APU Starting - Gulfstream V
 

Guys

Could anyone confirm for me if the GV can start the APU on only one of the two batteries. Or do they have to work in parallel?

If anyone could provide me any details, i'd really appreciate it.

Many thanks

high-flyer

I've been out of the aircraft for a couple of years now, but to answer your question: When on the ground (or inflight with two operating generators), you use both batteries when starting, inflight and on one generator, you only use one battery. I should also add that inflight, with no generators, use both batteries for start.

Now, this may an old procedure, but my AOM states the reason for using only one battery inflight (with only one operating generator) is to "conserve battery power, and it's been proven effective for APU starting, especially at high altitude." APU starts are guaranteed to start up to FL390, and may start up to FL430, but in my case, the APU failed to start after two attempts at FL370 after I had a GCU failure which knocked off one generator while over the Pacific.

On the ground both batteries must be on.

In the air, no generators operating - both batteries must be on.

In the air, at least one generator operating - one battery must be off to prevent the already windmilling APU from over-accellerating.