Why do airliners still have a switch for the non-smoking sign? I've wondered why airliners have a switch in the cockpit to turn off the non-smoking sign. Why isn't it illuminated all the time, or a better question: Why is it still there, now that everybody should know.

Smoking was outright banned on flights in the US in 1998/2000 which was in reality not all that long ago. It should be noted that smoking on domestic flights under 2 hours was banned in 1988 and under 6 hours in 1990. With that in mind we must remember that there are plenty of planes that are still in service and older than that, many were designed long before that time as well. In the view of the airlines its simply cheaper to leave the lights and switches there than put in a new interior panel in many cases.

Also as mentioned in the comments planes are built for the global aircraft market and there are still countries that allow smoking on flights. This question is similar and has some good info as well.

But here in the US the main reason is because the FAA mandates the signs,

For charter (135) operations

  § 135.127 Passenger information requirements and smoking prohibitions.

  (a) No person may conduct a scheduled flight on which smoking is
  prohibited by part 252 of this title unless the “No Smoking” passenger
  information signs are lighted during the entire flight, or one or more
  “No Smoking” placards meeting the requirements of § 25.1541 of this
  chapter are posted during the entire flight. If both the lighted signs
  and the placards are used, the signs must remain lighted during the
  entire flight segment.

For scheduled commercial (121) operations

  § 121.317 Passenger information requirements, smoking prohibitions,
  and additional seat belt requirements.

  ...

  (c) No person may operate
  an airplane on a flight on which smoking is prohibited by part 252 of
  this title unless either the “No Smoking” passenger information signs
  are lighted during the entire flight, or one or more “No Smoking”
  placards meeting the requirements of § 25.1541 of this chapter are
  posted during the entire flight segment. If both the lighted signs and
  the placards are used, the signs must remain lighted during the entire
  flight segment.

The reason they are not lighted the entire time most likely stems from history. Since there is a switch to turn them on chances are there is a check list item to flip the switch. You will most likely see them go on and off when the pilot hits that item on the pre flight checklist that may occur at the gate or on the taxiway heading out for take off.

The Piper Archer I fly still has ash trays (there is even one in the pilots seat arm rest)...


What type of variation in temperature does the wing undergo? Generally what is temperature variation does the wing of the commercial aircraft like A380 undergo , flying at mach speed of 0.8 and how does it affect the aircraft other than icing , what type of literature can one go through to study the temperature effects on aircraft

The temperature rise that is caused by flying at high subsonic/transonic speeds is approximately 40 degrees Celsius. But this happens only at the stagnation point (near the leading edge). Ref: aerodynamics text books.

The A380 and other airliners experience -55 to -60 degrees Celsius during cruise at altitude. Ref: aerodynamics (properties of the atmosphere)

On the ground they may experience up to 60 degrees Celsius of air temperature and with the sun radiation the surface temperature can rise up to approx. 80-90 °C. Depending on color and geographic location on earth. Ref: hard experience :) and Environment control system Analysis.


What are the radius of containment (Rc) and horizontal protection limit (HPL) and how are they related to Type Code? In ICAO Document 9871 (Technical Provisions for Mode S Services and Extended Squitter) page 30 they have mentioned it in the form of a table. But they haven't explained HPL and Rc in detail.

Mode S ADS-B messages use DF17 or DF18.  The type code field with the DF17/DF18 is set to reflect the current navigation performance.

The Containment Radius (Rc) is the radius that there is a 95% probability the aircraft is within that radius of its stated position, both horizontally and vertically.

HPL is computed by the GNSS and is the theoretical 100% containment (protection) limit in the horizontal only. It is approximately double the value of the Rc. Since HPL is horizontal only, the vertical is mostly addressed by the cases of 1) no altitude, 2) baro altitude or in its absence, 3) the GNSS height.

So based on the presence and value of HPL and altitude data, the appropriate Type Code can be set by referring to the table. The receiver of the message can then determine the transmitter's Rc.


What if one of the navigation lights failed to function on a certified aircraft? What is the implication if one of the navigation lights failed to function, would it affect the airworthiness certificate of the aircraft?

In the US, you would not be able to fly that particular aircraft at night and/or IFR since IFR flight requires all day and night equipment to be operable according to Title 14 Part 91.205. Only VFR day flight is allowed.

You would need to check your Minimum Equipment List and/or Kinds of Operation Equipment List to see if the manufacturer would allow flight with that particular piece of equipment inoperable. Then, placard the position light switch as inoperable. It would be best to get it fixed ASAP, just in case you or the next pilot to fly that plane has a flight run late.

If you are already in flight when you noticed that the position light failed, you handle it just like any other failure. Land as soon as practicable. To do this in the case of no position light while VFR at night, I would immediately get on flight-following and explain to them the situation. If you are already IFR, simply inform ATC of a position report with a safety of flight change.

I would prefer to land at an airport with an operating control tower with radar. I am lucky in the fact that I have a few nearby. Just be wary that the failed light is just a failure of the light. And, that it is not indicative of greater electrical failures.

Also, make sure your Transponder is operating in either mode C or S. And, make sure both your ADS-b in and out are currently operating as a safety net.


How do the blades on a propeller generate thrust? I am having trouble understanding how this type of propeller generates thrust:

It is so much different than a propeller on a Cessna and thrust would be provided differently. I am also confused of how the turbofan blades in a jet engine provide thrust:

Doesn't the turbofan push the bypass air back really fast providing thrust?  How do each of the these propellers (turbo prop and turbofan) produce thrust?

The picture of the turboprop is probably confusing you because you are looking at a shutdown engine.  For a multi-engine propeller airplane a desirable feature is that the propeller with auto-feather when shutdown, so that an in-flight engine failure will cause the prop to be in a minimal drag configuration.  This minimal lift, minimal drag configuration is what you posted, and this is not producing thrust.  When the engine is started and system pressure (oil, hydraulic, whatever controls the adjustable pitch prop for that particular engine) will drive the propellor pitch angle into lift-producing regimes.  Turboprops also typically feature "Beta" propellor pitch, which allows the propellor pitch to be adjustable past zero-lift into negative-lift and is used for landing rollout and (in some airplanes, perhaps not many) slowing down in-flight or steep descents.  During normal flight the turboprop propellor is producing lift just like the propeller on the cessna you are familiar with.

The N1 fan in a turbofan (the big one you see when you look at the front of the engine) is a ducted fan.  The individual blades of the N1 fan are angled to push air backwards.  This works the same way as a big box fan you can buy at walmart.  The key difference is the N1 fan rotates an order of magnitude faster than a box fan.  The bypass air is accelerated by this fan and exits through the rear of the engine to produce thrust.


How much leverage do commerial pilots have on cruise speed? If you fly frequently there are chances you have seen some delays in departure  where you end up waiting in the aircraft sometimes for multiple hours.

Almost every time that happened I remember the PIC announcing something in the lines of We will try to make up for the lost time...

And they manage to do a very good job at that. One of my recent flights was delayed 2 hours on departure but arrived only 1 hour late.

Its quite exciting when they say that, its like wow he/she will speed up! but how much leverage do they have to accomplish that? I'm sure there are commercial as well as regulatory requirements to remain within a range but how broad that range is for general commercial aircraft?

The aerodynamics and engineering part of this problem I know about, I'm mostly interested in the commercial aspect of it. Are the speed ranges set by commercial interests?

There is something called the "Cost Index" - it is basically how you choose between speed and fuel economy. Company dispatchers, after knowing that a flight has been delayed, will calculate this value, and the pilots simply input the updated value into the FMC (Flight Management Computer). That will instruct the autopilot to output more thrust, i.e. fly faster, but less fuel efficient.


How many kills did Neil Armstrong have? I realize this is slightly off topic, but there's no other SE site that it would at all fit into.

Anyway, I was just thinking about Neil Armstrong, and I wondered how many confirmed, and/or possible, kills he had in combat.

I tried to look it up, but couldn't find anything with Google.

None, his combat unit was ground attack, not air to air, so it is unlikely he ever was involved in air to air combat.


What are the lateral limits of Class D airspace in the USA? Class D airspace was normally 5sm (4.4nm) with extensions for approaches, when they are less than 2nm.  If any extension is over 2nm, then the extensions are normally Class E.  Many publications claim a 4nm Class D, but searching JO 7400.11A 1, there are many Class D airports with 4.2 or 4.4 or even greater lateral limits.

Some non-FAA publications claim that Class D is 4nm, but few Class D are in fact 4nm, most are larger, and many have extensions.  KFDK has a 5nm lateral limit for Class D, and Niagara Falls, KIAG has a 5nm lateral limit with an extension for approach.  Reading PA has a 4.2 and 4.8nm lateral limit depending on which side of the airport you are on.

My understanding that that Class D may be influenced by gradients for IFR operations, but also that Class D is frequently a customized airspace.

Furthermore, as an example, Class C airspace, when the radar is OTS (out of service) has the tower revert to Class D.  Will that be 4nm or 5sm?

Also, an operating federal control tower does not mean that an airport is Class D.  There are airports with towers which lack WX reporting, and are not Class D.  One which comes to mind in the past is LCQ, which is now KLCQ.

So where is the definitive set of rules which define Class D?

Where does a pilot obtain the lateral limits of Class D when Class C (or B) is not in place because of radar outage(s)?

JO 7400.2L, Procedures for Handling Airspace Matters, describes how the size of Class D airspace is determined. Per paragraph 17−2−5. DETERMINING CLASS D AREA
SIZE:

The size of a Class D area, and any necessary extensions, is determined
by the use of a 200 feet per NM climb gradient and information obtained
from the person responsible for developing instrument procedures (see
FIG 17−2−1).

The figure lays out the formula for determining the radius and gives an example. In short, it depends on the distance from the airport reference point (ARP) or geographic position (GP) to the end of the outermost runway, and the terrain surrounding the airport. This is why the difference varies at different airports.


What options do pilots and mechanics have when an aircraft owner doesn't pay up? If someone does a contract flight, or a mechanic does contract maintenance for an aircraft owner and they refuse to pay after the fact, what options do they have to "encourage" the owner to pay?

One of the big problems is that this tends to happen informally:

  Owner: "Hey, can you do this flight for me?"
  Pilot: "Sure, I charge $xxx." "
  Owner: "Okay, great.  See you on Monday morning at 9:00."
  Pilot: "Sounds good, see you then."

So they show up, do the flight, send an invoice, and wait.  And wait..  And wait....  After a few weeks or 30 days, they send the invoice again.  Give it a bit and make a phone call.  Eventually it becomes clear that they just aren't that interested in paying a lone individual without the typical resources of a larger company.  Unfortunately, this happens more than you would think in this industry.

It probably isn't enough money to actually go out and hire a lawyer for, but it's irritating and they want their money.  It's the principle!  I've heard of people placing a lien against the aircraft.  Is that something that an individual can do, or do you have to hire a lawyer?  Is small claims court an option?

I'm looking for an answer that describes general approaches that can be taken, as obviously specific legal advice cannot be given without details of a situation like this.

You should be able record a lien against the aircraft.
Avionics News ran a Legal Ease piece about just this, which is well worth reading fully:

If a lien is properly asserted, the lien claimant (the aircraft mechanic) has encumbered the aircraft in question, meaning the aircraft no longer has clear title.
Clear title is highly desirable to an aircraft purchaser, who can determine if an aircraft has any liens on its title through a simple title search. Once there is a lien on an aircraft, to sell the aircraft with clear title, the aircraft owner must obtain a release from the lien claimant. This means the owner must pay you for your services before they are able to sell the aircraft with clear title.
If the owner fails to pay the lien claimant to have the lien lifted, the aircraft will be sold subject to the lien. This means the aircraft does not have clear title, and although the aircraft will have a new owner, your lien will remain in effect.
Most buyers, however, will not purchase an aircraft subject to a lien, and thus, you usually will manage to receive the money owed to you when the owner decides to sell the aircraft.
If you do not want to wait for the aircraft to be sold to satisfy your lien, you can bring a foreclosure proceeding, forcing the sale of the aircraft, usually at an auction.
The proceeds from this sale go to the lien claimant to extinguish the lien. If the proceeds are greater than the lien, any money exceeding the amount of the lien goes to the aircraft owner. Additionally, if there are no bidders at the sale (an unusual occurrence), the aircraft may be given to the lien claimant for the price of the lien.

One thing worth bearing in mind, is the Aero Liens List - a free resource which lists liens placed against aircraft owners. If your new client is on their "deadbeat client list" then you may want to think twice about doing the trip or get paid in advance!
You asked whether a lien could be registered by a pilot for lost wages (rather than a mechanic for lost labour/parts); just searching the above list for "John", I found at least one pilot who has two liens (against seperate companies) for lost wages: #1 #2
Another lien (PDF unavailable) lists its nature of the claim as "Salary owed".


Where to get Initial EASA Class 1 Medical? Can somebody suggest a list of EASA medical centers, where I can get Initial Medical 1?
Any EASA county is OK.
I'll appreciate any links, thank you!

Amendment:
I've found lists of AMCs or at least medical examiners approved by CAA for the following countries: UK, Spain, Serbia, Poland, Finland, Croatia, Ireland, Malta, Switzerland, Romania, Greece, France, Danmark

Full list of EASA countries and list to it's CAAs can be found here. And some of examiners all over the EASA here.

Does somebody know about other countries like France, Germany...? I have not found any lists of AMCs approved by CAA or at least medical examiners for these countries

It depends on the country you are going to take the medical examination.

Normally, the national civil aviation authorities of each European country will have this listing. For instance, in Spain, AESA publishes here the approved medical centers where applicants can take their initial and successive examinations.

So I suggest to first find out the authority from your country and always make sure with the medical center that you are going to take a certified EASA Class 1 medical examination.


What FAA requirements exist for electronic ignition systems on piston engines? Most GA piston aircraft still use dual magnetos for their ignition system, but there are some STC kits available to add electronic ignition to common piston engines, and new aircraft often come with FADEC systems.

Are there particular FAA requirements for electronic ignition systems?

If so, what are they and how can you demonstrate compliance?

The ignition requirements are pretty straight-forward:

  §23.1165   Engine ignition systems.

  (a) Each battery ignition system must be supplemented by a generator
  that is automatically available as an alternate source of electrical
  energy to allow continued engine operation if any battery becomes
  depleted.

  (b) The capacity of batteries and generators must be large enough to
  meet the simultaneous demands of the engine ignition system and the
  greatest demands of any electrical system components that draw from
  the same source.

  (c) The design of the engine ignition system must account for—

  (1) The condition of an inoperative generator;

  (2) The condition of a completely depleted battery with the generator
  running at its normal operating speed; and

  (3) The condition of a completely depleted battery with the generator
  operating at idling speed, if there is only one battery.

  (d) There must be means to warn appropriate crewmembers if
  malfunctioning of any part of the electrical system is causing the
  continuous discharge of any battery used for engine ignition.

  (e) Each turbine engine ignition system must be independent of any
  electrical circuit that is not used for assisting, controlling, or
  analyzing the operation of that system.

  (f) In addition, for commuter category airplanes, each turbine engine
  ignition system must be an essential electrical load.


How is a Class E airport distinguished from a Class G airport, based on the identifier? Some small uncontrolled airports have "K" identifiers such as KPHK (Palm Beach County Glades) "Pahokee". Others such as 42M (Thayer Mem) "Thayer" have a numeric identifier. Both have 122.9 CTAF listed. Pahokee is Class G, Thayer is E.

My question is how is an "E" airport distinguished from a "G" airport on the basis of the identifier?

Airport identifiers do not distinguish the airspace that surrounds them. As for why airports start with a K you can look at the answer here. To figure out the airspace that an airport sits in you must look at the airspace designation lines around it (see page 10 here).


Does the weather condition of the runway affect the braking of an aircraft with regards to wheel braking and reverse thrust? I was on a 737 that landed on a snowy runway in northern Finland the other day. We had to wait around 30 minutes to land as they were waiting for it to stop snowing and then for them to clear the runway.
The landing was fine but it felt like they used a lot of reverse thrust when landing. Admittedly, it's been 10 years since I last flew, but it got me wondering; in the event of such  conditions, would a pilot use reverse thrust more than wheel braking?

On a 737, you have essentially two detents for reverse thrust, which for lack of a better term you could call "normal" and "maximum".  You can use levels of reverse thrust other than that by raising the reverse thrust levers to some intermediate position, but the performance numbers are all predicated on either no reverse thrust, normal detent, or maximum.

The condition of the runway absolutely affects how effective the wheel brakes are, and when there is a lot of snow coming down -- even with a freshly plowed runway, you really don't gain much by using less reverse thrust than you have available. Plus, if anything bad were to happen, it's easier to explain yourself when the flight data recorder shows that you went immediately into max reverse thrust right after touchdown & had the anti-skid cycling all the way down the runway -- you used everything you had available to stop the aircraft.

On a long, dry runway, you have lots of choices you can make. You can use reverse thrust and a long rollout to minimize brake wear; you can use no reverse thrust (if your airline permits that option; not all do) and more wheel braking to minimize noise -- which I've experienced at Frankfurt in the early morning; or you can use a good bit of brakes & reverse thrust to make an early turnoff from the runway -- nice if your parking spot is closer to the approach end of the runway than the departure end of the runway.

With contaminated runway conditions, those options boil down to, let's get this thing slowed way down as early and as certainly as we can.  Quiet isn't so much of a concern, brake wear isn't so much of a concern, taxi routing isn't so much of a concern; we'll use all the tools we have to reduce all the risks as much as we can.

So yes, you could well see more thrust reverse being used on a snowy day than you might see on a clear, dry day.  The relative contribution of the reverse thrust and the wheel brakes is one of those engineering questions that needs a lot of specific numbers to answer... just how slick is the runway?  (Braking will be less effective, so the contribution of the TR's will be higher.)  How cold is it? (Reverse thrust is more effective in cold air -- more thrust.)  How quickly did the braking get into the anti-skid cycling? (You somewhat expect the anti-skid to be cycling on a snow-covered runway -- that means you're getting all you can out of the wheel brakes, given the friction with the runway they have to work with.)  And etc.  As a pilot, the salient point isn't that X% of my stopping came from the one and y% came from the other; it's that we used them both & reached the gate, on time & with zero groundspeed!


Are air marshals on every flight? These guys say (in the discussion) that they were the only three passengers on board.

Does that mean that there was no Air Marshal on board (or one of them was?).

Aren't air marshals present on every flight?

The exact number of air marshals is not public information, and they certainly don't disclose what flights they fly on or other operational details. However, the number has been reported to be on the order of ~3,000-4,000 and reports indicate the number has decreased somewhat since then. All of them are, of course, not on duty 24/7/365. There are around 87,000 flights a day in the US alone, but only around 28,000 are commercial passenger flights, where air marshals are presumably most likely (hopefully there's not a need for air marshals on military flights, for instance).
So for some back of the envelope math, let's conservatively say there are 3,500 air marshals who all work five days a week, they all work alone (in reality, they appear to work at least in pairs), and they somehow manage to average protecting four flights a day. Even with these conservative assumptions, that would only be 5000 flights/day covered by air marshals. From this, it should be clear that there cannot possibly be an air marshal on every commercial flight in the US.
The President of the Air Marshal Association/CWA (their union), not entirely a disinterested party, agrees:

"There are around 30,000 commercial flights per day over the U.S.," says Casaretti. "If you were to attempt to place a team of just two FAMs on each flight, it would require an agency of over 75,000 FAMs (accounting for training and days off). FAMs cover a very small percentage of commercial flights."
Which flight air marshals get on is determined by a computer program that assesses the probability of threat based on the aircraft, departure and destination cities, as well as the amount of fuel on board. This is the threat matrix that comes out of the missions operation center.
The TSA will not release statistics on the number of air marshals. TSA's Pascarella acknowledges only "many thousands." But Biles estimates that there are approximately 3,300 FAMs and of those, 34% are filling ground assignments in training, operations and management.
"We call them 'chair marshals,' riding out their career in management," says Biles. That leaves 66% of the workforce to perform in-flight security duties.
"If one accounts for vacations, sick leave, medical leave and days off, some air marshals working in operations have told me that this accounts for less than one half percent of all U.S.-flagged aircraft being covered by federal air marshals," he says.


How can the breath of a pilot be recorded? On a plane, as a passanger, I can't hear my own breath. I can't hear my own breath even in a silent room.

On a plane, there is a continous background noise.

And the microphone recording the noises in the cockpit, are probably not directly at the lungs of both pilots.

I am really wondering, how can the breath of a pilot simply be recorded on the cockpit, if it wasn't designed specifically for that (or it isn't a very high quality recorder placed directly to the body of the pilots)?

One of the channels of the Cockpit Voice Recorder is the microphone on each pilot's headset. This is much closer to the source of the breathing noise than your own ears. The microphone may also not have a wind filter so breathing on it will generate a lot of noise.


Where to find Tach hour and clock hour equivalence rpm? There is a revolution counter built into the face of the Tachometer in most piston powered GA planes.  This counter is calibrated in hours.  Most planes also have a Hobbs meter, which is a clock.

Only at a certain RPM are tach hours equal to clock hours.  This equivalence rpm is different among the various manufacturers and models, and it is published somewhere.  For a Piper Archer II with the standard Lycoming O-360-A4M engine, what is the equivalence RPM, and in what document is it found?  It is not in the Type Certificate Data Sheet (TCDS) for the Archer II (PA-28-181).

As far as I know the only place to get this information is the tachometer specifications (or at least I know Mitchell provides it for their tachometers).
As you noted, it's not on the TCDS, nor have I ever seen it in the (Piper or Lycoming) maintenance manuals. (It is of course possible I've missed it in the maintenance manuals - they're pretty thick books.)

If you are flying around in a plane with a working tachometer and don't know the hour-meter's equivalence speed you can always determine it with a watch: every 6 minutes is 0.1 hours, and when the tach is recording at that rate you've found the equivalence RPM.
(For the Archer I assume it's the same as my Cherokee 180 - around 2300 RPM.)

  It's worth noting that while you would think the tach's hour meter would be "accurate" (1:1 correspondence) at typical cruise powers that is often not the case!
  Using the Archer as an example, 65% power cruise at 7,000 feet is around 2500 RPM, so the tach hour meter will be running slightly faster than 1:1 in a 65% power cruise at 7,000 feet.

The watch-check I described above doesn't help you if the reason you need to know this information is your tach has died and you need a replacement - fortunately tachometer manufacturers all know this and publish recommended applications for their tachometers.
Mitchell lists their D1-112-5023 (2300RPM) tach as the appropriate replacement for the PA28 family, which matches up with the watch-test on my Cherokee.


Why was a flight delayed because of a bird in the cockpit? This Washington Post article is about a Delta Airlines flight that took off after an initial delay, before turning back again shortly after, because of a bird that managed to stowaway in the cockpit.

My questions,

Would it be dangerous having the bird in the cockpit?
Was the decision to turn back expected or over the top?
Do Delta regulations (or relevant regulations) actually cover something this specific, or would it have been under some catch-all? If so, what would that be?
Have there been any similar incidents?
Does this ever happen on small private aircraft?  (It's not unheard of to find a small bird sitting in your car for some reason - maybe it's the same?) Has it ever happened to anyone here, what's the outcome?

and mostly,

Why didn't they just kill it?

(Aircraft kill small birds by the thousands, I mean - chicken was probably served on board.)

Having a small bird in a cockpit, or anywhere on board, would not be a problem during a normal flight because a normal flight should have a wide safety margin.

However, a situation can change extremely rapidly from safe-and-normal to heavy workload to full-emergency due to any number of factors, including weather, mechanical issues, airspace/congestion, etc.   In a high stress situation, a small bird could be the proverbial tipping point.  So I see and understand the decision to turn back.

It is remotely possible that a small bird could get somewhere it shouldn't, like behind a panel or near electrical lines and cause a short or other serious problem.  Its not terribly likely, but with 100+ lives at stake, why would you risk it?

As for why they didn't just kill it:  Killing it involves catching it, and catching a small bird while still flying a plane is not easy!!


What causes stall buffeting? From other answers I've gathered that stall occurs when the air flow separates from the wing surface. And also that this starts at the back of the wing and progresses forward as AOA increases.

Is this process not uniform? What causes the buffeting just under the stall AOA? Is it simply the turbulence behind the point of separation?

Also, what factors, such as speed, altitude or air density affect the amount of buffeting?

This article states it pretty well (better than I can word it).

  When the angle of attack (AOA) of the wing increases, the point where
  the airflow separates will move forward and the streamlined airflow
  will become turbulent and separate from the wing. This turbulent wake
  then meets the aft fuselage and tail section of the aircraft. This
  will be felt by the occupants of the aircraft as a rumble or buffet.
  Not all aircraft have a pronounced buffet, this depends on the size
  and location of elevator.

Interestingly enough you can also induce a stall (and first high speed buffeting) by gong too high and too fast while trying to maintain level flight which will cause the center of lift to move aft along the wing. Basically your stall speed and your critical mach number eventually converge this is known as the coffin corner. There is a nice discussion on it here.


Where does the term 'greased landing' come from? I've heard this term used a few times to describe a really smooth landing (one where you hardly feel a bump).  But where does this term actually come from?  I'm not sure how grease (a lubricant) came to symbolize a low g-load on landing?

I've always heard this referred to as a "greased landing" or a "greaser", but never a "greaser landing".

My understanding is that it is referring to a landing that was so good that somebody must have greased the entire runway so that you didn't even feel the airplane touch down.  If you've ever tried to pick something up that has been well greased, then you know what they are referring to.  It's very slippery and slides right out of your hands no matter how hard you try.


Why is a blunt trailing edge a better stabilizer at hypersonic speeds? Here is what I read about the X-15 spaceplane:

The X-15 had a thick wedge tail to enable it to fly in a steady manner at hypersonic speeds.[14] This produced a significant amount of drag at lower speeds;

A wedge shape was used because it is more effective than the conventional tail as a stabilizing surface at hypersonic speeds. A vertical-tail area equal to 60 percent of the wing area was required to give the X-15 adequate directional stability.

The X-15 does indeed have flat trailing edges on its stabilizers. Some photos show this.

So why does this produce better stability at hypersonic speeds? I thought stabilizers were more about the total surface area anyway. It just seems so counter-productive to make a flat end like that giving huge drag, especially for hypersonic stuff.

A converging shape at hypersonic speed in a low-pressure medium will produce close to vacuum pressure on its surfaces (hypersonic shielding). A small sideslip angle will only result in a very small pressure difference between both sides.

Contrast this with a diverging shape which produces higher than ambient pressure on both sides. In hypersonic flow this pressure grows approximately with the square of the inclination angle. The same sideslip angle, therefore, will result in a much higher pressure difference, rendering the diverging shape more effective in sideslip.

A more detailed discussion can be found here, page 11-6 to 11-8.

A wedge shape was chosen since it allowed to predict forces and temperatures with greater confidence than would had been possible with a more complex shape.


Why do planes fly so high? It so occurs to me that commercial airliners cruise at altitudes of over 30,000 feet. But why do they fly so high if there are many dangers such as cabin de-pressurization when they can simply fly lower?

Aircraft fly high because it puts them above the weather. This is at least the historical reason why aviation has desired higher flying aircraft over the years and subsequently driven design that way. When it comes to weather altitude gives you diversion options, avoidance possibilities and in some cases the ability to simply fly over a system instead of through it.

Jet engines are more efficient at high altitudes which makes it beneficial to fly them up there (you can find the full explanation of that in this Q/A) but piston planes can fly quite high as well jets have prevailed for lots of reasons and that is a different discussion all together.

Altitude, in some cases also provides a safety margin for things like loss of engine power. With sufficient altitude you can have an outcome like this instead of this.

As for cabin depressurization that is not really a huge issue. Aircraft are equipped with oxygen masks to keep everyone safe in the event of a depressurization and all aircraft are certified to be able to do a decent from cruising altitude to 10,000ft. (non supplemental Oxygen altitude) in a specified time. Some newer systems will even bring the aircraft down automatically in the event of a depressurization.


How is thrust vectoring controlled by the pilot? Thrust vectoring is used to extend the manoeuvrability of aircraft outside a `normal' flight envelope, by providing (optionally differential) vectored engine thrust, as explored in many previous questions (this and this).

How is the direction of vectoring actually controlled by the pilot during flight? Does a flight control computer automatically interpret "traditional" control surface inputs under extreme conditions and move the nozzles appropriately to create the desired effect? Or is vector direction a separately controllable interface?

I've noticed in my flight sim of choice, XPlane, that the configuration panel allows the mapping of an analogue axis on my joystick/pedal setup to 1D vectored thrust. I've no idea if this is representative of any real fast jets, but if it is, it seems that this approach could create a lot of extra "pilot workload" -- given that it's another one (to three!) control axes to be manipulated -- and manipulated at the same time as pulling potentially very aerobatic manoeuvres with little room for mistakes. This seems like a Bad Idea.

On the other hand, it might be the case that independently controlled vectored thrust allows for a wider range of aircraft manoeuvres than that which could traditionally be 'expressed' by control surface movements alone. Giving fast jet pilots the extra workload would, therefore, be worth the risk.

Thrust vectoring isn't controlled by the pilot directly, except being able to turn it on or off in various circumstances. If it is on, the aircraft computers control the vectoring based on external conditions, the state of the aircraft and control input.


What is a SAAAR / RNP AR instrument approach? I understand that a SAAAR / RNP AR is a "special" approach and that special approval is required to even get the approach plate, but what exactly is it?  Aspen is an example of an airport that has one.

First allow me to give a quick introduction to RNAV and RNP before geting to SAAAR / RNP AR.

Area Navigation (RNAV) is a method of instrument flight rules (IFR) navigation that allows an aircraft to fly on any desired path within the coverage of referenced navigation beacons, rather than navigating directly to and from the beacons. In other words, waypoints can be defined at arbitrary locations and paths betweens those points (and traditional navigation beacons as well) can be defined.

RNAV routes are coded into the navigation database by ARINC 424 path-terminators. Whilst RNAV routes can be designed in such a way that the lateral path is strictly described, in general the lateral path has a quite some freedom due to floating leg types (e.g. turn at altitude, fly heading etc) and wiggle room for the aircraft to negotiate the turns.

When the route is described only by TF (track to fix) and RF (radius to fix) path terminators, the lateral path is fully fixed. These fixed lateral paths allow procedure designers, for example, to design approaches through mountain valleys down to the runway.

RNAV defines a 95% accuracy bounds. For example, RNAV 1 requires the aircraft to be within 1 NM from the path centreline 95% of the time. The route designer will ensure a 2 NM obstacle free zone around the path in such a case.

Note that RNAV provides no assurance against exceeding the 2 NM zone. There is no automated system monitoring required.

Potentially causes of deviations between the path intended by the procedure designer and the actual flown path can be grouped into three categories:

First, there is the Path Definition Error. This is caused by database
coding mismatch with the original path design.
Second, there is the Path Steering Error, caused by the combination
of display inaccuracies on the Navigation Display and the inability
of the pilot or the autoflight system to stay exactly on path (Flight
Technical Error).
Third, there is Position Estimation Error, which is the difference between the position of the aircraft estimated by the navigation system and the true position.

It is not unthinkable that while normally (95% of the time) the aircraft will fly within e.g. 1 NM of the intended centre line, there are cases that the aircraft will exceed the 1NM by far, possibly even busting the 2 NM obstacle free zone. That could potentially ruin your day if it happens in a mountain valley.

This is where RNP comes in. RNP (Required Navigation Performance) is basically RNAV with added protection. For example, RNP 1 again defines a 1NM accuracy for 95% of the time, but it also offers 99.999% assurance that it will not exceed the 2NM. It will raise an alert if the 2 NM value will potentially be exceeded. So in addition to what RNAV offers, it includes a system monitoring function that will detect navigation errors and alerts for them.

The RNP value alway gives the 95% accuracy, the 99.999% assurance (integrity) limit is always at twice that value. So RNP 0.3 means that the aircraft has to stay within 0.3 NM of the designed path centreline 95% of the time. And if it exceeds the 0.6 NM threshold, an alert will be raised with 99.999% certainty.
RNP systems therefore require a system monitoring function.

To ensure that the RNP values are met, each of the three error sources mentioned earlier must be under control. For RNP values down to 1 NM that is not much of a challenge. Standard procedures and equipment are deemed to be sufficient here. (of course the required RNP values must be met by the Actual Navigation Performance)

If an approach requires tighter limits, such as RNP 0.3 or 0.15, then special authorization is required.
This is where SAAAR comes in (Special Aircraft and Aircrew Authorization Required), now renamed to RNP AR (RNP Authorization Required). RNP AR routes only make use of TF and RF leg types to fully fix the lateral path. RF legs are not supported by all navigation systems by default.

To get authorization for RNP AR, the aircraft needs to comply with the applicable functional and performance requirements, the crew needs to be trained and lot's of documentation must be maintained. Basically proof must be provided that all of the three error terms are under strict control.

In a sense it is somewhat similar to ILS CAT III approval.

References:

AC 90-101A describes a means of compliance for RNP AR

RNAV / RNP presentation gives a good explanation of RNAV and RNP


I'd like to know the name of this aircraft I recognize it but can't recall the name, if anyone can tell me that would be great.

This is a P-51D Mustang. The main clue for the "D" model is the bubble canopy.
To identify it as a P-51:
It has D-day paint stripes, which means it is not an obscure prototype of some other American fighter design.
It has a belly-mounted cooling air scoop, square rudder, wingtip and elevator tip profiles, and an induction air inlet under the prop spinner- which all distinguish it from the P-40, along with the bubble canopy.
It has a 4-blade prop, which distinguishes it from the P-39.
It has the engine in the nose and no cannon firing through the prop spinner, which distinguish it from the P-39 and the P-63.


How does ceiling relate to IFR and VFR? I'm working on a Python script that takes in metar data and decides if an airport is VFR/IFR/MVFR etc. This is the website that I'm getting the info from:

https://www.aviationweather.gov/metar/data?ids=kbwi&format=decoded&date=&hours=0.

I'm using this website to decide if an airport is IFR/VFR. I understand the visibility requirements, but not the ceiling. What if an airport is overcast at 500, broken at 5000, scattered at 3000? What takes priority to decide the ceiling requirement?

https://www.aviationweather.gov/metar/help?page=plot

There are many websites and apps that do this for you already.  The website SkyVector will show colored dots that indicate what the airport status is.  There is also a ForeFlight app that will show colored dots on their maps.  I am not endorsing any products, simply pointing out tools that accomplish what you are asking.

All these companies use information found in AC 00-45H.  I added color for clarification.

Personally, I would stay away from getting into the details of what class airspace an airport is currently using.  Although, the information can be easily found, it may be a challenge to code successfully.  The airspace above an airport can also change depending on whether an control tower is in use, the day of time or other factors.

The other reason, is 91.155(c).  Hence, any ceiling below 1,000 FT makes the airport IFR.

  Except as provided in §91.157, no person may operate an aircraft beneath the ceiling under VFR within the lateral boundaries of controlled airspace designated to the surface for an airport when the ceiling is less than 1,000 feet.

To answer your other question.  The ceiling is defined as the lowest BKN or OVC layer.  In your example above, the ceiling is OVC 500.


Would it be safer if Drones carried transponders? The current FAA regulations don’t permit UAS above 400’ AGL, but that doesn’t mean that the machines are not capable of flying higher than that.

Since a Mode-C (at the minimum) transponder is required in various airspaces, is it a good time to start considering the fact Drones should start carrying some sort of altitude-reporting transponders?

It is of course a good time to begin considering this, and in truth, it's already a consideration. It's also an assumption by many in the private sector that the FAA will mandate this for commercial drones. Recreational drones will not be allowed to fly at high altitudes any time in the near future, however, as companies that aim to autonomously transport clients with drones are starting to test their aircraft, it will be very necessary.

The difference between recreational drones and commercial drones is largely their operating space. A recreational drone pilot has no good reason to fly anywhere near 1000 feet, though the technology is becoming more easily available to do so. If you operate under the assumption that the majority of drones are likely to be under 1000 feet, you can somewhat rule them out as factors in commercial operations, for now. Recreational drones are also very small, and they are generally looked at as having similarities to bird strikes - the difference is, there are effective ways to get rid of drones, and not as many effective ways to get rid of birds!

Beyond the fact that commercial transport drones would be flying at higher altitudes, they would also be much larger, and could cause much more damage in an accident. ADS-B will no doubt be a requirement for commercial drones (perhaps of a certain size or above a certain altitude), in the near future. The FAA actually broached this topic with the industry at EAA this past summer.


How do I convert my FAA PPL to the equivalent in the UK / Europe? I am returning to the UK and want to convert my FAA PPL to a UK PPL. Does anyone know the process for doing this?

I am getting lots of conflicting information.

As a disclaimer, this answer is based on Googling, not on personal experience, and compared to the US the situation seems very complicated. I'd suggest contacting the CAA directly; EASA delegates licensing to its member states, so the practical details depend on the country you're in. You can read about one person's experience here, although it's in Hungary, not the UK.

Anyway, it looks like there are two processes: validation and conversion. A validation is a temporary license valid for 12 months only (or 24 months, according to some sources), whereas a conversion gives you a full EASA license. The purpose of a validation seems to be to let you fly while you work on conversion; I couldn't find any definitive sources on the process.

As for conversion itself, the requirements I found on various sites are consistent with EASA's own information:

  If you hold a Private Pilot Licence obtained outside Europe or not
  according to the relevant EASA licensing regulations, you can convert
  it to an European one. In order to do this you will need to pass an
  exam on Air Law and another exam on Human Performance. You also need
  to undertake a skill test and have at least 100 hours as a pilot in
  the relevant aircraft category.

That doesn't sound too bad, although I have no idea how much effort and expense there is in practice. If you're instrument rated, though, the requirements seem quite onerous compared to the US because of the large amount of theory required (this is from the same EASA source):

  Competence Based Instrument Rating (CB-IR): This rating is for those
  who already have an Instrument Rating issued outside Europe (e.g.
  FAA). This reduces the requirements of obtaining an Instrument Rating
  to at least 80 hours of theory and 40 hours of instrument time, 25
  hours of which must be training.

And to add more complication, it appears that the UK currently allows FAA license holders to fly using their FAA license but in the UK only, i.e. it isn't an EASA license and therefore not valid across Europe. There's an ongoing discussion with EASA about it, so it might not be a good long-term option but I really have no idea.

There's also something in the UK - and perhaps other countries? - called an NPPL, a National Private Pilot License. But that also has limitations, and isn't valid outside the UK.

Finally, although it's common to see N-registered aircraft in Europe, if you're a European resident then you can't fly them with just an FAA license. You also need an EASA license.

Someone who's actually converted an FAA license to EASA could probably give you a better answer.


Was the Hughes H-4 Hercules capable of flying out of ground effect? According to the wikipedia article the Hughes H-4 Hercules (Spruce Goose) reached a maximum altitude of 70 feet on its flight.  At this altitude the aircraft was still in ground effect.  Would the H-4 have been capable of flying out of ground effect?  Why or why not?

The answer can only be given by comparing it to other, broadly similar aircraft. My three references would be the British Saunders-Roe Princess, the Martin Mars and the Boeing 314 Clipper, all three at their time huge flying boats.

Obviously, the H-4 has the highest wing area relative to its installed power and its intended maximum take-off mass (MTOW), but does not look totally out of the range of the two smaller specimen. The Princess was conceived as a pressurized airliner and is of a more advanced design than the other three. With the lower wing loading come lower speeds, so the lower power loading looks adequate. Another huge military transport plane of that time which was derived from a cargo glider (the initial requirements asked for a cargo volume equivalent to a Reichsbahn standard cargo wagon) had a wing loading of just 150 kg/m², a very similar power loading of 23.56 HP/m² and flew just fine. Stick forces were massive, however, and stability was marginal.

The exact performance would depend on details like airfoils, aspect ratio, flap settings, hull design and stability, but in general it looks as if the H-4 would have been capable of flying out of ground effect. But its performance would not have been spectacular - a little more installed power would had made it better.


Aside from the Stratolaunch, how many other aircraft have split bodies? So there's a lot of excitement about the new (and massive) Stratolaunch

Split bodies are uncommon (although launching spacecraft from them commercially is a new thing). The only other airframe that I've seen like this would be Virgin's White Knight 2 (also a spacecraft launcher). Do any other aircraft use a split body like this?

Depends on how you define it but there have been a variety over the years:

The P-38 Lighting has 3 bodies there was also a later experimental version the XP-49 that only saw a single airframe.
The F-82 was a a twin fuselage version of the P-51
The boomerang which was also designed by Burt Rutan (the designer of the stratolaunch)
A one off twin fuselage piper cub was built but never saw production scale.
As @DanPichelman points out in the comments, the Yak-110

  ...although launching spacecraft from them commercially is a new thing

This is not entirely true, piggy backing rocket planes on larger aircraft has been widely done since the 50's


Why does transonic drag happen? I have heard of transonic speed and it is between supersonic and not supersonic. What is it and why does it happen to aircraft and how does it produce a lot of drag. How do you prevent it from happening?

Airflow around aircraft and especially over wing is not uniform. The lowest transsonic speed is when the airflow at some point of aircraft (usually over wing) goes supersonic. Depending on aircraft, this happens around M0.8. When the airflow around entire aircraft is supersonic the transsonic region ends.

The excessive drag is due to the shockwave(s) that forms in the airflow at the location where airflow has accelerated to speed of sound. As airflow ahead of it hits the shockwave the energy of flow dissipates and there is sudden drop in air pressure across the shockwave. As there is less pressure behind the shockwave than there is in front of it additional drag is induced in the process. This called wave drag.

This effect can be counteracted by designing an airfoil that forms the shockwave initially as close as trailing edge as possible and then the entire airfoil goes supersonic as quickly as possible as speed increases. See https://en.wikipedia.org/wiki/Supercritical_airfoil

The formation of shockwave is the reason why supersonic aircraft has pointed noses as air is not pushed ahead of an aircraft. The pointed nose creates an oblique shockwave that has creates less drag along the aircraft flight path.

Pointed cones can also be seen in engine intakes of supersonic aircraft (see SR-71 and Mig-21). The additional oblique shockwave formed by the cone ahead of the engine is used to slow air entering the engine to subsonic speeds. The cone is moved back and forth as mach number changes to keep the shockwave away from the actual engine. Concorde used adjustable ramps within engine intake for same effect.


Would knowing the exact weight that has been loaded on a commercial plane and it's distribution be useful? There's been a bit in the media about weighing passengers in order to get more accurate take off weights for commercial planes.  I'm guessing the delta between a heavy set of passengers and a light set might be 3000 kg.  If there was a cheap way of determining the weight that has been loaded onto a commercial jet would it be valuable out not, given this level of weight difference? I am after an actual cost. What is the cost of an airliner carrying the
additional fuel required by current rules if it assumed the overall mass estimate is 3000kg too high throughout its life? It won't be using that fuel but it will have to carry it.

YES.

The obvious solution is to roll the plane over a scale.  Useful CG data can also be obtained by weighing the front wheel and comparing its torque to known values.  A light front wheel means an aft CG.  This could be corrected by moving fuel BEFORE the plane is airborne, as well as while in flight.

Of course, moving passengers and cargo are an option too.

For example the plane weighs in at 2200 lbs total on the ramp ready to go.  The nose wheel weight is 200 lbs.  The distance between the main and nose wheels is 11 feet.  The aft CG limit is 0.75 feet forward of the mains.

CG is calculated as follows:  200 lbs/2200 lbs = 1/11.
          CG is 1/11 * 11 feet = 1.00 feet forward of mains.
          CG is with in limits.

And how accurate weighing the nose wheel can be (due to long torque arm):

Nose wheel weight 100 lbs.  Total weight 2200 lbs.
        100 lbs/2200 lbs = 1/22.
         CG is 1/22 * 11 feet = 0.500 feet forward of mains.
         CG is NOT in limits.


How is data exchanged between Eurocontrol and FAA? Let's say I want to fly from Europe to USA.

Then (probably):

I'm filling flight plan message(FPS) and it goes to Eurocontrol system.
It is somehow transmitted to FAA. How?

Flight plans are distributed to all air traffic control units that will be providing services along the route over the Aeronautical Fixed Telecom Network (AFTN).


How to ignore faulty instrument readings in glass cockpits? When an instrument fails in the cockpit, it is better cover it with something, either a dollar bill or a gauge cover (if you happen to have one of those), so we won't accidentally process the information from the faulty reading. My instructor taught me to literally smash the gauge, so the status of that instrument is not in question.

This works well in cockpits with rounded gauges. Nowadays, more and more GA aircrafts are fitted with glass cockpits. Obviously I can't just smash the screen, or else everything will be gone! What are the steps that one can take to avoid reacting to the faulty reading?

Like in a steam gauge cockpit, you can put adhesive INOP stickers on parts of the glass panel. Stickers for the Garmin G1000 are available commercially, and I had to use them extensively for my instrument rating.

Keep in mind, though, that glass cockpit aviation systems will detect a faulty sensor automatically, and the faulty instrument will just appear X-ed out (like the picture on the INOP sticker) instead of showing wrong values.

But even multiple sensor source cross checks doesn't keep you safe from misinterpretation. See Birgenair 301 accident for example.


How do I find a plane's history when booking a flight? While booking tickets for a commercial airliner, is it possible to know the name of the aircraft (not the model, but the designated name) and then search the history of the plane, on how old is it, how many repairs has it gone through, has it ever had an accident etc.

Unless you are booking at the very last minute, no there is no way to find out which particular aircraft you'll be on until you're strapped in. The airline themselves plan in advance but as soon as one plane needs unexpected maintenance, or is excessively delayed, the schedule is thrown out the window. For this reason more than anything no airline to my knowledge publishes this schedule.

Once you are at the gate you might be able to see the aircraft registration. If you google that you can see if it has been in any serious incidents, when it was delivered and how old it is. You won't be able to find out how many repairs it has gone through, only the airline has that (hint: the answer could be hundreds of times if you're counting minor issues).


Should I hold my breath in case of a decompression? If I'm, for example, in the lavatory where there are no oxygen masks, would it be advisable to hold your breath until you can reach an oxygen mask, or until the pilot brings the aircraft down to an altitude where we can breath again?

Is it even physically possible to hold your breath after a  decompression accident?

No. Holding your breath might cause breaking blood vessels in your lung (barotrauma). It is important to equalize the pressure inside your lung with the exterior. That is in fact the most fundamental rule for all scuba divers.

Also see this related question: Is it possible to suffer barotrauma during decompression?


Which FAA regulations require compliance with TCAS II Resolution Advisories? I've always heard that complying with a TCAS II Resolution Advisory is a required action for pilots qualified and operating an equipped aircraft. I am not familiar with the regulatory basis for this, though. I'd like to get a bit more specific with the context. For aircraft operating under 14 CFR 91, is there a regulation that can be referenced?? For aircraft operating under 14 CFR 135, is there a regulation that can be referenced? And what about for 14 CFR 121?

I'd also like to know if there are exceptions to any regulatory requirements.

This answer mentions that aircraft must respond within 6 seconds. I believe the source is AC 120-55C but I'm not totally sure.

The requirement to respond to the TCAS II resolution advisory is somewhat indirect.  one key fact is that any TCAS installation has to be approved:

  14 CFR §91.221   Traffic alert and collision avoidance system equipment and use.

  (a) All airspace: U.S.-registered civil aircraft. Any traffic alert and collision avoidance system installed in a U.S.-registered civil aircraft must be approved by the Administrator.

  (b) Traffic alert and collision avoidance system, operation required. Each person operating an aircraft equipped with an operable traffic alert and collision avoidance system shall have that system on and operating.

Key points here:  1. The installation must be approved.  2. If it's installed, it has to be used.

From Part 121:

  14 CFR §121.356 Collision avoidance system.
  Effective January 1, 2005, any airplane you operate under this part must be equipped and operated according to the following table: {Detail omitted}

This says anyone under Part 121 must have A TCAS installed and operating.
If you go back to Part 21, you can find that the installation approval requires a Type Certificate, Supplemental Type Certificate, or an Amended Type Certificate.

Part of getting that installation approval is a requirement for Airplane Flight Manual (AFM) or an AFM Supplement.  With regards to TCAS, the airworthiness approval is addressed by

  AC 20-151B Airworthiness Approval of Traffic Alert and Collision Avoidance Systems (TCAS II), Versions 7.0 & 7.1 and Associated Mode S Transponders

Chapter 5 and Appendix A cover the requirements for the AFMS for TCAS.

While the AC is advisory, it is spelling out a means of complying with the rules, which in Part 23 (small A/C) and Part 25 (air transport) require a flight manual.

Elsewhere:

  14 CFR §91.9 Civil aircraft flight manual, marking, and placard requirements.

requires operation in accordance with the limitations of the AFM.

In Part 121, airlines operate in accordance with their Op Spec, which will include similar rules.

And there is specific wording to address clearances and response to TCAS:

  14 CFR §91.123  Compliance with ATC clearances and instructions.
  (a) When an ATC clearance has been obtained, no pilot in command may deviate from that clearance unless an amended clearance is obtained, an emergency exists, or the deviation is in response to a traffic alert and collision avoidance system resolution advisory. However, except in Class A airspace, a pilot may cancel an IFR flight plan if the operation is being conducted in VFR weather conditions. When a pilot is uncertain of an ATC clearance, that pilot shall immediately request clarification from ATC.
  (b) Except in an emergency, no person may operate an aircraft contrary to an ATC instruction in an area in which air traffic control is exercised.
  (c) Each pilot in command who, in an emergency, or in response to a traffic alert and collision avoidance system resolution advisory, deviates from an ATC clearance or instruction shall notify ATC of that deviation as soon as possible.

This basically acknowledges that pilots will respond to an RA and that they should report it as soon as they can after the fact.


Where can i find aircraft blueprints for study purpose? I'm a 3D artist and i want to start my new project. I'm going to create an exact model of the Embraer 190 aircraft. I need this for my graduation project at the university (I chose such a project, there is much more than just modeling, but this is the first step). But at the zero step, I was faced with the fact that there are simply no free blueprints in the public domain. There are all sorts of approximate schemes of the aircraft, but they can hardly be called accurate. Even in the manual from Embraer, only exemplary drawings.
Where can I find such things? I am ready to buy them, if necessary.

Fifteen euros gets you what you need here: https://www.the-blueprints.com/vectordrawings/show/1750/embraer_190/

This one is six euros: http://www.lulu.com/shop/elodie-roux/3-view-drawing-plan-3-vues-embraer-190/ebook/product-20233147.html


Why is the CFM56 produced with two different thrust reverse options? According to Wikipedia, the CFM56 could support several reverse thrust options, and it appears that it has actually been built with 2:

Boeing seems to prefer the cascade type
Airbus seems to prefer the pivoting door type

Is this a simple case of catering to customer preferences, or is there a more in-depth reason for having multiple reverse thrust options?

Hispano-Suiza has delivered the world's first target-door reverser for a big turbofan, the A320's CFM56

The extending petal-shaped doors type is a Hispano-Suiza specialty. It's a French company and one of the three major suppliers of reverse systems.
In the 80's Hispano-Suiza had to be innovative to capture a bigger market share. Their door type was the first ever on a high bypass engine. They believed investing in R&D will help increase their sales (it did). The petal reversers also double as airbrakes.

Why not on the Boeing 737?
Since the CFM56 on the 737 is close to the ground, the doors would scrape the pavement. And—more importantly for other aircraft types—Hispano-Suiza's competitors are Rohr and Boeing. Boeing definitely would like to keep things in-house with their translating/cascading reversers.
Nowadays with the jet engines of the smallest regional jets to the wide-bodies being as wide as the fuselages, the cascading type is the better choice.

Sources:

Flight, 1986 / 1600
Flight, 1994 / 0230


What does ATC do when a VFR flight in the mode C veil has a malfunctioning altitude encoder or transponder? Recently I replaced the altitude encoder in my airplane because ATC could not receive my altitude during VFR flight following. Up to that point I had been flying VFR under the class B shelf for some time, and I assume my transponder wasn't transmitting the altitude to ATC. It may have been non-functional for several months.
Was I causing panic in the control tower because my plane wasn't reporting the altitude, and I wasn't on any ATC frequencies for them to contact me? Can ATC determine my altitude from their ground based radar? Is ATC able to contact VFR airplanes when their transponders/encoders are off, or tuned to the wrong squawk code, or malfunctioning? The transponder is tested every two years, so that is a lot of time for something to go wrong.

A lot of this has to do with whether or not you're talking to ATC.

If you're talking to ATC and your Mode C disappears or goes insane they'll ask you to report your altitude (and if your Mode C altitude reporting is wildly off they'll probably tell you something like "Stop altitude squawk - altitude differs by 500 feet". This is your cue to take the plane to an avionics shop and have the system checked/serviced, and not to attempt to enter B or C airspace, or fly above 10,000MSL, until its fixed.

In most cases ATC will continue to work you in the system until you are clear of the Mode C veil (possibly expediting your exit if having no altitude readout on your target is messing up their day) because it's better to be talking to you than not.

If you're not talking to ATC things get a bit more complex:
If your Mode C altitude readout is missing ATC will generally report you as "traffic, altitude unknown" to other aircraft and apply lateral separation exclusively (nobody is allowed within the minimum lateral separation distance of your target unless they have you in sight and can maintain visual separation). If/When other pilots spot you ATC will usually ask them for your type and altitude so they have some idea of who you are and what you're doing.

If your encoder or transponder is malfunctioning and reporting an incorrect altitude that's substantially more dangerous: ATC has no way of verifying your altitude other than asking you (or another pilot), so they'll be maintaining separation based on an incorrect altitude. This is why even VFR aircraft equipped with Mode C need an encoder check.
In this case ATC will find out about a malfunction when you're called as traffic to someone and they respond with "Is that my traffic above/below me?"


Are centrifugal compressors/turbines less efficient internally, and if so, why? From my related question which found a good example of a centrifugal turbine jet engine, the Henkel Hes 3.

Picture Source Website (it's in Czech). Thanks to Jan Hudec for finding it.
My understanding of centrifugal engines is that they have larger diameters and therefore larger nacelle drag, and therefore aren't favored.
So in this question, I want to ask, are centrifugal engines less efficient internally? That is, for a given thrust at given conditions, will the centrifugal have more, less, or equal fuel consumption than a "normal" axial-flow engine?
I can't imagine that friction of air flowing around a winding path, or related viscuous effects, could amount to any noticeable penalty. But I can't think of any other reason why centrifugals would be internally less efficient.
Note, another related question, one answer did say that centrifugal compressors will have higher losses than axial compressors, for a given compression ratio, but did not explain why.

Internally the big difference is that with axial compressors, it's easy to have a multi-stage compressor to give considerably higher overall compression.
While it is possible to link centrifugal compressors together into a multi-stage engine, it's considerably less common, so most centrifugal compressor engines are limited to the compression they can get from one stage (usually around 4:1).
Axial flow engines get lower compression per stage (usually around 1.2:1), but it's easy to have multiple stages, so engines with 10-15 (or so) stages are fairly common. Given the difference in compression per stage, an axial flow engine typically needs about 8 stages to produce higher overall compression than a single-stage centrifugal compressor.
It is also possible to combine the two. At least to my knowledge, the most common layout in this case is multiple axial-flow stages, followed by a single final stage using a centrifugal compressor.
Here's one paper about using a final centrifugal compression stage, in case you care: https://doi.org/10.2514/6.2019-0944


Why would an ILS installation need a “reflecting surface” around the glideslope antenna? According to the NTSB, the installation of a glideslope serving runway 11 at KHTS (Tri-State Airport, Huntington, West Virginia) was delayed for over twelve years by the lack of suitable terrain for the glideslope antenna, and, when the glideslope was finally installed (following a CFIT accident involving an aircraft making a nighttime approach to runway 11), these same terrain considerations forced the use of a nonstandard installation utilising an offset antenna (my emphasis):

An instrument landing system was scheduled for installation and commissioning at the Tri-State Airport in June 1958.  The localizer, middle marker, and outer marker installations were completed at that time, but there was insufficient terrain to provide adequate reflecting surface for the glide-slope antenna, within the existing criteria.  Three applications for runway extension, which would also provide suitable terrain for the glide-slope antenna, were submitted to the FAA in Fiscal Years 1967, 1970 and 1971.  The 1967 and 1970 requests were not approved because the necessary “matching funds” from the sponsoring agency were not available, and consequently the Federal funds were not committed.  The 1971 request was still under consideration at the time of the accident.
Subsequent to the accident, concurrent negotiations involving the FAA, West Virginia State Aeronautics Commission, Wilcox Electric Company, Inc., and the Tri-State Airport Authority, resulted in the installation of a nonstandard glide slope for Runway 11, paid for by Federal funds only.  Prior to installation, the FAA estimated that there was a 50 percent probability of success with the glide slope.  A Wilcox Mark I, Series 8020 transmitter was placed 1,211 feet south of the runway centerline and 960 feet west of the Runway 29 threshold.  The elevation of the site was 805.2 feet m.s.l. and the antenna was rotated 13.5° to align with the middle marker.  This offset was required to place the site on suitable terrain, and resulted in an unuseable signal below 1,075 feet m.s.l.  Consequently, there was no reduction in the minimum altitude authorized for the instrument approach.  However, the signal generating capability of the facility to date has been as reliable as standard systems.  [NTSB AAR72-11, page 12 (numbered as 9); the runway has since been extended, and now measures 7,017 feet (and is now runway 12/30, due to changes in the local magnetic declination over time).]

The requirement for “adequate reflecting surface” is surprising; intuitively, one would expect that UHF-radio-wave-reflecting surfaces near your glideslope antenna would be a bad thing, due to the potential for multipath interference from reflected glideslope signals.  Why is this not so?

Source: FAA 6750.16E - Siting Criteria for Instrument Landing Systems

The more common G/S antenna type works by reflecting the signal off flat ground, called "image type".

A non-image type was not available in the 70s as it's a mid-90s invention (patent; IEEE).


Are there generic routes all pilots can fly? The recent question Is the destination of a commercial flight important for the pilot? stoked my curiosity but the answers were rather explaining that a pilot does not necessarily need to know where he is flying in advance (and general planning, broadly speaking).

I was more interested to know whether a pilot can fly anywhere. To take an analogy: I have a European driving license. With it, I can drive on all public roads in France and whether I got to Bordeaux or Calais does not matter. The road can be more or less complicated but all of them are accessible to me.

I can also drive to Germany. Sure, there re some minor differences in the regulations, but everything is basically the same.

I can also drive in the US. The differences are more pronounced but at least my European driving license allows me (in short) to drive there.

How is this with pilots?

Are there "generic" airports all pilots can land in? I know that a special license is required to land on some (the old airport in Hong Kong for instance) , but does this mean that "any airport is OK, except the ones which require special licenses?)
Same question for routes: are all domestic / international / overseas routes open to all pilots? Or one needs to have a special permit to fly one of these?

I know that each airplane type requires a license (or families of aircrafts) - similarly to my driving license type B for which a family car is OK but a truck is not. My question is on routes and destinations, once you fly something you are allowed to.

In short, yes it is a lot like travel on the road. There are treaty agreements that came from the Chicago Convention on International Civil Aviation in the 1940s which allow quite a substantial freedom of international travel and cross recognition of pilot certificates.

In the USA most routes are open to most pilots, the restrictions are based on the conditions and chosen rules of flight. In an emergency the pilot is legally allowed to do anything needed to address the emergency and get the aircraft on the ground without regard for any routes or other rules, as such I will not mention the emergency exceptions for each separate item and situation.(91.3[b] in an in flight emergency requiring immediate action, the pilot may deviate from any rule of this part to the extent required to meet that emergency)

As you said for driving, the rules of driving may change by country but this applies to all drivers equally, it is mostly the same for pilots.The restrictions for pilot certificates mainly relate to the carry of passengers or cargo for hire not the location or route of flight, similar to the divide between private family car and a taxi or delivery service. Exceptions are the very limited hobby flight categories (ultralights, light-sport, and recreational) but this would be similar to a small moped or Vespa which is not allowed on highways marked above 40mph(60kph).

Flying under visual flight rules generally does not strictly adhere to designated routes. The primary designated routes are federal airways(for the space between) and preferred departure and arrival procedures(near the airport), these routes are actually designed to assist instrument flight rules flight planning and the ATC managing said IFR traffic, however following these routes while VFR is allowed. VFR is literally visual, just look out the window and see where you are traveling. Flying under instrument flight rules will require an instrument rating on your pilot certificate, however the instrument rating applies to both private and commercial certificates.

Certain airports are designated as ports of entry and have customs offices, just like old time marine ports and road border crossings; a port of entry is the first landing after crossing the border, though it may be hundreds of miles from the border. A filed flight plan is recommended to reduce border problems but not strictly required in all cases.(see Chicago convention) A port of entry is open to domestic flights just the same as any other public airport.

There are additional restrictions on the choice of route and airport for regularly scheduled commercial operations, as compared to unscheduled air-taxi and private operations. Also the practical physical limits of the airplane and landing surface; length, width, strength of pavement, climb over local obstacles, etc.

We [USA] have airspace classes A, B, C, D, E, G and "special use". A and B are positive controlled meaning that you must negotiate with ATC for clearance to enter. Most special-use are associated with military training or high security areas, though some are simply alerts or caution areas for other potential hazards such as a large flight school in the area.

Class A is everything between 18000 feet above sea level to flight level 650 (about 65000 feet depending on barometric pressure) and class A requires instrument flight rules which will require both filing a flight plan and an instrument rating on the pilot's certificate.
B is used for the busiest airports, every flight in B must talk to ATC and get explicit clearance to enter B, IFR flights get priority. When ATC is very busy VFR flights that are just passing through and not landing within the class B area may be turned away. B generally covers an area up to 30 miles from the primary airport, though it has a complex shelf structure that steps up as you get further from the airport and allows other airspace below and above the shelves.
Classes C and D are also airport tower controlled but they are smaller than B. C is around secondary international and primary regional size airports, and D is for the least busy airports with a control tower.The main difference is that class C requires a radar transponder with altitude encoding and has a 10 mile radius with one shelf, D has a 4 to 6 mile radius no shelf and no transponder requirement. Both require two way radio acknowledgment from ATC but they do not require explicit permission to enter, planes with no radio can be accommodated if arrangement is made with ATC at least one hour prior.(this is to allow for antique aircraft or flights to repair stations) C, D, and E are controlled but not positive-control airspaces, as such IFR traffic is looked after and kept separated by ATC while VFR traffic just minds its own business for the most part, mainly contacting ATC during landing or for departure. Many D airports are so small they close the tower at night and revert to class E or G pilot-controlled airports.(The Boeing factory airports are all public class D) My local air-force and army-airfield bases are both class D and while I usually just cut through (near my preferred airport and I don't want to take the long way) they do allow some non-military landings with prior permission.
Class E is controlled enroute space, it is all the area between B, C, and D where ATC support is available. Low level Federal airways are all in class E, VOR "victor routes" are the most common type and usually are from 1200feet above ground to 18000 feet above sea level and 8 miles wide, though there are a few T routes [GPS or inertial navigation]. These routes are designed for IFR but they are not restricted, any VFR pilot can fly on them or in between them, though IFR will fly at 1000ft altitudes[eg 5000, 6000] and VFR will add 500ft[eg 5500, 6500]. E also covers air above FL650, though all airspace above FL450 is considered point to point and there are no designated routes. Most airspace above 1200ft is now E, some places E starts at 700ft or at the surface near some airports.
G is all the space between where ATC is not available, also known as uncontrolled airspace, mostly found from ground to 1200ft, where ATC does not have radar coverage G can go as high as 14000ft. G has no IFR because there is no ATC, and no designated airways because there is no IFR, the grey middle is a class G airport with an instrument approach, generally the instrument approach requires minimum cloud base/decision height above the G to E boundary. Flight in IMC is allowed in G without an active flight plan, at your own risk.
Special use airspaces are of several types and can be active only select hours (military training fighters or artillery range) or full time; and they can be only an alert to hazards like heavy student training or moderate military operations; "restricted" during certain hours for heavy military use (though you can still radio the controlling agency and ask them for permission to pass); or fully prohibited.(the only prohibited around here is a ballistic missile submarine base, and it only extends to 2500 feet above the surface)

We also have VFR flight plan filing in the USA, but this is voluntary and not permission to fly. A VFR flight plan is only a statement of intended route and estimated time so that a search can be made if you do not contact the service within 30 minutes of the stated arrival time. Flight plans can be changed in flight or canceled and closed by the pilot over the radio without actually completing the trip as filed. IFR flight plans can also be filed, opened, changed, canceled, and converted to VFR by the pilot while in the air.


What is the minimum speed for a scale-model of a modern commercial aircraft to fly? Suppose a commercial jetliner (say an Airbus A320 or Boeing 737) were scaled down into  a remote-controlled drone, so that its wingspan were two feet wide. My questions regarding this scale-model are:

1) Would jet engines work if scaled-down to such proportions?

2) Would the wings, tailplane, ailerons, flaps etc. work if exactly scaled down in the same ratio as the fuselage?

3) At what velocity should the scale-model taxi in order to take off?

4) At what speeds should the scale-model fly to achieve stable flight, if the length and breadth of the wings etc. are made correctly to scale?

5) Is it possible that the flight speed of a scale model of a commercial airliner can be scaled down to the extent that it can realistically be remote-controlled by a person on the ground in a city environment, such as a park?

6) One of the things I am asking here is: can the plane shown in this video be genuine? Or is it necessarily a hoax, made with computer graphics?

If you scale down the structure of a modern airplane, it would work nicely. Since volume scales with the third power of length, but area scales with the second power, the wing loading would decrease with the scaling factor. Therefore, the dynamic pressure required to fly would also decrease with the scaling factor, as would all aerodynamic pressures. This means that all stresses within the structure will also come down, so the structural safety margin increases with the scaling factor.

What scales less nicely are the flow phenomena. The Reynolds number will come down with the 1.5th power of the scaling factor (1 power for the length and 0.5 power for the reduced speed), so the boundary layer would be relatively thicker. This would reduce the maximum lift coefficient and would make the gaps between the high lift devices of the wings (slats, flaps) too small to work properly. A simple logarithmic scaling law works well only over small changes and can not be applied here. After all, the scaling factor is close to 60. I would guess that the maximum lift coefficient is only half of what it is for the real aircraft, so the take-off speed is reduced by a factor of $\sqrt{0.5\cdot scaling\;factor}$. If the take-off speed of the original is 260 km/h, the model could take off at maybe 45 or 50 km/h.

This is quite a bit lower than the speed of the original aircraft, but still too high to fly it comfortably in a park. A wide open field would be more suitable.

At the same time, the relatively thicker boundary layer means the drag of the scaled aircraft is relatively higher, so the L/D of the aircraft comes down. Unfortunately, the flow inside the scaled gas turbines will also be negatively affected by the Reynolds number, so they will produce little thrust. In all, I am quite sure that the scaled Airbus or Boeing would not be able to accelerate to the required take-off speed since both drag increase and thrust loss due to scaling will make this impossible.

I saved the hardest part for the end. The flow in the tiny hydraulic lines would be thick as honey (but you could increase the hydraulic pressure by the scaling factor before the lines burst!), and scaling all control circuitry would result in electronic components which would cease to work completely.

In the end, my answer would be a clear no. It will require a lot of adaptions, and only then a scale model could be made to fly.


When is an aircraft handed over from Center to Approach? I'm trying to understand how an IFR flight an ACC (center) controller communicates the hand over to the pilot to contact local airport frequencies.

I tried listening LiveAtc but my English is not so good and I still have a couple of questions. I must emulate a center hand over to local destination frequencies, is this order correct for pickup the right frequency?

Approach (if present)
Departure (if present)
Tower

Is departure eligible if an approach frequency is not available?
If approach is available, which ATC gives landing clearances, tower or approach?

Also at which distance from airport ACC should do the hand off to the approach frequency?

In general, aircraft are handed over on frequency to the next controller via a simple instruction to change the frequency:

  R: "Lufthansa One Two Tree, contact Langen Radar 128.550"
  A: "Contact 128.550, Lufthansa One Two Tree"

The simplified order of contacted stations for a commercial flight, depending on availability and airspace structure is:

  Delivery (if available)
  Apron/Ground (if available)
  Tower
  Departure (if available, sometimes handled by Approach)
  Enroute ACC/Center (multiple stations along the route)
  Arrival/Approach
  Director (if available / in use)
  Tower
  Ground (if available)

The point and altitude or flightlevel where the handoff is initiated is agreed upon in Letters of Agreement between the different sectors or ACC/ARTCC stations.

(Source: SentryRaven - Own Work)

The above picture shows the airspace around Köln/Bonn (EDDK) Airport, with the Köln Arrival East (KAE) sector being actively displayed in black. The STAR entry / clearance limit fixes are GULKO and KOPAG, in the east. Most traffic not arriving via NOR VOR in the west will terminate at these two fixes, which also serve as the handoff fix between the center controller (Paderborn High, Taunus and/or Rhein Radar Upper Control) and the arrival controller responsible for Köln East Sector. The Letter of Agreement between those sectors states that traffic arriving to Köln/Bonn via GULKO and KOPAG is to be cleared to FL100 and cleared for the respective STAR out of GULKO or KOPAG. The handoff is initiated approaching FL100 and approaching the entry fix, before the sector boundary.

The handoff is therefore based on airspace structure and sector boundaries, not on a preset distance from the airport. While arrivals from the east are handed off at FL100 over GULKO and KOPAG, arrivals from the west at NOR VOR are handed off at FL140-FL170.

Landing and Take-Off clearances are issued by the Tower controller, as the approach controller is not necessarily based at the same airport but in most cases in a remote facility together with other approach and center controllers. They have no visibility of the airport and can thus not issue these clearances.

The handoff to Tower usually happens when the aircraft is established on the final approach segment of the published approach (usually after passing the Final Approach Fix (FAF)) or a visual approach to the runway.

The phraseology is the same as above:

  R: "Germanwings Two Six Alpha, contact Tower 124.975"
  A: "124.975, Germanwings Two Six Alpha"


Does the Reynolds number on a smaller model need to match the one of the original aircraft? 1.Airbus 380-800 :
The overall length of it , is 72.72 m and its cruise speed is 903 km/h. Based on the mean chord of wing , its Reynolds number in cruise phase is around 75 millions. Now , a 1/18 scaled model is built for the purpose of wind tunnel testing. Assuming similar flow condition , the Reynolds number of wind tunnel  tests would be around 4.15 millions. This is great difference. Is Reynolds number , as a very important  similarity variable, is so different for wind tunnel testing comparison  with free flight condition, what is the advantage of performing such tests?
2.do we always need to match Reynolds number exactly?

In wind tunnel testing you need to match several similarity parameters; the most well known are the Reynolds number and the Mach number.

Since the Reynolds number depends on flow speed, viscosity and physical size while the Mach number also depends on flow speed, it looks like both can only be matched when the physical size of the model remains unchanged. But when fluid pressure and temperature are also changed, it is indeed possible to get both close to the real value. This requires an actively cooled, pressurized wind tunnel.

Such tunnels are expensive and have a long waiting list, so other tunnels exist which match both parameters less well. In that case, the researcher needs to pick which is more important and select one of the many facilities in existence.

For preliminary development, it is in most cases sufficient to test at a much lower Reynolds number and then apply correction factors, just as it has been done in the early days of aviation. If, for example, you need to find the lateral stability of a design or test its spin behavior, a smaller Reynolds number is not critical. In order to trip the boundary layer where it would have its natural transition between laminar and turbulent flow, the flight surfaces of such models have artificial roughness applied at the right chord location, so the flow is made as similar as practical.


Is it possible that as the Reynolds number increases, a laminar bubble increases in extension? I'm studying the Benedek 10355 airfoil (Plot), which should be a profile used in air-controlled models.
While I was carrying out a boundary layer analysis, I realized the particularity that I have placed in the title.
By making an incompressible analysis at Re = 500,000 and alpha = 2 deg, the profile has a laminar bubble on the upper surface (H index which diverges from 2.5 to 4 and then falls to 1.4, negative friction coefficient and plateau of the pressure coefficient) and then it also looks like a bubble on the lower surface.
In this last case, the H index starts from 2.5 reaches about 3.5 then drops to values of 2.5, a sign that the boundary layer separates but there is no turbulent transition. The friction coefficient assumes slightly negative values.
For Re = 1e6, alpha = 2 deg, the extension of the bubble on the upper surface decreases, while the bubble on the lower surface increases; H starts at 2.5 goes to 4 then drops back to 2.5 (so once again there is no transition on the belly).
A Re = 8e6, no bubbles, either on the upper or on the lower surface.
What is the cause of this abnormal behavior on the lower surface? It happens at every angle of attack, at every Reynolds.
Thanks to those who will be able to help me!

The laminar "bubble" on the bottom is caused by the wavy contour. There is a pressure rise at about 25% on the lower side which causes the boundary layer to thicken, but the subsequent flat pressure profile keeps the boundary layer laminar until it separates at the trailing edge. Here is the plot from XFOIL and I placed a green circle over the spot:

With a higher Reynolds number the flow is less stable, the boundary layer is thinner and the waviness makes itself felt more than at lower Reynolds numbers. That explains the larger "bubble" at Re = 1,000,000. With Re = 8,000,000 the boundary layer transits to turbulent flow ahead of the disturbance and no "bubble" can be observed.
I guess you play around with XFOIL. Go to MDES and PLOT the Qspec, then MODI the contour so it becomes more smooth. The result below (first pressure, then H) should prove my point:


When is International Procedures Training required? The companies that I have worked for in the past require International Procedures Training like the ones offered by Scott IPC, Flight Safety, CAE Simuflite, etc.

Under what conditions is this training required?  (I.e. do I need it to fly to Canada, Mexico, or the Bahamas or is it just to cross the Atlantic/Pacific?)

What regulation requires this training and how often is it required?

I have never heard of a specific "International Procedures"  program/rating. However, this was taken from one of the websites offering this training:

  "it will satisfy the training requirements needed for MNPS, RVSM,
  RNP-4, RNP-10, B-RNAV and P-RNAV Special Use Airspace approvals"

My guess is this course is offered as a bundle of MNPS/RVSM/RNAV training programs to the operators.

For the operator to be certified to fly in MNPS airspace, they need to have a specific authorization from the regulating authority (in FAA they specifically need OpSpecB039) which in turn, requires specific training programs for the pilots. The same is valid about operation in RVSM,RNAV,etc.

There is no specific recurency training period; however, each approval certificate, for each specific operator, must include an approved 'initial and recurrent training program' which will specify the training frequency. At most, these periods must abide
by the operator's program for proficiency check and line checks.

8900.1 4.1.4 98(d)

  NAT/MINIMUM NAVIGATION PERFORMANCE SPECIFICATIONS (MNPS) AIRSPACE.

  Each  aircraft is suitably equipped and capable of meeting the MNPS standards.
  The operator has established operating procedures that
  ensure that MNPS standards are met.
  The flightcrews are trained and capable of operating to MNPS requirements.

  [...]

  All NAT/MNPS approvals are granted by issuing OpSpec paragraph B039,

ICAO NAT Doc 007 § 1.2.1 (I'm really not an FAA guy, somebody might find the Part 135 / 91 equivalent)

  All flights within NAT MNPS Airspace must have the approval of either
  the State of Registry of the aircraft, or the State of the
  Operator[...] These aspects include: the navigation equipment used,
  together with its installation and maintenance procedures; plus the
  crew navigation procedures employed and the crew training
  requirements.

  The ICAO doc goes on to further detail what that training should include (1.3.8 - > 1.3.12), but does not specify a training frequency or the need for recurrent training.

Appendix G to Part 91: Operations in Reduced Vertical Separation Minimum (RVSM) Airspace
Section 3 Operator Authorization

  (b)An applicant for authorization to operate within RVSM airspace
  shall apply in a form and manner prescribed by the Administrator. The
  application must include the following:

  (2) For an applicant who operates under part 121 or 135 of this chapter or under subpart K of this part, initial and recurring pilot
  training requirements.

AMC1 SPA.RVSM.105 RVSM operational approval

  (c) Training programmes, operating practices and procedures :
      The operator should submit training syllabi for initial and recurrent training  programmes together with other relevant material.


What are the advantages of electrical systems over pneumatic systems? What are the advantages of using electrical systems as a alternative to pneumatic systems in the Boeing 787-9? Is it a maintenance advantage?

Just on example: The energy taken from the engine as bleed air is contained in this bleed air as heat and as pressure. Now pipe this energy to someplace where it is needed, and the air will cool down and lose some of its pressure. Also, if you want adequate insulation and low transmission losses, the cross section for the piping will be substantial.

Compare this to taking the energy from the engine by a driveshaft turning a generator: Friction losses will be a few percent at most, energy conversion in the generator will be at above 90%, and transmission losses are low again if your cable cross section is sufficient. Note that the cables will be much thinner than any bleed air line would ever be.

Add to this the advances made in converting electrical energy between different voltages and frequencies, and it becomes clear that modern aircraft systems can be made more efficient when run electrically. The use of compressed, hot air was only a better choice when modern power electronics were not yet around.


What are the requirements to take the private pilot check ride? In the US, what are the requirements that a student pilot must demonstrate to their examiner  before they can take a checkride for their private pilot airplane certificate?

Private Pilot Airplane Single-Engine Checkride Requirements

Eligibility Requirements (14 CFR 61.103)

Be at least 17 years of age for a rating in other than a glider or balloon
Be able to read, speak, write, and understand the English language
Instructor logbook endorsement certifying your aeronautical knowledge (14 CFR 61.105) and that you are prepared for the written test
Passed the written test and can present your original embossed Airman Knowledge Test Report
Instructor logbook endorsement certifying your flight proficiency (14 CFR 61.107)and that you are ready for the flight test
Log all required aeronautical experience (below)

Aeronautical Experience (14 CFR 61.109):

40 hours of flight time (35 for 141 schools) that includes:

20 hours of dual instruction
10 hours of solo flight training

3 hours of cross-country dual
3 hours of night dual (to get an unrestricted license) that includes:

1 cross-country flight of over 100 nautical miles total distance
10 takeoffs and 10 landings to a full stop (with each landing involving a flight in the traffic pattern) at an airport

3 hours of instrument dual
3 hours of dual in preparation for the practical test within 2 calendar months
10 hours of solo including

5 hours of cross-country time
1 150 NM solo cross country flight, with full-stop landings at three points and one segment of the flight consisting of a straight-line distance of more than 50 NM between the takeoff and landing locations
3 takeoffs and 3 landings to a full stop (with each landing involving a flight in the traffic pattern) at an airport with an operating control tower