Originally Posted by
Zeffy
Would an unserviceable APU indicate that electrical bus configurations may have been changed at some time during the flight?
Perhaps I'm assuming too much -- does ETOPS on a 777-300 require an operational APU for dispatch?
According to the FAA MMEL you can do 180 minute ETOPS on the 777 with an inop APU generator with both engine IDG's working and backup AC checked before every flight. Some of this MEL stuff is grandfathered from the 767 ETOPS certification three decades ago.
I've never been comfortable with generator inop dispatch on an ETOPS twin but there is indeed MEL relief in many cases.
I too am curious whether the APU was dispatched inop or was unable to start due to some electrical fault? Or was an IDG dispatched inop and some glitch propagated through the electrical system when a breaker opened or failed to close with a bus loss on the first approach?
Years ago I took a non-ETOPS 757 with an IDG inop. There was an unusual pause before the legacy CRT screens came back up after the first engine start, maybe some relay clicked out of sequence. Airborne the heading bug on the EHSI became unsynced with the HDG window on the MCP. We were in VNAV and it didn't look right so we tried FLCH and then both lights were illuminated. It was the old days and a short leg so we popped off the autopilot and flew the plane to the destination without the benefit of autoflight (oh, the horror
). On the ground the mechanics removed all power from the plane and restarted, it seemed to reboot the FCC's and we handed the aircraft to another crew.