What happens during a powered descent? I was having a discussion with my friend about equilibrium condition in flight:

Scenario:
While going in straight and level flight, say I reduced my airspeed by 30 mph.
At the same time keeping the airplane's attitude strictly the same as before
(doing whatever it takes to keep the nose where it was before).

Reducing the speed means, the aircraft develops less lift: Aircraft is supported by less pounds of lift force (meaning which lift is less than weight)

What happens next? (imagining that pilot does not nose down)

My take:
1. Since weight > lift, aircraft drops attitude and falls like a stone that was dropped in midair unless the nose is down.

My friend says:
2.  The airplane finds new lift. This sinking motion creates lift
for aircraft. But it will not maintain straight level flight but descends. It will be a steady descent not accelerating descent. (not like a stone falling out of sky). He says this is called power descent

My question is:

1) Who is right here

2) If my friend is right, if aircraft can find lift after it descends (which means it found equilibrium) , why can not it maintain straight and level flight. And what exactly caused it to find new lift? Has angle of attack changed?

Neither of you are necessarily right, but you both have some understanding which is accurate.

Let me reiterate what you have stated, for clarity's sake. The scenario starts with the aircraft flying straight and level. Then the airspeed is reduced by 30 mph through a power reduction while the attitude is held constant. Regardless of what else happens we all recognize that this will result in some type of descent.

You are right in that the airplane has lost "lift" from the lost thrust and will thus descend. Depending on the aircraft and the starting airspeed, you might be right that the  aircraft might respond with an uncommanded attitude pitch down. If that were the case, it would be due to the scenario resulting in an aerodynamic stall. However, even if the aircraft were to stall it would not drop like a stone (that is, with no lift to oppose gravity), but would descend at what would still be a substantial rate of descent while still producing some lift to oppose gravity. Moreover, considering the possible entry speeds and attitudes, a stall would be unlikely in this scenario.

Your friend is right in that, with sufficient airspeed and no aerodynamic stall—both of which depend on the airspeed at which the maneuver was started—this scenario will result in a descent. It would be accurate to call this a powered descent. Depending on what he means by it, your friend may not be quite right to think that any "new" lift would be produced by the sinking motion itself, but this might be a difference of semantics. Let's explore this further.

Let's consider a Cessna 172 cruising straight and level at 110 mph. We then reduce the power to maintain 80 mph and hold the pitch attitude exactly where we started. In this scenario we have transitioned from cruise speed to something closer to the aircraft's best rate of climb speed. This means that we have transitioned from a high speed, high drag region of flight to a lower speed, lower drag region of flight. At the same time, by holding the aircraft's pitch attitude constant, we have changed from a low angle of attack, low coefficient of lift region of flight to a high angle of attack, high coefficient of lift region of flight. This increase in angle of attack is due to the new angle of the relative wind introduced by the aircraft's descent. The overall amount of lift doesn't change, but the way the lift is created does change. As the speed is reduced the wing's ability to create lift (expressed by the coefficient of lift) increases with the increase in angle of attack. Thus the lift doesn't change, but the lift is now due more to the angle of attack than the airspeed. If this is what your friend means by "new" lift introduced by the sinking motion, then he is right.

However, this "new" lift must be understood to be due to the angle of attack change, not an increase in net speed (kinetic energy). The lift isn't actually changing, merely the way in which it is created—angle of attack as opposed to speed. However, if the scenario were different and we allowed the aircraft to pitch down as we reduced power, the aircraft would pitch down to maintain about 110 mph, and the wing's coefficient of lift would change very little as the airspeed and angle of attack remained relatively constant.


Can the APU provide emergency thrust? By David Monniaux (Own work) [GFDL, CC-BY-SA-3.0 or CC BY-SA 2.0 fr], via Wikimedia Commons

Many larger airplanes have gas turbine APUs (auxiliary power units). It seems that their exhaust is oriented to the rear and might provide some thrust.

How much thrust does an APU provide and would it be enough to keep flying an airplane if the main engines went out?

An APU lacks the critical component that produces thrust, a propelling nozzle.

  A propelling nozzle converts a gas turbine or gas generator into a jet engine.

and

  Most modern passenger and military aircraft are powered by gas turbine engines, which are also called jet engines. There are several different types of gas turbine engines, but all turbine engines have some parts in common. All gas turbine engines have a nozzle to produce thrust, to conduct the exhaust gases back to the free stream, and to set the mass flow rate through the engine. The nozzle sits downstream of the power turbine. (NASA)

Would it be enough to keep flying an airplane if the main engines went out?

It would, in the sense that it will provide electrical and pneumatic power for the different aircraft systems, but no thrust. Or airplanes would have just been built with a few of those tiny APUs. :)

Another alternative for backup systems power when airborne is the Ram Air Turbine.

RE comment about turboprops having some exhaust thrust, they also have nozzles, which an APU still lacks. (NASA)

  Before entering the nozzle (...) the exhaust velocity of the core is low and contributes little thrust because most of the energy of the core exhaust has gone into turning the drive shaft.


Do the FACs compute every speed value shown on the PFD speed scale, or only stall speed and maximum speed? On an Airbus aircraft, the Flight Augmentation Computers (FACs) control the rudder and have windshear detection, and the FACs also are responsible for speed computations. I know the FACs continuosly compute stall speed and compute the maximum speed but do the FACs also compute every other speed on the speed scale; VLS, alpha protection, alpha floor, green dot speed, flap retraction, etc., so basically the FACs compute every speed on the speed scale?

Yes. Kind of--the air data computers do some of the computations and display those based on hard coded limits.  For example, an ADC will compute current AOA and may have the AOA limits hard coded therein.

The air data computers also provide input to the FACs, which further limit the aircraft speed envelope based on altitude, speed, and configuration.  The FACs are necessary for configuration information and flight control positions.

A detailed explanation of the what the FACs accomplish is here.
There is a related question.

Other examples of ADCs and their respective displays appear here and here.  The first shows mechanical systems which compute a normalized AOA based, and later in the same article, a Gulfstream display shows feathers for Max AOA on the ADI, as seen here.


What does a numbered dot mean on a sectional chart? What does this point (125) mean on a Sectional Chart?

Is it the field elevation, or just the highest elevation on the area?

It’s a local elevation at a particular point, generally in a flat area as a reference base elevation for the area.


First actual flight lesson, what to keep in mind? With any luck, I'll soon be going into the air for my first actual flight lesson.

Short of the obvious (get a good night's sleep before; eat appropriately; try to not stress out; etc.), what should one keep in mind in anticipation of such a milestone in one's pilot training?

Bring a camera. That's about it.
Unless you're training part 142 (you probably aren't) and were given homework (you probably weren't) your first flight is where you get to see what it's like to be in a small airplane, feel the controls, and get a sense of practices and procedures.
Nobody expects you to be good at anything at this point.

Instructor responsibilities during the first lesson:

Ensure the safety of the flight
Introduce you to the airplane and to basic flight operations, including straight and level, basic turns, climbs, and descents.
Answer your questions
Get your contact information and learn when and how you would like to be contacted.

Student responsibilities during the first lesson:

Be a sponge: look, listen, absorb.  You're not going to understand everything the first time, but start getting the general feel.
Ask good questions. Your instructor will be able to answer them, or if they're not relevant, she'll defer them to a later time when you have more foundational knowledge to build an answer on.
Ask stupid questions.  You're on day one.  How are you supposed to know a good question from a stupid question? If you're afraid to ask the stupid ones you'll miss out on asking the good ones.  Your instructor doesn't care about stupid questions. She'll either defer them or respectfully let you know that they're not relevant. If she's an excellent instructor she'll also file away the fact that you asked as a point of possible misunderstanding to touch on later when you have a better base of knowledge.
Get your instructor's contact information and learn when and how she would like you to contact her.
Take a bunch of pictures. It's your first flight lesson!

Only one of these requires advance preparation. Got a camera? Good. Go have fun.


Can different airliners of the same type feel different to a pilot? (There's a related question Do two of the same model of aircraft feel different to fly? already. But:

It's not about airliners, and most of the answers concern other aircraft.
Not one of the answers discusses feel - subjective experience. They discuss performance, position and orientation of controls, where the air-vents are, the lighting - but not how it feels (or sounds or even smells). I'm concerned with this subjective experience.)

By "different airliners of the same type" I mean examples of exactly the same model in the same configuration with the same engine options.

By "feel" I mean how the aircraft responds and behaves, as experienced subjectively by the pilot.

Given a pair of cars of the same model in the same configuration, after a year or so you might well find that one feels different: the steering in one may be twitchier or looser, the clutch bites differently, the brakes respond sooner, it bounces more excitedly over bumps, the gear lever is stiffer.

There may also be different noises from the suspension, or sound from the engine at idle. Perhaps one car smells different on wet or hot days.

Are similar subjective differences apparent to pilots of different examples of the same airliner?

By "feel" I mean how the aircraft responds and behaves, as experienced subjectively by the pilot.

Yes, there are differences but they are generally small and might not be equally apparent to all pilots. That, of course, is a problem with "subjective differences."

However, I do remember a 747-200 that I flew that did have a distinctive difference from other -200s of the same configuration, and a difference that other pilots noticed.

"...when I pulled the power at 50 feet, the plane sunk like a rock....The captain later apologized for not warning me that this particular airplane (I hadn't been in it before) had a tendency to drop out of the sky when you pulled the power."

The quoted excerpts are from the third paragraph of https://terryliittschwager.com/Journal/1995-07-04.html.


What is a take off roll? Reading about 737-900ER take off roll (3000 meters) from another question, I would like to know what this means.

Is it intended that the aircraft needs 3000 meters before it can pitch up to take off or at 3000 meters is has acquired sufficient height and should be airborne?

The take-off roll, also called ground roll, is the roll distance before the aircraft becomes airborne.

In case of the 737-900ER, it will be in the order of 2000 meter.

The quoted 3000 meter is probably the take-off distance required (TODR) or take-off run required (TORR) at maximum take off weight. That assumes a full throttle acceleration to about half of the runway (1500 m), then an engine failure, continued acceleration on a single engine, rotation and take-off at 3000m. In case of TODR, the climb to a height of 35 ft is included as well (for FAR Part 23 aircraft it is 50 ft).

This means the 737-900ER requires a runway of 3000 meter length to take-off with an engine failure or to stop when the failure happens before the decision speed (V1). Since engine failures are unpredictable this is the minimum runway length required for take-off planning.

This all assumes ICAO standard atmosphere conditions. For runways at higher altitude ( > MSL) / higher temperature (> 15 deg C) the TORR will be even higher.


Can I use the private pilot written exam for sport pilot? I'm planning to first get my sport pilot license and then continue on to private pilot, to save on written exam costs is it possible to just take the private pilot written exam for the sport pilot license or will I have to take both?

No.  You will have to take both written and practical exams for sport and private pilot, if you go that route.  I’d recommend that, if you do ultimately want to obtain a PPL, that you not pursue an SPL as part of your training and solely concentrate on obtaining your private only.  You can exercise all the privelages of an SPL with a PPL, and it cuts out the excess costs and time with the SPL testing and checkride prep.


Can a pilot transition from a localizer approach to an ILS approach? I was recently looking at the approach to RWY 8L at Honolulu, Hawaii (PHNL).

Looking at the approach IAFs, I see the LOC RWY 8L approach has many different options, and has an intercept altitude at 2,300 ft. The ILS RWY 8L approach has three IAFs but none are south of the airport, and the glide slope intercept altitude is 2,700 ft.

In the scenario where a visual approach isn't appropriate and an ILS may be necessary, are there procedures/rules in place for a pilot to transition from the LOC approach to the ILS with glide slope once they are lined up? I know the LOC intercept is at a lower altitude, so can a pilot just intercept the glide slope from that altitude or are the two procedures incompatible and radar vectors are required to line the pilot up for the ILS?

I'm looking specifically at the JULLE5 STAR into the LOC 8L approach. JULLE5 ends at ALANA. The LOC has a IAF from ALANA, while the ILS doesn't (only BOOKE).

You can't legally switch from the LOC to ILS approach without ATC approval in this case, since they are different enough and are on different plates. However, if you're outside the FAF you can ask ATC to switch from LOC to ILS, and proceed with the ILS if approved. However, in lost comms, if you got initial approval for the LOC approach but no mentions of ILS, you can't switch to the ILS. Unless you exercise your emergency authority.


During night flying, which color lens for a flashlight is most beneficial? I went on a night flight tonight after not flying for a few months.  I didn't have any monochrome lights, so I actually just covered a flashlight of mine with red athletic tape (which acted as a filter really well).

I know that using monochrome is the most important thing about preserving night vision - but does it particularly matter, while flying, which color I use?

You will want to use red light.

Why?

See Does red light preserve your night vision? on the Biology StackExchange for a good explanation of the biology and physiology involved, and how it relates to perceptual ability.

As stated in this answer (by leonardo) to that question:

  If one is exposed to red light (above ~650 nm), it would activate the L-type cones mainly (possibly some M-type activation), but no rod activation. Rods are the low light receptor cells in our eyes, and as such, are very sensitive to the photon density, or brightness, entering the eye.

  This is just my speculation, but I think it's plausible that if you were in a completely dark environment with just a red light, filtering out the higher frequencies, night vision could be spared in the sense that we don't activate the rod cells.


Can the debris pattern from a crash site confirm explosion as the cause of a crash? Is there any precedent or can the debris pattern positively confirm the cause of a crash due to:

an internal explosion OR
strike from a missile or other military projectile?

If a particular flight path is necessary to facilitate the question, assume the 1988 Airbus flight.

No, not an explosion, just break-up.

The debris field can prove if some parts of the aircraft broke off in the air, before the main impact. However the aircraft can break up also if the pressure vessel fails, if intense fire compromises the structural integrity, or due to mid-air collision.

And on the other hand, an explosion can make the plane uncontrollable without breaking off any large parts e.g. if it severes the hydraulic lines (which can also start fire as the hydraulic fluid is flammable).

An explosion can only be proven by collecting pieces of the wreckage and looking for traces of spalling, shrapnel damage and traces of an explosive.


What is this aircraft with a big gun on its back? It looks like there is a really big gun on the back of this aircraft.

https://www.instagram.com/p/BQVqnYCAlZU/

I found it on Instagram. What is this?

That's a German WWII V-1 flying bomb.

  It was an early cruise missile and the first production aircraft to use a pulsejet for power.

The pulsejet being the tube on top.

(Source)


What drives N1 during a jet engine start? A typical jet engine start sequence that I understand is as follows:

ENG Start Switch to Ground → Start Valve open → N2 increases → N1 increases → ENG Start lever to Idle (when N2 has reached a certain number) → Fuel flow starts → EGT rises → ENG Start Switch cutout

As far as I understand, N1 and N2 are mechanically seprated. If that's the case, what drives N1 before it starts to rotate from the following combustion?

N1 is driven by the starter flow through windmilling. N2 is started through a gearbox as described in this answer, driven by an air starter or by an electric motor. This causes air to start flowing through the engine, and the LP turbine blades pick up energy from this airflow.

Above graph is from The Jet Engine by Rolls Royce, and shows that the LP spool (N1) starts to turn in the dry cranking (starting) phase, after N2 has been accelerating for a while. The speed with which N1 spools up depends on the engine type, but even the large inertia of a helicopter rotor is slowly starting to be driven around by the starter flow.


What is this aircraft with elaborate folding wings? I noticed this plane in the background of this car advert. Can anyone identify it? I'm assuming that may have been used on an aircraft carrier, hence the elaborate folding wings?

Fairey Gannet ECM.6, c/n F9311, stored at White Waltham Airfield in the county of Berkshire in England. This place is incidentally where the Fairey Aviation Company built and test-flew the Gannet. An aerial picture from Google Maps:

Farey Gannet XA 459 at White Waltham Airfield. Google Maps
In Feb. 2020 the aircraft was Finally moved to Solway Aviation Museum to be heavily restored for public display.
The wings can be folded in order to park the aircraft on a carrier deck, or on its storage areas. Unfolding the wings (video).

Fairey Gannet ECM.6
Fairey Aviation was a manufacturer which worked a lot with the British Royal Navy's Fleet Air Arm (FAA). With the role played by German and Japanese submarines during WW2, the FAA reinforced its anti-submarine warfare. Fairey Aviation developed the carrier-borne Type Q, later renamed Gannet version AS.1 quickly upgraded to a more powerful AS.4.

Fairey Gannet AS.4. Source
The prototype first flew on 19 September 1949 and made the first deck landing ever by a turboprop aircraft, on HMS Illustrious in June 1950. The anti-submarine role was later taken by helicopters, and AS.4 versions were converted for electronic countermeasures (ECM.6). A third seat was later added over the wing trailing edge for a second observer. This disturbed the airflow over the horizontal stabilizer, requiring the addition of small finlets:

Fairey Gannet ECM.6 with three seats. Source: Gothic-Air

Fairey Gannet landing on Australian HMAS Melbourne. Picture David Tomkinson, source
The Fairey Gannet was powered by a dual Armstrong Siddely Mamba, driving two contra-rotating propellers. One engine could be shut down in flight to conserve fuel if required.
XA 459 RN
A total of 348 Gannet were built, this particular airframe is c/n F9311 registered XA 459 RN for the Royal Navy. It entered 814 NAS in March 1957 as AS.4. Here at RNAS Culdrose in 1976, after it was converted into ECM.6:

Fairey Gannet ECM.6 at RNAS Culdrose, 1976. Photo by Ray Barber at flickr
The aircraft was decommissioned in 1978 and later displayed at Wales Aircraft Museum (Cardiff EGFF):

Fairey Gannet ECM.6 at Wales Aircraft Museum, 1982. Photo by Chris England at ABPic
The museum was disbanded in 1996. The Gannet was then acquired by private individuals in order to restore it. However tragical events prevented the restoration. It was finally bought by White Waltham airfield in 2006.

White Waltham from 2006 to Feb. 2020

XA 459 at White Waltham. Photo by Renegade53 at ipernity

XA 459 at White Waltham. Photo by Jon Wickenden at Flicr
Ian Meredith told us in February 2020 the Gannet was moving to a new place:

Tonight the Gannet and its spare engine(s?) was aboard a low loader
for a UK museum. A place of restoration, a place in the dry.

This place is the Solway Aviation Museum at Carlisle Lake District Airport. On the move:

Fairey Gannet XA 459 moving to its new place, Feb 2020. Source.
Solway Aviation Museum since 2020
Video of its arrival

More about the aircraft:

Exhaustive description of the Fairey Gannet: Alchetron
Pictures: Fleet Arm Association of Australia
Pictures: Flickr
History: Stephen Metcalf's page
History: South Wales Aviation Group


Why did Cessna get rid of manual flaps in their 172? At the club I fly at, there is an older Cessna 172 that has a manual "Johnson Bar" that is used to put the flaps down.

In the newer 152, and I believe the rest of the planes (I have yet to fly them), the flaps are controlled via a electronic (or hydraulic?) lever.

It appears to me that the manual flaps are more reliable, more maintainable, and a hell of a lot more fun in my opinion. Additionally, the manually flaps don't require a lot of strength to operate IMO. Does anyone know why the automatic design is favored over the manual counterpart? Same question applies to car transmissions...

Nobody can definitively answer this for you except Cessna's 1965/1966 engineering team (the year they made the change), but there are two reasons I can think of:
Because switches are cooler than Johnson bars; or Because everyone else is doing electric flaps.

Much like with manual transmissions, some people just don't like the extra work of manual flaps, and for those folks electric "flip a switch and don't worry about it" flaps are a selling point.

In terms of reliability it's a trade-off (as are all engineering decisions), so let's look at a few of the factors:

Mechanical Flaps

+Flaps still work when the battery is dead.
+The pilot can control the extension/retraction rate to some extent.
+Usually cross-linked with a bar (so you can't have a "split-flap" condition)
+Simple to rig, adjust, and maintain.
-Actuation requires more pilot skill
You need to develop the muscle memory to grab the handle without looking.
You need to learn to govern the extension/retraction rate smoothly.
-The failure mode is usually "Flaps Up"
You could lose your flaps on short final if the cable or lock mechanism fails.

Electric Flaps

+"Easier to Operate" (you don't need to reach down to the floor)
+Extension/Retraction rate is constant (governed by the motor)
+Fewer moving cables running through the fuselage (wires replace them)
+Typical failure mode (e.g. dead battery) is "Flaps stuck where you left them"
Less chance of losing your flaps on short final.
+Depending on the design they may save some weight over a mechanical system.
-You lose control of the flaps if the battery dies (no-flap landings are more likely)
-You have one or more motors to maintain/replace if they fail
-Depending on the design it's possible to have a "split-flap" condition

Cessna's engineers and marketing folks looked at those factors (and probably many others) and decided that electric flaps "made sense". On the other side of the GA fleet, Piper's engineers looked at the same factors and decided to keep the Johnson bar flaps (which are still found in the PA-28 series today).

From a manufacturing standpoint it makes sense for all of the aircraft a manufacturer produces to use the samecontrol mechanisms -- either all the planes use mechanical flaps or all the planes use electric flaps because it simplifies production and allows everything to run through on one assembly line rather than stopping at the flaps and diverting aircraft to different teams.


Aerodynamic Pressure Loads in FEA of Lifting Surfaces - Query Let me give a brief summary of the process involved in the FEA of lifting surfaces with the wing as an example:
1. The wing is modelled as a hollow surface body in Ansys, meaning only the exterior aerodynamic surface is specified.
2. Internal structure made of composites is modelled next.
3. Aerodynamics loads and Boundary conditions (fixed edge at the root of the wing) are specified.
4. The solution is obtained in terms of displacements, stresses and failure criteria etc.

As part of Step-3, aerodynamic loads are generated in the form of Cp values (Coefficient of Pressure) at discrete points on the exterior surfaces of the wing. This data is generated from XFLR5.
Cp values are converted into pressure values and applied on the exterior surfaces of the wing. To do the same, the following formula is used:

Pressure values obtained from the LHS of the above expression are applied over the exterior surfaces of the wing. FEA process is completed and the solution is obtained.

FEA predicts that the wing cross-section is unable to maintain its airfoil shape and the wing cross-section essentially gets "crushed"'.

Observe the crushing of the wing cross section in this figure where the top surface and bottom surface come close to each other and airfoil geometry is completely lost

However, it finally struck me that there has to be an internal air pressure that will support the cross section from the inside as what happens with hollow structures on earth, eg. a hollow can be placed on the ground doesn't get crushed into itself since the external and internal pressures cancel each other out.

Hence, we should not be using absolute pressure but rather gauge pressure (difference in external and internal pressure) should be used. Otherwise, it essentially means that there is a vacuum on the inside and air pressure on the outside.

Once this change was made, we no longer observe the "crushing" effect.

Finally, we still want to be sure if the internal air pressure would be equal to the static pressure at that altitude as has been assumed in the usage of gauge pressure.
Our assumption is that the pressure inside the wing body would be equal to the static air pressure at that altitude from thermodynamic relations even if the wing is completely sealed. IS THIS ASSUMPTION CORRECT? ANY SUGGESTIONS WOULD BE HELPFUL?

There is fuel inside the wing, and there is definitely a connection with the outside atmosphere for venting while fuel is flowing into the engines. The fuel tanks are sealed from the outside airflow. In a document about the B737NG from Smartcockpit.com (now via Scribd) it says:

  The purpose of the fuel vent system is to prevent damage to the wings due to excessive buildup of positive or negative pressure inside the fuel tanks and to provide ram air pressure within the tanks. The tanks are vented into surge tanks which vent through a single opening at each wing tip.

A recent development, long recommended by the NTSB but deemed too expensive to mandate by the FAA, from this site:

  Boeing has developed a Nitrogen Generating System (NGS) which decreases the flammability exposure of the center wing tank to a level equivalent to or less than the main wing tanks. The NGS is an onboard inert gas system that uses an air separation module (ASM) to separate oxygen and nitrogen from the air. After the two components of the air are separated, the nitrogen enriched air (NEA) is supplied to the center wing tank and the oxygen enriched air (OEA) is vented overboard. NEA is produced in sufficient quantities, during most conditions, to decrease the oxygen content to a level where the air volume ... will not support combustion. The FAA Technical Center has determined that an oxygen level of 12% is sufficient to prevent ignition,


How does the reusable holdback bar work? Sources: wikimedia.org and ar15.com

Holdback bars are used to hold a carrier plane at full thrust until the catapult pulls it for launch.

Older bars (right) use a disposable shearable block (item 5) between the bar and the plane.

How does the reusable holdback bar (left) work?

Source: YouTube

The bar is placed between a tong-like (two hooks) device on the aircraft, and when released, the body of the holdback bar envelops the hooks (note the disappearing red paint on the tips of the hooks) forming a collet.

On the inside, as the plane pulls on the bar (1), the walls (2) compress a chamber filled with hydraulic fluid (3). The fluid pushes into a channel and pushes against a sphere (4). At the right pulling force, the sphere is pushed which allows the fluid to fire the piston (5) freeing the inserted hooks from the bar.

Source: YouTube

Reference: Repeatable release holdback bar, US Navy patent US4101099A


Do tanker aircraft distribute their own fuel? Do tanker aircraft, (such as the KC-135, KC-10, S-3B, etc), distribute fuel from their own fuel tanks, or is it strictly from a separate cargo tank?

Obviously, some cargo tanks are going to be involved, as an aircraft carrying only the fuel in it's wing tanks isn't going to be a whole lot, and some of these aircraft are known to fuel some very thirsty birds, such as B-52's, etc.

Sub question: What proportion volume of the aircraft's fuselage is taken up by the addidional fuel. Do they just pack it as full as they can with fuel? Seems like this would very quickly add to weight, and you would struggle getting such a fuel laden ass bird off the ground.

Both the KC-135 and KC-10 can burn the fuel it carries on board for refueling (the notable exception was the KC-135Q, which carried separate tanks of JP-7 for the SR-71 Blackbird).

Both indeed do have significant fuselage tanks - the KC-10 is notable for being 'dual-mission' capable, meaning it can carry both fuel and cargo, and the KC-10 is also air-refuelable (so a KC-135 can offload extra gas into a KC-10 when their crew rest is up, allowing the KC-10 to stay on station and refuel other planes longer). The maximum fuel load of a KC-10 is 356,000 pounds. This is over 7 full loads of gas for a B-52 (B-52G and H could carry 308,000lbs of fuel, so 365,000 capacity of KC-10 would potentially fully fuel a B-52 one time, with enough fuel left to get the KC-10 home. Of course the B-52 would never be completely empty in the air so the KC-10 would not need to offload the full 308,000lbs), or 30 full loads for an F-16 with external tanks, and the maximum fuel load of a KC-135 is 200,000 pounds, or over 4 full loads of gas for a B-52.

As for how much of the fuselage is taken up by fuel tanks, you can look at cutaways of the KC-135 and KC-10 (unfortunately the captions for the KC-10 are in a foreign language, as I could not find a high-enough resolution one in English). In both cases, the fuel tanks are in the lower half of the fuselage - the reason the KC-10 has a cargo mission as well is because it is a larger aircraft and has a much higher gross weight. The KC-135's cargo space is much smaller, and as such is not used for transporting large items. This technical document for the KC-10 also gives volume of each tank (called Fuel Cells):

Forward Fuselage - 8,250 gallons in 3 sections, 6' deep
Aft Fuselage - 9,870 gallons in 4 sections, 6' deep

You are correct that it is a struggle getting them airborne when fully loaded - several of the KC-135 pilots I have talked to have taken until the very end of 10,000 foot plus runways to get airborne, and one of the KC-10 pilots I know said they would occasionally take off with less than a full load then take on fuel from a KC-135 to make it easier.

Page 3-45 of this technical manual has a chart for calculating minimum runway for a particular speed - for example, a sea level takeoff at 30 degrees (Celsius) at Max takeoff weight would require about a 13,500 foot runway.


Why are the A300/310’s electric pitch trim switches inhibited with the autopilot engaged? The A300/A310, like most other aircraft (except for some small general-aviation aircraft), has an adjustable-incidence-angle horizontal stabiliser, which is used to trim the aircraft in pitch (for instance, to change the aircraft’s speed or compensate for shifts in its center of mass) without the need for large elevator deflections (which would increase the stress placed upon the elevator control linkages and actuators, shortening their lifespan, and, if the autopilot was flying the aircraft, would  result in large pitch excursions upon autopilot disconnect as the elevator returned to its neutral position).

There are three methods by which the horizontal stabiliser can be moved:

The A300/310’s autopilot, like those of most other autopilot-equipped aircraft, automatically trims the aircraft in pitch when engaged; it moves the stabiliser by applying power to a set of electric motors which rotate the stabiliser jackscrew, moving the stabiliser’s leading edge up or down.
In manual flight, the aircraft is usually trimmed by using two sets of electric trim switches (one on each of the two control yokes), which, like the autotrim system, apply power to a set of electric motors which rotate the stabiliser jackscrew.
As a backup, a manual pitch trim wheel is mounted on the center console between the pilots; this wheel is connected to the stabiliser jackscrew via a cable mechanism, and, when used, manually rotates the jackscrew directly.

If the autopilot is engaged, the electric pitch trim switches are inhibited, and cannot be used to trim the aircraft; the aircraft can only be manually trimmed by rotating the manual trim wheel, which disconnects the autopilot.  As a result, in the event of an autotrim runaway, the pilots need to take one hand off the yoke to manually trim the aircraft against the malfunctioning autotrim.  This is especially critical in two specific autopilot modes (LAND and GO-AROUND), where pulling or pushing on the yoke to use the elevators to manually counter the autotrim-induced pitching moment will not disconnect the autopilot if the aircraft is less than 400 feet AGL (and, originally, would not do so no matter what the height AGL); indeed, doing so will cause the autotrim to trim further and further against the pilots’ control inputs, exacerbating the problem at a time when maintaining pitch control of the aircraft is (due to the very limited altitude available with which to work with) far more critical than in most other phases of flight.

So why are the yoke-mounted electric pitch trim switches inhibited and inoperative whenever the autopilot is engaged?

Like with two human pilots, you want control1 to be explicitly in one hands. With autopilot, it's the same: it should be either autopilot or you.

In the case of 'breaching' the normal transfer protocol for whatever reason ("I have control" - "You have control", which in case of autopilot would be the autopilot disconnect button), there are two possible courses of action when the pilot just starts to control the aircraft:

Immediately give control by explicitly disconnecting the autopilot.
Keep control by ignoring/overriding the pilot as much as possible.

Apparently, Airbus espoused the second strategy. It made sense for them to ignore the pilot (whether for trim or main control) until s/he explicitly requests control. (There is not much the aircraft can do when the pilot starts to trim the wheel manually, so it still disconnects).

If the trim switches were not ignored, there could be two options.

Disconnect the autopilot. But this changes the whole ideology, and other things would need to be changed to be consistent.
Just change the trim. But the autopilot (which is still in control) would have to fight against it in order to keep doing its job (e.g. flying level), either by trim or elevator.2 This makes no sense and creates dangerous confusion.

Arguably, completely ignoring the pilot is not a very good idea, so Airbus had to change the algorithm at least in some situations.

1 By 'control' I mean guidance control, excluding things like stability augmentation systems.

2 Unless this is a simple autopilot which does not actuate trim at all and may then need help from the pilot. This is the case for some GA aircraft, but not for A300/310.


Why doesn’t the A320 family suffer from the same design constraints regarding engine placement/landing gear length as the Boeing 737 family? This answer gives a pretty good description about the design issues which lead to the problems of the Boeing 737 Max (basically the same as in a video I watched a while ago):
The landing gear of the 737 is fairly short. One benefit at the time was that this eased baggage/cargo loading by hand. The JT8D engines for which the original 737 was designed were slim enough to fit under the wings.
However, these engines performed poorly when compared to later generations. Unfortunately, later generations of engines such as the CFM56 are also larger in diameter, so Boeing had to resort to various tricks to squeeze modern jet engines underneath the wing, while still ensuring sufficient ground clearance.
Increasing the height of the landing gear, thus adding enough ground clearance in order for the bigger engines to fit underneath the wings, was not an option. As the landing gear retracts into the fuselage in flight, its length essentially is limited to the distance between its mount points on the wings, minus some clearance.
Mounting the landing gear further outward on the wing would have required a structural redesign to cope with the increased torque from the landing gear. Retracting the landing gear with the wheels in “tandem” (one behind the other rather than both next to each other), or shortening the gear upon retraction (either by a telescope mechanism or an extra hinge) would also have been major design modifications, which would have been costly and taken extra time to develop.
Therefore, Boeing opted to reduce the engine diameter as far as they could (which helped a bit but not enough), and move the engine further forward and higher up on the wing. Because the latter alters certain handling characteristics, they added an electronic system known as MCAS to compensate for that. As this change was not clearly communicated, pilots were not aware of it, which eventually lead to two crashes and the grounding of the entire fleet.
What none of these two sources addresses: the 737’s main rival, the A320 family, was designed two decades later and had the larger engines from day one, along with sufficient space underneath the wings to accommodate them.
So how does the A320 design address this? Longer landing gear with attachment points further outward on the wing (which I assume is fairly easy to do on a new design but comes at a significant cost when upgrading an existing one)? Or something else?

So how does the A320 design address this? Longer landing gear with attachment points further outward on the wing [...]?

Yes, the A320 has a longer and therefore wider landing gear. You can find general aircraft dimensions in the Airplane Characteristics for Airport Planning documents.
Airbus A320-200: 7.59m wide landing gear

Boeing 737-800: 5.72m wide landing gear

The same document also lists the ground clearances at different points. At MTOW (max. takeoff weight) or MRW (max. ramp weight), the ground clearance
below the fuselage is
A320: 1.72m, 737-800: 1.30m
and below the engine nacelle it is
A320: 0.57m, 737-800: 0.48m

Sources: Airbus, Boeing


Is there any reason for why the cabin temperature would suddenly become very high? I was flying a Fokker 100 a few months back over central Europe. We had probably just reached cruising altitude when the cabin temperature suddenly skyrocketed without reason, with the air coming out probably around 30 degrees (Celsius). After complaints by fellow travellers it became cooler. Is there any reason why it would do this?

I guess the pilots might have done it, but I see no reason for it, so could the aircraft have done it on its own accord?

Over Central Europe in the winter time, air becomes tremendously cold. Since warm bleed air from the compressor stage of a jet engine is used for cabin heating, the pilots might have set temperatures to maximum in order to warm the cabin.
But being in a climb, almost all power of the engines is required for lifting the aircraft, thus leaving only little excess bleed air to be used for heating. During normal days and outside air temperatures this should be enough, though.

By levelling out the aircraft, the engines are spooled back (less power required than in climb -> hence more excess bleed air available -> higher ability to warm the cabin in cruise than in climb). If the pilots/cabin attendants just didn't realize this circumstance rapidly enough, the cabin is being flooded with maximum heating air from the engines.


Why do airliners have "pressure bulkheads"? Image source: FAA

What part of the fuselage aft of the bulkhead would leak pressure? Or is it just there to reduce stresses?

How does a DC-9/MD-80/90 incorporate aft bulkheads when there's a staircase in the way?

(Image source)

What part aft of the bulkhead would leak pressure?

That's a partial misunderstanding of what a bulkhead is there for.

You could build the aft cone section to keep the pressure, but it would be a much heavier solution.

The shape of the final aft section is not well suited to resist pressurization stresses: the best shape is a sphere; the cylinder (with spherical terminations) comes a close second. The conical shape would require serious stiffeners to survive pressurization cycles for the whole life of the aircraft; the bulkhead solves this problem by using a shape that is naturally more resistant to stresses - and thus can be built with less material - leading to less weight, and hence fuel savings (in addition to the increased safety).


What is the definition of “airport boundary”? While flying in to KBTR in a helicopter, I called tower and stated “10 west, landing south ramp with information Mike”. They responded “proceed to the airport boundary”. When I was closer I got the landing clearance to the ramp. Does the phraseology “airport boundary” have a specific meaning, or is it simply in lieu of a pattern entry instruction. My local controllers typically give a reporting instruction like “continue inbound, report 1 west”

It's effectively a reporting point consisting of the point at which the controller expects you to cross the perimeter fence line around the airport property.  If the controller uses that term, I would expect that there is a pretty obvious perimeter fence, and the controller isn't too concerned with the precise location at which you cross it, within reason.


How can one enter an airliner without stairs or a jet bridge? I see that big planes (B737, A319 etc.) always need a staircase or a boarding tunnel in order for crew or passengers to enter the cabin since the position of the entry door is quite high (meters above the ground). What solutions are there if none of these options are available? (Except, obviously, for aircraft like DC-9's/MD-82 and 727's which had the rear entrance) How could the pilots get in? Is there some sort of manhole under the aircraft that can be opened to get inside with a sliding staircase or similar?

Living in Africa, I have been to a couple of airstrips where these aircraft do land. Obviously all the airports had stairs but since we cope with some strange situations over here, the question came into my mind. What is the alternative should something go wrong and no traditional means be available to get in the plane?

There are no rear entrances these days, but many smaller jets like the Avro-RJ, Bombardier CRJ series or Embraer regional jets have their own air-stair on the main (front left) door. On the smaller planes the door are hinged at the bottom and the stair are part of the inner side of the door, on the larger ones there may be folding stairs stowed beside the door. B737 can have those too, but it's optional, so many operators choose not to have them (and on second-hand aircraft the operator sometimes bother removing them, but rarely adding them back). I've never heard of them on A320 family as it's a lot higher.

You can get always out using the emergency slides and in cockpit they have a rope to climb down through the side window (where it's too high to jump from it) in case the cockpit door can't be used (happens sometimes).

However the only way in is using stairs. It's hard to imagine you wouldn't be able to scramble at least a ladder even at very remote landing strip where the plane has made an emergency landing. Regular landing will obviously not be done to a place without regular stairs (unless the plane has integral airstairs, of course) and if it was emergency landing you need to bring in mechanics and fuel to get the plane out, brining a ladder is not much extra trouble.

Edit: As Kevin noted below, many aircraft have engineering access hatch in or behind nose wheel well. Not an option for boarding passengers, but the crew can use it when they don't have stairs/ladder handy.


What controllers are used in Airbus/Boeing fly-by-wire systems? I was wondering, what controllers are used in airbus or Boeing aircraft fly-by-wire systems to control servos? Who manufactures such controllers, or are the systems controlled from flight computer directly?

The systems used by complex aircraft are typically made specifically for an aircraft platform and all the different manufacturers of both air-frames and the control systems will have slightly different system architectures.

For example, a system will have a flight control "computer" made by one manufacturer, this will send commands via a data bus to the actuator control unit which will move the control surface via a hydraulic actuator.
Another may have the flight control computer directly control the actuator.
Remember that with flight control computers there will be multiple computers all performing the same task, providing redundancy should one fail. Duplex and Triplex flight control systems have historically been used.

Companies like BAE Systems, Thales, Rockwell Collins, GE Aviation, Parker Aerospace, Safran are just some examples of the many companies involved in the complex supply chain for aircraft parts.

Flight control systems for a single aircraft may be made by separate manufacturers to ensure that no single design fault causes a catastrophic failure or loss of control. This is known as dissimilarity. One manufacturer might make a flight control computer with a PowerPC processor and another will use something totally different.

In other cases, the same ASIC (Application Specific Integrated Circuit) will be specified to two separate integrated circuit manufacturers who will both build the same part.

This interesting article covers some of the points covered above
https://www.aviationtoday.com/2001/10/01/a380-more-electric-aircraft/


What's the meaning of "straight and level"? Indeed a very strange question.

My understanding of straight and level is: The aircraft is flying at a constant heading and constant altitude, and maybe at a constant speed, and this has nothing to do with the aircraft attitude. However I was reading this in "Big Red Today":

  "If you just keep it straight and level, the chances of surviving are
  better," Ms. [...] said. "But as soon as you start to turn, you put
  yourself at risk of a stall-spin.

Here this is clearly about maintaining the aircraft neutral attitude while landing, so losing altitude, and probably speed.

Is this use of "straight and level" correct? What is the definition of straight and level, if any, regarding heading, attitude, speed, altitude?

Note: Please explain for all parameters mentioned above to remove all ambiguities.

Is this use of "straight and level" correct? What is the definition of
  straight and level, if any, regarding heading, attitude, speed,
  altitude?

In the airplane flying handbook the FAA defines straight and level flight as

  Straight-and-level flight is flight in which heading and altitude are
  constantly maintained.

My understanding and the instruction I have received has always lead me to understand that Straight-and-Level is independent of Attitude and Speed. However to maintain straight and level flight at a given speed you will have to put the aircraft in a given attitude. Generally speaking at lower speeds aircrafts have a higher nose up attitude to maintain level flight and a more nose down attitude at high speeds to maintain level flight but this can vary by design and wing mounting.

In this case I would say it was used a bit improperly. The statement should have been more along the lines of "the pilot should have maintained his heading and conducted a straight ahead emergency landing. You can read more on why that is here.

You can refer to the full NTSB report of the accident here for all the details.


Tracking freighter and charter planes between two specified airports Is there a way to find the historical data of the freighter and charter planes between two airports

If you know the tail numbers of the aircraft, you can go to FlightAware.Com and request flight history there. Even if they have not filed flight plans (highly unlikely if they are commercial flights), if they are equipped with ADS-B the odds are high they will be picked up by the system at some point during their flight.


Why is the gradient line for climb in a one-engine-inoperative condition during take off under CS-25 described in percentage? Appeciate an explanation in terms of definition of climb in terms of gradient & an explanation of the reasons behind each percentage condition for the different air craft types: twin engine, three engine, four engine, maybe propeller as well?

Gradient as percentage is defined as the ratio between vertical displacement and horizontal displacement. For example, a 5% climb gradient means than for every 1 000 meter of horizontal travel, the aircraft climbs 50 meters. If you want to convert it to an angle you have to use the inverse tangent:
$\textrm{atan}(0.05) \approx 0.05 \ \text{rad} \approx 2.86 ^\circ $

In take-off configuration with the landing gear retracted, the steady gradient of climb for one-engine-inoperative (OEI) is not less than:

2.4 % for two-engined aeroplanes,
2.7 % for three-engined aeroplanes and
3.0 % for four-engined aeroplanes,

(source EASA CS-25, Amendment 20, CS 25.121)

The reason for the difference is that two-engined aircraft loose 50% of their thrust, while four-engined aircraft loose only 25% of their thrust in a OEI situation.

In other configurations there are similar differences.


Do propellers generate static electricity in flight and how is that handled? How is the risk of tribocharging (static electricity generation) by the propeller managed on an airplane? Regardless of airplane size, it seems the rotation of the propeller or engine blades could cause tribocharging somewhere in the electrical system, and that charge would have to be grounded or dissipated somehow.

While these might not be specifically for static from the prop, static dischargers help bleed charge away from the aircraft. Static definitely does build up on an airframe, requiring grounding (electrically) your plane before fueling.


What is required to fly privately from a region with high levels of the ebola virus (Nigeria) to the UK? My dad will be flying us in a private aircraft from Nigeria back to the UK.

I know that he has been in touch with someone from the UK about this, but since I wasn't present for the conversation I'm not sure what was discussed.

What precautions and declarations should a pilot make when coming from a heavily infected area? We will be landing at a private airport so the current screenings done by major airports will not be considered.

You'll be on a flight plan. You'll have to clear customs at a designated airport and file the appropriate paperwork. More info here:

Notification of Flights

If you notify the border agency it will make recommendations if they think your flight poses a risk. There is only screening at Gatwick and Heathrow.

Ebola Specific Information


Why can we not use full throttle in a C172 when cruising at lower altitudes? My flight training manual (FTM) says that at low altitudes we throttle back our trainers in order to not exceed recommended power settings.
But why is that? Is the air close to sea level just too dense for the standard Cessna 172 engine? And at 8000 feet it's just thin enough for us to cruise at full throttle?

These engines are not designed to run at maximum horsepower output all the time with a lean mixture.  They are designed to cruise at 50-75% of their rated max power, and deal with that level of internal heat and friction over the long term.  Even this is fairly hard compared to a car that runs at perhaps 20% of rated power when cruising at 60 mph.
Running them wide open means maximum heat, maximum wear, for not much benefit considering the power required to go faster is nearly the cube of the speed increase. You must run with the mixture full rich to keep the engine cool at all, and fuel burn is a lot higher because you are dumping unburned fuel used for cooling at full power out the exhaust.  It's not worth it in other words, unless you are racing, so the concept of cruising at not more than 3/4 of rated max power is a very old convention in piston engines, and mixture leaning shouldn't really be done above that.
You can run one of these engines at full throttle with a rich mixture with the RPM near red line all the time if you want, but only if you don't mind paying for the 20 thousand dollar premature overhaul from flogging the poor engine like a mule (the exhaust valves will hate you for all eternity).
It's pretty much the same thing as hooking up a big heavy trailer to your car, that required foot on the floor all the time just to stay at highway speed.  How many miles do you think that car's engine would last?(Although the Lycoming being run that hard will still probably outlast the car engine in the same shoes.)
However, when you go up, by the time you get to 8000ft, 75% of maximum output is all that is available with wide open throttle (WOT) in the thin air, so 75% cruise, normal operation, requires WOT and no harm is done. And as you go up further, you find you can't even get 50% with WOT and pretty soon you're at your service ceiling.


What item is a pushback operator holding up after pushback? After a pushback I saw the operator of the pusback truck standing next to his truck and showing the pilots a "thumbs up" with his right hand. In his left hand he was holding something up. It looked like a key or some kind of cotter.

I could imagine that it is some kind of part that he could only have if he really is clear from the plane and didn't forget to disconnect something.

Am I right? Is this some standard procedure? If so, what was he holding?

It's a steering bypass pin which isolates the nose wheel steering and enables the tug to turn the aircraft.

The operator holds it up so that the captain can see it to confirm that it has been removed.

This Wikipedia article refers to it

On some types, there may also be a "downlock" pin which prevents the nosewheel gear from retracting whilst the aircraft is on the ground.  In this case, the captain is looking for 2 pins being held up.  More often though, the ground lock pin(s) are removed before pushback and stowed onboard.


Why are piston engines so unreliable in airliners? Before the first jetliners appeared, all airliners used piston (reciprocating) engines, which were astoundingly prone to failing in flight, to the point where an inflight engine failure was an everyday, expected occurrence.  To quote Wikipedia:

  Engine failures were considered fairly routine events on piston-engined airliners in the 1940s, so the crew elected to continue the flight to Dallas, and Captain Claude announced to the passengers that they would switch to another airplane upon arrival.

In contrast, in-flight failures of modern turbofan engines are so rare that most pilots will go their entire careers without ever encountering one.  Even in the 1950s, jets were already more reliable than piston engines, which was one of the reasons they quickly seized centre stage for long-distance operations.  For low-altitude short-haul flights, where jets are inefficient compared to propellers, airliners still switched away from piston engines, moving to turboprops en masse despite piston engines having better fuel efficiency than turboprops.  All of this is despite turbine engines placing far greater thermal and mechanical stresses on their components than any piston engine.

Nowadays, piston engines are generally used only on very small general-aviation airplanes... and are no less reliable than the turboprops and jets on larger aircraft.

What is it about piston engines that makes them so unreliable on large aircraft, yet extremely reliable on small aircraft?

This statement is not entirely true. the R2800 engine was considered at the time to be quite reliable in comparison to the R3350 and the R4360. Those engines represented the evolutionary dead-end of big piston power, where pushing to more power began making the engines less reliable than their lower-power predecessors had been.

Part of this was simple statistics, where the probability of failure of a machine scales with the number of parts it contains. In crude terms this means doubling the number of pistons doubles the opportunity for something to go wrong with one of them in the engine. Note also that those extra pistons do not provide redundancy, in the sense that a failed piston will fill the oil system with broken metal, causing the other pistons to fail not long after, or start the engine on fire.

Turbine power plants provide more uptime and longer TBO's than the piston engines they replaced as well as more power for less engine weight. These attributes offset the greater replacement costs and higher fuel consumption in applications where uptime and power were required to enable a viable business model.

Cost-sensitive, low power applications still make use of pistons, with the breakpoint being around ~300HP. This is at least partly due to the fact that as turbines are scaled down in power output, their efficiency usually suffers, and their manufacturing costs do not fall fast enough to compete with pistons in the 250HP arena.


How does one resume a VNAV climb in a B737 NG after being instructed to level off at an altitude below the Cruise altitude? I am referring to a Boeing 737NG.
Assuming I am on a VNAV climb but I am instructed by ATC to climb only to an altitude lower than my FMC Cruise altitude.
After leveling off, how do I resume my VNAV climb to my FMC Cruise altitude after I am cleared by ATC to do so?
I obviously have to set my FMC Cruise altitude in the MCP Altitude window, but as VNAV is already engaged from before ans is the active mode, will the aircraft start climbing automatically, or do I have to disengage and re-engage VNAV by pushing the VNAV button OFF and ON again?
Or, alternatively, do I have to press the ALT INTV button to resume the VNAV climb to my FMC Cruise altitude?

So your CRZ page shows your cruise altitude as FL 410, but you've leveled off at FL370, which is what's in your MCP Altitude window. Now ATC clears you to climb to 410.
You set 41,000' into the MCP Altitude window. At this point, your FMA vertical mode changes from VNAV to Altitude Hold. The light in the Alt Hold button is on, and the light in the VNAV button is not. To initiate the climb, press the VNAV button, and observe the FMA change from ALT HOLD to VNAV Speed. At this point, the autothrottles advance the power, the autopilot increases the pitch to maintain your FMC-computed airspeed, and you're climbing again.
The key is that when you initially leveled off at FL370, the FMA stayed in VNAV Speed, but as soon as you changed the MCP Altitude, the FMA changed to Altitude Hold. Thus, one tap on the VNAV button re-engages VNAV & you resume the climb.
Side note: why doesn't the FMA change immediately to Alt Hold when you level off at 370? While Boeing may have another answer, my best explanation is that if you change your cruise altitude in the FMC from FL 410 to FL 370 after you leveled at 370, you stay in VNAV, and the FMA just swaps from VNAV Speed (i.e. the climb mode) to VNAV Path (i.e. level-at-cruise-altitude mode). So at the intermediate level-off, it stays in VNAV, waiting to see if you'll reset the MCP altitude (to continue the climb) or if you'll reset the FMC cruise altitude (to make this your cruise altitude). In the former case, the VNAV button starts the climb; in that latter case, no MCP buttons need pressing.
Added:
The case where Altitude Intervention will start your climb is different: in that case, you're AT your FMC cruise altitude, either because you climbed there directly, or else you leveled off at an intermediate altitude and then changed your FMC cruise altitude to match.  The latter is NOT common practice, but there are scenarios where it could happen.
Either way, you're at cruise in VNAV Path.  Now ATC clears you higher.  So you set the new, higher altitude in the MCP altitude window.  At this point, the FMA still displays VNAV Path.  Press Altitude Intervention, and that changes the FMC cruise altitude to what's in the MCP.  With VNAV (still) engaged and your altitude below both the MCP altitude and the FMC cruise altitude, you'll get a climb.
The difference in these two cases is being at, or not being at, the FMC cruise altitude.  In the case discussed first, you're below it.  In the second case, you're at the cruise altitude.  In the first case, Altitude Intervention won't help you (because you're in ALT HOLD and not VNAV); pressing VNAV will.  In the second case, you're in VNAV, so pressing that button won't help you; resetting the FMC Cruise Altitude (either by entering it in the FMC via the CDU, or by pressing ALT INTV) will.
This stuff is complicated, and the manual doesn't generally do a great job walking through every scenario and "what if".  After you've seen it in the jet (or a simulator with good fidelity) a few (dozen) times, it makes much better sense.
I'm not aware of any 737 setup where anything varies varies from what I've discussed above, although if the Smiths FMC is replaced by something else, all bets are off.  There are some things that vary from one aircraft to the next (geometric path descent vs idle descent logic being one -- it's selectable by the airline), but nothing here, as far as I know, is in that category.
As far as simulators go, I can't speak to which ones have fidelity to what goes on in the real aircraft or not.  (The ones I train in are extremely accurate that way, but they're not running on a PC!)


What is primary cause of shock induced separation (shock stall)? In the video link above describing Prandtl Meyer Waves, lecturer stated (at 22:40) a very important fact on which he based his first half of the lecture. "Mach wave (mach lines) deflect the flow through an infinitely small angle".

Now, lets look at the flow over the airfoil. First the flow over the top surface will accelerate to supersonic speeds(and above) until it reaches the point(roughly) of maximum camber. Due to acceleration, mach lines will diverge and of course no shock wave will form. But, after the point of maximum camber, where adverse pressure gradient will be introduced and decelerate the airflow than mach lines will start to converge (coalesce). Once they do it the shock wave will form above an airfoil (picture below). If aircraft countinues to accelerate, the mach lines would intersect each other more lower and lower to the airfoil bringing a shock wave down, until it meets the airframe (this sentence is my assumption and I would like confirmation if it is correct). At that point(once it touches the airframe) the boundary layer will always separate and cause a shock stall(also my assumtion, will it happen always?).
My question is:

Is boundary layer separation caused by the extreme instantaneous pressure increase on the airfoil surface, or because of the convergence of mach lines and deflecting the airflow regardless of the pressure(and density) change? Or is it combination of both?
Also if the statement from the lecturer is correct, shouldn't the mach lines deflect the airflow sooner and not only at the point when they all merge together?

The simplest answer is that a shock wave for a boundary layer means a sharp adverse pressure gradient. You probably know already that adverse pressure gradient will thicken a boundary layer and thick boundary layers are more prone to separation. Also, if the adverse pressure grad. is so strong, it can immediately produce a detachment of the flow from the wall.

Add to this that a separation bubble forms in the near region and this interacts with the shock. All these phenomena are quite complicated and to explore their underlying physics Large-Eddy Simulations (LES) are used for the Navier-Stokes equations. This is a topic of Ph.D level research. If you want an introduction you can check this source and discover further on your own.


What's the purpose of airline CREW tags? I see it sometimes on airline crew luggage, but not always. I see these come with airline name, sometimes airline base code and large CREW.

What is the purpose of these airline crew tags? After all, I got one in Crew Outfitters store as "collectible". Is this official airline tag which gives priority, different way of airport handling or something?

What would happen if I put it on my suitcase (either checked or carry-on).

It’s not an official/legal tag. Just a reminder for ground crew. At my company, luggage handlers unloading checked in luggage from the cargo will leave the bag near the aircraft (to be picked up by the crew) rather than bring it in to the terminal through the normal luggage flow. The ideea being that bag belongs to a crew member (active or positioning) and he might move arround the apron without ever going into the terminal.

Mind you this is just a courtesy, not a guaranteed thing. Should you put this on to your (checked in) bag there is a good posibility a ground operator will leave it under the plane for a while, then, when no crew comes to claim it, it will go through a lengthy process back to terminal. So your bag will have to honor of being one or two hours late to the conveyor belt.


Why this formula says jet engine is efficient at any speed? Wikipedia gives the following equation for the efficiency of the jet engine, here:

$$\eta_p = \frac{2}{1 + \frac{v_e}{v}}$$

Where V is the aircraft speed and Ve is the exhaust speed. It is backed by some reference to the book I have no access to so cannot clarify what do they want to say by that.

I am still deeply puzzled, how it could be the efficiency increases all the time with the increase of the aircraft velocity, even after it exceeds the exhaust speed many times. I think I have read somewhere that the efficiency declines and not keeps growing after the aircraft speed approaches exhaust speed.

This is the result from the simple momentum balance. In order for the propulsor to produce thrust, the exit speed after the propulsing element ($v_e$) must be higher than the incoming speed ($v$):

$$T=\dot{m}(v_e-v)$$

where $\dot{m}$ is the total mass flux through the propulsor.

So the correct way to read the efficiency formula is: the closer the exit speed is to the incoming speed, the more efficient it is! Therefore, the more mass flux you can generate at a smaller speed difference, the more efficiency you can attain without sacrificing the thrust. This is the overarching reason why bypass ratio makes engines more efficient.


How is the cabin pressure maintained inside aircraft? When aircraft is at high altitude, atmospheric pressure will be too low but inside aircraft pressure is maintained such that it is comfortable for crew and passengers. But how is it maintained?

As I understand that at higher altitude pressure difference can be too large which can deform the plane than how this is handled.

Once the airplane is closed up, all doors and windows secure, pressurization comes down to the following:

how much air is being pumped into the cabin?
how much air is being let out of the cabin?

Air enters the cabin (on a jet powered airplane) through bleed air taps in the high pressure compressor of the engines.  This air is routed through air cycle machines, or "packs" as they are commonly referred to.  The packs condition the air for temperature and humidity (typically taking all of the water out of the air) and then pump this air into the cabin at high pressure such that it is at the proper temperature after expansion to cabin altitude.

Air exits the cabin through outflow valves, which are typically at the rear of the pressure vessel.  These can be manually or computer controlled and will open and close to regulate how much air leaves the cabin.

To provide constantly fresh air, the incoming air from the packs is constantly supplied and as such the cabin pressure is almost entirely regulated by the outflow valves.  These valves have to be able to exhaust more CFM of flow than the packs can supply in order to let the cabin climb and when providing less CFM
than the packs the cabin will descend.

The cabin altitude will be managed so that:

it stays below a maximum pressure differential with the ambient atmosphere outside,
cabin altitude rate of change is limited,
maximum cabin altitude is kept below 10k feet (and typically below 8k feet) such that supplemental oxygen is not needed.


What exactly was the American WW2 smokebomb used in naval warfare? In WW2 the Americans used a kind of smoke/gas-bomb that they mounted under the SBD planes in naval warfare.

What was the purpose of that device and what is it called?

The ocean is featureless, floating smoke bombs were used to mark a spot on a body of water so pilots could get back to the same spot. Smoke plumes can be seen from a long distance, they also let you gauge wind direction and speed.

Smoke bombs were often used when attacking submarines, if a pilot spotted a periscope or caught a sub on the surface before it dove he could drop a smoke marker on the spot before coming around to drop a depth bomb on it. Smoke bombs were also used to mark people in the water, for instance downed pilots or sailors, so they could be rescued.


What do the different types of approach abbreviations used on the A320 MCDU exactly mean? On the MCDU I have noticed after setting up the approach there are a number of different codes which appear next to the runway designator these are namely as below:
CI
CF
FI
CD
FD
Can someone kindly explain what these codes mean.

CI = course to intercept
CF = course to fix
FI = fix to intercept
CD = course to DME
FD = fix to DME
These are AIRINC 424 leg types. You can find more information on them here


How to encode an altitude in ARINC429? How can I encode an altitude (ft) in ARINC429? I didn't understand if I just need to transform it in binary number and then use the "Bipolar Return-to-Zero".
Like for example with an altitude of 25 000 ft.

From ARINC 429, Attachment 6:

  Label 025, Selected Altitude (BCD)
  Five binary coded decimals.  Range is up to 50000.  Resolution is 1
  foot.

  Bit 29 (MSC) ------------------------------ Bit 11 (LSC)
  4 2 1 | 8 4 2 1 | 8 4 2 1 | 8 4 2 1 | 8 4 2 1

  1 0 0 | 0 0 0 1 | 0 0 0 0 | 0 0 0 0 | 0 0 0 0
  The above line codes to 41000 ft.
  Note: Negative sign is annunciated in the sign/status matrix.

  Label 102, Selected Altitude (BNR)
  16 bits of data. Range of 65536. Resolution (value of LSB) is 1 foot.

  Bit 28 (MSB)------------------- Bit 13 (LSB) (Bits 12-11 are set to 0)
     1 0 1 0 0 0 0 0 0 0 1 0 1 0 0 0

  The above line codes to 41000 ft.

  Note: Negative values are encoded as the two’s complements of positive
  values and the negative sign is annunciated in the sign/status matrix.


Is it possible for a non-towered airport to have keyhole extensions Class E starting at the surface? (skyvector.com, modified)

The Springfield, OH airport, KSGH, is a non-towered airport with both precision and non-precision instrument approach procedures. To support these approaches, there are a couple of "keyhole" Class E transition areas; however, these particular Class E transition areas start from the surface (magenta dashed lines) depicted on VFR Sectional Charts.

I'm really confused how the Class E areas extend from the surface when the airspace directly over the non-towered airport is Class G. Is it possible that the VFR Charts are in error and the magenta dashed line should be removed or converted to a magenta vignette indicating that the Class E starts at 700' AGL?

There are several indications in my mind that this is simply depicted as an error on the VFR Sectionals:

The VFR Sectional says, "See NOTAMs/Supplement for Class E (sf) eff hrs"; however, when consulting the Central Eastern Supplement for KSGH, there is no "Airspace" item listed under the airport.  Which substantiates the VFR Sectional chart designation that the airspace directly above the airport is Class G.
Since there is no "Airspace" in the Supplement (nor NOTAMs), there is no "effective hours" as the VFR Chart suggests that there should be for the two depicted Class E (sfc) areas.
As depicted, it appears as if the a pilot could enter Class E controlled airspace and then quickly transition out of it and into Class G uncontrolled airspace as they continue on the approach.  This doesn't make sense when you consider the intent of the Class E transition areas are to help IFR traffic be provided separation from Class G traffic.
The Airman's Information Manual (para 3-2-6.e.2) describes "Class E airspace may be designated as extensions to Class B, Class C, Class D, and Class E surface areas."  It does not include Class G airspace in that list of airspaces that Class E may be designated as an extension.
The AIM (para 3-2-6.e.2) goes on to say, "Surface area arrival extensions become part of the surface area and are in effect during the
same times as the surface area." Since there is no surface area in effect, it seems to be another indicator that the Class E (sfc) is also not in effect.

Can anyone explain how it's possible for these two Class E (sfc) areas to be legitimately marked, or are they simply errors?

There was a control tower at SGH which closed. The FAA issued a rule which removed the Class D airspace as of December 10, 2015.

This leaves the class E airspace chunks. As you noted, the Chart Supplement for SGH has no information about the airspace, and FAA Order 7400.11A (the current version of airspace definitions) states only that, after an initial NOTAM announcing the effective dates and times, (p. E-183)

  The effective dates and times will thereafter be continuously published in the Airport/Facility Directory.

So, is the airspace between the surface and 700AGL in these two areas class E or G? I'm not a lawyer, but I think you could make a strong argument for the airspace being class G, unless the chart supplement gets an update or a NOTAM is issued.

Finally, to the question: why are these two areas there? Two thoughts come to mind.

The class E extensions existed alongside the class D airspace, and nobody thought to remove them. (This is the most likely, to me.)
There is some other operational reason for the class E airspace. There are instrument approaches to the field, though they terminate well inside the radius of the two airspace segments, so that's not very likely. Also, the class D airspace could be reactivated by NOTAM if a high-traffic event at SGH were to occur; the class E extensions could be part of that. However, both of these options are really stretches - my guess is that we've found airspace that someone just forgot.

2019 update: those extensions are no longer visible on the sectionals:

(skyvector.com)


Why didn't the EASA enforce the 2 man cockpit rule BEFORE the Gemanwings accident? International numbers state that planes downed by pilot or co-pilot due to suicide are a rare but still possible occurrence.

In the United States such a safety procedure is standard (as of 9/11 - if I remember correctly). Why didn't the EASA think of that earlier?

Because aviation procedures and rules develop from historical occurances.

In some cases, the actual occurance and the resulting change in procedures do not have anything in common or are not related, e.g. some will argue that the two-man rule would not have prevented 9/11. It is also being discussed that the two man rule would only have had a psychological effect to deter the pilot/copilot from deliberately crashing the plane (as in the Germanwings crash), some will argue that a pilot or co-pilot intent to deliberately crash the airplane will not be deterred by a flight attendant in the cockpit, who due to lack of flight education would not be able to counter the pilot's/copilot's input in the FMC/AP.

The cockpit door measures to deny unauthorized access to the cockpit were implemented because the threat was assumed to come from outside the cockpit. You cannot implement measures that will work against everything and every threat, internal or external. Hence why EASA (and this is only speculative, because we can't know for sure) did not implement a two-man rule and currently has not implemented one, the two-man rule is a airline SOP issue at the moment.


AF447 stall and failure to recover To my knowledge Air France Flight 447 experienced stall. How was the stall detected and why wasn't the crew able to recover?

The stall, for the most part, was not detected by the pilots: That was the entire problem.
There were many alarms and indications in the cockpit and that caused crew confusion, they neither knew which data to believe nor understood the situation that they were in. For much of the descent they could have recovered from the stall if they had been fully aware of the problem and had worked together. One pilot did try to recover the situation (by telling the other pilot to push the nose of the aircraft down) but he was not successful.

That answers the second part of your question too: The crew was able to recover from the stall but did not, due to their own confusion.


Why does the turn coordinator ball move to the right during a climb? In a light aircraft like a C172 or PA-28, during a climb the ball in the turn coordinator moves to the right. Why?

There are 4 left turning tendencies in aircraft with "clockwise" (as seen from the pilots seat)
turning propeller, 3 of which may apply during a full power climb out.  The four are:

Prop torque  - prop turns right, plane rolls left - more noticeable at high power/slower
  speed
Gyroscopic precession - nose goes down - plane yaws left - not a factor in a climb - some
  effect as plane levels out, also there on tail draggers as rear of plane rises during take off
  roll
Asymmetric prop blade thrust at higher AOA (p factor).  Differences in thrust of ascending
 and descending prop blades will cause yaw to the left.
Spiral slipstream striking vertical stabilizer and side of fuselage, causing yaw to left.

Number 1 has to be watched in higher performance engines during takeoff roll.  Lifting off with insufficient airspeed will cause the plane to roll over and crash.  Fortunately, in a Cessna 172, this tendency is much more modest but should not be ignored.

3 and 4 are probably the main culprits of left yawing tendency in the climb.  The answer:  pitch to safe climbing airspeed (generally Vy) at full power and "step on that ball" with
right rudder.

Post script:  the rolling tendency caused by high power lower speed torque may cause the pilot to feed in more right aileron when the better input is coordinated with rudder.  As the plane accelerates from rotation and liftoff speed to Vy, it would be easy to miss you've rolled slightly to the right due to increased aerodynamic force.  In straight line flight this would not be a major problem (unless you were dangerously near aileron reversal stall speed).  I would work on glancing down at the ball as soon as safe climb is established, perhaps while checking airspeed.  Stay coordinated.


Looking for an API that can provide the amount of flights bought from point a to point b on daily basis I would like to know if any of you could help me finding an API source to gather information on daily bookings/sales from point A to point B, i.e. how many seats were sold landing or finishing a trip in Dallas airport and where was the beginning of the trip (point of departure).

I will truly appreciate any help, data does not need to be real time, a day or two, even a week delay would be fine. I am trying to correlate demand with other multiple variables but need to get the data from the demand side.

Thanks in advance for your comments

Ben

Not sure you can get the data easily.
IATA developed the NDC standard an API for airlines, which might enable you to check flight bookings between two destinations.
Nonetheless, as with any industry wide standard, it is interpreted in many different ways by the companies implementing it. Hence a pain to develop.

The most simple solution would be to use a set of well defined APIs from an airline ticketing company. Amadeus is one of them and I am almost sure they provide these kind of information.

In both cases, you are looking at quite a high upfront cost (in the thousands).


HEPA filters, airliner HVAC and COVID 19 There is this report that says the risk of aerosol spreading on a commercial liner is low due to HEPA filters.
But it is not considering the cases when A/C is OFF. This seems to be quite common when the plane is on the tarmac but away from the gates. At the gate the air is supplied by the airport. There are numerous reports of planes being delayed for hours in hot weather and passengers suffering. I have been in that situation myself a few times.
This is explained on quora:

It's kind of a double-edged sword. Simply put, cabin air in flight comes from intakes just behind the engine compressors. In flight, you're getting fresh, clean air that is inducted, mixed and filtered. It circulates through the cabin and eventually, lots of the circulated air gets sucked out by air blowing past the plane at nearly the speed of sound. However, its a different story when you're sitting on the tarmac. Engines at idle are still producing fumes, and these can get inducted along with fresh air because there's no air thrusting the fumes away from the plane as there is when you're moving at 500 knots. That mix can be filtered to a degree and is safe to breathe, but it's still going to smell awful, and even burn your throat. If you fly often, you'll often notice an awful smell of fuel when you get on the plane that clears up after takeoff. Granted, some of that smell at idle also comes from open passenger doors, but you get the idea. Also, due to changes resulting from in-flight fires, and 9/11, the pilots are isolated, and can often be unaware of how uncomfortable it is getting in the passenger cabin. Someone has got to bring it to their attention. Its not like a thermostat in your house, where you just set it and forget it. The crew has to control the cabin air on a more or less manual basis. Ever been to a restaurant that's freezing cold? Lots of times, the thermostat is controlled by people working in the hot kitchen, and the kitchen crew may not be aware (or even care) that their comfort is turning your fingers into icicles. Same principle.

So if the AC is OFF on the tarmac due to fumes, would it not make sense to use 100% recirculation in this instance and switch to fresh air whilst airborne? Can the pilot control this from the cockpit?

The air that enters the cabin of an airliner usually comes from a mixing manifold, like e.g. shown here for the Boeing 737:

(Boeing 737 NG FCOMv2 2.31.7 Air Systems - Air Conditioning System Description)
There are three ways to supply air to the mixing manifold:

From the PACKs (Pneumatic Air Cycle Kits): these are the air conditioners on the aircraft, which are supplied by hot and high pressure bleed air (either from the engines, the APU (Auxiliary Power Unit) or via an ASU (Air Start Unit) on the ground). During flight, the engines supply the bleed air to the PACKs, which results in fresh air entering the cabin.
From the Ground PCA (PreConditioned Air) hose: here the air conditioner is on the ground (usually in the airport building) and it supplies conditioned air to the mixing manifold while the PACKs are still off. See also What is this tube connected to a 757 for?
From the Recirculation Fan: here air is taken from the cabin and the fan returns it into the mixing manifold. You can see the filter in the diagram in this related answer in front of the recirculation fan, which is the HEPA filter preventing the spread of a virus via the mixing manifold. Even in flight, some air is always recirculated to reduce the required amount of bleed air from the engines.

Your question seems to focus on the time where the aircraft has already left the gate (so ground PCA is out of the question), but is still on the ground. At this time, the engines are usually running, so they could supply fresh bleed air to the PACKs. For longer waiting times, the engines are usually switched off to save fuel, but the APU would be running to power the aircraft. The APU could then also provide fresh bleed air to the PACKs.
As the quote from quora you included shows, this bleed air is not always of the best quality on the ground. It can therefore be switched off by the pilots. The following picture shows the bleed air panel of a 737-800:

(Boeing 737 NG FCOMv2 2.10.2 Air Systems - Controls and Indicators)
At the bottom are the bleed air switches for the engines and the APU. When they are switched off, the only source of air into the mixing manifold is the recirculated air. So in this case, you are already running on 100% recirculation, which is then HEPA filtered. Since the air does not go through the PACKs, it is not conditioned though, so it will get hot and stuffy in the cabin.
The top row of switches on the panel are for the two recirculation fans. They can also be switched off, in which case no air would enter the mixing manifold any more. This would make the cabin even more uncomfortable on the ground and of course also remove any HEPA filtering.


How does an airline open a new route? How do they manage to open a new route? For example Dubai-Panama. Do they have to open new airways?

No. You do not need to create new airways. You stick up to the already existent waypoints or not, if the route flies through a segment of free-route airspace.

Also, the engineering department of the airline studies the route, for instance: computes the MSA (Minimum Safe Altitude) for every point, engine failure and depressurization simulations are done in order to avoid possible hazards in critical points, if the aircraft is ETOPS certified they will decide which alternative airports are available for the route, fuel computations, chart generation for arrival and departure (most of the airlines use their own charts instead of those provided by the ANSP), et cetera.

Each airline has its own policy and the process may vary but fundamentally the procedure done is to make a study of all the parameters that can affect to guarantee safety and efficiency.


How to know the material of key-top? Posted it here originally.
There are keys (push buttons) on the front panel of an avionics device that fits inside the aircraft cockpit. I need to know the material of which those key-tops are made from.

I can guess the material is some type of clear transparent plastic and then its painted with black color. The text on it is un-painted key surface. There is green light under the keys (buttons). That green light glows the text (due to transparent plastic) on the key-top as green in color.
This cockpit device is from a very old aircraft model of 1950's so we can say it is not using any modern high performance thermoplastic or composite material. How can I best identify the material of these key-tops?
Edit: How do I know if the key-top material is compatible with NVIS (Night Vision Imaging Systems)?

The part looks injection-molded. The choice of transparent, moldable polymers available in the 1950s is manageable. The most likely candidates are:

PVC (back then the most widely used polymer, but normally not used in injection molding)
Celluloid (unlikely due to its high flammability)
PMMA (plexiglass)
Polystyrene

PVC can be detected when a heated copper wire is pressed into it and then again held into a gas flame. The copper will react with the chlorine of the PVC and color the flame greenish (Beilstein test). The last two candidates can be easily identified by the smell they produce when molten. Styrene in the case of polystyrene and derivates of benzene in case of PMMA. Since PMMA is rather soft, it can easily be notched but also has low mechanical strength. When dropped on a table, PMMA parts will create a more muffled, lower frequency sound than parts made of polystyrene.
Both are similarly well suited for being painted. Some plastics like polypropylene and polyethylene are unsuitable for painting because of their low surface energy. But while already known in the early Fifties, those materials were not yet used for parts production. The best substrate for painting would be ABS, but similarly while being known back then, transparent ABS types suitable for molding were not yet used.
My guess would be polystyrene, but given the few hints I am not really sure.


Is there a serious effort underway to move from a highways-in-the-sky approach to a mesh-network approach? As far as I'm aware, there are certain "motorways" or corridors which air traffic uses, rather than navigating more directly from origin to destination.
I remember listening to a documentary which mentioned that in the early days of the standardisation of flight, the navigation system was being decided. The Americans put forward the "motorways" system because they already used intermittent beacons to guide aeroplanes across the country, which naturally form a kind of road system analogue.
While the British (or Europeans) put forward a direct point-to-point system.

Anyway, the US won, and everything was hunky-dory until we get to today with our extremely crowded skies. So the documentary went on to say that investigations were underway into a new system in which each plane communicates with the planes around it continuously, forming and reforming impromptu mesh networks to avoid collisions. In this way, planes can fly more direct routes and potentially save time and fuel.

My question is whether or not this suggestion is feasible, is it being investigated, and is there a push to move towards it at a level which could affect the international air community?

Currently SESAR (Single European Sky ATM Research) works on implementing a similar system in the European Union.

As stated on the website :

  SESAR’s vision builds on the notion of trajectory-based operations’ [...] meaning that aircraft can fly their preferred trajectories without being constrained by airspace configurations.

The aim is to improve capacity in the European sky and be more flexible among the actors too (like temporary closed airspace for military training, handle volcanic eruptions and disruptions of the airspace).

SESAR has different projects to address the needs of imporving Air Traffic Management in Europe that you can find on their website.

Edit

There are current concrete solutions from SESAR and EUROCONTROL (the European organisation for ATM in Europe) to make this happen at the moment in the European airspace, such as the Free Route Airspace with set target of implementation (that we could consider "serious effort") :

  By the end of 2017, 51 ACCs have either fully or partially implemented Free Route Airspace operations [...] By the end of 2019, most European airspace is expected to have implemented FRA, with all airspace having this type of operations by 2021/2022.


Why does the MD-87 have strakes on its engines? Apparently, the MD-87 has a strake on both engines:

Source: Airliners.net
If I'm not wrong, the engine strake attaches the airflow at high angles of attack on the wing. But in this case the engine is behind the wing. So what is the purpose of this little fin? Is it a strake or something else?

They are indeed strakes which serve to reduce flow separation on the lower rear engine fairing by creating a vortex which will mix the outer, faster flow with the slowed down boundary layer on the lower rear part of the fairing. You will notice that the nacelle is mounted at an angle of 3 degrees to the fuselage: This is to position the intake and nacelle in line with local airflow, which is pointing slightly downwards at the rear fuselage due to the wing's downwash. The exhaust is again pointing directly back, so the thrust will be aligned with the lengthwise axis of the fuselage and will not produce pitch moment variations when thrust is changed. In combination with the nacelle incidence this produces a more pronounced curvature on the lower side of the nacelle, which in turn is more prone to flow separation.

You could as well place a row of vortex generators on the bottom of the fairing, but the strake will produce less drag when downwash is low and its service is not needed. With higher downwash, the strake will produce a stronger vortex, just when it is needed most.


Why does my wind tunnel experiment give two different stall angles of attack? When I increase the angle of attack from 0 to 20 the stall begins at 18 deg.
When I decrease the angle of attack from 20 to 0 the stall ends at 13 deg.
Why the difference and what value (13 or 18 deg) should I use as the stall angle?

This is called stall hysteresis. You have two different situations and the flow reacts differently in each of them.
When increasing the AOA
The flow is attached to the wing and the boundary layer is resisting the adverse pressure gradient as much as possible. At some point the flow detach from your profile and you have stalled let's say at 18°. At this point a huge recirculation bubble appears on the succion side of the airfoil.
Decreasing AOA / recovery from the stall
This recirculation bubble represents an area where the average flow speed is close to 0. Looking from the outside, for the free stream flow coming at your wing it looks like you have a new airfoil profile which is made from the old airfoil and the recirculation bubble. Most of the time this recirculation zone extend far beyond the trailing edge of the actual profile, reducing thus the overall aspect ratio (thickness/chord) of the profile. Slimmer profiles have less tolerance to stall and lower stall AOA thus explaining why your recovery only comes when the AOA goes below 13°.
Once the flow is reattached, you are back to the first configuration and you can go back up to the initial stall angle 18°.
Your stall angle is thus 18° but if you are in an airplane it means you'll have to lower the nose below 13° of AOA to recover.
There's an excelent thesis on this subject here from which this picture is taken showing the hysteresis phenomenon.


How do I execute this instrument approach at Larnaca (LCLK)? I am on course 200 degrees and got a clearance for the VOR-ILS X RWY 22 approach at Larnaca International Airport (LCLK):

Where is the/an IAF in this case? Do I have to join a holding pattern over the LCA VOR for a course reversal to course 041 inbound to the VOR, and then another base turn for a course reversal to the final approach course?

If you're course 200 then you are more than 30 degrees off the initial outbound track of the approach, therefore you should join the hold prior to commencing.

In more practical terms, if you're VMC at any point and your happy with your terrain clearance, then there would be nothing to preclude a request for a straight in, although from experience, LCA can get busy!


Difference between engine rev up and run-up Explain please the difference between these jet engine terms:

rev up
run up

Obviously they are completely different procedures. The reason I ask this question is because I'm not a native speaker and have some problems differentiating these 2 things.
You don't necessarily have to go deeply into technical details about these two procedures, however it would be welcomed ;)

In general English usage, including in aviation, "rev up" is a verb form describing the act of increasing the speed of something.  "Rev up the engine" just means give it a shot of power to make it go faster.

"Run up", as used in this case, is actually a noun, describing a procedure to test an engine against go-no-go criteria.  "Do an engine run-up" means perform the run-up procedure, which may include accelerating the engine to a specific speed to put things under a bit of stress, and testing various systems while at speed to detect degraded or failed components or subsystems that are revealed only when under stress.