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This answer made me wonder if engines are stopped automatically after an emergency landing as soon as one of the exit doors are opened.

(...) if the engine is still running, you're about to run forward into the area where you're at risk of being sucked into the running engine.

I'm not sure how high the risk would be to be sucked in or being blasted away by the jet-blast, I guess a lot of the emergency landings are because of engine failure so they aren't running anymore.

Maybe as an added extra - how long does it take for an engine to spin down to a safe RPM (so that it won't suck in people or blast them away)?

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    $\begingroup$ Generally, whenever you find yourself asking "will planes automatically do X in situation Y?", then ask yourself what the consequences will be if there is a malfunction and the plane does X when it wasn't supposed to because the sensors detected situation Y (or the computers believed the sensors did) when in reality no such situation existed. There has been a fairly large number of accidents the cause of which trace back to some sort of sensor failure, including some pretty high-profile ones (frozen or otherwise blocked pitot tubes seem to be a classic, but are certainly not the only ones). $\endgroup$ – a CVn Jan 2 '18 at 13:44
  • $\begingroup$ @MichaelKjörling well, at least for me, aviation was always top notch technology - and as cars are gaining more and more automatic features, I was thinking along the lines of "surely planes have this already". My car is doing things which I wouldn't do at times, but there is always the manual override (at least for the things I've encountered so far) - I guess it is an engineering question which one is worse. Pilots are highly trained personell, so maybe opting for less automatism is best here. $\endgroup$ – Arsenal Jan 2 '18 at 13:51
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    $\begingroup$ Building on @MichaelKjörling's comment, engineers would examine not only the consequences, but also the probabilities of each situation. All sensors have some failure rate. Maybe your exit door opening sensors fails once per 100,000 flights. That's not too bad. But if an emergency landing is only once in a million flights, then whenever you detect the door opening, it's actually 10x more likely to be a sensor failure than a real event. I made up these numbers but this is the kind of thinking that goes into design. $\endgroup$ – Daniel Kiracofe Jan 2 '18 at 16:53
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    $\begingroup$ @Arsenal: But "top notch" (admittedly a subjective definition) cars tend not to have those sorts of automatic features. Those are either for the terminally lazy (e.g. automatic transmissions, or self-opening rear hatches on SUVs), or for gearheads (e.g. Tesla's Autopilot). $\endgroup$ – jamesqf Jan 2 '18 at 17:57
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There is no automatic shutdown. However, shutting down the engines is part of the evacuation checklist done by the flight crew.

It's happened before that the controls link was severed and an engine could not be shutdown, such as in Qantas Flight 32.

Upon landing, the crew were unable to shut down the No. 1 engine, which had to be doused by emergency crews until flameout was achieved.

Normally the captain would then instruct the cabin crew to not use that side of the plane. Same thing happens when there is a fire on one side, in that case the captain would also steer the plane so that the good side is upwind.

Aircraft are tested to ensure all occupants can evacuate with 50% of the emergency exits not working (glass half-full: 50% of the doors working). See: How are evacuation tests made as realistic as possible?

About how long it takes for the engine to stop producing thrust, it's about 5 seconds. If there is no or little thrust, there is no suction to worry about. Also note that figure is for a spool down from full thrust (not from idle thrust, which is to be expected after landing).

enter image description here
(Source: Jet Transport Performance Methods)

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  • $\begingroup$ Thanks for the added data on the engine spool down, that is quite interesting. I would have thought it'd take much longer because of the momentum the engine has. $\endgroup$ – Arsenal Jan 2 '18 at 10:21
  • $\begingroup$ "the captain would also steer the plane so that the good side is upwind." Now that's clever! $\endgroup$ – Fattie Jan 2 '18 at 14:55
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    $\begingroup$ @Fattie sadly, it's not so much 'clever', as experience. A whole family I knew died because of 'bad side upwind':( $\endgroup$ – Martin James Jan 2 '18 at 21:21
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I guess a lot of the emergency landings are because of engine failure so they aren't running anymore.

That is not correct - there are many types of emergency landings: inoperative or stuck control surfaces, landing gear problems, bird strike, explosive decompression, etc. Engine failure is one of the failures people talk more about because it is easy to practice.

In an emergency, obviously some system is not working. Therefore there is no automatic mechanism to shut down the engines - the pilots may need them running in a scenario that is not accounted for by the engineers. The timing of that action is determined by the pilots. (Actually there is never a mechanism to auto shut down the engines - emergency or not. Even in the event of an engine fire, the pilots have the option to continue running the engine).

How long does it take for an engine to slow down its RPM? Around 20 seconds seems enough. I have no data to support this though.

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  • $\begingroup$ For the time to slow down an engine, the information may be available in the chronology of NTSB's incident reports for incident involving engine failure (I haven't search yet) $\endgroup$ – Manu H Jan 2 '18 at 11:33
  • $\begingroup$ Even if the emergency landing is because of engine failure and all engines affected by the engine failure have fully shut down, it's not necessarily a given that all engines have failed. $\endgroup$ – a CVn Jan 2 '18 at 13:34
  • $\begingroup$ Is the mechanism for keeping the engine running in a fire simply "don't pull the fire handle", or is there an override for the handle's fuel shut-off? $\endgroup$ – Mark Jan 3 '18 at 3:14
  • $\begingroup$ @Mark That sounds like the beginnings of a decent separate question, but I'm pretty sure that in airliners, pulling the fire handle is an irreversible action. $\endgroup$ – a CVn Jan 3 '18 at 10:59
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There have been incidents, like Continental flight 426 in 1975 (DEN, cause was a microburst) in which the engines continued to run after the crash. Fortunately from the NTSB report it seems like the running engines didn't prevent passenger egress.

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