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I think that the glass cockpit of a modern plane has some sort of a central power supply or at least some central controlling software.

What happens if this central power suddenly disappears, or the central software freezes? Yes, of course, this would be a severe failure and would put everybody's life on the plane in serious danger.

Is such a failure possible?

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    $\begingroup$ I see that you removed the speculation. I have reversed my close vote. $\endgroup$ – Simon Mar 25 '15 at 21:06
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    $\begingroup$ Thanks for removing the speculation and please do not add further questions, or manipulate existing questions, to speculate on any real incident. It is a very sensitive subject and no-one here wants to comment until the accident report is published. We have no way of knowing if you, or any other user, are actually a journalist who may quote something said on this site. I am not saying that you might be, just explaining why we don't like speculation here. $\endgroup$ – Simon Mar 25 '15 at 21:13
  • $\begingroup$ I remember to have heard about an Airbus whose Displays (not sure if it was the whole system) shut down during a maneuver where the sensors of the airplane sent values to the computer that it thought must have been wrong (gotta be one heck of a maneuver) and thus did a restart to reboot all the sensors. I think this Display failure last for about 3 seconds, then everything was back up and working. I'm still searching for a report though, so don't quote me on that! ;) $\endgroup$ – Maverick283 Mar 25 '15 at 21:18
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    $\begingroup$ @Maverick283 That's not a bug, that's a feature. When sensor informations are thought to be inaccurate, aircraft try to prevent it to interfere with pilot action and decision process by... Removing it. Some pilots use tape to hide non-glass cockpits instruments once they are believed to failed. $\endgroup$ – Antzi Mar 26 '15 at 4:08
  • $\begingroup$ @Antzi Jupp totally agree didn't mean to make it sound like a bug... $\endgroup$ – Maverick283 Mar 26 '15 at 7:54
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If the power suddenly disappears to any aircraft (ie, a total electrical failure including the batteries), then all the aircraft systems will be failed regardless of whether or not they were glass. This is highly unlikely because there are several power generation backups that would have to fail, including the batteries themselves, before this ever became a reality. Unfortunately though, if the aircraft only has electrically controlled, hydraulically actuated control surfaces (fly-by-wire), vice actual mechanical linkages (or backup controls), then a total electrical failure would be 100% fatal if power cannot be restored. The control surfaces would not be movable.

However, more to the question regarding software bugs, all primary flight instruments are backed up to prevent such disasters from happening. I have personally lost all the digital displays in my cockpit and flown a no-gyro, surveillance approach in bad weather using nothing but a peanut gyro. Its possible, but definitely not a good time.

Anything is possible. However, even though the odds of a total electrical failure, or complete loss of instrumentation (including backups) is nominally greater than 0%, the statistical probably can still probably be rounded to 0.

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  • $\begingroup$ No aircraft where no control surfaces would be movable without electric power exist! In most large aircraft they are not movable without hydraulic power though. $\endgroup$ – Jan Hudec Mar 26 '15 at 5:51
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    $\begingroup$ @JanHudec The Super Hornet is one such aircraft. $\endgroup$ – Rhino Driver Mar 26 '15 at 6:45
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    $\begingroup$ Hm, true, aerodynamically unstable fighters would not be controllable with mechanical backup anyway. It does apply to airliners though. All airliners have (hydro-)mechanical backup. $\endgroup$ – Jan Hudec Mar 26 '15 at 7:01
  • $\begingroup$ @RhinoDriver (sorry for the late react) I think these various power sources are selected and regulated by some unit, which decides when, from where to transport the voltage into which direction. This unit/device is a critical part of the plane, if it dies, everything dies. It would be possible to make also this redundantly, for example to have at least 2 of them, but it would much more than double the complexity of the circuitry. And more part means also more fault... $\endgroup$ – Gray Sheep Dec 7 '18 at 1:51
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While total electrical failure in a transport-category aircraft is extremely remote, even fly-by-wire airliners such as the A320-380 and B777/787 have redundant backups that would work under the scenario: in the case of the Airbus, you'd fly using the rudder pedals for yaw and roll and manual stabilizer trim for pitch, while Boeing uses a pair of spoiler panels for mechanical roll backup instead of the rudder.

All of this, of course, depends on the presence of actuator hydraulic power - if you have no hydraulic power and no electric power on a FBW Airbus or Boeing (including a loss of the dedicated FADEC/EEC backup permanent magnet generators), you're toast because not even "fly by thrust lever" a la UAL232 and OO-DLL will save you in that case.

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    $\begingroup$ If all hydraulic and electrical power fails at once, then you're probably firmly in "hypothetical scenario" land (and at some level, all planes will crash if enough stuff fails). $\endgroup$ – cpast Mar 26 '15 at 1:24
  • $\begingroup$ @cpast -- closest I've seen would be the Aloha zip-top 737 -- I suspect the controls on that plane did go into manual reversion... $\endgroup$ – UnrecognizedFallingObject Mar 26 '15 at 1:38
  • $\begingroup$ A total electrical failure assumes you don't have PMGs or battery power, in which case you wouldn't have FADECs either. To end up in this scenario you'd need to have a bad battery during the same flight you shed both gens and then shredded both AMADs leaving you with no PMGs. To add insult to injury you'd also be flying via rat powered hydraulics, so life would suck a lot. Maybe if you got hit with a manpad... but even then you probably wouldn't have a wing to fly with anyway. $\endgroup$ – Rhino Driver Mar 26 '15 at 3:03
  • $\begingroup$ @RhinoDriver -- yeah, I suspect this might be worse than a mere MANPAD that hit you...more like a SA-2 with a bad prox fuse poking a hole in your lower forward fuselage then exploding! $\endgroup$ – UnrecognizedFallingObject Mar 26 '15 at 3:10
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    $\begingroup$ @raptortech97 -- a double uncontained engine failure would be luck of the draw, yes -- it depends on the plane whether you still might have a hyd or not though. For instance, an A330 would automatically be in bad shape in that case (all the hyds on that plane are driven off one engine or another), but an A320 would have a chance (it depends on whether the blue system survived) and the same holds for the Boeing non-reversion twinjets as their center systems do not have an engine driven pump. $\endgroup$ – UnrecognizedFallingObject Mar 26 '15 at 3:53
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But, is such a failure possible?

The answer to if such a failure is possible is on some level yes. But for what its worth no. There are a few things to consider.

Redundant and Independent systems: Aircraft typically have not only redundant systems but independent systems in other words not only are there back ups but they are often separated so that a failure in a single system or set of systems should remain isolated. From a power standpoint a plane gets is electrical power from the turbines driving a generator. Each turbine has at least one generator (maybe more Im not sure) so if a single engine were to cut out you would not lose power generation. You may need to shut the lights off to not over draw the generator but you could still power the key systems. Aircraft also have batteries in the case of total engine failure. keep in mind that in a total engine failure you will be on the ground long before you kill the batteries I would think.

Multiple Electronic Busses: To my knowledge larger airplanes have multiple electric busses each of with can be independently tied to and disconnected from the main buss as well as joined if needed. If one buss fails you can switch over to the other to draw power for the aircraft. Keep in mind that if a surge causes the failure the components would be protected by the fuses.

This is even finding its way into smaller GA airplanes. It is possible to order some small planes with 2 alternators now I believe the Cirrus SR-22 can be had in such a configuration.

Now that we have established that there are actually multiple central power connections lets look at why its so remote they fail. If you take 2 systems that are (for the purpose of this example) created equally, have the same run times on them and are serviced the same etc. they would have the same chance of failing at any given moment in time. That being said the chances of them both failing at the same point in time is so remote it can almost be ignored. The idea here is that we can accept a single system failure, complete the flight, and then send the plane in for repair.

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There have been incidents where the primary flight displays have failed somewhat as you describe: example 1, example 2 (one each for Boeing and Airbus so I'm not taking sides). So yes, things can fail, causing cockpit displays to go blank and other problems.

That said, there's a lot of redundancy in these systems. Cockpit display systems are somewhat separate from flight control systems, so the failure of one may not impact the other. As UnrecognizedFallingObject notes, there are even some options for manual control in the event of a total fly-by-wire failure.

Modern glass cockpit aircraft have a small display, usually toward the center, with standby instruments (Airbus calls it the Integrated Standby Instrument System). This is a separate LCD display, powered independently by the emergency bus and driven by its own computer, designed to display altitude, airspeed, and attitude. This provides the crew with essential information toward making an emergency landing.

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