Is someone holding an EASA PPL (A) allowed to operate a "November" registered aircraft in Europe? Is someone who holds a current EASA PPL(A) allowed to operate an FAA "November" registered aircraft in Europe? Of course I'm talking about a type of aircraft and of operation he or she would be allowed to conduct with an, for example, German-registered aircraft.

This is regulated by the FAA in FAR 61.3 and local regulations specific to each country

  (a) Required pilot certificate for operating a civil aircraft of the
  United States. No person may serve as a required pilot flight
  crewmember of a civil aircraft of the United States, unless that
  person:

  (1) Has in the person's physical possession or readily accessible in
  the aircraft when exercising the privileges of that pilot certificate
  or authorization—

  (i) A pilot certificate issued under this part and in accordance with
  § 61.19; (ii) A special purpose pilot authorization issued under §
  61.77;

  (iii) A temporary certificate issued under § 61.17;

  (iv) A document conveying temporary authority to exercise certificate
  privileges issued by the Airmen Certification Branch under § 61.29(e);
  or

  (v) When operating an aircraft within a foreign country, a pilot
  license issued by that country may be used.

To operate a US-registered aircraft you either need an FAA license or a pilot license issued by the country where the aircraft is operated in. This also means that you are not allowed to fly into another country, unless you also have a license issued by that country. Even if individual countries allow foreign registered aircraft to be operated by a license holder of another (non-FAA) country, it would still be a violation of FAR 61.3.

Bottom line: if you want to fly a N-registered aircraft without an FAA pilot license in Europe, you need a pilot license issued by every country you're flying into. For example, if you plan a trip from The Netherlands to Portugal you would need 5 different EASA PPL licenses issued by The Netherlands, Belgium, France, Spain and Portugal.


Could a wing be designed to exploit both normal flying and ground effect? Ground Effect planes' wings are stubby and the height over the ground or water is limited to wing span.
Could a wing be designed to exploit both normal flying and ground effect together to give the plane more clearance over waves without loosing all the benefits of the ground effect?

Ground effect is measured using the non-dimensional height parameter 'h/c', i.e. the height above ground divided by the chord length. By increasing the chord length, the height of the maximum efficiency height is raised, as the location of the h/c does not change.
Increasing the span also adds efficient lift due to aspect ratio effects, however creating too much lift is not always better, because it will move the operating altitude above the most efficient height (h/c max).
Ground effect therefore favours larger chord length to get the required ground clearance, however larger aspect ratio wings are better for atmospheric flight. An aircraft could be designed to operate in both modes, but it will always be a trade-off between efficient ground effect flight and efficient atmospheric flight, there is always going to be a compromise of one or the other or both.


What is this weapon spotted at an airshow in South Africa? I was at an airshow in South Africa, and they had this trailer sitting about.  No one knew what it is.

Those little red plates all say "warning, high voltage".  Those buckets are open at the bottom, and made of aluminium.

These finned pointy things are hollow, not sure what they are made of.  Were not solid plastic, but didn't look like fiberglass either.

A couple of specific questions:

What is it?
If the hollow things are covers, why are they so oddly shaped?  And if they are covers, why do they share features with liquid tanks?
Why are there half a dozen "High voltage" stickers attached?
What are those bins and chains?

@mins got this one right. It's a British Tigercat short range surface to air missiles launcher system. The cones are protective weather covers for the missiles which are removed prior to launch.

As to the 'buckets and chains' I'd venture a guess that they are a device to deflect and dissipate the rocket blast during launch but I am not totally sure. But they can be seen on YouTube (at 0:07 and 0:39).

From YouTube, on the right the blast being deflected up/down.


How safe is the Beechcraft 1900? While reading the tragic Accidents and incidents section of this Wikipedia page, I began to wonder how the Beechcraft 1900 ranks for safety.

The page describes 22 known severe accidents and incidents involving the Beechcraft 1900.  According to the article, there were 695 of the aircraft built, with just 341 in service as of July 2015.  That's less than half.

How does one compare these statistics to the norm?  How does the Beechcraft 1900 rate when it comes to safety?

I would say that it is a reasonably safe aircraft, but, like most aircraft of that class, often operated in unsafe conditions.
The Wikipedia page does not have description for many of the listed accidents, but you can turn to the Aviation Safety Network which does.
There are 41 total hull losses listed there. From them:

Most common type of accident is controlled flight into terrain. That has nothing to do with the type and everything with operating to/from remote airports in mountainous terrain with limited choice of navigational aids around.
Then there are quite a few collisions, both midair and on the ground. That also has nothing to do with the type and much with operating at smaller fields often under VFR and without any radar.
Then there were several accidents where pilots mishandled engine failure. The aircraft is capable of flying on one engine and it had to be demonstrated during certification, but the pilots have to follow the correct procedure and may easily lose control if they don't. This kind of accident is more common in turboprops than in jets, but it does not seem to be more common in B1900 compared to other turboprops.
Only the three accidents that were contributed by improper installation of elevator or elevator trim control cables really have something to do with the specific type. They still have a lot to do with operating by smaller airlines and maintaining in smaller facilities with less experienced staff.

So no, the relatively long list of accident does not suggest any serious problem with the type.
Also, the accident rate and types are similar to the other types used in similar operating conditions like DHC-6, EMB-120, L410 or Do-228.


What Does "By ATC" Mean for an SID Route? I can understand that altitudes may be "by ATC", but why can a route also be marked with "by ATC"? All SID routes need prior clearance by ATC, right?

For example, in SID RWY 16 for ZGSZ/SZX, MEPOG-7X and LKC-7X are "by ATC", while others are not. I know that LKC-7X is not a regular route flown, but still: what does "by ATC" mean here?

(Source: ZGSZ AD 2.24-7F, AIP China)

It means, don't file that transition yourself.  ATC may assign it, but it's their option to assign it or leave you on what you filed.


why does the flow need to decelerate (by a thermal throat) in a scramjet? I have a question about the thermal throat in a scramjet. From my textbook:

"The scramjet, on the other hand, needs an area increase as combustion occurs. For this reason, on the scramjet the mechanical throat is substituted by a thermal throat that decelerates the flow through
tailored heat release."
why does the flow need to decelerate in a scramjet?
if flow in a scramjet is supersonic, wouldn't heat release
accelerate the flow? (from general 1d form of equations du/u=1/(M^2-1)*(dA/A+dF/P-dQ/CpT))
Where is the thermal throat in this flow located?

I found an answer, for those who are curious. The thermal throat described in a scramjet is not an ideal case. Essentially, when the flow is supersonic, heat addition done in the combustion chamber can slow the flow down to subsonic speeds (based off the 1-d heat velocity, Rayleigh Flow). When this happens the flow is considered thermally choked, and is a bad case for this engine. To prevent this thermal choke from happening, the area of the combustion chamber increases with the direction of the flow (area increase increases velocity for supersonic flow).


What is the difference between a trim tab and a servo tab? They both seem very similar but can someone please explain their main differences and principle of operation?

A trim tab is operated by an independent control to a variable position that is normally fixed once set, unless readjusted, and is done to cause the control surface to aerodynamically want to hold a position that is different from its normal "trail" position, without any input from the cockpit end.  Think the typical elevator, aileron, or rudder trim used to correct a roll or yaw tendency, or to set the "hands off" trim speed in the case of elevator trim.

A servo tab is integrated into the flight control's operating components in such a way as to drive, or help to drive, the control surface during normal control inputs.  Sort of "poor man's power steering".

You can use a servo tab to operate the control surface, that is otherwise free to trail in the airstream, completely on its own.  The stick in the cockpit is connected only to the servo tab itself.  Such control surfaces will often hang down at the bottom of their travel until airspeed "blows" the surface into its normal trail position, from where the servo tab then drives the surface up or down based on cockpit control inputs.  DC-9s and Bristol Britannias use pure servo tab operated flight controls.

Or you can use the servo tab in conjunction with a normal control circuit to boost a normally mechanically operated surface, by mechanically gearing it to move in a way that applies a local aerodynamic load that helps with the pilot control input, like having someone push on the trailing edge to help you while you move the controls.

There is a kind of hybrid arrangement you will see sometimes, called a "Spring Tab".  This is a servo tab who's input linkage is also connected to the control surface by a torsion spring torque tube, typically on an elevator system.  When you move the control in the cockpit, the control circuit input drives the surface directly, but though the springy torque tube so the surface lags the input to the extent that the torque tube twists under load.  When the torque tube twists, at the same time the input side is connected to a servo tab that displaces to help the surface move.  The surface works like a pure servo tab driven one with small inputs, but as the inputs get larger there is more of a direct force acting on the surface from the torque tube like a regular control.

This is used to get the light control forces you get with a pure servo-only driven control surface, but with the ability to still drive the surface directly to full travel when called for.  Spring tabs are popular on DeHavilland Canada transports like the Dash 7 and Dash 8.

Then there is the "anti-servo" tab. The anti-servo tab, by gearing to move in the opposite direction to a servo tab, is used to deliberately increase the normal restoring forces working on the surface when displaced from its trail position. You might add an anti-servo tab because the control forces are too light, or you want light forces near neutral but want the forces to build faster than they would without the anti-servo tab.

Mechanically operated "all flying", or Stabilator tails, such as used on the Cessna Cardinal and Piper Cherokee line, depend on an anti-servo tab to provide all of the restorative forces for the control surface, for basic stick-free static pitch stability.  They actually do double duty, and at the same time have an adjustable fixed "neutral" position, varied by the trim wheel in the cockpit, that provides for normal elevator trim (speed seeking).


What brakes are used between line-up and takeoff? I was wondering if an airliner was instructed to line-up on the runway ("line-up and wait"), will the park brake be used or will manual braking be used (pedals) during the wait until the take-off clearance is given? Same for holding short the runway before line-up / take-off clearance? Does it make a difference which brakes are used in the first place?

Just toe brakes. Typically the instruction between line-up-and-wait and clearing for takeoff is very short, maybe ten seconds.
In simpler aircraft, the parking brake just "pinches" or closes off the brake fluid line to keep the wheel brakes held, but in the fly-by-wire airliners, the parking brake just clamps the normal wheel brakes as if the toe brakes were held.


Why is landing on a carrier not handled by a computer? Landing on a carrier seems like a difficult and risky task for military pilots, especially at night when the carrier should keep low profile and is practically unlit.

It seems exactly like a problem which can better be performed by a computer rather than a human being. A machine can take in account exactly the motion of the carrier and other parameters and land the aircraft precisely where it should. The fact that there should be no enemy aircraft nearby also means that the initiative of a pilot is not needed.

The system can:

Either be exclusively inside the aircraft (doing image recognition of a carrier and trying to determine where to land; not sure how easy and reliable this can get),
Or be presented as a subsystem within the carrier which sends the encrypted information to the authenticated aircraft about the exact position of given points of the carrier and a second subsystem inside the aircraft which relies on this information to make the controlled landing.

Why isn't it handled (yet) by a computer? Are there projects of implementing such system?

Computers can, in fact, control the approach of a Super Hornet all the way to touchdown.  However, there are limits to the sea state. Gross deviations in glide path resulting from a pitching deck would make a coupled approach impractical.

However, the most compelling reason to hand fly all our approaches is that we fly a $60 million jet. Murphy's Law tells us that the most junior guy, with the least experience behind the boat, is going to get an engine fire, at night, in rough seas.  If our fictional JO wasn't proficient hand flying the ball behind the boat this could result in catastrophic consequences including both the loss of aircrew and aircraft. As often as possible, we prepare for the 1 percentile, not the 99th percentile, so when we do get that engine fire at night we get the upgrade OK, and not the cut pass/ ejection.

Plus, its just plain eerie letting the jet fly itself to the boat, and the current system isn't reliable enough that most guys would feel comfortable letting it fly itself on a regular basis.

Edit:  Heck, new guys aren't even allowed to perform auto approaches (auto throttle) to the boat for the same reason.


What is the physical definition of turbulence? To aviators, the definition of turbulence by measuring the results is widely known: example. But if we were to generate a turbulence forecast as a meteorologist, there need to be some kind of physical parameters that constitute the different levels of turbulence.

Maybe something like "wind vertical velocity" or "vorticity" etc. ...

What are these parameters and what different levels are defined?

Image source

Turbulence is merely the measure of Reynolds number of a fluid at rest or motion ( (turbulence occurs when fluid is in motion) let's say you light up a cigarette and when the smoke is at the tip of cigarette you see it flows upwards uniformly and this is because the fluid is in laminar flow and as it expands into its vicinity it becomes turbulent. so what is the physics here? basically, reynolds number defines if a fluid is laminar or turbulent. Reynolds number is defined as the ratio of inertial to viscous forces experienced on a body. when divided it gives a number without any units. If the Reynolds number is less than 2100 then the flow is laminar and greater than 4000 it's turbulent and if it's between 2100 and 4000 its transitional flow (which is rare and instantaneous)


When Airplane is reducing altitude from flight level (cruise), which one is more efficient When an airplane is reducing altitude, say due to preparation for landing, the nose is tilted down. That I got from a video on Youtube which explains the way an airplane is going down until it reaches a certain altitude and until the nose is revert to tilt up. Then my question:

Is that explanation true that during reducing altitude the nose is tilted down?
Which one is more efficient compare to if the airplane is tilted up as the position of an airplane when it landing. "Efficient" here is about which one faster, more fuel efficiency.
What is the allowed maximum angle tilt down nose?

There are (mostly) two ways to reduce altitude:

Reduce speed until your wings don't generate enough lift in level flight. Typically the nose will drop by itself since you are no longer at your trimmed airspeed. You might be able to re-trim so that you are in a level descent.
Drop the nose manually without reducing (or even increasing) speed

Airliners at altitude operate very close to what is called the coffin corner where an increase in speed means you overspeed the aircraft, and a reduction in speed means you stall. So preferably the pilot will simultaneously reduce the throttles while lowering the nose to maintain a specific speed.

Tilting the aircraft up (nose up) will reduce your speed and eventually you will fall to the earth (as you stall). This is a very inefficient way to get down (not to mention it scares the hell out of the passengers). The aircraft buffets, a wing may drop if the plane is not kept coordinated, and is overall a very dangerous thing to do (see the coffin corner link above).

The reason the nose is raised while landing is so that the aircraft can bleed off extra speed and reduce the descent rate for touch down (as well as reducing the stress on the nose gear). This is also a high-drag situation and is, in that effect, inefficient.

  What is the allowed maximum angle tilt down nose?

90° because after that you're tilting up...

In all seriousness you can nose-down until you hit the maximum airframe speed without causing damage. For airliners this is usually a lot more than passengers are comfortable with (especially if the stewards have the rolling carts out), so pilots make a concerted effort to keep the floor as level as possible. For smaller aircraft like the 172, you can configure it such that you won't exceed this speed and point the thing almost straight down, it's actually pretty fun.


Was a six-engine 747 ever seriously considered by Boeing? The Boeing 747 can carry a fifth engine on the side. As the airframe looks quite symmetric, I think that it would not be big work to hang a sixth engine on the side as well.

From here, we seem to be quite near to the six-engine aircraft - a few extra pipes and wires are probably all we need to get these engines turning.

Was a six-engine 747 present at some time of its development history? I think this could be, assuming:

less powerful engines than eventually were available
maybe it could take off with less runway
some special uses with very heavy payload.

There are no six-engine variants mentioned, built or proposed, on Wikipedia.

The expected answer would mention some sources relevant to the design decisions through the history of this aircraft.

The "fifth engine mount" option on the 747 is not designed to handle a running engine. It was an option used only by Qantas as a means of ferrying spare engines to remote locations, where flying a plane for a long distance to a maintenance facility on three engines was not possible. Only four of the Qantas fleet of 747s (totalling more than 60 aircraft) had this fifth engine option.

The mount for the fifth engine was not designed to transmit any thrust the engine would have delivered if it was running, and it fact the engine is partially disassembled by removing the fan to reduce drag (which reduced the loads on the 5th engine mount, as well as drag on the plane as a whole).

Some pictures and videos here: https://www.flightradar24.com/blog/how-qantas-ferried-an-engine-on-the-wing-of-a-747/

To convert this into "a 5 or 6 engined plane" would require a lot more than just "a few pipes and wires". The wing structure would have to be redesigned to handle an extra 50,000 pounds (or more) thrust from each extra engine, plus the extra weight of a proper pylon and nacelle structure. Considering the aerodynamic wing flutter problems with the initial 747 design, sticking another two engines on the wing would most likely have required a complete redesign of the wing.


What are the bars protruding from this C-130? This C-130 was photographed on approach to Ellington Field (EFD), Texas.

What are the protruding, truss-supported bars aft of and below the wing?

There's an airshow coming up in ~3 weeks at EFD, so it may have something to do with that, especially considering the fancy underwing paint job.

It is a civilian owned C-130 Hercules used for aerial spraying operations. It is owned by the International Air Response company based out of Mesa, AZ.

The aircraft is equipped with a RIDSS spray system for use in things like oil spill response (for spraying dispersants). You can read more about the system here.


Can thrust be produced only using the forward speed of a nozzle? Why can't a nozzle that is already in relative motion to the air produce thrust by speeding up the air that passes through inside it?
So let's pretend you're in a glider with two converging nozzles (without fans or burning fuel), one attached to each wing. Shouldn't the air passing through speed up due to continuity, and provide a forward force on the plane?
Obviously this does not work in real life so I would like to know why. Is it because the bottom an top surfaces essentially function as a diffuser, which slow the air around?

Something has to provide the energy that is needed to accelerate the air.
In the simplest combustion engines this is the combustion heat. Air expands when heated and when the route out the back is the easiest to take, it will flow that way. More complicated engines use this heat energy to raise the pressure of the air inside the nozzle so there is excess pressure energy that can be converted into speed.
In your converging nozzle there is no excess energy available. In order to stream out the back, the air must have at least ambient pressure when leaving the nozzle. In order to speed up, the pressure ahead of the nozzle must be higher than ambient. But since the air enters the converging nozzle already with ambient pressure and flight speed, it cannot accelerate any more. Instead, the face of the nozzle will block all the air that will not fit through the smaller exit cross section, forcing it to flow around your nozzles. This is almost as effective for producing drag as putting a solid disk into the air stream.


What factors contribute to the poor off design performance of turbofans? I am looking to understand why turbofans have a higher specific fuel consumption when ran at lower power settings and what can be done to improve it.

How much does the rpm of the various spools and load factor in? Which carries a greater weight in the efficiency? If the engine were at full speed (like a turboprop) but low load would the efficiency drop much? Perhaps a variable pitch fan is the best solution even as difficult as they are to make?

Would it make sense to use an electric motor as a torque fill or to increase the rpm of the compressors when at lower power settings? I have read about regenerative cycle engines which feed heat back into the combustor but these only seem to add a small amount of efficiency in practice.

Thank you.

I am looking to understand why turbofans have a higher specific fuel consumption when ran at lower power settings and what can be done to improve it.

Actually, a turbofan has a higher efficiency at lower than max (read take off) performance. Why? Engines spend the majority of their life at cruise conditions, so compressors, turbines and fans are designed and optimized to deliver the cruise performance at the best efficiency that is possible according the technology at design time.

The manufacturers achieve this by designing the optimal blade shapes and angles for the condition the most amount of time is spent. Obviously, when you are further away from that optimal point the more likely you encounter non ideal conditions which lead to less efficient flow around the blades and as such this is translated to a higher specific fuel consumption. This is illustrated by the compressor/fan off-design characteristics, also known as compressor/fan map. A compressor/fan map shows the relation between the pressure ratio, efficiency and the corrected (non dimensional) mass flow for various spool speeds. This is shown from the Wiki image shown below:

Note that this is the performance of the isolated compressor, when connected to a turbine, an equilibrium (operating) line is established, ultimately, this operating line should follow the path of the "Peak efficiency line". This compressor map also shows than for a high spool speed (N4) to a low spool speel (N0) the efficiency first increases, to later decrease again. This is caused by the design and the way the flow enters the compressor stages and is exactly why the performance of the compressing turbomachinery has not the same efficiency throughout the whole operating area.

If you would sweep an engine (for real or through a simulation) from take-off power to idle power, the specific fuel consumption would decrease to cruise power to increase again to idle power. This graph, from a simulation of high power setting to a low power setting of an older turbofan engine with a bypass ratio of about 5, illustrates that:

  Perhaps a variable pitch fan is the best solution even as difficult as they are to make?

Variable pitch fans are needed when the fan pressure rise becomes low (below about 1.35); these low pressure ratios are seen in very large (geared) bypass designs as on the Rolls Royce Ultrafan design.

  Would it make sense to use an electric motor as a torque fill or to increase the rpm of the compressors when at lower power settings?

It would make sense to assist during take-off so that you essentially can use a smaller engine. Take-off power is several times more than cruise power. Also, the powers in gas turbines are so high and the electric motors are very big and heavy (and certainly the batteries) that this can be seen entering in the very far future. This is commonly known as hybrid propulsion.

  I have read about regenerative cycle engines which feed heat back into the combustor but these only seem to add a small amount of efficiency in practice.

Indeed, recuperating heat from the exhaust (which is on of the 3 major losses in gas turbine engines) would mean that you have to use less fuel to get to the same combustor exit temperature. This has been investigated in the European Clean Sky 2 project called NEWAC. The problem with recuperating heat is that on one side you have the highest (combustor/high pressure compressor exit) pressure, and low exhaust pressure on the other side, causing mechanical challenges. Also the core flow is at an enormous high speed, so there is little time to exchange heat; this means you need a very big surface area to exchange the heat. The bigger the area, the higher the weight, the higher the weight the heavier the aircraft the more drag and thus power are required.


How do people smuggle stuff with private airplanes? I get it, the question seems as if I'm reaching out for answers from experienced smugglers! But no. As a matter of fact, I'm trying to get answers on air surveillance & security.

Love it or hate it, these kind of smuggles are being done all over the world. However, recently I heard a story from a retired soldier stating that he used to know people who knew people who smuggled jewelries, hard drugs, guns and even people from middle eastern countries to Europe, specifically, Germany! Via planes!

In fact, he said some stuff was too valuable for them to "risk it" by land transports. He added that the pilots were experienced World War II pilots who specialized in flying at high speed in very low altitudes to make deliveries for infantry units on distress, making them unnoticed on radars and unstoppable for air defense systems.

So that's for World War II, which ended on 1945, so the question is, how can people still do this considering all the enhancements and improvements or even inventions (which some boldly have "foolproof" labels attached to their names) implemented on radar and satellite technologies? Especially on a country like Germany, with superb defense and military status?

There are lots of ways to smuggle goods with planes and it depends what you are smuggling and the aircraft on which you are smuggling it. Smugglers often bank on the fact that most countries do not have or allocate the resources to search every aircraft throughly enough from top to bottom before every flight as that is simply impractical on some level. Some times all you need is a good audio equipment road case.

Generally you need to get past customs which happens on the ground and is its own set of issues. In the USA the Customs And Border Protection takes care of a lot of the searching. Smuggling sometimes happens on commercial aircraft and there is plenty of info on it here on the CBP website. In this case the goods are smuggled on aircraft that are very much on radar and flying at assigned ATC speeds. Sometimes they are even loaded by official personal. On occasion even the head honcho is involved, moving some strange things.

It is possible to "fly under the radar" but that also depends on where you are going and what their radar coverage is. Steps have been taken over the years to combat this issue. It seems that some of the smugglers have once again resorted to small aircraft.

Barry Seal, the inspiration for the movie American Made was historically a pretty prolific smuggler. The movie takes some poetic license but is based on some facts.

  Seal used his knowledge of aviation to become the infamous smuggler he
  was. Once in U.S. airspace, Seal would drop to 500 feet and slowed to
  120 knots to mimic, on radar screens, helicopters which frequently
  flew from oil rigs to the coast.

  Within U.S. airspace, Seal would have people on the ground monitor for
  any signs his planes were being tailed. If they were, the mission was
  aborted. If not, they would continue on to drop sites over the
  Louisiana bayou, where duffel bags full of cocaine were dropped into
  the swamp. Helicopters would pick up the contraband and take them to
  off-loading sites, and then on to Ochoa distributors in Miami by car
  or truck.

Smugglers are still attempting to move product in older, but fast, biz jets with fake or missing registrations. To avoid being discovered they are apparently destroying the planes after they use them sometimes.

There is a great article on some of the history of air smuggling here. Which dates back to the early days of aviation.

This is a fairly interesting story...

Just remember, aviation smuggling is Illegal very illegal


Why are engines angled toward the fuselage? Source: twitter.com

I saw a picture of a 777 from overhead and I was wondering why the engines point "in" to the fuselage, rather than being parallel to the fuselage.

It's called 'toe-in' and it's done basically to match the local airflow which is slightly divergent (heading outboard along the underside of the wing). If the engines were mounted exactly parallel to the fuselage, they would be moving slightly obliquely through the local airflow and therefore incurring extra unnecessary drag.

Another view of a 777 showing the engine toe-in:

  Source: airliners.net

The Boeing 747 has a 2 degree toe-in on all four engines, as can be seen in the following plan:
[Key: BBL 0 = Body Buttock Line zero, the centreline of the fuselage; WBL = Wing Buttock Line, parallel to that centreline; NAC BL0 = Nacelle Buttock Line 0, the centreline of the nacelle body]

and in this photo:

For rear-engined aircraft, the opposite is true: the engines are mounted slightly' toe-out' to match the local airflow which is converging around the tail of the aircraft.


Where can I find/download infos about Special Use Airpsace (SUA) around the world? I would like to know if there are any websites where I can find information (and possibly download it) about Special Use Airpsace (SUAs) around the world in terms of time validity, geographical coordinates, flight level restrictions...
If am not mistaking, aixm.areo is a website where I can find such information regarding the European region; I would like to know if there are other websites that allow to download such infos for the rest of the world (North America, South America, Africa, Asia, Oceania....)

If you know please could you also provide some links?

Note: the following quantities should be contained:

time validity
geographical coordinates (lat/lon)
flight level restrictions

EU: aixm.aero

France: sia.aviation-civile.gouv.fr

Upper space
RTBA map (military, low altitude)

USA: sua.faa.gov

AIXM Data: nfdc.faa.gov

Diverse locations: soaringweb.org

This is a community wiki, just add to it.


How much extra work to get a glider licence? I have my SEL Private VFR licence.  I recently went on a glider flight, and I loved it.  How much extra work does it take a typical pilot to transition from SEL to gliders?

What extra material will I have to learn?  And what overlaps?

(I am assuming your question is asking about the FAA regulations.)

If you already have a PPL, then the requirements are modest. According to the Soaring Society of America:

  Additional Pilot Rating
  Holders of a valid FAA Power plane license with 40 hours as pilot-in-command need a minimum of 10 solo flights to qualify to take the glider flight test. No written exam is required to add a glider rating to a power license. In all cases, refer to the Federal Aviation Regulations for details on pilot licensing.


What happens with the avionics if in midair there is loss of power or fuel flow interrupted? What happens if in midair there is loss of power, how will the avionics perform in such a situation (cockpit display, flight plan)?

This is somewhat dependent on the aircraft of course, so I will focus on the Boeing 737 NG series as an example of a typical airliner. Details will differ with other aircraft, but the general concept should be the same.

When there is loss of thrust on both engines, both engine driven generators will stop providing power. The battery will take over powering some of the systems immediately. If two batteries are installed, all emergency systems can be supplied for at least 60 minutes:

  Two 24 volt nickel–cadmium batteries, main and auxiliary, are located in the
  electronics compartment. The batteries can supply part of the DC system. The
  auxiliary battery operates in parallel with the main battery when the battery is
  powering the standby system. At all other times, the auxiliary battery is isolated
  from the power distribution system. Battery charging is automatically controlled.
  Two fully charged batteries have sufficient capacity to provide standby power for
  a minimum of 60 minutes. Battery voltage range is 22–30 volts.

(Boeing 737 NG FCOMv2 6.20.12 Electrical - System Description)

The batteries power some DC buses directly and the AC standby bus via a static inverter:

  Standby Power System - Normal Operation

  The standby system provides 115V AC and 24V DC power to essential systems
  in the event of loss of all engine or APU–driven AC power. The standby power
  system consists of:

  static inverter
  AC standby bus
  DC standby bus
  battery bus
  hot battery bus
  switched hot battery bus
  main battery
  auxiliary battery.

  [...]

  Static Inverter

  The static inverter converts 24 volt DC power from the battery to 115V AC power
  to supply the AC standby bus during the loss of normal electrical power. The
  power supply to the inverter is controlled by the standby power switch and the
  battery switch on the overhead panel.

(Boeing 737 NG FCOMv2 6.20.16 Electrical - System Description)

The FCOM contains a long list with all systems that are powered in this configuration. In general, only the captain's side instruments will be available. I will not quote the full list here, since you only asked about "cockpit display, flight plan". The relevant items are:

  All Generators Inoperative

  The following list identifies the significant equipment that operates when the main
  battery and the auxiliary battery are the only source of electrical power.

  emergency instrument flood lights
  Captain's pitot probe heat
  VHF No. 1
  upper display unit
  Captain's outboard and inboard display units (EFIS/MAP or PFD/ND)
  clocks
  left EFIS control panel
  Standby instruments
  FMC
  left CDU
  heading/track indications
  VHF NAV No. 1
  ILS No. 1
  left IRS
  left GPS

(Boeing 737 NG FCOMv2 6.20.19 Electrical - System Description)

This allows the Captain to continue flying the aircraft via manual reversion (no hydraulic pressure will be available, no autopilot is available). An emergency descent will have to be initiated without thrust. The checklist in the QRH will aim at restarting one or both engines. If that fails, the APU can be started in flight below 25,000 ft to provide more electrical power (all AC buses powered, all displays available again, electric hydraulic pumps available again).


Can I use cellular data to receive in-flight weather on my iPad? I would like to use an iPad for preflight planning. Can I also use the iPad to check weather while I'm en route?

Can you? Yes, but service might be slow or spotty.

May you do so legally? That probably depends. The FAA doesn't specifically prohibit the use of any electronics in GA aircraft; they only state that under 14 CFR §91.21, those aboard an IFR aircraft can't operate electronic devices unless they are

  Portable voice recorders;
  Hearing aids;
  Heart pacemakers;
  Electric shavers; or
  Any other portable electronic device that the operator of the aircraft has determined will not cause interference with the navigation or communication system of the aircraft on which it is to be used. [emphasis mine]

It's possibly questionable that you as the pilot are an authority on whether or not your devices will cause interference.

The FCC, however, has banned the use of cellular phones in flight per 47 CFR §22.925:

  Cellular telephones installed in or carried aboard airplanes, balloons or any other type of aircraft must not be operated while such aircraft are airborne (not touching the ground). When any aircraft leaves the ground, all cellular telephones on board that aircraft must be turned off.

Whether or not that can be interpreted to apply to an iPad's 3G connection is pretty iffy.


How can you fly at 0kts without stalling? At 0g, stall is theoretically impossible.

In practice, can a maneuver be performed that, by bringing the aircraft to, or very close to 0g, also brings the aircraft to a temporary standstill, or near standstill, in terms of true air speed?

Can such a maneuver be performed without exceeding 30° pitch?

If so, how?

No, stalls can occur at any airspeed, attitude, or load factor.  All that is needed is to exceed the critical angle of attack and you have stalled the airplane.

Some places this can occur and does happen if mishandled by the pilot is at the top of inside loops, where the airplane can come very close to a zero airspeed if it's done wrong.  Another place this does occur is a hammerhead stall where the stall occurs in the vertical, just as the aircraft is at or comes very close to zero airspeed.


Where can I find the various operating limitations of the ATR 72-500? Where can I find the various operating limitations of the ATR 72-500? Is there any document that lists them?

LIMITATIONS

  PAGE : 001 APR 11 EASA APPROVED

  Model : 212 A
  AFM 1

  2.01.01 | INTRODUCTION

  Observance of the limitations contained in this chapter is required by law. When
  operating in accordance with an approved appendix or supplement to
  this manual, the limitations of this basic Airplane Flight Manual
  section apply, except as altered by such an appendix or supplement.

  2.01.02 | KINDS OF OPERATION

  The airplane is certified in the
  Transport Category, JAR 25 and ICAO annex 16 for day and night
  operations, in the following conditions when the appropriate equipment
  and instruments required by the airworthiness and operating
  regulations are approved, installed and in an operable condition :

  VFR and IFR
  Flight in icing conditions.
  Reverse thrust taxi (single or twin engine)

  2.01.03 | MINIMUM FLIGHT CREW

  2 pilots

  2.01.04 | PERFORMANCE CONFIGURATION

  Refer to 6.01.03 for airplane configuration associated with certified
  performances.

  2.01.05 | MAXIMUM OPERATING ALTITUDE

  25000 ft

  2.01.06 | MANEUVERING LIMIT LOAD FACTORS

  Gear and flaps retracted : + 2.5 to -- 1 g
  Gear and/or flaps extended : + 2 to 0 g

  2.01.07 | CONFIGURATION DEVIATION LIST

  Refer to 7.01.02

  2.01.08 | NOISE CHARACTERISTICS

  The aircraft meets the requirements of ICAO annex 16,
  Chapter 4 with no weight restriction. Refer to noise characteristics
  in Appendix 7.01.01 of this manual for noise levels.

  2.01.09 | MAXIMUM NUMBER OF PASSENGER SEATS

  74 as limited by emergency exits
  configuration

  2.02.01 | WEIGHTS

  STRUCTURAL LIMITATIONS

  MAXIMUM WEIGHT KG LB

  RAMP 22970 50640
  TAKE-OFF 22800 50265
  LANDING 22350 49273
  ZERO FUEL 20800 45856

  PERFORMANCE LIMITATIONS

  Maximum take-off weight and maximum landing weight may be reduced by performance
  requirements related to the following (see chapter 6) :

  climb performance (first and second segment, final take-off and en route, approach and landing climb)
  available runway length (take-off and landing)
  tyre limit speed
  brake energy limit, observe BRK TEMP alert for take-off
  obstacle clearance (take-off and en route)
  en route and landing weight

  2.03.01 | AIRSPEEDS

  MAXIMUM OPERATING SPEED VMO / MMO

  This limit must not be intentionally exceeded in any flight regime.

  VMO = 250 kt CAS
  MMO = 0.55

  MAXIMUM DESIGN MANEUVERING SPEED VA

  Full application of roll and yaw controls, as well as maneuvers that involve angles of attack near the stall
  should be confined to speeds below VA.

  VA = 175 kt CAS

  CAUTION: Rapidly alternating large rudder applications in combination with
  large sideslip angles may result in structural failure at any speed.
  MAXIMUM FLAPS EXTENDED OR OPERATING SPEEDS VFE

  FLAPS 15 185 kt CAS
  FLAPS 30 150 kt CAS

  MAXIMUM LANDING GEAR EXTENDED OR OPERATING SPEEDS

  VLE = 185 kt CAS
  VLO
  lowering = 170 kt CAS
  retracting = 160 kt CAS

  2.03.02 | OPERATIONAL PARAMETERS ENVIRONMENTAL ENVELOPE

  Note : Refer
  to 2.04.05 for fuel temperature limitation. TAKE–OFF AND LANDING –
  Tail wind limit : 15 kt – Maximum mean runway slope : ±2 %

  2.04.01 | ENGINES

  PRATT&WHITNEY CANADA PW127F or PW127M or PW127N

  Operating limits with no unscheduled maintenance action required;
  Beyond these limits refer to maintenance manual.

  OPERATING CONDITION TIME LIMIT TQ
  (%) ITT ($^\circ$C) NH (%) NL (%) NP (%) OIL PRESS (PSI) OIL TEMP ($^\circ$C)
  (2)

  RESERVE TAKE OFF 10 mn (6) 100 (1) 800 103.2 104.2 101 55 to 65 0 to 125

  NORMAL TAKE OFF 5 mn 90 (1) (5)
  101.9 101.4 101 55 to 65 0 to 125

  MAXIMUM CONTINUOUS none (7)
  90.9 (1) 800 103.2 104.2 101 55 to 65 0 to 125

  GROUND IDLE 66 mini 40 mini (4)
  -- 40 to 125

  HOTEL MODE 715 55 to 65 125

  TRANSIENT 20 s 120 840 106.4 106.8 106 (3) 40 to 100 5 s 120 20 mn 140

  STARTING 5 s 950 --54 mini

  Value linked to 100 % NP.
  Oil temperature must be maintained above 45$^\circ$C to ensure protection for
  the engine air inlet against ice accumulation.
  Permissible for completion of flight provided TQ does not exceed 75.2 %
  during climb and 73.13 % during cruise.
  Up to 75 % NH only.
  ITT limits depend on outside air temperature. Refer to 2.04 page 2.
  Single engine operation only, beyond 5 mn.
  MCT rating is the max
  power certified for continuous use. In-flight emergencies are the
  only conditions for which MCT use is authorized.

  NOTE : Flight with an
  engine running and the propeller feathered is not permitted

  2.04.02 | PROPELLERS

  TWO HAMILTON STANDARD HS 568 F
   – 1 GROUND OPERATION
  Engine run up must be performed into the wind.  Avoid static operation
  between 41.6 % and 62.5 % NP.  Avoid operation in feather above 66.6 %
  TQ.

  GROUND OR FLIGHT OPERATION  If a propeller is involved in an
  overspeed or in an engine overtorque refer to the propeller
  maintenance manual.

  FLIGHT OPERATION  ATR airplanes are protected
  against a positioning of power levers below the flight idle stop in
  flight by an IDLE GATE device.  It is reminded that any attempt to
  override this protection is prohibited. Such positioning may lead to
  loss of airplane control or may result in an engine overspeed
  condition and consequent loss of engine power.

  04 POWER PLANT 2
  LIMITATIONS PAGE : 001 DEC 96 EASA APPROVED
  --Model : 212 A AFM 4 AUG 07 FEB 05 R JUL 06 SEP 06 R R R

  2.04.03 | OILSYSTEM SPECIFICATION Refer to specification PWA 521 type II.

  2.04.04 | STARTER

  3 starts with a 1 minute 30 seconds maximum combined starter running time followed by 4 minutes OFF.

  2.04.05 | FUELSYSTEM

  Acceptable fuels : Jet A, Jet A1, JP5 and RT, TS1. Use of JP4 and Jet B is prohibited.

  TEMPERATURE

  For flight
  preparation, a minimum fuel temperature must be taken into account to
  ensure adequate relight :

  3 4 o C JET A, JET A1 and RT, TS1.
  2 6 o C for fuel type JP5. •Maximum temperature : 57 o C for fuel types JET A, JET A1, JP 5 and RT, TS1.

  REFUELING

  Maximum pressure 3.5
  bars (50 PSI)

  USABLE FUEL

  The total quantity of fuel usable in each
  tank is : 2500 kg (5510 lbs)

  NOTE :Fuel remaining in the tanks when
  quantity indicators show zero is not usable in flight.

  UNBALANCE

  Maximum fuel unbalance : 730 kg (1609 lbs)

  FEEDING

  Each electrical pump is able to supply one engine in the whole flight envelope.
  One electrical pump and associated jet pump are able to supply both
  engines in the whole flight envelope

  2.05.01 | AIR PRESSURIZATION

  Maximum differential pressure: 6.35 PSI
  Maximum negative differential pressure 0.5 PSI
  Maximum differential pressure for landing 0.35 PSI
  Maximum differential pressure for OVBD VALVE full open selection 1 PSI
  Maximum altitude for one bleed off operation 20000 ft

  2.05.02 | HYDRAULIC SYSTEM

  All hydraulic fluids compliant with technical
  specification : NSA 307110 Compliant fluids are listed in the AMM
  (Chapter20, 20-31-30)

  2.05.03 | LANDING GEAR

  Do not perform pivoting (sharp turns) upon a landing gear with fully braked wheels except in case of emergency.
  In case of ground speed over 165 kt all tires to be replaced.
  Towbarless Towing is prohibited, unless the towbarless towing operations are performed in compliance with the appropriate
  operational requirements (JAR--OPS--1 for Commercial Air
  Transportation) using towbarless towing vehicles that are designed and
  operated to preclude damage to the aeroplane nose wheel steering
  system or which provide a reliable and unmistakable warning when
  damage to the steering system may have occurred. Towbarless towing
  vehicles that are specifically accepted for ATR aircraft are listed in
  ATR Service Letter 72--09--6001.

  2.05.04 | FLAPS

  Holding with any flaps extended is prohibited in icing conditions (except for single engine operations).

  2.05.05 | AUTOMATIC FLIGHT CONTROL SYSTEM (AFCS)

  Minimum height for autopilot engagement on take off : 100 ft
  NAV mode for VOR approach, using either autopilot or flight director is authorized only if :

  a co--located DME is available, and
  DME HOLD is not selected

  Minimum height for use of either autopilot or flight director :

  Except during take off or executing an approach : 1000 ft
  VS or IAS mode during approach : 160 ft
  CAT 1 APP mode : 160 ft Refer to 7.01.03 for CAT II operation

  2.05.06 | INSTRUMENTS MARKING

  Red arc or radial line : minimum and maximum limits Yellow arc : caution area Green arc : normal area

  2.05.07 | CARGO DOOR OPERATION

  Do not operate cargo door with a lateral wind component of more than 45 kt.

  .../... 05 SYSTEMS 2 LIMITATIONS PAGE : 001 AUG 14 EASA APPROVED
  --Model : 212 A AFM 2

  2.05.08 | ELECTRICAL

  Single DC GEN operation : In flight, if OAT exceeds ISA + 25, flight level must be limited to FL200.

  2.05.09 | MFC

  Take off with two or more failed MFC modules is prohibited

  2.05.10 | COMMUNICATIONS

  Not applicable

  2.05.11 | TCAS

  When installed, Refer to appendix 7.01.0


Is there a class E corridor in the class B north of San Diego International? I am a relatively new pilot in the Los Angeles area and I have a question related to the Class B Airspace north of San Diego International, adjacent to Torrey Pines Glider Port.  The LA Terminal Map and Fore Flight show what appears to be a corridor or brake in the Class B Airspace. It shows the B Airspace to be 18 to 100, however there appears to be an altitude box just to the left of this area with an arrow pointing to the area in question that says floor of 18 to ceiling of 32 & floor of 68 to ceiling of 100.

My interpretation of this is that this box designates a Class E corridor just above 3,200' and just below 6,800'.

I have asked a number of pilots more experienced than myself and have received conflicting answers to my interpretation. Some agree and some do not.  I have attempted to find references online, but the only reference to a corridor in San Diego is the VFR corridor that overflies San Diego International above 3,300 and below 4,700 Northwest to Southeast.

I have attached a photo of the chart from Fore Flight for the area in question.  I would appreciate if someone who has flown this area could clarify this for me I would be very grateful as I don't want to bust B Airspace. Is my interpretation of the chart correct?  If not can someone explain to me what the box is saying?   Thank You.

I'm a frequent VFR owner/flyer in that area for past 12 years. The box is clearly identifying the floor within in the box it is pointing into.  That 1800/3200' is to keep transitioning aircraft either below or above the MIRAMAR MCAS departure corridor.  Aircraft that are inbound to Montgomery Field will often transition with a Class B clearance when flight followed by SoCal on 119.6, at 2500-3000'  Inbound commercial jets for Lindbergh Field will come thru that zone at 6800' and above. And yes, as depicted on the chart, offshore of Torrey Pines and west of the OCN 152 radial, the floor is 1800'.  If you're looking for a "corridor"to the South Bay onto Brown Field, you could fly the shoreline at 3600'-4600', from Del Mar, over Mt Soledad, and then join the VFR corridor over Lindbergh Field, and onto Brown Field.


How much do you have to respect checklist order? In a fighter aircraft, if the checklist says turn on the radar then turn on the Heads Down Display, and the pilot turns on the HDD first would he be reprimanded for that if it makes no difference?
Is there any leeway in checklist order or are you expected to follow it to the letter? Does it just depend on the organization?

Yes, the published sequence must be respected. Here is a quote from published instructions on checklist usage by one of the major manufacturers based in the USA:

". . . . The crew may need to stop a checklist for a short time to do other tasks. If the interruption is short, continue the checklist with
the next step. If a pilot is not sure where the checklist was stopped,
do the checklist from the start. If the checklist is stopped for a
long time, also do the checklist from the start."

If this philosophy is not already spelt out for some current aircraft types, the Regulatory bodies and Industry are (correctly) pushing it that way. Tedium is not considered as a sufficient reason to dump the C/L sequence, it is actually one reason for having a checklist!
The purpose of cockpit checklists for both Normal and Abnormal/non-Normal situations would largely be defeated if the published sequence were not followed as they are designed to ensure that the aircraft is correctly configured and safe for the next step.
In an unusual situation though (read esp: impending catastrophe), the above is to be understood in the light of the necessary disclaimer, quoted from the same manual that's quoted above:

"The flight crew must be aware that checklists cannot be created for all conceivable situations and are not intended to replace good
judgment. In some situations, at the captain’s discretion, deviation
from a checklist may be needed."

The statement - “ . . even if it makes no difference . . “ is a tricky one and it evokes a response of, “where do you draw the line?" - checklists are a manifestation of the need for Standardisation.
Here's a sum up, intended to complement the advice given by  many on this page.

Checklists are made very scientifically, but even so, the endeavor is based on a best effort basis and checklist philosophy is constantly evolving.
instances of abnormal/non-normal  situations can exist or can be conceived to support either side of the discussion.
Checklists are aimed at providing the highest probability of a successful outcome based on the best knowledge of the day and age.
Institutional Policy must be sufficiently evolved to look at variations from SOP in a practical manner.
A C/L sequence that regularly invites 'modification’, as reported by crew or as found by a surveillance system, requires a rethink.
In current day practice, ‘one off’ occurrences of a breach of checklist sequence are looked at in a benign manner by all but a few agencies.
As a policy, “not following the checklist sequence” cannot be  regularly condoned.


How does bleed air maintain pressure for pressurization after being cooled? I found on aerosavvy.com/aircraft-pressurization the paragraph below, which talks about bleed air on airliners:

  Most modern airliners use bleed air from the compressor section of the engines to pressurize the cabin. This very hot air must be cooled to a comfortable temperature before it’s directed into the cabin.

If it is cooled too much it wouldn't be under high pressure, right?

The cabin needs high pressure air because the air at 30,000ft is at too low of a pressure, so they need to simulate a 6000-8000 feet pressure. This bleed air is very hot high pressure air, I understand you have to cool it because it is way too hot for anything to operate with it.

But if you cool it, doesn't it lose pressure, so it would be low pressure air which is not what we want? I don't know where I am getting confused at.

That's one of the reasons why bleed air is compressed again before cooling.

  In Air Cycle Machines, high-pressure bleed air from the engines is first passed through a compressor, further squeezing the already hot gas. It is then routed through a heat exchanger or two to remove heat. The now cooler but still highly compressed air then passes through an expansion chamber into a larger chamber. The combined effects of driving the turbine and expanding into a larger chamber dramatically cools the air (usually down close freezing; water traps are critical in the system to prevent freeze-up). (Source)

Simple diagram:

(Source)

The outflow valve is what regulates the pressure, it makes sure the right amount of air leaves the cabin.

  The automatic controller normally maintains the proper cabin pressure altitude by constantly adjusting the outflow valve position so that the cabin altitude is as low as practical without exceeding the maximum pressure differential limit on the fuselage.


How can V1 and VR (rotate) speeds be calculated? I want to learn about how can the V1 and VR (rotate) speeds be calculated for take off. And which factors are affecting this calculation?

Basically it may depends on the aircraft weight, runway length, engine capacity and flap rates. But what is the other factors and what are the V1 and VR formulas. Is it possible to explain, e.g. for a Boeing 737 which is taking off from a 6,791 ft (2,070 m) runway in good weather conditions?

There is no general equation/function that you can use to calculate V1/Vr... the manufacturer test out the aircraft's performance during certification, and you then compare your current aircraft and conditions against the known manufacturer's aircraft and conditions to get your results.

V1 is the border between accelerate for takeoff, and STOPPPPPP! by the end of the runway.
* Acceleration is dependent upon the engine thrust being used, the atmosphere providing oxygen for combustion and nitrogen for jetflow mass, the aircraft's mass that has to be accelerated, the drag of the used flap setting, and the possible drag of the runway surface and slope.
* The STOPPP! aspect is dependent upon the drag of the flaps and speedbrakes, the drag of the runway slope and surface, and the mass of the airplane.

Vr is nothing to do with V1... it's just a margin below V2 (5kts? 10kts? depending on thrust setting) that allows you to rotate earlier than V2 but still accelerate (in the air) to then achieve V2 by 15m/50ft. And V2 depends on the weight of the aircraft and the flap setting.


Is wingtip design mature? There are many wingtip design, all made to reduce vortex related drag, and neither boeing nor airbus seems to prefer one over another. They move from one design to another at each new aircraft, always claiming the new choice is more efficient than the previous one. In detailed, all generation mixed, it looks like (non exhaustive list):

winglet: B737NG, A330, B747-400, A320NEO, A350

wingtip fence: A320, A380, B737MAX

raked wingtip: B787

EDIT: The other elements of aircraft design are almost the same for all new aircraft (low wing, engines under the wing, classical landing gear, APU in the tail, ...), so I assume it has reached a great level of maturity, nothing has to be improved and introduced on a new aircraft generation. This is obviously not the case for wingtip.

The wingtips are a unique part of the aircraft in that they really have one job; minimize drag. Their design is easy to see, and they are a fairly recent addition to transport aircraft. Developments continue to be made in the study of aerodynamics, with modern computing power and methods allowing much better modeling of flow patterns to evaluate designs, and improvements in materials allowing more complex designs to be built.

The key is that the winglet must be properly designed. As wing designs change, the flow over the wings changes, and new winglet designs are invented.

Since it is heavily dependent on the specific application, it's more relevant to look at the evolution of the designs on different aircraft. The design chosen is dependent on the technology available at the time, both for evaluating the design and building it, the design of the wing, intended use of the aircraft, and the previous experience of the manufacturer.

The 737 is an old design that has evolved over time: Original/Classic: none, NG: winglet, P-8: raked tip, MAX: split scimitar

The A330 is a fairly new design: Current: small winglet, neo: winglet

The 747 has also evolved over time, and the latest version shares technology with the 787: Original: none, -400: small winglet, -8: raked tip

The A320 has also evolved over time: Original: none, Current: tip fence, neo: winglet

The A380 is a new design: tip fence

The A350 is a new design: winglet

The 787 is a new design: raked tip

The 777 is a fairly new design: Basic: none, -200LR and -300ER: raked tips

You will notice a trend from smaller designs to larger ones. On larger aircraft though, the weight of a large winglet and the loads it produces can get too large. New designs like the 777, A380, 787, and 747-8 all use either raked tips or small winglets.

As for other parts of aircraft, engines are changing more than you think. The jet engines on the early jet transports look very different from modern high-bypass turbofans. The GEnx engines on the 787 and 747-8 have chevrons at the back to reduce noise. All you see on the outside is the nacelle that minimizes drag; most of the changes go on inside. Also, if you look closely at the front, fan blades on newer engines have curves in them instead of having straight edges.

Most other parts of the aircraft have more complex jobs, not primarily external. A fuselage should be efficient at carrying things inside but also keep drag low. If you look closely you will notice that new planes like the 787 and A350 have a lot in common with previous fuselages, but they are shaped differently as well. It's harder to see the other drastic changes like the use of composites in place of traditional aluminum, electric systems instead of hydraulic or bleed air, fly by wire, etc.

Control surfaces must provide sufficient control while minimizing drag. The size and shape has also changed over time, though the general design has remained.


What is the resistance range for the Bendix King KN-64 DME Photoresistor? Does anyone know the resistance range for the Bendix King KN-64 DME photoresistor?

According to http://www.flymafc.com/docs/manuals/king-KN62_KN62A_KN64.pdf, The Maximum Sensor Range for the Bendix King KN-64 DME is determined by altitude and ground station output power and sensitivity. Under normal circumstances, the KN-64 DME has a maximum display range of 389 Nautical Miles, as shown below:

The Change in Accuracy of the KN-64 DME change from .1 Nautical Miles or .14 Nautical Miles from 0 to 99.9 Nautical Miles, as shown below, along with Sensitivity:


Will a portable ADS-B unit, like Stratus, meet the requirements for my aircraft to be ADS-B equipped by the 2020 mandate? There is a lot of confusion around what it means to have ADS-B.  What is the minimum equipment required to meet the mandate? Can I use a Stratus to meet that requirement?

The short version is no the Stratus will not meet the requirements, and for several reasons.

The final rule requires ADS-B OUT (and the Stratus is only ADS-B IN) that meets particular TSO requirements (see below), and portable units will not.

The FAA has an ADS-B FAQ on their website which has a lot of great ADS-B information.

The minimum equipment required to meet the mandate is addressed by:

  What equipment is required by the new rule?

  The rule specifies ADS-B
  Out equipment compliant with either Technical Standard Order
  (TSO)-C154c (Universal Access Transceiver) or TSO-C166b (1090 ES).
  However, to operate in Class A airspace, aircraft are required to
  equip with avionics certified to TSO-C166b.

The FAQ also specifically addresses the question of portable units and says that they will not be allowed:

  Will the FAA allow portable/handheld units, or will they have to be panel mounts only?

  Installed transponders and GPS units must meet certification
  standards. Handheld devices and displays that serve only for
  situational awareness have more flexibility and are not certified
  installations. In order to comply with 14 CFR § 91.225 and 91.227
  aircraft intended to fly in ADS-B airspace must have installed and
  certified equipment. Portable installations are not compliant to the
  rule and would only be usable for receiving FIS-B services for
  situational awareness. The FAA is in the early stages of investigating
  a portable device for glider aircraft.


Does the size of code F aircraft parking apron enough for 2 code C plane? When I look at Inner Thames Estuary Airport (Isle of Grain) masterplan, they shows a funny figure about the terminals layout.

The report describes that  It shows the ability for most
stands to handle either a large wide bodied (Code E/F) aircraft or two narrow bodied (Code C) aircraft.

The question is, is it true?

This type of parking system is called MARS (Multi Aircraft (or Apron) Ramp System) and is being used or explored by many airports.

You can see markings for them on the ground at CLE.  Here is a google maps link to one of the stand areas.  CLE terminal

Here is an article on the stands.


What is the maximum allowed intensity for light beams pointing at the sky for non-aviation purposes? In Hong Kong, I'm designing a show with light beams and i'm thinking using Robe Megapointe lights (https://www.robe.cz/megapointe/). I've been ask by the client to follow the aviation regulation. Though the aviation regulation doesn't give any figure, only subjective indications, and I have no idea if my lights are acceptable or too strong.

The website of Robe announces: 2.200.000 lx @ 5 m and 137.500 lx @ 20 m. I'm trying to find similar regulation references in other countries to make up my mind.

Any of you have seen any figures in that domain?

Article 80(1) of the Air Navigation (Hong Kong) Order 1995 stipulates that

  A person shall not exhibit in Hong Kong any light which —

  (a) by reason of its glare is liable to endanger aircraft taking off from or landing at an aerodrome; or

  (b) by reason of its liability to be mistaken for an aeronautical ground light is liable to endanger aircraft.

  Any such contravention is liable on summary conviction to a fine.

The full text of the regulation can be read here.

Given this text, if your show is going to be anywhere near the approach or departure path to/from the airport (anywhere on Lantau Island, or east/west of the Gold Coast) you should probably refrain from using such lighting. I would strongly suggest you get approval from the authorities well before the event using an experienced local consultant, and prepare for that approval to be given or denied based on subjective analysis.


My windsock is erect, what does this mean? I know that airport windsocks are calibrated to reach full erection at a particular wind velocity. At half that speed, the first half of the windsock should be erect and the second half should droop sorrowfully. At one third the speed it will be one third, and so on.

Trouble is that not all windsocks are calibrated the same way. How do I find out what wind velocity will bring my airport windsock to a fully erect state?

Windsocks come in various sizes and speeds, but an FAA Standard Wind Sock aligns with the wind at 3 knots, and is fully extended at 15 knots like CGCampbell pointed out.

A typical wind sock (at least around here) looks something like this:

The stripes are actually useful:

The first stripe indicates a 3-knot breeze
(The wind sock has turned and aligned with the wind - usually you should look for an anemometer near the wind sock to determine if there's any appreciable wind because often the first segment is held open by the frame.)
The second stripe is ~ 6 knots
The third stripe is ~ 9 knots
The fourth stripe is ~ 12 knots
The last stripe is 15 knots or higher
If the windsock is missing you probably shouldn't be at the airport.
If the pole is missing you're probably on your way to Oz.

(You can actually get a far more precise estimation if you're willing to do some trigonometry, but this works well enough for most purposes.)


Why are airports in Greece blurred and low res in Google Maps? Why are airports in Greece blurred and low res in Google Maps?

The short answer seems to be that some countries have persuaded Google to blur out specific areas for "national security" reasons. Wikipedia has an article on it with some more (limited!) information. Interestingly, I couldn't find any official Google article on blurring in Maps, apart from some general references to Street View. And, as it turns out, Street View at ATH works as normal.

FWIW, it seems that Greece didn't persuade Microsoft to play along, because Bing Maps has much better images. That strongly suggests that the blurring is mostly security theater.

(By the way, I'm not saying that there are no security/privacy risks with Google Maps, Bing or other tools; it's just that some risks are more credible than others. security.SE would be a good place to ask more about that.)


How can I tell if a G430 or G1000 has WAAS or not? Both the GNS430 and G1000 are/were available with and without WAAS, and I believe it's even possible to upgrade a GNS430 to add WAAS support. When I get into an unfamiliar rental aircraft, is there a quick and easy way to see if WAAS is available, by checking the avionics themselves? Is anything physically different about the units, is there some properties/status page I can check, or is there something different on the display?

Obviously asking the operator and checking the aircraft handbooks would be the right thing to do, but sometimes that doesn't work out, e.g. the FBO's instructors are all out flying and the admin people just don't know.

NOTE: as pointed out in the comments, none of these quick verification steps actually guarantees that the airplane you clambered into is certified for LPV approaches, or for IFR GPS usage at all!

On boot, a 430W will display that it's a 430W:

Aside from that, I'm sure there's a version info screen somewhere (on both G1000 and GNS430), but the best solution I can think of is to check the satellite status screen. I'm trying to find examples of a 430W displaying it, and failing, but on a G1000, you'll see this:

 (source)

If the G1000 supports WAAS, it'll display that under the 'SBAS Selection' header and you'll see satellites at the bottom numbered in the 100s - 124, 126, 129, etc - all the 100-series satellites are the WAAS augmentation satellites. The satellites augmented by WAAS will also have a "D" at the bottom of the signal strength column.


Is there any work on improving fuel tanks so they could store hydrogen? I think that hydrogen is among the best fuels for use in supersonic and hypersonic flight, is there any work on improving fuel tanks so they could store hydrogen?

What would be the best state to store hydrogen for use as an aircraft fuel: solid, liquid or gas?

What are the complexities for storing it at each state?

First, to debunk a myth regarding the Hindenberg, which always gets brought up whenever hydrogen is mentioned. Hydrogen is less safe than liquid fuel, but it is not less safe than natural gas or propane. Hydrogen has a higher flame propagation velocity than hydrocarbon gasses, but contains much less energy per unit volume than hydrocarbon gasses. A huge airship filled with natural gas would be just as hazardous as a huge airship filled with hydrogen, yet we have natural gas pipework running to our houses and with proper controls there are very few incidents.

Nevertheless, hydrogen is not a good fuel for aircraft for the following reasons.

(Source: Wikipedia)

Above shows that hydrogen contains about 142MJ/kg of energy compared with about 42MJ/kg for kerosene. However it contains a lot less energy per unit volume. Liquid hydrogen contains only 10 MJ/litre while kerosene contains 33MJ/litre. Therefore hydrogen fuel tanks would need to be more than 3 times the size of kerosene fuel tanks. Gaseous hydrogen at atmospheric pressure would occupy hundreds of times more space, while hydrogen at 700bar is only about a factor of 2 worse than liquid hydrogen, but the weight of a vessel for holding 700bar pressure would negate the weight advantage of hydrogen.

Therefore the most practical way of storing hydrogen in an aircraft would be in the liquid state, as is used in spacecraft such as the Space Shuttle. Use of hydrogen would result in some weight savings and hence fuel savings. However the fuel tanks would be so big that the savings would be partially negated by the the additional drag (not to mention the additional weight of the larger tanks.)

Hydrogen is expensive to produce and liquefy. Most hydrogen is produced by reforming natural gas and steam into hydrogen by the reaction CH4 + 2H2O = CO2 + 4H2, which is a highly energy intensive process. Therefore, although a hydrogen fuelled plane might consume less energy than a kerosene fuelled plane, this does not take into account the energy used in the process of producing and liquefying the hydrogen, nor the cost involved in doing so. Overall, hydrogen fuel is likely to be more expensive.

Hydrogen is also more difficult to handle. hydrogen tanks are never perfectly insulated, so hydrogen boils off, and the tanks ice up. It is also, more hazardous than liquid fuel if a spill occurs, as it will evaporate and create an explosive mixture in air (though, as I have said above, this issue also applies to natural gas.) Liquid hydrogen is much colder than liquefied natural gas, and so creates more problems with materials, boiloff and icing.

Industrial gas turbines can run on hydrogen without too much modification. But with the extensive certification procedures for aviation, modifying an aircraft engine for hydrogen will be quite costly. Also the faster flame velocity of hydrogen means that NOx is more difficult to control and this is likely to cause problems with emissions regulations.

In conclusion, the only way hydrogen is ever going to be viable in the aviation industry in general is if it turns out to be easier to use in a fuel cell driven craft than a hydrocarbon fuel.

If economically feasible, a fuel cell / electric motor drive would be more efficient than a combustion jet engine. That said, the practical and safety issues mean that the aircraft industry will be one of the latest adopters of such technology.


What is the purpose exactly of a ‘Control Check’? I recently watched an Air Crash Investigation episode where Qantas flight 32 lost an engine shortly after takeoff. It was revealed that a stud pipe in a Rolls-Royce engine was made incorrectly, causing the pipe to snap and burst through the engine and the aircraft's wing, severing major hydraulic systems, and causing the ECAM to display pages and pages of errors.

On the final approach, the captain announced he wished to perform a ‘control check’.  He said (and this is approximate):

  When the aircraft is damaged, you have to certify it is safe to land before you try to land.

I assume this is so that the captain can make the necessary preparations if he feels his aircraft is not safe to land. On flight 32 this was done by moving the stick left and right to simulate lining up with the runway.

Perhaps a better question is back to the post's title.

What are the purposes of in-flight Control Checks?

In my example of Qantas Flight 32, the stick was moved left and right on final approach to simulate lining up with the runway. This was only small left and right control deflections.  The flight deck had only minutes until landing.  What was the captain expecting to see, or not to see?  Can the captain after that brief manoeuvre be aware of his aircraft enough to make a decision?

Does this mean then that a Control Check only comes, or should only be done, if you are worried that the aircraft cannot land?  Can it be done at any other time?  In other words: is an in-flight control check only done for landing?

SOURCES:

Wikipedia
Flight 32:
https://en.m.wikipedia.org/wiki/Qantas_Flight_32

Technically speaking, a control check is part of any pre-flight.

In the case of Qantas 32, one engine had exploded, punching holes in the wing and setting off a host of warnings, so there was a reasonable expectation that some of the controls might also have been damaged.

What the pilot did was put the plane through some basic maneuvers to see how the controls responded in their now potentially damaged form. And found that roll rate had been affected, something he factored in on the subsequent landing. He also found that pitch control had not been affected, which meant he could make a reasonably conventional approach to the runway.

Better to find out how much the controls had been affected when there is time and altitude to recover from an unexpected response, than to find out on final approach, where the margin for recovery is very slim to none at all.

During flight, this is not normal. It is prudent if an inflight incident may have damaged some of the controls, so that the pilot knows the level of controllability they have to work with.


F4u race wing design Can anyone suggest a good airfoil for racing the F4U Corsair? I'm building an RC model but I want it to be fast unlike scale warbird. Any suggestions on wing design and airfoil would be greatly appreciated. I know I can always throw more power to it but I want the fuselage and wing designed to match.

Thanks

The MH 24 airfoil has been popular for years at international radio-control pylon racing events.  Just ensure that your chord and airspeed give you a Reynolds number exceeding 400,000.

Because airfoils designed for high speed often work poorly at low speed, consider equipping your model with flaps, to make landing easier.

At lower Reynolds numbers, the Eppler E220 has a good reputation.  It's also easier to build (more tolerant of inaccuracies) than airfoils in the mostly-laminar-flow MH series.


What was the reason why 9M-MRO burned more fuel on one engine? MH370 Factual Information reported "Right engine consumes average 1.5T more fuel per/hour compared to left engine" on p.28 (page 47 on page count)

http://mh370.mot.gov.my/download/FactualInformation.pdf

Looking at spotters photos on the web I spotted the following difference:

Some kind of visible replacement (partial or total) to the left engine was made after Oct 28 '13 and before Jan 22 '14.

Before - Two shades, longer curving, bigger bulge on top engine border before exhaust.

After - One shade, steeper curving, smaller bulge on top engine border before exhaust.

Google Drive document with links to 9M-MRO photos (I can't post more than 2 links since not enough reputation still)

https://docs.google.com/document/d/1tkY6H8zQmOyJj0M2_gd_j81iDr2MeumBoIlrYNtbcus/edit?usp=sharing

Those engines all look the same to me.

1.5T per/hour difference does seem excessive, but probably not unheard of.  It could be just because one engine is newer than the other and has less wear on it.

If you look at APPENDIX 1.6B of that same report it shows that the right engine consumed about 1.5% more fuel during Takeoff and Climb, not 1.5T more, so it may just be a typo.

(APPENDIX 1.6B WF is fuel flow in lbs/hr)

Here are some crops of the photos you linked to:

Jan. 15, 2012

Feb. 16, 2013

Oct. 28,2013

Jan. 22, 2014

Feb. 8, 2014

Feb. 10, 2014


Is it possible to control a drone with a link mediated by the cellular phone network? If that were possible, it would allow an operator to control the drone from a very remote place, and without resorting to satellite radio links, as military drones do...

Possible: yes

Probable: no

The simple fact is that the cell network is not advantageous for drone control at least not the kind that people prefer. The architecture of the network by nature allows the signal to drop out bandwidth from tower to tower is not guaranteed. This would allow a situation where a drone flying along would get handed off to a tower that has no available bandwidth and the control signal drops out. Dedicated satellite networks allow point to point communication as well as assured bandwidth when its needed.


Can a small UAV restart its engine in mid-flight? Is it possible for a small UAV, say a small piston-engine aircraft with a low windmilling effect, to restart its engine in mid-flight following an engine shutoff?

Some gliders have pop-up engines to extend range if they cant't catch rising air (known as turbo-sustainers) which start by in-flight windmilling, but I wouldn't count on it with an engine not designed to be started this way. Additionally, if the shutoff was not intentional it seems likely that whatever caused the engine to fail will make it even harder to start in this manner.


Where can I find data on past forecasts of planned aircraft production? Does anyone know of a database which would list the expected production rates for various aircraft, at the time those aircraft started production?

Finding actual production to date is easy, but I would be interested in what was the original planned production. I am not interested in current forecasts, I am interested in past forecasts that have been made before or at the start of production for the particular aircraft.

E.g. Cessna 152 was assumed by the manufacturer to be sold at the volume of XX aircraft per year, when the production plan was put into place.

Yes both Airbus and Boeing deliver 20-year forecast for the complete market. For Airbus there is a spreadsheet which may function as your database.

IATA also publishes 20 year travel forecasts, here is the latest. Airline travel is going to double over the next 20 years.

At he time of first production, forecasts for the aircraft are made based on market forecasts, plus the expected market share that the aircraft may achieve. Information that is of interest to the stakeholders of the company.


In simple mechanical stick linkages, is there crosstalk between the aileron and the elevator movement? The background story:

I'm an aviation enthusiast (who has played a lot of sim in his life and will play lots more :D) but I've never actually flown any plane myself, as in, actually used the controls (but I'm planning to make my PPL one day, I've always wanted to have wings :).
I also have an idea in my mind which involves a simply constructed stick control column.

While looking at some pictures of the mechanical construction of the linkages that translate stick movement to aileron/elevator movement, I've stumbled upon this design analysis of the Mitsubishi A6M3 Zero, a japanese WWII fighter plane.

The bewilderment:

Looking at this drawing of the linkages on the stick,

I was wondering:

If the stick is rotated exactly and only around the aileron axis (thus describing a pure 2D movement along the surface of a circle, basically, the stick does not rotate around the "bolt" (A) with which it is mounted to the bell crank), it looks to me as if this would inevitably lead to a change in angle on the elevator, since the distance between the point where the push pull rod is linked to the stick (B) and the point where it is linked to the "elevator hinge" (C) and the push pull rod would pull stronger on the elevator (leading to a higher AOA) the further the stick is rotated around the aileron axis.

The question(s):

Does this mean that in aircraft with similar stick mechanisms, the further you rotate the stick to the left or right, the more you would have to push it forward/the less you would have to pull it back in order to not change the pitch of your elevator?[1]

If this is the case, is it a problem or does one intuitively get used to compensating for this "crosstalk"?

[1]: I'm not talking about lowering your AOA the more you bank to avoid stalling. Just imagine you're in a steep bank and push the stick to the side quite far to level your wings. Would you have to push forward so you don't increase your AOA while levelling out?

In simple mechanical stick linkages, is there crosstalk between the aileron and the elevator movement?

In almost all cases, there is no intentional-- or discernable-- mechanical coupling between aileron deflection and elevator deflection.  However in the Schleicher Ka-6 sailplane, the mechanical linkage is designed to raise both ailerons a little bit, effectively increasing washout in the wing, when the stick is far aft.  See for example page 3 in this manual.  Some other aircraft may share this unusual feature.  You can imagine why it is desirable to have more washout in a low-airspeed thermal turn than in high-airspeed cruising flight.


How can the Airbus A380 have such a high lift/drag with a relatively low aspect ratio wing? The Airbus A380 has a wing with aspect ratio between 7 and 8.  Reference here.  The lift to drag ratio is somewhere between 19 and 20, which is comparable to aircraft with higher aspect ratios and superior to aircraft with similar aspect ratios.  A reference to the lift/drag number is here.  How can the A380 achieve this?

The aspect ratio of the aircraft is usually kept as high as possible to reduce the induced drag. However, it forms only one part of the total drag acting one the body.

The L/D ratio can be improved by either increasing the (coefficient of) lift or decreasing the (coefficient of) drag.

While no data is available in open sources, it is likely that the wing airfoil was designed for high lift in cruise conditions. Also, the wing has a number of high-lift-devices to increase lift like the flaps, droop nose etc.

For example, in order to improve the L/D ratio during initial takeoff and climb, the A380 incorporated a droop nose device in the inboard leading edge. This improved the lift by around 5%. The figure below shows A380 deploying droops during landing

"A380 F-WWEA LEGT" by User:Keta - Own work. Licensed under CC BY-SA 2.5 via Commons.

The aerodynamic drag on a body is a combination of a large number of components like

Induced Drag
Parasitic Drag
Wave Drag.

The (lift) induced drag is lesser for aircrafts with higher aspect ratio. In designing the A380 however, the limitations of airport operations meant that the wingspan was limited. This resulted in a rather low aspect ratio of 7.8. However, the same effect(of higher aspect ratio) can be achieved using wingtip devices such as winglets. A380 uses wingtip fences to reduce induced drag.

"British Airways Airbus A380-841 F-WWSK PAS 2013 10 Wingtip device" by Julian Herzog. Licensed under CC BY 4.0 via Wikimedia Commons.

As the speed increases, the induced drag reduces and the parasitic drag (of which the form drag is a component) comes to dominate the drag produced.

"Drag Curve 2" by Original uploader was GRAHAMUK at en.wikipedia - Transferred from en.wikipedia; transferred to Commons by User:Sfan00_IMG using CommonsHelper.. Licensed under CC BY-SA 3.0 via Commons.

The major part of the parasitic drag is the form drag, caused by the movement of aircraft through the air. The A380 design reduces this by reducing the control surface areas through the use of Fly by wire system.

This is also achieved by reducing the drag caused refining the aerodynamics of the aircraft, such as by using improved flap track fairings and increased size of the belly fairing.

"Singapore Airlines A380 9V-SKH" by Simon_sees - Singapore Airlines A380 9V-SKH. Licensed under CC BY 2.0 via Wikimedia Commons.

The overall aircraft configuration and not just the individual components were analyzed using CFD, which led to further optimization of the aerodynamics design and reduction of drag by changing the spanwise distribution of camber and twist from root to tip (around 2%).

The airfoil used was most probably optimized for reducing wave (transonic) drag, though no data is available in open literature.

Even though all these improvements were only marginal individually, put together, they have a significant impact on the overall L/D ratio.

One more thing to note is that though the L/D ratio might appear high, the value is actually comparable (and even less than) the aircrafts that enter service after A380. So in a way, there is nothing surprising about the L/D ratio of A380 except that it illustrates the steady progress being made in civil airliner aerodynamic design.


How to find TAS for given CAS, FL and OAT? Here is another question for my PPL Exam. If anyone can illuminate me with explaining every step to achieve TAS with given parameters, it would be great.

Given:
Calibrated airspeed (CAS): 155 kt. Flight level (FL) 80.
Outside air temperature (OAT): -15° C.
The true airspeed (TAS) equals...

When seeing this question there is only one thing is coming up to my mind and which is: Temperature drops 2° C every 1000 ft but I cannot connect the dots to find TAS.

My trusty E6-B flight computer (I can't believe we still teach people to use what is essentially a slide rule) has the following printed on it:

AIRSPEED CORRECTION
Set PRESS. ALT opposite °C in window. Opposite CAS on inner scale read TAS on outer scale. Read Density ALT Centre ▲

Following the instructions and setting -15°C against 8,000 ft reads a TAS of 170 kts for a CAS of 155 kts


What steps can pilots take to mitigate the risk of controlled flight into terrain (CFIT)? One of the inherent risks in flying an aircraft is a controlled flight into terrain (CFIT) incident. CFIT occurs when a flight impacts terrain while under positive control. Aside from incidents of suicide, this means the terrain impact came as a surprise to the pilot.

Controlled Flight Into Terrain Awareness is a special emphasis area in the Federal Aviation Administration's (FAA) practical test standards (PTS). The FAA felt it necessary to include this as a special emphasis area because of the prevalence of this type of incident.

What steps can pilots take to mitigate the risk of CFIT?

There are a few things you can do to help mitigate it.

Get An Instrument Rating: Some CFIT accidents happen during a nasty mix of mountain flying, scud running and an inevitable flight into IMC, which ends with hitting the side of a mountain, an instrument rating here can be a truly valuable thing in these situations.

Plan Your Routes and Minimums Carefully: This takes place in the preflight and you should always check your charts for minimum altitudes as well as man made obstructions that may be in your flight path. Once you have your minimum altitude selected, stick to it. If weather does not permit that altitude either alter your course or scrub the flight. There is some good info from AOPA on it here.

Synthetic Vision: Apps like ForeFlight are quickly becoming common place in aviation as are glass cockpits, and these have proven invaluable in terms of terrain awareness and avoidance as many of them now include synthetic vision with terrain maps. Good preflighting is still key and you should always inform your self of all potential terrain before a flight, while technology can aid in avoidance you should always have a backup plan.

Avoid The Mountains: This is sometimes not an option but if you as the PIC feel uncomfortable you should always choose a route around terrain if possible.

Practice Mountain Flying: Just as you would with any other aspect of aviation you can always get an instructor and practice mountain flying. The FAA has some tips here but mountain flying carries its own risks and unique cases that you should be ready for. Mountains can have turbulent airflow and you should make an effort to understand how wind flows over them, you can find a discussion on it here.

Get a FIS-B Weather Receiver: As mentioned above winds can be important when flying. It's worth it to have an FIS-B weather in receiver so that you always have the most up to date information.


Why are the B-52 thrust levers advanced inside-out? As I understand, the standard procedure for advancing the throttle (for take-off) is as follows:

Advance throttle to desired engine input & output (N1 & N2)
Release brakes
Gradually increase the throttle to maximum
Throughout steps 1-3 either the pilot or the co-pilot control the throttle but not both

However, in this video of a B-52 we see a rather strange way of controlling the throttle. Starting at 0:44 the pilot and co-pilot take turns advancing the throttle in an inside-out manner. What is the reason behind this? Is there really a standard procedure for advancing throttle? Or does it vary based on the aircraft?

Note: Below is valid for applying takeoff thrust (part of the question), but it's now evident it wasn't the takeoff being shown in the video. Refer to OSUZorba's answer.

According to the video description, that B-52 belongs to the 2d Bomb Wing, which operates the B-52H variant.

According to the declassified B-52H manual, the pilot flying should advance all the levers "deliberately and evenly" to the thrust gate. The thrust gate is adjusted prior to takeoff, usually by the copilot, to limit the levers to the set takeoff power setting.

(15) Thrust gate

Initial reference to EPR (Engine Pressure Ratio) is not required. The pilot not flying then adjusts the proper EPR setting for each lever. So the standard procedure is close to what you have in mind.

(Click to view full page)


If a commercial airliner enters into a spin at high altitude, is it possible to recover? Often flying I have this fear, that something will snap, and the plane will start plunging to the ground in a spin.

My question is, once a passenger aircraft (e.g. an A320) goes into a spin, can the pilots recover it, stabilize it and make it glide, or is it too late?

A similar question was asked before, but I am looking specifically for answers regarding large passenger aircraft.

How to stabilize a spinning aircraft

Stabilizing a spinning aircraft is fairly easy. If the center of gravity is not too far forward, the rudder is deflected in spin direction and the elevator fully up (adjusting the horizontal tail trim helps, too), the spin will continue until the aircraft hits the ground. In some cases, the spin might oscillate between two stable modes, and the aircraft will continuously pitch up and down between them. An airliner with its high wing loading will loose a couple of hundred meters per turn in a spin, but will not accelerate once the spin has fully developed. Increasing air density on the way down will actually decrease the rate of descent.

But I guess you wanted to ask something entirely different.

Ending a spin

Ending the spin is equally easy and is performed by the opposite commands which stabilize the spin. Proving that the aircraft will easily come out of a spin is actually part of certification requirements. The stable rate of descent gives the pilots ample time to end the spin, and even if the engines have failed, emergency systems will ensure that the pilots can control the aircraft. The risk that an otherwise normal flight will end in an unrecoverable spin is practically zero.

I would actually prefer that the airplane enters a spin. If the center of gravity is in the forward part of the allowed range, it is more likely that it will enter a spiral dive after stalling. Now the pilots need to react quickly and with measure, because drag is much lower in a spiral dive than in a spin, and the resulting higher speed poses a real danger. For that reason the flight control system in the type of aircraft you mentioned, the A-320, will prevent the aircraft from entering a spiral dive in the first place.

What if something snaps?

So far, we have assumed that all systems work. What if something snaps? The surprising answer is: Mostly nothing. A fundamental design principle for aircraft demands that primary structural parts or equipment can snap without the aircraft breaking apart. This is called redundancy: Every primary structure and every flight-critical piece of equipment is duplicated, so if one part breaks, the other, redundant part will continue to carry the loads and the flight can be terminated as planned. Regular inspections make sure that such damage is caught quickly, and the manufacturers continue to improve the existing fleet once a weakness has been spotted.

Even if something snaps, it is extremely unlikely that the aircraft will enter a spin, and even if this happens, it is easy to end. Your fears are unfounded.


Why wouldn't a helicopter ejection seat eject sideways? Or forwards? This question got me thinking. Ejecting from a helicopter is necessarily more complicated than ejecting from a fighter jet or other fixed-wing aircraft. The answer to this question states that ejection-capable helicopters blow the blades first, then the canopy, then eject the passengers.

This seems to me like a lot of explosions above your head, which seems only slightly preferable. Why not eject the passengers either sideways or forwards?

Well to me it seems that in your question you consider the helicopter flying straight and level and clear of any terrain. Well that's not true so let's take each case separately:
Eject forward
That seems like the most dangerous option to me. What if you are into CFIT? The ejection system will actually "spit" you into terrain with your helicopter's speed plus the speed of the acceleration. Ouch. Even if you survive this, the point is to escape the helicopter. And guess what its trajectory is: forward.
Also consider that the free stream works against you so you will need more acceleration to get away of the incoming helicopter.
Finally, right in front of you there is equipment like dashboards machine guns sensors et al. that need to get out of your way before you go.
Eject sideways
That sounds a least dangerous option. But what if the helicopter is banking to one of the sides? If the crew is seated side by side do they have time or even the option, "I go first you go after"?
Also bear in mind that attack helicopters' nature is to fly low and maneuver a lot. So there are high chances to be low and bank at the same time when in need to eject.
So the above 2 leave you with one option: eject upwards. But then you have one (or maybe 2) big propellers rotating above your head. But that's "easy": you get rid of them the same way you get rid of the canopy and then eject. Once the blades are released, the centrifugal will do what it knows best and the blades will be out of your way in no time. Well, hopefully.
Considering the "too many explosives above ones head", it's not rare practice to use explosives to get rid of things that are in the pilot's way like for example the canopy. That's been around for a while. But changing the trajectory of escape that will be a new concept and it will need lot's of testing.


Are there any new orders for the B747 passenger version? I was reading an article about the shortcoming and decline in the use of the A380, based on the modification of the model to move people, and there is a comment saying that both the 380 and 747 are already halting production, and the only one surviving is the 747-8 in freighter mode.

Also I didn't performed an extensive search, but I can't find orders later than 2018.

Does this mean no one is operating the 747-8 in passenger flights anymore?

I will assume that you have conflated "orders for 747s" with "airlines operating 747s", and you are actually asking if any airline has a passenger 747 on order with Boeing.

Per Boeing's Order & Deliveries page, there are no unfulfilled 747-8 (the passenger variant) orders.

You can generate the report by going to http://www.boeing.com/commercial/#/orders-deliveries, selecting "Report by Model", and then selecting "747-8" for "Current Model Series".