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On the Qantas Flight 32 incident, the Airbus A380's number two engine suffered from an uncontained engine rotor failure and partially damaged the controls of number one engine as well.

According to Wikipedia, engines one and four entered a 'degraded mode' after the explosion, and number one could not be shut off after landing.

So it seems that in case an engine loses all communication signals from the aircraft's control systems in the cockpit, it could somehow remain operational. To me that definitely sounds a lot safer compared to shutting down and risking the plane lose all thrust.

So do jet engines, by design, keep producing thrust in case they lose contact with the control systems?

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    $\begingroup$ That depends on your definition of 'safer' - would you rather glide an A380 on zero power, or land one on full power? (My own preference would be full power, that way I can fly around above an airport until I run out of fuel, then glide to a landing) $\endgroup$ – Jon Story Jan 11 '15 at 21:24
  • $\begingroup$ As a side note: "Degraded or alternate engine mode indicates that some air data or engine parameters are not available." (Page 2 of ATSB Aviation Occurrence Investigation AO-2010-089) $\endgroup$ – user12485 Jan 30 '16 at 22:21
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    $\begingroup$ This Citation even restarted after the pilot had left the cockpit. Lucky enough, the aircraft was in water :-) $\endgroup$ – mins Jan 31 '16 at 13:32
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General rule here: the engine will remain at its last power setting should the FADECs lose comms with the flight deck controls (in your A380 case) or the thrust lever cables come unhooked (in the case of an older aircraft with mechanical cable-and-pulley controls).

However, the fire handle will kill the engine even if the main controls fail -- it operates the firewall fuel and hydraulic shutoff valves. In QF32, this didn't happen because the cable for the #1 engine fire handle itself was damaged by shrapnel entering the wing.

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    $\begingroup$ That sounds like a horribly bad design: an accident that causes an engine fire may also cause the fire suppression system to fail. The usual norm is fail-safe: if the safety shutoff valves become uncontrollable for whatever reason (implies significant unforeseen damage) then they should fail closed. Of course, this implies that there should be redundant control of those valves lest they become a SPOF for an engine. $\endgroup$ – MSalters Jan 13 '15 at 21:22
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    $\begingroup$ @MSalters In this case it isn't clear whether fail closed is the fail safe option. If we were discussing a power plant turbine or a ship board engine I'd agree. But in the unique operating envelope of an aircraft shutting an engine unwarranted may have equal or greater damage potential than not being able to shut down an engine. $\endgroup$ – curious_cat Jan 31 '16 at 0:50
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    $\begingroup$ @curious_cat Especially when it's the remaining engine on the side where you already lost one engine. QF32 would have been in serious trouble had the #1 engine shut down in flight. They were having a hard time controlling it as it was. $\endgroup$ – reirab Feb 5 '16 at 19:56
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    $\begingroup$ @reirab Good example. The point is that fail safe isn't always fail closed. $\endgroup$ – curious_cat Feb 6 '16 at 2:39
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    $\begingroup$ @Sean Adding to what UnrecognizedFallingObject said, there's also a metric crapton of jet fuel in the wing tanks of many modern airliners. You'd need to cut off the engine feed from those tanks, and you might not want to pump all that into the fuselage and then back again just so you can have a cutoff valve within the fuselage (which may or may not do its job properly after an uncontained engine failure, even if it wasn't for the possibility of a fuel leak directly from the tanks...). $\endgroup$ – a CVn May 3 '18 at 18:30

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