What kind of problems can a flight have if passenger weight is miscalculated?

In general, an incorrect takeoff weight can have serious consequences for an airliner, especially when the actual TOW is close to the RTOW (regulated takeoff weight, see e.g. this question: What is RTOW and how is it different from MTOW?). It is possible that the aircraft is unable to takeoff within the available runway length. This is particularly important in case of an engine failure during the takeoff, since normal performance with both engines operating typically has enough margins. Even on a long runway, the pilots might rotate too early because of an incorrect rotation speed (VR), which could result in a tail strike.
In this particular case, the difference in performance was minimal. The AAIB (Air Accidents Investigation Branch of the UK) investigated the incident and concluded:

Whilst an incorrect takeoff weight was used for aircraft performance planning, the thrust
required for the actual TOW and environmental conditions (88.2% N1
) was marginally less
than the thrust used for the takeoff (88.3% N1
). This meant the safe operation of the aircraft
was not compromised.

The report also shows the difference in the performance calculations with the incorrect (left) and correct (right) TOW:

The difference in the V speeds for takeoff is just one knot, which is not significant enough to have any adverse impact on the takeoff.


Is ETOPS satisfied solely by range circles?

No, ETOPS is not satisfied solely by range circles, but (among other things) by the "time needed to fly to that airport".

See the requirements of 14 CFR 121.633 (emphasis mine):

  (a) For ETOPS up to and including 180 minutes, no person may list an airport as an ETOPS Alternate Airport in a dispatch or flight release if the time needed to fly to that airport (at the approved one-engine inoperative cruise speed under standard conditions in still air) would exceed the approved time for the airplane's most limiting ETOPS Significant System (including the airplane's most limiting fire suppression system time for those cargo and baggage compartments required by regulation to have fire-suppression systems) minus 15 minutes.

Paragraph (b), for ETOPS beyond 180 minutes, gives the same "time needed" requirement.

So, if a scenario existed as the question describes where "there is terrain between the route and the airport which makes [the ETOPS alternate] absolutely unreachable", then that flight could not reach that alternate in the required time (since the alternate is not reachable), and the flight could not be dispatched listing that alternate.


Why is a turbofan engine less efficient when air leaks over fan blade tips?

If it was to leak, it's still going through the intake to the compressor or bypass duct.

This is incorrect. A "leak" would cause the compressed air to circle around the fan and exit again from the front, reducing the efficiency of the fan, because part of the power would be used to compress air that does not do any useful work in the engine.

The circling around is a consequence of the work the fan itself does: after the fan the air is at a higher pressure than the air in front of the fan, this means that the air outside is pushed back by the air inside, and if there is a leak, the higher pressure air (inside) leaks out from the front.

Minimizing this "leak" helps maximising the efficiency of the fan, and of the engine as a consequence.


Twofold (at least): firstly it results in less energy going into the tip vortices, secondly, is the reduction in lift is gradual towards the wingtip then it tends to reduce the spin tendency - the angle of attack of the tip is typically lower than at the root and so it will stall later than the root.  In a slow-flying aircraft such as a paraglider the airspeed may be significantly lower at the tip when turning, and so the angle of attack for a given sink rate will be higher, increasing the risk of a spin.


What's the difference between a "flight line" and a "tarmac"?

The nuance is between aircraft that have been / will be flying imminently, and aircraft that are more than a few hours away from doing so.

Apron (U.S., ramp) is where aircraft refuel, load/unload, etc.
Flight line is, in the popular press, where aircraft are parked, maintained, and displayed.  This usage is duplicated by aeromodelling clubs, although their time scale is closer to minutes than hours. (Wikipedia claims, without substantiation, that flight line is the U.S. military term for tarmac, ahem, apron.)
Tarmac (U.S., asphalt) is a paving material, one possible surface for runways and roads.  It's not an aviation term.  Informally, it means apron: we hear about tarmac delays, never about flight line delays.


How to check if (small) aircraft's radio is working properly?

Here are some things you can do, there are probably more. I'm assuming you're mainly interested in checking COM, not NAV.

Controlled airport

Check if you can hear the ATIS, Ground or Tower; if you can, then at least you know you can receive. But you might as well just call Ground immediately and ask for a radio check. The correct phraseology in the US (see the Pilot/Controller Glossary) is "how do you hear me?":

  Bowman Ground, N12345, radio check please. How do you hear me?

Uncontrolled airport

Listen to the AWOS, if there is one, to determine if you can receive. Ask UNICOM or another aircraft to give you a radio check. If none of those options are available then you can use a handheld airband transceiver to test. Tune it to the frequency you're listening on and click transmit a few times, as if you're turning on pilot-controlled lights (PCL). If you hear the clicks in your headset, you can receive. To test transmission, do the opposite: click the transmit button on the yoke and listen on the handheld.

Airborne

You could call Approach, Center or FSS; try activating the nearest PCL (works best at night); tune and identify a navaid (that doesn't verify COM works, but at least you know something's working); listen to 121.5 (in the US, you should be doing that anyway) because there's usually some bored pilot asking for sports scores on it and some other equally bored pilot yelling at him to "stop talking on guard!".

Troubleshooting

As always, if you have any problems with transmitting or receiving do some basic troubleshooting first: check you have the correct radio selected; check you have the correct frequency; check the volume controls on your headset and/or panel; turn the squelch up/down/off; check your headset is plugged in correctly; if you have a right-seat passenger, see if they can hear/transmit; and anything else you can think of.


Does True Course, Magnetic Heading, or Magnetic Course determine cruise altitude?

Magnetic course is to be used in determining the cruise altitude.

From 14 CFR 91.159, "VFR cruising altitude or flight level":

  Except while holding in a holding pattern of 2 minutes or less, or
  while turning, each person operating an aircraft under VFR in level
  cruising flight more than 3,000 feet above the surface shall maintain
  the appropriate altitude or flight level prescribed below, unless
  otherwise authorized by ATC:

  (a) When operating below 18,000 feet MSL and—

  (1) On a magnetic course of zero degrees through 179 degrees, any odd
  thousand foot MSL altitude + 500 feet (such as 3,500, 5,500, or
  7,500); or

  (2) On a magnetic course of 180 degrees through 359 degrees, any even
  thousand foot MSL altitude + 500 feet (such as 4,500, 6,500, or
  8,500).

The same is true for IFR flight: magnetic course determines IFR cruising altitudes. See 14 CFR 91.179, "IFR cruising altitude or flight level".

This is true under FAA regulations. ICAO regulations are similar, but reference magnetic track rather than magnetic course; for these purposes the two terms have the same meaning.


What is this part of an aircraft (looks like a long thick pole sticking out of the back)?

That is called a Survey Tail Boom and includes sensitive instruments that need to be mounted away from the aircraft body for clean measurements.
You can see the name of the manufacturer LCAS printed on the boom. In this case, it seems to be a tail boom for magnetic field measurements installed on a Douglas DC-3, which is used for Survey according to Borek Air's fleet information. The LCAS website has a detailed description of the tail boom:

LCAS’ fully certified (Supplemental Type Certificate) tail-mounted transition and boom assemblies carry the magnetometer sensor and requisite electronics. The aft part of the boom system contains the provisions for the magnetometer sensor, the mid section houses the amplifier and flux gate and the transition assembly can house optional electronics such as pressure/temp sensors. The transitions or forward boom assemblies can also be modified for installation of optional video cameras.  The orientation of the sensor is adjustable, to provide optimum coupling with the earth’s magnetic field. This innovation eliminates the traditional towed bird system and offers significant advantages in data quality, pilot work load reductions, survey flight efficiencies, and safety in all types of terrain.
The mod kit includes all the necessary doublers, support assemblies and attaching hardware, as well as new ‘end cap’ with Nav. light provisions, this allowing the aircraft to be flown without the tail boom and the OEM tail cone assembly to remain un-altered.

(lakecentral.com)


Will landing gear with wheel fairings keep spinning due to airflow?

This is a very general question. So the answer is:

Sometimes they spin, sometimes they don't.

Have you ever seen a car with a bicycle on a trunk rack, and the front wheel is spinning. Sometimes they spin fast, sometimes slow, sometimes not at all. It just depends on the air flow.

Airplane wheels are the same way, and it all depends on the airflow, the tires and the bearings. The airflow over tires sticking out from wheel pants is going to be turbulent and unpredictable. Sometimes it happens, sometimes it doesn't. I've seen both.


Is the A350 more efficent than the B787?

The answer as to why companies seem to be favoring the 787 over the A350 is in several parts, none having very much to do with efficiency.

First, a grand total of just 6 A350 XWBs have been built. The A350 is just ramping up production this year, while the 787 has been in production about 5 years now. The 787's teething problems have spurred some interest in its competitor, but as the first composite airliner to start accepting orders, the Dreamliner has a distinct first-mover advantage.

Second, Airbus has seen some production problems in its larger airliners, which tends to make airlines nervous. The A380 saw cancellations totaling over $10 billion in lost revenue primarily due to its inability to make them fast enough, causing Airbus to indefinitely delay production of freight variants that major shipping companies were waiting for. Smaller, older production lines have been doing better but the A380 line is still taking up a lot of Airbus's resources that could be spent making 350s.

Third is simple cost. A 787-8's base price is about \$225 million. An A350 starts at about \$270 million. \$45 million a plane is nothing to sneeze at; it means you can have 6 Dreamliners for the cost of 5 A350s, and the major airlines are buying 40-50 of these planes each so the savings is considerable.


Firstly to clarify:

What are the differences between “inherent” and “treated” flame resistant fabrics?
Inherently flame resistant fibers are materials that have flame resistance built into their chemical structures. Aramid fibers from companies like DuPont create inherently flame resistant fibers, with brands such as DuPont™ Kevlar® and DuPont™ Nomex®.....

With that information:

Laundering’s impact on flame resistance
An essential thing to keep in mind when assessing flame-resistant technologies is that inherent flame resistant properties cannot be washed out or damaged through exposure to chemicals in the workplace or laundering practices, whether at-home or commercial.
FR-treated garments, however, may be damaged by chlorine bleach, the combination of hydrogen peroxide (“oxygen bleach”) with hard water, or exposure to oxidizing chemicals in the workplace. Source

An extensive DuPoint Nomex Laundering Guide
For the 'treated' fabrics, reading this DuPont document might be interesting.


Can planes benefit from Mitsubishi's Air Lubrication System?

NASA tested a similar concept. They call it Active Flow Control, or AFC.

A full-scale 757 tail, equipped with active flow control, has demonstrated increased rudder effectiveness in wind-tunnel tests by Boeing and NASA that could lead to smaller, lower-drag vertical tails.
"Sweeping jet" AFC actuators were mounted on one side of the fixed stabilizer, just upstream of the rudder hinge line to blow on to the leading edge of the deflected surface. The 37 actuators were supplied with variable mass-flow pressurized air from an external source and were individually addressable so that different spacings and zones could be tested.

Tail fins are huge to help compensate for engine failures. But with such system blowing pressurized air out of holes upstream from the rudder, manufacturers can design smaller tails to save on drag and weight.

Another system that works by suction (not blowing) at the leading edge is on the 787-9/10. It is used for both the horizontal and vertical stabilizers on the -9, but Boeing dropped the horizontal stabilizer system on the -10. There were plans to use it on the upcoming 777X, but Boeing dropped it. That system is called hybrid laminar-flow control (HLFC).


How does a mechanic determine if a repair or alteration requires a Supplemental Type Certificate?

Repairs and alterations are defined at FAR 1.1, FAR 43 App(A)(a)(1-4), FAR 43 App(A)(b)(1-4)

"Major alteration means an alteration not listed in the aircraft, aircraft engine, or propeller specifications - (1) That might
appreciably affect weight, balance, structural strength, performance,
powerplant operation, flight characteristics, or other qualities
affecting airworthiness; or (2) That is not done according to accepted
practices or cannot be done by elementary operations."
Minor alteration means an alteration other than a major alteration.
Major repair means a repair: (1) That, if improperly done, might
appreciably affect weight, balance, structural strength, performance,
powerplant operation, flight characteristics, or other qualities
affecting airworthiness; or (2) That is not done according to accepted
practices or cannot be done by elementary operations.
Minor repair means a repair other than a major repair.

In the US, to be airworthy (FAR 21.183) all aircraft must "conform to type design and condition for safe flight". To "conforms to type design" there must be some type of approved authorization for every piece on the airplane. There are several ways to do this.

The manufacture may have pre-approved the equipment you wish to install. Under CAR 1,2, & 3 (~prior to 1958) regulations a separate document for the aircraft called a "data sheet" showed approved equipment. After 1958 aircraft where certified under FAR's and used a "Equipment List". The "Equipment List" for light aircraft is usually found at the back of the Pilot Operating Handbook (POH). An example for a 1978 C152 is shown below.

If a manufacture did not approve the equipment than it may be installed under the authority of a "STC" (equipment pre-approved by the FAA).

...or an "alteration" that a AI (Authorized Inspector) gets approval from the local FAA FSDO office by filling out Form 337 and have it field approved.

The owner is required to keep a copy of either a "STC" or Form 337 "alteration" to show the equipment is legal for each annual inspection. If an aircraft has equipment installed that is not authorized by a Data Sheet, Equipment List, STC, or Form 337, the aircraft is un-airworthy and illegal to fly.
There are three small exceptions:

The FAA provides an alternate approval for small common parts (FAR 21.303-4 and Court Order 8110-42A)
such as wheel bearings, chemicals i.e de-iceing fluid, etc via a "PMA" authorization.

The FAA approves replacement of some parts that meet industry
standards (AC 20-62e) without need of authorization for parts such as sheet metal,
electrical components, minor hardware, etc.

In certain circumstances (FAR 21.303-2 and AC 20-62e) the owner may have a part built or manufactured that is no-longer available for purchase. This provision is often used for old bi-planes and war birds.


Does the required torque to spin a propeller increase with RPM?

Of course. More and bigger blades is more drag. Drag is also proportional to the velocity squared. Even maintaining the RPM, a bigger propeller (diameter) will have the additional diameter flying faster.

To maintain a higher RPM (or to use a bigger prop) the force to cancel the increased drag is higher, and thus the torque (force times distance) that drives the propeller.

Place the propeller in vacuum, and the engine will have no trouble with the propeller apart from any loads on the shaft (but there won't be any thrust).


Helicopter or Airplane, which is the most difficult to fly?

Unfortunately, this is an opinion based question. My opinion is based on the fact that my first few hours of helicopter instruction were harder than my first few hours of fixed wing instruction.

Takeoff in a helicopter was fairly easy after hover taxiing to the takeoff pad and hover turning 360° with yaw control to visually clear the area. Landing in a helicopter was fairly easy up to the point of bringing the aircraft to a hover. In both cases, the hard part came in the form of any of the low speed maneuvering. That includes just getting the skids off the ground and putting them back down under control.

Takeoff in a fixed wing aircraft was easy except for directional control to remain on centerline before rotation and the extended centerline after rotation. Landings in a fixed wing aircraft are in another realm of difficulty until you get the hang of it. From stabilizing the approach to slowing down to a speed appropriate to turn off the active runway and everything in between are hair-raising and nerve-wracking your first few hours of instruction.

Cruise flight in both is fairly simple and enjoyable once the aircraft is trimmed out and the friction locks are set properly. Although, changing flight parameters in a fixed wing can be done with as little as input on one control. Say for instance, changing the throttle input in a trimmed out airplane will make you change altitude. Changing flight parameters in a helicopter will involve input into more than one if not all of the controls. Changing the collective will require a change in throttle input, which will require input into the anti-torque pedals, in order to change altitude in a helicopter without a governor at low speeds.

The biggest difference is that a good instructor can verbally walk you through flying an airplane up until short final on your first flight. Although, they will always be ready and prepared to take the controls at any time. In a helicopter, the instructor will be on the controls the entire time your first flight. They will give you command of each control, one by one, as your confidence and competence grows.

Bottom line is that hovering is the deciding factor on whether it is harder to fly either a fixed wing or a rotary wing aircraft. Although, it is easier in a fixed wing. In a fixed wing aircraft, all you need is plenty of altitude, and a headwind that matches your airspeed (or an aerobatic plane with lots of thrust). In a helicopter, you need to be able to juggle while riding a unicycle.


When were airbrakes used for the first time in aviation?

(Flight magazine 1914)

I'll answer the title question, as the complete history is too broad. That would be the Avro Scout (model 511) of c. 1914. Only one was built. Yes, that suspiciously looks like flaps. Back then +100 years ago that invention was called an air brake, flaps are air brakes after all.

From Wikipedia:

  Most unusually for its time, the inboard lower wing featured landing flaps air brakes, so the 511 landed at a sedate 35 mph (56 km/h).

This is what the plane looked like:


The center of gravity (cg) should be right above or below the center of lift. Otherwise the airplane will start to pitch and never stabilize.

But you do not select the position of the cg, instead, you adjust the center of lift such that lift will act along the same axis as weight. This is called trimming the aircraft and is done by adjusting the elevator deflection (or the incidence of the stabilizer). Of course, you should select the cg position such that the available elevator deflection range will not only shift the center of lift to the cg, but leave enough margin for manoeuvring.

The next condition is to ensure proper natural stability. Once the tail surface produces more lift per area than the forward surface, the aircraft will be instable, so that any angle of attack deviation from the desired state will quickly increase. Therefore, the cg should be placed slightly ahead of the neutral point of the airplane. The neutral point is the cg location at which angle of attack changes will not cause a change in pitching moment. The neutral point of a single wing is near its quarter chord point (it moves forward from the quarter chord point with decreasing aspect ratio), and the neutral point of the whole aircraft is the mean of the neutral points of all components, adjusted for their lift curve slope.

A good first position for the cg is at the quarter chord point of the wing. This ensures that the tail surface will be only lightly loaded, but it might be that stability at this position is not satisfactory. To increase stability (and reduce pitch agility), move the cg further forward, and vice versa. If you want to optimize the aircraft's lift-to-drag ratio (and minimize trim drag), select the most backward cg position with still acceptable stability.

GA aircraft are normally very stable, and their cg position might even be close to the leading edge of the wing. Details depend on tail size, aspect ratios of all surfaces and the desired agility.


Why are digital autopilots better than analog?

Early autopilots would only control one degree of freedom. Starting with the yaw damper of the Me-262, they were a simple feedback loop involving a gyro, a single control surface and some damping circuitry. Example: A roll gyro was coupled to the ailerons and kept the wings level. Commanding a bank angle would simply shift the zero point of the gyro to a different angle, and some damping made sure that the movement was slow and did not overshoot.

This, however, would neglect any cross coupling. Banking flight needs more thrust to keep altitude, but the roll autopilot would not "know" of engines or throttles, just ailerons. The same was true for analogue pitch and altitude hold systems which had a simple feedback loop with the throttle and the elevator, but no other controls.

Modern digital autopilots, starting with the one in the X-31, control all axes in parallel and use a multitude of sensors and feedback loops to control the whole aircraft in one go. This is much easier to achieve with digital control, and gives smoother responses since cross-coupling effects can be anticipated and corrected before they manifest themselves.


Why do light taildraggers swirl uncontrollably on runways in a simulator?

A taildragger is more or less a shopping cart being pushed backwards, or a car driving fast in reverse.  It's dynamically unstable when rolling and wants very badly to switch ends, requiring constant input to the steering.


Why are some aircraft's life limited by both cycles and flight hours?

Some fatigue related issues that are not directly tied to departures and arrivals, like wing bending from gust loads, but may be randomly continuous throughout the flight, need an hour limit.  Taking it to a comical extreme, if the airplane flew for 3 years straight without ever landing because it had a new pixie dust powered engine, it would have close to 26000+ hours of bending fatigue time on the wings and tail, engine mounts etc., but only one flight cycle.

Also, there will be an analysis that establishes the average amount of time per flight cycle, overall across the fleet, and this may be applied in some cases to give an hours life limit that is roughly equivalent to the target number of cycles, when applied in the aggregate.  That ratio of hours/cycles suggests that the average flight time per cycle for the PC-12 is somewhere around 1.1 hours.  In the Regional Jet world, the average flight cycle is about 1.3 hours.  The 30000 hour limit prevents a PC-12 operator who does a lot of long range flying with 2 hour+ trips from running his airframe up to 50000 hours before it gets to 27000 cycles.

30000 does't sound like a lot, but corporate aircraft generally live fairly pampered low-utilization lives and take quite a long time to get those hours, perhaps 30 to 40 years.  A regional jet gets to 30k in only 10 years.


What is the proper procedure for a piston engine fire on the ground (e.g. during engine starting)?

As you said, the "proper" procedure is whatever is in the aircraft's operating handbook. Having said that, there is a general pattern, at least based on a few POHs I have to hand. Note that they all list the procedure as "engine fire on startup"; there's no general "engine fire on the ground" procedure.
The 'generic' steps are:

Continue cranking as usual to pull the fire and fuel into the engine
If the engine starts: let it run for a few minutes then shut down as normal and inspect the aircraft for damage
If the engine doesn't start: open the throttle, cut off the fuel (mixture, fuel pump, and/or fuel cutoff as applicable), and evacuate the aircraft

Here's an example from a Cessna 172S POH (Lycoming IO-360-L2A engine); bold items are memory items:

Ignition Switch -- START, Continue Cranking to get a start which would suck the flames and accumulated fuel into the engine.

If engine starts:

Power -- 1800 RPM for a few minutes.
Engine -- SHUTDOWN and inspect for damage.

If engine fails to start:

Throttle -- FULL OPEN.
Mixture -- IDLE CUT OFF.
Cranking -- CONTINUE.
Fuel Shutoff Valve -- OFF (Pull Full Out).
Auxiliary Fuel Pump Switch -- OFF.
Fire Extinguisher -- ACTIVATE.
Engine -- SECURE.   a. Master Switch -- OFF.   b. Ignition Switch -- OFF.
Parking Brake -- RELEASE.
Airplane -- EVACUATE.
Fire -- EXTINGUISH using fire extinguisher, wool blanket, or dirt.
Fire Damage -- INSPECT, repair damage or replace damaged components or wiring before conducting another flight.


What are various specifications of Engine oil used in Piston and Turbine engine aircraft?

Here is a general answer for a general question.

Function of oil is three-fold for both piston and turbine engines:

Lubrication - reduction of friction;
Cooling - carrying away of heat; and
Cleaning - carrying away of contamination.

Oils used in jet engines must be able to withstand temperatures that are much hotter than piston engines.

Here is a link to some of the lubricating oils used in navy jet aircraft and the various specifications.

Jet Aircraft Engine Lubrication Systems

Piston aircraft engines tend to be air-cooled and are therefore manufactured with larger tolerances. This results in an engine that uses up oil (burns it). Most POH of piston aircraft that I've seen call for ashless dispersant oil, which refers to an oil that has non-metallic additives and has the ability to suspend combustion particles.

Here is an article that describes piston aviation oils.


Smoking in the cockpit - how is this tracked?

Yes, they would be breathing second hand smoke, but aircraft are well ventilated. The other cockpit crew would be exposed to some amount of smoke. The amount that makes it to the passengers from a single cigarette in the cockpit would probably be undetectable.
Smoke detectors are not very effective at detecting cigarette smoke. I believe this is because most of the smoke passes through filters (the fairly ineffective one on the end of the cigarette and the two very effective ones in the smoker’s chest) which remove particulates and it is therefore not very dense. It takes pretty thick cigarette smoke to set one off.
I don’t know about the rules in Bangladesh, but most of the time airlines are not allowed to listen to cockpit voice recordings. In the US that would be a violation of eavesdropping statutes. The US law stipulates that they may only be used for accident investigation purposes and only transcripts of relevant portions may be released publicly. They can be subpoenaed for a trial only if the publicly released transcript is insufficient and

discovery of cockpit voice recorder recordings is necessary to provide the party with sufficient information for the party to receive a fair trial.
ISBA Amendments of 1990, 104 Stat. 4655.

The pilot’s unions are very much against using the recording or transcripts for any other purpose than accident investigation.
It would end up being down to the other crew reporting them. I doubt it occurs often enough for anyone to keep track of the number of reports for it, and i doubt it would be reportable to any aviation authorities. It would be handled internally to the specific airline.


What would happen if the blades of a variable pitch prop did not all have the same pitch?

Never say never, but that's not a prop malfunction that I've heard of or that was ever addressed in the turboprops that I've flown.  We had various prop malfunctions, but the ways that things could fail that we considered would pretty much leave all blades in the same place.  So without claiming that it could not, ever, ever, no way no how, not in all possibility ever happen, I'll say that it's not very likely.

If you did get something like that, the vibration would probably be bad enough that you'd shut the engine down, and at that point the interesting question would be, do all the blades feather for you?  (The answer to that probably depends on what type of prop you have and what specific failure mode led to the condition in the first place, and now we're into too much speculation for any answer to be very enlightening.)


What is the simplest way to explain a sonic boom that is still technically correct?

I will try to explain the principle, briefly and practically as you requested.

Imagine that we have an airplane flying in position 1. It is flying at supersonic speed.

Good, now this airplane moves forward. But it is not the only one moving forward, the perturbation that the airplane produces over the air moves as well, but at a different speed, the speed of sound. In the next figure you will see that the perturbation (or pressure wave) moves less distance than the airplane, which moves from 1 to 2.

The airplane keeps moving to position 3, and at position 2 there are some perturbations (pressure waves) that are also generated and also move as speed of sound. However, I have smartly selected a perturbation that reaches exactly the same point in space that the perturbation (pressure wave) that I selected is reaching as well. So both perturbations meet at the same point.

As you imagine these two are not the only perturbations (pressure waves) that are meeting at this point, there are several points between 1 and 3 that also generate perturbations that join. Actually, this is also not the only point in space where perturbations (pressure waves) join together: there is a line that envelopes the points where the pressure waves meet at each instant. Well, actually a surface in 3D.

OK, if you do the same with a better painting tool than me… you draw the same but also evolving with time like this:

Which is the image in Wikipedia. What is the effect that you experience?

So the orange observer that is located in advance/before the blue lines does not feel any perturbation due to the airplane, nor hear it, as the pressure wave have not reach him yet.

However, the green observer has already felt the airplane passing by and sees how the air is altered by the airplane (imagine that you are close enough).

Finally the brown observer is just in the middle, coming from a region which has not yet experienced the perturbations made by the airplane and finds suddenly a concentration of perturbations (pressure waves) as described above. That is a sudden change in air flow properties and is experienced as a sonic boom.

To give a real end to this, notice that the further you are from the airplane the less strength the pressure waves have when they arrive at the blue line, making the sonic boom less and less intense.


Was this Gulfstream way below the glideslope?

There's no incident here. St Martin has a very short runway which spans a small stretch of land between 2 beaches, it's an airport where jets need to be on the numbers. It's famous among plane watchers and there are hundreds of videos of aircraft coming in low enough it seems as if you could reach up and touch the landing gear.

So if there was a glideslope this aircraft was certainly below it, however it's not an instrument landing so glideslope had nothing to do with it.


Are Boeing 737 winglets adjustable from the cockpit?

Winglets are fixed to the ends of the aircraft. As can be seen below, the winglet has no movable parts and is fixed to the end of the wings.

http://www.sae.org/dlymagazineimages/2861_2313_ACT.jpg

Boeing 737 winglet; image from sae.org

What you'd seen is an optical illusion. The port and starboard side winglets would not be much different, usually (except that they are mirror images externally).

Interestingly though, Boeing has filed a patent for an adjustable winglet. Airbus is also working on a similar project, called the morphlet.Both of these are geared towards reducing drag and saving fuel.


Why does the B-52 have such a tiny rudder?

There are two reasons and they date back to the early designs for the aircraft. Keep in mind the tail is different now than when it was originally designed. Boeing has originally planned for an all moving vertical stabilizer but engineers doubted its reliability and the systems to operate it simply would not fit in the tail at the time. More importantly the original designs had sufficiently larger control tabs but this lead to an elevators and a rudder that had a lower critical mach number than the wing (i.e. the empennage would stall first). The engineers shortened everything to create a more stable situation as is noted in this passage:

  Concerning the rudder, the situation is much worse. The B-52 rudder
  and elevator have an exceptionally narrow chord. Most airplanes have
  at least a 25% chord, which allows sufficient power and effectiveness
  in both yaw and pitch during takeoff, landing, and asymmetric
  conditions. The same is not true of the B-52 with its 10% chord rudder
  and elevator. The chord was reduced because original designs of the
  aircraft had the tail exceeding critical Mach prior to the wing. The
  chord of the tail was reduced to ensure that the wing reached critical
  Mach first.[15]

  The original designers knew that the rudder was underpowered. An
  aircraft the size of the B‑52 requires a massive rudder that does not
  exist. This rudder is insufficient for the basic needs of the
  aircraft, let alone for asymmetric engine-out scenarios. Original
  plans called for an all moving vertical tail, the first of its kind.
  However, Boeing doubted the reliability of the hydraulic actuators
  necessary to achieve this. The design was also too heavy for the tail
  structure to sustain. Therefore, Boeing designed, built, and
  incorporated the yaw-adjustable cross-wind landing gear,[16] what is
  known to B‑52 aviators as ‘cross-wind crab.’ This system allows the
  B-52 to operate during normal conditions of take-off and landing in
  crosswinds. However, the true problem was asymmetry.


Why can't we extract more from exhaust gases in gas turbines?

It can be done, but the better specific fuel consumption does not compensate for the extra weight. We all know that aero engines have to be as light as possible. In land, stationary installations, where weight matters but little, regeneration, intercooling, and even combined-cycle (in electricity generation, using a gas turbine that drives an alternator, but with the exhaust gases generating steam for a steam turboalternator, for example...). The efficiency is very, very high, but the weight and bulk are considerable, too...

But it has been tried: https://airandspace.si.edu/collection-objects/allison-t78-2-turboprop-engine

https://www.flightglobal.com/pdfarchive/view/1963/1963%20-%201880.html


How are fuel tanks tested and certified?

The exact regulations governing an aircraft's fuel tanks depends on many factors such as type and number of engines, construction material, mounting method, number of passengers, aircraft gross weight, etc.

But a good overall set of requirements is given in 14 CFR 23.965 - Fuel tank tests. It includes such items as pressure testing, vibration, sloshing, inertia loads, venting, duration and number of cycles of each test, etc.

14 CFR 23.967 thru 23.101 - Fuel tank tests provides additional criteria but also includes requirements for components such as access panels, fuel sensors, filters and strainers, lines, pumps, drains, valves, jettisoning, etc.

Other than a visual inspection for leaks and corrosion, the primary field test for an installed tank is to plug all the orifices and pressurize the tank to 2-3lbs for about 10 minutes. Large rubber stoppers that look similar to corks (with a bolt running through them that expands the rubber) are often used to plug the larger opening such as fuel filler openings.


It's because the "rules" people are traditionally taught about creation of lift, basically that a wing is a semi-venturi that is sucked up by venturi effect as it moves, is a gross oversimplification that overlooks most of what is going on, which is the wing motivating a large package of air to move down and creating a Newtonian action/reaction, of which the venturi effect is a part.

Anything that is more or less flat-ish, moved through the air at some angle, will make some amount of lift if it's able to induce some of the air to move from up here to down there as it passes.  The front door of your house, your hand stuck out the window of a car, or a wing with a weird reverse curve on top.  Enough to make an RC airplane fly at least.  Probably wouldn't work so well with a full size one.


Are there any low time lucky CPL holders who operate as PIC on medium or heavy jets?

There have been periods of time in the past (and I think at present as well) where a lack of experienced pilots meant airlines had to resort to hiring CPL's as SIC's on turboprop and some regional jets. I know that American Eagle did that for a while -- they used to call them the 500 hour wonders. Some were hired with even less time if they showed exceptional skills.

However, to log PIC time in an aircraft that requires an ATP ticket, you have to have the ticket. Sole manipulator of the controls is not enough for a CPL to log the time as PIC on those aircraft.


Do ballonets control the buoyancy of a Zeppelin NT?

The NT, being semi rigid, does not work like a balloon where buoyancy of the airship is controlled by adding or releasing helium. The quantity of helium carried is set at the beginning of the flight, and is set so that the aircraft is heavier than air. Vertical motion is then controlled by engine power. Buoyancy control is not the ballonet's purpose.

Ballonets are used to maintain constant pressure in the hull, as this is required for structural integrity. Whatever additional volume is required beyond that consumed by the helium carried is filled by air pumped into the ballonets. This air may also be released to control pressure as the craft ascends, and pumped back in as the craft descends. The hull is not designed to be pressurized beyond 5mbar.

Zeppelin GMBH technology

  Envelope - Non-flammable Helium, contained in a high strength, multi-layered laminate, provides the necessary lift. The envelope pressure is maintained at only 5mbar above atmospheric. Air chambers, the so-called “Ballonets” help to keep a constant interior pressure at all flight altitudes, and maintain a rigid hull.


Why aren't any wingsuits able to sustain flight?

I'm aware that under zero power it is a glider, but there are gliders
  that sustain flight and have enough lift to climb etc.

This statement is a bit incorrect. Gliders don't climb like aircraft as they are constantly falling to the ground unless they catch a thermal, wave lift or ridge lift, in which case they can ride the updraft to gain altitude. In theory, a wingsuit could do that if you could maneuver to stay in the thermal but wingsuits are not maneuverable like a glider and tend not to have nearly the glide ratio of a glider so they sink far faster than a thermal could cary them up.

There is an interesting discussion on it here.


Why is the autopilot of the DHC-6 Twin Otter powered by bleed air?

The reason (back in the day) was an envisioned low-cost autopilot ownership in smaller planes,$^1$ but it was a troublesome system as it aged.

  The first production [Twin Otter] aircraft left the Downsview factory with an option for the Honeywell H-14 autopilot. This system used large pneumatic servos to control the aircraft. This was a popular option at the time however as the aircraft and autopilot aged the maintenance involved in keeping the system serviceable resulted in many operators disabling or removing the system (rockymountainaircraft.ca).

It works via pneumatic servos; pistons that are actuated by pressurized air.

  Source: NASA

$^1$: NASA contractor report (prepared by Honeywell) on "fluidic" flight control systems (also covers the aforementioned Honeywell H-14 autopilot).


What is the length of the escape rope in the cockpit? specifically A330-300 (If possible)

For the A320, this can be found in the CCOM (Cabin Crew Operation Manual)...

So the A320 is a 5.5 meter (17.04 foot) knotted rope stored above the side cockpit windows. There are 2 ropes in the cockpit (one on each side).

I can't find the CCOM for the A330 but it should be a similar size.


Is there any global reference describing when flight crews have to make contact with ATC?

On the ground, you need a clearance from ATC when you are on the maneuvering area, which consists of taxiways and runways. The ramp/apron is typically not part of the maneuvering area, and as such not controlled by ATC, although many large airports have some sort of ground control for these area.

In the air, you need a clearance from ATC whenever you are in controlled airspace. Some countries additionally require pilots flying IFR to be in contact with ATC even in uncontrolled airspace.

Note: ‘controlled airspace’ means an airspace of defined dimensions within which air traffic control service is provided in accordance with the airspace classification; (from SERA, EU 923/2012)


Why don't big commercial planes have full aircraft parachutes?

The reason for not using full aircraft parachutes can be stitched together by looking at the many related questions. Let me do this for you:

Parachutes will only help when something essential fails at sufficient altitude for parachute deployment. As paul said here, most accidents happen at take-off and landing where a parachute cannot be successfully deployed.
Parachutes big enough to slow down a whole airliner will be very heavy, reducing payload and increasing the number of flights to transport the same number of passengers. The biggest parachutes designed so far were for the solid rocket boosters of the Shuttle, and paul gave their mass a 3 x 990 kg plus 550 kg for the drogue chute. Wikipedia gives the mass of one SRB at 91,000 kg. Scale this for the zero-fuel mass of an A-320 of 62,500 kg, and the mass will be approx. 2,500 kg. That is equivalent to 25 passengers, or 16% of the A-320's capacity. Adding the parachute will translate into 16% more flights, just to compensate for parachute mass. This is most likely underestimating the true impact because I did not add the mass for structural reinforcements.
The opening shock at travel speed would destroy both airplane and chutes. If we want the parachute system to work in as many cases as possible, we need to make deployment possible at up to Mach 0.85, and then the maximum g-load on aircraft and passengers must not exceed 6 g. (See here for Eiband diagrams which give time- and direction-dependent limits for the maximum deceleration a human being can survive). This is possible with staggered deployment of several chutes with increasing size, and by sewing parts of the canopy and the parachute's strings together, so they can rip apart during opening, which slows the unfolding process. But I expect that this will add to the mass of the parachute system. It will certainly add to the mass of the aircraft's structure, which is currently limited to +2.5 / -1.0 g.

By looking at point 2 above alone, it becomes clear that the addition of parachutes will most likely drive up air travel casualties. If we need 16% more flights to make the cruise part less dangerous, and still most accidents happen during take-off and landing (which are now 16% more numerous), we gain little. Crashes now involve fewer passengers, but their number goes up. Tickets will become 20% more expensive at least (more if the parachute system costs something, which is very likely), and we all know how the majority of passengers votes when faced with a choice of dearer, somewhat safer flights and 20% cheaper flights at almost the same accident risk.


Credible Sport Project: Is it possible to revive the idea with modern avionics?

It wasn't a lack of technology. The technology to automatically fire the rockets is not actually very complicated: a radar altimeter, airspeed data and maybe input from the landing gear load sensors hooked up to a simple computer. All of that existed back then, and the rocket system was in fact computerized:

  The Lockheed test crew then assessed that the computer used to command
  the firing of the rockets during the landing sequence needed further
  calibration, and elected to manually input commands.

So the plan was to use computer control, but it needed more development than they had time for - as were in a very big hurry they decided to do it by hand.

If they'd had more time to adjust things they no doubt would have succeeded with the technology of the time. The reason that the project was canceled was not a lack of technology but that the hostages were released.

In reality the plan to use rockets to slow down the airplane so quickly was extremely risky, and if it went wrong the US military would have had their best special forces units stuck in the middle of Tehran! I personally don't think this would have gone ahead even if the tests had been successful. The fact that they continued to develop the concept into the MC-130 Combat Talon II without the rockets indicates to me that the military thought the braking rockets part of it wasn't worth it.

So no, modern avionics really would have nothing to do with it.


Does the temperature of the body of an aircraft increase its efficiency?

As your speed increases, your temperature will increase due to fluid friction of the air. When metal gets heated, it becomes weaker and more malleable. Think about when a blacksmith is hammering on a piece of iron over a hot forge. Due to this, your Vne should be reduced so your wings don't fall off.

As far as your initial question, if temperature affects efficiency; not really, unless your body gets so hot and you are going so fast as to alter the shape of the aircraft (which could happen, I suppose.)


Can we apply landing minimum with ALS when ALS is available with low intensity only?

The ILS to RWY 3 at ABQ (ILS RWY 3 ABQ plate) shows a required RVR of 1800  (not vis in sm) with everything working.  Using the inop component table (no special provisions for this in Operations Specs) shows a required increase to 4000 RVR with the MALSR (ALS) inop. (look at table)

The fact is that the "LOW INTST ON CONS" (low intensity on continuously) does not provide any benefit since the MALSR (ALS) is shown (by NOTAM) as being out of service.

This is the way I understand the issue.


What do those writings mean that are on the landing gear doors?

For a US Navy jet, it is usually the plane captain (who is responsible for checking the plane and making sure it's flight ready) on the landing gear door.

In the image above, the plane captain's rank abbreviation (AE2) and name are on the first line and hometown is underneath.


In what way are the airfoils used for a propeller different from the ones used in turbofan engine?

The angle of attack range of a propeller airfoil is larger than that of a turbofan. Therefore, the turbofan can get away with a thinner airfoil and much more camber. Also, the aspect ratio (ratio between length and chord) of a propeller blade is much higher, so the airfoil needs to be thicker to allow the blade root to carry the radial loads and to produce less torsion so the propeller blade does not twist too much under load. Were the turbofan blade as thick, the higher solidity of a typical turbofan would mean that the fan blades would block most of the flow path.


What are these suffixes used after the call sign?

Heavy - all aircraft with maximum take-off weight greater than 300,000lbs (whether or not they're operating at that weight) It's to highlight to the controller that wake turbulence could be a problem for a following aircraft.

Super - Airbus A380: As for 'Heavy', but more so.

Flight of X - All the rest relate to groups or formations containing that number of aircraft.

These originate in the FAA regulations and are summarised on Wikipedia

There are a number of other unusual suffixes including 'Concorde' (used only by British Airways for the now retired Concorde), Lifeguard (for medical flights), and others


Are there any speed and altitude limitations on the autopilot?

It depends on the autopilot and you need to read the AFM to know what the limitations are.

All of the business jets that I have flown prohibit the use of the autopilot below a specific altitude (between 50 and 1,000 feet depending on the autopilot and the configuration of the airplane). Nothing prevents then from being used lower but it isn't allowed.  They will engage on the ground (in fact it is part of the required preflight tests) but have a specific prohibition against use for takeoff and landing.

Other airplanes and autopilots however are approved for autoland all of the way down to a full stop, and some for takeoff as well.

Speeds also depend on the autopilot.  Some automatically disconnect if the aircraft receives a stall warning or overspeed signal but others don't.


What is a TAPS combustor and how does it differ from any other annular combustor?

See this question.  It is a single annular combustor (one ring of full nozzles).  I think that "twin" refers to the fact that within a single fuel nozzle, there are two different fuel streams: the main stream and the pilot stream.  This video might also help explain it a bit.


Everything in Dave's answer is entirely correct.  To add to it, AIM 4-3-20 says:

  The following procedures must be followed after landing and reaching taxi speed. Exit the runway without delay at the first available taxiway or on a taxiway as instructed by ATC.

(emphasis mine)

Controllers are not supposed to give pilots a turn off the runway until they've already reached taxi speed, but at busy airports, I've seen that rule stretched. You don't have to comply with any ATC instruction that you deem unsafe, but if you do and you slide off into the grass, it's your fault.


Is it possible to log IFR currency in a flight simulator without an instructor?

UPDATE: 83 FR 30232, updated the requirements of 61.51(g) where an instructor is NO LONGER required to be present in order to log time in a flight simulator or aviation training device for instrument currency. Note that an instructor is still required in order to log simulator time that counts towards a rating or certificate and that a FAA approved device must be used. This particular change was effective July 27, 2018.

The following is no longer accurate, but retained for historical purposes:

There has been quite a bit of confusion in this area due to language in a preamble to the 2009 Final rule on Pilot, Flight Instructor, and Pilot School Certification, which implied that an instructor was not required for instrument currency and 14 CFR 61.51(g)(4) which says that an instructor must be present. I believe this all started with an email to John King of King Schools, where Lance Nuckolls at AFS-810 stated:

  ...approved uses for a BATD and an
  AATD are governed by § 61.4(c) and the LOA. The LOA states that an
  authorized instructor must certify the instructional use. Simply
  satisfying the requirements of § 61.57(c)(2) is not considered
  instructional use, therefore an authorized instructor does not need to
  be present.

(Emphasis added)

Interestingly enough, the PDF of this email is no longer available on the King Schools website. Instead users are redirected to the Rebird TD page where it now implies that an instructor is required to maintain instrument currency.  A copy of the message text is available here.

Of course, this was too much of a good thing, so someone had to get the lawyers involved! In Keller (2010), the FAA's Office of the Chief Counsel made their opinion known:

  ...in order to log the time an instructor must be present to observe
  an individual using a flight training device or flight simulator to
  maintain instrument recency experience.

This position was reasserted in Stewart (2014), which references the Keller letter and explicitly cites 14 CFR 61.51(g)(4).

So we now have a situation where the FAA doesn't agree with itself! Whose opinion wins?  The lawyers', of course! In Perry (2010), the Chief Counsel's office states:

  ...where two interpretations address an identical scenario and reach
  an inconsistent result, the interpretation issued by the Assistant
  Chief counsel for Regulations takes precedence.

Some additional background:

I believe the author is referring to the Redbird Flight Simulations' FAA approval page where it states:

  When using the Redbird to maintain instrument currency an instructor
  is not required to be present. This has been discussed with and
  confirmed by AFS-810. A current Instrument pilot is not required to
  have an instructor on board the real aircraft to log approaches in
  IMC, therefore it follows that the FAA trusts a pilot to correctly log
  an approach preformed in the Redbird.

On its face, this statement appears to be in direct conflict with FAA's legal interpretation. Of course, one could try challenging this position (an interpretation is an opinion, after all), but it won't be me!


Has there ever been a successful 'bail-out' during an airliner test flight?

In this experiment to observe a deliberate airliner crash

http://en.wikipedia.org/wiki/2012_Boeing_727_crash_experiment

the crew exited in flight down the tail stairs...


Can someone/something other than the pilot trigger the ejection seat?

In a word, yes.

There is a switch which controls this and the default position is "both".  If any handle is pulled (pull down over the face or the one between your legs), then both seats fire.  If solo, the switch is turned to "solo" so that the rear seat is not ejected and the front seat gets to leave a little bit quicker.  If the switch is left on solo, and both seats are occupied, then each crew member can eject on their own.

You would also have if set to "solo" with an untrained passenger in the back.  You wouldn't want someone getting a bit excited and firing them both out of a perfectly working jet.

See this question about what happens, and this one to understand why you won't hit the canopy.

As far as I know, there is no computer controlled ejection system.  I don't think anyone would trust it to know better than the crew when it's time to bail out.


What is the longest period of time an aircraft type has been grounded due to safety concerns?

The Yak-42 was grounded from June 1982 to October 1984 (26 months) for a cause similar to Alaska Airlines Flight 261.


VORTAC symbol over KMOT airport - is the small dot the center?

The dot in the center of the star means that there is a rotating beacon available on the airport from sunset to sunrise.

See the FAA Aeronautical Chart Users Guide Page 8.

The actual center of the VORTAC is the small dot between the runways:

Which you can find the description of in the chart users guide on page 8 as well:


Could a pilot navigate using distances and radials from an RNAV waypoint, similar to VOR navigation?

In a modern B737 (NG/MAX) (and probably most other comparable aircraft), this is trivial. The simplest (and most realistic option for an emergency turn procedure) would be to fly the procedure in HDG SEL:

Enter FOBAR on FIX page
Add a 2 nm range ring for FOBAR on the FIX page. This ring will be displayed on the ND (Navigation Display)
Add the 90 radial for FOBAR on the FIX page. This radial will be displayed on the ND.
Fly the procedure in HDG SEL, monitoring the ND.


What is the purpose of the black and white stickers on test aircraft?

They look very much like position markers to identify known points on the aircraft, for analysing video footage.  You see similar markers on crash-test dummies used in vehicle impact trials, for instance, and also in motion-capture in the synthetic movie industry (and in orthopaedics).


What would be the challenges to taking off and landing a typical passenger jet at FL300?

These are the main challenges I can think of:

High takeoff and landing speed: To generate enough lift for takeoff in the thinner air at FL300 (gravity has almost not decreased, so required lift stays almost the same), very high speeds are required. Combine this with less thrust from the engines available and you need very long runways. It should still be possible to accelerate and takeoff eventually since FL300 is still below the maximum altitude most jet airliners can climb to (coffin corner).
Tires: The tires used on aircraft have a maximum speed which would be exceeded when taking off or landing. Other tires could be developed, but it is a major challenge to make these work in the cold temperatures (rubber does not like freezing temperatures, that is why Mars rovers do not use rubber tires).
Cold Temperature: It is cold at FL300, around 220K on average or around -50°C. This is not only problematic for the tires, but also for fuel, which would be constantly close to its freezing point. A heat exchanger between e.g. engine oil and fuel would be mandatory to operate an aircraft from here.
Wind: Wind speeds can easily reach 150kt at FL300. The runway would have to be perfectly aligned with the wind to have a pure headwind component. Otherwise, the crosswind would quickly exceed the limits for the aircraft.
Engine Failure: FL300 is above the maximum altitude for OEI (One Engine Inoperative) flight, which implies one cannot return to this airport after an engine failure. An aircraft would be forced to drift down to a normal airport for landing.


What is the go-around pattern and procedure for Heathrow?

Needing to return shortly after taking off is not very common, and as such there is no specific established procedure or route to be followed. The pilot will inform air traffic control of their intentions, and ATC will route the flight back for an approach. Depending on the situation, the flight might require priority, in which case other approaching flights will get bumped back in the sequence.

Transponder codes are used to identify flights on ATC radar. Simply speaking, one specific flight will have one specific transponder code during the whole flight - it is not changed because the flights needs to do something unexpected. Transponders are not used to transmit intentions (although there are a few special codes that can be used in case normal means of communication are unavailable).

For a flight needing to return to Heathrow, the return path will be similar to that of any other aircraft approaching the airport.


Are there any safety or technical reason airlines do not display flight information to passengers in real-time?

If data is continually updated, nervous flyers will fixate on every minor change.

The altitude changed by 30 ft in one second?That is a descent rate of 1,800 FPM!  Surely we're going to crash!
The speed changed from 480kts to 470kts in one second?At this rate, we will stall in less than a minute!
The plane was at 260kts at 9,800ft?
This crazy pilot is breaking FAA regulations and must be reported!

By updating less frequently, there is a natural filtering and smoothing of the data to obscure tiny measurement changes due to instrument limitations or conditions like turbulence.


Why did my business class seat have a three point shoulder harness?

(Source) Your Asiana A350 ride.

On the same plane the economy seats don't have that shoulder strap. It's not new either. There are various reasons:

Most business class seats are not forward facing. For your ride it's a slight angle but it's there.
It allows* reclining the seat during taxi, takeoff, and landing.

  [Qantas will] offer the world’s first seats that let passengers recline in their seat from take-off through to landing. Key to the break-through product’s safety is an over-the-shoulder belt.

It protects the head from hitting the seat walls.
It protects the head since there is no cushion (the knee-breaking seat in front of you in economy).

  (...) the three point seat restraint is used in the larger premium class seat, because there is no seat back close enough to the traveler to cushion his/her head in a sudden stop.

It will keep you in place during turbulence when the seat is reclined.

On the return flight aboard Korean, based on flightaware it was probably a 777-300ER or a 747-8. The missing shoulder strap could be because the seats are forward facing on both types, and/or Korean wasn't interested in the option to recline during takeoff/landing.

* Allows, but not necessarily allowed by the airline, i.e., some airlines may still insist on the upright position for the takeoff/landing.

I also found this supporting text:

  9.20.3 Three-point Seatbelts
  Three-point diagonal fixing seatbelts are occasionally installed in premium seats, including those positioned at an angle away from the forward/aft axis of the aircraft. The intent of the three-point harness is to protect the occupant from contact with the forward side of the seat shell.

— IATA Cabin Operations Safety Best Practices Guide (skybrary.aero).


What's the purpose of depiction of visual flight track on some Jeppesen approach charts?

From the Jeppesen chart legend PDF:

Visual flight track is shown when the missed approach point is prior to the runway threshold.

So this depiction is when the MAP is before (and not at) the threshold.

FAA style:
(airnav)
It's quite hard finding an early MAP, but here it is above as depicted by the FAA. It means to expect a visual segment as shown above when/if continuation below the visual descent point is not approved.
I also found this very nice read: Where To Start The Missed Approach


Would an F-15 or similar stand in be able to continue flight at high speed if it lost its canopy?

Several F15's have had incidents of canopy loss, and all the ones I have found came back and landed safely. The latest incident I can find was in 2014 off Okinawa. I see no reason why there would be any such catastrophic failure of anything on the aircraft unless the canopy impacted some part of the aircraft as it departed. Ejection systems are designed to allow the crew to exit the aircraft at pretty much the entire flight envelope. Yes, at supersonic speeds the crewmember will probably be sore for quite some time, but it's been tested and used in real life and it works.


What is the relation between number of crew members (pilots and attendants) and fleet size in airlines?

My answer may not directly answer your question but from MIT's The Airline Data Project, I extract data for year 2014 and put in table as follow:

Employees Per Aircraft                                  Southwest    United    American Airlines   Delta Airlines    Jetblue Airways
----------------------------------------------------------------------------------------------------------------------------------------
Pilots & Co-Pilots (Crews)                              6.0          8.3       6.8                 7.4               6.5
Flight Attendants (Crews)                               5.9          8.8       7.3                 6.8               5.0
Maintenance (Inhouse)                                   3.5          10.5      17.4                11.4              3.8
Passenger, Cargo and Aircraft Handling (Inhouse)        29.2         63.9      30.7                36.7              27.1
Other (Inhouse)                                         6.9          6.9       10.8                18.1              10.0
----------------------------------------------------------------------------------------------------------------------------------------
Total                                                   70.9         132.2     98.1                107.5             68.2

note that total number of crew does not add up with each type of crew in the table

Hope it gives you some idea about the ratio of pilot and flight attendant


What responsibility does a pilot have for people on the ground when making an emergency landing?

Factors in pilot choices are often subject to political spins, as few people are able to objectively evaluate the information available to the pilot, the bandwidth to manage the events, and the conditions which may have added complexity as well as the experience level of the pilot. A student pilot logically is held to a different competency expectation than a commercial/ATP with 15,000 hours in type, intimately familiar with the conditions, etc.

In common law, the pilot is supposed to protect in order, innocent third parties, the passengers, the crew, and property of others.

Where there were people impacted (no pun intended) who were not seen or known to the pilot/crew, that becomes a mitigating factor.

The bulk of civil liabilities on flight crews is established in case law, as there are few statutes which address that, at least in the US and Canada.

Addendum #1 Protection of innocent third parties, is first order as they have not elected to become part of an aviation event.  Passengers need protection because it is the duty of the crew to protect passengers, even if non-paying. Of course passengers assumed some risk by electing to fly. Crew need protection because they are humans.  Property is last.

Addendum #2, incorporation of comments, per requests. Comments are largely unedited, simply included to preserve the record. The comments were in response to a challenge for authorities on the common law obligations of pilots.

HLS Torts 2, Aviation under the Common Law, Francis H. Bohlen , and for contributory relation: Recreational boating accidents: Which law applies? Kevin Donius, for duties: TRITCH, ALLAN M. University of St. Thomas Law Journal: Fides et lustitia 2014/04/01, Vol: 11, p331, for practicality, and legislative mix: Fifty Years of Torts Harvard Law Review, Vol. 50, No. 5, Kohr, 504 F.2d 400 (creating federal common law of contribution in aviation accident). Kohr figures prominently in Professor Field's theory of federal common law, see Field, supra note 14, at 913-15, but almost certainly does not survive the refusal to create a federal common law right of contribution in antitrust cases. Tex. Indus., Inc. v. Radcliff Materials, Inc., 451 U.S. 630 (1981)

But see Musick, Peeler & Garrett v. Employers Ins. of Wausau, 508 U.S. 286, 292 (1993) (creating "ancillary" common law right of contribution in implied Rule 10b-5 right of action). Indeed, within seven years of Kohr, even the Seventh Circuit did not think to use federal common law to deal with the complex conundrums of choice of law analysis in an aviation accident. In re Air Crash Disaster Near Chicago, Ill. on May 25, 1979, 644 F.2d 594 (7th Cir. 1981).

The Bohlen one, while dated (~1937) hits many of the foundations. But the boating one points out that by being a passenger you accept a greater risk than an independent third party. In the Torts class, I did a couple of papers on aviation torts. The rest of the cites become rather obtuse, because the focus in most litigation is not on common law, but on statutes. Yet, in NY, the bar exam covers common law. Go figure.

I cannot comment of EASA regulations, but generally the FAA regulations do not cover tort liabilities. Tort law and common law, where applicable, would appropriate references. This may be more relevant for SE Law. FAA regulations cover operational matters, certification, registration and administrative aspects of aviation.

Also the liabilities can be quite complex, for example in the Chicago crash, state Public Utilities Act was invoked, which added one of many local complexities to the litigation. That kind is stuff is, I believe, beyond the scope of SE Aviation.

This congressional intent not to exclude state statutory and common law from the field of aircraft safety is further illustrated by the existence within the Federal Aviation Act of a savings clause. 49 U.S.C. app. 1506 (1988)


What is the meaning of Minimum Flight Weight?

This is the weight in an operational condition(with engine oil, hydraulic fluid, unusable fuel in the tanks[maybe also with a specific usable amount like 30 minutes], and some other misc items), zero cargo, with minimum crew.

The minimum weight at which the airplane can fly. You may also have maximum zero fuel weight, maximum landing weight, maximum takeoff weight, and maximum taxi weight.


What is the average climb gradient of an aircraft during the takeoff and early phase of a departure procedure?

The upper limit is a function of the airplane's performance at rated climb power at the normal speed used, modified somewhat by the wind (the gradient is based on ground speed).  What actually happens on a departure is simply whatever numbers that airplane's performance produces using the standard speed and power setting for that airplane.

In a jet you are generally going somewhere around 200 kt once the flaps are up, then accelerate to 230-250 kt once past 3000 ft up to 10000 ft.

From the table below, assuming no wind, an airliner climbing at 3000 FPM at 200 kt will have a gradient of roughly 1000 ft/nm between the initial acceleration altitude (say 1000 ft) and 3000 ft:


What prevents aircraft with a tailcone APU from using tail-mounted airbrakes?

The airlines prevent them or: the airlines won't buy them if they were offered

The photos you have already show an APU in the tail section (exhaust on the starboard side).

Adding air brakes requires increased structural integrity (weight; money) and additional system connections (weight; money).

When they are of no use, they're simply not added. Why are they of no use?

Well, pure air brakes (as opposed to speed-brakes/spoilers) have 1–2 functions (for jetliners):

Compensating for the lack of thrust reversers
Performing steep approaches when the thrust-to-weight ratio is high (small plane that has too much power). As I noted here: The thrust-to-weight ratio for the RJ100 is 0.28:1, compared to 0.16:1 for the comparable Boeing 717. It's even higher for the smaller RJ's.

Neither affect most jetliners (note that the babybus (A318) can be certified for steep approaches, and it doesn't need such an air brake).

The airlines would rather carry payload (paying load) and not bother paying for maintenance to regularly check and fix a novel item – not all airports are London City: high thrust-to-weight ratio is good for taking off from short runways and performing steep climbs from in-city airports for noise reduction.


Do I need to descend towards the Minimum Descent Altitude if I have the airport in sight?

No, you do not need to descend all of the way to the MDA if you have the required visibility to continue. In fact, I would recommend against it since it puts you awfully close to the ground while you are maneuvering to align with the runway.  Why do that if you don't have to?

MDA stands for Minimum Descent Altitude, and is just that.  The minimum.

As far as going missed, you would fly the missed approach in the same way because while you may have obstacle clearance where you are now, the missed approach procedure assumes that you fly it the correct way, and in this case you just have some extra padding since you started out higher.


Is airflow deflected inwards or outwards by wing sweep?

As a partial answer following up on those to date, here is an image from Where is the spanwise flow? How does the span wise flow point the air towards the wingtip?, showing a snaking in-then-out flow over the wing. Note the inward flow over the leading edge and wing section, which is just the point where wing fences are located.

On sharply-swept deltas which sit inside the bow shock cone at supersonic speeds, 1980s studies of supercritical attached flows show the air flowing upwards round the leading edge and forming a crossflow to meet an inboard "crossflow shock". See for example W.H. Mason, “A Wing Concept for Supersonic Maneuvering,” NASA CR 3763, December 1983. But it is less clear to me whether this inbound crossflow is physical, or a theoretical notion along the wing profile which, due to the sharply tapering chord with span, physically might still flow outwards:

This contrasts with the low-speed vortex flow over such wings (e.g. Concorde) at high angles of attack, where the vortex inflow is detached and the boundary layer flows outwards.

So it seems the full the answer must be complicated, with the pressure distribution along the chord, and hence the in-out flow changes, depending on the angle of sweep, the speed of flight, the angle of attack and how far above the wing you are considering.


How can flight attendants respond to an immediate medical emergency?

If the pilot knows before committing to take-off and reaching the point of no return then he will abort the takeoff and ask the tower to send an ambulance and stairs.

If he is committed to take off then he will get into the air and then tell the tower of the emergency; circle around (possibly dump fuel depending on the severity) and land again to get the passenger off board on the ambulance waiting near the runway.

Whether the plane can then top up the tanks and take off again will depend on whether the landing was overweight or not. If it was then the plane needs to be inspected before it can be put back into use and the other passengers will need to leave the plane and wait until the next plane can ferry them on.

The cabin crew will apply first aid until the ambulance crew can take the sick passenger.


Did the XF-84H Thunderscreech really cause "900 sonic booms per minute"?

I think it is a matter of where you stand (literally).

From the front or the rear the shock waves from the propeller tips would hit your ears continuously, and the result would be constant noise.

When standing laterally, the propeller tips would move towards and away from you and produce a variation of noise intensity of the frequency produced by the product of propeller RPM and blade count.

It seems that the design RPM of the XF-84H propeller was 3000, and since the propeller had three blades, the frequency should have been 9000 per minute, not 900. The airframe could be split ahead of the cockpit to allow the installation of several nose sections with their own gearbox and propeller. Several gearboxes and propellers were prepared with propeller design speeds between 2100 RPM and 3000 RPM, but the test program was ended prematurely, so most of the planned variations were never flown.

I can only judge from the little information available online and count myself lucky not to have witnessed a power-up of the XF-84H (for me personally, the loudest aircraft is still a Sukhoi 22M-4 – you think "man, this afterburner is loud!" and only then the pilot switches the afterburner on), and it seems that the 900 per minute figure must have lost a zero on its way of becoming an internet meme.

Note that I only speak of a variation of noise – as Jon Story writes, a sonic boom is what arrives at your ear, not what is produced by the propeller.


How is a plane with only ailerons and jet (no props) controlled?

The ailerons in most flying wings can also move together up and down, then working as an elevator. This is called an "elevon", combining both words as the device is combining both functions. Since flying wings mostly use reflex airfoils, loads on the rear part of the wing tend to be small and the force to keep elevons at their right deflection is small, too. In case of the SB-13, they are pre-loaded by a small, adjustable spring but otherwise free-floating.
In this case, however, it could be that they only work as ailerons.
When used for pitch control, elevons must move up and down together on both sides. This means they will be freely floating and must be held in position by some force. It would be easier to cross-link them so they only can move against each other, and then they only work as ailerons.
The airplane, called OpenSky M-02, is the brainchild of Tokyo University of the Art professor Kazuhiko Hachiya and has been built by Aircraft Olympos of Japan. OpenSky M-01 was a lighter, unpowered version.
As Louise Hose writes on Kitplanes:

Hachiya designed the project and is the only pilot to fly the resulting “Open Sky M-02J”. He started with a hand-launched, scale model to test the airfoil characteristics. Once he was satisfied with the basic design, he partnered with aeronautical engineer Tota Ueno of Olympos Company in Tokyo to scale up to a glider capable of carrying one person…Hachiya himself. The glider, first flown in 2006, was launched from the ground by teams of people pulling a bungee cord. Once satisfied with its flight characteristic, Hachiya and Ueno worked to find the “right” engine to add as the powerplant. Between 2010 and 2013, they were doing high-speed taxi tests and working through issues…particularly powerplant and regulatory issues. They ultimately decided to use the NIKE jet engine made by AMT Netherlands which produces 176 pounds force. The jet was designed and mostly used in target drones.

At least the model couldn't be steered by weight shifting, and looking at the harness of the pilot, his capacity for weight shifting is rather limited. My impression is that weight shifting is primarily used for ground control. If you watch the YouTube movie, it becomes apparent that he is barely capable of controlling the direction on the ground, and has to lean to the left on take-off to prevent it to escape the runway. Also, his movements are more sideways than back-and-forth. The control surfaces hardly move, but show linkages on the bottom side, so they are moveable. If you look closely, you can see pulleys on the left and right of the pillow Hachiya-san is lying on, and as @quietflyer says, they should control the elevons, but he adds his weight to help controlling both pitch and roll.
Louise Hose of Kitplanes again:

To date, Hachiya has made about 150 “jump” flights and 70 circling flights. He has flown it up to nearly 500’ agl but believes it can fly much higher. (Airspace restrictions in Japan have prevented him from trying to fly higher.)


What does AOE on the sectional chart mean?

It stands for "Airport Of Entry" (see VFR Terms) In other words there are customs facilities there.

  All civil, private aircraft entering the U.S. must first land at an
  airport of entry before continuing to their destinations, unless other
  arrangements are made with U.S. CBP. Advance notification must be
  provided electronically to CBP by means of the eAPIS. See the APIS
  section for more information.
  (source)

To my knowledge this is also common for international operations outside of the US/FAA jurisdiction although im not sure how its marked on various maps elsewhere.


How would gyroscopic effects affect push-pull configuration vs conventional twin engine in the event of engine failure?

Gyro precession effects from a propeller are minimal when at flying speed and making modest pitch and yaw motions, where the precession is mild and there is lots of aerodynamic damping.  You don't really notice it. Propeller slipstream over the rudder has a much bigger effect, which a lot of people may confuse with precession.

You have to make large sudden pitch or yaw motions at low speed, like when taking off a taildragger with a very large propeller. If you raise the tail suddenly at low speed, precession of the propeller will make the airplane swing noticeably.  Or, with aerobatic airplanes that make extreme pitch and yaw motions and where precession will have an effect that has to be taken into account (as well as putting massive stresses on the crank at the prop flange).

For wing mounted engine twins, the effects of offset thrust are the main limitation, with a minimum control speed that is usually well above the stall and below which the airplane will roll over.  Centerline thrust aircraft avoid this problem for obvious reasons.  In any case, I don't believe gyro precession is a factor at all in a Cessna 337, on either engine, or on a regular twin for that matter because the pitch and yaw rates you generate aren't enough to create significant precession effects that could affect controlability.

In the end though, with piston twins, gyro precession is the least of your problems.  The biggest one is the fact that the loss of 50% of thrust leaves you with almost no performance reserve.  Wing mounted engines leave you with a somewhat more dangerous situation due to the ability to lose complete control well above the stall by dropping below minimum control speed, but even with center line thrust, the single engine performance is so marginal that if you are at gross weight and above sea level and it's hot, you are going down anyway. Yes there is no Vmc limit, but you are still faced with having to maintain minimum speed for performance and chances are you are still going to crash land eventually and you may ending up stalling and spinning it the regular way if you panic trying to will the plane to fly, just like a regular twin.

For this reason I don't believe center line thrust aircraft have all that much better a safety record following engine failures than regular twins.


Does preheating fuel before it reaches the turbine result in a performance improvement?

The key here is understanding the purpose of pre-heating. Combustion occurs very rapidly to produce the power stroke in piston engines and thrust in jets.
It's time in the combustion chamber to do so is measured in fractions of a second.

Ideally, a mixture of 2 gasses, methane and air for example, would ensure efficient and complete combustion.  This is your common kitchen stove.

Mixing liquids with air is more problematic, as now you have a mist of small droplets instead of ready to mix gas.  This is good and bad.  The good is the evaporation of the fuel helps keep the engine cooler. This is a benefit of "full rich" setting.  The bad is the fuel is not mixed as well with the air when it burns, lowering efficiency and releasing harmful byproducts such as carbon monoxide.

Proper design (operating temperature) and choice of fuel may eliminate the need for pre-heating, especially once the engine is "warmed up".

Aside from the dangers of heating fuel, gains may be made by standardizing the temperature of fuel inflow for pollution control. Another possibility is to use the heat from turbo compressed air to warm it.  Tight control of octane rating is also beneficial.

But aircraft operators adjust their richness based on RPM and usually on the rich side to avoid overheating the engine, which is far more disastrous than slightly lower fuel milage.

In design, using engine heat to evaporate the fuel may eliminate the need for pre-heating, except for extreme arctic applications.


Is an EASA STC valid if it mentions issue 1 of a Master Drawing List that was later revised?

This sounds like a case where I would contact the STC holder and ask them what's up.
In the USA I'm used to seeing STCs with the magic words or later approved revisions (which means that the manufacturer can revise the document and get it re-approved without needing a new STC), but if a specific revision is called out and those magic words aren't present then later revisions are no longer "approved data" (or whatever the EASA equivalent term is) and technically can't be used.

In all likelihood the two revisions are materially identical and this is just a "paperwork problem", but you're better off being sure (and either getting a STC with the "later approved revisions" wording or getting the original issue of the drawing list so you have it in hand and comply with the STC you have) rather than having your local regulatory authority decide your installation is illegal because you didn't use approved data.

  If there is a changelog on the document in question your mechanic could theoretically make the determination themselves - Added drawing #123 has no material effect if your installation doesn't reference that drawing. At that point it depends on how picky the folks approving your installation are though - again, they could say since it's a later revision it's not the approved revision.


Can you escape an aircraft through the lavatory?

Depends if there is any pressurized space behind the lav, and if there are any hatches in the pressure hull within that space.  On most airliners I would say it's not plausible, but looking at a VC10 cutaway it looks like the pressure hull extends all the way back to the tail cone, to a small bulkhead under the rudder, and there is a hatch forward of that.  IF the mechanism can be worked from the inside, the hatch could be opened when taxiing because the hull is vented to atmosphere at that point.  It's possible that a panel in the aft most lav would expose a service hatch in the non-pressurized bulkhead where the engine support beam goes across, which would lead to the tail cone hatch.

Lot of ifs there, but from what I can see I wouldn't rule it out.

https://www.flickr.com/photos/27417638@N07/7408063162


What is the best design to stack wings of a triplane?

Wing stagger was mostly chosen to improve pilot vision: In single-seaters, a positive stagger would allow to place the upper wing ahead of the pilot, improving the field of view.

Large bi- and triplanes had no stagger. Here the pilot sits ahead of the wing and large aircraft fly mostly straight, reducing the need for the pilot to observe the airspace around him.

However, if you look for a proven design of a very compact triplane, I would like to suggest the Italian Pensuti triplane. It had a wingspan of only 4 meters and a total weight of just 230 kg. Emilio Pensuti, a test pilot with Caproni during WW I, designed it as an easy to fly aircraft for the common man. Therefore, it is sometimes also called the Caproni-Pensuti triplane. The first version was powered by a 35 HP Anzani engine while a later development, the Breda-Pensuti 2, used a 80 HP engine.

Of course, its wings had no stagger.

Drawing of the Pensuti triplane (picture source). Yes, it did fly!

Pensuti triplane in flight (picture source)

If you build one, I would strongly suggest to change the wing airfoil to a thicker one with the same amount of camber.


You can think of the propeller as a screw. Take a screw, a screwdriver, and starts screwing. The threads of the screw drive the screw into the block of wood.

The propeller works in a same way: the engine drives the propeller that "screws" through the air.

It also works the other way around. Well kind of, with the screw, because of the high friction btw the block of wood and the threads of the screw, but forget about the friction for a while, if you can.

If you stop twisting the handle of the screwdriver, and instead push the block of wood against the screw + screwdriver combo, what should happen? The screw should rotate just as if you were screwing it with the screwdriver, as the threads are still sinking deeper into the block of wood.  The screwdriver would of course rotate with it.

Again, it's the same with propellers (and engines). If you have speed, and you shut down the engine, the airflow will push against the propeller just as the (magically frictionless) wood against the screw. The propeller will keep rotating in the same direction, and as it does so, it keeps the engine turning also.

Now, in the case of you no longer twisting the screwdriver handle or the engine driving the propeller, there is no longer a force driving the screw or the propeller through the medium they are engulfed in. Instead, the medium (wood or air) is imposing a force on the screw & the screwdriver, or the propeller & engine to keep them turning.

If you do a google image search with words "propeller tip contrail" you'll find pictures displaying nicely how the propellers are actually screwing their path through the air.


Why is Python used on aircraft although it may not be certifiable?

Just because aviation developers use Python, does not mean that Python actually goes flying.

Lots of aviation development is about testing, stressing, validating, analyzing, and documenting the code that does go flying.

Python is an excellent language for all that validation work, even though it stays on the ground.


Cockpit smoke will come from either of two sources:

The air conditioning pack supplying it, such as the air cycle machine gone bad (more or less a turbo charger like device) with bearings and seals failed.  This usually results in smells more than smoke.  Another one is smoke from the engine compressor - unusual because are aren't really major sources upstream of the bleed ports unless something is introduced from outside.  Cooked deicing fluid is the biggest source.  Fluid gets in the compressor, and the temperature at the bleed discharge ports can be 500-800F at takeoff thrust.  If the bleeds are started right after deicing without a clean-out engine run first to purge the compressor, you'll get stinky haze in the cabin/cockpit from cooked fluid.  This has caused many a turn-back.  Another one would be smoke from an APU that blows up while supplying bleed.
You can also get smoke from burning out fan motors in supply ducting, but cockpit smoke so intense that it causes a control crisis is almost always from burning wiring in the cockpit itself, such as behind control panels or interior panels (see Swissair flight 111).

So the main thing is, smoke coming from the air conditioning system can be reduced by turning the system off, but that isn't the problem.   It's smoke originating from within the cockpit itself, mostly from wiring.  Considering how rare those events are, it's not really practical to create a hermetic seal between the space behind interior panels and the interior space and still have a maintainable and reasonably light airplane.


Why are there no cargo aircraft with "flying wing" design?

Flying wings can be made to have acceptable flying qualities without any artificial assistance.  Just look at the Jim Marske glider designs.

The principal downfall of flying wings is that stability in pitch is pretty much achieved the same way as with a conventional tail, with a down force balancing out the center of gravity forward of the fulcrum of neutral point of the lifting forces, but it's all being done over the very short moment arm of the wing chord itself.  In other words the "tail" has been moved forward to the trailing edge of the main wing.

There are a lot of issues that result from this, pitch sensitivity and damping issues and all that, but the biggest one from a cargo aircraft's perspective is a very narrow center of gravity range.  Not a big deal on a bomber with a concentrated bomb bay load, or a glider that doesn't have to cope with loading variations, but a bigger deal on a freighter.  You are forced to spread the load, and the fuselage volume, laterally, creating way more frontal area than necessary (you're in effect turning the fuselage sideways), so you end up cancelling out the drag benefit of doing away with the tail in the first place, and still end up with a "temperamental" configuration.


What does this black triangle placard on board an A320 denote?

If there is a problem on-board and the crew is unsure about the condition of the aircraft, the triangle indicates what window should be used to inspect flaps, slats or engines or look out for icing.

This saves important time in case of an emergency, as the crew doesn't has to search the right window to look out.

For example if there is a failure of the flaps condition display, it has to be verified visually that the flaps are extended properly. From the window with the triangle, this can be seen:

Source, added square

Now the crew can compare the position of the flaps switch in the cockpit, with the actual extension of the flaps.

There are usually four of these triangles in the cabin. One to inspect the forward of the wing for icing, the slats and the engine on each side and one at the back of the wing for the flaps.

I have searched for cabin pictures and found this 360° cabin view by SAS.

The following picture shows the triangle on an Airbus A330 at the front of the wing. You can see a part of the engine through the window.

Source, added squares

And this picture shows the rear triangle.

Source, added squares


What is the difference between OAT, RAT, TAT, and SAT?

As you measure temperature moving at high velocities, your outside thermometer will measure a higher temp than what is actually outside (what a non-moving thermometer would get). That's because as the air rams into your thermometer it gets a little bit compressed, and that makes it heat up a little bit.

Amazingly, some smart people have even calculated how much that "ram rise" is, and you can actually compensate (well, in theory) from the indicated temperature to calculate what the actual outside air temp is:

$$Ram~Rise=SAT\times0.2\times{M}^2$$

Where $SAT$ is Static Air Temperature in Kelvin, $M$ is Mach number

Problem is, not all instruments will compress that air in the same way, and not all of them will pick up this Ram Rise entirely. So they will publish a $K$, a ram-rise-coefficient (also called recovery factor) meaning how much of from the theoretical Ram Rise they actually pick up.

(OAT/SAT) Static Air Temperature = noted as $T_S$, actual temperature of the air outside, the same your thermometer will pick up if you were not moving
(say, in a balloon?)

(RAT) Ram Air Temperature = noted as $T_M$, actual measured temperature by your instrument.

$$RAT=SAT+k\times{Ram~Rise}$$

(TAT) Total Air Temperature = noted as $T_T$, total temperature as measured by an instrument with $K$-coefficient of $1$.

$$TAT=SAT+Ram~Rise$$


First, I don't believe you need to be vectored to the FAF, just the final approach course, in order to forego a published procedure turn.

Also, you could be cleared "straight-in" when ATC gives you the clearance for the approach.  It may seem subtle, but it makes a difference. Here is the definition in the pilot-controller glossary:

  "STRAIGHT-IN APPROACH IFR. An instrument approach wherein final approach is begun without first having executed a procedure turn, not necessarily completed with a straight-in landing or made to straight-in landing minimums."

Also, don't take it literally.  If you approach at a 45 degree angle to the final approach course and are cleared "straight-in", you still approach at a 45 degree angle; there's just no procedure turn.

Using the below approach as an example here the difference would be, "Cleared 0M3 RNAV RWY 2" (Must do the PT) vs. "Cleared straight-in 0M3 RNAV RWY 2" (Shall not do the PT).

Another indicator I know of is notation on the MSA ring that declares a range of radials of approach as "No PT" such as this one.  Note that the MSA and radius on both halves is the same, so the only reason it is split is to declare no PT on the southwest approaching side.


The spinning blades in the compressor stage of a jet engine or turbo fan are themselves airfoils, like the aircraft's wings. The operation of the engine depends on the smooth flow of air over the blades.

Just like a wing, an individual blade, or a small component of one, can experience an airfoil "stall", where the air flow over the blade separates into a cell of "stuck", highly turbulent air behind the blade, and the air flows around the cell instead of smoothly around the blade.

When a flow separation occurs, the airfoil's ability to push the air in proper direction at the right flow rate—and thereby contribute to the compression of air behind the fan assembly—is inhibited.

Since these blades are rotating, the blade quickly moves away from the packet of stagnant air. Of course the stalled air packet has some momentum from the intake air, and it will experience a drift along with the rotating blade, but it is not moving with the average flow of the air through the engine anymore.

Thus the next blade spinning round tends to encounter the stalled air packet. If the stalled air cell is not particularly large, it may be absorbed by the air flow at this stage and dissipated. Alternatively, it might be large enough to stall the subsequent blade as well. At this point, it is called a "rotational stall".

If the stall continues to propagate, the ability of the fan stage to deliver air to the subsequent compression stage is impeded, and it will lead to an abrupt drop in pressure inside the combustion chamber. This causes a reduction in available oxygen for combustion. The engine's performance, measured by the thrust delivered, is strongly impaired, and there is likely to be a lot of unburnt fuel remaining after the oxygen in the compressor is exhausted. That unburnt fuel may ignite in a bright exterior flame as it escapes out the back of the combustion chamber and mixes with the oxygen-rich bypass flow, or in the case of a jet engine, after it exits the engine altogether.

The drop in back pressure in the compressor will, under normal conditions, enable the compressor fan blades to begin operating as proper air foils again.

An alternative type of stall is a compressor surge. In this case, the problem is caused by unexpectedly high pressure in the combustion chamber (or in the compressor), which forces its way forward as well as backwards, against the incoming flow rate. Again, this disrupts the operation of the compressor blades as airfoils.

See Advanced Control of Turbofan Engines by Hanz Richte