777 Total Electrical Failure - then what?

[TheDrop]

Despite all the redundancy, what would happen to a 777 experiencing total electrical failure?

Many systems are electrically powered, including flight controls. But if there isn't any electrical power?

If some major failure, explosion or other extreme event happened in a critical place, like in the MEC, which totally fries the electrical system - and renders all generators, RAT, batteries, and buses useless in an instant.

I know it is "impossible" with all the redundancy, but so was the triple redundancy on the DC-10 hydraulic systems - yet a single failure took out all three systems. So just for a moment, presume all electrical power is lost (apart from autonomous systems, like the engines, ELT, flashlights, Rescue 406 etc)

Aircraft is until the time of that event on auto pilot and in trim.

What will happen to


Engines - as they make their own electrical power and have mechanical fuel pumps that suction feed - will they keep operating at the last set power setting?

Flight Controls - will they remain, center or be free moving? Assuming hydraulic pressure is still there

Flight Controls - are there any mechanical backup, any hydraulic, wire, rods or similar which gives any control of primary or secondary flight controls?

As fuel is burned, will aircraft stay in trim more or less, or have a tendency to pitch up or down? Will it keep stabilising, though at varying altitudes? Can all the fuel be suction fed from engine driven pumps?

Cabin pressure - what happens to the outflow valves if power is lost?

Can the ELT be manually activated from the flight deck, if all electricity is lost? Maybe even the wire between the ON-ARM-OFF switch, and the ELT itself, has been broken by whatever caused the failure.

[atakacs]

I would say that complete electrical failure = major structural failure. To get there you would have some (chain of) events that will imply that the aircraft is otherwise significantly crippled. I don't think there is any other scenario possible, however improbable.

[Dont Hang Up]

I would say that complete electrical failure = major structural failure. To get there you would have some (chain of) events that will imply that the aircraft is otherwise significantly crippled. I don't think there is any other scenario possible, however improbable.

And, while thousands of posts on another thread join a very small number of dots to draw any number of wild and mystical creatures, I suspect that is exactly what we will find. The only question will be the cause of the major failure.

[TheDrop]

Fly the aircraft. That would be your main concern. What if flight controls didn't even respond?

Imagine the scenario, all goes black, and all you have is your flashlight and the light of the stars and moon, if at all. Emergency lights may work?

EDITED

[ArmstrongR]

Could just switch it off and switch it back on again. Or put more money in the meter.

[Dont Hang Up]

Imagine the scenario, all goes black...,

On the other thread every other guy is trying to write a Hollywood screenplay. Now you are starting on this one!

Please read atakacs reply and leave it there.

[TheDrop]

Yes, you are right, I deleted that part.

Shouldn't we know our systems well enough to know what options we have in such situations?

Do you know your own aircraft type well enough to answer the questions above?

[SMOC]

Engines would still run - suction feed.
Engine thrust levers "MAY" work as the thrust lever resolvers are powered by the EEC. (But doubtful).

Hydraulics ok - engines running.

Packs still run - power fail, they fail ON/RUN however the packs would go to high flow and over pressurise the cabin as the pressure control system would have stopped, the over pressure relief valves which are mechanical would open around 9.2psi

Flight controls - mechanical cable input to one spoiler each wing & stabiliser via the manual stab trim levers and all possible with hydraulics available.

Fortunately the A/C should be in trim and speed stable.

Reasons for complete power failure.
1. Oxy bottle explosion like the QF 744 (other thread confirms location of oxy bottle in the 777 is next to the MEC).
2. Galley water leak flooding the MEC, once again a QF 744 that ended up on battery power.
3. Decompression near the MEC causing structural damage to the MEC and therefore it's failure.

1. Would lead the cockpit crew unconscious & the A/C drifting through the sky for who knows how long and in which direction.
2. Crew able to fly but effectively lost, stby compass only, ISFD would fail without power.
3. Would be a combination of possibly 1 & 2.

All cases extremely difficult to pull off successfully without a fantastic moonlit visual night for visual reference.

[LME (GOD)]

Not all the critical boxes are in the MEC. Some are stashed in the forward cargo sidewalls to give limited flight controls. The RAT should auto deploy and/or APU auto start.
So.....You will have limited flight controls. Might be a dark cockpit, but the engines are self contained and will keep running. EEC's powered by the dedicated generator on the engine. Whiskey compass will work to give you a dead reckoning course. The rest will involve a bit of luck!

[SMOC]

I think the problem is all the power distribution is in the MEC so the boxes will become unpowered, but if any power is available at least some things not near the MEC would be ok. :ok:

[TheDrop]

Air Accidents Investigation: N786UA Report Sections (http://www.aaib.gov.uk/publications/formal_reports/2_2009_n786ua/n786ua_report_sections.cfm)

United Airlines had a fire in the MEC, while they were on the ground, just around push-back.

What if they had experienced this same problem in flight?

If there is a major disturbance in the MEC, either fire, explosion, flooding - how can you discount a total electrical failure?

[tdracer]

Engines would still run - suction feed.
Engine thrust levers "MAY" work as the thrust lever resolvers are powered by the EEC. (But doubtful).


Why do you say 'But doubtful'? EEC is powered by a dedicated engine generator, 100% independent of the aircraft power system, and thrust set is determined by the actual throttle position, as determined by the EEC driven throttle resolver (as you correctly noted).
Assuming suction feed works (may or may not, depending on altitude and how 'weathered' the fuel is (i.e. how long it's been at altitude, and how much air is still dissolved in the fuel), the only thing that would prevent the engines from operating more or less normally is if the throttle resolver wiring between the flight deck and EEC was severed.


BTW, the 777 has, on each engine (in addition to the dedicated EEC power source), a 'normal' IDG, a VSCF (each engine's VSCF capable of powering the aircraft critical system), and a dedicated FBW generator. Oh, and addition to the battery there is a generator on the RAT. Within the EE bay, redundant systems are separated by a minimum distance (it's been a long time since I worked the 777 development, but 5 feet sticks in my mind).


Baring something really nasty happening in the EE bay (such as a large bomb blast), there is simply no way to loose all those redundant, independent systems at more or less the same time.

[EEngr]

LME (GOD) (http://www.pprune.org/members/7636-lme-god-):

Whiskey compass will work to give you a dead reckoning course. The rest will involve a bit of luck!

Following the loss of all navigation equipment, I think any resourceful flight crew would round up some PAX iPhones with GPS and head for somewhere with a runway. And once within range of cell service, phone in with their status.

[SMOC]

Why do you say 'But doubtful'?

I say doubtful due to the fact that if the MEC is damaged (structurally / fire / water etc) so badly to basically shut down the cockpit it probably severed / shorted the connection between the cockpit and the engines.