What are the criteria that govern the choice between titanium, composites, and more common materials, like aluminum? In the newest large commercial jets, composite materials seem to be all the rage. The first thing I wanted to know is why composites were chosen instead of titanium? If I'm not mistaken, titanium has even more specific tensile strength.

Let's also be clear about what exactly composites are. "Composite" just means a mix of two or more materials, and in aerospace, it is predominantly autoclave-cured carbon-epoxy.

Ultimately, it would be good to understand the criteria that govern any choice among titanium, composites, and aluminum. Specifically, which areas of the plane are candidates for an advanced material? and why? What factors dictate the decision?

What are the criteria that govern the choice between titanium, composites, and more common materials, like aluminum?

Three main criteria: cost, strength-to-weight ratio, and fatigue resistance.

Cost. Of the three, aluminium used to be the clear winner, with composites having made large advances due to improved manufacturing processes. Titanium is the most expensive and is difficult to machine.
Strength-to-weight.

Buckling. Titanium alloys have higher strength-to-weight than aluminium (this answer, more on temperature below), but aluminium is lighter and that gives it an advantage in structures loaded with compression stresses: buckling resistance is a function of cross sectional dimension as well. For the wing upper surface aluminium would be lighter than titanium, despite the lower specific strength. Composites have the highest specific strength of all.
Temperature. The graph in the linked answer also shows the influence of temperature on the specific strength of materials: aluminium is first to drop, and at higher temps titanium is the best next choice, as from the comment by @PeterKämpf.

Fatigue resistance. Titanium alloys, like steel allows, have a fatigue endurance limit. If stresses remain below this limit, the construction can endure an endless number of cycles. Aluminium does not have an endurance limit, and will eventually fail even from small stress amplitude cycles: aluminium constructions require careful monitoring and maintenance for prevention of fatigue failure.

Composites do not have an endurance limit, but fibre orientation and material choice can improve fatigue life.

Image source


How much lift do supercritical airfoils produce? Compared to your regular asymmetric cambered airfoil, How much does lift do supercritical airfoils produce?

Supercritical airfoils produce comparably more lift than conventional cambered airfoils but less than optimised high-lift airfoils. This is because

they have blunter noses which work over a wider angle of attack range,
the blunt nose also allows to use effective slats or Krüger flaps,
they have plenty of camber in the aft section of the airfoil and
the high rear loading allows for thin, highly cambered flaps.

From history.nasa.gov:

  In the course of developing the wings for these flight programs, it was learned that the supercritical airfoils had excellent high lift characteristics because of their large leading-edge radii. This important benefit tended to offset the fact that their subcritical profile drag is higher than for comparable 6-series sections.

However, the forward part contributes relatively little to lift because it has negative camber. Also, the rear loading causes a high pitching moment.

In the supercritical speed region their upper side produces more suction since local speeds can reach up to Mach 1.3 while conventional airfoils must struggle to keep speeds subsonic. Part of that advantage is used up by making the airfoil thicker so suction on the lower side is also higher than on conventional airfoils, but an advantage remains. More recent airfoils add some more lift at the nose by designing a slow speed rise on the lower side while the upper side accelerates the local flow more quickly. Their main lift, however, comes from the thin, highly cambered aft section.

When R. Whitcomb researched supercritical airfoils, he noticed their high subsonic lift and modified the general shape by adding more forward camber into the GA(W)-1 and -2 (General Aviation Whitcomb) airfoils which became popular choices for modern GA aircraft due to their high lift and benign stall characteristics (witness 93 hits on Dave Lednicer's incomplete guide to airfoil usage, among them the Piper PA-38, the Glasair and the Edgley Optica).


What are the visual differences between the ATR42 and the ATR72? I tried to find the visual differences between the ATR42 and the ATR72. I downloaded some images from Google but I can't find any. Would you help me?

By Julien.scavini (Own work) [CC BY-SA 3.0], via Wikimedia Commons

The ATR72 is quite a bit longer than the ATR42, and has several more windows to allow for more passengers.

According to Wikipedia:

  The ATR 72 was developed from the ATR 42 in order to increase the maximum seating capacity (from 48 to 78) by stretching the fuselage by 4.5 metres (15 ft), increasing the wingspan, adding more powerful engines, and increasing fuel capacity by approximately 10 percent.

So it's longer, and has larger wingspan. The stronger engines and larger fuel tanks can't be seen from the outside.


How hazardous is it if an engine cowl falls off? There was recently an incident where the engine cowl of the starboard engine of a United Airline's Boeing 777 fell off during flight:

'Scariest Flight of My Life.' United Airlines Made an Emergency Landing After an Engine Cover Flew Off
Engine Cover Blows Off on United Airlines Flight
United Airlines passenger jet's engine cover rips apart over Pacific Ocean

All available articles seem to suggest it was 'sort' of an emergency and they did in fact do an emergency landing...

  A United Airlines flight from San Francisco to Honolulu made an
  emergency landing Tuesday after an engine cover reportedly flew off
  mid-flight.

... with people even asked to brace for impact:

  “They let us know that we had to brace for impact in case there was a
  rough landing,” she said.

It seems logical that the cowl coming off could be a sign of loss in structural integrity around the engine (also of the engine itself?).

Another issue could be ingestion of debris (especially near the engine inlet).

How hazardous is such a case of the engine cowl falling off?

Note: I do understand that a twin engine aircraft can continue flying after a single engine loss however due to the reduced performance an emergency landing would make sense.

I work in aero engine safety but not for the company that manufactured the engine in the event you mention.

Parts falling off engines is Not Good. We worry about them hitting people below the aircraft. And as Koyovis mentions, losing the nacelle or portions thereof (looks like in this case it was the intake and fan cowling) can change the aeroelastic properties, thus inducing vibration, which is not comfortable for the passengers or crew (reducing their ability to do their jobs) and adds additional loads to other engine parts.

It is not true as mins states that the cause or consequences are unknown. The regulatory authorities require manufacturers to submit a detailed (thousands of pages long) Failure mode, effects, and criticality analysis (FMECA) that covers every part of the engine, what could go wrong, what the consequences could be, and what we are doing to make sure it won't go wrong or that the effects are minimized if they do. While I don't work on that engine, I am confident that structural failure and release of the intake is in the FMECA.

In my professional judgement, in the scale of failures affecting engines defined by the FAA (catastrophic, hazardous, major, minor), this failure would be major, due to a large part falling off the aircraft able to hit a person below, the reduction in safety margins caused by increased vibration, and the damage to critical parts (fan blade) from debris ingestion as mentioned in one of the other answers.

Since the fan blade was seriously damaged, the pilots likely shut down the engine (otherwise the vibration would have been insanely high). But as you mention a single engine shut down is not considered hazardous - we design for that situation. Nevertheless many pilots choose to land after a single engine shutdown.


Is there standard ticket data format specification for commercial flight operators? I am new to this group and what brings me here is I am doing a research on ticketing solutions for commercial airlines. So I just wanted to find out if there's a international standard specification for data exchange between ticketing solutions and where can I find it (if it exists) ?

By specification I am referring to data fields and sizes that should be captured on a ticketing system like PNR, departure/destination, datetime & airport, ticket number & cost, no shows, etc

IATA does have a standard for Boarding Pass Bar Codes that outlines a lot of encoding information and other things. This holds so long as you are not showing up to a Cuban airport in your own plane. There are lots of numbers and codes on boarding passes that mean all kinds of things. Ticketing systems may contain even more information than the boarding pass its self and that is up to the implementation of the system. The effective minimum set of identifying information is likely to be (more or less):

Departure airport code
Arrival airport code
Departure time typically a local time although most aviation things run on Zulu time in practice.
Seat number
Flight number (code share possible)
Date of flight
Passenger Name
Record Locator (Some kind of ID for the information)


What does Top 1% mentioned by ATC refer to? I have watched Live ATC tons of time. But I still don't know which airline is called "Top 1%". Ex: Delta 81 right Bravo right Kilo give way to company A380 and follow the Top 1%".

Just wanna know what "Top 1%" means. Or that is only for JFK?

I'm guessing you're referring to a clip such as this one. JFK ground is just being a bit informal and fun (as you can tell from the rest of the clip) with their instructions. Although it isn't mentioned, the controller is probably referring to a business jet flight, such as ExecJet.

The "top 1%" refers to a ranking based on income, specifically those not in the lower 99%. The controller is basically telling them to follow the rich people in their fancy private jet. JustSid found another video where the controller explains it as "someone richer than both you and me."


What happens to a large plane after a successful gear-up landing? There are plenty of videos of non-fatal gear-up landings - even of airliners. I can find none that show the recovery of the aircraft after safe evacuation of crew and passengers and completion of safety procedures.

How is the runway cleared? Is the plane towed away (scraping along the ground)? Are there cranes available in large airports? Can a single crane lift and move a large airliner?
Is the plane considered a write-off or can some be repaired and continue in service? Where would such repairs take place?

This answer varies wildly depending on the size and type of aircraft involved, but in general:

How is the runway cleared?

They remove the aircraft, then sweep the runway for smaller debris and then inspect the tarmac to make sure the aircraft didn't gouge into it, and tear up chunks.

Is the plane towed away (scraping along the ground)?

No. The aircraft will usually be lifted and placed onto an oversized platform with either cranes or hydraulic  Jacks, and then towed. Dragging it along the tarmac would damage the tarmac (more so then the landing already did) and do further damage to the aircraft.

Are there cranes available in large airports?

Gear up landings (and catastrophic hard landings where the gear collapses) are so rare that no airport (that I'm aware of) has the heavy duty mobile cranes required standing by. It would cost way too much to maintain them and keep operators for them on the payroll when they'd just sit and rust for years and MAYBE be useful for 3 or 4 days. It is much cheaper to hire a crane and operator.

Can a single crane lift and move a large airliner?

Maybe; aircraft manufacturers will often publish manuals for how to recover and salvage the aircraft, and the crew removing the aircraft would refer to those.

Is the plane considered a write-off or can some be repaired and continue in service?

Not necessarily. This part varies depending on the age of the aircraft, how hard the landing was, and a million other factors, but the aircraft can usually be salvaged. The repairs could be astronomically expensive, and the work could take several months if not a year or more.

Where would such repairs take place?

This also depends. If the airline has a hanger at the airport where the plane is being salvaged from, the answer is simple. If not, that's when it gets tricky and expensive. Usually this means renting hangar space (which is SO much more expensive then any other commercial space) and either flying in your own mechanics or hiring a local crew. The necessary repairs and inspections would be done to get it to the point where it could safely fly back to an airport where the airline has the personnel and equipment to finish repairs.


Why is this F/A-18 flying through a hailstorm of sparkles? The F/A-18 Super Hornet squadron VF-102 Diamondbacks, flying from the USS Ronald Reagan, has posted a montage video of its 2019 Indo-China cruise.
At about 5:15, the video shows a night-time cockpit view of the aircraft flying through a shower of sparks. There is also the view looking backwards. It's like a sci-fi special-effect.

What would cause this phenomenon?

source - YouTube

The sparks in the video come from the F-18's Vulcan cannon being fired at night.
During daytime you'd only see muzzle flash accompanied by a pretty puff of smoke. Low light conditions bring out the sparks, or rather, residual gunpowder still burning (or glowing) as it exits the barrel.


Do any airlines have Braille emergency checklists? In reading the report into the crash of UPS Flight 6, I noticed that one of the items of feedback from pilots in a simulated inflight-fire scenario utilising a smoke-filled simulator was (page 287 of the report):

  In the thickest smoke, only Braille will help. What bigger font does to you, if there is any "break" in the smoke, it allows you to see more letters (group), therefore part of words. From that you can deduct what the action on the checklist is for the next step.

(Emphasis added.)

Which makes sense, as Braille, unlike most scripts, is read by touch rather than by sight, and is, thus, unaffected by limited or nonexistent cockpit visibility, while visual scripts, even with large, simple glyphs, have their legibility severely impaired by a smoky cockpit (in dense smoke, the pilot(s) essentially have to wait to do anything until the smoke momentarily lifts), and are completely useless in a zero-visibility environment.

With this in mind, do any airlines (passenger and/or cargo) have Braille checklists for use in situations of severely degraded cockpit visibility (such as a cockpit filled to the brim with dense black smoke)?

It would be counter productive

It takes time to learn (especially touch reading)
It takes time to keep proficient

This is time spent on a skill useless for >99,999999% of flights

This is time NOT spent on more useful safety trainings

This wouldn't work anyway

It would be very slow to find the correct checklist then read it
If the aircraft is shaking, it would hinder your speed/prevent your from reading
You have to take your hands of from other controls to read

There is better alternatives

Simply having a recording/speech synthesis/speech command would solve it.

  This is time NOT spent on more useful safety trainings

This one is a killer


Why do jet generators produce a higher frequency power then household electricity? I know in most homes your local transformer provides a 50Hz or 60Hz power source. So all your hairdryers, dishwashers etc. are built to consume 50Hz or 60Hz power at 110 volts or 220 volts, depending on where you live in the world.  On the aircraft engine generators use a much higher frequency (400Hz). Why is this?

This is a bit speculative, and if I am wrong, I will stand corrected.

Based on my little experience with power plant gas turbines, the frequency depends on the rpm of the turbine and the number of poles of the generator. A power plant turbine runs at 3000 rpm (for 50 Hz) or 3600 rpm (for 60 Hz), with two poles (this is the most reliable design, and works with turbines with rotors up to about 4 m diameter.

An aircraft APU is much smaller, and will run at higher for optimized power output. So, for the 400 Hz, you would have, for example, 12000 rpm and 4 poles (or 24000 rpm and 2 poles).

It already has been mentioned that transformers can be way smaller and lighter for higher frequencies, and it may also be that the higher freqencies of the harmonics cause less interference with other systems of the aircraft.

The speed of the generator is held constant, regardless of the engine's rpm, by the use of a Constant Speed Generator or Integrated Drive Generator.


What does Ryanair do without Sick Bags? Sorry for the slightly strange question, but Ryanair (Europe's Largest Low Cost Carrier) decided that seat back pockets took too much effort and got rid of them, and it appears the sick bags in the process.

(source: poloconghaile.com)
So the question comes up...
What happens when Ryanair flights encounter turbulence? I can hardly imagine the Flight Attendants handing out bags ad-hoc when it's sufficiently shaky to cause motion sickness among the passengers.

Well how many people get airsick during each flight and how many of those really vomit? And of those, how many actually use the provided sick bags? I'm not familiar with getting air sick but I'm sure there are not a lot people really using these bags. There is also no legal requirement for having sick bags. It is an item for 'additional passenger comfort'. Ryanair probably thought this way and so they saved some more money.

They also don't hand out sick bags when they are encountering chops but I'm sure they will have one for you if you ask them.


What is the average time and distance needed to reach cruising height? I am trying to compare trains with airplanes and the distances where taking a train is more viable than an airplane. I guess this would depend on the type of plane, but the Airbus 320 seems like a common enough plane in Europe so I have something along that type in mind.

As far as I know, it would be a good model for airplanes to separate the takeoff and landing phase, where they cover less ground and does take appreciable time on shorter hauls and the cruising phase. I found average speed for the latter but I don't know how much time takeoff takes and how much ground the aircraft can cover during this. Same goes for landing, so my question is, how much time do these take and how far does the aircraft get during these?

I'm also assuming that when looking at city center to city center travel times, taking a plane has about a three hour overhead (airports are far and it takes quite a long time to get in, security check and all), but if anybody actually knows some statistics on this I'd be much obliged :)

I answer directly to the title of the question:

  What is the average time and distance needed to reach cruising height?

The Takeoff takes very little time, but the climb phase depends on the cruise flight level clearance. Assuming you climb with a vario of 2000ft/min with an average IAS of 200kts. The time to reach the cruise level is equal to:

(Cruise level in ft - takeoff terrain elevation if ft)/2000, the result is in minutes.

So if the departure is at sea level and the cruise altitude is at 30000ft, the climb phase will take : 30000/2000=15min

The descent till arrival could be more complicated because in addition to the pure descent you have to level before intercepting the approach phase which occurs relatively at lower speed. If you are lucky, not having to hold above the airport, the total descent might take 20 to 30 minutes

Routes are not necessarily straight lines, nevertheless you may assume an average cruise True speed of 500 knots.


What is the aircraft in the 'Be Altitude' album cover? In 1972, the Staple Singers released the "Be Altitude" album, which has them posing in a jet engine's intake.

My question is what aircraft does that engine belong to? And why would someone let them use it for a photo shoot?

Its a Boeing 747 courtesy of Delta Airlines as per the album credits. Photo by Gerry Griffith. For the right amount of money its not that hard to take pictures in, on, or near jets.


Did commercial airliners have microwave ovens in the past? So I went on 2 long (total of 16 hours) flights with a major US airline, and they did not provide a free in-flight lunch (grr) during either flight. I had brought a sandwich with me just in case, but when I asked the flight attendant if they could heat it up they said that they did not have microwaves. This was I think a 757 or similar aircraft.

When I landed I was asked about my trip, the microwave thing came up and was told (by an older person) that airlines did have microwaves and that mothers with children would often ask the flight attendants to warm up bottles of milk for them...?!

So now I'm curious, did aircraft used to have microwaves in the past? Were they removed? I now know the food they serve on airplanes is "heated via hot air ovens" but why would there not be a microwave on board? Even if just for crew use?

Generally speaking, airliners do not have microwave ovens for safety reasons. I could not find any reference where commercial airplanes used to have microwaves. Probably some smaller business jets have them.

Some flight attendants mention that they can warm your food, but some say that they will not for legal and health reason.

As also mentioned by sweber in comments to the question, meals are not heated at the airport. Airline catering companies like LSG Sky Chefs prepare the meal near the airport and deliver it to the airplane. Inside the airplane, they use convection ovens to heat it.


Reasons for significantly lower than normal approach Not sure if this is going to be answerable to be honest, as I'm sort of asking for a bit of retroactive mind-reading! But here goes anyway!

I was driving along Clifton Drive North, Lytham Saint Annes, England on 17/11/18 (~3:30 pm if that matters) and I saw a plane approaching the adjacent Blackpool Airport at an exceptionally low altitude (not sure on model but looked like it might have been a Cessna 400-series). It's always hard to estimate altitude accurately (particularly given I was also driving at the time) but somewhere in the order of 200-300ft at the point it crossed over the road and descending (suffice it to say I was at least half expecting a crash!)

It was highly unusual - I've lived in the area for 5+ years, and travel that road frequently (typically at least 1-2 times a day and have been using the airport for even longer) and I've never seen a plane take that approach before. Here's the aerodrome chart for BPL:

Pretty much every plane I've ever been on (either flying or being flown) has approached and landed on runway 28 - even when coming from the west (e.g. coming from IOM) the approach has always been from the SW, bearing around 50° and then turning right to about 270-280° before descending to runway 28 to land.

As far as my limited knowledge allows I believe standard altitude for approach to BPL for this is 2000ft and there is not a cat in hell's chance that this plane was anywhere near that!

I think it is possible to land on runway 10 - but that the approach path for doing that is to be coming in from the east at 1600ft bearing 256-281° and flying over before turning right to 92° and descending. The OCA for this path is 450-1000 depending on aircraft category, it's distinctly possible that the plane was at 450 (as I mention above my altitude as estimate was based off Mk 1 eyeball from a moving car so unlikely to be especially accurate!) but curiously I'm 95% certain that the aircraft didn't pass over coming from the east, I had been on the road for a good few minutes and there's nothing that would have obscured my view of them doing so - and I must admit I'd been watching the sky quite closely as I'd spent a large amount of the drive musing that conditions were fantastic and wishing I'd booked myself a lesson for that afternoon!

The plot thickens in that probably less than a minute after the plane passed over a helicopter (reasonably large - probably a offshore-rig transport) flew over on roughly the same path, but if anything even lower!

So I was wondering whether there was some circumstance causing ATC to advise a different approach from typical and what that might be?

As I mention above conditions were fantastic wind was very slight (unusually so for Blackpool at this time of year!), visibility was great  - sunny with light hazy cloud that was well above (would probably have said 10,000-12,000ft +). Could operations at WRT (~6 NMi to the SSE) have had an influence?

The winds were coming from dead East 090°: See METAR, at >15kts. This strongly favours a landing on runway 10. The predominant winds in Blackpool are from the West, which may be why this is unusual to you.

The approach you mention is just one of the possibilities. The charts also give the option to approach directly from the West. Outside of the published approaches, one could imagine that ATC vectored the Cessna in on a quicker path to beat the incoming helicopter.


How are airspace violations detected? Are airspace violations (e.g. entry to class B without clearance) based on primary radar and/or Mode C transponder, or something else?

I read that Mode C altitude is based on pressure altitude, i.e., set to 29.92" ... but presumably that's adjusted at the ATC facility based on the current pressure before being used for altitude enforcement.

This begs the question, what would stop one (hypothetically), just winding back the altimeter pressure reading to appear to be at a lower altitude?

So to summarize: How are airspace violations detected:

What data input is used?
If Mode C reading is used, is it based
on pilot's altimeter?
Would winding back the altimeter make a
plane report a lower altitude?

The transponder usually uses its own pressure reading, not what is set in the pilot's altimeter. So to prevent cheating as you describe, it is inspected and calibrated every 24 months. Tampering with it would be difficult to do on the fly because you'd have to adjust it based on the current atmospheric conditions and what altitude you want to seem to fly at. But yes, you could, in theory, adjust its readings to broadcast something different.

As far as I'm aware, only major violations are really pursued, or if ATC knows who you are when you commit the violation.


Airplane generations - how does it work? I was reading about Atlas B763 that was involved in an accident on Feb 23rd, 2019. Based on what I read plane was 25 years or so old.

As a person who has no relationship about aviation industry except occasional flying as a passenger, I'm curious to find out if these planes also have generations or models like car manufacturers do e.g. Honda civic, 2015, 2016 or 2017 models where there are small but distinct changes.

Based on Wikipedia pictures, cockpit photos are different for various generations as technology is improving/changing.

Are pilots rated on particular generation of the plane or once you are rated on B763, you can fly any one of them whether it was built 25 years back or yesterday?

While airliners don't have "model years" like cars do, they are certainly changed over time.

There are major "generations" of some aircraft types, like the 737. The "original" (-100,-200) was replaced by the "Classic" (-300,-400,-500) which was replaced by the "Next Generation" (-600,-700,-800,-900) and most recently replaced by the "MAX" (-7,-8,-9,-10). While technically still the same aircraft type, there can be major differences between them, especially from the pilot's perspective.

The 767 hasn't had any major "generations," but it has had multiple models, as is common with airliners. These are mostly just adjustments to fuselage length, fuel tanks, and structures. Other than small changes to systems, or different guidance to prevent a longer fuselage from stiking the ground on takeoff or landing, there is minimal training required. The 767 cockpit was even designed to be common with the 757 to minimize required training.

The FAA requires pilots to get a specific "type rating" to fly any aircraft over 12,500 lb max takeoff weight. The scope of this rating is negotiated between the manufacturer and regulator like the FAA. This could change with new versions, as with the 747-400, or even be common, as with the 757 and 767. There may also be training for each minor model, though not as in-depth as a new type certificate.

There are also changes made within the minor models over time. The biggest changes would probably be things such as modifying the winglets or adjusting the engine installation to get better performance, or a new cabin interior design. There are also many smaller changes that occur throughout the airplane. There isn't really a regular schedule for these like in the car industry, as there's less turnover in the aircraft market and major changes can be very expensive to certify. There would have to be a significant benefit to make a change requiring new pilot training, which is why those changes tend to happen in the more major "generations."


What does " X miles in trail, runway 25R cleared to land" mean? I was listening to the LiveATC Phoenix North Tower feed as he was clearing aircraft to land. He said something like "Southwest fifteen sixty five, Phoenix Tower, (aircraft type), X miles in trail, runway 25R, cleared to land".

What does the "(aircraft type) X miles in trail" portion mean?

Is the controller pointing out the aircraft behind the aircraft that is being given the landing clearance? If yes, why would the aircraft in front care?

The controller's telling Southwest 1565 it's cleared to land (otherwise they would use the other aircraft's identification), and by the way there is an airplane of a certain type coming up behind and to take that into consideration in the event that Southwest 1565 was thinking of spending too much time on the runway after landing instead of promptly getting out of the way.

That kind of comment added to the landing clearance suggests that the airplane behind is a little closer than usual, or is going significantly faster, or it's just really busy with airplanes spaced at minimum separation, and Southwest should expedite clearing the runway.


Was it possible to land a Boeing 707 with 300 feet cloud ceiling in the 70s? In the movie Airplane! (1980), the main characters had to land a Boeing 707 in Chicago airport in low visibility. The dialog says the pilot "should be able to see the runway at 300 feet".

Given the ground equipment and flight instruments of that era, is it possible to land a Boeing 707 in such condition? For example, did they have ILS? Or did they at least have VOR-DME approach that would allow the pilot to adjust the descend rate?

ILS approaches were in common use in 1970 when I got my instrument rating. The normal (Cat I) ceiling minimum was 200 feet. So, yes, a 707 would have been able to land with a 300 foot cloud ceiling in the 70s.

I checked Wikipedia and and found the history paragraph below:

  Tests of the ILS system began in 1929 in the United States.[14] A basic system, fully operative, was introduced in 1932 at at Berlin-Tempelhof Central Airport (Germany) named LFF or "Lorenz beam" due its inventor, the C. Lorenz AG company. The Civil Aeronautics Administration (CAA) authorized installation of the system in 1941 at six locations. The first landing of a scheduled U.S. passenger airliner using ILS was on January 26, 1938, when a Pennsylvania Central Airlines Boeing 247D flew from Washington, D.C., to Pittsburgh, Pennsylvania, and landed in a snowstorm using only the Instrument Landing System.[15] The first fully automatic landing using ILS occurred in March 1964 at Bedford Airport in UK.[16]

The CAA referred to in the quote was the forerunner of the U.S. FAA.


Can a commercial airplane overtake another airplane going in the same direction? If there are two commercial airplane flying towards the same destination, on the same flight path, and the second plane is being faster than the first plane, is the second plane allowed to overtake the first airplane?

If so, how close are two planes allowed to fly while overtaking each other?

Faster aircraft often overtake slower on the same routing. This is usually accomplished by flying at higher or lower altitudes. This is called vertical separation. They can also be separated laterally by radar vectors so that they are 3-5 nautical miles apart. The exact distance will depend on the ATC standards for the particular airspace.

Often as they approach the destination ATC will ask one aircraft to speed up and one to slow down slightly. This can sometimes allow the faster aircraft to pass the slower aircraft, but it also insures they have the required separation when they are on approach to land.


What do the pilots do if the plane they are operating does not have an anti-ice system? Anti-icing equipment is designed to prevent the formation of ice, while deicing equipment is designed to remove ice once it has formed. These systems protect the leading edge of wing and tail surfaces, pitot and static port openings, fuel tank vents, stall warning devices, windshields, and propeller blades.

.What if the plane does not not have any anti - ice systems
Here is my research about one type of plane that does not have an anti - ice system and what do the pilots do to deice the plane.

A Cessna 172 has no anti icing system, as long as I remember a electrical pitot heater for preventing freezing over the pitot tube and a carb heater for preventing formation of ice in carburetor are the only two ways to prevent ice from forming; for that the C172 cannot fly in icy conditions.

I have researched about this topic and I am still looking forward to learn from the users who answer my question.

If an aircraft is not equipped with anti-ice or de-icing systems, than the answer is simple: You don't fly into icing conditions. This is usually listed as an operating limitation in the POH/AFM/FCOM of the respective aircraft. For a Cessna 172, you can e.g. find:

KINDS OF OPERATIONS LIMITS
The Cessna 172S Nav III airplane is approved for day and night, VFR
and IFR operations. Flight into known icing conditions is prohibited.

(C172 POH, Section 2 Operating Limitations)
If you are approaching icing conditions, there are usually two options to avoid flying into icing conditions:

Reduce the altitude: The temperature is higher at lower altitudes. If you can reduce your altitude enough to raise the temperature above 10°C, you are out of icing conditions.

Change course: If you see a cloud ahead and the temperature is below 10°C, you cannot enter the cloud because that would mean you enter icing conditions. You can however deviate from your current course and fly around the cloud.


Derivation of the Takeoff equation I am trying to understand the derivation of some simple equations to calculate the neccecary takeoff speed for an airplane (under ideal conditions).

Which is taken from 15. Takeoff and Landing. My main issue is the derivation of the horizontal equation

To get from the first to the second line my guess is that we use

R = W - L   and    m = W / g

My main problem is understanding the details between what happens from line 2-3 and 3-4. I would love if someone could give me a brief explenation of the symbols used, what does S denote?

We want to reduce (or simplify) equation 2, to get get dV/dt by itself, so we multiply both sides by g/W.  On the right hand side, this reduces to dV/dt.
On the left hand side it reduces to what is given in equation 3, but let me show you how:
 1. First term is T x g/W
 2. Second term is -D x g/W
 3. Third term is -u x g/W (W - L).  By the distributive property, we have -[u x g/W x W] + [u g/W x L]. The first part of this term simplifies to u x g.

Finally, I want to group like terms together.

The first term combined with the first part of the third term give me: T x g/W - ug = g(T/w - u).
The second term combined with the second part of the third term give me: -D x g/W + u g/W L = g/W(u L - D).

This yields equation 3: g(T/w - u) + g/W(u L - D) = dV/dt.

Finally, recall that L = 1/2 p S V2 Cl, with a similar equation for Drag, and we can substitute these directly into L and D to get equation 4.

S is the the wing planform area. Other sources use A, like this one: NASA - Lift equation.


How did the Brazilian Civil Aviation Authority have MCAS on paper from Jan 2018? how could they know but nobody else did? Did they buy the extra sensor or something?

Of course the airlines knew about MCAS.  Do you think the maintenance manuals, maintenance program documents, tech training, wiring diagrams, and all that stuff was left out so it was totally top secret?  There would be a controller, wiring and software on board even though there were no cockpit indications or controls, so certainly the techs who might have to troubleshoot it, and others on the tech/engineering side, would know.

All that happened was MCAS was excluded from differences training, as that document shows, so that it was not included in the ground school differences course pilots took when moving from one 737 model to another (avoiding sim time, which was the point).

So pilots never got a formal briefing on its existence, and it could just be considered part of the "PFM" of the various black box systems who's level of function is too in-depth to be included in pilot training (PFM means "Pure F-ing Magic" and is a term instructors use to describe black box function that is beyond the training because covering it would extend the course to months).

I have little doubt there were pilots, those who dig into the aircraft more deeply than most and might even peruse maintenance manual descriptions, who would have known of the system, but just not on an official level, with official procedures and protocols that affected the flight crew.

Sort of like the subsystem that applies the brakes after you lift off to spin the wheels down right away. It just does its thing in the background, and pilots may or may not be aware of it, but everybody on the technical side does.


How is a fuselage 'puncture' repaired? Operator on phone, GoAir plane hits aerobridge

How is such a 'puncture' repaired? Is the cabin pressurization also affected by such a puncture, and approximately what is the cost incurred to repair such a puncture?

The first step for repairing damage to a fuselage skin panel is to cut out the damaged area1. Cracks tend to propagate, so an area much larger than the damage will be removed to ensure that all damaged material is removed. The stiffeners that are behind the fasteners will need to be inspected for damage as well.

A filler plate will be cut to fill the hole in the skin. One or more doubler plates larger than the removed area will then be cut and all plates will be riveted together. The doublers will possibly be on both sides or at least thicker than the surrounding skin. See here for some examples.

It's likely that a larger repair such as this one will need to be inspected regularly to ensure that the repair holds strength.

It's hard to tell where exactly this damage is located, most of the aircraft skin is part of the pressure vessel. However, the airplane is not completely airtight, so a certain amount of leakage is normal. A hole of this size will probably not prevent the fuselage from pressurizing, though larger ones will.

The cost will depend on the extent of the repair, but could be from \$5,000-\$15,000 (300,000-1,000,000 INR) based on this estimate.

1Actually, the first step in repairing damage to an airplane is consulting the structural repair manual (SRM). This is provided by the manufacturer and describes general methods for repairing minor and typical damage to airplane structure. If the damage is beyond the allowances in the SRM, the manufacturer will be consulted. All of this is to ensure that the repair will meet or exceed the strength and life of the original structure, or if this is not feasible, that the limitations of the repair are documented and understood. Major repairs will require extra inspections to ensure that the structure is still in good shape. Aircraft skin will not be welded, since this can cause heat damage to the metal, requires careful skill and care to do properly, and will not hold up well to fatigue.


What are accurate flight simulation models called? Is there a standard model? I'm risking a question that might be "opinion based", but I hope it will not be seen as that.

This question is touched upon in the following questions:

What are the differences between PC and professional simulators?

Is this opinion on personal computer flight simulators too strict or is it actually true?

What are the limitations of the aerodynamics modelling used in flight simulators?

However, they fail to answer what I'm asking here, even if some particular things are discussed, such as stating that the coefficients are a mixture of CFD, wind tunnel data and flight test data, or that gust loads can be modeled with Markov matrices. However, no flight model package or system is named that I could see.

For racing simulators, or car simulators, simulators that are accurate are sometimes referred to as Milliken & Pacejka or "Pacejka-like", depending on the particular implementation. This appears to be a reference model that many simulators are compared against. I'm not a tyre simulator expert, so forgive me if I just said something that is stupid.

What about flight simulation? The flight model part of the simulator, is there a "gold standard", that is typically used with most respectable simulators?

Flight simulator games often talk about the "flight model" and describe it as accurate. While I can easily imagine that this flight model is based on some simplification of Navier-stokes,

I have software background myself, and although I didn't write a flight simulator myself yet, I understand the need to simplify, and that no simulation will ever be 100% accurate. All models will inherently have various trade-offs and make some sort of sacrifices. However, that doesn't mean there isn't a relatively accepted way of performing such simulation.

I'm not asking for an opinion based answer, "this model is the best". I'm certainly not asking for a list of "the best" flight simulators. I'm curious what underlying flight model is used -- that said, I wouldn't mind one or two examples of "this famous model described in the following academic paper, is used in flight simulator X and Y".

Basically, I'm simply curious if, in the industry, a typical model or small set (a couple) of models are considered either the actual "gold standard" or more of a de facto standard.

If there is no such thing, that pretty much every flight simulator does it differently, then I'll accept that as an answer. If there is a small set of terms that everyone in the industry is familiar with, I'd love to know then. It would let me easily search up papers that describe these systems.

I'll also accept an answer that lists an overview paper on the challenges of accurate flight simulation on modern computer systems.

14 CFR Part 60 regulates what constitutes a Flight Simulator Training Device (FSTD) for a particular aircraft model. FSTD is divided into two broad categories: Full Flight Simulators (FFS) and Flight Training Devices (FTD). A big difference between the two categories is FFS requires having motion cues, whereas motion cue is optional on FTD. Furthermore, the required accuracy of simulated flight dynamics (compared to flight test results) is much more stringent for FFS than is for FTD.

Each FFS and FTD is further divided into qualification levels (Level A to D for FFS, Level 4 to 6 for fixed-wing FTD). The higher the level, the more fidelity the simulator has to the actual aircraft. You may only get credit for Part 61 if you get training on the simulators with the appropriate levels for the systems/flight phases you are working with.

The simulator manufacturer must submit a Qualification Test Guide to the FAA to demonstrate that the simulator is good enough on aerodynamic model, flight deck, visual system, motion cue, sound system for the appropriate level.

Anyone can make a flight simulator, to any arbitrary level of fidelity; but making a flight simulator good enough for the FAA is hard and expensive. Read this for a more in-depth but lay-man explanation of the different qualification levels.


How much of an improvement would a 1% weight decrease on an airplane be to the industry? Say I thought of a very easy and inexpensive way to reduce the takeoff weight of a commercial airplane (body, fuel and passengers) by 1%. How much would this mean to the industry? Would it make much of a difference, or would the savings be insignificant enough to not really be worth anyone's time?

There is an easy way to get an idea of what magnitude the savings are: The Breguet equation can answer this. You first calculate a reference aircraft and then start all over with one that weighs 1% less. The difference in fuel consumption shows how much fuel is saved per flight.

Our reference design is the A320 which has an L/D of 18 and we let it fly a trip of R = 2,500,000 m. $m_1$ is take-off mass and $m_2$ landing mass. Allow for 3 t of fuel reserves and plug that into the Breguet equation, using a fuel burn of $b_f$ = 0.000018 kg/Ns and a speed of Mach 0.78, which equates to $v$ = 262 m/s in 11,000 m altitude:
$$m_1 = m_2 \cdot e^{\frac{R\cdot g\cdot b_f}{v\cdot L/D}}$$
The landing mass $m_2$ is the operational empty mass OEW + 18 t payload + 3 t of fuel reserves = 63.6 t. The take-off mass $m_1$ is 10% higher, so the difference in fuel consumption is 1% of that trip fuel of 6,239 kg or 62 kg. That is not much for a single trip.

But now consider that this one A320 will fly 50,000 trips before it retires. Over its lifetime the 1% in mass reduction will save 3,119 metric tons of fuel. This fills 29.4 DOT-111 railway tank cars!

And there are about 12,000 airliners of 150 seats and more and easily twice that number if all regional jets are included, flying 3.8 billion passengers and 53 million tons of freight per year on 35.4 million flights. If we make the heroic assumption that our A320 flight is typical, this translates into global fuel savings of about 2.2 million tons of fuel per year if only 1% of mass could be saved on every airplane.

Another way to approach this is the average fuel efficiency of modern airliners which consume between 3 and 3.5 liters of fuel per 100 passenger kilometers. Using ICAO's number of 6.6 trillion passenger kilometers in 2015, this would equate to 174 million tons of aviation fuel used per year for revenue passenger transport, assuming a mean density of kerosene of 0.81 kg/l. The same source gives an average load factor of 80%, so one fifth of seats is empty; the efficiency number above is for a full airplane, however. Therefore, our estimate needs to be increased to 217 million tons.

Saving only 1% of this would reduce fuel consumption by 2.17 million tons per year, which comes pretty close to the first estimate. This is enough to fill more than 41 Panamax oil tankers (the maximum size for the old Panama canal) or 18 Neopanamax oil tankers.

Or, to look at this from a different angle, with the current price of kerosene of 1.76 USD per gallon, the saved fuel equates to 1.25 billion USD if everyone paid US prices for Jet A-1 fuel. Compared to the average net profit of all airlines per year between 2007 and 2017, which amounts to 13 billion USD, this is almost 10% of yearly profits.

Now this doesn’t look so insignificant any more, does it?


What was Korean Air 672 doing at the time of Malaysia Air 370's disappearance? In the first part of this YouTube video, you can see an aircraft supposedly flying 4x faster than the surrounding aircraft, at the time the Malaysian 777 went missing.

After replaying this on Flight Radar 24, KAL672 departs Kuala Lumpa a short while before MAS370. It then does a 180, flies back towards the airport, then appears to do another 180 and rockets across the ocean:

Here are the playback links for 2014-03-07 16:55: KAL672 and MAS370.

Essentially, my question is, what is this oddity that FR24 is showing? (to ward off conspiracy theorist nuts).

With the way in which it suddenly switched back and forth it appears to be either a software glitch or bad data from one of the feeders.

All aircraft displayed in yellow on FlightRadar24 are detected by volunteers with their own ADS-B receivers, of varying quality in hardware, software and range. When aircraft reach the very edge of someone's receiver range you can occasionally get corrupted data, perhaps showing the aircraft somewhere back along its path or far off it.

Another scenario is when a receiver is having trouble uploading its data to the FR24 servers because of a bad internet connection or similar, so position updates arrive later than they should.

Sometimes the FR24 servers get conflicting info, for the same reason, where one ADS-B feeder is providing good data and the other bad. When that happens you can see the plane seem to jump backwards and forwards until one of the receivers is out of range.

It's something I've seen fairly often, even with my own receivers. FR24 does try to filter the anomalies out but it's a difficult task.


Can we show through simple geometry rather than formulae or graphs that the best glide ratio occurs at the maximum ratio of Lift to Drag? For an unpowered glider, can we show through simple geometry involving force vector diagrams, rather than mathematical formulae or graphs, that the best still-air glide ratio is achieved at the angle-of-attack that gives the maximum ratio of Lift to Drag?

Let's start with a Lift/Drag/Weight diagram, and draw the velocity vector as well:

Since no thrust is involved, Lift+Weight+Drag must sum to zero. Let's shift the origin of these vectors around a bit:

Now, let's finish the velocity triangle, drawing a (horizontal distance), and b (vertical distance). The ratio between a and b is by definition the glide ratio.

The key idea here is to notice that the triangles L-W-D and V-a-b are similar, that is, they are the same triangle up to a scale.
The similitude goes: W <-> v, D <-> b, L <-> a.
This means that the ratio between a and b is the same as the ratio between L and D. The latter is of course the Lift-To-Drag ratio.
So, in any condition, the glide ratio is the same as the Lift-To-Drag ratio.
It then follows that the best glide ratio is achieved for the best Lift-To-Drag ratio.


How does fuel efficiency depend on wing configuration? Which of the following wing configurations is the most fuel-efficient?

The largest losses on a wing usually occur at the tip, where high pressure air flows around the end from the underside to the top side. This can be minimised by making the wing longer and thinner, or tapering it so the tip is smaller. You can also add winglets to reduce tip losses, but they're tricky to get right.

If you fly near the speed of sound, you get shockwaves that cause a lot of extra drag. You can slightly raise the point where they become a problem by sweeping the wing, and wing sweep also helps to reduce the drag when you are supersonic - but supersonic is never an efficient choice.

Drag is proportional to speed squared, so if you just want to fly for as long as possible, it's most efficient to fly slowly. However if you want to cover distance it's more efficient to fly really high where the air is thin.

You can put all this together to get an airliner, with a long, thin, highly tapered wing (and winglets), flying so high that the air is only just dense enough to support it, and just below the speed that shockwaves cause extra drag.

You ask about wing position, and there is some interference drag where two surfaces meet. It is minimised by making the angle between the two surfaces as large as possible. Thus a mid-wing is slightly more efficient than other designs, but it's a relatively small effect. Wing position is usually determined by the undercarriage design and the pilot's field of view.


What is the technical name for the “time boxes” on an instrument approach plate? Some instrument approach plates include a list of groundspeeds and times from the FAF to the MAP. What is the real name for these time boxes?

Per the FAA Aeronautical Chart User’s Guide for Terminal Procedure Publications, in the revision effective 29 March 2018 on pages 30 and 31, it is a Time/Distance Table.

  Time/Distance Table

  When applicable, a Time/Distance Table is provided below the airport sketch. The table provides the distance and time
  that is required from the final approach fix to the missed approach point for select groundspeeds.


Why don't most military transports use modern commercial engines? Why don't most military transports use modern commercial engines?

More specifically planes like C-17, the Antonov's use older less powerful engines while modern efficient and powerful engines are available in the commercial sector.

Some do; the C-17 you mention uses the Pratt & Whitney PW2000 which is also used on the Boeing 757. The USAF and USN also fly the C-40 which is the military variant of the 737 and carries the same engines.

Generally the answer is that military aircraft are built on spec for the military which is a bit different than the way the civilian market works. Civilian builders shop a design around to airlines to get some deposits then build the airframes (the notable exception being the 747 which was largely the idea of Pan-Am CEO Juan Trippe). This often causes there to be new aircraft every few years on the civilian side as Boeing needs to stay in business... On the contrary the military will put out a request for designs to meet their needs, evaluate the submissions and chose what is to be built. They can do this as often or as little as they so please (or as budget allows). If there is no active conflict or need for new tech then the military will keep flying what they have. Many military aircraft have cutting edge tech from the era they were designed in, they may however be dated by todays standards.

Much like the FAA here in the US the various military branches have their own certification programs and regulations thus upgrading and bringing in new gear may require something to be approved this can unfortunately stifle new technology being included due to high time and cost of approval. Similarly military requirements may be different, while a civilian airframe may suffice they may have takeoff length requirements or something similar that necessitate more thrust than their civilian counterpart thus variances in outfitting may occur.


Can you breathe with a drop down mask under water? Say a passenger jet lands in the ocean. Could the captain being the last person to get off the jet use the drop down dry chemical oxygen generators to breathe while checking for passengers? I know they are flimsier so depending on depth they would collapse.

No, you cannot - at least not with the default masks.

In principle, the oxygen systems on board can all provide at least 15 mins. of oxygen, in some of the worst conditions (indeed, that's what they're designed to do). However, their sole purpose is to make high altitude air breathable. The key principle here is partial pressure. Basically, the partial pressure of a gas is the fraction of a certain gas in a gas mixture times the ambient pressure. Since normal air consists of about 21% oxygen, the partial pressure of oxygen at sea level is 0.21 atm (atmosphere). If the partial pressure of oxygen is too low, your lungs actually lose oxygen to the atmosphere when you breathe - much like a deflating balloon.

When the cabin pressure drops, the partial pressure of oxygen drops proportionally. In that case, oxygen masks are provided. They do not raise the pressure of the air you breathe in, but raise the partial pressure of oxygen by filling your mask with oxygen. If the cabin pressure would drop to 0.2 atm, and you would be given 100% oxygen, the partial pressure of oxygen would be 0.2atm, which is about the same as at sea level - perfectly survivable. The mask as such does not need to be airtight - it just needs to make sure that there's enough oxygen flowing into your mask to displace all the useless nitrogen in the air. Indeed, the mask you will see on airplanes are generally flimsy, plastic masks.

Under water, these masks are not sufficient at all. They will probably turn into a frothy, bubbly mess of a water/oxygen mixture, especially when the aircraft is filling up with water, due to strong currents. So, you would have to wait for the currents to diminish, and then hold your oxygen mask in such a way that no water will enter it - this probably means you will have to face upwards all the time.

Of course, you can get creative (pull the mask of and breathe from the tube), or luck out with a high quality mask that happens to work underwater. But I'm afraid that as soon as your plane is sinking, it's too late to play the hero, and your best bet would be to get out and at least save your own life.


What is the make and model of this plane? I came across this picture taken in the late 1920s. Could you please help identify the make and model of this plane. Thanks.

That info helped. Looks like a Travel Air 2000, but without the prop spinner.


What are a few main differences between ATC interactions for rotorcraft vs fixed-wing? The title says it all. In particular, I'm wondering what the differences are in reference to:

Takeoffs and landing - can rotorcraft be cleared to take-off / land directly from / to the helipad?
When rotorcraft want to head VFR to a location, are they treated like normal fixed wing aircraft (e.g. given an altitude and / or heading restriction)?
In fixed-wing IFR, aircraft are sometimes put into a holding pattern. If a rotorcraft is asked to hold, is it legal for them to hover at whatever location they want?
I think that helicopters are sometimes asked to surface taxi / hover taxi / air taxi at airports to keep everything in order.

Feel free to add any other differences between ATC interactions between rotorcraft and fixed-wing I might have missed.

A helicopter can be cleared to depart from any position on an airfield, however there are a lot of considerations that would go into that.

There is no regulation in the US, and I'm almost certain there isn't an ICAO SARP that states a rotary winged aircraft must depart from a designated position on the airfield. Based on local conditions, volume & types of air traffic, and how familiar controllers are with handling a helicopter, there may be some localized procedures, but nothing regulatory.

As far as hovering, there are no prohibitions aside from local airfield procedures. If given a hold during an IFR flight, the rotary wing pilot will fly it in the same fashion as a fixed wing aircraft. To hover in a specific spot for an extended period of time at altitude of not practical due to lack of visual cues needed to hover. Some have a system of Auto-Hover, but that's generally used for extended hovering close to the ground.

Even if it were desired, in many cases it wouldn't be possible. Hovering requires a significantly higher amount of power when done so outside-of-ground-effect (OGE), which is a key metric you need to understand prior to every flight based on that day's conditions and how heavy you are. The extra power required burdens more gas, and in many cases requires a good percentage of the pilots available attention.

If burning the extra gas isn't enough, most civilian rotary-wing aircraft are not equipped with the power needed. Even those military helicopters with two engines (think UH-60 Blackhawk) are limited at higher attitudes.

I think that was all the questions.


What are the implications of building a private airfield in the United States? I've always wondered what it would take to build my own airfield.  I live close enough to an area where this would likely be possible (50 NM radius around Front Royal, Virginia, obviously outside the DC SFRA) and there are a number of private strips in the valleys adjoining mountain range I live near:

Here are the parameters I would consider, which would allow operation of one or more small general aviation aircraft:

Runway width - 50-75 feet
Runway length - 2200-2500 feet.
Runway surface - grass
Buildings - Space for a hangar (converted barn?) and a moderately sized house.

Answered Questions:

What are the legal implications in the United States?  Do you have to get permission from the government to do this?  Is this airspace dependent?  Answered in linked post and this post.
What about permission from neighbors?  I'm going to guess this will be harder to answer, since it likely depends on jurisdiction.  However, if anyone has done this, perhaps they can share their experience in this area.  Somewhat answered in revised post.  Still interested in additional experiences.

Outstanding Questions:

What would it cost to maintain this installation, above and beyond the cost of maintaining any piece of property of this size?  What's included in these costs?
Are you required to pay to have an airfield listed on charts?
Do the parameters I've listed seem reasonable for the requirements I've mentioned?

This has been somewhat covered in other questions here. You can find the legal requirements in the answer to this question (somewhat of a dupe to this question). There are some notes on security in this question.

  What would it cost to maintain this installation, above and beyond the
  cost of maintaining any piece of property of this size? What's
  included in these costs?

For a grass strip you will need a good ride on mower and possibly something to level/press the ground. Maybe some filler if there are any divots etc. But all in all the cost to maintain a strip of grass is pretty cheap.

  Are you required to pay to have an airfield listed on charts?

Im not sure of this one but there may be some requirements you need to meet which could cost you money.

  Do the parameters I've listed seem reasonable for the requirements
  I've mentioned?

Yes, 22-2500 is more than common, FWIW a bit on the short side but you should have no problem getting your common GA planes in and out of there. Keep in mind that with trees at the end and on either side this could get tight. In reality runways (at least nice paved ones) have a lot of clear space around the immediate area.


Has any prior accident been caused by a psychologically unstable and/or suicidal crew member? I am aware a lot of psychological tests are given to pilots to prevent such a scenario, but those can hardly be perfect, so has any aviation accident been caused (or attempted) by the conscious intention of one of the crew?

Confirmed (or Highly Probable)

LAM Mozambique Airlines Flight 470: A report from the government of Mozambique states that the captain deliberately crashed an Embraer 190 in Namibia on November 29, 2013. Cockpit voice recorders were the primary evidence in the report, which found that the other crew members were locked out of the cockpit by the captain. There were 33 fatalities, and Mozambique Airlines was banned from flying in EU airspace. No psychological overview was done of the officer.
EgyptAir Flight 990: A Boeing 767 crashed near Nantucket (Massachusetts) on October 31, 1999, killing 217 people. It was found that the first officer, was responsible. The NTSB and the Egyptian Civil Aviation Authority both conducted individual investigations. The Egyptian report states

  [the] First Officer . . . passed his full medical examination and psychiatric
  assessment, which was performed by the Egyptian Air Force Medical Council as part of his full medical examination for fitness to be a pilot in the Egyptian Air Force, on December 11, 1958. He passed his medical examination for his Commercial Pilot license on July 27, 1961. A psychiatric assessment was not conducted as part of the medical examination for the relief first officer’s medical review for his Commercial Pilot license. During his military and civilian flying career there was no reported history of psychiatric consultation nor any reports regarding his behavior, either professionally or in groups.
  . . .
  First, there is no evidence to support a conclusion that the First Officer intentionally dove the airplane into 142 the ocean in fact, the evidence available refutes such a theory, a determination confirmed by expert medical opinion, technical and human performance analysis.

The NTSB did not agree that the most probable cause was a mechanical failure. Their conclusions, and the relevant rebuttals by the Egyptian investigators, can also be found here.
SilkAir Flight 185: On December 19, 1997, a 737 operated by SilkAir crashed in Indonesia, killing all 104 people on board. The aircraft was almost entirely obliterated. The Indonesian NTSC report (link broken at the moment) said that the cause was impossible to determine. The pilot appeared to be mentally stable, but there have been some doubts. Cockpit recorders stopped at some time, making the case different from that of, say, JetBlue Airways Flight 191 (see below). The NTSB was not happy, severely criticizing the Indonesian findings. Their analysis seem to rule out mechanical issues.
Royal Air Marco Flight 630: 44 people were killed in a crash in Morocco on August 24, 1994. A government investigation ruled it an intentional suicide
Japan Airlines Flight 350: The crash of a DC-8 on February, 1982, was caused by actions taken by the captain before being restrained by other crew members. Because of their actions, the majority of the people on board survived.
1999 Air Botswana Incident: On October 11, 1999, an Air Botswana pilot deliberately crashed an Aérospatiale ATR-42 into two other planes on the tarmac at Sir Seretse Khama airport, killing only the pilot. He was the only one on board, having taken the plane rogue and then flown it about the airport for hours. All the planes were destroyed, though the other two were unoccupied, as the airport had been effectively shut down. The pilot was on medical suspension.

'Close Calls' but no resultant accidents

JetBlue Airways Flight 191: Midway through the flight, the captain of the aircraft appeared to suffer a nervous breakdown. He began yelling about religion and was eventually subdued by passengers after being locked out of the cockpit by the first officer. He was charged with "interference with a flight crew", according to the FBI, which said

  As the plane was leaving JFK and climbing in altitude in its scheduled five-hour flight, [the captain] said something to the first officer (FO) about being evaluated by someone, but the FO did not know what he meant. [The captain] then talked about his church and the need to “focus” and asked the FO to take the controls and work the radios. [The captain] began talking about religion, but, according to the FO, his statements were not coherent.

I also found the same incidences as cpast, from Yahoo! News.

On some of the flights listed, the results of the investigations deemed the pilots obviously mentally unstable. On others, though, the conclusions were disputed, and it may not be possible to truly prove the cases one way or another.


How unique are waypoint names supposed to be? I had thought that someone such as ICAO was coordinating the assignment of five-letter waypoint names such that they were globally unique.

Now I notice that OpenNav knows three different waypoints named PINTO, two of which are on the same continent.

Is this supposed to happen? Are there rules for how close identically-named waypoints can be to each other?

(A significant factor in the AA 965 crash was that there were two NDBs with the same ID close to each other, and the FMC selected the wrong one to fly towards. This might be inevitable when NDBs usually have one- or two-letter IDs, but surely with a big fat five-letter namespace uniqueness ought to be achievable?)

The names are not globally unique and when entering the plan into the FMC, the crew should check the leg distance.  They are sufficiently far enough that the crew will see 1,812 miles instead of 135 miles.

Many FMCs will also only offer "sensible" choices and a deliberate action is required to select a "nonsensical" waypoint.

Often, a mistake in choosing the wrong waypoint will also alert them with a "not enough fuel" message, or an obvious gross error such as a total distance of 3,323 miles instead of the 756 miles expected.


Does a Boeing 747-830 exist and if it does, is there any difference to a 747-8 (748) Two years ago I've uploaded a video of the Lufthansas Boeing 747 "D-ABYA" to Youtube. I am currently receiving some angry comments on that video because the title reads "747-830 with new Lufthansa livery performs low pass at Hanover Airport". Many people are angry with the label "747-830", telling me that no such thing exists and that the featured airplane is a 747-8 or a 748.
Back when making the video, if I recall correctly, I looked up the type on Jetphotos. It reads "Boeing 747-830". The same is true on Flightradar24. airframes.org tells me the type is B748 and the model is 747-830. However, I could not find a reference to "747-830" on boeing.com.
What are the differences between type and model? Is a type 747-8 always a 747-830? Or are there other models with a similar name (747-8xx)? Am I correct in saying that the airplane is a 747-830?

Until 2016 Boeing included customer codes into the aircraft model names. Your example 747-830 decodes as follows:

747: This is the general aircraft series.
-8: The 747-8 variant (in this case, a 747-8I, where I is for Intercontinental, the passenger variant).
30: The customer code for Lufthansa or Condor Flugdienst (see e.g. Wikipedia for a list of customer codes).

So this makes it a Boeing 747-8 produced for Lufthansa (Condor does not have one).
The term B748 is the ICAO code for the 747-8.


What is the correct technique for working on an airframe with a pneumatic rivet gun? I currently work as a trainee AME and want to eventually start specialising in sheet metal / composite repairs as I've heard the money is really good for these specialist skills. I've bought myself a pneumatic rivet gun to start practicing some basics and have an array of sets for the rivet sizes and types.

My question to any aircraft structural engineers / experienced sheet metal workers in this forum is how to stop getting the smiley faces on the solid universal rivet head? I'm putting enough pressure on the gun to stop it bouncing and the bucking bar is setting a good rivet tail but on some of my rivets I have this smile crease / dent at the bottom of the rivet head. Does this mean the gun isn't in line enough with the rivet? I'm always trying my best to keep the gun 90 degrees to the sheet metal. Or am I doing something else wrong? I've been told I'm using the correct set and air pressures so I'm sure it's my technique letting me down on some of these rivets. Although less mistakes are happening when I get someone to hold the bucking bar so I can use two hands I still have the same smiley face problem on some. Any tips and tricks would be much appreciated.

I banged rivets on a production line in a previous life (in the 70s). A trick that works wonders (although it may be frowned upon by purists, and your school instructors may prevent you from using such a "cheat" while learning) until you get good at holding it perfectly perpendicular is to put a little piece of masking tape over the tip of the rivet snap.  It moves the snap a few thousandths of an inch away so that more misalignment is tolerated as well as putting a barrier between the edge of the snap and the skin surface if it does touch.  You will find your smiley rate goes way down.

I tried to draw a little picture of what I meant in Paint but I couldn't do it without it looking like a rude bathroom stall drawing, if you know what I mean...

The other thing I see people doing is just shooting it full blast, then off.  Don't do that.  The gun has a "feathering" trigger that lets you ease in the air for a reason.  When you start to set the rivet, ease on just a bit of air, just enough to get it ratatatatting, and feel for the feedback of the bucking bar on the other side to tell you you have good contact, then give it a full shot.

Each shot should sound like, "ssstat tat tat tat tat tat brrrrrrrrrrrrrrrrrrrrrrrrr".

Especially when you have a partner bucking, you'll know right away if they don't have the bar in place on the shop side.  This helps prevent depressing the metal around the rivet, as well as reducing the risk of smileys.

Another one is don't hold the rivet gun by the handle like a pistol.  You have to be able to push in line with the snap.  Old time rivet guns were made U shaped for this purpose, but all the modern ones have the terrible pistol shape.  Move your hand as high as possible so you are pushing with the heel of your hand on the back of the rivet gun's body, with your wrist more or less in line with the snap.  Your index finger will be too high, so use the middle or second last finger to work the trigger. Like this:


Is the Harbin Y-11 a fully indigenous Chinese design? One book characterized the Harbin Y-11 as a "successor" aircraft to a design based on the Antonov An-2, however, it looks completely different than the An-2, which is a single-engine aircraft. Is the Harbin Y-11 a fully indigenous Chinese design with no significant elements copied from some other aircraft?

Though Harbin Aircraft Manufacturing Corporation (HAMC) said Y-11 is a fully indigenous design, no other direct evidences prove/reject what it says. However, some indirect evidence shall be considered:

1) Except Y11, the only brand new design from HAMC is Z15 in 2008(Coperation with Airbus), other designs from HAMC are either authorised production or modification from existed model.

2) Y11 was designed in the period of the Cultural Revolution. There is insufficient engineers and research process is often influenced by political movement. However, Y-11 started first flight 8 months after the requirement is issued.

Based on the evidences i dont think it is a fully indigenous Chinese design, as they dont have experience for fully indigenous design in such a short period.


How does an airliner deal with cabin altitude at an airport above 8000 ft? There are a number of airports above 8000 ft altitude. FAR 25.841 states:

  Pressurized cabins and compartments to be occupied must be equipped to provide a cabin pressure altitude of not more than 8,000 feet at the maximum operating altitude

How does an airliner operating from a high airport, say from El Dorado, deal with cabin pressure? Do they actually pressurize the cabin after takeoff and depressurize it after landing?

Note: the answer can be of any jurisdiction though FAA seems relevant here as US airlines operate from there.

Here is the text extracted from Boeing's 777 Flight Crew Operations Manual:

In cabin altitude controller cruise mode, maximum cabin altitude is 8,000 feet. When the takeoff field elevation is higher than 8,000 feet, the cabin descends to the cabin cruise altitude while the airplane is climbing.
When the destination airport elevation is greater than 8,000 feet, cabin altitude controller cruise mode maintains a cabin altitude of 8,000 feet.
(...)
At touchdown, the outflow valves open to depressurize the cabin.

Therefore, when the airplane is on the ground, its cabin altitude is always equal to the ambient altitude. When it is in the air, the maximum is 8000 feet. Whether the cabin altitude will climb to 8000 feet or descend to 8000 feet depends on field elevation.
The reverse happens upon landing. If landing at an airport at 10,400 feet, the cabin altitude is <= 8000 feet until touchdown, then raises to 10,400 feet.
This make sense - if the outside pressure is greater, how do you open the door? (well with enough force you can, but I will leave it to your imagination as to what happens the moment the door is opened).


Can an aircraft engine be started midair? Can one start the aircraft's(commercial/fighters) engine midair at high altitudes especially turbojet or turbofan engines?

As long as there is engine (e.g., N1) rotation, no structural damage, no fire, etc., generally speaking an in-flight restart may be attempted.

There are certain guidelines/conditions that control whether the re-start attempt can be done with a windmilling engine or if a cross-bleed start (using air from the other engine to rotate the failed engine for starting purposes) needs to be done. (other conditions that must exist are shown in the in-flight restart procedure available to the crew).

The aircraft manufacturer typically provides an In-Flight restart procedure published in the QRH (Quick Reference Handbook) or Emergency Checklist.


What liability does an aviation inspector have for errors & omissions? In reading online, I've come across the term "pencil-whipping". The actual term is new to me but I'm familiar with the practice; it's when someone fills out the paperwork that attests something is true, without actually verifying it himself (at least not to the standards required). Technically that's fraud, but it's also usually a "who'll watch the watchmen" situation; if you don't know what the guy is required to do and watch him do it, or else call in a second opinion, you won't know anything's been skipped.

I purchased a home a few years ago, and the home inspector did a good job of finding the things we'd have to get fixed. If he hadn't though, State of Texas requires these inspectors to have "errors and omissions insurance" on top of a "general liability" policy. If the inspector said he has checked something though he didn't; or he made a mistake checking it; or he didn't check something he was supposed to, he and his insurer are liable for any damages resulting from the new homeowner trusting that report. This generally discourages pencil-whipping in the home buying industry, as after the first instance of the insurer having to pay out for an electrical fire caused by an outlet the inspector attested to be fine, the guy's likely out of a job.

The question here is, do A&Ps in the United States carry a similar liability? If I were to hire a guy and pay him thousands of dollars for a pre-purchase inspection of an aircraft, get the all-clear, buy it and then find out the aircraft actually isn't airworthy because of something he missed, what recourse do I personally have against the inspector? How would I report this misfeasance and to whom? Assuming nobody was hurt and I just have a loan payment on a museum piece (or a fat unexpected repair bill), what damages can I claim?

I only can speak for Canada but we use much of the American regulations in Canada as part of our regulations. In Canada, all mission critical systems Ie flight control systems etc ... have to be signed off by 2 inspectors for a total of 3 people working on the system. The maintenance engineer will sign of there own work and the inspector will sign off the inspection. A second inspector will sign off the secondary inspection. So typically if there is an error one person is typically not solely responsible for it. Additionally all inspectors and maintenance engineers licenses are only valid while working for a maintenance organization AMO. The organisation's insurance typically covers the employees working for them. When I went through my licensing I was told that we could still be held liable for criminal prosecution if we were willfully negligent. It was explained to us this only incurred once previously.  If memory serves me correctly it was the mechanic responsible for a plane that went down in the Florida everglades.


How can an altimetry system error during cruise (500 ft at 35000 ft high) cause an insufficient fuel situation? So my boss gave me a question today as my daily quiz: Let's say an A321 is cruising on a 6-hour flight. It reaches FL350 30 minutes after take-off. After another 8 minutes there's a discrepancy between 2 altimeters. PFD 1 reads 35000 ft while PFD 2 reads 34500 ft. The pilot decides to make an air-turn back due to insufficient fuel, despite having enough fuel filled while on ground.

The question is, did the pilot make the right decision?

I've done some research. The difference between 2 altimeters is not supposed to exceed 245 ft at 35000 ft. But I don't know how that is related to fuel shortage. Worst case scenario the static port is contaminated.

If the aircraft is cruising at FL350 it is operating in Reduced Vertical Separation Minima (RVSM) airspace (between FL290 and FL410).

With an altimetry discrepancy between the two altimeters of more than 245ft, the aircraft is no longer RVSM approved. It shall therefore descent or climb out of the RVSM altitude block.

For the Airbus A321 the operating ceiling is below FL410, so the only option is to descent to FL280 or below. Since the fuel consumption in those altitudes is significantly higher the aircraft is unlikely to complete its 6 hour flight with the amount of fuel on board. Therefore the decision to return is likely the right one.


What does "MERMA" mean on the Los Angeles TAC chart? Just wondering what "MERMA" means on the Los Angeles TAC chart:

MERMA is an aviation waypoint

  Waypoints used in aviation are given five-letter names. These names are meant to be pronounceable or have a mnemonic value, so that they may easily be conveyed by voice.

According to this page back before the FAA decided all waypoints must have 5 character names, this waypoint - being out in the ocean - was called "Mermaid" and after renaming this became simply MERMA.


What is the difference between aircraft integration and assembly? I have never had a clear understanding of the difference between aircraft assembly and integration. My understanding is that putting together the airframe alone is assembly and putting together the avionics and other systems in order to get the aircraft flight-ready is integration. I'm not sure if this alone captures the difference. It would be great to have inputs regarding this.
Thanks in advance!

I was many years with an OEM.  Integration is process of coordinating and incorporating, harmonizing you might say, the unique engineering of systems and processes of two engineering and production organizations or products, to make them work together in the final product.  To integrate them.
For example, a manufacturer designs and builds an airframe.  An avionics suite, or some other system, designed and manufactured by a second party, not specifically for a given type, is selected to be used in this new airframe.
Someone has to integrate, or adapt, the pre-existing avionics suite into the airframe and systems of the host.  The integrator is responsible for all of the activities of incorporating that system;  where/how it fits, how it interfaces with host systems, etc. In other words, the integrator is responsible for making the second party system work smoothly in the host system.


Why does the Antonov AN-225 not have any winglets? Winglets provide a lift boost that would be useful to a plane of this size. But the An-255 does not have any winglets.

Why is it so?

Winglets are less effective at producing added lift than an equal-length wingspan extension. They are used on airliners when simply enlarging the wing would put the plane into a larger size class, or outside the 80 m "box". A longer wingspan, which the An-225 has (10% over the limit), is better at producing lift.

The An-225 is a special purpose cargo aircraft for delivering very large loads such as the Buran space shuttle. It doesn't have to care for commercial airport traffic patterns meant for high-throughput operations - servicing thousands of planes separated into fixed size groups.

In its original role the An-225 would operate from airstrips purpose-built for it, and seeing little other traffic. Today, on the rare (or not so rare, but its most public deliveries are to remote destinations) occasion when it has a commercial airport in its itinerary, they can deal with the extra requirements of a somewhat larger plane.

Think of it like a wide load truck: they can go outside the 102"+3" limit at the expense of pre-planning the route. It's always a special delivery with these planes.


What implications does automobile electrification have for the supply and cost of Avgas? The electrification of automobiles has been picking up pace recently, with various countries and manufacturers setting targets for an electric- or electric/hybrid- only future.

If these plans come to fruition and are widely adopted, the demand for gasoline, and therefore its supply, would decrease considerably. While avgas is something of a specialty product, I would guess that it shares the bulk of its components, and their manufacture, with automobile gasoline.

Have there been any studies of the consequences of this change on the inflation-adjusted cost and its supply of avgas (though I imagine it will be available at some price), and also on motor gas for those aircraft that can use it?

I have not seen any studies on this, nor would I expect to as Avgas is such a niche product and the price of it is not heavily dependent on the price of the underlying fuel itself. If you look at this answer the reason avgas is so expensive is that it has special requirements for making it, storing and transporting it and so little is produced that there's no economy of scale.

In any case your question is based on the premise that gasoline production is going to decrease. Even with the rise of electric cars most oil companies aren't forecasting a drop in gasoline demand until the 2030s, maybe even the 2040s as the increase in demand for new cars will oustrip the number of electic cars for some time. As a decline in consumption does not guarantee a price rise, any forecasts of this kind would be premature, and not likely to be reliable.


What variant of Mi-8/Mi-17 is this near Kennedy Space Center? A tweet by Julia Bergeron showing pad activity near Kennedy Space Center also showed what seems like an unusual visitor for the area.  I've attached the relevant picture.  It's clearly in the same family as the Mi-8, but has the following unusual features:

The tail rotor is on the left, which I think places it in the Mi-17 (export) family?
The rear doors are a flat ramp, not a clamshell
There's a lump over the right door that might be a winch but also distinctly reminds me of the heater bulge forward of the right main landing gear on the Mi-8s that I'm used to, which this seems to lack?
It's a five-blade main rotor and three-blade tail rotor, so I don't think it's one of the newer Mi-38s.

The closest I've come so far is an Mi-17MD, but I'm not fully satisfied with that identification.

I have a better candidate than the Mi-17MD now:  what I think is the next version after that, the Mi-17V-5.  The feature that really prompted the question was the heater not being in the place I'm used to; the V5s have an enlarged right-side door, and that apparently necessitates moving the heater to the top-right position (from where the KO-50 used to be, right, extending from the same bulge that extends forward from the right main gear).  Oddly, it's not clear to me if all V-5s share the door or not--Airforce Technology makes the right-side door sound optional, and it's tough to tell if various internet sources are just using stock of any Mi-8 when they refer to some country or other purchasing V5s or if they're making sure they're getting it right.  Mi-17MDs in the service of the Colombian Air Force seem to delete the heater unit altogether.

The only other thing I'm wondering about now is the large open hatch above the right-side landing gear.  Most Hips have round windows there.  That might some kind of optional equipment though.

...there also may be a roundel just behind that hatch, but I can't tell what it is.  The CH-178s had similar roundels there, but I really really don't think it's one of those.


Can a GA magneto-spark plug ignition survive an EMP? Can the coil and capacitor (condenser) magneto/spark plug ignition system as exists on most general aviation aircraft survive an EMP? Let's talk about a standard Lycoming or Continental engine. How about most turbine engines? I'll use a PT-6 as an example. I assume the FADEC would be toast? How about other parts of the electrical system such as the battery? Is there any data or research on this?

Can the coil and capacitor (condenser) magneto/spark plug ignition
  system as exists on most general aviation aircraft survive an EMP?

Like anything it depends on the EMP's strength, the angle of incident to the device and the device in question. The various things in an aircraft will break down for different reasons. But for the rest of this lets assume an EMP that is sufficient to fry stuff. A magneto will suffer toasted coils as the induced current could potentially generate enough heat to degrade the resin coating on the wire they use on coils. It should however be noted that the magneto is more than likely shielded to prevent interference with avionics which will play out in your favor here.

  How about most turbine engines? I'll use a PT-6 as an example. I
  assume the FADEC would be toast?

Most likely yes. Again the unit is generally housed at least in some capacity in a shielded case but modern PCB components don't play nice with large induced currents. Turbines do have an Igniter system that may see some damage depending on the severity.

  How about other parts of the electrical system such as the battery?

Things like interior lights will most likely blow out, batteries (depending on type and casing) could go. Overheating is a concern if enough current is forced over the line.

  Is there any data or research on this?

There is some Mil-Specs (MIL-STD-1541 (USAF)) out there that cover it for the military. This question covers it for airliners. You can find at least one book on the topic here. There was a lot of research on this that pertains to missile systems as one anti-missile defense was to detonate a nuke in front of the oncoming unit. If the blast did not take it out the resulting EM field would fry what ever guidance and control systems were on board (assuming it was not ballistic). As such, work went into making the units EMP hardened. I'm not sure that work is very public though. The soviets were big users of vacuum tubes as they believed them to be far less susceptible to EMP's. It looks like this company does testing and research on EM hardened aircraft.


what is a flap hinge moment? I am a bit confused on how to come up with the flap hinge moment, like, what force is involved and where is the center that the force is wrt.
And why is the moment as shown in the above diagram seems to be in a different direction from that shown in the diagram below

( video is at

            )

You have to think that your flap is a small wing by it's own. The fixation point of this wing, through which all loads must be transferred is at the leading edge. Then there is a moment created at this hinge by both the aerodynamic lift and the aerodynamic moment if your profile is not symmetrical. You can calculate this moment by calculating the lift $L_f$ and aerodynamic moment $M_{0_f}$ at the aerodynamic center and then adding them after multiplying the lift by it's lever arm which is one quarter of the flap chord $c_f$. For a unit length of flap you get the following :
$$ M_h = L_{f}*\frac{1}{4}c_{f} + M_{0_{f}} =\frac{1}{2} \rho c_{f} C_L{_\alpha} (\alpha +\delta) V_\infty^2 * \frac{1}{4}c_{f} + \frac{1}{2} \rho c_{f} C_{m_0}V_\infty^2 $$
For the second part of your answer, the first diagram is showing the moment exerted on the flap to keep it down while the second one is showing the moment applied by the flap on the wing. Newton's third law gives you everything else.


What would happen if one of the engines failed during takeoff and other engine is on full power? Assume the left engine failed and the right engine is at full power. The pilot has pulled his nose up and turned towards left. Is it possible for him to land the plane on a runway to his left? The plane is an ATR-72 turboprop design

No, no, by all means don't turn left. See also Why should you not turn in the direction of an inoperative engine?.

Transport category aircraft are capable of climbing out on one engine. It is a certification requirement for them. So if the left engine failed after rotation, the first thing the pilot has to concentrate on is to keep the plane flying and under control. That means ease the pull on the stick a bit to avoid stalling as the plane is not able to climb as fast and push the right rudder pedal to keep the plane flying straight¹.

Once the plane is in straight climb at $V_2$ speed, it's time to deal with the engine. First both pilots cross-check the instruments and the rudder position to determine it was the left engine that failed. Then they feather the propeller (auto-feather might have done it already) and cut fuel to the failed engine. If the engine fire warning is on and did not extinguish when fuel was cut, they discharge fire extinguisher.

These things are done according to standard emergency procedure that the pilots have to remember and train in simulator. I don't know the specifics for ATR-72, but in all aircraft it is roughly like above.

Meanwhile the aircraft climbs to safe altitude and then they should level off and let it accelerate a bit to get some safety margin for manoeuvring.

The plane is now in relatively safe condition. Even if engine was on fire, it is unlikely to spread while the aircraft is flying. So the pilots now have time to declare emergency and ask the controller for what options they have for landing. Whether they do a complete circuit and land back on the same runway or turn around and land in opposite direction or land on some other runway then depends on wind and where they are relative to the runways at the time.

There were many accidents where plane crashed after one engine failure during take-off because pilots started manoeuvring before they attained sufficient altitude and safe speed. It is better not to hurry, engine failure does not require it.

¹ Of course provided there are no obstacles in the way. For example if you were taking off from VQPR runway 33 and your right engine quit, you'd still have to do a right turn rather early to avoid the Mr. Smith's house right in the axis of the runway and quite a bit above it. But for any airport that require such avoidance (and there is quite a few of them in various mountains), the pilots are specifically briefed and trained for that airport which includes instructions on how to best handle engine failure during take-off and during approach and viability of the procedure is verified in simulator and with a test flight. The above answer just outlines the generic procedure.


Could an ultralight hypothetically takeoff without power on if it were windy enough? I don't know if takeoff would be the right term, but the wing should generate lift with any headwind.

It could, but eventually drag would cause the ultralight to start moving in the same direction as the wind and it would lose any apparent forward airspeed.


What is the lifespan of a level D simulator? We have a few interesting questions about the normal ways aircraft end their lives.  What about simulators?  How long do they typically last?  What is the typical reason for retirement?
I am particularly asking about high level simulators used for airliner type ratings.
This question was inspired by discussion of the time taken to reboot a simulator:
Do Flight Simulation Instructors stop the simulator before a simulated crash?
Related questions:

Why are some aircraft's life limited by both cycles and flight hours?
Under what conditions do airliners retire aircraft and sell them to other airlines?
What limits the lifespan of helicopters?
What is the lifespan of commercial airframes (in general)?

As long as it's maintained, and replacement parts are available, there is no limit. Although maintenance could end up costing more than the simulator itself:

CAE says the Series 5000 will offer a 25% reduction in lifecycle costs, which tend to be two to three times the original cost of the simulator during a 20-year lifetime (...)
— flightglobal.com, 2008

The 20-year lifetime mentioned above is what would a training center expect, as that's typically how long an airliner model stays in service in sufficient numbers to promise a continued demand.
Delta Flight Museum still operates a full-motion 737-200 simulator (Delta introduced that model in 1983, almost 40 years ago).


What is the purpose of drag and anti drag wires? What are drag and anti drag wires,and how important are they to the performance and strength of the wings of an airplane?

Definition from the Stearman Restorers Association (emphasis added):

  Drag wires run from a point inboard and forward in a bay to a point outboard and aft.  In this position, the Drag wire is there to RESIST drag forces that would tend to pull the wing tips aft as the airplane travels through the air.  Anti-Drag Wires oppose the drag wires running from an inboard aft location to an outboard forward point in its bay.  As the name indicates, these anti-drag wires oppose forces in the reverse to the direction of flight.

In a wing without a structural skin like on a fabric covered aircraft, they provide rigidity in the horizontal plane by creating a wire braced truss system of the spars, longitudinal tubes called compression tubes spaced at intervals between the spars and holding them apart, and the drag anti-drag wires forming an X between each pair of compression tubes.

The drag/anti-drag loads are not that high so fairly small wires can be used.  An Aeronca Champ's fabric wing uses about 1/8" steel rods for the job. Some homebuilts just use 1/8 steel control cable.  The wires at the root see the most load.

You can also use diagonal tubes that just run from one corner to the other of each bay and take both compression and tension loads.  Wires are generally a bit lighter.

For your ultralight, bracing could probably be made from 3/32" cable with thimbles and nicropress fittings at the attachments.

You can see the drag/anti-drag wires in this Goat glider.  The plans are open source so there is probably a lot you could copy from this design.