View Full Version : Air China loses power to cabin, comms, navigation, and RADAR?

16th Dec 2017, 20:53

Seems like some rather desireable avionics lost for what appears to be the loss of just one engine (would have thought the remaining engine and APU would be more than capable of covering the deficit). Is this more likely to just be the media getting it wrong again?

Water Wings
16th Dec 2017, 21:26
I have some issues with the report. Something has obviously happened but the aircraft (from avherald) returned to Auckland at FL330 which would be a pretty darn impressive engine out drift down altitude to maintain!

Incident: Air China B789 over Pacific on Dec 15th 2017, half lit, half dark (http://avherald.com/h?article=4b268b68&opt=0)

16th Dec 2017, 21:30
The press has it wrong. It is normal in a twin to load shed non essential electrical systems after a engine failure. I suspect that is what happened.

16th Dec 2017, 21:34
My thoughts exactly. With APU available, would it not be reasonable to expect ALL cockpit avionics to remain functional?

16th Dec 2017, 22:13
Nav, Comms, and radar are all essential AC powered devices. These loads would not be shed during SE OPS. The operating engine generator automatically powers the failed engine's AC bus and a manual bus tie can be initiated if needed.

The only common scenario where the above mentioned avionics would be lost is if there was an AC bus failure, or electrical control box failure, however, it would only be half as the remaining side (NAV1 or NAV2, etc) would remain powered.

As essential electrical equipment*, communication radios, navigation gear, and radar would be unpowered in the case of the loss of GEN1, GEN2 and the APU generator or a bus failure as mentioned above. Even in such an emergency electrical configuration, there typically remains at least one COM, one NAV unit, etc operational. This arrangement is fairly standard across all large transport category aircraft.

*with the exception of the HF radios and SATCOM, if fitted.

16th Dec 2017, 22:36
Just as I thought.

So to lose com and nav they're going to have to lose both engines, APU, RAT, and the battery - at which point they probably have more pressing issues to deal with. Unless as you say, some very unusual bus / switching issues.

SMT Member
16th Dec 2017, 22:45
Or, alternatively, the 'all'-electric architecture of the 787 has just shown us a failure mode which shouldn't be possible. Then again, the battery was supposed to be fail-safe too. Until it wasn't.

The 'report' from passengers saying all lights went out on the same side as the shut-down engine are, if correct, certainly very interesting. That probably shouldn't be possible either.

16th Dec 2017, 23:26
There is always the possibility that some of the problems resulted from the reaction of the crew.
And the first link shows a piccie of a 777, whereas the second mentions that it was a 789... can't anybody get anything right?

Needle Knocker
17th Dec 2017, 02:06
Accuracy and balance have never been strong points when it comes to the media; even moreso with aviation "articles".

17th Dec 2017, 08:31
Incident: Air China B789 over Pacific on Dec 15th 2017, half lit, half dark (http://avherald.com/h?article=4b268b68&opt=0)

Avherald initially reported it as a "787-900" (and GEnx-powered!).

Engine type now corrected to Trent 1000.

17th Dec 2017, 08:58
The AvHerald report is slightly misleading, “ the left hand engine failed causing the loss of electrical power for ...”.
An engine shutdon usually involves loss of a generator, but not the consequential loss of electrical systems as described, particularly if this was an ETOPS rated aircraft.

17th Dec 2017, 10:40
So it's either a bizarre aircraft system failure or a bizarre aircraft pilot failure. At least it will be investigated by the Kiwis, who are more likely to produce a useful report than some other authorities on the way to Beijing.

17th Dec 2017, 13:57
It doesn't say it lost ALL the comms, does it?
Possibly just had a dead bus (not that that's good after an engine fails on a twin), shutting down either the nr 1's or the other sets..
Should be easy to find out for some of the ATC tape wizards, there's probably one in Auckland;)

17th Dec 2017, 15:42
The press has it wrong. It is normal in a twin to load shed non essential electrical systems after a engine failure. I suspect that is what happened.

Well, having flown this airplane, I can assure you that there is no ‘load-shed’ to half the aircraft. There is something else at fault here.