Originally Posted by
elonmussk
In case of engine failure ,Most of instructors were saying that we should start the apu for electric backup source.
meanwhile there was one instructor who says that we might want to reserve the battery power by not starting the apu,
because he said the Starting APU uses battery power..
He was insisting that if the apu didnt start for some reason then it would end up using battery power.
Which means, if we get to lose remaining generator for some reason (I dont think so,. but...)
it would lead to electric emergency configuration,
if we had have used battery power with starting apu, saying that it would shorten the time with electricity .
I looked up the FCOM. but I couldn't the answer.
Anyone knows the answer?
He was kind of disrupting person anyway.
But I kinda wanted to know the real answer.
I thought the remaining generator could start the apu even with the engine failure.
If the APU doesn't start, whatever battery power you lost would be replenished by the remaining generator. To take the instructor's logic to the absurd conclusion, why ever start the APU at all?
We don't have a defined point at which we start the APU after engine failure. We just do it when we get to it. As somebody said, this is usually done by the time we're reviewing the ELEC page.