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I was thinking of asking this question at Worldbuilding, because it is for a book I am writing, but I hope this site will fit better. You can migrate this question if you find Worldbuilding more appropriate.

Let's imagine a flying helicopter, something like Eurocopter EC135. What happens if all electric equipment suddenly stops working? The reason of this failure is not important, just imagine all electricity is "gone" without any warning: all screens are black, all lights are gone, all communication is cut, GPS not working anymore etc.

I suppose the main engine is still running, no reason for sudden falling, right? But... is the pilot still able to fly it? Is it probable he would land successfully? Does the helicopter need any electricity to stay flyable?

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    $\begingroup$ Comments are not for extended discussion; this conversation has been moved to chat. $\endgroup$ – Farhan Feb 9 '18 at 16:57
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The reason for the failure is important actually. If all the electrical systems on an EC135 helicopter fail in your classic EMP scenario then the helicopter has to make an emergency landing as the jet engine is run by a computer system which requires electricity. A power failure of that system would most likely cause the engine to revert to manual backup, which means it's still running but you need to get it down ASAP. It's also possible the engine could fail entirely, in which case the helicopter would have to autorotate, i.e. land without engine power, which is survivable, if hazardous and extremely exciting.

If you are asking about a more straightforward electrical failure of flight instruments and comms with the engine still running then the pilot would continue to fly the chopper and use backup instruments to complete the flight. Even fully "glass cockpit" aircraft have a set of "steam gauge" instruments, some which require no power whatsoever, like an altimeter and airspeed gauge which use air pressure measurements, a magnetic compass for navigation, etc. Some will also have a backup Attitude Indicator which is powered by an isolated battery system and would give the pilot attitude reference even in cloud or poor visibility. So it's less of an event that you might imagine, although instrument failure is always an interesting experience, trust me.

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    $\begingroup$ It seems to me that you have a funny idea of what's exciting and interesting... :-) $\endgroup$ – a CVn Feb 8 '18 at 14:51
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    $\begingroup$ Yeah, but first there was an explosion! And it was in space! Great example though @MichaelKjörling $\endgroup$ – GdD Feb 8 '18 at 15:12
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    $\begingroup$ Yeah, but at that point, they didn't know they'd had an explosion. All they really knew was that a bunch of instruments were showing readings that they weren't supposed to show at that point in the flight and that systems were dying left right and center... So it was still an instrumentation problem at that point. A pretty dramatic one. $\endgroup$ – a CVn Feb 8 '18 at 15:46
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    $\begingroup$ Citation needed on the loss of engine power. FADEC engines are typically designed so that the HMU remains in its last position during a FADEC failure, so the engines will remain running. (A plausible scenario being the FADEC is resetting and will come back up in a few seconds) Another example is the QF32 accident, loss of control wiring resulted in an engine stuck running after landing. $\endgroup$ – user71659 Feb 8 '18 at 22:58
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    $\begingroup$ @user71659 HMU appears to refer to the final valve that actually controls fuel flow into the engine? My understanding is that gas turbines are fairly unstable without active (hydraulic or electronic) controls, and an engine with a fixed fuel valve would quickly over-speed or stall. As for QF32, my understanding is it's probably the throttle signals from the cockpit to the FADEC, not the FADEC itself. $\endgroup$ – Someone Somewhere Feb 9 '18 at 5:11
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It turns out you picked a particularly susceptible helicopter. Unlike other helicopters which are still largely mechanical, the EC135 has digital engine control. The simplest solution is to pick a different helicopter.

I suppose the main engine is still running, no reason for sudden falling, right?

I have some bad news. The EC135 uses a sophisticated computer to control the engine. Safety is typically guaranteed with multiple fully redundant computers and wiring paths, but if all electrical devices fail at the same time the turbine is no longer under control. To quote Wikipedia:

  • If a total FADEC (Full Authority Digital Engine Control) failure occurs, the engine fails.
  • Upon total FADEC failure, pilots have no manual controls for engine restart, throttle, or other functions.

No electricity, no engine.

Fortunately we can safely assume the turbine is at least engineered to fail safe, it won't spin itself out of control. Unfortunately that means "shut down". So yes, you lose main engine power.

Fortunately there will be some residual power in the turbine as it spins down. That plus the energy in the rotors can be used to autorotate as covered by GdD.

But... is the pilot still able to fly it? Is it probable he would land successfully? Does the helicopter need any electricity to stay flyable?

Yes, fly-by-wire helicopters are very rare. While they will no longer be augmented, stabilized, or power assisted, the mechanical linkages will still work. And they'll be able to autorotate, as @GdD described, and as demonstrated in this Smarter Every Day video.

However, sudden loss of engine power, and of all their flight control augmentation, and any electronic instruments, might confuse the pilot. An experienced pilot will still autorotate and land, but it probably won't be as pretty as in the video. I found an actual crash report of an actual EC-135. The experienced pilot thought they'd lost all engine power, went into autorotation, and landed with no injuries, but trashed the aircraft. In fact the engines were fine, but they lost their Stability Augmentation System. Reading that report might help with your book.

Helicopter pilots train for a sudden loss of power and emergency landing. If they still have control over the aircraft they will be able to land it.

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    $\begingroup$ The EC135 is not a FBW helicopter. It has conventional mechanical linkages with hydraulic assist (like power steering or a Boeing 737). It has electronic augmentation, but it isn't necessary for basic flight. The first FBW civilian helicopter, the Bell 525 came 10 years after the EC135. $\endgroup$ – user71659 Feb 9 '18 at 5:39
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    $\begingroup$ @user71659 Did I misread the Defense Aerospace article? Was that an experiment? $\endgroup$ – Schwern Feb 9 '18 at 7:29
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    $\begingroup$ @Schwern The article clearly states is was a demonstrator... a production model that was retro-fitted with the Fly-By-Light system. $\endgroup$ – MichaelK Feb 9 '18 at 9:53
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    $\begingroup$ @Schwern The article describes an event from 2002 while EC135 are flying since 1996. But indeed it's written in a way that's confusing without researching further. Although it mentions that it's NH90 that will be the first production fully FBW helicopter. $\endgroup$ – Agent_L Feb 9 '18 at 16:57

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