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On the Qantas Flight 32 incident, the Airbus A380's number two engine encountered an uncontained 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 losing 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
    Commented Jan 11, 2015 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
    Commented Jan 30, 2016 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
    Commented Jan 31, 2016 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
    Commented Jan 13, 2015 at 21:22
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    $\begingroup$ @MSalters -- two points. First is that an uncontained engine failure (such as QF32) is essentially a game of roulette as to what suffers from the shrapnel bombardment the plane just received -- one day it may be the fire handle cable for the engine next to it on the wing, the next day it might be a hydraulic line feeding the outboard slat actuator. Second, engine mountings in modern jets are designed for the most part (center engines in trijets are the only exception that's newer than the very first jetliners) to come off the aircraft cleanly if they do experience an uncontrolled fire, AIUI. $\endgroup$
    – UnrecognizedFallingObject
    Commented Jan 20, 2015 at 2:23
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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
    Commented Jan 31, 2016 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
    Commented Feb 5, 2016 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
    Commented Feb 6, 2016 at 2:39

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