How can I find out the reason for an aborted takeoff? I was listening to ATC at LAX today and heard them cancel AA 253's takeoff clearance and instruct them to abort their takeoff; it sounds like they were already rolling down the runway when it happened. The call to stop was pretty insistent.

In a lot of hours of listening, I don't remember hearing that happen before, I'm really curious why they did it. Is there any good way to find out?

In addition to listening to ATC audio recordings as suggested by previous answers or comments, you can also try to visualize the traffic situation at the time of the event using the playback feature of flight tracking websites like FlightRadar24.

On those radar images, you can possibly see other aircraft, whether there was the danger of an imminent runway incursion, maybe the go-around of another aircraft nearby or something similar which prompted ATC to cancel the takeoff clearance. If you combine those radar playbacks with the audio recordings that you already know, you might get a pretty accurate picture of what actually happened.


Are there any documented example usages of film (ie, film film, not video or digital) for in-flight entertainment? Regarding this excellent question: What was the inflight entertainment in the early seventies?

There's a mention that the "TRANSCOM 8mm film cassette" (that was film-film, ie the plastic stuff you can see-through, not video tape) was used on some planes.

I've found all the references to this on the WWW are poor references copying each other with no details (but I may be missing something).

Can anyone find literally an image of film-projector technology being used for in-flight entertainment?
Are there any specific references / image examples to the "TRANSCOM 8mm film cassette"
What year was about the last year film projection technology was used (if it was ever used?)

Or indeed -- memories of these things, even better! Cheers.

I know film projectors were definitely used on early 747s - converting part of the passenger area into a theater is part of the design. I was able to dig up the photo below showing the projector mechanism, which is pretty impressive to look at.

I'm not sure whose system that is, but it looks like a 35mm projector so it probably predates the TRANSCOM cassettes.

Can't help you with #2 or #3 though.


What airport is this? A friend of mine asked for some help identifying the airport in the picture below. He needs it for a geocache.

Google reverse image search was, perhaps unsurprisingly, not very helpful. We've spent some time on Google maps, but there are many airports :-). Other than that, I'm really out of ideas.

We have some reason to believe that it is located in Europe, presumably excluding Turkey and Russia.

Brute forcing Google maps finally paid off. It's Bordeaux airport:


Where are the grounded 737 Max planes being kept? With various countries grounding the 737 Max, where are they (their carriers) keeping the grounded planes?  Are they simply being kept at Gates of various airports (which I doubt since gates are expensive and/or logistical reasons)? Are there "holding areas" at some airports?

While I understand some carriers just fly a few of these, what about those carriers with larger fleets, such as ones in China or the EU?

They're at whatever airport they were at (or next landed at) when they were grounded. Airports are big enough places that there's room plenty of room to park planes that aren't currently in use, and it's completely normal to have such planes parked at an airport. Just look at a few in Google Maps satellite view.

At least in Europe (and presumably elsewhere), the directive banning flights does allow one ferry flight (of up to three legs) to get the plane to a location where any corrective action can be taken. But note that this does not allow moving the plane just to get it to a more convenient storage location.

Great Circle Mapper's featured map for 14th March showed the actual location of the 737 MAXes owned by US airlines, as of the previous evening.  Those aircraft are spread across around 30 airports in the US and Caribbean.

Thanks to Antzi for pointing out the ferry flight exception.


What provides the greatest thrust in a high-bypass turbofan engine? I'll try to make as much sense as I can with this question.

I've been flying quite often in 2015, and I have recently wondered this question regarding high-bypass turbofan engines. I know that there are two primary parts to the high-bypass turbofan: the fans themselves that pull air from the front of the aircraft through the engine, and the fraction of that air that gets compressed and undergoes combustion inside the combustion chamber.

Given those two main parts that I know about (or so I think I know about), which provides the greatest amount of thrust for the aircraft, the suction and escape of non-combusted air out of the back, or the hot combusted air that is ejected out of the back of the engine?

Thanks for reading, and I hope this question makes sense.

I analyzed a Pratt & Whitney F100 turbofan last semester in my aerothermodynamics course, so allow me to answer this question. The short answer: the un-compressed air provides the majority of an engine's total thrust since the compressed air powers the engine.

Correction: I forgot to mention that the fans also compress entering air. That is, all air entering an engine is compressed a bit by the fan. Some of this compressed air enters the turbojet core and the rest of the fan-compressed air bypasses the engine core. I ignored this for the sake of simplicity, but I should have explained this since you directly asked about air compression in a turbofan.

Long answer: see below!

1. The fan(s)

Air enters the engine through a fan (or fans in the case of the F100 engine). These are the giant fans with a spinning insignia in the middle that you see inside an engine.

Update: The spinning insignia clearly show if the fan is spinning so workers don't get injured.

The fan(s) increases the pressure of the air that enters an engine. Some of this compressed air is diverted around the rest of the engine and is directed straight out of the engine. The bypass ratio is a measure of how much air bypasses the "jet" core (bypass air/core air).

2. The compressors

The rest of this air is then compressed through a combination of more fans and a converging duct. The data from my thermo project tells me that this stage increases the pressure of the core air by more than 10,000%, but I'm not too sure about that*. Sufficed to say, this core air now has a lot of energy--let's add some more :D

Quick note: The compressed air now has insignificant velocity relative to the bypass air. Most of the compressed air's energy is "in" its pressure (senior SE members, please correct me if I'm wrong).

3. The combustion chamber (aka, combustor aka magic chamber)

Now the core air enters the combustion chamber. Here the air enters small chambers, mixes with jet fuel, and is ignited. The main parts-of-an-engine diagram I posted makes it seam like the combustion chamber is one big part of a jet-engine, but really the combustor consists of a bunch of smaller chambers surrounded the main shaft of the engine. Here is a gif that shows what I mean:

How the combustion chamber operates is beyond my scope of understanding, but consider that a combustor is essentially trying to keep a candle alight in the middle of a hurricane. Awesome engineering goes into designing better and more efficient (hotter-burning) chambers.

4. The turbine (aka more magic section)

Now that hot and even more energetic air enters a the turbine section which consists of a diverging (increasing in area) duct and more fans. Whereas the compress "inserted" energy into the air, the turbines draw out energy from the air. As the air enters the larger (in volume) turbine area, it expands and spins the turbine fans which power the compressors and the fan. This Back Work Ratio (BWR) is a measure of how much turbine power it takes to spin the compressors.

5. The nozzle

The still energetic core air is once again concentrated before being shot out of the back of the engine.This thrust, together with the thrust of the bypass air, propels the air forward following this model:

$F_{thrust} = \dot{m}_{bypass} \times \Delta v_{bypass} + \dot{m}_{core} \times \Delta v_{core}$

Where $\dot{m}_{bypass}$ is the mass flow-rate of air that is bypassed and $\Delta v_{bypass}$ is the change in velocity of that air as a result of the fan.

And $\dot{m}_{core}$ is the mass flow-rate of air that is combusted and $\Delta v_{core}$ is the change in velocity of the core air as a result of the fan, compressor, combustion chamber, and turbine.

The uncompressed air contributes about 60% of the total thrust. The "processed" air loses a significant portion of its energy to powering the engine. However, the compressed air still provides about 40% of the total thrust. Adding an afterburner can increase this contribution to 50%. How is this possible? Dead algae from a billion years ago.

The hydrocarbons in jet fuel pack a lot of energy into a small space and mass (two completely different concepts). Burning those hydrocarbons releases a lot of energy that powers the fan, compressors, and electric generators of an aircraft before pushing the airplane forward. This high energy in a small place/space is also why electric cars/anything weren't practical until LiPo batteries (story for another article).

I applaud you for noticing that the uncompressed air contributes to an engine's thrust. I think the term "bypass" confuses some people into thinking that this air is "thrown away". it's not. The bypassed air is actually sped up by a series of fans and imparts forward momentum to the aircraft.

I'm studying Aerospace engineering right now (Whoop!), so my excitement at being able to answer this question rather side-tracked me from your original question, but I hope you enjoy the extra info on how a turbofan operates.

Additional info

The hotter a combustion chamber burns, the hotter the core air gets and the more energy it can provide for engine operation. Furthermore, hotter chambers waste less jet fuel and result in relatively cleaner and safer fumes. Increasing CC max temps and designing the rest of the engine (i.e., the turbine blades) to handle the increase in temp is the cutting edge of engine research. This is one of the most challenging and lucrative materials science/engineering problems in the world since efficiency is paramount in today and tomorrow's aviation industry.

Here is a nice article describing how GE, Rolls-Royce, and other engine companies sell thrust, not engines. It's a big long, so you may  read it on your next flight :)


Propeller Curve Modification on Test Rig this is my first stack exchange question so please bear with me if I have missed a rule: I tried searching for this question to no avail.

I have an off-the-shelf propeller for the purpose of eventual high-altitude flying. I used the airfoil profiles to make an approximate propeller efficiency/c_thrust/c_torque/c_power vs advance ratio curves, as well as the power/thrust/torque/rpm vs airspeed.

My question is: if I had to spin up this prop on a test rig on the ground, there are two major changes I can see - atmospheric air density, and the fact that airspeed is zero. How can I predict how the propeller will behave when the airspeed is held zero (the rig will cancel out the thrust generated). Looking for things like max possible RPM, torque, etc. and how the behavior of the propeller changes.

Thanks a lot, happy to provide more details.

Fortunately, the speed in the propeller plane is not zero once the propeller runs. It will suck in and accelerate the air ahead of it as much as it pushes air out the back, accelerating it further. This was already formulated by Robert Edmund Froude and is called Froude hypothesis. Read this answer for more.

Using the equations from the linked answer you can already calculate your propeller's efficiency and the flow speed in the propeller plane once you run it on your test bench. Most likely your propeller is designed for more than the flow speed achievable with static conditions, so this will help you to calibrate your calculations only for low prop speeds. But since there is a flow speed already, all equations will work.

Your propeller has an advance ratio that tells you how fast it should be spun for a given flight speed. In order to extract more thrust, the propeller should be spun a bit faster, so a positive angle of attack at the blades results over the whole propeller span.

In static conditions, you will not achieve a good angle of attack over the whole span. The faster you spin the propeller, the more it will experience too high an angle of attack, a condition that will be worst at the root and only the tips will exhibit close to proper flow conditions. Since the inner part of the propeller is stalled, it will create lots of drag for little thrust. Therefore, the max. RPM and torque numbers are very hard to predict, and measurements at that point will be of no value for predicting the behavior of the prop once it runs at its design advance ratio. Air density should be less of a problem - it will drive up dynamic pressure and, consequently, the power which is needed to run the propeller at a given speed.


What is the feasibility of fitting all aircraft with black boxes? In the wake of the tragic helicopter crash on January 26,2020 which killed Kobe Bryant and eight other people, it would seem to make sense to follow transport category aircraft standards and fit all aircraft, except ultralights, LTA unpowered, or powered parachute, with a cockpit voice recorder and a flight data and GPS telemetry recorder?

These systems aren’t that heavy - roughly 10 lbs or so - so it would represent a minimal loss in useful load compared with other standard of optional equipment.  I’m guessing with a little ingenuity, such systems can be made lighter and better tailored to light aircraft.  And these systems have been indispensable in accident investigations and may well greatly improve light aircraft safety.  Modern AHARS systems retain some telemetry data, one of which was responsible for piecing together this stall spin accident of a Cirrus.

One downside may be the requirement to place these systems in the tail boom of an aircraft for maximum survivability in an accident, and placing even light equipment that far from the aircraft datum, can cause dramatic shifts in Moment and CG location.

It would be very difficult to mandate new equipment into older aircraft. Look how much it took to mandate ADS-b. Mandating it into new or future built aircraft would be easier. We may try to incorporate the telemetry-like data we are getting now into some type of solution. Companies like Sentry and Stratus could design a portable unit that records all AHRS, GPS, traffic, cabin pressure altitude, and carbon monoxide presence data for less than $1000. Combine that with a personal electronic device like a tablet or smartphone and a patch cable or Bluetooth connector, and you have most of the capabilities of an FDR/CVR combo. It would not record the position of flight and engine controls, or engine performance data, however.

The use of this may be easier to mandate. $1000 is fairly reasonable in aviation economics.

Making it mandatory for ALL passenger and property carrying commercial flights may be more feasible and likely. The federal government would implement it under the auspices of protection of the consumer or for the good of the public.


How and why does the ATR-72 sometimes use reverse thrust to push back from its parking position? Travelling with Czech Airlines via Prague in an ATR-72 I have already experienced multiple times that instead of pushback service the planes simply used their reverse thrust to leave their parking position, even doing a 90° degree turn while rolling backwards.

Personal experience as well as a Google search show that this is rather uncommon. What makes the ATR-72 special to be able to perform such kind of manoeuvre?

As other answers note, for most aircraft, the risk of the engines ingesting FOD while powering back is too high. This is particularly true for turbofan engines mounted under the wings.

Turboprop engines tend to be mounted on high wings (such as on the ATR-72), and they tend to serve smaller airports where an airline may not have tugs available for pushback. Regional and private jets, which often have fuselage-mounted engines, also tend to serve such smaller airports. These planes were designed with the engines mounted higher specifically to reduce the risk of ingesting FOD, thus allowing them to safely power back when needed.

Note that powering back still burns a lot of fuel, and even with high engines the FOD risk isn't zero, so when operating at larger airports that do have tugs available, airlines will generally use them.


Can Microsoft Flight Simulator help me learn to fly (or make me a better pilot)? Microsoft Flight Simulator has "flight lessons" with a virtual flight instructor, some of which teach concepts that are taught during actual flight training. These simulators are becoming very realistic, and I can see them being helpful as an introduction to a subject prior to running the Hobbs meter and paying for actual flight time. Will this experience help or hurt someone who decides to become a real pilot? Is it a tool which can help students/instructors in an actual training environment?

Clarification:This was written about Microsoft Flight Simulator X (FSX).   Parts of the answer probably apply to the new Microsoft Flight Simulator (2020 release), but that isn't what I had in mind when writing this.  Maybe a new answer will be appropriate after using MSFS for some time.

@Pondlife gave a very good answer, and I'll add a few bits to that.
Even after having gotten my license, I still use flight sims (mainly Microsoft FSX and X-Plane 10) for some practice.
Before flying into an unfamiliar airport, or over an unfamiliar area, I'll often load it up in a simulator, and fly it.
Especially when I was a student, I found this incredibly helpful for my long cross country flights. You can look at a map all you want, but its still not the same as sitting in the simulator, and looking around ("I see the mountain on my left.... and the lake below me.  I can follow this valley all the way to the airport..." etc). And I've generally found the simulator, with good terrain and textures loaded, can be pretty close to reality.
The night before I did a student flight from KBFI to KVUO, I flew the entire thing in FSX. The next day, it really felt pretty much like making the same flight all over again. Based on the landmarks, timing, views, etc, I knew exactly where I was, and I was confident that everything was going right.

That said, in my opinion there are some things simulators do very poorly.
Some of these are:

TakeoffsThe application of power and left-turning tendency on the ground just doesn't feel realistic at all. The climb out doesn't feel right.

LandingsGround effect is difficult to observe in a simulator. The flare doesn't feel like reality, and touching down (or bouncing) is not realistic at all.

Cross Control, Slip, Spin & Unusual AttitudesAnything beyond basic maneuvers up to 30 degrees bank or 20 degrees climb doesn't match reality.

This is dependent on your simulator, some perform certain things more realistically than others.
Because of these limitations, I would NOT use a flight simulator to try to learn takeoffs, landings, or certain maneuvers. (You can learn the "procedure" in a simulator... when to reduce power, when to add flaps. But the "feel" will be all wrong).

If you're going to try to incorporate flight sim into your training, there are some basic things you should do:

Spend LOTS of time configuring itUnlike a video-game, this is not "plug-n-play". Spend time learning all the controls.
Turn on RealismWhen adjusting your controls, set all "null-zones" to zero, set "Sensitivity" to maximum, turn off helpers like "auto-mixture" and "auto-rudder", etc. (However, I do keep "Gyro-Drift" turned off in my sim.  Its annoying, and adds little practical value)
Turn on WeatherThe flight simulators typically come pre-setup with zero wind, good weather, standard temperature, etc. Configure yours to pull from real-world weather sources, or add some clouds, a variety of winds, and don't always fly at noon. Set the timing for early morning flights, twilight flights, night flights, etc.

Another "fun" area where flight simulators can be slightly helpful is in emergency procedures.
Typically in real-world training, my instructor told me:  "We're going to practice engine-out emergencies" and my mind immediately starts preparing for that... And naturally, we have to do them at a safe altitude in a safe area.
In a flight simulator, you can set up the computer to give you a random emergency at a random time. You might get the problem on short-final, or over a metro-downtown area. Something that you just can't do in reality.
I haven't had any real-life emergencies, so I don't know how accurate a flight simulator is. But I believe that some practice is better than no practice at all, and flight sim lets me fly into storms, icing, get lost in fog, fly approaches below minimums, have an engine seize up on me, etc, all without risking my butt or a $200,000 airframe.

Since @Lnafziger suggested more specifically addressing flight training:
I do believe that flight sim can help with certain aspects of training, but in other areas, it is no help at all, or actually harmful.
Training Areas simulators can help with:

ProceduresReviewing steps and procedures before going in the air.  For example, for a student, steep turns or stall recovery can be a little nerve wracking at first. It may be much easier (and cheaper) to do it in a sim with an instructor, discussing all the steps and reasons for actions. Then when the student gets in the air, they won't have the "feel" for it, but at least the general process is already familiar.

NavigationTuning and identifying VORs, and interpreting the needles can be done just as well be done on the ground as in the air. If the sim has good, realistic terrain (I prefer MegaSceneryEarth), it can also be used for some visual reference lessons.

Instrument interpretationScanning and cross-checking the 6-pack of instruments can be done in a simulator just fine, and a student can practice doing it for long periods of time for a fraction of the cost of flight time.

Training Areas simulators are very bad at:

On the ground & Outside the planeAnything on the ground, such as taxiing and parking, or anything outside the airplane, such as pre-flight inspection, or weather interpretation, just doesn't work in a sim.

RadiosI haven't seen any flight sims that really work for the practice of talking on or listening to the radios. (I haven't used VATSIM, which might help). I don't think there's any good substitute for actually flying in a real airspace while simultaneously engaging in real radio conversations.

FeelEven the best full-motion sim isn't a substitute for the forces a student feels in a real airplane. This is especially true on ground-reference maneuvers, takeoffs, and landings, where I feel sims fall far short of reality.  No one will ever get a "feel" for the plane from a simulator.

For much more information on the topic, I recommend these books:
Scenario-Based Training with X-Plane and Microsoft Flight Simulator

Microsoft Flight Simulator X For Pilots Real World Training

And here's a picture of my old simulator rig.
(Its been improved a bit since this picture)


How to trigger warnings on an unplugged aural warning unit? I got an old 80-0557-11 Rev A manufactured by Grimmes from an EMB-120 Brasilia, and I was wondering how to make it speak.

I powered the component with a 28VDC power supply. It only said "Aural unit Ok" while I was expecting a lot of warnings, due the lack of connected sensors.

Checking an old wiring manual, I realized that most of the sensor inputs have a single connection, not a "HI/LO (+/-)" lines.

Does someone have some idea about how make it play alarms?

Thank you in advance for anyone who can explain me the logic of the system. Please, keep in mind that I'm just a enthusiast trying to better understand how this system works.

Answering my own question based on tips posted on comments:

As @Gerry suggested on comments, they are OPEN/GROUND, if i ground any of sensor cables it'll trigger the alarms. Those lines are 5V, and i think that most of sensors are just simple switches, except for the Fire Alarms, that i  couldn't trigger and has 6.8V over its line.

For now i got my AWU speaking.

Thank everybody who commented with their suggestions. Those were very very very useful,  you guys are awesome!


How does a US registered pilot obtain approval to fly to Cuba? Because of US foreign policy, flights between the US and Cuba are prohibited except for certain conditions.  If I am flying there for an approved reason (such as to visit immediate family), how do I obtain the proper permission to do so?

To obtain approval to fly to Cuba you must first sumbit an application for an OFAC (Office of Foreign Assets Control) License through their Cuba Travel website or by mail:

Office of Foreign Assets Control
U.S. Department of the Treasury
Treasury Annex
1500 Pennsylvania Avenue, NW
Washington, DC 20220

Once you have your OFAC license, that completes your US legal requirements, as far as I'm aware.* There are other requirements that you have to fulfill to receive a Cuban visa upon entering, but since you have asked about obtaining US approval I haven't looked into that in detail.
For the record, this is the same method that anyone would use to travel to Cuba. Pilots flying to Cuba must ensure that all their passengers also have their own individual OFAC license.

* I am not a lawyer. Please do not consider this to be legal advice. I would recommend calling OFAC and inquiring for further help with the process.

Sources:

Cuba: What You Need To Know About U.S. Sanctions Against Cuba - OFAC
OFAC Contact Info


What are the advantages of the B747-8 airfoil over B737's airfoil? The Boeing 747-8 has a new airfoil design much different than a Boeing 737's airfoil.

Boeing 737 airfoil:

(source: How Airplanes Fly?)

Boeing 747-8 airfoil:

(source: Boeing)

I am a little confused of why it is shaped like this. What are the advantages of this new profile?

It is also more thin, wouldn't that reduce the amount of fuel stored in the wings?

The airfoil profile you've shown is called a supercritical airfoil.

Typical airfoil sections are curved on the top and the bottom. The airflow over the top of the airfoil is accelerated i.e. the airspeed over the top of the airfoil is more compared to the free stream velocity. The associated reduced pressure helping to create lift.

Source: www.symscape.com

From the figure, two things can be inferred:

The pressure over the upper surface is lower compared to the lower surface
The pressure gradient is favorable in the forward section of the airfoil (where most of the lift is produced), while the gradient is adverse in the rear half, which can cause boundary layer transition and possibly separation, if the gradient is too severe.

Source: code7700.com

For low speeds (and low angles of attack), this causes no problem in lift generation. However, most of commercial airliners fly at in the transonic regime (with speeds ~ Mach 0.9), the flow over the top of the wing may reach supersonic speeds even when the aircraft itself is flying at subsonic speeds.

Source:fluid.mech.ntua.gr

The speed at which this happens (flow over wings becomes supersonic) is called the critical Mach number. The flow decelerates through a normal shock wave, resulting in a severe adverse pressure gradient over the rear of the airfoil.

Source: fluid.mech.ntua.gr

This causes serious problems like:

The adverse pressure gradient over the shock wave causes flow separation, decreasing lift and increasing drag. The speed above which the drag increases significantly is called the drag divergence Mach number

Source: history.nasa.gov

As the speed increases, the shock wave moves to the rear, as does the lift producing region. This causes a nose down pitching moment and stability issues.

"Transonic flow patterns" by U.S. Federal Aviation Administration - Airplane Flying Handbook. U.S. Government Printing Office, Washington D.C.: U.S. Federal Aviation Administration, p. 15-7. FAA-8083-3A.. Licensed under Public Domain via Commons.

The supercritical airfoils are designed to overcome (or delay) these problems. Designed by Richard Whitcomb, the main characteristics of these airfoils are,

'flattened' upper surface
highly cambered aft section
smaller leading edge radius compared to the traditional airfoils (that is why they are so thin)

Source: aerospaceweb.org

The main advantages of supercritical airfoils are,

It increases the drag divergence Mach number. For example, in the F-111, the drag divergence Mach number was increased from 0.76 to 0.88, a 16% increase.
The shock waves are developed further aft when compared to the normal airfoils
They greatly reduce the shock induced boundary layer separation, reducing drag

The figure below shows a supercritical airfoil in a transonic flow. Note the location of the normal shock compared to the 'normal' airfoil.

Source: space.bas.bg

The supercritical airfoils were not available when the Boeing 737 was first designed. However, the 737 NG airfoil incorporates elements of supercritical design,as does the Boeing 747-8 airfoil.

The supercritical airfoils reduce the fuel required, as they allow the aircraft to cruise at higher speeds with lesser drag. Additionally, the Boeing 747-8 has a wing span of ~68 m, which gives plenty of storage space for fuel. Also, improvements in engines and airfoils means that the 747-8 has nearly 50% more range compared to the original 747-100.


Can you request a new squawk code if you don’t like the one being assigned? Just out of curiosity. If you get assigned a squawk code and you don’t like it out of superstition or other negative associations you have with it, can you request a new one?

No, there is no procedure for assigning a new squawk code because a pilot is superstitious. The whole system behind assigning squawk codes is fairly complex, and requesting new codes for non-operational reasons would put extra load on the system for no reason. In many cases, the controller doesn't even have the option to manually change the code, and doing so could result in significantly increased workload (actually getting the code, updating the flight data record, communicationg with the pilot, coordinating with downstream sectors etc.).
Squawk codes are a limited resources, we only have 4096 of them, and the system is already near its limit in busy airspaces. If we started to change codes just because we feel like it, we may very well run out of codes. And how should we choose which codes to avoid? Some probably wouldn't like codes such as 4666, others 1313. What about a pilot not liking 2403 because it happens to be the date a relative of his died? 4 is an unlucky number in Chinese culture, should we avoid all squawk codes with 4 in them?
We use numbers in aviation for all sorts of things, all the time, and it simple does not make sense to avoid some of them for non-operational reasons.


How long will it take a new pilot to start flying more advanced planes like a Cirrus SR22T or Piper Malibu? Here is my scenario.   I'm 53 years old and getting ready to sell my business and retire.  I've always been fascinated with aviation and have done lots of research and taken multiple training flights.

What I keep reading is "match your plane to your mission".  Makes sense.  Here is my mission.

I live in Kansas City and would like to fly to a second home approximately 900 miles away.  Also visit kids, vacations, etc.  Most flights in the 400-1,000 mile range.

Plan is to start my PPL once the business sells and I can commit to two-three lessons per week.   Hopefully get my PPL in 60 hours or so, then start on my instrument rating.  Another 50 hours for that appears to be typical.  As such, instrument rated with 100-120 hours logged within 12-18 months.

For my typical mission, something like a TTx, SR22T or a Malibu sound appealing.  Pressurization would be nice.  I don't see myself flying a 172/182 900 miles comfortably.

I figure I will be flying by myself 50% of the time.  With a second person 25% of the time and with a third person 20% of the time.  Only rarely with 4 seats occupied.  Budget around \$700K to max \$1M.

What is a realistic path for me? At what point is it reasonable for me to safely and legally pilot these high performance planes?   How would you suggest I get from newbie to mission capable?

Thanks!

You have a few questions here that should be addressed individually.

  What is a realistic path for me?

Get your PPL then start to consider what you can fly/own. As you train you will inevitably learn about the various major airframes people fly and what it takes to own one.

As a word to the wise you should read this thread about a young guy who figured he could get his PPL and buy the fastest plane out there for his mission. Its lengthy but paints a good picture of reality.

If you are flying long distances alone and don't need the useful load, like speed, and want to stay in your budget you should take a look at the Mooney's. You can get one of a few models they have made since the 90's for well within your budget.

You should join AOPA and make use of their resources to get more information on owning and buying a plane. They have been a great resource in my recent plane search. They can give you a realistic idea on finance options as well as what your insurance rates are going to look like.

As for whats common (at least what I have seen) to some extent depends on your flight school and the quality of the planes. Many people do their VFR PPL in a rented plane (C172 or PA-28 being the most common). Then those that really like it and are serious about it look to buy an entry level plane to do the IFR in as well as build hours, get to know the national airspace system and just fly fly fly. Many buy what they trained in or step up a bit to something like an M20C or Arrow etc. Once they have their IFR the trips get bigger, longer and you really start to cross some distance. At this point you can expect anywhere from a few hundred hours to upwards of well more than that depending on how much spare time you have to fly around. Generally speaking most owners I have spoken to put about 100 hours on their plane every year (unless they use it actively for business).

To flat out answer the question, we must first say "it depends" but generally speaking I would say it will take you in the ball park of 300-500 hours to get into a high performance complex plane like a TTx or SR22 at least from what I have seen. Although to be honest some people train in an SR22 (see the above linked thread discussion, that guy trained in an SR22). The Malibu is a bit of a different beast and would take more time to get into. You can realistically fly 500 hours in 2 years if you fly ALOT, at a regular pace expect it to take 4 to 5 years to get to that point.

Legally, you can go buy an SR22 right now, pay a hefty insurance premium and do all your training in it. As long as you complete what ever the insurance company wants you to do, you can fly the plane. The broader question is "should you?..."

  At what point is it reasonable for me to safely and legally pilot
  these high performance planes?

The reality of this will come down largely to your insurance company and what they will allow you to fly for an affordable insurance premium. You list quite a range of planes here but generally if you want to fly high performance/complex airplanes your insurance company will look favorably if not mandate an instrument rating. For a turbine and or cabin class aircraft a commercial ticket wont hurt but is not necessary by any means. There will be some checkout hours required for any of these planes before you can fly them solo but the general expectation is that you are stepping up into them from another personal plane, or from a lot of hours in a rented plane. Most high performance newer aircraft will also sport a glass cockpit setup (G1000 or Avidyne etc). Insurance companies (and just common safety sense) will want to see some glass time if you plan on stepping into a plane like this.

Legally speaking you will need at least a PPL as well as a high performance endorsement (as all of these planes are over 200HP) and a complex endorsement for the Malibu as it has folding gear, moveable flaps and a variable pitch propellor. For a pressurized plane you will also need a high altitude check out.

  How would you suggest I get from newbie to mission capable?

The same way every pilot does, fly and fly often. There are no short cuts in aviation training. Nothing can replace time in the left seat. Plenty of people go from nothing to flying for the airlines in just a few years. However in that time they log a lot of hours (over 1500 to be exact) and they train in all kinds of scenarios.

The most important thing to keep in mind is to be patient, your PPL training will be hampered by weather, broken planes, busy instructors, delayed check rides and all sorts of things. This happens to everyone and you should not let it paint a negative picture for you or discourage you.


Why are CJ2+ Anti-Ice & De-Ice Systems separately controlled? Why are the CJ2+ anti-ice and de-ice systems separately controlled? Wouldn't it be easier for both systems to be controlled with one button/switch (minimize chance of error from occurring)? Are there any aircraft that have the two systems controlled by one button/switch that would be activated as soon as ice is detected?

Because they do two different things.

To quote FlightSafety's CJ2 Pilot Training Manual:

  Anti-ice protection systems are incorporated into wing, engine
  components, windshield, pitot-static, and angle-of-attack systems, and
  pylon ram-air scoops.  These systems should be activated prior to
  entering icing conditions.

  The tail deice system consists of pneumatic boots on the horizontal
  stabilizers.

Basically, anti-ice is used to prevent ice from forming in the first place on the protected surfaces of the aircraft.  This is done where it would either be "bad" to have it form in the first place (pitot-static, angle-of-attack, etc.), or where it would be "bad" to have the ice come off after it has formed (and then go through an engine, etc.).

Deice is used to remove ice after it has formed.  In this case it is used on the tail which a) isn't critical if it has a little ice, and b) the ice can be broken off after it has formed and it will just fly off the back of the airplane without damaging anything.

Since they serve two different purposes (and protect different parts of the aircraft), there are two different controls/switches.


Is it possible to calculating sea-level pressure with an unknown base station altitude? I'm trying to program a BMP180 pressure/temperature sensor to calculate altitude.  The method I've seen used is to input your current base station altitude to calculate the sea-level pressure.  It seems a little tedious to input the base station altitude everytime, so I was wondering if it is possible to calculate sea-level pressure without a known base station pressure.

I've been trying to calculate sea-level pressure through iteration.  I would set the default sea-level pressure at 1013.25 mb, use this number to calculate an estimated altitude, use the estimated altitude as my current base-station altitude to calculate a new sea-level pressure, use this new number to calculate an estimated altitude, etc...  However, I noticed that my results are diverging.  Is there a better way to calculate the sea-level pressure?

Calculating sea level pressure depends on knowing your altitude.  A function that does this is the hypsometric equation $$\Delta z = \dfrac{R \overline{T}}{g}\ln\dfrac{p_1}{p_2}.$$  This function gives the depth ($\Delta z$) of an atomspheric layer with average temperature $\overline{T}$ between pressure levels $p_1$ and $p_2$.  In your case, the station pressure is known and the height of mean sea level is known; in order to calculate your height or to calculate sea level pressure, you must know the other quantity.  The average temperature is also an unknown, but you can approximate this or use a value based on the lapse rate of the standard atmosphere.


Why is the angle of the horizontal stabilizer marked on the fuselage? Why are the angles displayed on the fuselage?

I understand having markings with depth on the hull of boats, but I don't understand the use case on a plane.

Photo of the root of the trimmable horizontal stabilizer on an Embraer ERJ-170 (wikimedia.org).

I don't have the reference but it's showing the trim setting.  The picture looks like is an Embraer 170 on which the entire horizontal stabilizer moves.  The gauge gives a quick visual setting to confirm the the trim set in the cockpit matches the actual trim.


Why aren’t diesel piston engines used on aircraft like the Saab 340 or L-410? In contrast to this question (link), I would like to know the opposite - why diesel piston engines aren't used on aircraft with comparable role and configuration to Saab 340, L-410, ATR-42?

There's a very similar question here, but it was mainly focused on small GA aircraft and private owners, while I'm more interested in commuter type piston airplanes.

Here's my thoughts so far after some reading (please note, some of them are just my assumptions and might be wrong).

Pros of diesel engine:

Engine itself is significantly cheaper
Cheaper to maintain
More economical according to this discussion (link)

Cons of diesel engine (vs turbine):

Likely they are heavier and more bulkier than turbine of similar
power output (link to similar discussion)
Diesel engine pylon is less aerodynamic (more drag) due to presence
of necessary air inlets for engine cooling
Possibly altitude (and thus performance) limited. I'm not really sure
about this point though. It's a well-known fact that commuter
turboprops can fly at 20-25k feet. I don't have any data for diesel
piston engines. I can only assume that diesel engine with a
turbo-charger might actually reach similar altitudes and performance.
Require more frequent maintenance

Perhaps this is worth asking as a separate question.

How heavy and big would be diesel piston equivalent of PW120 engine? (some ideas can be found in this discussion)

PW120 EASA data for weight, dimension and thrust (link):

Length 2130 mm
Width 635 mm
Dry weight 417.3 kg
Take off shaft power 1342 kW
Maximum Continuous shaft power 1268 kW

There are many reasons but Ill address your points directly first

  Engine itself is significantly cheaper

This is only true for non aviation engines. Even if you were to obtain a type certification for an automotive engine the cost of that would reflect a huge increase in price. This has been tried before and proved so costly the engine maker ended up dropping the FAA type cert due to costs.

  Cheaper to maintain

Again this is only true for auto or industrial application engines. Any part carrying approval down to the spark plugs has a large price mark up over their non aviation counterpart (even if the parts are more or less identical). On the whole piston engines tend to also have a shorter TBO than turboshaft engines.

  Likely they are heavier and more bulkier than turbine of similar power
  output

This is perhaps one of the most important cons. In aviation weight is the name of the game. Airlines make money not only on passengers but the carriage of freight in empty baggage space cutting into that cuts into profits.

Piston engines once did rule the skies in that size class, the venerable DC-3 is about as big as what you mention and has long since been phased out of routine use.

For the altitude space in the FL200-FL250 range you also need pressurization which is much harder to drive from a piston engine. A turbine allows you to pull bleed air for pressurization while a piston engine requires a whole separate unit driven by the engine somehow. This adds complexity and again, weight. Over the years there have been some pressurized piston planes but they have fallen out of popularity and use.


How do weapon pylons attach to a fighter's wings? How do weapon pylons attach to a fighter's wings? I'm particularly interested in the inner structure.

The pylons are not just for weapons; the term used for the Typhoon aircraft is the Wing Pylon Station Unit (WPSU) and some of those are designed to be able to carry external fuel tanks.

Some aircraft (such as the vernerable F-4 Phantom II) had 4 wing pylons which were more or less permanently attached (unless they were defective in which case they could be replaced); certainly in the years I worked on them I never saw an aircraft without all 4 pylons.

Other aircraft (such as the Typhoon) have pylons that are not necessarily all fitted
(there are locations for up to 8 wing pylons)

Here is a fit using only 6 of the pylons and all 5 fuselage hard points:

Here is a different setup using all 8 wing pylons:

Source

The attachment is relatively simple (it has to be as it can be a hangar operation for operational fit); the pylons are physically attached with mechanical mounting and electrical connectivity (to actually operate the items being carried); the pylons that can take external tanks also have fuel feed points.

The pylons also have communication links for the aircradt to 'talk' the whatever happens to be fitted on the pylons (the data could be commands, video feed, sensor data, stores readiness - whatever is required for a particular type of store on the pylon)

It is important to note that the all the hard points are considered safety critical as you do not want to fire / jettison something when not commanded and you do want that at the appropriate time.

The inner structure of the pylons is almost completely full (very little space unused) which keeps the unit as small as possible (which enhances its ability to withstand aerodynamic forces) and as light as possible.

The electronics within the pylons are somewhat expensive as the internal temperature can be as low as -50C or lower at high altitudes; the leading edge is a low drag surface to minimise heating by air friction.

Different pylons will have slightly different attachment methods but they all need to withstand the aerodynamic forces and provide electrical and communication functionality.

Update

Here is a close up of an F35 pylon (designed for air to air weapons):

Source

The mounting bolt position is clearly shown (there is another on the other side of the pylon). The pylon fits into an acceptor slot and all the various connections are made simply by placing the pylon in the correct position and sliding it in. The direction of sliding is from the front so aerodynamic pressure keeps it in position.

Interesting fact. One fine day I was working on the flight line at RNAS Yeovilton when an american F-4 flew over; he was doing a bit of hot-dogging. The aircraft had two external wing mounted Sargent Fletcher fuel tanks and when he did a high G pullup, the tanks separated from the wing pylons and landed on a roundabout in the middle of the road.

This is one of the issues with wing pylons and stores; they impose a g limit on maneuvering or things literally break away.

I understand his boss was not at all pleased.


What is significant about the number 8069 ft? On a sectional chart legend, the airport icon with a solid magenta or blue disk is labeled as "Hard surfaced runways 1500 ft to 8069 ft in length".  This seems like an extraordinarily arbitrary number to use as the upper limit before a different symbol is used.  When I convert this to meters, or yards, or furlongs, or any other common unit, it doesn't correspond to any even number so it doesn't seem like a conversion from another system of units.  What is the reason for this unusual dimension for a runway length?

Apparently you aren't the only person who wondered this; the FAA actually has it in an FAQ:

  What is the significance of a runway 8069 feet in length and why are two different aerodrome symbols used to depict hard surface runways on
  Sectional charts?

  For purposes of airport depiction, specialists
  represent a runway between 7970 and 8069 feet in length as 8000 feet,
  which equates to a line 0.192 inches in length on the Sectional chart
  scale. In this case, a circular aerodrome symbol is used.

  If a runway
  is between 8070 and 8169 feet in length, specialists round to 8100
  feet, which equates to a line 0.1944 inches in length on the sectional
  chart scale. This line is too long to fit into the largest circular
  aerodrome symbol FAA has available. Therefore, specialists place a
  line-work around the runway pattern forming a polygon (enclosed shape)
  for anything over 8069 feet in length.

  Specialists also place these
  polygons around the runway pattern of aerodromes with multiple runways
  that are less than 8069 feet, in cases where the multiple runway
  pattern does not fit into the largest, circular aerodrome symbol.


What is the aerodynamic advantage to a cuffed wing like the Cirrus SR-22? What is the aerodynamic advantage to a cuffed wing like this Cirrus?

Here we go:
http://whycirrus.com/engineering/stall-spin.aspx

  Spin Prevention
  Cirrus chose, in the very earliest stages of designing
  the SR20 to take on the challenge: to minimize the risks associated
  with inadvertently stalling an airplane. The approach chosen was to
  employ wing technology developed by NASA reducing the potential for
  spin entry after an inadvertent stall. The most visible aspect is the
  discontinuous leading edge dividing the wing into distinct parts.
  ...
  How does this wing design work?
  The outboard section of the Cirrus wing flies with a lower angle of
  attack than the inboard section. When the inboard section, which
  produces much of the lift, stalls the outboard section, where the
  ailerons are, is still flying. The result is that a stalled Cirrus
  airplane can be controlled intuitively using aileron.


Are airline ICAO codes unique? Tiger Airways Singapore's IATA code is TR while Tiger Airways Australia's one is TT, but the ICAO code for both is TGW. I thought that the ICAO codes are meant to be unique from one airline to another, not the other way around. Is this the only case?

ICAO three-letter codes are always unique. The official source, ICAO Document 8585, says the following:

1.2 The same designator will not be registered for more than one aircraft operating agency, aeronautical authority or service.
1.3 No more than one three-letter or telephony designator will be registered for each aircraft operating agency, aeronautical authority or services.

In your example, Tiger Airways Singapore only exists as a single airline in document 8585. The fact that they have an Australian division does not mean that it is a separate aircraft operator, and thus no separate ICAO code can be assigned.
You can find more rules regarding ICAO identification codes, including a complete list of every ICAO code in the world, in doc 8585: http://dcaa.trafikstyrelsen.dk:8000/icaodocs/Doc%208585/DOC%208585,%20Edition%20no%20149.PDF
Interestingly, British Airways seem to contradict the above rules with their seasonal "Santa" flights. Around Christmas, certain British Airways flights will operate with the XMS ICAO code (radio callsign "Santa"), instead of the usual BAW ICAO code (radio callsign "Speedbird").
In ICAO doc 8585, the XMS code is registered to "British Airways Santa", which I very much doubt is the name of a real company, so it does seem there are ways around the rules quoted above.


Is flying a UAV via a VR controller (e.g. Oculus) legal in the US? I've heard claims that flying a UAV using a Virtual Reality headset (for example, the oculus rift) is illegal per FAA regulations.

Is this true? I cannot find any definitive answer either way.

According to Model Aircraft Operations one of the requirements for flying a model aircraft is:

  Keep the aircraft within visual line of sight at all times

If you are wearing a VR headset, then your visual line of sight stops at the headset screen.

Note that the above linked page lists the "visual line of sight" as a safety guideline. However, according to Section 336, an aircraft is not considered a "model aircraft" unless it is:

  (2) flown within visual line of sight of the person operating
  the aircraft

None of the above restricts you from flying with a friend where one of you is wearing the VR headset and the other is piloting the aircraft.


Barometric altimeter data during high vertical g-forces? I’m contemplating that that under high vertical acceleration (such as the maximum limit of 2.5g for commercial airplanes), that hydrostatic atmospheric pressure wouldn’t be a complete model. Wikipedia states for atmospheric pressure:

  In most circumstances atmospheric pressure is closely approximated by the hydrostatic pressure caused by the weight of air above the measurement point.

The derivation of the Barometric formula presumes hydrostatic pressure:

  And assuming that all pressure is hydrostatic:

    dP=-ρgdz

It appears to me that without correction for the g-forces, a vertically accelerating barometric altimeter could potentially indicate uncorrected altitudes which are lower or higher (depending on the design of the altimeter) than true altitude even if all other factors had been corrected.

Is this a correct understanding and do Air Data Computers (ADC) described below make these corrections? If yes, can anyone provide an approximate formula or mathematical model for altitudes near ground level?

Another Aviation Stackexchange answer states:

  However, altitude is also used for the purpose of traffic separation, and for this purpose, neither QNH or QNE is corrected. This might sound counter-intuitive, but as long as your altimeter is showing the same error as any conflicting traffic, you can be safely separated, therefore: The altitude shown on the altimeter is not corrected at all (except by calibration for possible aerodynamic interference, such as compressibility, venturi-effects etc).

  In technically sophisticated aircraft, barometric altitude input is used for vertical navigation. Since vertical navigation is concerned with the true altitude of the aircraft, the aircrafts Air Data Computer (ADC) will calculated a true altitude based on information available to it (either through sensors, or through pilot input). The true altitude is however, as stated, not shown on the pilots primary flight instruments.

In the formula $dP = -\rho gdz$, $g$ is the local gravitational field that is pulling on the fluid (the atmosphere).  The apparent value of $g$ within the airplane is not relevant.

So other than making sure the sensor itself isn't affected by changes in apparent weight, there's no need to correct for accelerations of the barometer.

  And yes I am intending to ask whether the sensors are designed such that their “apparent weight” (or more generally their mass acted on by any directed force) is not an appreciable factor in their reported measurements?

My understanding is that no, it's not.  Altimeters already have a measurement error at level flight, and they have a lag when altitude is changing.  Additional errors due to apparent weight would have to exceed those to be worrisome.

"vertical acceleration" is rather small for almost everything that's not a military fighter.  But a plane could easily pull 3g's in a level turn, and you would want your altimeter to remain accurate.

Obviously it's possible to design an instrument that is more susceptible to such inaccuracy (such as have the pressure vessel balance against a weight to indicate the altitude), but that shouldn't be a problem for a normal instrument.

The aneroids in a diaphragm barometer can be oriented so that downward forces have no effect on the reading.  Also, the smaller and lighter the disks, the less that any acceleration will affect the reading.

I found lots of articles on various corrections for barometric altimeter readings based on temperature and different atmospheric profiles, but none on g-load corrections.  That suggests to me that no correction is necessary for standard instruments.  Perhaps someone can find published performance data for an installed instrument that calls it out explicitly.  The lack of information I found appears reasonable, but not completely satisfying.


Difference between FMCF and AIMS on B777? What is the Difference between Flight Management Computing Function and Airplane Information Management System on B777?

The B777 uses an Integrated Modular Avionics (IMA) architecture. AIMS is the modular computing platform on the B777. It's basically a bunch of computers in a box with it's own back plane network and operating system. It replaces multiple unique stand alone computing boxes.

FMCF is the software that performs the Flight Management function. It is loaded onto the AIMS platform. In older aircraft architectures (B737, B757, B767) it was contained within a dedicated stand alone Flight Management Computer. In the B787, AIMS was replaced with the CCS (Common Computing System). It also has an FMCF software function.


Where can I find real-time flight tracking with the least amount of delay? I am an aviation fan, relatively new to the industry.  While I thoroughly enjoy plane spotting at my local KORD airport, at times I tune to LiveATC and Flightaware to get my fix.

Unfortunately, my observations are that flightaware is a bit delayed 3-5 minutes, and not all air traffic is shown.

I tried Flightradar24, it is more current, but wildly inaccurate at times and a bit "synthetic" as they try to fill in the data gaps.

Aside from getting into an actual ATC tower, which I am sure is nearly impossible for a civilian, what are my best options as far as getting my fix in?  Apps, services, etc (paid and free), doesn't matter.

You can buy a DVB-TV USB stick for around €20, which will allow you to receive ADS-B data:

Up from that, you can get a high-end ADS-B receiver that costs about €750:

Finally, FlightRadar24 offers free hardware in selected locations:

Bear in mind that these devices will only allow you to receive signals within a relatively small area.

One thing worth noting is by contributing the data received by these devices, you get a free FlightRadar24 Premium subscription.

Lots more information is available at FlightRadar24 > Increase Coverage.


Can I do a VFR night sightseeing flight in Europe? I am an American living in the Netherlands, and I recently converted my US PPL to an EASA PPL.  I have significant night flying experience in the US, but I understand that night VFR in Europe is uncommon, and in fact only this year became authorized in NL.  I know a flight plan in required, but I'm unsure whether I can file a plan with departure and destination the same, then just go fly around a bit and return at the specified time.  Or must I have an actual route to a destination that I have to adhere to?

Yes you can file a flightplan with the same departure and destination. You generally do not need to include detailed routing, unless local rules require you to do so (but if you are planning to cross a country border, you probably need to include a point of crossing and estimated time). One thing to consider is that the EET in your flightplan should be accurate, since alerting service is based on that (if you don't arrive within a certain amount of minutes after your ETA, search and rescue efforts will be initiated). However, as long as you are contact with ATC while in the air, you can always just inform them of a revised ETA, and they can pass that on to your destination airfield.


How do you know which fuel an aircraft uses? Other than the decals on the plane, how would you know what fuel to use in an aircraft? Where is this limitation documented?

For some aircraft, does this limitation include some sort of substitute fuel for emergencies? For example, I have heard that if Jet A-1 is not available, some aircraft may have approved emergency fuels, such as AvGas.

Where would this information be found?

The actual fuel type limitations will be listed in at least two places: the aircraft type certification data sheet (TCDS), and the limitations section of the aircraft Flight Manual, Operating Handbook, or equivalent.

The fuel placards placed at the fuel filler ports might not list all approved fuels, or may state "Type X fuel only" when additional fuels may in fact be approved. These placards should be understood as a precaution against inadvertently fueling with an unintended or wrong type of fuel. In some cases ignoring these placards can have fatal consequences.

Some aircraft do indeed have approved emergency fuels. This information would also be found in the limitations listed above.

For example, the TCDS for the Beechcraft King Air B200 with PT6A series engines is lists the following for normal approved fuels:

  Fuel
  JP-4, JP-5 (MIL-T-5624); JP-8 (MIL-T-83133); JET A, JET A-1, and
  JET B conforming to P&WC S.B. 1244 or ASTM SPEC. D1655; in addition for
  B200 and B200C Chinese No. 3 Jet Fuel. See NOTE 6 for emergency fuels

Note 6 in the TCDS reads as follows:

  NOTE 6. Emergency use of MIL-G-5572:
  Grades 80/87, 91/98, 100/130, and 115/145 are permitted for a total time period not to exceed 150 hours time
  between engine overhauls. It is not necessary to purge the unused fuel from the system when switching fuel
  types.

Likewise, the EASA TCDS for the King Air B200 lists the same limitations.

The Flight Manual for the King Air B200 also lists these limitations, as applicable, as well as some additional altitude constraints when using emergency fuels due to electric boost pump requirements.

In contrast to the actual fuel limitations, the placard placed at the fuel port for the King Air B200 lists very little of the actual limitations:

Source: Beechcraft King Air 200 Maintenance Manual


Is there a roadmap to satellite / inertial only based navigation? GNSS is the most accurate mean of navigation available on the flight deck but it relies on satellite being available and under control. Inertial systems are autonomous, but far less accurate.

While GNSS and inertial systems relieve authorities from the burden and cost of building and maintaining terrestrial navaids, terrestrial navaids (VOR/DME) are still imposed as a safety net in case instruments fail (GNSS) or drift (inertial).

As a matter of fact it's not possible to deliver an IFR certificate to an aircraft without a VOR-DME navigation equipment.

Note: Taking comments into account, this last sentence may be not true for IFR certification in the US. However flying IFR in controlled airspace, or flying some approaches may mandate VOR/DME/ADF, depending on the country. E.g. "ADF, DME: Until about 2013, the UK Air Navigation Order required an ADF for all IFR in controlled airspace. The ADF requirement now remains only for instrument approaches that contain an NDB." (source).

Is there any credible roadmap to remove those constraints and have IFR aircraft relying only on GNSS/Inertial? If so what are the mainlines of this new framework?

I'm not aware of any program at present that does away with ground based infrastructure completely. Present plans are to have the ground based stations as a backup in case of a GNSS outage/interference.

The present FAA plan, for example includes DME while reducing the VOR coverage:

Navigation- En Route Transition; from FAA navigation Programs Update Sep 2013

As far as ground based navigational aids are concerned, the plan is to reduce the VOR coverage with VOR Minimum Operational Network (MON) as a middle step. However, the plan appears to be to retain DME at the expense of other Ground Based Navigation Systems (GBNS).

FAA's Alternative Positioning, Navigation, and Timing (APNT) project is geared up towards maintaining aviation operations in case of a GNSS outage. According to FAA:

  The Alternative Positioning, Navigation, and Timing (APNT) project is investigating alternatives for providing higher precision back-up for Global Positioning System (GPS)-based position, navigation, and timing (PNT) services.

However, Ground Based Systems are still a part of the program (though VOR is not) and serve as a backup for the GNSS. One of the options is to modify the existing DME facilities in order to improve coverage/accuracy.

International Civil Aviation Organization (ICAO) 2013-2028 Global Air Navigation Plan also stresses the importance of having some 'conventional' ground based systems as a back-up for GNSS:

  Conventional navigation aids (VOR, DME, NDB, ILS) are in widespread use globally, and most aircraft are equipped with the relevant avionics. The vulnerability of GNSS signals to interference has led to the conclusion that here is a need to retain some conventional aids or alternative navigation service solution as a back-up to GNSS.

ICAO also concurs that DME is the most appropriate ground based equipment to be used in the future navigation system:

  The implementation of PBN will make area navigation operations the norm. DME is the most appropriate conventional aid to support area navigation operations(i.e. assuming DME multilateration on board capability),since it is currently used in multi-sensor avionics for this purpose.

At present, as far as I'm aware, there is no available roadmap for satellite/inertial only based navigation systems as far as civil air transport is concerned. Though GNSS will remain the primary means of navigation for the foreseeable future, plans still retain ground based systems as a backup.


What are good books to learn basic aerodynamics in plane design? Well, since this stack is in beta, I thought I'd take a wack at asking a book question to see how it fits in this particular community (of if it even fits to begin with).

I'm very curious about how aerodynamics work in plane design (especially wing design), but it's hard for me to ask questions here because I'm lack knowledge of so many of the basics.  So I wondered if I could get a recommendation on a good book to learn the basics of aerodynamics?  Keeping in mind that my understanding of math is limited, so I would need a book that explains the math being used to some extent.

Bear in mind when answering:  This is a Q&A site, so try and have some reasoning behind why your book is the best.  Especially if you could show it has good explanations of the math and, also, the books is good for the somewhat beginner.

Let's see if this works...

Beginner

Fundamentals of Aerodynamics by John D. Anderson, Jr.
Introduces the basics of aerodynamics with historical background, the mathematical explanation and some practical applications. In the latest edition,  Computational Fluid Dynamics is also discussed.
Mechanics Of Flight by Warren F. Phillips.
Anderson's book is a good text for understanding the building blocks of fluid dynamics, such as the different types of flow. It is good for understanding how airfoils and wings work, as well as understanding the microscopic flow considerations. Phillips' text also talks plenty about flight dynamics and control, so you can better picture the forces acting on an airplane.
Anderson's and Phillips' make a very good learning pack.

Intermediate

No books found as of yet

Advanced

Fluid Dynamic Lift & Fluid Dynamic Drag both by Hoerner
I wouldn't consider these to be great "learning" textbooks, and the math can get very intensive at times, but these are still go-to reference text, and they are a great resource if you want to start a "deep dive" into aerodynamics and the practical effects of various design decisions. Both books are replete with wind-tunnel testing information and diagrams, as well as the supporting equations to back it all up.

Classics / Older

Aerodynamics for Naval Aviators by H. H. Hurt Jr.
This is a good primer on basic aerodynamics - as the title implies it's primarily aimed at naval aviators, but the material is pretty accessible and much of it is applicable to all fixed-wing aviation. There's even some helicopter stuff in there, though the section is rather thin.
This book is available from a number of publishers. It is also known as NAVAIR 00-80T-80 or NAVWEPS 00-80T-80 and available from the FAA in PDF form.

Additional references

As far as mathematics goes, you can get Stewart's Calculus text. It is a pretty good book with quite satisfactory explanations, and you can get an older edition for almost nothing (make sure you get the full text with both single variable calculus and multivariable calculus sections). Without a basic understanding of calculus it will be difficult for you to get a good grasp of the aerodynamics material.


How did this incident report detailing a flight taking off and landing at Glasgow result in safety changes at a distant airport? While reading this report detailing a tire failure and actions taken, I noticed a peculiarity: The flight took off and landed at Glasgow without continuing to Malta (its intended destination) yet the Actions taken says:

  For flights from Malta, takeoffs to be carried out with flaps 5 only.

How would the operator find an issue with flights out of Malta for a flight intended to land in Malta, that never did (by virtue of returning to Glasgow)? Is it policy or practice to check all aspects of the flight including those that were not reached due to the incident? Was something not mentioned likely to have been found at Malta (perhaps damage from a previous takeoff)?

The precise truth cannot be known without consulting the authors of the report.  However, assuming it was not a typo, there are several contributing factors that may lead to this result.

Primarily, aviation is a very conservative business, and every opportunity to mitigate risk will be taken.

In this instance, not only did the aircraft lose a tire, the tire also damaged the hydraulic "A" line, and the flaps.

The main issue to address was the tires themselves, but it was noted that the tire blowout appeared to occur at "rotation", which puts the greatest stress on the main gear tires.

While the airplane may be about to take wing and unload the landing gear, the moment the aircraft's nose rotates up is the moment of peak main gear loading.  The weight of the aircraft is no longer supported by the nose gear, and not yet supported by the wings.  The elevator pushes the tail and empennage downward in order to raise the nose, which further burdens the main gear.  And during takeoff, the aircraft flaps will be lowered to aid in generating more lift while still at low air speeds, BUT, lowering the flaps aerodynamically causes a nose-down "moment", which makes the elevator's job that much harder, and that additional force is also transferred to the main gear at the moment of "rotation".

A couple ways to help alleviate the burden on the main gear are to not drop flaps as much, and to "rotate" more gradually.  Also, since flaps were damaged in the tire incident, having your flaps tucked up higher puts them less in harm's way of a possible exploding tire.

But why that directive in Malta?

According to the link below, the main runway at Malta Luqa Airport is 11627 feet long (3544m), which is fairly long as runways go, so an aircraft can take its time getting airborne if necessary.

Malta Luqa Airport charts, at SkyVector

It's not the longest runway around, but it's longer than necessary for most commercial aircraft, especially at sea level.  Malta is also a very flat place, with its highest point only 253m above the Mediterranean. (830 feet)  This makes it a reasonable place to use a procedure that would result in a longer take-off roll and more gradual climb (from the less-deployed flaps.)

So there are reasons it would possibly be more doable there than at some other airports.  However, I think the dominant factor is this:

  Boeing 737-33A, registration 9H-ADH, is a Maltese registration (as indicated by the 9H, and the aircraft belonged to Air Malta at the time of the incident.

I used the past-tense, since the current ledger of aircraft registered in Malta does not include that aircraft.  In fact it was transferred (sold?) to Air New Zealand in 2008, and is now in Bahrain, to the best of my knowledge.

737 s/n 27459 registration history

While I do suspect there is more to the story details than we are privy to in that one publication, it's my opinion, as a certified aircraft mechanic and persistent internet sleuth, that the change in practice was made as a matter internal to Air Malta operations at their home airfield.

Bonus: A photo of the actual aircraft, after the incident in question, sitting cordoned off, on the ramp at Glasgow International Airport (GLA).  Click the link above the pic for a little more info, and additional resources.

Boeing 737, registration 9H-ADH

Cheers!


Is it possible to recover from a flat spin? In Top Gun, Maverick's F-14 enters a flat spin after flying through another F-14's jetwash, forcing him to eject and causing the death of Goose.

Is this scenario possible or was it only created for theatrical purposes?

If not, how does it happen, and how can it be avoided, especially for other types of aircraft such as the B-2?

The F-14 is special; to stop the flat spin you need to pull on the stick. Then the spin can be recovered from.

This is different from what you learn about regular spins, where pushing the stick would be a better recovery method. In a flat spin, the forward fuselage dominates the aerodynamic forces, and we all know there are no control surfaces which could influence this flow. Wings and horizontal surfaces are fully separated, and elevator deflection is mostly useless. As others have pointed out before, a flat spin can only be stopped by shifting the center of gravity forward or deploying a spin chute. The F-14 was an exception.

Spinning the F-14

Early on, the Navy lost several F-14s due to flat spins. They then studied the phenomenon at Pax River, and in the end Bill Bihrle found out that the elevator shields airflow from the two vertical tails of the F-14 when the stick is pushed, but moves out of the way when the stick is pulled full aft. You have to know that the elevator of the F-14 is a full-flying surface, and the movement range is from -20° to +70°. At +70° it is almost in line with the airflow in a flat spin, and now the vertical tails are no longer in the wake of the elevator. They now can reduce the high yaw rate, which in turn reduces the high pitch-up moment of the rotating fuselage. With the lower inertial pitch-up moment, the elevator then has to be moved back to neutral, and the drag from wing and elevator is enough to pitch the aircraft fully down and out of the spin.

Naturally stable flying wings never enter a flat spin; their spin modes are all fairly steep due to the lack of a strong inertial moment from the lengthwise distribution of masses.

Influence of mass distribution

I guess I now need to explain the inertial moment which causes the high pitch attitude in some aircraft. The axis of the spin rotation is close to the aircraft's nose, and the tail has the biggest distance from this axis. In a flat spin the axis of rotation is even more back, close to the center of gravity. All parts of the aircraft rotate with the same yaw rate, and the centrifugal force from this yawing motion grows linearly with distance from the spin axis. This difference in centrifugal force along the lengthwise coordinate of the aircraft pulls the aircraft in a near-horizontal attitude.

Watch this movie of the spinning XB-70 to get an idea how it looks. Depending on elevon settings, the spin axis is somewhere between the cockpit and the forward tip of the wing triangle. With the damaged configuration (watch without sound for no distraction) you get a typical flat spin with the spin axis close to the center of gravity since there are few suction forces acting on most surfaces - only drag and the nose vortex (more on that below) remain.

How to avoid flat spins

If you have a configuration which is prone to flat spins, you need to change the shape of the fuselage tip. A rotating fuselage tip at high angle of attack will produce vortices at its side, and the yawing moment of these vortices will grow stronger with increasing yawing motion. This is why a flat spin is self-stabilizing. One way to suppress these vortices is the placement of small spoiler strips along the nose (which fixes the vortex position and reduces this self-stabilizing effect), and another is to make the nose shape flatter.

Unfortunately, this can only be done long before take-off.

Answer to your question

Regarding the "Top Gun" scenario: If the F-14 is at high angle of attack and the jet wash hits it asymmetrically, the airplane could enter into a spin. But from there it is still some way to the fully developed flat spin, and I would expect that a skilled pilot could recover from this momentary upset.


If I do PPL ground school online, do I have to do all of it? I am not doing normal ground school (I chose to do it online). I have passed my PSTAR, and will be doing my ROC-A in the upcoming weeks.

With this in mind, must I do the entire online ground school course? I do not know if my instructor (or worse, the FAA) will check if I have finished all of the online work.

You need at least 40 hours of ground school, according to the Transport Canada regulations (421.26). So you will need some sort of evidence to show that you have done so.

I do hope that you weren't seriously considering doing this. Please read the answers to this question.

You will see a common theme - most accidents are caused by the pilots themselves. Knowing aviation theory inside and out is the best protection you have against joining them in those statistics. It is not a stretch to say that your life depends on the attitude you bring to your flight - starting from the first lesson of ground school.


Could an aircraft like a Boeing 777 take off with flaps fully deployed? I have wondered this for years.  Could an aircraft successfully take off with the flaps fully extended to the landing position? To make this more concrete, let's say a B773-ER at ATL runway 8R.

Given the right weather, and takeoff weight, yes it could leave the ground. Will it be able to attain the regulatory climb gradient? Probably not. Will it be safe in case an engine fails? Most definitely not.

Landing flaps add lots of drag. That's why they are retracted during an aborted landing for example.

On takeoff, too much flaps means you can stop easier if an engine fails. But it also means you need longer distance to accelerate if the decision is to continue. That means the go-speed will be slower than the stop-speed. See: How is minimum runway length related to V1?

There can't be two decision speeds. Limiting the flight to the slower go-speed will significantly limit how much fuel/payload the plane can carry. And of course if an engine fails during the initial climb, the remaining engine won't be able to keep the plane climbing at a safe rate.

Manufacturers test the different configurations in all conditions, such as weight, runway length, winds, etc. After the data is collected, and with some interpolation, the takeoff and climb performance tables are produced and approved by the regulatory bodies. Any configuration used that is not approved would fail the regulatory and safety requirements, and put everyone in great risk.


Is there a formula to calculate ground distance traveled given rate of climb and true airspeed? I'm looking for a formula to calculate the horizontal distance (guess it is the Ground Distance) passed during the phase of ascent (or descent), having the rate of climb in ft/min and the TAS in knots. I did not found a clear answer about this question. I think it may concern with the Climb Gradient.
Refering to the image below, I'm trying to calculate d, having:

h = 11200 ft
RoC = 1250 ft/min
TAS = 75 kn

ClimbGradient = (RoC / TAS) * 6000 / 6076,12 = (1250 / 75) * 0.9874 = 16.45%
d = h / (ClimbGradient * 100) = 11200 / 1645.78711 = 6.80525 nm

Is this correct calculation? I will update this question with the correct formula in other case.

You need ground speed not TAS. GS is affected by the head- or tail-wind components.

Assuming in your example GS is 75 knots, then just check how long it takes to change altitude.

11,200 ft at 1,250 ft/min takes 8.96 minutes, or 0.1493 hours.

At a speed of 75 knots, that's 11.2 NM.

$$\frac{\text{altitude change (ft)}}{\text{rate of climb (ft/min)}\cdot60}\cdot\text{ground speed (knots)}$$

Since the density of air changes during a climb/descent, it affects the rate of climb/descent. Fancy planes have green bananas or similar indications on the navigation display to show where you'll reach the target altitude (it updates in real-time).

The green arc is that green banana (altitude range arc).


In Ethiopia, what are the minimum hours to be a pilot in a passenger jet? With regards to the flight crew on board the Ethiopian flight, I have read many times that the young F/O with only 200 hrs wouldn't have been allowed to transport passengers if he were a pilot in the USA. Like in this article:

  In the Ethiopian Airlines crash this week, one of the pilots had just 200 hours of flight time, less than a seventh of the time the F.A.A. generally requires to fly a passenger plane.

I don't know about FAA regulations, but cadets that come out of MPL or Integrated ATPL route have around 250 hrs and hold an ATPL frozen that allows them to be a co-pilot of a jet with hundreds of pax. Even stranger for pilots with an MPL who are not allowed to fly in single pilot planes until 1500 hrs.

Are Ethiopian requirements really so different compared to western countries (North America, Europe, Australia, NZ)?

  On Mar 18th 2019 the airline clarified, the first officer had accumulated a total of 350 flight hours

from AVHerald

For Commercial Pilots: 250 hours; For ATP: 1500 hours.

Source: ecaa.gov.et (PDF; see Sections 3 and 6).

The flight hours requirement does not seem to be different for Pilot and Co-pilot. (See Section 6.6)


What is this aircraft that appeared at Oshkosh 2017? This photo is an image from a youtube video of Oshkosh 2017.

That would be the Boeing YL-15 a scout plane of which only 12 were built.

Here is the EAA's article about the airplane from the airshow.


Will ATC proactively route traffic around bad weather? When thunderstorms or other severe weather crop up, will the Air Traffic Control in the area proactively route traffic (horizontally or vertically) around the trouble area, or do they leave it up to the individual pilots to request an alternate route?

My intent was asking about commercial aircraft flying IFR, however the information about general aviation and VFR is appreciated

Yes, ATC will reroute flights that are operating on Instrument Flight Rules (IFR).
There are lots of videos of flights getting routed around severe weather floating around on the internet! Atlanta is a great example, as is Memphis, FedEx's hub.
In addition, NASA is working on a product called Dynamic Weather Routes that will help controllers be smarter about amending planned or unplanned weather reroutes.
Sort of, for aircraft operating VFR.
VFR flights that are talking to ATC may get advisories about weather and suggested headings from the controller. I've received notifications about things like 'moderate to heavy precipitation 5-10 miles ahead' many times when operating on VFR flight following.


What do pilots do, when there is a long wait before take-off, after gates are closed? Pilots are supposed to carry out the mandatory checks before the flight take-off or taxi. But what happens when there is a delay, when the aircraft cannot push back from the gate, due to non-clearance from ATC, or due to heavy traffic etc.

Do the pilots, re-run the checks, or carry out more extensive checks of the aircraft?
Do the pilots just chit-chat, eat, or make phone calls to their family?
Is there any standard procedure to be followed during this wait time?

Edit: As someone tagged this as duplicate, my question no where suggests time spent by pilots during long haul flight, its about what they do when the pushback is delayed. Hope it helps.

Apart from what Daniel listed already, they're also nervously watching the clock.
If they're late by too much they may miss their mandatory crew rest period and have to cancel the flight or hand over to another crew.

This can of course get very expensive for the airline, especially if all or most passengers have to be accommodated in hotels overnight for a departure the next day in case no replacement crew can be arranged or the forced delay causes the flight to be unable to take off due to closing of the departure airport before departure or closing of the destination airport before arrival there.


Would it be a benefit to install winglets on a Hawker 400XP? Would it be a benefit to install winglets on a Hawker 400XP? If so how much would the performance be increased?

Hawker 400XP with winglets.

  HAWKER WINGLET BENEFITS

  3-4% range increase and precise handling characteristics
  9% reduction in time to climb
  Fast cruise speeds at same fuel flows
  Increases resale value

  — txtav.com

Related: Is a winglet better than an equal span extension?


What are the advantages and disadvantages of a double bubble fuselage? Double bubble is mostly used for Cargo Aircraft with 2 intersecting circles which is in other words: they are 2 floor which are used for more space for freight and also passengers. this type of fuselage mostly used in the past by some small airlines but today they are only used for cargo. i wonder to know all the things above mentioned by me are right or not?
and the other question is that what ARE advantages and disadvantages of A380 fuselage? and how it is designed that able to carry a large number of passengers although its fuselage is not double bubble?

Double bubble is the lightest way to make a pressurized fuselage taller than it is wide.  It maintains the pressure hull elements, skins and formers, closest to pure tension, like a balloon, so they can be a bit lighter since they see little bending stress from pressure (only the interconnecting floor beams see significant bending loads, from the weight of the payload).
The A380 went with an ovalized cross section because it provides a better packaging compromise when you want two decks of roughly the same floor area, although it would be somewhat heavier than a DB cross section because the frame elements of the partially flattened sides are subject to a certain amount of bending because the pressure loads are trying to circular-ize the oval (the floor beams help but the oval sections away from the beams are still subject to that stress).
Think about what would happen if you really cranked up the pressure inside the A380, and imagine how the pressure hull would deform under stress; it would swell out to a more circular shape except where retained by the floor beams, before going "POP" (you'd end up with a kind of "triple bubble" before it went bang).  That deformation load trying to make the oval a circle has to be absorbed as bending loads in the frames, so they have to be heavier than they would be if they were already purely circular.
The packaging advantages over a pure double bubble make it worth the weight penalty.
The original double bubble pressure hull was the Curtiss C-46, which was originally designed as a pressurized airliner (otherwise they would have used an oval cross section), and used the configuration to make a pressure hull that was a light as possible while keeping it relatively narrow.  Then you had the Boeing 377 Stratocruiser, which also went that way in order to graft a passenger cabin on top of a B-29 fuselage and wing without making it too heavy.


Regulations regarding cleaning of water cooking equipment on planes? Inspired by this question over at MiYodeya, does anyone know of specific practices or regulations regarding the use and cleaning of water urns on commercial planes?

Specific questions would be

are water urns on planes only used for water?
are they washed? (or do we saw that they don't need to because they only contain water)?
are they washed in dedicated washing machines for water urns or with other food containers/dishes?

These might seem weird questions but some Jewish travelers who observe Jewish dietary laws (i.e., eat kosher) will decide whether they can drink coffee on planes based on these answers.

From observing catering operations as a passenger on many flights:

Hot water is served from the same pots as coffee, so that only one type of hot liquid container is needed per flight. The pots are clearly intended for hot water or coffee. This doesn't mean that the flight attendants haven't used it for something else. For example, the galley sink might get clogged and the flight attendant uses the pots as a scoop to move the liquid to the toilet. I've seen this at least once.
Yes, everything with food contact has to be washed and disinfected, especially on international flights for phytosanitary reasons. They even will wash the trolleys. They cannot disinfect the pots on the aircraft, so at the end of the flight, they are placed back in the metal catering containers, and will be washed in the catering facility with all other supplies ("rotables").
There's no regulation or non-religious reason why you'd want to separate the coffee pots from the rest of the equipment, so I doubt any airline does this. Here's a page showing pitchers being washed with serving trays and drawers.

In the majority of galleys, the hot water comes from the coffee maker or dedicated water boiler, which operates like a commercial coffee maker: there's a constantly heated internal hot water tank that is automatically refilled from the aircraft water tanks. My understanding is that it may be best to have hot water dispensed directly from the maker, since that is dedicated for water use.


What are the VOR channels used for? I'm looking at different VORs on a sectional chart and I see the frequencies but I also see a channel number associated with them as well. What are these channel numbers and how do you use them?

They are DME (TACAN) channels. If you look close the the VORs, you'll see that they are either a VOR/DME or a VORTAC station. DME is the distance portion of a TACAN. When added to a VOR, you have a VOR/DME. If a complete TACAN is co-located with the VOR it is identified as a VORTAC.

The military uses TACAN. If you were to have a TACAN receiver, you wuold tune it using the channel number.

DME is available to civilian users with a DME receiver. The DME channels are paired to VOR/ILS/VHF frequencies (It's a multi-page table in the DME standards.) For convenience, DME receivers are tuned using the paired frequency.

When you tune a VOR or ILS, that frequency is also sent to the DME automatically tuning it to the proper channel. They are channels because DME actually uses two frequencies, one for transmit and one for reply.

So, to answer the question: unless you have a TACAN receiver, you don't do anything with the channel number. They are on the chart for reference.


What would prohibit a T-38 Talon from being certified in the Acrobatic category? The definition of the acrobatic category in FAR 23.3 reads as follows:

  (c) The acrobatic category is limited to airplanes that have a seating configuration, excluding pilot seats, of nine or less, a maximum certificated takeoff weight of 12,500 pounds or less, and intended for use without restrictions, other than those shown to be necessary as a result of required flight tests.

Considering that the Northrop T-38 is a two-seat, twin-engined supersonic jet trainer aircraft with a USAF service maximum takeoff weight of 12,093 lbs (from their factsheet), what traits of the T-38 would have prohibited Northrop from applying for a civil Type Certificate for the T-38 in the acrobatic category?

That an aircraft is eligible for a category is not a basis to say that the aircraft should be certified in that category. In other words, though there is nothing prohibiting T-38 being certified in acrobatics category, FAA will not certify it unless someone approaches it for that reason.

The T-38 would come under military surplus aircraft, which is covered by FAA Advisory Circular 20-169 for Military and Special Mission Modifications and Equipment for Commercial Derivative Aircraft.

However, there are some T-38s being operated by civilians in US, which are type certified under FAA Experimental Category (most are used by NASA, Boeing etc for research). One of the aircraft owned by Thornton Corp. is certified under the 'Exhibition' category, which permits the user,

  to exhibit an aircraft’s flight capabilities, performance, or unusual characteristics for air shows, motion pictures, television, and similar productions, and for the maintenance of exhibition flight proficiency.

I'm not sure if this aircraft has been used in that manner though.


How exactly should I understand the term "accidental hull loss"? How can the IATA claim that the year 2015 saw no accidental hull losses, if we had the Germanwings Flight 9525 accident? Even if this one is not considered "an accident" then there are a few others (for instance Metrojet Flight 9268) that can be clearly taken as "accidental hull losses".

How should I understand "accidental hull loss" exactly, or what is it that I am missing?

EDIT: While I agree, that I may be missing some certain points and the general definition given in IATA article and while I agree with all answers and comments given here, I think that on contrary Carson Air Flight 66 fits pretty perfectly into "accidental hull loss" definition. It is from 2015 and it is a bit interesting, why IATA "forgot" about it in their report?

Both the MetroJet and GermanWings incidents were deliberate acts of destruction, not accidents in any common understanding of the word, or indeed in the sense defined by the Convention on International Civil Aviation.

The Chicago Convention, as it's also known, defines an accident as:

  An occurrence associated with the operation of an aircraft [...] in which  [...] a person is fatally or seriously injured [...] except when the injuries are [...] inflicted by other persons.

My emphasis added - see Annexe 13 of the Convention for the full definition - it's quite dry but interesting, if you're interested in that kind of thing. The exceptions it lists are illuminating.

Deliberate acts and "incidents"

I do think that the definitions in the Annexe are slightly odd. You'd think that the deliberate destruction of an airliner in flight should be called an incident, but an incident is apparently:

  An occurrence, other than an accident, [affecting safety].

I guess that's one way of describing a bombing or deliberate crash into terrain... but then there's also a Serious incident which is merely:

  An incident involving circumstances indicating that an accident nearly occurred. [my emphasis again]

So that would make the GermanWings and MetroJet cases incidents, but not serious incidents!

However: since "Appendix 7" of the ICAO Accident/Incident Reporting Manual lists "types of incident", and deliberate acts of destruction are not amongst them, I can only deduce that they are classified as neither incidents nor accidents. I am not sure exactly what the official terminology is for them.


What causes the reduction in speed across the shockwave? Wherever I read about shock waves, it is mentioned that there is a reduction in speed across the shock wave.

Can someone please explain what happens at the molecular level, i.e. the physics of the problem?

If you look what causes the shock, there must be an obstruction at the root of it. See the sketch below for a straight and an oblique compression shock:

In case of the straight shock this can be a blunt body or an intake filled with slower moving air of higher pressure. In case of the oblique shock this is clearly the bend in the wall contour which forces the flow to change direction.

The index 1 denotes conditions ahead of the shock, and 2 those downstream of the shock. For weak straight shocks the product of the speed ahead of the shock $v_1$ and the speed past the shock $v_2$ equals the square of the speed of sound: $$v_1\cdot v_2 = a^2$$
If we call the local Mach number $Ma$, and if $Ma_1 > 1$, then $Ma_2$ must be smaller than 1, so the flow is always decelerated to subsonic speed by a straight shock. The same holds for the normal component of an oblique shock: It also becomes subsonic. Since the total energy of the gas doesn't change, its pressure, density and temperature rise when it is decelerated.

The incremental pressure change $\delta p$ due to the bend with an incremental angle of $\delta\vartheta$, expressed in terms of the undisturbed flow with the index $\infty$, is proportional to the change in the streamlines:
$$\delta p = -\frac{\rho_{\infty}\cdot v^2_{\infty}}{\sqrt{Ma^2_{\infty} - 1}}\cdot\delta\vartheta$$

Gas pressure on a molecular level is the number and severity of particle collisions. The air molecules experience more collisions on the downstream side of the shock, since air pressure is higher there. The average  direction of the additional collisions is indeed orthogonal to the shock, because it is the boundary between blissfully unaware molecules at ambient pressure ahead of the shock and their bruised brethren downstream which have just crossed that boundary. Once a molecule has passed the shock, the collisions are coming again equally from all sides and its speed does not change any more.

In subsonic speeds this pressure change can radiate in all directions and becomes a shallow pressure gradient. In supersonic speed, no information about the upcoming pressure change can travel forward, so the change is concentrated in the shock front.