Originally Posted by
HUD Engineer
I don't think it was quite as you suggest, but with reported loss of primary displays and reported loss of control it is instructive to note that in the anticipated situation for which FAA-2015-0936 Interim Airworthiness Directive that at a predictable point in time the 4-off Generator Control Units could simultaneously go into Fail-safe mode and deprive the aircraft of AC electrical power, it "could result in loss of control of the airplane" and could occur regardless of flight phase That related to exceeding a 248 day powered period, so the AD instructed that power was removed at least every 120 days.
Regarding the 120 day maintenance action interval, note that in 2020, FAA-2020-0205 (not an Interim AD) was raised due to counter/timers associated with the Common Core System, that could affect data integrity after 51 days, and a power-down repeat interval of 25 days was specified in B787–81205–SB420045–00, Issue 2.
There may well be other mechanisms that have similar symptoms, so
In this case, they should have a lot more info from the aircraft, although if the CCS was interrupted, the Enhanced Airborne Flight Recorder might have some missing ARINC 664 data.
The immediate take away is that whatever did occur, the point in the flight and the actions taken recovered the situation, which 787 pilots will hopefully learn more about soon.
Disconnect and reconnect power at least once every 120 days, but maybe it should be every 25 days.
Wot cood posiblie go rong?
It's as if the writing of and functioning of software in aircraft systems isn't the subject of standards. If only software engineers could anticipate the remote possibility that the software they design will be running continuously in hardware that doesn't take a coffee break.