I guess we'll know if this was the case if the new procedure from Boeing to address this fault is:

1. Power up APU;
2. Power down both donks;
3. Wait for APU-powered electrical busses to come back on line;
4. Pray that both donks (or at least one) can be restarted.

That fault report (thanks JumpJumpJump) is interesting reading.
Question: How do the time stamps relate to the actual flight? Quite a few faults are logged around 20-Dec : 02:55 (Zulu, I assume) and then a few more at 20-Dec : 03:46. This appears to be a few minutes after landing. But since this incident seems to have gone on for around 3 hours, the earlier logged times don't appear to correspond with the onset of the problems.

Lots of discussion about the AC busses, looks like an ELMS failure to me. Electrical Load Management System going haywire.

I'm pretty sure the ACE's (Flight Control System) are powered by 28v DC from PMG's (Permanent Magnet Generators on each of the engines) which is independent of all the AC power distribution systems. The fly by wire system would likely have been unaffected by the loss of AC power on the three busses.

It is interesting to hear that the RAT did not reconnect AC power to the busses. Were both bus tie circuit breakers tripped? or was the ELMS load shedding everything? How is it the transfer bus remained unpowered with the Rat deployed???

Hat's off to the crew, very impressive presence of mind and aviation skills.

If like the 787 then ACEs on independent PMG, but PFC on normal electrical network. Hence loss of autopilot and other degradations.

Any more news on this incident?

Megan touched on the question of ETOPS (23rd Dec); I'm guessing this was not an ETOPS flight; correct?

But even if not, was the aircraft maintained and equipped as an ETOPS aircraft?

I wonder how things would have gone if an unconnected (or indeed connected) engine failure had been added to the crew's problems, shortly after the electrical failures at 0254 and 0255?

All 777's are ETOPS qualified - its not like the old days where you had some 757's that were ETOPS and some that were not and they had different components on them.

Two decades years of certifying 777 electrical systems and I have never seen anything like this before.

Having read the limited public informational available (particularly the AHM report), and just thinking aloud, I can't help thinking...

The 777 has only a single Back Up Converter controlling both Back Up Generators and both Transfer Busses.

..and wondering...

Would this incident still have happened if each Back Up Generator had it's own, completely independent, Converter?

I am not speculating on the cause - I just don't have access to the detailed information to answer this question.

At least they have the entire undamaged aircraft, so hopefully the real cause will be found and remediated.

It does appear that the backup generator/converter system was involved and may have been the root cause of this sequence of events. If so, there are two possible solutions: Provide separation within the backup system so as to eliminate a single fault from taking both main AC buses with it. Or make ELMS smarter so as to clear faults with greater selectivity and not disconnect unfaulted sources and buses.

It all comes down to certification costs. While redesigning the backup system to provide additional channel separation would seem to be a more sound solution, there is a strong motive to 'fix it in software'. So I'm betting on a patch to ELMS.

Surely it comes down to safety.

If the design is faulty it needs to be fixed, "putting a patch on it" but leaving the root cause to rear its ugly head some time in the future, isn't an option.

Luckily this time no lives were lost, that might not be the case if it happened again.

Please remind me how the B787 battery issue was "solved". Was the root cause addressed or a "safe(?)" box put over the battery?:)

Well, the battery was completely redesigned. The battery charging system was completely redesigned. Then, because the damage to the event batteries was so severe they were unable to conclusively determine root cause, as a failsafe they put the battery inside a steel box that would contain any possible battery failure.
Appears to have worked - prior to the redesign there were two failures on 50 aircraft in a few months. Seven years later, with about 600 aircraft in service, there has been a grand total of one battery failure - which due to the battery redesign was contained to a single cell.
So yes, they fixed the 787 battery problem by putting a box over the battery :ugh:
Constantly repeating the myth that all Boeing did was put the battery in a box doesn't make the myth true.

Fixing ELMS logic to clear faults more selectively (i.e. not dumping all the sources) is a legitimate fix. One may not be able to identify all possible future fault conditions. Even by redesigning the backup converter. The redesign of which might create a whole new batch of unforeseen failure modes. So handling them properly would be a good approach.

Its providing more (possibly better, possibly worse) complexity, but not addressing the SPOF, therefore not a legitimate "fix", but merely an enhancement that hasn't removed what can still turn out to be an un-recoverable failure.

Had ELMS not dumped two perfectly good generator sources, there would have been no single point of failure. At most, a change in the ETOPS capabilities.

Usually, that is discouraged in such situations. Closing a breaker into what might be a fault could result in even more serious damage. Cycling a circuit breaker can be OK to 'shake loose' a brain-dead processor. In that case, if you opened the breaker, you can close it (deferring to the published operating procedures, of course). But if it tripped on its own, I'd be hesitant to re-kindle a fire someplace.