 2
  spares) can be included in either cabin or checked baggage.

In other words, they appear pretty liberal on the matter.


How long will an aircraft need to fly before it can land without dumping fuel? Now, I know perfectly well that the literal and unhelpful answer to the question is long enough to burn sufficient fuel that it is no longer overweight for landing. What I'd like to understand is whether it is possible or not to give an answer about what's typical.

I am surprised that after flying all the way from Moscow to Ireland this aircraft had enough fuel on board to be still overweight (even given that it still had to go all the way to the Dominican Republic):

  An Azur Air Boeing 767-300, registration VP-BUX performing flight ZF-973 from Moscow Vnukovo (Russia) to La Romana (Dominican Republic), was enroute at FL320 about 90nm south of Shannon (Ireland) when the crew decided to divert to Shannon reporting all their lavatories were blocked. The aircraft dumped fuel and landed safely on Shannon's runway 24 about 90 minutes later.

Typically, how much of an airliner's flight will be in an overweight-for-landing condition?

Does it vary so much between aircraft types, distances, passenger/cargo weights and other conditions that it's not simply possible to say what is typical, or is it possible to say that the case above is (for example) unusual?

Does it vary so much between aircraft types, distances,
  passenger/cargo weights and other conditions that it's not simply
  possible to say what is typical

This is pretty much the case. For example in a lot of smaller trainer aircraft you are more or less always in the CG range to make a successful landing. On the contrary in larger aircraft fuel burn schedules are extremely important to simply keeping the aircraft airborne.

Dumping fuel is generally not idea from a strictly business standpoint you are basically throwing money out of the aircraft which no airline wants to do on purpose.

What varies heavily between all flights is that at some point its up to humans, and humans make mistakes. Fuel loads may be calculated automatically but some guy still needs to usually shut the pump off at the right time, the pilots need to fly the plane as prescribed and the conditions need to be as expected. Any variable in this could create an issue for you.

For example lets say you take off and get an unexpected tail wind of 100 Kts for the whole ride. Lets also say that you loaded up as much fuel as you could on account of you were flying to a smaller airfield and you were unsure they had enough fuel on hand to get you home. You knew you could bring enough to get there and back but you would be right at the limit of the load config. That 100Kt tail wind is going to save you a fair bit of fuel you intended on burning and due to unforeseen things you may now be over weight.

Now lets say you are flying short haul in a 737, you are doing a 30 min hop and its the end of the day. You have the the required fuel plus reserves so you are flying pretty light. A light passenger load and not much cargo to haul, you may be in range for the whole flight.

Those are just two of a very long list of examples of different load configurations that can lead to always in range, or substantially out of range situations.


VFR Navigation, rerouting timing corrections due to wind - rule of thumb? Consider this reroute on a VFR nav trip from Great Malvern to Chipping Norton.
Maintaining 120 TAS.
Track 110 °M
Heading 103 °M (taking 3/4 of Max Drift - MD)
In still air this 30nm section would take 15 minutes.
However, with a 5-10 headwind the groundspeed would be lower than TAS, around 110-115 kts
Is there a good rule-of-thumb, or quick method in the air to estimate the timings and ETA when considering the effect of headwind or tailwind on the timing of a reroute leg?

If you know or have a reference to Ground Speed, estimating reasonably accurate flight timings is straightforward. Whatever your GS, you will cover 1/10th of the distance in 6 minutes. So at 90kts, 9 miles in 6 mins. At 70kts, 7 miles in 6mins and at 120kts, 12 miles in 6 mins etc. If you mark your pen/pencil with 5 & 10nm distance marks measured in the same scale as your map, it’s easy to interpolate say, 7nm (for say 70kts GS) and mark your map with 6minute marks. If needed dissect these markings in half, for 3 minute markers.


Has the FAA ever granted anybody a license honoris causa? Say, anybody who made an outstanding contribution to technology, flight methodologies, etc (for example, the Wright Brothers); has the FAA ever issued a license (private pilot, etc.) to anyone that deserved such honor?

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

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

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

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

Orville Wright
Evan J. Parker

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


What is CAS and EAS and how to calculate from IAS? I am trying to understand IAS, CAS, EAS, and TAS. I was under the impression that CAS is IAS corrected for instrumentation error and position error. The error is specific to the type of aircraft. Why then on the wikipedia page for CAS is there a formula to calculate CAS which is a function of just dynamic pressure? Where did this formula come from and how can it be valid if the correction for CAS is aircraft specific?

Also, EAS is CAS corrected for compressibility. What does this really mean? How can I convert a speed in CAS to EAS?

If you don´t mind, I´ll keep it in simple terms.

We start off with IAS - that´s the airspeed you see on your instruments. You have static port - registering pressure around your aircraft, pitot tube, registering how many molecules of air getting inside. And by subtracting one from another, you get your IAS.
Dummy example: Static registers 100 molecules around. Pitot registers 200 molecules, which would equal to speed of 100kts.

CAS - it the speed corrected for instrument error. Because no instruments are perfect.
Again, just one example, since a/c is moving through the air, pushing the air aside, it does create lower pressure around the a/c. Which in term, does affect reading of static and pitot tubes (registering wrong amount of molecules).
As a pilot, CAS is less relevant speed, as it will be used mostly for certification process.

CAS - EAS is made by allowing for compressibility effects. At very high altitude and very high speeds (jet fighters/bombers/space shuttle), there are different rules in action.

There is another speed, TAS. If you want to do everything perfect, first you need to convert IAS to CAS, (by using special table for a given airplane) and then convert CAS to TAS.
TAS is your real airspeed, moving through the air. It might differ greatly from IAS depending on pressure and temperature. In standard (ISA) conditions CAS will be equal to TAS.
But what happens when you fly at an altitude of 40.000 feet? Well, air is a lot less dense. For a given cube of air, there are a lot less molecules.
In order to fly and not to stall, you must see "100kts IAS" on your airspeed indicator. Ssince there are so fewer molecules in the air, your real airspeed through the air must be 2-3 times higher, in order to hit all those 100 molecules. Does it make sense?

As a pilot, greatest importance for you is IAS. It shows you how many molecules of air you are hitting (dynamic pressure). Stall speed, never exceed - all based on IAS. Your TAS can be whatever, but IAS is the one affects your airplane.

So why do we care about TAS? Well, based on TAS and wind, we can derive our GS - ground speed. And GS is important! It will tell you, how long time will it take for you to get from A to B. Based on time, you know how much fuel you will need. Perhaps, you would need to make an extra refuelling stop on your way. Or you calculate and see that airport will be closed by the time you arrive there?
Later on, as an airline pilot, you know if you are early/late, duty times, etc, etc.

There is Mach number as well, but since you didn´t ask, I´ll just say you will need it flying at higher altitudes (approx. above 25,000 feet) and at those altitudes, it will take over IAS.


How do the linearised equations of motion work? I am reading this book: "Flight Dynamic Principles" by Cook, second edition.
You can read it here:
https://aerocastle.files.wordpress.com/2012/04/flightdynamicsprinciples.pdf

First, go to the page 76, read the sentence:

  Further, the only significant higher order derivative terms commonly encountered are those involving $\dot w$.

Why is the only $\dot w$ involved here? the $\dot u$ and $\dot v$ have the same roles, huh??

Second, same page 76, section 4.2.3, the sentence:

  The assumptions applied to the aerodynamic terms are also applied to the control terms thus, for example, the pitching moment due to aerodynamic controls may be expressed.

And you can see the equation (4.32)

it is totally different from aerodynamics terms equation..why is that?. Why are moments not dependent u, v, w, and p, q, r like aerodynamics terms.

Lastly, look at the example 4.2 at page 80, what is the meaning of this example? where do the values of dimensionless longitudinal derivatives at page 81 come from? What are they? The book said seeing the appendix 2 at page 413. Now go to the page 413, where do these multipliers come from?

Um..it's a bit of a counterintuitive and hard to visualise field of aeronautics. There are six degrees of freedom (if we assume that the aircraft is rigid) that need to be transformed from aircraft axes into earth axes. And since we're looking at aerodynamic stability, we need to consider wind axes to introduce disturbances: if the aircraft moves as an effect of the disturbance, the relative wind changes.

Since we're working with transformation matrices, we can only solve these analytically if there are simple multipliers in the matrix, as soon as there are trigonometric terms such as sines & cosines introduced, we'll need to use numerical methods. So we linearise by looking at small disturbances only, and set $cos(\phi)$ = 1 and $sin(\phi)$ = $\phi$. Usually OK from a body axis perspective, since stall occurs at 15 degree which is a small enough angle. But..

..to make it all even worse, it is one of the few remaining bits of engineering where the dark art of quaternions are used, since when the nose is pointing straight up some of the Euler angles are undefined and we need a fourth dimension to provide continuity.

I reckon if you're interested in this book, the only prior knowledge you need to have is the realisation that it is going to be complex. What has always worked for me is just taking the results at face value, start to work with it to gain experience, then look it up again so that the context is much clearer.

The book does indeed seem to be a bit laborious to read. What they're saying with the statement on $\dot{w}$ is that in the end result, the linearisations and simplifications are justified, in that no big inaccuracies occur if effects of $\dot{u}$ and $\dot{v}$ are neglected. Effects of $\dot{w}$ are significant though and do need to be considered, which the authors do in the rest of the text.

Equation 4.32 is the most generic statement there is on moments - what is says is: the total moment is (how the moment changes with a variable) times the variable. It does not yet consider what the cause of the moment change is.


Does a safety pilot for a PPL practicing under the hood in VFR conditions need a current medical? Am I legal to fly under the hood with a safety pilot who does not have a current medical? VMC only, not IMC.

As explained in AC 68-1A, a safety pilot requires a current medical:

  A pilot acting as a safety pilot per part 91, § 91.109(c), however,
  would be a required pilot flightcrew member by regulation rather than
  a passenger. Section 91.109(c) provides that no person may operate a
  civil aircraft in simulated instrument flight unless the other control
  seat is occupied by a safety pilot who possesses at least a private
  pilot certificate with category and class ratings appropriate to the
  aircraft being flown. Because a safety pilot is a required pilot
  flightcrew member, the safety pilot is required to hold a valid and
  appropriate medical certificate in accordance with § 61.3(a).

For information on a safety pilot using BasicMed see this question.

By the way, by definition a safety pilot is only required in VMC. In IMC you're in actual instrument conditions; see this question.


Are the requirements for an initial type rating the same across types? If a pilot wishes to obtain an initial FAA type rating - say, for a Boeing 737 - are the requirements to obtain that rating the same as if they were getting a type rating for an Airbus A320? If they are different, where can these requirements be found?

Assume that in both cases the pilot is ATP-rated.

Actually, it doesn't matter whether you are a Private pilot or an ATP, the requirements for a type rating are in the Airline Transport Pilot and Aircraft Type Rating Practical Test Standards, which apply regardless of the aircraft type.

In the PTS, it says:

  Practical Test Book Description

  This practical test book contains the Airline Transport Pilot and
  Aircraft Type Rating Practical Test Standards—Airplane.  The Airline
  Transport Pilot and Aircraft Type Rating Practical Test
  Standards—Airplane includes Areas of Operation and Tasks for the
  initial issuance of an airline transport pilot certificate and for the
  addition of category, class, and aircraft type ratings to an airline
  transport pilot certificate. These Areas of Operation and Tasks also
  apply for the issuance of an airplane type rating to a private or
  commercial pilot certificate.

You basically cover everything needed for the ATP.  The differences between the different airplanes come out during the practical test just like they do for any other checkride.  The examiner (who will be typed in the airplane) asks you about the things that are specific to each airplane, but this isn't really a lot different than him asking you questions specific to a Cessna or a Piper during your private pilot checkride.

The PTS specifies general Areas of Operation's instead of saying exactly what needs to be tested for every aircraft type.

Here they are for a type rating:

  Section 1: Preflight Preparation

  Areas of Operation

  I. Preflight Preparation
  Task A: Equipment Examination
  Task B: Performance and Limitations
  Task C: Water and Seaplane Characteristics (AMES/ASES)
  Task D: Seaplane Bases, Maritime Rules, and Aids to Marine Navigation (AMES/ASES)

  Section 2: Preflight Procedures, Inflight Maneuvers, and Postflight Procedures

  Areas of Operation

  II. Preflight Procedures
  Task A: Preflight Inspection
  Task B: Powerplant Start
  Task C: TAXIING
  Task D: Sailing (AMES/ASES)
  Task E: Seaplane Base/Water Landing Site Markings and Lighting (AMES, ASES)
  Task F: Pre-Takeoff Checks

  III. Takeoff and Departure Phase
  Task A: Normal and Crosswind Takeoff
  Task B: Glassy Water Takeoff and Climb (AMES/ASES)
  Task C: Rough Water Takeoff and Climb (AMES/ASES)
  Task D: Confined-Area Takeoff and Climb (AMES/ASES)
  Task E: Instrument Takeoff
  Task F: Powerplant Failure during Takeoff
  Task G: Rejected Takeoff
  Task H: Departure Procedures

  IV. Inflight Maneuvers
  Task A: Steep Turns
  Task B: Approaches to Stalls and Stall Recovery
  Task C: Powerplant Failure—Multiengine Airplane
  Task D: Powerplant Failure—Single–Engine Airplane
  Task E: Specific Flight Characteristics
  Task F: Recovery from Unusual Attitudes

  V. Instrument Procedures
  Task A: Standard Terminal Arrival/Flight Management System Procedures
  Task B: Holding
  Task C: Precision Approaches (PA)
  Task D: Nonprecision Approaches (NPA)
  Task E: Circling Approach
  Task F: Missed Approach

  VI. Landings and Approaches to Landings
  Task A: Normal and Crosswind Approaches and Landings
  Task B: Landing from a Precision Approach
  Task C: Approach and Landing with (Simulated) Powerplant Failure—Multiengine Airplane
  Task D: Landing From a Circling Approach
  Task E: Rough Water Approach and Landing (AMES/ASES)
  Task F: Glassy Water Approach And Landing (AMES/ASES)
  Task G: Confined-Area Approach and Landing (AMES/ASES)
  Task H: Rejected Landing
  Task I: Landing from a No Flap or a Nonstandard Flap Approach

  VII. Normal and Abnormal Procedures
  Task A: Normal and Abnormal Procedures

  VIII. Emergency Procedures
  Task A: Emergency Procedures

  IX. Postflight Procedures
  Task A: After-Landing Procedures
  Task B: Anchoring (AMES/ASES)
  Task C: Docking and Mooring (AMES/ASES)
  Task D: Beaching (AMES/ASES)
  Task E: Ramping (AMES/ASES)
  Task F: Parking and Securing


Does the Boeing B787 have safety issues with its battery and windshield? AVHerald has reported

An incident of battery overheating. That is after the aircraft has been grounded and parts of the battery system redesigned. AVHerald provides a detailed report on the battery issue.
An incident of a cracked windshield. A cracked windshield typically results in declaring an emergency. AVHerald lists 15 incidents of cracked windshields since 2012. This happens in other aircraft too, but apparently not in the same way. On other aircraft, only the outer of several layers cracks after some time. On the 787 it seems to happen on start or landing, always resulting in a return to the airport. It should be noted, that the 787 windows have fewer layers and larger windows than any other type.

Also Forbes reports, that there have been at least four incidents with the batteries after the FAA mandated four-month grounding, and a physics professor at Canada's Dalhousie University states battery failures are an indication of a problem within the cells.

Incidents with both issues have been reported since 2013, when the 787 was allowed back into service after the FAA mandated four-month grounding.

To me reading this report is disturbing.

Doesn't this mean, that the aircraft is flown with knowingly unsafe battery and windshield?
As a passenger, does one have to be worried about flying in this particular type?

The 787 is among the safest airliners currently flying. At the time of writing, it has been involved in zero hull loss incidents and there have been zero fatalities due to incidents.

While you can find numerous incidents including those you mention there have been exactly zero total losses and no loss of life on board (due to the aircraft itself - its possible people may have perished on board due to other factors not involved in aircraft safety).

It should be noted that A boeing report on this subject points out (page 19) that most of the aircraft which have had zero hull losses have also not accumulated 1 million departures. Therefore it might be too early to tell if there is any fundamental safety issues with these types. However, there has been 50+ years of learning about safety with regard to aircraft operations - and all of that feeds in to these modern aircraft.

All in, I would consider flying on the B787 to be objectively safe (or, at very least equally so as other similar airliners). Does there exist some "wrinkles" to be ironed out? Perhaps - but they do not affect the overall safety of this type.


Is the hydraulic fluid artificially colored? A normal aircraft has multiple hydraulic circuit, identified by colors (e.g. according to the ATSB final report of the QF32 the green hydraulic line was disabled; according to the BEA final report of the AF4590 the Concorde had a yellow, a blue and a green circuit, ...). I understand the need to be equipped of several independant hydraulic system (redundancy) and the need of being able to identify those.

Thanks to the previous example, I figured out the hydraulic circuits are identify by colors.
Does it mean the hydraulic fluid is colored (useful in case of leak)? Does it means the elements of each circuit is painted accordingly (usefull for maintenance)?

A common hydraulic fluid used in aircraft is called Skydrol. The fluid is artificially colored, but this does not depend on which circuit it is in. The FAQ on the manufacturer's site addresses the color.

  Skydrol fluids are given a purple dye to make it easy to distinguish them from other fluids. But the dye does not usually last as long as the fluid does. The color may change from purple to gray or yellow or green, yet the fluid can still meet all used fluid specifications. Color is not a reliable indicator of fluid quality, and we recommend that the system be sampled for chemical analysis to determine if it is suitable for use. A dark amber color, however, is a cause for concern, and can indicate a severely stressed fluid. Call Solutia's Technical Service for assistance if you are unsure about a fluid's color. Our technical bulletin has a color chart to use as a guide.

Initially the color helps to distinguish from other fluids, and having multiple colors would make it more complicated. It notes that the color also does not remain constant, so even if it were colored initially, it would probably end up changing anyway. It also mentions that a dark amber color can be an indicator of issues.

I can't find any good pictures, but the lines are probably not color coded. Any colored hydraulic system components are generally purple (like the fluid). The lines themselves can be labeled, but the standard for hydraulic lines is blue and yellow. The end fittings are colored to identify the tube material type.

The maintenance manuals will show the layout and label the different lines. Also, on this ASRS page, one report is from a mechanic that confused the green and yellow system fittings, which probably wouldn't have happened if they were color coded.


What is the loading diagram for a C-130J? I'm a student participating in a design project wherein we have to develop a paper design for a payload to be airdropped from a C-130J.  Naturally, I'd like to look at the weight and balance of the C-130 to see what sort of limitations we have (since we'd like to literally fill the cargo bay with multiples of this payload), but it does not seem to be available anywhere.  I found a CNI-MU emulator on Google Play that gives some basic information (basic weight/arm, crew weight/arm, fuel weight/arm), and I have a loadmaster form from the 2015 Defense Transport Regulations that shows me the cargo hold layout. However, something's not lining up.

The default information loaded into the emulator places the basic weight at STA 730 and the fuel at STA 750, which is roughly where the aircraft ramp begins according to the DTR cabin layout (which labels it as corresponding to the B/E/H models, but, according to the DTR, it applies to the J model as well), but it seems strange because, according to the CNI-MU emulator, that's around the quarter-chord of the wing, which is a little behind the center of the cargo hold.

In other words, I'm a bit confused and am looking for anyone who might be able to either make sense of the above or answer the following question:

What is the loading diagram for a C-130J (i.e., what is the basic weight/arm, crew arm, fuel arm, and payload stations within the cargo cabin)?

As listed on a CNI-MU emulator designed for use by C-130J loadmasters, the following is a list loads and moment arms for the aircraft:

Basic weight: 80,000 lbf/STA 530
Crew weight: 600 lbf/STA 153
Fuel weight: 38,000 lbf/STA 551 -- this weight is, naturally, variable,
although the moment arm appears to stay relatively constant.
CG limits: 21-30% MAC

Finally, payload moment arms can be determined via use of of DD form 2130-2 on page III-V-17 of the 2015 Defense Transport Regulations (http://www.ustranscom.mil/dtr/part-iii/dtr_part_iii_app_v.pdf).


Where can I find that video of a college built blown wing aircraft? I once found a video of a single engine, piston and propeller, high wing plane that had been built, or modified by a US college/university. They added a 200 HP turbine engine behind the baggage compartment up high in the fuselage and it drove a turbine compressor. Pretty much like a airliner starter turbine.

The high pressure air from the compressor went out to the flaps pivot axle and then into the flaps inner space. The flaps pivoted at the trailing edge, and so folded out by hinging down and back. Then, the edge that had been buried in the wing's underside forward of the pivot point was now the trailing edge. This trailing edge was a rounded tube of about 1.4 inches to 2.5 inches in OD. It had a jet flap blowing along the top surface and caused entrained air fom the top of the wing to go down 90 degrees.

It cruised around 150 to 200 mph, but landed around 30 MPH. Pretty incredible. I can't for the life of me find it again in Google or Youtube. Does anybody know about this project? I'd love to save that video down to my hard drive. Even better, I'd love to go see the plane.

FINALLY found it! IT was named using the technical name for blown flaps, 'Circulation Control'. I found it using the search 'state name' stol aircraft. Just so happened I chose the nearly right name first off, 'Virginia'.


Why do most single propellers have a clockwise rotation? Why do most single propellers have a clockwise rotation (seen from the pilot's point of view)?

There are though multi-engine planes that have each propeller rotating different directions, but in the case of single propellers, it seems that clockwise rotation is dominant, or even the only option. Is there any single propeller plane with counterclockwise rotation?

I wasn't able to find any good historical references, so this answer is pure opinion.  (sorry).  I'll break this down into two separate questions.

Is there any reason for single-engine propellers to turn the same way?

Yes.  When flying, the spin direction of the prop has several effects.  Helical prop wash, p-factor, gyroscopic precession, differing blade angles of attack all are due to the asymmetry of spinning in a single direction.  An experienced pilot will want to understand and compensate for these effects when necessary.  It is easy to see that once this is understood, a single configuration will be preferred within a community to minimize differences between aircraft.

Is there any reason to prefer CW rotation over CCW as a convention in a single engine plane?

None that I am aware of.  It appears to be simply an accident of choice.  I had wondered if the majority of engines available to early manufacturers was in that direction and made it preferable, but I couldn't find anything suggesting that.  Indeed today the majority of automobile engines rotate the opposite direction.  Making (piston) engines rotate the other direction is not a huge problem.  Twin-engined aircraft and watercraft often have counterrotating engines and propellers.


What is the difference between "flight level" and "altitude"? I have seen references to "FL180" and "FL300", and I know that they stand for Flight Level 180 and Flight Level 300. I've also seen references to "an altitude of 18000ft" or "an altitude of 30000ft".

What is the difference between flight level and altitude, how do they relate to each other, and when and why would one be used instead of the other?

Flight levels use QNE or pressure altitude, while altitude references QNH or local pressure adjusted to sea level pressure.  Altitudes are used at low levels and flight levels at higher levels.  The transition between altitudes and flight levels differs by country and is generally just above the highest obstacle in that country.  In the US the transition altitude/level is 18,000' / FL180.  Some countries transition as low as 5000' / FL050 and the transition altitude/level may vary from airport to airport.

In the altitudes knowing accurate elevations relative to the ground and obstacles is important for collision avoidance and this is the reason QNH is used here.  Each airport will report QNH and controllers will issue the current QNH as needed.  You need to know the QNH for obstacle / terrain avoidance but you need to be using the same QNH as those around you for aircraft vertical separation.

Above all terrain/obstacles the only thing we care about is vertical separation, so we no longer need to know about the actual pressure and instead use a standard reference pressure, QNE / 1013.25 hPa / 29.92" Hg.

Note that flight levels drop the last two zeros of the corresponding altitude and so 30,000 is FL300, not FL30000.  When checking in with a controller, FL300 would be pronounced flight level tree zero zero.

It is also worth noting that an altimeter cannot actually determine altitude.  It can only determine pressure (technically local static pressure compared to a reference pressure).  It converts this pressure to an altitude using a calibrated non-linear scale.  To illustrate the point, look at this map of 500 mb heights:

500 mb correlates to 5500 m or 18,000 ft in a standard atmosphere.  In a real atmosphere this height varies and is not actually level.  An airplane flying "level" at FL180 from LAX to NYC last night will have actually descended almost 300 m while indicating a constant altitude.  These deviations in true altitude from indicated altitude are acceptable, however, since they effect everyone equally in the same locality and separation is maintained.


Why is this plane flying in such a tight circle? I was in a car in NYC on 2/18 going from Queens to Manhattan. While going over a bridge I noticed some (what looked to me like) very tight circular contrails in the sky.

The plane was still there but very high up and/or far away and I couldn't make it out.

The photos here are from my phone, through the window of a moving car on a bridge, so not the best, but it's all I could get.

I never noticed anything like this before and I was curious what this might be.

those look like Holding pattern. Air Traffic controllers manage the flow of air traffic to and from airports. Sometimes it is necessary to hold a few of them before they can start an approach for landing.


Why is it called "Dry Thrust"? When reading the specifications of a jet aircraft anywhere on the Internet, it usually states that its engine produces X pounds of "dry thrust".

Why is it called "Dry" Thrust? As opposed to what?

Dry thrust usually means the non-augumented thrust i.e. thrust without the use of afterburners or liquid injection. The maximum thrust produced by jet engines w/o afterburner is sometimes called military thrust.

The thrust of a jet eingine can be increased by using methods like water(+methonol) injection (mostly in older turbojet engines) or by using afterburners (reheat). In such cases, the (higher) thrust produced is called wet thrust.


Why is the F-16 still in service? Reading the Wikipedia page, I see that the F-16 began production in 1973. That seems pretty old to me. So I ask, why is the F-16 still in service in many countries around the world? Is it that a superior fighter has been not been designed yet, or are there other reasons?

The simplest answer to your question is that the F-16 has not yet been retired because, for its cost, there's nothing better being built in enough numbers to replace the nearly 4500 Falcons produced.

The F-16 was designed on the trailing edge of a surge in technological development by the U.S. military in the wake of Vietnam. The U.S. had fought that war with an air force primarily designed for a standoff engagement with the Soviet Union directly, thus emphasizing interceptor-style fighters targeting bombers at extreme range using missiles. Robert McNamara, U.S. SecDef for the Johnson and Nixon administrations, also emphasized a "one-size-fits-all" approach to aircraft design, requiring the USAF and Navy to collaborate on common aircraft designs that covered a multitude of mission profiles. This created the F-4, a fast but heavy plane that was a handful to fly, weaknesses that were exploited by pilots of technologically-inferior MiG-19 and MiG-21 aircraft in close combat engagements that the Phantom was ill-prepared to fight.

The lesson "dogfighting isn't dead" prompted a renaissance in jet fighter design in the 70s, producing the F-14 and F-15 long-range air superiority fighters, and the smaller F-16 and F/A-18 multirole fighters. Maneuverability, a wide range of weapons from guns to long-range missiles, and high pilot situational awareness by reducing workload and integrating flight and fire control systems, were all emphasized strongly.

The Soviets were taken somewhat by surprise at this surge; as of when the F-16 first flew, the Soviet air force and those of its allies had nothing that could compete. They answered a few years later with the MiG-29, a smaller twin-engine design similar to the larger Su-27 which was in pre-production to answer the F-15. These six fighters - F-14, F-15, F-16, F/A-18, MiG-29 and Su-27 - represented the cutting edge of fighter design as of the collapse of the Soviet Union in 1991.

The new U.S. designs to enter production since, the F-22 Raptor and F-35 Lightning II, are themselves fairly old; the first production F-22 was built in in 1996 and flew in 1997, almost 20 years ago, the result of a design competition with planes flying back in 1990, and the initial RFP originating in the 1980s. The F-35 first flew in 2006, itself derived from the X-35 JSF testbed which first flew in 2000, so that design is between 10 and 15 years old now depending on how you count. Their protracted development times are a direct result of the reduction in pace of the U.S.-Russian arms race since 1991; with no other technologically-advanced military adversary on the horizon, there simply hasn't been the impetus to get these planes out to the front lines (there is some civilian talk of restarting the F-22 production line to bolster Raptor numbers, as the Sukhoi PAK-FA and Chengdu J-20 are very close to production and the F-35 is way behind projections and proving a disappointment so far, but another 100 new Raptors are projected to cost a ludicrous $225 million each due to increased costs of restarting the line and producing them in parallel with the F-35).

The F-35 also had the handicap of being a return to the "one-size-fits-all" design mentality, being intended as a replacement for practically everything besides the Raptor in the U.S. air arsenal, Air Force, Navy and Marines, with an F or A in its designation. That's caused a lot of technological headaches, since any replacement for the Marines' AV-8B Harrier is going to need STOVL capability, and the Navy and Air Force have always had a different though overlapping set of requirements relating to the Navy's basic need to operate aircraft from a ship at sea that's maybe a fifth as long as the USAF's minimum runway length requirements for its airbases. The resulting design is big, heavy, and relies on the most powerful single engine the U.S. has ever put in a fighter, which pushes the boundaries of the stress limits of the materials we use to make jet engines.

Lastly, military spending in the last 10 years or so has been preoccupied with developing and fielding technology to fight a low-tech insurgency; our enemies know they can't beat us in a toe-to-toe fight, so they don't fight that way, instead targeting our multi-million-dollar military hardware with Vietnam-era milsurp RPGs and oil-drum IEDs costing maybe $100 a shot. On this kind of battlefield, stealth air-superiority aircraft are kind of redundant as the enemy doesn't even have radar, much less an air force to exercise superiority over. That's why the F-22 has never seen real combat; the U.S. has enjoyed "air supremacy" by default in its primary combat theaters, as its enemies have never fielded an air force to speak of.


What do the callouts "approaching minimums" and "minimums " mean? When landing, what exactly do the phrases "approaching minimums" and "minimums" mean in a commercial jet aircraft,  when heard from the onboard cockpit voice.

The "Approaching Minimums" callout is made by the Pilot Monitoring (or, in some cases equipment, the GPWS -- Ground Proximity Warning System) as the aircraft is descending on an instrument approach and has reached an altitude 100 feet above the minimums for that approach -- the Decision Altitude (DA -- typically used for a Cat I ILS, and set as XXX' MSL) or Decision Height (DH -- typically used for a Cat II or Cat III ILS and set as XXX' or XX' on the Radio Altimeter) or Minimum Descent Altitude (MDA -- typically used for a nonprecision approach and set as XXX' MSL).  The response by the Pilot Flying is usually standardized and indicates he is looking outside in order to acquire the visual references he'll need to land.

The "Minimums" callout is made at the minimum altitude, and this is the point that the Pilot Flying has to make a decision -- continue or go around.  His response at this point is again standardized so that the other pilot is entirely clear on the course of action.  His response is usually something like "Landing" or "Continue", or else "Go Around."  Often, the autopilot comes off at this point as well & you hear the horn indicating such on the CVR as well.


Is aluminum electrical wire used on aircraft? Aluminum electrical wire got a bit of a bad reputation in household wiring due to reacting badly with terminals not properly rated for aluminum.  Properly handled, it works fine, but it's so distrusted for small branch circuits that distributors won't even stock it.

Aluminum is a worse conductor than copper, by almost half. But that only considers it by volume (e.g. Wire diameter).  By mass, the advantage swings back to aluminum.  Nearly twice the ampacity for the same weight.  Where would that matter?  Aircraft.

Transport class aircraft are increasingly electrical, like the bleedless 787 where electrical does much of the heavy lifting.

Is aluminum wire actively used in aviation?  Or is it "taboo" like it is with houses?

Cable is not just the metal wire. It's also insulation, installation, cable channels, extra space at tight bends where cable flexibility is insufficient, and maintenance of said cable. Aluminum corrodes in a lot of conditions and happens to be one of the most fatigue-susceptible metals.

For these reasons, most aircraft wiring is copper and silver-plated or nickel-plated copper. Such wiring is reliable even under imperfect conditions.

But there are cases where different considerations prevail. Sometimes it's just the need to have some minimum cable thickness, for mechanical and handling reasons. Other times it's a thick bus bar where weight makes a difference and quality is easy to ensure.
So beside copper there is some steel, copper-nickel plated aluminum, copper-nickel plated steel, and pure aluminum wiring in aircraft.

In aircraft, safety is ensured and validated with engineering and testing; risks of the kind one can take with home wiring are not accepted. The price of aluminum wire is installation and maintenance complexity instead. The ends need to be cleaned and crimped or welded, sometimes the aluminum wire is terminated with a bimetallic insert. As a result, aluminum wiring is more expensive than copper, not less. It will likely require more maintenance work in the future.

Until recently, aluminum has been mostly avoided for these reasons, and used only for thick wires and bus bars. Currently there is enough confidence in quality management and maintenance that aluminum wiring is getting more use in attempts to save some weight, the A380 in particular uses aluminum wires up to 22 AWG. Such weight savings come at the cost of more parts and more work, both in production and later in service.

Specific percentages vary widely, but generally non-copper wiring accounts for more than 10% and less than 50% of overall wire weight in a production commercial aircraft.


When the winds aloft are light and variable, what wind direction and speed should I use for flight planning? What do you input in a navlog for wind direction and velocity, when the wind and temp forecast says 9900+18? I know 9900 means light and variable winds less than 5kts but how do I determine the average wind direction to use for my navlog?

Light and variable means there's no meaningful windspeed or direction, so you can just ignore it. For planning purposes, you can simply plan as if the wind was calm.

But, it's very possible that the winds will actually be stronger and more directional than forecast. You should check your actual track and times against what you planned, and adjust your navlog in flight as needed. That's one of the cross-country navigation skills that pilots are expected to learn.


What are the requirements for logging SIC time? I am going from KPRC to KVGT with a friend in his C-182.  I don't have a high-performance endorsement, but can I -- as a private pilot -- log as SIC at any time during our flight?

If so, what rules do I have to follow?

From what I understand:

I can log SIC time since the aircraft is a SEL
I can't log landings, obviously
And SIC time really doesn't mean anything

Am I right in assuming those things?

You can basically log SIC time if you are a required crewmember and are not able to log PIC time.

So, generally in an airplane like a C-182 which is certified for only one pilot, you can't log SIC time because you aren't a required crewmember.

There are a few exceptions though, like being a safety pilot for the PIC while they are using a view limiting device (like an IFR hood), etc.

SIC time is not pointless because it still adds to your total time!

As far as landings, you can log them only if you are the sole manipulator of the flight controls, in which case you are allowed to log PIC time (even though you aren't allowed to act as the PIC since you don't have your high performance endorsement).  Oddly enough, in this situation the pilot who is acting as PIC isn't allowed to log it because they don't meet any of the requirements for doing so. It's one of the only situations where the PIC isn't allowed to log it as such.


How to decide on which side of the runway the approach path indicator (VASI, PAPI) are placed? This answer provides pictures and drawing of implementation of both PAPI and VASI. In all pictures I found, I cannot figure if there is a rule to put those lights on the right, on the left, or on both sides.

Is there some rules to decide if the path indicator lights should be placed on the right or on the left side of the runway?

Path/slope visual indicators are usually located on the left side of the runway (as seen when approaching), but may be on the right side when impractical. Good reasons for moving the aid on the right side:

Obstacle clearance, terrain, intersecting runways or taxiways.
Interference may occur on the left side, between PAPI lights and nearby lights. This is emphasized in FAA AC 150/5340-30G - Design and Installation Details for Airport Visual Aids: "Because PAPI system is dependent upon the pilot seeing a red and/or white signal from the light units, care should be taken to assure that no other lights are located close enough to the system to interfere with the signal presentation."

Installing them on both sides is beyond ICAO recommendations and FAA orders, but can be done:

For visibility improvement
In order to give better roll guidance

Some countries don't implement ICAO rules the same way, for instance in the UK, PAPI for governmental airports "may be provided on both sides of the runway" (source)

For airports providing a visual guidance for STOL operations. The PAPI associated with the steeper approach path may be located on the right side of the runway (source).

PAPI at the usual location, on the left side of the runway (source).

From Wikipedia:

  The international standard for PAPI is published by the International
  Civil Aviation Organisation (ICAO) in Aerodromes, Annex 14 to the
  Convention on International Civil Aviation, Volume 1, Chapter 5.
  National regulations generally adopt the standards and recommended
  practices published by ICAO.

From FAA JO 6850.2B - Visual Guidance Lighting Systems:

  The basic PAPI configuration is described in chapter 1, section 2,
  paragraph 16, and is shown in figure 5-1. All lamphousing assemblies
  (LHA's) should be located on the left side of the runway, as viewed
  from the approach direction. However, where terrain, cross runways,
  or taxiways make this arrangement impractical, the light units may
  be located on the right side of the runway.

  [...]

  The VISUAL APPROACH SLOPE INDICATOR (VASI) system is no longer
  installed by the FAA as a new facility. Specific details and installation
  criteria have been moved to Appendix E to provide technical support for
  existing VASI equipment and facilities.

  [...]

  The basic VASI configurations are described in appendix D, section
  1, paragraph 1 and shown in figures 1, 2, 4, and 5. All boxes (or
  light units) of the two-box; four-box, and six-box configurations are
  located on the left side of the runway (as viewed from the approach
  direction). However, where terrain or cross runways, etc., make this
  impractical, they may be located on the right side of the runway.

Washington Dulles Int'l Airport  offer several location variations, chosen for practical reasons. There is a PAPI on the left side for runway 1C and on the right side for 19C, but a reverse scheme is used for 1R/19L, and 1L/19R is just standard:


How does the Mi-26 tilt its rotor like this? I watched this video on YouTube, which shows an Mi-26 taking off with its rotor tilted forward about 45 degrees. Is the video fake or is it real, and if it is real, how does the Mi-26 do such a thing?

It's real and it's simply the blades running at the flapping hinge limits with the cyclic stick full forward.  The blade on the back is at its up limit and the one at the front at its down limit, resulting in an overall disc angle of about 30 degrees off horizontal.  It's being done to accelerate along the ground as fast as possible.  In the air, the machine's body will follow the tilt of the rotor quickly enough that this sort of angle is almost never experienced unless the pilot made a sudden extreme input in flight.

This (blades hitting flapping limits) is something that only multi-blade articulating rotors can tolerate.  You can't do that with a two blade teetering rotor because contacting the blade flapping travel stops, known as mast bumping, will break the mast.


Can commercial airliners fly over central Antarctica during winter? For example, if an airline decided they wanted to run year round flights on the great circle from Perth to Buenos Aires with a commercial airliner (e.g. A380 or B747), would they be able to do so? Or would it be too cold to fly?

I'm aware that there are a few sightseeing flights during the summer over Antarctica, but the winter temperatures in central Antarctica are lower than anywhere else on Earth (with surface air temperatures occasionally reaching around −90 degrees Celsius).

Edit: To clarify, by "winter" I mean the coldest time of year, i.e. roughly May to September.

Surface air temperatures aren't really going to be relevant for an airliner. The temperature of the troposphere doesn't vary that much. In fact, the troposphere is warmer at the poles (from Wikipedia Troposphere):

  At middle latitudes, tropospheric temperatures decrease from an average of 15 °C at sea level to about −55 °C at the tropopause. At the poles, tropospheric temperature only decreases from an average of 0 °C at sea level to about −45 °C at the tropopause. At the equator, tropospheric temperatures decrease from an average of 20 °C at sea level to about −70 to −75 °C at the tropopause.

Sightseeing flights are indeed run during the summer months, but that is because it's actually possible to see things, not because it's any warmer. It wouldn't be very interesting to do a sightseeing flight in darkness.

The biggest obstacle to doing winter commercial flights over Antarctica is the lack of suitable alternate places to land in the event of an emergency.


How can coefficient of lift on the ground with flaps in the takeoff position be calculated using airfoil data? In essence I'm working on a design project and I'm specifically looking at takeoff analysis at the moment. I already have access to great textbook resources, but I'm struggling to determine the coefficient of lift $(C_{L_G})$ on the ground with flaps in take-off position for the following equation taken from Appendix K-4 of Synthesis of Subsonic Airplane Design by Torenbeek:

$$\frac{a}{g} = \frac{T}{W} - \mu - \left(C_{D_G} - \mu C_{L_G}\right) \frac{\frac{1}{2}\rho V^2 S}{W}$$

Similar equations can be found in other textbooks, but I haven't found any reference to how $C_{L_G}$ can be determined from airfoil data. Currently I'm considering just using the zero geometric angle (ie compensating for the AoA the wing is mounted at) coefficient of lift for the airfoil, but how would I then account for the position of the flaps?

There is quite a lot written on the topic, especially as part of "ground effect" vehicles research.
For example, Cui and Zhang cite two different types of lift coefficient. The first one (simpler and given here) is based on flat plate airfoils and is a modification to the well-known
$\frac{dC_l}{d\alpha}=2\pi$:

$$C_L=2\pi\alpha(1+\delta^2)(1-2\zeta)$$

with

$$\zeta=\frac{\sin\alpha}{4(h/c)}$$

and

$$\delta=\frac{\cos\alpha}{4(h/c)}$$

In the above expressions, $h$ is the height of the wing above the surface (ground, water, etc.), $c$ is the chord and $\alpha$ is the angle of attack.

I strongly recommend you check out "ground effect"/"Ekranoplan" literature - should be useful.


What additional US-power or ICAO requirements apply to a departing US-based crew with a US-registered aircraft flying to land in Mexico? What are additional requirements (equipment, licenses, identification, etc.) for a flight operation with a US-based aircraft and crew leaving the US to enter and land in Mexico that are imposed on the operation by the US authorities such as the government or any of its agencies and comprehensive international agencies such as ICAO?

This differentiates from similar questions because I am not asking about the governing set of laws in international territory or what laws of a different country than the home country would apply to the flight; of course ICAO is international in all cases so could be applied as valid in any home country that an aircraft may depart from.  Each other, non-US, country's specific laws may vary, so they are removed from the scope of my question.

The only aviation-related requirements on crossing the US border are:

All flights crossing the US's Air Defense Identification Zone (ADIZ) in either direction must be on an IFR or DVFR flight plan, talking to ATC and have a discrete transponder code.
A list of all passengers and crew must be filed with eAPIS at least 24 hours before crossing, in either direction, and the plane must have an eAPIS decal.

The only difference between leaving vs entering that I'm aware of is that you don't need to leave from a designated port of entry. (Some other countries do require that.)

As a practical matter, there are a handful of aviation-related things that apply to most/all other countries that US pilots don't have to worry about in the US:

The pilot(s) must have ICAO-recognized license(s). FAA Student, Sport and Recreational licenses are not.
The pilot(s) must have appropriate medical certificate(s). No BasicMed.
The aircraft must have a normal airworthiness certificate. No experimental aircraft.
The aircraft and at least one pilot must have FCC radio licenses.

Technically, you don't need passports to leave, but you'll need them to go anywhere else (and to return) by air, so they are effectively required for both.

There are thousands of other laws that apply to all people or goods leaving the US regardless of mode, such as not exporting restricted technology or weapons, human trafficking, fleeing prosecution, etc.  (And there are even more for entering.)  I doubt anyone could list them all, and that is probably off-topic anyway.


Can a turbojet jet or turbofan powered aircraft land and take off from water? Can a turbojet jet or turbofan powered aircraft land and take off from water?  How much clearence from the water surface would it need for its engines so that it does not suck up water?

Yes, they can.

In service today:

The Canadair CL415 is a turboprop water bomber with water landing capabilities (typically, water skimming capabilities, to skim across a lake and refill).

The Shin Maywa US-2 is the latest in a series of rescue/maritime patrol aircraft that have been in service for some time. The design uses the engines and wing of a C-130, with an interesting STOL feature: ducts that blow air across the top of the flaps so that they can be set at a more extreme angle for extremely short takeoff.

The Beriev BE-200 has seen limited production in Russia. It uses high bypass turbofans, mounted high and behind the wings to protect the engines from water spray.

From the Soviet era, were the ekranoplan sea skimmers, that flew entirely in ground effects. All were turbine powered.

In a prototype stage is the AVIC AG-600 in China. Powered by four turboprops, it appears to be an upsized copy of the Shin Maywa design.

A one-off production flying today is the Doriner DO-24ATT, essentially a WW2 DO-24 maritime patrol aircraft that was re-engined with turboprops. It is currently flown by Claudius Doriner's grandson.

Four turbine powered amphibious/flying boat aircraft that were developed but never saw service were the Convair Sea Dart, Martin SeaMaster, Saunders-Roe Princess, and Saunders-Roe SRA1.


How do I find the serial number and other important information of an old airplane I have? My dad has passed away and I have his plane. I can't find the paper work but I want to get a replacement title from FAA. Their site says that I need manufacturer name, model designation, N-number, and serial number.  I have the N-number but don't know where to find the other info. Could you please help me find that information?

There are three pieces of paper the FAA issues which would fall under the concept of "title" to an aircraft.

The first is an aircraft lien (typically held by a bank when you take out a loan collateralized by the aircraft). This is probably not what you're looking for, but you should inquire as to whether any liens are held against the aircraft before doing any work, just to be sure you have "clear title" to the results of your work.

The second is an Aircraft Registration Certificate - this is a record tying the N number (in your case N97554) to the aircraft itself.
In your case the registration is Revoked, so once reassembled the aircraft would need to be re-registered to be flown. This would be a "Call your local FSDO" situation - Presumably the registration was revoked when the aircraft registry changed to a 3-year expiring registration period.  Also as there are multiple owners listed on the registration re-registering may require more work.

The final piece of paper you need is an Airworthiness Certificate - this should be in the aircraft, and is valid forever. If it's not in the plane you can get a replacement - again, contact your local FSDO.

If you need information you don't have, or want to confirm it before talking to the FAA, look for the aircraft data plate. On Stinson aircraft (going by the N number you provided) the data plate is usually located on the firewall above the copilot rudder pedals as shown here.
On newer metal aircraft it is often located on the tail, under the horizontal stabilizer.

For more information on the aircraft itself check out stinsonflyer.com.


How is a wing designed to be stall or spin proof? Yeah, it sounds like two questions, but I suspect the answers are very closely linked (or maybe even have the same answer.)  I was told in this question that trainer planes are often designed to be stall or spin resistent.  I was wondering how this is accomplished?

How does one make a wing resistant to stalls or spins?  Or perhaps, more generally, how does one make a wing predictable and stable?

It's really two separate questions. In both cases the wing is not alone, it is the whole configuration, especially when it comes to spins.

A stall is unavoidable. At some point the airflow over the wing will start to separate, and if this flow separation is extensive enough to limit the increase in lift with increasing angle of attack (AoA), the wing stalls.

To make stall characteristics benign, the outer wing should still have mostly attached flow to enable the ailerons to correct roll angle. If the stall starts on one wingtip, causing a local loss of lift, the aircraft will roll uncontrollably. The downward movement of the wing tip during the rolling motion increases angle of attack further, thus making the stall unrecoverable. You achieve roll control by using washout at the wingtips and/or by using airfoils with a higher maximum AoA, eg. by using slats on the outer wing.

The second condition is a gradual flow separation, starting from the trailing edge. Old five-digit NACA airfoils had a nasty stall characteristic with flow separation starting from the leading edge, resulting in a sudden drop of lift. This is achieved by designing the upper surface with an appropriate chordwise pressure distribution. Then the loss of lift over AoA will be gradual, giving the pilot the opportunity to recover easily.

In all cases, the tail (or in canards the main wing) needs to remain in the attached flow regime to enable pitch control and pitch damping. In addition, the vertical position of the tail should be slightly lower than the wake from the separated flow, still close enough to have some turbulence hitting the elevator (so that the pilot feels the stall with the stick/yoke), but low enough that the airplane will not enter a deep stall (where the wing is fully separated and the tail in the wake of the wing, which reduces control authority to a point where the pilot cannot pitch down anymore).

Spinning needs a fuselage with some mass along the length. The rotation of this mass at a high AoA produces a pitch-up moment which is needed to stabilize the spin. The tail must be able to produce the remaining pitching moment and a yawing moment to stabilize the spin, but also to end it when the pilot so wishes. For this, it is important that the rudder is not in the wake of the horizontal tail. The deHavilland Tiger Moth has two aluminum strakes ahead of the empennage; without them a stall is unrecoverable because the rudder authority is not sufficient. To end a spin in the F-14, the all-flying tailplanes had to be pulled all the way to their minimum angle of -70°, so they would not obstruct the flow to the two rudders. Only when the pilots would pull, they could end the spin.

Just to be clear: Normally you need to push to end the spin. Especially in gliders with their relatively small rudders and large wing inertia, this will put most of the wing back into the normal flow region, and roll damping will stop the rotation. This ends the inertial pitch-up from the fuselage, and the aircraft can be recovered.

In more fuselage-dominated configurations, you end the spin by applying rudder against the spin direction. This reduces the rotation, reducing the inertial pitch-up and allowing the airplane to recover to normal AoAs.

Other than the stall, a spin is not always possible. Sometimes, especially at forward center-of-gravity locations, the pitch authority will not be sufficient to stabilize the spin. You can stall and apply rudder, but the airplane will only enter a spiral dive. Especially on jets the forward fuselage is a major factor in spins, because it produces a wake at high AoA which stabilizes the spin. Details in the shape of the fuselage will determine if the wake is sufficient to enable spins. This is a complex topic - sorry, but this scope makes it hard to get into more details.


How does a helicopter rudder work? So occasionally I will be flying my rc helicopter and I turn it left to right (rudder) but see nothing moving on the helicopter. On an aircraft there is a vertical stabilizer that has a moving rudder. So how does a helicopter work? The same thing occurs with my quadcopter.

In helicopter, the yaw control is usually obtained by adjusting the pitch of the tail rotor, that changes the 'thrust' produced by the tail rotor; this rotates the helicopter about its yaw axis.

Source: cfidarren.com

In case of helicopters without a tail rotor, the yaw control is obtained in different ways. The NOTAR used a method similar to the tail rotor, by varying the thrust. In case of tandem rotors (like Chinook) , the yaw control is obtained by differential lateral cyclic.

Source: tech-mp.com

The quadcopters obtain yaw control by adjsuting the speed of the rotors. In quadcopter, two rotors (say 1 and 3) rotate in one direction, while the other two (2 and 4) move in the other. By slowing down 1 and 3 while speeding up 2 and 4, you can make the quadicopter yaw to the left. The torque of 2 and 4 spinning to the right makes the body spin to the left. Conversely, by slowing down 2 and 4 while speeding up 1 and 3, the quadcopter yaws to the right.

Source: safaribooksonline.com

In case of coaxial helicopters like the Kamon Ka-25, the yaw control is obtained by varying the torques (i.e. by varying the pitch) of both the main rotors simultaneously in opposite direction.

Source: simhq.com

Coaxial helicopters (like Kamov Ka-25) do have movable rudders like aircraft for use in forward flight as it reduces the main rotor adjustment required and is more effective.

Ka-25 rudder, image from travelforaircraft.wordpress.com

The image below shows the control methods used in different types of helicopters.

Image from unicopter.com, credited to Rotary-Wing Aerodynamics.


Why force the nose of 737 Max down in the first place? Can someone here explain a pretty basic question that I have had  ever since this controversy came to light? I don't understand why any aircraft manufacturer, engineer, software developer, would make a device that forces the nose of the plane down. You can't land unless you're in control and landing safely is the only reason to go down that I know of. So I just don't get that as an initial thing, but the second part of that is, given the hazards of pointing the nose down, which are obvious even to me, why would you not design the system so that it's a warning, and allow the pilots who are actually sitting there to decide whether going down is a good idea or not? That just fundamentally, as a threshold issue, makes no sense to me at all. So I'm hoping you could help me understand. Thank you.

The main thing to avoid in aeroplane stability & control, is an aerodynamic nose up moment that is not commanded by the pilot. The uncommanded nose-up moment would not auto-stabilise, but rapidly get progressively larger with increasing angle of attack, and run away to a stalled aeroplane.

During certification of a passenger aeroplane, many tests are carried out to check if the airframe does not start to have a mind of its own.

If the pilot does not provide a control input, the airframe must return to the trimmed position.
Forces and inputs to move the aeroplane away from trimmed position must be such that there is an ever increasing force required to achieve an ever increasing nose-up position. The nose-up position must always be commanded by the flight control surfaces, elevator and stabiliser, in a predictable way.

One of the tests to be performed during certification is stick-force-per-g. Bank the aeroplane and start turning while pulling the stick back in order to maintain altitude. Then bank more and pull back more, in ever tightening turns. It must be progressively harder to pull back on the stick to maintain altitude, never easier.

It was during this wind-up turn that due to the engine configuration of the MAX an aerodynamic nose-up moment appeared, which would cause the pitch stick force to suddenly become less than expected. Not as bad as a runaway pitch, but still an undesirable situation when the pilot is still straining to maintain the manoeuvre. This is the situation that MCAS was originally designed for, to auto-compensate for this situation only. The aeroplane should always stabilise itself and manner of control must be predictable and within the reaction times of humans.

More info in the links in this question, very interesting articles which illustrate how MCAS design bloated from the original scope, under time pressure.


How does the UK declaration for FAA pilots work? I came across http://publicapps.caa.co.uk/docs/33/SRG2140_Issue02_Enabled.pdf

This seems to suggest that an FAA PPL doesn't have to go through any exams / checkride / etc (other than the rudimentary "confirmation knowledge of Part FCL Air Law and ATC procedures") in order to be allowed to fly up to 28 calendar days per year in UK airspace.

Can anyone share additional details on how this process works, such as how long does it typically take to have the declaration verified, what costs (if any) are involved, whether this process has to be repeated every so often or is permanent, etc. ?

Having gone through this process, I thought I'd share my experiences and timescales:

Useful Docs:

https://publicapps.caa.co.uk/docs/33/InformationNotice2017029.pdf
http://publicapps.caa.co.uk/docs/33/SRG2140_Issue02_Enabled.pdf

1 Oct 2018

Get a checkout from an instructor and get them to sign the SRG2140 form and also certify copies of the docs required (log book, licence, medical etc, - details on SRG2140 form)

See https://www.caa.co.uk/General-aviation/Pilot-licences/Applications/Documentation/How-to-get-copies-of-your-documents-certified/ for details on how copies are certified i.e. the wording that must be used.

Scan and submit my SRG2140 form to the CAA via email to pilotvalidation@caa.co.uk

25 Oct 2018

Phone the CAA and talk to a very helpful person who says I need to

also send in SRG2142 and use fclweb@caa.co.uk
pay £45

So I filled in that form and sent it off by email again with my CAA reference number in the subject and to fclweb@faa.com and pilotvalidation@caa.co.uk

29 Oct 2018

Got a phone call (that I missed) and an email asking for my credit card details to pay the £45
I called them back and paid the money
Later that day I got another email confirming they had sent a request to the FAA and suggesting I chase the NAA:

We are contacting you to inform you that we have processed your application for the Verification of your Third Country ICAO licence, and a verification request has been sent to the FAA.
To help ensure that the verification is received in a timely manner, you may wish to contact the NAA directly. Additional requirements may need to be met in order to release your personal details to the UK CAA.

8 Nov

I discovered that the FAA has an online portal that allows you to request a validation report so I went to https://amsrvs.registry.faa.gov/amsrvs/main.asp and asked it to send a report to me and also directly to fclweb@caa.co.uk and pilotvalidation@caa.co.uk

12 Nov

Received the validation receipt:

As the current holder of an FAA licence with a validating medical certificate, you are entitled to exercise the private privileges of the ratings for which you are qualified on your FAA certificate in UK Airspace without remuneration.
Please note that your privileges on G-registered aircraft are restricted to day VFR regardless of the medical held, as stated in ORS no.1228: ORS4. FAA Certificate holders with a valid IR flying N-registered aircraft may continue to exercise IFR privileges in UK Airspace.
Should you be ramped checked, you will have to produce a copy of your declaration made on form SRG2140 and a copy of this email.

So now I can fly G-Reg aircraft in the UK.

In hindsight, if I had to do it all again I would:

submit both forms at the same time
once they had taken the money, gone on to the FAA website and request the validation be sent directly to the two CAA emails addresses

Next step is to do a conversion to an EASA licence which involves:

(a) pass a written examination in Air Law and Human Performance;
(b) pass the PPL, BPL or SPL skill test, as relevant, in accordance with
Part-FCL;
(c) fulfil the requirements for the issue of the relevant
class or type rating, in accordance with Subpart H;
(d) hold at least a Class 2 medical certificate, issued in accordance with
Part-Medical;
(e) demonstrate that he/she has acquired language proficiency in accordance with FCL.055;
(f) have completed at least 100 hours of flight time as a pilot.

As per https://eur-lex.europa.eu/legal-content/EN/TXT/?qid=1524553458669&uri=CELEX:02011R1178-20160408

ANNEX III – Part B “CONVERSION OF LICENCES”


How does the pressure change in the Air Cycle Machine? In this picture:

#3 says:

  "Air expanding to ambient pressure turns expansion turbine, is greatly cooled, and drives compressor."

I understand all of that except for the "air expanding to ambient pressure" part.

Ambient means relating to immediate surroundings of something so the pressure can change. I understand that if it decreases in size like at #1 it would get hotter or if it increases in size it would become colder, but how can it be ambient if all the air is expanding to the same size when at #3 the column that the air passes through doesn't change shape to change the pressure?

Basically, how can it be ambient pressure if the column doesn't change size?

Strictly speaking you're right, the authors used a brief and easy to visualise but slightly inaccurate phrasing. The blue bit is open to the cabin, and at the end of it will have cabin ambient pressure. At the beginning of it the pressure will be slightly higher, but very much lower than before the turbine.

The pipe diametre does not need to change for the pressure to vary. Air streams from high pressure to low pressure, upstream pressure will always be higher than downstream pressure, by an amount to overcome the friction forces.