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I read many items on the avherald.com site where it says "engine shut down during flight" or words to similar effect.

I'm wondering if there are any instances where an engine could not be shut down or the pilots had trouble shutting down the engine when commanded. What sort of backup systems are in place to avoid this kind of scenario?

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    $\begingroup$ Fuel valves will reliably shut down any combustion engine. So will an empty tank. $\endgroup$ – Peter Kämpf Jul 30 '18 at 20:54
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    $\begingroup$ I distinctly recall at least one serious accident where a timely evacuation would have saved all lives, but for the inability to shut down an engine: either this slowed the evac, or they chose to delay the evac while they futzed with the uncooperating engines. $\endgroup$ – Harper Jul 31 '18 at 5:35
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    $\begingroup$ @PeterKämpf The thing on large jets is that fuel valves are electrically operated. A common issue with many jets is that if the power supply to the HP valve is lost, shutdown with the LP valve will take some time (60 seconds at idle on the A320), and have a tendency to damage the HP fuel pump. $\endgroup$ – user71659 Jul 31 '18 at 6:49
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    $\begingroup$ @Harper Link / source? $\endgroup$ – Cloud Jul 31 '18 at 11:32
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    $\begingroup$ Probably Saudia 163. The fact that the cabin remained pressurized and engines running was likely a side effect of crew incapacitation, and not an inability to shut down the engines. I think it's unfounded to say that fatalities would be avoided if engines were shut down; fatalities could be avoided if the incident was handled with urgency. The poor CRM and captain's approach to the emergency was the root cause. $\endgroup$ – user71659 Jul 31 '18 at 16:38
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Qantas Flight 32

Enroute to Sydney, Engine Number 2 of the A380 disintegrated explosively. The shrapnel of the explosion destroyed many systems, including a hydraulic system, the anti-lock braking system, flaps and electronic controls.

After emergency landing, the pilots were unable to stop engine number 1, because the controls had been destroyed by shrapnel. Emergency services had to douse the engine until flameout was achieved.

Qantas 32 Engine Douse

Source

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  • $\begingroup$ What was the cause of the Engine 2 spontaneous combustion? $\endgroup$ – Cloud Jul 31 '18 at 11:33
  • $\begingroup$ @Cloud I believe it was a cracked fanblade that caused catastrophic failure. $\endgroup$ – jwenting Jul 31 '18 at 11:52
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    $\begingroup$ @Cloud: Per the Wikipedia page, which matches my memory for the period (I'm interested in engines), it was a miss-bored oil pipe in the engine, which cracked due to metal fatigue, starting an oil fire, which led to the failure of the intermediate-pressure turbine disc. $\endgroup$ – John Dallman Jul 31 '18 at 16:11
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    $\begingroup$ @Cloud It actually shows how safe flying is today and that aircraft are still able to fly even though around 50 systems got destroyed. Maybe it helps :) $\endgroup$ – Noah Krasser Aug 1 '18 at 6:45
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    $\begingroup$ I'd argue that this incident wasn't caused by an inability to shutdown the engine. It was a side affect, and it caused problems after landing, but the cause was the other engine exploding. $\endgroup$ – Greg Aug 2 '18 at 6:49
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Cathay Pacific flight 780 on 13 Apr 2010

Fuel contaminated by super absorbent polymer jammed fuel valves caused engine control problems. The aircraft eventually landed with one engine at about 70% N1 at significantly higher than normal airspeed, burst some tires from the increased braking necessary and was evacuated.

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    $\begingroup$ AFAIK, this wasn't strictly an "unable to shut down engine" but a loss of thrust control instead. One engine got stuck at 70% N1 and the other got stuck at 17% N1. For obvious reasons, the pilots kept the engines running until after landing, at which time both successfully shut down. $\endgroup$ – user71659 Jul 30 '18 at 23:12
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    $\begingroup$ @user71659, on the other hand it was an accident directly caused by the inability to control thrust as opposed to the others where the inability to shut down the engine was a result of the accident. $\endgroup$ – Jan Hudec Jul 31 '18 at 6:50
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Etihad Airbus A340-600

This famous crash happened on the acceptance engine run-up test. The causes were unrelated to engine problems, but after the crash, due to damages, two engines couldn't be shut down. One of them ran for 9 hours (!) after the incident, until it ran out of fuel, creating obvious hazard for the emergency crew. (Luckily, there were no passengers to evacuate).

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There is this business jet with two engines that didn't quit for 20min after it overran the runway and splashed around in a Bay. Investigators found it attempted the landing with a 10kt tailwind on too short of field and the touchdown too far beyond the threshold.

Screengrab from vido showing jet in water with engine running
May 15, 2005, in Atlantic City, NJ , USA

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    $\begingroup$ If memory serves, it wasn't just a long tailwind landing, but a long tailwind landing on a runway too short for the aircraft (and which was specifically designated off-limits to jet aircraft in the A/FD). $\endgroup$ – TypeIA Aug 2 '18 at 21:15
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    $\begingroup$ I don't think the mfg has approved it for water taxing either. $\endgroup$ – jwzumwalt Aug 2 '18 at 22:52
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Air France 72.12 Sept 1993. Aircraft (747-400) went off the runway in Papeete. Due to electrical damage (aircraft nose was in the water) the engine could not be shut down from the cockpit and AFRS had to 'drown' the engine by hosing a lot of water into the inlet.

My understanding is that the failure mode of engines is to be fail-safe, ie to minimise the impact of failure. With FADEC (full authority digital engine control) the problem is what would be the best action if signal were to be lost from the control box to the engine? It was explained to me that the lesser of two evils will be to have the engine running rather than shutting down so the protocols were designed accordingly.

While this does not answer your question on backup..It is more sense if you look at it from a different angle.."what is the backup in case control of engines is lost". In this case the backup would be the engine would continue to run rather than shut down.. If this happenned in the air you would be better off with a working (albeit uncontrollable) engine rather than a dead one.

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    $\begingroup$ "If this happenned in the air you would be better off with a working (albeit uncontrollable) engine rather than a dead one." I'm not sure whether that holds up for multi-engine domestic flights, but there are plenty of scenarios (say, a trans-atlantic flight) where you absolutely prefer an uncontrolled but still powered engine over a dead one. $\endgroup$ – Mast Aug 1 '18 at 9:02
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    $\begingroup$ And Papeete involves quite a long water crossing, so... $\endgroup$ – Brian Drummond Aug 1 '18 at 17:59
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    $\begingroup$ @Mast I would think that if your machine can't land with an uncontrolled engine, you could always circle until you run out of fuel, whereas if the engine just shuts off then you'd better have a landing strip of some kind within your glide radius. $\endgroup$ – Perkins Aug 1 '18 at 20:24
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What sort of backup systems are in place to avoid this kind of scenario?

As I understand it airliners normally have a "fire handle" for each engine which is independent from the normal engine controls. This handle can be used to cut off fuel to the engine and optionally discharge the fire extinguishers.

I can't seem to find an official source but from what I can gather the fire handle did not work in the Quantas case, likely due to the severe damage from the uncontained failure of the other engine on the wing.

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    $\begingroup$ Is the fire handle placed at the interior or exterior of the plane? $\endgroup$ – Mast Aug 1 '18 at 9:03
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    $\begingroup$ @Mast It's the kind of thing you really want accessible from the interior if at all possible since getting to an exterior one in flight requires having Tom Cruise aboard, and if you're on the ground then you generally have a fire crew nearby and won't really need it. $\endgroup$ – Perkins Aug 1 '18 at 20:28
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    $\begingroup$ @Perkins Since it sounds like a measure of last resort, I imagined it being as close to the motor as possible. So I had to ask :-) $\endgroup$ – Mast Aug 2 '18 at 6:03
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    $\begingroup$ @Mast Engine fires can get really hot. It at least needs to be far enough back that you can reach it without melting your skin off. That's why the emergency shutoff valves at fuel stations are 30 feet or more from the pumps. $\endgroup$ – Perkins Aug 2 '18 at 17:26
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In addition to the posts above, it is worth pointing out that this exact scenario is part of the flight testing of any new aircraft. If you can find it, there is a whole episode of the PBS show on the B777 that shows this test being carried out.

It was an especially odd one, because the aircraft had P&W engines and brakes designed to handle that, but they wanted to test the performance as if it was equipped with the more powerful RR engines. The chief pilot originally said no, but as the engineers at the various companies said ok, he relented.

The test required the aircraft to go to maximum power, in this case higher than the official rating so they could test the RR case. After it reached a certain speed, they put on full brakes, with the engines still at max power. When it finally came to a stop, the brakes were bright yellow. It then had to sit for a time (5 minutes IIRC) to simulate the emergency vehicles arriving, which then sprayed the brakes with water. It was quite impressive.

As they were careful to say, the idea of the test is not to pass some requirement, but to simply give future pilots an understanding of what to expect in the case it happened.

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