Should landing on a runway that has been closed by NOTAM be a violation of the FARs? At an airport without an operating control tower, should it be a violation of the Federal Aviation Regulations to land an airplane during VMC daylight conditions on a runway that has been NOTAMed closed?

There's no specific rule against it, so whether it should be a violation is a matter of opinion. FWIW, AOPA's legal counsel believes it isn't a violation per se, but the FAA has still pursued action against airmen for doing it.

The 'obvious' regulation involved is 91.13:

  (a) Aircraft operations for the purpose of air navigation. No person may operate an aircraft in a careless or reckless manner so as to
  endanger the life or property of another.

The NOTAM is presumably there for a good reason and even if the runway seems clear and usable from the air, there may be hazards or poor surface conditions that you can't easily make out. As AOPA's counsel pointed out in the article above, the FAA apparently ignores the requirement to prove "endangerment" but the NTSB also seems to back them up on that, so as a pilot you probably have little chance of arguing successfully that a landing wasn't reckless.

A famous (infamous?) example of landing on a closed runway was Senator Inhofe in 2010. Afterwards he said that no one checks NOTAMs anyway and it just wasn't a big deal, despite there being workers and equipment on the runway at the time. As it happens, he's a member of the Senate Transportation Committee, which oversees the FAA, and he represents Oklahoma, where the FAA has its headquarters. He was required to do remedial training and that might or might not have been appropriate but personally I suspect that if I buzzed some construction workers and then told the FAA that I didn't care about NOTAMs, I'd be a lot more likely to get enforcement action.


Do I need explicit clearance to taxi on an inactive runway? I received taxi instructions from ground at a class D airport in the USA as follows (I was at ramp): Taxi to runway 04, Right on Bravo, left on 10, right on Alpha (no explicit clearance or hold short instructions for 10 were given). 10 was an inactive runway that intersected 04 with the Alpha taxiway turning off prior to the intersection with 04. I held short when I got to the 10 threshold and asked for clearance to taxi on the runway. The controller followed with Taxi left on 10, right on Alpha, but again no explicit clearance to enter the inactive runway at which point I taxied as instructed. My question is did I need to ask for clearance to taxi on the runway given the original instructions above?

Yes, you need an explicit instruction (not clearance) to taxi on any runway - and you got one!

The controller told you to "taxi on [runway] 10" which is about as explicit as it gets. If he did not want you to taxi onto the runway, he would have explicitly told you to hold short of runway 10. Note that it doesn't really matter if the runway is "active" or not. In the eyes of ATC, a runway is always a runway. Don't expect the controller to say something like "cleared to enter runway xx" - because it is not a clearance, but an instruction. The phraseology used will be along the lines of "enter runway xx", "taxi on runway xx", "cross runway xx" etc. - never "cleared". The only time you will hear "cleared" and "runway" in the same sentence is in a takeoff clearance or landing clearance.

That said, you did exactly the right thing. If in doubt, stop and ask. Especially when it comes to runways, if in doubt, never assume you have been instructed to enter a runway. Runway incursions are very dangerous, and the controller would much rather clarify an instruction instead of risking a collision.


Fly over or fly by question As far as I know, we're to fly-over a RNAV fix if such is drawn surrounded by a circle. But, in non RNAV procedures, how do I know that I must fly-over a fix?

E.g.:Taking this chart into account:

For instance, 14.5 KLO (IF). If my inbound course is 242º, can I break that course before D14.5 to join the final course 155º, or should I first reach 14.5 (overshoot then) and go catch the 155º?

Thank you vm

Good question. I was taught to anticipate turns and my Garmin 430 will anticipate turns so that you do not overfly the fix. But I don’t remember any specific guidance on the matter, so I looked it up. I found this in the AIM.

  5−3−5. Airway or Route Course Changes

  a. Pilots of aircraft are required to adhere to airways or routes
  being flown. Special attention must be given to this requirement
  during course changes. Each course change consists of variables that
  make the technique applicable in each case a matter only the pilot can
  resolve. Some variables which must be considered are turn radius, wind
  effect, airspeed, degree of turn, and cockpit instrumentation. An
  early turn, as illustrated below, is one method of adhering to airways
  or routes. The use of any available cockpit instrumentation, such as
  Distance Measuring Equipment, may be used by the pilot to lead the
  turn when making course changes. This is consistent with the intent of
  14 CFR Section 91.181, which requires pilots to operate along the
  centerline of an airway and along the direct course between
  navigational aids or fixes.

  b. Turns which begin at or after fix passage may exceed airway or
  route boundaries. FIG 5−3−1 contains an example flight track depicting
  this, together with an example of an early turn.

  c. Without such actions as leading a turn, aircraft operating in
  excess of 290 knots true air speed (TAS) can exceed the normal airway
  or route boundaries… Consequently, the FAA expects pilots to lead
  turns and take other actions they consider necessary during course
  changes to adhere as closely as possible to the airways or route being
  flown.


Is there a new "best practices" technique for demonstrating stall recovery? This is a question that is probably best suited for active flight instructors. I was doing an FBO checkout and the CFI asked me to demonstrate power on and power off stall recoveries, but well before the stall he asked me to recover. His explanation is that it is the new best practices for teaching and demonstrating stalls to recover "before" the aircraft actually stalls. In essence, the recovery demonstrations consisted of setting up the plane for landing and take-off config, and slowing it down till the stall warning came on, then almost immediately "recovering." It seems too easy. However, his reasoning made sense, but I have never heard it before:

It prevents new pilots from getting comfortable flying with the stall warning buzzing.
It teaches pilots to avoid the stall in the first place. (Prevention)
Its safer.

While his points are all factually correct, I think this defeats the purpose of knowing how to recover from a stall.

Any current CFIs out there that can explain if this is a new "best practice" for demonstrating stall recovery?

It looks like its related to this safety alert for operators that was issued back in may. You can find the full text from the FAA here but the pertinent chunk for the private pilot is...

  (1) Private Pilot – Airplane ACS, Power-Off & Power-On Stalls. With
  the exception of performing a thoroughly briefed full stall maneuver,
  a pilot should always perform the stall recovery procedure when a
  stall warning occurs


How do you know if an aircraft engine has a supercharger? The engine I'm specifically thinking of is for the C-130J Hercules, it's the AE-2100 D3.

As Bianfable has pointed out, the C-130 Hercules does not have a supercharger or a turbocharger. No turbine-powered aircraft have them. Turbine engines do not need these forced-induction chargers since turbine engines compress the intake air themselves. It would be impractical to design a supercharger or turbocharger for them.
The easiest way to know if a piston-engined aircraft has a supercharger or a turbocharger is to check the aircraft’s POH. If one is not handy, you can look at the aircraft engine itself.
An engine with a supercharger will have an accessory belt (usually wider than the other accessory belts) attached to the crankshaft or flywheel. In older aircraft (WWII, Korean War, etc), the supercharger will be less obvious. These may even be chain or gear-driven. The application of superchargers in this case would be for large, powerful engines.
An engine with a turbocharger will have the exhaust manifolds converge down to one pipe. That pipe will feed into the exhaust turbine of the turbocharger. Although, the exhaust turbine might not be readily visible, the housing for the compressor impeller should be more obvious and may obscure the turbine. What would be more obvious would be the additional manifold piping and ducting.
If neither of the above are accessible, just look at the model name of the aircraft. Most modern small General Aviation aircraft manufacturers will want to advertise that their model is turbocharged. A manifold pressure gauge that goes beyond 30 inches of Mercury may be an indicator as well.


What advantages would a triangular shaped spy plane have over a an SR-71? This is a picture of the supposed SR-72 Aurora. What kind of advantages would this have over the SR-71, in terms of its triangle design? Paper airplanes have the same shape, and fly really well.

The SR-71 design that I am comparing it to.

The 'triangle' wing design that you refer to is pretty common. It is called the delta wing design and is used in a number of high speed aircraft, for example, the North American XB70 Valkyrie.

In fact, the SR 71 wing planform is also a delta, if one removes the engines. One of the reasons is that the wings of the aircrafts are kept inside the Mach cone formed by the aircraft. The Mach angle is given by,

$\mu = sin^{-1} \frac{1}{M}$,

where M is the Mach number.

As the aircraft speed increases, the Mach angle decreases, which means that the aspect ratio should become smaller and smaller. At hypersonic speeds, the delta wing (or a modified one) is the best option as the wing needs to be pretty short for aerodynamics and structural reasons while able to carry the required fuel and generate lift.

The main advantage of the SR-71 Blackbird is its speed, which was about Mach 3.3. It is logical that its replacement should have better speed characteristics. SR 71 used a ramjet during its high speed dash, while its (rumored) successor is expected to use a scramjet engine.

"Turbo ram scramjet comparative diagram" by GreyTrafalgar - Own work. Licensed under CC BY-SA 3.0 via Commons.

The first one(a) is a turbojet engine, the second one(b) is ramjet, and the third one(c), a scramjet. The ramjet and scramjet engines are similar, though the combustion happens at supersonic speeds in the scramjet engine.

NASA has a hypersonic aircraft for experimental purposes called the X43,which uses a scramjet engine, though the aircraft size is pretty small compared to the A340.

Source: hapb-www.larc.nasa.gov

The closest actual aircraft have come to the shape of the 'Aurora' are the experimental aircraft like the X-37, which has short wings.

"Boeing X-37B inside payload fairing before launch" by US Air Force - http://www.af.mil/News/Photos.aspx?igphoto=2000374856 (direct link). Licensed under Public Domain via Commons.

There are a number of aircraft with triangular wings, most notably almost all European combat aircraft have delta wings.

And by the way, the Lockheed Martin SR 72 Aurora concept looks like this.

"Lockheed Martin SR-72 concept" by Source (WP:NFCC#4). Licensed under Fair use of copyrighted material in the context of Lockheed Martin SR-72" href="//en.wikipedia.org/wiki/File:Lockheed_Martin_SR-72_concept.png">Fair use via Wikipedia.


Why is there such a long displaced threshold on 22R at JFK/KJFK? This video seems to raise a whole bunch of questions, but here's one I have:

Why such a long displaced landing threshold on 22R at JFK/KJFK? (Scroll down to the 4L/22R section for details.)

Certainly Rockaway Blvd. is sufficiently distant from the end of the pavement (TODA) to allow closer landings.  And further upstream from that is Idlewild Park.  No residential areas for a good distance away from that runway.

That's a 3425-ft. displaced threshold on a 12079-ft. runway.  Is that some sort of record? ;-)

Its to maintain proper clearance over the park on approach from the north and avoid trees. They tried to extend the runway in 2013 but were ultimately denied due to minimum altitudes. Its covered in the October 2013 document Runway 4L/22R Improvements John F. Kennedy International Airport

They submitted for

  Relocate the displaced landing (arrival) threshold on Runway 22R 3,316
  feet to the north.

but ultimately...

  Two of the elements, the relocation of the Runway 22R arrival
  threshold 3,316 feet to the north and the relocation of the Runway 4L
  end (departure starting point) 460 feet to the north, would have
  resulted in aircraft being at lower altitudes than existing conditions
  over areas to the north of the runway, including Idlewild Park. The
  lower altitude of aircraft would have resulted in up to 800 trees in
  Idlewild Park becoming obstructions, as defined in FAA Order 8260.3B,
  United States Standard for Terminal Instrument Procedures (TERPS). FAA
  Order 8260.3B specifies the minimum measure of obstacle clearance that
  is considered by the FAA (the Federal authority) to supply a
  satisfactory level of vertical protection for aircraft operating at an
  airport. If the project described in the May 2012 Draft EA were to be
  implemented, up to 800 trees in Idlewild Park would have required
  removal to comply with FAA standards. The project described in the May
  2012 Draft EA has been modified to avoid this impact as explained in
  the following paragraphs.

  In order to minimize the number of trees to be removed from Idlewild
  Park, the Port Authority made the decision to redefine the proposed
  project as described in Section 1.3 of this Revised Draft EA. The Port
  Authority no longer proposes the relocation of the Runway 22R arrival
  threshold 3,316 feet to the north. The arrival threshold on Runway 22R
  would remain in its existing location, which does not result in lower
  landing elevations north of the Airport.


Is there a wordpress plugin for live NOTAMs? How can I embed live notams to my wordpress webiste?
Is there a plugin to get live NOTAMs updates on my website?

As mentioned, this is off-topic and more related to understanding APIs and Wordpress plug-ins.

If you want a place to start:
https://developer.laminardata.aero/documentation/notamdata might give you API access, but you'll have to build it yourself which is beyond the scope of this site.

As @Zach Lipton mentioned in the comments, even the official sites have a disclaimer, but here are a couple official sites you could check out:

https://notams.aim.faa.gov/notamSearch/nsapp.html#/
https://www.notams.faa.gov/dinsQueryWeb/

Somewhat related: Is there a Flights API to get flight information months in advance?


What would happen if a takeoff is not rejected following an elevator malfunction? A few weeks ago, the University of Michigan basketball team was on a plane that was in an accident.

Link

How bad could this have been?  From my understanding the issue was here:

Is this the kind of thing that is checked before takeoff?  From my understanding they were traveling at nearly 200 mph when the pilot rejected takeoff.

EDIT:  What would have happened if the takeoff wasn't rejected?

There are a number of scenarios that I can see happening, most of which depend on the aerodynamics specific to the aircraft.
Scenario 1: Nose Down Force > Up Force
I believe this to be exactly what happened in this instance. What happens is that the downward deflected elevator overpowers the upward deflected elevator creating more down force than up force. This means that the pilot can't rotate the aircraft into a climb attitude. This seems the most probable otherwise the pilots would have lifted off after V1 and went around.
Scenario 2: Nose Down Force < Up Force
If the pilots were able to get the aircraft into the air, and the asymmetric elevator didn't act like ailerons, they would probably have noticed that the aircraft would easily pitch down but be very difficult to pitch up. They would have noticed that as they got faster, pulling back on the stick would have resulted in less of a pitch up. Depending on the pilots, if they noticed this quick enough they could reduce power and control it for a landing. If they didn't realize what was going on and remained at TOGA power, they may have pitched into a stall.
Scenario 3: Extra Ailerons
If the elevators had enough of a roll effect, it would cause the aircraft to roll. They could have probably countered this with opposite aileron, but depending on the amount of up force versus down force scenario 2 would have taken over, only now they would have difficulty turning. (As per Kevin) The asymmetric deployment with the elevator at the top of the tail may create a yaw component, so the aircraft may also be slipping. This can put a lot of force on the tail, especially a twisting force as the pilots put in rudder to counter the yaw.

What it really all boils down to is that the pilots were probably right in rejecting the take-off, and probably would not have noticed the problem until Vr, which is after V1. Learning how to fly a crippled aircraft is not something you want to do at low altitude. If they did get it up and managed to get it in the air, they probably would have gained as much altitude as possible and spent time learning how to fly it while burning off extra fuel. This is pretty much what happened with United 232, where they had to learn how to fly the aircraft again.
Were the pilots right? Probably, but I believe they really didn't have a choice. I'm not sure that the aircraft would have rotated at all. Once they hit Vr and realized they couldn't get the nose off the pavement, it takes a couple seconds to make the decision to pull the power and hit the brakes. At 200mph you are traveling 293 feet per second. If they took 3 seconds to realize the problem and power down, that is almost 900 feet of runway gone.


Is propeller wake turbulence quantifiable based on operating conditions? I know the propeller does work on the air and thus the flow behind a propeller is higher than the airspeed. However, what is the quality of this flow? If I were doing a heat transfer analysis of an object behind a propeller, other than the accelerated flow speed, the effect of turbulence would matter too, where turbulent flow will contribute towards higher forced convection. I'm not sure how to quantify the added turbulence from a propeller. Is there a simple rule of thumb?

As a rule of thumb, use fully turbulent flow at the elevated speed of the propeller wake on all surfaces wetted by it. The speed increase will result in higher friction drag compared to the propeller-free case and results in a drag increase that looks about right.
A very interesting paper on the efficiency of an installed propeller can be found here. By comparing the gliding qualities of a Luscombe 8E with drag in level flight, the authors measured the drag increase of the airframe caused by the propeller wake. A drag increase of 30% from the propeller effect was measured, resulting in an overall propeller efficiency of only 62% when the propeller alone had an efficiency of 81%. The paper cites another result where the installed propeller on a Bellanca showed only 58% efficiency, but the paper is unavailable on the Web.
For pretty pictures you can consult this paper which analyzed the propeller wake - wing interaction on a C-130 J with 6-bladed Dowty propellers using CFD. The picture below is taken from this paper and shows surfaces of the same vorticity.

CDF simulation of propeller-wing interaction. The tip vortices of the single propeller blades can be seen impinging on the wing surface which suggests that local flow speed will vary with the frequency of the propeller wake hitting the wing. Also, the local turbulence is higher on the side of the down-moving blade. However, most of the wing surface shows only a minor increase in local turbulence, judging from the vorticity of the wing wake. Note that the engine air intake - nacelle intersection contributes a wake of its own which technically must be added to the propeller effects.
However, I doubt those details can be accurately subsumed in a simple rule of thumb; therefore I recommend to use a constant, elevated flow speed on all areas wetted by the prop wake.


Are non-military aircraft allowed to fly with no registration numbers (tail numbers)? There have been several news reports about aircraft (light planes and helicopters) flying without visible registration numbers or identifying marks in the USA:

  The NYPD referred to the helicopter only as “23”—a reference to the
  number of police officers killed in the 9/11 terrorist attacks—and
  initially the aircraft had no registration number painted on its tail
  or side. source

and

  Cimbolic was beginning to worry that he had overreacted when he
  noticed, on the same flight-radar Web site, the second plane flying
  higher in the sky, carving bigger loops above West Baltimore. The Web
  site reported that this plane was a Cessna 560 Citation V, a small
  jet. But it showed no tail number, offering no possible trail to
  Federal Aviation Administration records. This only heightened his
  curiosity. source

Eventually these aircraft were identified (and in the case of the former, a registration number found). But the general question I have is:

Are non-military aircraft allowed to fly without visible registration numbers (tail numbers) in the United States?

Fine print: I am aware that military planes usually have visible tail numbers, this question is about non-military craft. So "non-military" in this case includes federal agencies and state and local police.

14 CFR 45 subpart C governs the display of "nationality and registration marks".

14 CFR 45.21 says:

  Except as provided in §45.22, no person may operate a U.S.-registered aircraft unless that aircraft displays nationality and registration marks in accordance with the requirements of this section and §§45.23 through 45.33.

Section 45.22 gives some exceptions for "exhibition and antique" aircraft, and for aircraft of unusual design that may need an alternative marking scheme.

I presume there is another regulation, or international agreement, requiring that foreign-registered aircraft must also display their registration marks, but I haven't found it yet.

As to which aircraft have to be US-registered in the first place, see 14 CFR 47.  It's a bit complicated.

The US military is generally not bound by FAA regulations (though they may choose to follow some of them), see How much jurisdiction does the FAA have over military aircraft?.


Why are Israeli planes followed by an armored police truck at ZRH? While I was actively traveling to Zürich (for three years before Covid pandemic), I noticed that the Israeli airplane is always being followed by an armored police car with a machine gun turret on top. The car moves parallel with the plane all the way during taxiing.
As far as I could notice, no other planes/companies had this security measurement. Does anyone know why is this happening? Are there some increased security risks connected to the planes/passengers coming to/from Israel?

It is happening as an extra security measure, probably attempting to mitigate the risk of an explosive-laden person or car breaching the perimeter fence - like many city airports ZRH has a multitude of roads running around the perimeter fence which cannot all be manned 24/7. Is it mostly for show? Who knows!
There has always been more risk associated with flying to Israel - anyone who flew there pre-9/11 was not surprised by the extra security measures added to all flights post-9/11 as they had been dealing with them since forever.
It seems that American might also get the same treatment at Zurich based on a photo here: https://www.airliners.net/photo/American-Airlines/Boeing-767-323-ER/531127/L


Why does the Boeing 787 engine nacelle exhaust have such an unusual shape? Why does the Boeing 787 nacelle have this unique shape at the exhaust:

I haven't seen it on any other airplanes, does it serve an aerodynamic purpose or help engine efficiency or is it just to look pretty?

Well, it does look pretty, doesn't it?

Boeing wanted to reduce the noise generated because of jet blast of the engines. Many airports around the world are implementing new noise regulations.

As mentioned by Boeing:

  To combat the sound of jet-blast from the rear of the engine, Boeing,
  General Electric, and NASA developed serrated edges called chevrons
  for the back of the nacelle and the engine exhaust nozzle. The
  chevrons reduce jet blast noise by controlling the way the air mixes
  after passing through and around the engine.

  The acoustic liners and chevrons are such effective noise suppressors
  that several hundred pounds of sound insulation may be eliminated from
  the fuselage.

As NASA was involved, they state (my paraphrasing):

  Chevrons are the sawtooth pattern seen on the trailing edges of some
  jet engine nozzles. As hot air from the engine core mixes with cooler
  air blowing through the engine fan, the shaped edges serve to smooth
  the mixing, which reduces turbulence that creates noise.

  ... The new Boeing 787 is among the most modern jets relying on
  chevrons to reduce engine noise levels. It sports chevrons on the
  nacelles, or fan housings.


What should you do when ATC gives you a number to call to discuss a violation? Generally speaking, for those that either have experience calling the number, or, preferably, for those that were paid to answer the phone, what are the benefits or pitfalls of calling?

I had a friend that climbed above his assigned altitude once and was given the number, and he called and had an exceptionally friendly chat, and that was that.

Are there any scenarios, such as gross violations, where it might be better to seek legal counsel first before calling, or not calling at all--especially if there is a discrepancy between airman and controller?

AOPA has an article on exactly this question (written by an attorney). Their advice is basically that it's a judgement call on your part and one that you should think about carefully. Not calling may antagonize the FAA, but calling if it's a major safety issue may be unwise:

  That doesn't necessarily mean, however, that you should call the
  telephone number or respond to the FAA's letter, and blather the most
  expansive defense you can conjure up. A little judgment is called for
  here--and, unfortunately, there are no hard and fast rules. If you
  think the FAA may be inclined to just admonish you orally or content
  itself with administrative action, then a humble, cooperative approach
  may be best. Saying you won't talk without a lawyer, when the likely
  outcome if you do talk is minor, may only prompt the FAA to propose
  sterner action. Before you talk, however, think carefully about what
  you want to say, how much to say, what questions the FAA is likely to
  ask and how you'll answer them.

  If, on the other hand, there is a substantial chance the FAA will take
  certificate action against you or will propose a fine, the best course
  of action, as I said above, is to hire an attorney. Don't ignore the
  FAA; be polite, but don't provide more information than the bare
  outlines of what is already known and obvious to all. State quietly
  that you understand the FAA's desire to investigate possible
  violations, that you take your obligations to fly safely very
  seriously, and that you will be happy to cooperate. Also say that,
  unless the FAA is not contemplating action against you, you feel it
  best to consult a lawyer before proceeding. Since the FAA likely won't
  give you any guarantees, its representative will be the one
  overreaching if he presses you to respond anyway. Politely decline if
  he does.

I also had a look through the AOPA discussion forums (members only, so no links) and my summary of their comments would be:

File a NASA ASRS form within the 10-day limit, whatever happened
If you know what you did wrong and you know it was minor, then make the call
If you don't know what you did wrong then call but be prepared to end the conversation immediately if you have no good response or you realize it's more serious than you thought
If you know you caused a major safety issue (actual or potential) then don't call and get a lawyer instead
If you know the person you have to call  - e.g. if it's the tower controller at your home airport - then you should give more weight to calling
In general, it's better to call and have to cut off the conversation than not to call in the first place
Whatever you say, keep it short and factual
When you find out what you did wrong, get some ground and/or flight training from an instructor to address that specific issue and have him endorse it in your logbook; this shows the FAA that you've taken the issue seriously and you've actively taken steps to make sure you won't do it again


Why is an approach that relies on both LOC and PAPI not considered a precision approach? I am an aviation layman. I am reading about PAPI lighting system and it seems like it provides vertical guidance, just like the glideslope component of an ILS.

Coupled with a LOC, both vertical and lateral guidance are available to the pilot.

Why isn't such an approach considered a precision approach?

Thank you.

I think you're overlooking the primary reason pilots fly instrument approaches: the conditions do not permit flight by visual reference.

The fact that a PAPI provides vertical guidance is more or less useless if you can't see it. Most ILS approaches involve a descent of at least 1500' from glideslope intercept.

If you break out from the clouds at ILS minimums, you can be as low as 200' above the runway surface; at 3°, that's around 3/4 miles from the touchdown zone and the PAPI. It's highly unlikely that the PAPI would be visible prior to that point, meaning the approach would be made with purely lateral guidance.


What is the function of the Apache's Strap Pack? I have recently been reading about the issues with the Apache's (AH-64) strap packs. I've read that the strap pack holds the rotor blades on to the hub.

However, it appears the blade also connects to the pitch housing assembly. So I don't really understand the function of the strap pack and why it's failure would cause a catastrophic failure leading to loss of aircraft.

Questions:

What is the Function of the Strap Pack?
Why does its failure lead to loss of aircraft?
Is this a common design on other helicopters?

Reference: Story

Image Source

Picture above is from Helicopter Performance, Stability, and Control by Ray Prouty, and shows the fully articulated rotor such as installed in the Apache. The Fully Articulated term means that the blades can rotate in three Degrees of Freedom: fwd/aft, up/down, and nose up/down. The rotation axes are single points of failure: when they break the blade is launched, unbalancing the rotor and rendering flying and autorotation impossible.

The problem with the Apache setup is with eight nuts degrading due to corrosion, as from this link:

  The order came after officials learned that bad weather and salt water in coastal regions could lead the eight “strap pack nuts” on each of the rotary blades to reach the end of their life expectancy sooner than projected.

Fully articulated hubs are the most common design in helicopters, the others being the teetering rotor such as in the Bell 212 and the hingeless rotor in for instance the Westland Lynx.


What is the difference between a leading edge flap and a slat? I always thought that the definition of slat was:

"Lift modifying and adjustable wing element on the leading edge of main airfoil."

and the definition of flap was:

"Lift modifying and adustable wing element on the trailing edge of main airfoil."

However, there are also leading edge flaps, also known as Krueger flaps, and they are located on the leading edge.

What gives these elements the name of "flap"? What is the main difference to slats?

Slats are leading edge devices on aircraft that enable higher angles of attack. Flaps are devices on the leading (Krueger) and trailing edge which increase camber and the depth of the wing. Slats create a "slat" between the slat body and the wing leading edge so the air can pass from the bottom to the surface to hold off a stall to a higher AoA, flaps merely extend it fore and aft and direct the flow downwards for more lift. Both are mainly used in the low-speed situations of take-off and landing.


What's the definition and the meaning of “soft dirt runway”? What's the definition and the meaning of "soft dirt runway"? You can read that expression in the following text:

  ..The aircraft's rolling resistance, μ, is determined by the type of
  runway surface and by the type, number, inflation pressure and
  arrangement of the tires. A thin, high-pressure tire operated over a
  soft dirt runway will have so much rolling resistance that the
  aircraft may be unable to move. A large, low pressure tire can
  operate over a softer runway surface but will have more aerodynamic
  drag if not retracted, or will take up more room if retracted. Values
  of μ for different runway surfaces are provided in the detailed
  takeoff analysis in Chapter 17. ...

Source: Daniel P. Raymer, Aircraft design: a conceptual approach. Chapter 5 Thrust-to-weight ratio and wing loading, paragraph 5.3 Wing Loading, sub-paragraph Takeoff Distance, page 88.

The are many types of runway. But the basic are paved, unpaved. Paved runway may be in form of rigid and flexible. Rigid is one which is made of concrete.Flexible runway are made of like bituminous. And the soft runway is one which is not paved. The runway may be on ice sand or water. But generally for a soft runway we can assume it as a grassy runway.    I did not find anything specific about the dirty runway. But in general we can think dirty means the runway conditions which are not so good for the engine when using of reverse thrust , applying brakes or maintaining direction while on take off roll.


Who owns wrecked airplanes in international waters? Reading about a Spanish treasure ship, I found that it eventually created a dispute between the company that found it (Odyssey) and the Spanish government, so the following questions came to my mind (focused on an international ocean wreck):

Is the same ownership law applicable to wrecked ships and wrecked planes?
Is there any difference between floating debris and sunk debris?

More specifically, regarding Malaysian Flight 370, who owns the debris discovered at La Réunion?

Insofar as it relates to MH370 the treaty sections Pondlife quoted would probably work quite smoothly if it were found by a government or someone working on behalf of the govt. The question arises as to what happens when James Cameron goes and finds it. (Inevitable, am I right?)

If it is located by a private party then the law would not be quite so clear. It would fall to courts and there would be legal claims falling under admiralty law, salvage law and those might even be superceded by laws governing criminal investigation at sea.

Generally under ocean salvage law the original owner continues to own it, but the salvaging party is entitled to a substantial award or prize. To complicate matters, there are two international conventions on salvage law, one from 1910 and a second one from 1989. Some countries recognize one of them and object to the other.

If Malaysian Airlines is no longer in business when it's found that will make things even more unclear. Probably the best analog would be the Titanic case. The company that recovered most of the artifacts sued to be declared owner. A US court declared jurisdiction and ruled that as compensation for the cost of recovery they had the right to display the items, but they do not own them.

  After a series of court battles, an American company, RMS Titanic Inc (RMST), emerged as the owner of the salvage rights, allowing it to keep possession and put on touring display the 5,900 artefacts it has lifted from the ship during six dives.

From an article in The Guardian

So far no one owns them since White Star Line is long gone. The US and UK quickly hashed together a treaty to declare them a public memorial so the artifacts can't be sold off to private collectors.

  An international agreement signed by Britain and the US designates the Titanic as an international memorial and seeks to protect it from being plundered or damaged by unauthorised dives.

from the same article*

With all these things at play there is simply no telling what would happen with it.


If pilot use rudder to roll the aircraft at high AOA in the F4 Phantom then one aileron from one wing and one spoiler from other will be deflected? I have heard that the F4 Phantom pilots can make barrel rolls at lower speed /higher AOA. They use only rudder deflection and keep the stick column centered (left /right wise)-only pull onto the belly to have the G's- to prevent adverse yaw effects. Does the spoiler on top of the wing move during the maneuver if the aileron stay neutral? The way it works for level rolls is : one side aileron deflected down but the other one is not (there is some slat(spoiler) on the other wing to assist the aileron down deflection. Is there a built in type of assistant like ailerons - rudder interconnection to help maneuvering? Or do the wings remain clean with no deflection of the control surface?

of course it depends upon the situation and the specific fighter. when maneuvering at high angles of attack and high G, I always used solely aft stick and rudder, never any aileron or spoilers input. Sometimes I would use full rudder, all the way to the stops. Other times, not so much.

A Barrel Roll is a maneuver where the aircraft flight path follows what would be the surface of a huge horizontal barrel in the sky. To do this you of course need to roll the aircraft. To roll the Phantom, no matter what maneuver you are attempting, requires that you create differential lift on the wings. (more lift on the up-moving wing than on the down-moving wing). At low angle of Attack (AOA), in any model of F-4, you use the ailerons/spoilers to do this. At higher AOA, the ailerons would induce adverse yaw, and therefore you need to create this differential lift by yawing the aircraft with the rudder (since it's a swept wing aircraft). As AOA increases above 10-12 units, the pilot needs to blend in more and more rudder, and less aileron, until at high AOA (19 units in early non-slatted aircraft like F-4B/C/D), he is using rudder exclusively. In later slatted aircraft (USAF F-4Es, F-4Js, USN F-4J/S, etc.) this effect was somewhat mitigated by the slats (they energized the airflow over the top of the wing), and the pilot could use some aileron throughout the AOA range, (but still less and less as AOA increased), all the way to 25 units AOA.
As to your other question about slat deployment, this happened automagically, based on AOA, at about 12-14 units AOA as I recall. And then would retract when AOA fell below 10-12 units... No pilot input was necessary.
So, in the execution of a Barrel Roll in the F-4, starting at 450 KIAS and low AOA at the entry point, the aircraft would climb and descend 4-5000 feet, and  slow to somewhere between 200-250 KIAS and higher AOA at the high point, and then accelerate back to 450 KIAS and low AOA at the completion of the maneuver. As a result, the need for aileron and rudder to effect the roll continuously and gradually changed throughout the maneuver.
NOTE. (to address comment made in the question relating to photograph). The F-4's ailerons did move up slightly when the stick was deflected towards that wing, but at high AOA, the aerodynamic effect was negligible due to the wing blanking the airflow back there. SO the F-4 also had spoilers on the top of the wing that would deflect upwards as well, both to decrease the lift on the wing and cause a roll in that direction, and to add drag on that wing to balance the drag from the down aileron on the opposite wing. The control surface deflected on the upper wing in the photo is the spoiler, caused by the pilot pushing the stick to the left.
The following is from the USAF F-4E flight Manual:


Is the Mach number shown by an Air Data Computer considered a "true" Mach number? I am trying to find more information on "true" vs. "indicated" Mach number (not airspeed). I've found older fighter aircraft manuals online that have a conversion chart from one to the other, but the modern jets I've flown don't have such charts.

During a recent flight at 41000 feet, at a Mach number of 0.81, a true airspeed of 476 knots was displayed on the EFIS. In the standard atmosphere, 81% of the speed of sound is 464 knots at that altitude. Sure enough, the actual temperature was some 13 degrees C warmer than the "standard" -56.5 C, hence the true airspeed of 476 knots instead of 464.

But that leads me to believe that the Mach number I am flying is not really "true".

The relevant flight manuals do not use the words "indicated" or "true" to qualify the Mach number.

For subsonic aircraft the Mach number is normally measured from dynamic pressure and static pressure, very similar to the way calibrated airspeed is measured.

$$M_a=\sqrt{\frac{2}{\gamma-1}\left[\left(\frac{q_c}{p}+1\right)^\frac{\gamma-1}{\gamma}-1\right]} $$

with:

$M_a$, the Mach number
$q_c$, the dynamic pressure
$p$, the static pressure
$\gamma$,  the ratio of specific heats (1.4)

If there is an error in the measurement of either the dynamic or the static pressure both the indicated airspeed and Mach number will be affected.

Note that the Mach number has no direct dependency on temperature.

The true airspeed is calculated by the ADC from the Mach number and the outside air temperature.

$$V_{TAS} = M_a \cdot \sqrt{\gamma R T_S}$$

with

$R$, the specific gas constant (287.05 for dry air)
$T_S$, the static air temperature

The indicated true airspeed has a direct dependency on the static air temperature ($T_S$,SAT) also known as the outside air temperature (OAT). The static temperature cannot be measured directly since the air will heat up on impact with the temperature sensor due to adiabatic compression. Instead the total air temperature ($T_\mathrm{total}$, TAT) will be measured.

The relation between the measured total air temperature and the static temperature is given by:

$$\frac{T_\mathrm{total}}{T_{s}}={1+\frac{\gamma -1}{2}M_a^2}$$

Since the measurement probe may not recover all the energy from the adiabatic heating a correction factor is introduced:

$$\frac{T_\mathrm{total}}{T_{s}}={1+\frac{\gamma -1}{2}eM_a^2}$$

This 'recovery factor' $e$ is determined empirically for the temperature sensor used.

The display on the EFIS will show the OAT, which may be slightly off if $e$ is not entirely correct. This will also affect the "true" airspeed indication.

To conclude; anything indicated in the cockpit can contain measurement errors, regardless whether it is called 'indicated' or 'true'.

With the introduction of digital flight data systems the error correction tables have been moved from the manuals to the computer, which automatically corrects for them.


DA 40 NG - Diesel option OAM 40-370 Diamond DA-40 NG Manual did say that to use Auto Diesel (EN590), OAM 40-370 must be installed. Does anybody know or have experience on this OAM 40-370 requirement?
I cannot find this document on the Diamond Website

You can easily find this out for yourself by searching on the OAM.
This leads to Diamond Aircraft service bulletins relating to the change.

Work instruction

AFM

Software notice

Looks from these that it requires 3 things:
2 placards relating to the different engine operation temperatures, and potentially a software upgrade to the engine management system (depending on the version currently installed).


Why there is such a strong correlation between the range of an airliner and its passenger capacity? Why we rarely see an A320 (or equivalent aircraft) on a long route with all premium business seats or an A380 (or equivalent aircraft) with high density seating and on a short route?

On top of that, it is a much easier task to design a long range light aircraft and a short range heavy/high capacity aircraft, so why have no airliners (as far as I know) ever been designed with these characteristics in mind?

A big part of the difference in range between small and large aircraft is simply mathematical. When you make a 3D object larger, area increases with the square of length while volume increases with the cube. The A320 has a wingspan of 35.8m, carries 150 (2-class), and carries 24,210L of fuel (standard). The A380 has a wingspan of 79.75m, about twice the dimensions of the A320. However, the passenger capacity increases by a factor of 4 to 644 (2-class), and the fuel capacity increases by over a factor of 10 to 320,000L. There is simply more room for fuel in a larger aircraft. Smaller aircraft may have options to carry additional fuel talks to increase range. Note that this trend also applies to business jets despite their market having less of a correlation between range and passenger demand.

In addition to the geometrical constraints, airlines have other reasons for not operating large planes on short routes, or vice versa, more often. Using small planes allows for more frequent service and more flexibility even if there is enough demand to use a smaller number of larger aircraft.


Can anyone help me identify the plane in this photograph? I'd be very grateful for any help in identifying this U.S. plane. Other photos in the album look like they're from WW2.

What you have there is I believe a Boeing Model 80A-1:

Source

Source

You can read more about it on Wikipedia: Boeing Model 80

The Model 80 air transport aircraft was built in the mid 1920's. It is notable as being the aircraft used for the first flight to feature a flight attendant, which were registered nurses at the time.


How will aiport operations at KOAK be affected when taxiway W is promoted to a runway? For the record, my question is not about mistakenly using a taxiway as a runway.

I've noticed recent changes to the sectional and TAC VFR maps around Metropolitan Oakland International Airport (OAK/KOAK) - it appears that Taxiway W is being "promoted" to a runway close to, and parallel to, Runway 12/30.

Based on the airport map (PDF) and confirmed by the Google Earth image below, aircraft departing and landing on 12/30 (presumably soon-to-be 12R/30L) will have to taxi up or down this new runway.  From the looks of it, this runway will just be marginally long enough (about 7200 ft / 2195 m) to handle short-range commercial operations; certainly the longer runway will still need to be used.

This then begs the question:  How would airport operations be affected if both runways were active?

From Google Earth and Skyvector.com

Oakland airport runway 12/30 is undergoing a "Rehabilitation" and during the rehabilitation taxiway Whiskey (W) will be serving as an alternate runway.

Therefore, your question "How would airport operations be affected if both runways were active" won't be an issue.   Please see the notice below.


What is a CRM and what does it stand for? I've always wanted to ask a pilot what a CRM was. Of course, I didn't really get lots of chances to ask pilots, no I thought of just asking here. What is a CRM and what does it stand for?

Crew Resource Management started out in the 70s as an attempt to eliminate human error but over time it's undergone a number of iterations and today the concepts have accepted reality and assume errors can't be eliminated, only mitigated.

Modern CRM tries to mitigate errors by attempting to require multiple errors to stack up in an improbable way before things become dangerous (called the "swiss cheese" approach, as in mutiple layers of swiss cheese where a single hole is unlikely to line up).  It also has added personality factors, human interaction factors, and leadership factors to the mix.

In practical terms, this means that, for example, captains are expected to act as leaders and not bosses. The FO is not just a gear puller and is encouraged to participate in assessment, planning and decision making.  Copilots are expected to speak up when in doubt about something.  Both crew members are expected to make sure that each is aware of the other's actions, and planned future actions, at all times.  Crew members cross check each other's actions continuously. Crew members learn standard phraseology for key actions and are expected to stick to it to reduce confusion. Crew members are expected to follow standard operating procedures and not invent their own ways of doing things.

ATC gives an altitude clearance change?  Pilot monitoring and talking to ATC dials the autopilot to the new altitude, and calls it out something like "Flight Level 350 set".  Pilot flying confirms the correct altitude is set and calls out "350 checks".  You generally announce everything you do as you do it and make sure your partner is aware (usually by responding "check").  It should just flow.  One major bonus is the standardization makes it possible for crews to smoothly interact without flying together for a period of time first.

A cockpit with good CRM will have a well-oiled machine aspect to it with the pilot and copilot well integrated mentally. The capt and FO cooperate on planning and decision making, notwithstanding the fact that it's the captain's final call.  They will look like they've been flying together for weeks when they've actually just met that morning.

I would say that the two biggest factors in the amazing safety record of airline transport in the last 30 years, from a crew performance standpoint, is the success of CRM, and the advent of the 2D moving map presentation when the glass cockpit came along, which massively improved situational awareness by eliminating the need to generate a mental picture of a navigation situation like in the steam gauge era.


Why do control towers have tilted glass panels? Almost all control towers I've seen have tilted glass panels:

Amsterdam-Schiphol tower (EHAM), source.

What is the reason behind this choice?
How is the tilt angle determined?

I'm pretty sure that has to do with reflections especially at night.

If you have ever stood between two mirriors you will understand the infinity mirror.

Light bounces back and forwards between the mirrors so when you look into them it appears like the scene goes on forever.

Window glass reflects a certain amount of light, like a mirror. In a control tower, where windows are all around you, if the surfaces of the windows are parallel you get that infinite mirror effect.

During daylight hours this can be seen as glare, but at night when you are trying to see that navigation light on Flight 594 amid a sea of runway and taxi-way lights, having your vision further confused by a myriad of reflections from the back window would be a bad thing. Further, since the room is a glass box, light can bounce all the way round the room. It would be quite possible to look off to your right and think so you see an unidentified aircraft approaching, but be actually seeing some truck's lights on the hill a couple of miles away over your right shoulder.

Tilting the windows outwards means the reflection angle is towards the ceiling, which is generally painted black, and the effect goes away.

Further, tilting out means you can no longer see your own reflection, or reflections from other lit workstations in the window. Ever tried looking out of a window at night into the dark and only see your own ugly mug staring back at you, then tried to move your head to the side to see around yourself. LOL

Of course, for all this to work, the ceiling should be dark.

A few other reasons include, less affected by rain, fewer refraction effects, and external reflections. Bonus feature, less greenhouse effect and AC bills. Downside... darn hard to clean.


Would a triplane be way more efficient if the wings intersected at the tips to create one wing tip vortex instead of 3? Would a triplane be way more efficient if the wing tips were joined at the tips to create one wing tip vortex instead of 3, at RE 200-600k? At that low of a speed, I assume interference and form drag are minimal.

I understand biplanes and triplanes are less efficient than a monoplane due to wing root interference drag and wing tip vortices.

Yet..... I understand boeing/NASA are experimenting with a biplane/braced wing airliner configuration, which would have extra induced/inference drag.

So, to reduce those nasty wingtip vortices, couldn't one just intersect the tips?

I'm thinking, the top wing would have anhedral, a straight middle wing, and bottom wing with dihedral, meeting at the tips.

Well, those nasty wing tip vortices really can't be helped if you are creating lift.  Amazing that airliner designers in this century are still considering biplane vs strutted mono plane vs cantilever mono plane concepts in their proposals.

Bringing 3 wing tips together will create all kinds of air flow issues (remember to model at all possible AOAs), reducing efficiency.

The most efficient way to create lift remains a high aspect mono wing.  I would look to designers actually reducing sweep a little (around 15 degrees for subsonic) and try for as high an aspect wing as possible, just like sailplanes.

However, wing span constraints and support benefits for very large aircraft may yet see the return of the biplane, with very thin, high AR wings.  These could be swept a bit more at the tips, and/or endcapped or wrapped.  Fuel and landing gear could go in a more drag efficient longer fuselage.  Note mounting them in "classic" Tiger Moth style retains the stability benefits of wing sweep, which may be lost in the newer "Prandtl wraparound" proposal.

It seems some designers just can't bring themselves to make a 21st century high AR Jenny.  It might be worth a try.


Why are trailing-edge control surfaces usually split? I've noticed on many military and commercial jets, the trailing edge control surfaces (ailerons and flaps) are separate from each other.

Why is this? Can't both serve the same function? It would save weight and complexity if one combined control surface ran the length of the trailing edge, instead of being split in half.

A particular example I found is the F-102 Delta Dagger. There's no conventional tail to experience disrupted airflow, so why have separate ailerons and flaps?

A similar idea that I know exists is the V-tail, such as in the F-117, which has "ruddervators"---combined elevators/rudders. It can still control yaw and pitch at the same time by somehow averaging the deflections. Presumably, combining and averaging ailerons and flaps should be even simpler, since they're both deflecting on the same axis.

Same reason you have split ailerons on most big airliners. The inboard surfaces deflect at higher speeds and the outboard ones are locked, reducing the twisting (torque) forces on the wings. It also allows for finer control (in fly-by-wire cases) as well. Like a lever, a small deflection of the outboard surface results is higher rate pitch/roll (in this delta wing elevon example) compared to same deflection of the inboard surface.


Why does a turbofan engine force bypass air into a smaller space? I asked a question about this same concept recently but this question involves the function of the bypass air.

In this YouTube video around 1 minute in the narrator says that the bypass air is pushed by the fan into a smaller and smaller space which increases the velocity of it, but why? Why increase the exit velocity of the air beyond what the fan already does? It can't increase thrust, can it? That would seem to violate some sort of conservation law since you could theorize an infinitely narrowing space and thrust would approach infinity. So what function does it actually serve to force air into an 'ever narrowing space'?

It can't increase thrust, can it?

It does increase the thrust. This is how jet propulsion works. The decreasing space is essentially a nozzle, without one the jet engine is a mere gas turbine.

You could theorize an infinitely narrowing space and thrust would approach infinity.

Not really, a very tight opening will create a huge back pressure, initially and very momentarily propelling the vehicle the opposite direction, before the gases shoot out the front stalling the engine (gases building up).

In fluid dynamics that would be a choked flow state. The mass flow out the nozzle reaches the maximum, which means inside the engine the gases will start building up (pressure increasing). If the theoretical tiny nozzle can withstand this pressure, the gases will only have one way to go, which is out the front.

So instead the nozzle is designed to decrease the pressure (by increasing the velocity) to match the free stream pressure as much as possible.

  The nozzle of a jet engine is usually designed to make the exit pressure equal to free stream (NASA).


Can the V-22 autorotate? Can tilt-rotors like the V-22 execute an autorotation landing?

If so, are the conditions under which that would be possible (and survivable) different from a helicopter?

The V-22 rotor disks are much lighter than a helicopter's. There's little energy available to use to cushion a landing, so although autorotation is theoretically possible, there's little point.

The Boeing V-22 handbook has this to say (see page 26):

  The V-22 is a tiltrotor and does not rely on autorotation for  a
  survivable power-out landing. The wide separation of the  engines and
  the ability to drive both rotors with one engine  make a power-out
  landing extremely unlikely. However, if  required, the V-22 can glide
  for a predictable run-on landing in  airplane mode, much like a
  turboprop

I've seen glide ratios of 2:1 and 4.5:1 quoted on the Internet, so it'll come down quite hard and destroy the rotors.

However, the design mitigates against this in various ways, or so the manufacturer claims. In the survivability section of the same handbook they say

  V-22 crashworthiness is a function of design. Heavy components,  such
  as the engines and transmissions, are located away from  the cabin and
  cockpit area. The proprotors are designed to fray or  “broomstraw”
  rather than splinter on impact with the ground. The  energy-absorbing
  landing gear system is designed to attenuate  most of the energy for
  hard landings up to 24 fps. The wing is  constructed to fail outboard
  of the wing/fuselage attachment in a  manner that absorbs kinetic
  energy and ensures the cabin area will  not be crushed, thereby
  protecting the occupants. An anti-plow  bulkhead prevents the nose
  from digging in on impact, and the  fuselage provides a reinforced
  shell that is designed to maintain 85%  of its volume during a crash.
  Aircrew and embarked troops receive  additional protection from
  crashworthy seats that stroke vertically to  absorb energy.


Why is a Lockheed MC-130J Commando II creating such a loud droning sound? Today I heard a loud droning sound which is really unusual in the area of west London I live in; so I went on ADS-B exchange and it showed a USAF Lockheed MC-130J Commando II flying literally right over my house. However, it showed the altitude as being 27,000ft! I didn't know you could hear airplanes which are flying that high. Is it a case of the engines being so loud on that particular case or maybe the wind transferring the noise etc?

There are two factors reducing the volume of a sound when travelling through the air:

The pressure wave expands as the surface of a sphere, which will reduce pressure as a function of distance $r$:

$$ p(r) \sim \frac{1}{r^2} $$

Since human hearing is logarithmic, we typically use Decibels (dB) as a unit for volume, rather than pressure directly:

$$ L_p = 20 \log_{10} \left( \frac{p_\text{RMS}}{p_\text{ref}} \right) $$

This means that an aircraft that is twice as far away will (at maximum) have a sound pressure of one quarter left, which corresponds to $ 20 \log_{10}(1/4) \approx -12 \, \mathrm{dB} $. An aircraft at 27,000ft will only be $ 20 \log_{10}(1/27^2) \approx -57 \, \mathrm{dB} $ less loud compared to an aircraft on final approach at 1000ft. For a large and loud turboprop, this is easily enough to hear it, considering the engines can reach up to 140 dB and aircraft on approach are typically up 80 dB loud:

The absorption of sound waves in air is frequency dependent. This physics.stackexchange answer explains the details. The following plot shows the absorption coefficient as a function of frequency for different humidities:

(image from Wikimedia)

Since turboprops are producing more lower frequency sounds with their propellers compared to turbofans, they can be heard further (they also typically fly lower).
This also matches the "droning sound" you describe. The higher frequency noise has been absorbed by the atmosphere.


What are the reasons to evolve from trim tabs to moving the entire surface (e.g. stabilizer)? Modern commercial aircraft use stabilizer to trim instead of trim tabs. What are the advantages and disadvantages of this design choice?

Have aileron trim and rudder trim evolved in a similar way to move the entire control surface rather than aileron / rudder trim tabs?

Trim is used to zero the stick forces at the desired flight condition, and with the small, slow early airplanes, an adjustable spring somewhere along the control cables would do. When speed increased, trim tabs were introduced, because their trim force goes up and down with dynamic pressure, whereas the spring would always create the same force. This would require re-adjustment with every speed change.

With the increasing size and speed of airplanes, manual control required ever more complicated means of force reduction (Flettner tabs, spring tabs), and the relative chord length of all moving surfaces shrank to allow for more control with less force. The moment around the hinge of a control surface increases with the square of the chord, but the lift change for a given deflection angle increases only with the square root of the chord.

In parallel, wing loadings increased, which required high-lift devices to keep take-off and landing speeds down. These add a lot of lift in the rear part of the wing, creating a strong nose-down moment, and now a simple control deflection would not suffice to trim the airplane. The reduced chord length meant that high deflection angles would have been required for trim, reaching far into the region of deflection angles with declining effectiveness. That is when adjustable stabilizers came up: The trim change with all configurations was simply too big to be covered by the elevator alone.

Transsonic flight was next, and here the adjustable tail incidence is crucial to trim the aircraft trough the transition from subsonic to supersonic flight. A contour break from a deflected elevator could cause shocks which could produce elevator reversal. The dynamic pressures of jet flight put an end to manual control - the last, famous examples were the Canberra or the Dash-8 (Boeing 707 prototype). Now hydraulic actuators were used, but still it makes sense to use aerodynamic means to reduce control forces, because the size and power requirements of the actuators can be reduced with clever hinge moment reduction. The trim tabs were initially moved by cables, but soon they used electric actuators.

Since rudder and ailerons are not affected when the high-lift devices (Fowler flaps, slotted flaps) are deployed, they still use simple trim tabs. Newest developments are electric control surface actuators which can help to save mass and avoid the messy hydraulics. The RQ-4 uses electric actuators because the hydraulic fluid would have to be pumped continuously through the lines in order to keep it warm enough at the high operating altitude. Only the landing gear still uses hydraulics for retraction.


Which aircraft have elevators (lifts)? How do they work? This Question came up reading this comment from  tohecz on this question: Is it possible to access the baggage compartment in flight?.

  No elevator to the cargo deck like in thriller movies? I'm disappointed :( /sarcasm

According to some statements on Internet, there are elevators(lifts) on 747s for persons and carts.

Does anybody have any evidence or photos of their existence on smaller planes than A380s?
How do they work?
Do they have an electric-motor department on top (This will take much space)?
Where are they going to? Are they going to the personnel sleeping cabin? (On the A380 it makes sense)

This one from a A380 doesn't seem for persons?

After researching myself and asking a colleauge I found out that the L-1011(one of my favorites)

and the DC-10 (thanks to @UnrecognizedFallingObject for the comment)

had persons elevator.

On the Tristar and the DC-10
The purpose are to connect the Main Deck with the personnel-cabin or the Lounge.
.

The Mechanism as "@ratchet freak" stated in the comment is an "rack and pinion gears" elevator with 1 electric motor with 1 outer shaft (primary) and 1 inner shaft, as stated in an report of an incident with one of these elevators.

On the A380 there is an elevator to connect the 2 main decks, but this one is only for trolleys.

Edit:

Additional Information on mechanism of elevator:

  Drive System

  Each lift is operated by an independent drive unit. Each drive 400-cycle, three-phase,
  alternating current (AC) motors. Each motor is connected to a gearbox with
  counter-rotating drive shafts and sprockets for a chain drive. The drive shafts are
  operated by a common worm gear within the gearbox. In the
  event of one motor failure, the other motor will drive the lift at
  half-speed. Two, independent, continuous loop, bicycle-type chains taking power from the
  dual-output sprockets on the drive units actively drive each lift.

  Limit Switches

  The range of travel of the lifts is controlled by limit switches installed
  within the wire duct attached to the forward side of one of the vertical lift
  tracks. There are two sets of two limit switches for each lift:
  one set located in the service center and one set in the lower galley.
  One switch is a normal stop switch and the other limit switch is for
  overtravel in the event the normal switch fails to operate.
  The limit switches are actuated by a cam plate mounted on the side of the lift.
  The cam plate has a machined offset to prevent actuation of the
  overtravel limit switch unless the normal switch fails to operate. In
  addition to the limit switches, mechanical stops are installed in the
  vertical lift tracks to stall and shut off the gear motors if both
  limit switches malfunction.

Further and detailed Information can be found here in this Incident.


What is the Keel Effect? What is the Keel Effect and how does it happen? Is it the same as Pendulum Effect or it doesn't exist?

The Pilot's Handbook of Aeronautical Knowledege by the FAA has an explanation that says:

  An aircraft always has the tendency to turn the longitudonal axis of the aircraft into the relative wind. This "weather vane" tendency is similar to the keel of the ship and exerts a steadying influence on the aircraft laterally about the longitudonal axis. When an aircraft is disturbed and one wing dips, the fuselage weight acts as a pendulum returning the plane to its original attitude

I know I'm like answering my own question, but is this explanation quite right? Because in this question it is said that perhaps it doesn't exists or it means something different.

According to the keel effect page on Wikipedia it is the rolling moment created by the fuselage and vertical surfaces in a sideslip if the center of pressure is vertically offset from the center of gravity.

Functions of a keel

The keel of a ship (besides shifting the center of gravity below the metacenter) provides a stabilizing side force when the ship rolls. The same is achieved by a tail surface, but in aviation this is called roll damping. The much larger wing tends to dominate roll damping, so the effect of the vertical surface is small.

The next task of the keel is to balance the side force and rolling moment from the sails in crosswind conditions. It does this by letting the boat build up a sideslip condition until the side force from the keel and hull balances the side force from the sails, and the rolling moment from the side force and from heeling balances the rolling moment from the sails. The keel effect is this rolling moment due to a sideslip condition.

A few aircraft with very small wings and large vertical surfaces do indeed suffer from excessive moments created by side loads on those vertical surfaces. The best known of those is probably the Lockheed F-104 Starfighter. The massive tail on the upswept rear fuselage made 10° anhedral necessary to get the sideslip-induced rolling moment right.

Pendulum effect

The Wikipedia page also mentions the pendulum effect and calls both the fuselage contribution to the dihedral effect. Man, if there is ever a competition for the most misleading name of an effect, this would be the winning entry.

A pendulum is a mass mounted below the pivot or the metacenter, so it will stabilize in the down position. It seems the adherents of the pendulum effect belief believe that the plane is somehow hinged at the center of the wing. This is so wrong! A flying aircraft is not hinged, so all motion is around the center of gravity.

This is different with airships: As @JanHudec points out in the comments, the buoyancy of the lifting gas always works against gravity whereas the lift of a wing acts perpendicular to its span and the airspeed. This does produce a moment when the airship rolls, and the heavy gondola is pulled down by the same effect which pulls down a pendulum. Also, due to an airship's low density (by definition very close to the density of the air it displaces) the aerodynamic side forces on an airship are much larger compared to the inertial forces. This lets the airship effectively pivot around a point near the center of the envelope. Note that airships have no means of roll control - it is just gravity which ensures that the gondola stays on the lower side of the hull.

Now you can argue that the same is true for aircraft, only with much smaller aerodynamic forces. Yes, but those side forces are vanishingly small in comparison to the wing's aerodynamic forces which, again by definition, are close to the weight of the aircraft. A small change there will completely dominate the picture, and the small loads on the fuselage are just a rounding error. By moving the control surfaces, the pilot can shift the lift vector around almost as he/she likes, and the forces on the fuselage are insignificant.

Note that knife edge flight, a situation when the side force on the fuselage really is close to the aircraft's weight, needs lots of fuselage area and a powerful engine. Fuselage loads in normal flight are a fraction of those in knife edge flight.


What plane is this, appearing in the movie Rampage? The plane's registration number is barely visible. Unfortunately it's the best quality I could find.

It's a Boeing C-17 Globemaster III. The tail markings appear to be those of the 437th Airlift Wing, US Air Force (thanks to TomMcW for the unit identification).

To answer the question yourself, note that you can see the US flag on the vertical stabilizer and the word "Force" behind the cockpit window. Wikipedia has a list of planes flown by the US Air Force and, although the list is quite long, it is categorized by mission, which cuts down the options quite a lot – the plane obviously isn't a fighter, for example, and, conveniently, "cargo" is early in the alphabet so close to the top of the list.

The serial number 2300 (or 7300?) painted on the nose doesn't correspond to an actual USAF C-17; it was probably temporarily renumbered while filming.


What counts towards the 250 hours required for CPL? FAR 61.129 states that "for a commercial pilot certificate with an airplane category and single-engine class rating must log at least 250 hours of flight time as a pilot that consists of at least:

  (1) 100 hours in powered aircraft, of which 50 hours must be in airplanes.

  (2) 100 hours of pilot-in-command flight time, which includes at least—

      (i) 50 hours in airplanes; and

      (ii) 50 hours in cross-country flight of which at least 10 hours must be in airplanes.

  (3) 20 hours of training on the areas of operation listed in §61.127(b)(1) of this part that includes at least—

      ..."

What counts towards the 250 hours of flight time as a pilot?  Planes? Helicopters? Gliders? Hangliders? Paragliders? Paramotors? Wingsuits? Hot air balloons? Lawn chairs with helium balloons attached to them?

I would think that the skills from flying balloons is not very transferable to planes, so what are people's views on half your hours being from "flying" a balloon, or something similar?  E.g. What do pilot examiners, employers, insurance agents, think?

It's just what the regulation says:  you must log at least 250 hours of flight time and at least 50 of those hours must be PIC time in airplanes and 10 hours of cross country PIC time in airplanes.  As for the other two hundred hours?  They can be in any other kind of aircraft you like.

It's actually a very common way to build raw hours.  A lot of fixed wing pilots get rotorcraft certificates in a fraction of the total time than if they started training from scratch in helicopters.  It also works well with gliders, hot air balloons, you name it.


What is the name for yaw, pitch and roll together? What is the name for yaw pitch and roll all together ?

I've heard CMD used to refer to all of that information but don't know what it stands for.

Is CMD correct? if so what does it stand for? is there some other word?

Roll, pitch and yaw are referred to in one word as the attitude.


What is this aircraft that has both piston and jet engines? A friend sent me this picture of a trimotor aircraft with what looks like two radial engines and a jet in the middle. He didn't know what is was and neither do I. Anyone recognize it?

It is a double-hulled "YAK-110" (which is two Yak-55's), it was only recently completed and will be at Oskosh 2018 (and so will I, so I may be able to add additional pictures in August).

Here is an article about it.

Here is another video with the jet engine at its first airshow (and the picture you have is a screenshot from it):

It also isn't the only aircraft set up this way (jet/piston), the Screamin Sasquatch is another airshow aircraft converted to have both.


Is it allowed and safe to carry a passenger / non-pilot in the front seat of a small general aviation airplane? Is there anything wrong with taking a friend in the copilot's seat of a small general aviation aircraft with me flying, or does he have to sit in the back (if there is one)?

There should be no problem in general with flying with a passenger in a front row seat in a GA flight, as long as the aircraft is certified for single-pilot operations. You'd want to check your national regulations to be certain, but I have a hard time imagining that it would be prohibited as long as you're allowed to carry passengers in the first place. In general, it's normal practice in small airplanes for passengers to fly up front.

However, especially for anyone not used to a cockpit environment, you would definitely want to brief them on expected behavior before beginning the flight, in addition to any pre-flight briefing required by legislation. Even if such legislation only require briefing before a commercial flight, it might be good, and put your passenger more at ease, to do something similar before a non-commercial flight as well. (How to get out of the seat belt, how to exit the aircraft, where the airsickness bag is, ...)

None of this needs to be complex stuff; what I have in mind here is mostly things like keep your feet clear of the pedals, keep your legs clear of the yoke, don't touch any of the controls unless told to, and similar. As Jamiec points out in their answer, it's very unlikely that someone not used to light aircraft would know what the rows of instruments, switches and controls are about, so a quick "fly safely in the cockpit" style briefing would absolutely be appropriate in addition to a general pre-flight briefing.

For a (somewhat humorous) example of what I have in mind, you might want to check out Preflight Announcement, Maule on Youtube.

Especially since this is someone you know, and you'd therefore presumably be able to gauge their reactions more easily than if they were a stranger, don't be afraid to sprinkle some appropriate humor into the briefing. For one example, I've heard of the airsickness bag being referred to as the rollercoaster bag.

It may also help put your passenger at ease if you specifically tell them what you're about to do before you do something unusual or non-obvious, such as the engine runup and magneto check. Particularly with non-pilot passengers, you don't want to get technical; something like "I'll do a few engine tests to make sure it's running smoothly before we take off" is more meaningful to them than "I'll bring the engine to 2391 RPM while holding position, and then check the magnetos and carb heat before reporting ready to Tower". Certainly when flying with another pilot you might just say "mag check", or even nothing at all (they'd probably be expecting you to do it).

Especially if your friend is an adult or an able teenager (but probably not for people much younger than that), do consider the possibility of enlisting their help with simple tasks during the flight. Regulations permitting and of course assuming that you as the pilot in command feel comfortable with it, you could even let your friend take the controls for a while, as long as you're able to take over if necessary and you're able to ensure that nothing untoward happens. If nothing else, they can definitely help look out for and call out nearby traffic while hopefully enjoying the view.

You could also show your friend how to use the radio to contact ATC in an emergency, and at least the very basics of keeping the airplane in the air (things like mostly straight and level flight; shallow turns, possibly without rudder; climb and descent; stall indication and response; where the throttle is and how to operate it; and possibly the IDENT function on the transponder). In the unlikely event that something were to happen to you, while not a guarantee, doing so would greatly increase the odds of both of you eventually making it out of the airplane in one piece. I have written a much more in-depth answer about this from the passenger's perspective which you might find informative. It's possible that there are even courses specifically tailored toward GA passengers in your locale, which would/could cover such topics; if not, any instructor worth their salt should be able to put something together easily enough for a given airplane type. If this is someone you expect to fly with often, that might be money well spent for both of you.


Is it true that different variants of the same model aircraft don't require pilot retraining? I'm referring to this Wendover Productions video - The Economics That Made Boeing Build The 737 Max.
The creator asserts that designing a new long range narrow body plane would be more expensive than modifying an existing design, which is uncontroversial enough.
But he also makes the claim (timestamp 6:13)  that there was pressure from American Airlines to provide a re-engined 737 over a new model, because existing American Airline pilots are already trained to use the 737.

Pilots are generally trained to operate just one type of aircraft. Some fly the a380, some fly the 777, some fly the a320, and some fly the 737, but they don't fly the 737-700 or the 737-800 or the 737-900, they fly the 737 airplane as a whole.
Pilots are trained to the aircraft, not the specific aircraft variant.
In general, pilots can and do switch between variants of aircraft even in any given day and are not required to do any substantial training to be certified on different aircraft variants.
Crucially, the FAA has never required that 737 pilots complete any simulator training before flying new 737 variants.
That's because a 50 year-old 737 more or less flies like a 1 year-old 737.
American [Airlines] wanted a refreshed 737 over a new plane since they already had thousands of trained and certified 737 pilots.
They had no pilots for a hypothetical new narrow-body Boeing and the cost of training their pilots to a new plane would be massive.

Is this characterisation correct, or is there some nuance missing here?
The thing that I'm finding a little hard to understand, is that these different variants of aircraft must have different handling characteristics, or different things to consider (ie. things unique to doing a longer flight), it does seem a bit crazy that no training would be required.
It also seems that the economic incentives are a bit backward - this kind of dynamic would stiffle aircraft innovation as a whole.

It appears to depend on how much changed. You do have to have some training between models. The selling point was that an airline with 737 pilots could fly the MAX variant with minimal retraining

  "The airplane is configured to be very common with the [737 NG]," Wilson, who is now retired, said, "and so a pilot can walk into here and will find everything he can just like he can in the [737 NG]."

  "FAA-approved this for two-and-a-half hours of computer-based training for the transition between the two aircraft," Wilson continued. "All the overhead panel switches are the same. The only minor difference is, because of the change in the display, is to move some of the center console items here on the forward console."

And from the Wall Street Journal

  To make the plane as inexpensive as possible for airlines to adopt, Boeing was intent on persuading regulators that pilots of earlier 737s should be allowed to start flying the MAX without simulator training. That training would have been required if there were substantial safety differences between the models, boosting the plane’s cost to airlines since training cuts into time flying paying passengers.
  “Our marching orders are no training impact on this airplane. Period,” Richard Reed, a former Federal Aviation Administration engineer, recalled a senior Boeing official telling him during a meeting in the early years of the MAX’s development.

  The company had promised its biggest customer for the MAX, Southwest Airlines Co. , that it would pay it $1 million per plane ordered if pilots needed to do additional simulator training, according to Rick Ludtke, a Boeing engineer who worked on the jet’s cockpit systems, and another person who had been involved in the airplane’s development.

And later

  Boeing officials were focused on making the MAX fly as similarly as possible to earlier 737s. The fewer differences, the less likely the FAA would require pilots to undergo retraining.

  Mr. Ludtke, the former Boeing cockpit engineer, said company managers put pressure on engineers to avoid tweaks in designs that could result in pilots needing to learn new maneuvers in a simulator.

Wasn't there a difference?

The issue was that the MAX had a system (MCAS) that could push the nose down to make it behave more like previous 737s. Having read several articles on it, the root problem was

The initial specs said it was a minor change with the same course of action to correct as a runaway stabilizer (i.e. it was something 737 pilots already knew)

  The company reasoned that pilots had trained for years to deal with a problem known as a runaway stabilizer that also can force the nose of the plane to dip. The correct response to an MCAS misfire was identical. Pilots didn’t need to know why it was happening.

Boeing made MCAS 4x more powerful without really notifying anyone. It could also operate at slower speeds.
Boeing apparently wrote its manuals based on the original MCAS spec. Assuming it was still a minor system, it was buried or omitted

  Southwest Airlines, the jet’s first and biggest customer, followed Boeing’s lead and deleted MCAS from the manuals and emergency procedures it devised for its pilots. Other carriers didn’t mention it, either.

As predicted, the previous crew of the aircraft that would be Lion Air 610 had issues with MCAS, but correctly diagnosed a runaway stabilizer and shut off MCAS in the process

  The puzzled cockpit crew checked a quick reference handbook, running through other emergency steps before successfully regaining control of the plane by executing the checklist for a runaway stabilizer. That turned off MCAS and the crew flew manually for the rest of the trip.

Lion Air 610 would not be so lucky. They only figured it out moments before the plane slammed into the ground. Apparently it wasn't as obvious to pilots as Boeing thought.


Why would a pilot want to land with less than full flaps? So for example if I am flying the Boeing 737-800, the FMC gives me three flap settings and approach speeds.

Why would a pilot want to fly with anything less than full flaps where possible?

Less flaps gives a faster approach speed. In some scenarios, a faster approach speed is better than a slow one, for example:

Strong crosswind
Possible wind shear
One-engine failure

A higher approach speed provides a better stall margin and higher control authority in challenging situations. For example, the Boeing 737 QRH calls for a flaps 15 landing in "One Engine Inoperative" and "Stabilizer Trim Inoperative" scenarios.

In the crosswind scenario, let's assume your approach speed is 100 knots, and the crosswind is 20 knots. The crosswind is therefore 1/5 of the approach speed, and you need a larger crab angle to keep the airplane aligned with the runway. If you increase your approach speed to 120 knots, then the crosswind is only 1/6 of the approach speed, and the crab angle is smaller, making landing easier.


is there difference b/w moving object in a fluid and static object in a moving fluid? wind tunnel is usually based on static object in a moving fluid, but wouldn't stationary/semi wind inevitably fill the tunnel after collision, but in the real world the moving object is always meeting a new particle and the previous ones always leave the field.

if indeed there is an actual difference wouldn't that render turbulence simulation impossible?, and also incorrect CFD simulations?.

since wind tunnel do exist there can't be any difference but why?

That's called Galilean invariance. There's no difference whatsoever between a steadily moving object in a stationary fluid, and a stationary object in a steadily moving fluid.

You seem to be thinking that in a wind tunnel, some air will always get trapped downstream of (that is, behind) the object; and that for an object flying outdoors, air will never get trapped behind (that is, downstream of) the object. Neither of those things is true.

I see that you're thinking about supersonic flight; you're saying that

it seems like if an object is flying supersonically, it will leave a vacuum in its wake, but
it also seems like if an object is stationary in a supersonic wind tunnel, it will not have a vacuum in its wake.

I actually agree with your intuition here; I also think it seems like these two things will happen.

But when my intuition contradicts a law of physics, it doesn't mean that the law of physics is wrong; it means that my intuition is wrong.


Where do airshow pilots practice? I would assume that buzzing the tower and general hot dogging around the airport is prohibited, so how do airshow pilots get practice? Do they practice at high altitudes? If that is the case, how do they practice stunts that by nature require low altitude, like Bob Hoover's waltzing landing?

Aerobatic pilots typically use "aerobatic practice areas" when they practice.  Many of the Part 91 rules which would need to be broken in order to practice aerobatics are waived within these aerobatic practice areas (such as the 1,500 ft. "floor" for normal aerobatics in 91.303(e)).

The FAA has to approve them, and their guidance includes a good description:

  4. AEROBATIC PRACTICE AREAS. Aerobatic competition pilots, airshow pilots, and others who wish to practice aerobatic maneuvers not
  necessary for normal flight and below an altitude of 1,500 feet above
  ground level (AGL) must use a waivered aerobatic practice area.  These
  areas are not to be considered airshow sites.  The aviation community
  uses these practice areas to establish and maintain proficiency as
  well as enhance competitive skills in all the recognized aerobatic
  maneuvers. They are established by the waiver applicant in conjunction
  with the local FSDO and may have dimensions of several miles in
  various directions or be as small as a contest box; i.e., a cubic box
  with a dimension of 3,300 feet on all sides. Inspectors should be
  receptive to the establishment of these areas, consistent with safety
  and the efficient use of the NAS.  It is imperative that the safety of
  all nonparticipating aircraft be considered when issuing a Certificate
  of Waiver or Authorization for an aerobatic practice area.

An aerobatic practice area may be established over an airport if coordinated with airport management, and can be used to practice landings like those that Bob Hoover does.

Besides the special rules in these areas, it is also a good way to warn other traffic that aerobatics could be taking place because they are listed in the A/FD and a NOTAM is issued whenever they are hot.


How do I keep the neighboring Remote Control Airfield from flying over my property? I live in the North Georgia Mountains. The neighboring remote control airfield was put in front of my house where my mountain view is. I have no issue with them flying over their lease, just not over my property and in front of my view. I have approached them to stop, but they refuse.
Do they have the right or can I have them served for trespassing?

I'm surprised that all the answers and comments so far have been about resorting to laws, other higher authorities, or anti-aircraft batteries, and that nobody has suggested being nice.
When you say that you approached them to stop and they refused, that sounds like you went and talked to people flying their RC planes.  Presumably the RC airfield is leased by a club, which is probably legally organized as a non-profit corporation, which therefore has a board that meets regularly according to bylaws.  In ordinary times I would suggest finding out when the club board meets, and paying them a visit.  (With the pandemic stalking the land you're probably better off telephoning the club president or other club officer.)  If you appear at the board meeting and identify yourself politely and state reasonable concerns without accusing anyone personally, then I would think most club boards would take your concerns seriously, raise the issue with the rank-and-file club members at the next regular meeting, put a strongly-worded notice in the club newsletter, and give you telephone numbers of several board members to call in case you have any more trouble.
Most clubs devoted to any hobby just want to pursue their hobby in peace, and in order to be left alone they need to be good neighbors, and so that's what most clubs try to do.  It shouldn't be hard to get people to not fly over your property and close gates after they retrieve planes that accidentally came down on your land.
Then there is your demand that they not fly planes in your view.  Are planes over their field in your view?  In that case your demand may be neither legal nor reasonable.  (Please know that I'm no lawyer.)  Even so they may be willing to negotiate if asked nicely, and for instance offer to fly only three hours a day for two days a week just to avoid trouble.


What is meant by these criteria for a stabilized approach? Based on regulation, there are several criteria for when an approach is stabilized. I want to ask:

Only small changes in heading/pitch.

How small?

The aircraft is in correct landing configuration.

What are those configurations?

The aircraft speed is not more than Vref+20 or less Vref.

Is this IAS or CAS or TAS?

Although I can’t find regulations regarding stabilized approaches in the FAR/AIM, the unofficial but generally accepted definition of a stabilized approach would be

“Only small changes in heading/pitch.
How small?”
Small changes in heading and pitch would mean changes only necessary to maintain a ground track on the lateral guidance and a consistent airspeed on the glideslope. These are to compensate for drift due to things such as wind.

“The aircraft is in correct landing configuration.
What are those configurations?“
Configuration is entirely dependent on the aircraft and situation.
Typically it would include things like:
Autopilot correctly set or off;
Boost pump on;
Carb heat to hot;
Gas on the fullest tank, both, or on;
Landing gear down and locked with indicator lights lit;
Cowl flaps closed;
Flaps at the correct setting;
Mixture set at best power for density altitude;
Prop speed set at fastest setting;
Landing, position, and anti-collision lights (if not in clouds or fog) on;
All auxiliary and/or unnecessary equipment off;
Sterile cockpit;
Seats and seatback set and locked in the upright position;
Seatbelts and shoulder harnesses on and latched;
Throttle/power set at a consistent setting to provide a descent rate on the glideslope;
Landing checklists complete.

“The aircraft speed is not more than Vref+20 or less Vref.
Is this IAS or CAS or TAS?“
Vref is usually in IAS. Especially since the occasion in which you are using it would be below 3000 feet AGL, and less than 200 knots.


Why wing ribs have diagonal struts Why do ribs have diagonal struts,why not vertical as seen in airfoils of Citabria airplane?

The diagonal struts are best to transfer shear. Imagine an upward pointing load at the nose. In order to get that load transferred to the fuselage, it first needs to be transferred to the wing spar. Imagine now that you hold the rib firmly in your right hand where the spar is and press the nose upward with your left hand. With parallel struts, the rib will have much less stiffness and the nose load will deform the rib easily. With the diagonal struts, the rib is much stiffer when that particular nose load is applied.


Can a tiltrotor fly safely with one engine? I am curious about tilt-rotor feasibility (such as AW609) against fixed-wing and rotor-blade aircraft (conventional helicopters).

One important issue that immediately arises in my mind is that both propellers must be highly robust against failures. This is translated in a significant disadvantage against traditional aircraft designs since:

Fixed-wing which are equipped with more than one engine have redundancy, or at least they can glide long enoughg if only equipped with one engine
Rotor-blade can still perform an emergency landing in the event of a main engine or tail-rotor failure, as this question points.

So the big question is: Can a tilt-rotor fly safely (or at least perform an emergency landing) with a faulty engine?

P.D.: For the sake of the question let's presume that the engine has not blown up or has suffered from structural integrity failure (e.g. one blade is missing).

Short Answer: yes. If they could not, they'd likely not get certified
One engine can drive both prop rotors.

After digging into an old version of the V-22 flight manual, I find a whole pile of tables in the chapter that cover single engine flight.   Gross weight and DA and flight configuration informs what the "best" airspeed is for single engine flight.
The general approach for single engine flight to a safe landing is to fly at a particular configuration and airspeed, and then to set up the aircraft for an approach to a run-on-landing "between 55 and 65 knots."  As I understand the procedures, that final approach will have the nacelles tilted up far enough to prevent the tips of the prop-rotors from striking the ground once the aircraft is on the ground.
Flight Safety Note: I am not going to replicate (cut and paste) these procedures here for a number of reasons, one of which is that I am referring to an out-of-date manual, and some of the details may have changed.  I suspect that the current procedures are similar.
Note on the source:
An old version in the A1-V22-NFM-000 series; Part V/Chapter 12; Emergency Procedures. (There will be a similar section in the Dash Ten for USAF CV-22's).
Where a run-on-landing is not achievable, the manual calls for an approach to ...

... maintain the highest suitable air speed until deceleration is required for a no-hover touch down.

This general method is very similar to the single engine procedures that we had in the SH-2F and the SH-60B helicopters that I flew from ships in the Navy.  The aircraft's Gross Weight and the Density Altitude of the day will lead to some variations in the "best" airspeed for this; there are tables in the manual (and usually in the pocket checklist) to determine the best airspeed to fly.
Then ...

A shallow approach into the wind maintaining 30 KCAS until right before landing is recommended.

This is a little bit different from how we did this, and taught this, in those two helicopter models; we would try for a constant angle of descent approach (not a shallow approach) to a spot if we, as was usually the case, did not have single engine hover capability.  The resulting landing would be fairly firm, but that was by design.
Bottom Line
Not only is single engine flight possible, as well as single engine approach and landing in a tilt rotor, it's a well known flight characteristic that has well established procedures to accomplish.  (At least for the V-22.  The AW-609 doubtless has similar procedures in its flight manual).