Hi Chris.
No, I do understand the role of the APU. Simplified: The APU must be available in an emergency, or other. The APU may need to acquire a start from the APU BATT. Fine. Let's say the APU starter circuit is not available, the APU BATTERY is used to spin up a start.
1. The APU starts, and provides power. Standby Batteries go off line.
2. Once started, the APU has two 225kva generators, capable of powering the aircraft without the need for additional power from APU BATT EMER.
3. The APU won't start in:
a. Normal flight? no problem, the Two main engines have ample power
b. Emergency? Now this is a problem, and the APU cannot supply power, it has not started. so,
c. The APU BATT can supply power to exhaustion, (What is that Requirement?)
d. The RAT deploys, providing ELEC. And HYDRAULIC.
I think my question would be: If using APU for ground power, the APU battery must be recharged in isolation, first, just as one would not attempt a start on APU with APU circuits open, the draw on its start BATTERY could be a serious problem....From the data of these two incidents, the problem seems to be around the BATTERY being on line when using the APU on the ground, and recharging the APUBATT at the same time.
So the answer in the interim may be to start the APU off the GEs before shutdown. And whilst airborne. GE starting Pratt Whitney, that's kind of....cute.....Keep the APU BATT as a STAND BY, unless in an emergency. It seems kind of, creepy, to see the APU started by a cleaning crew., using sensitive LITHION power.
As in JAL/BOS?
Last edited by Lyman; 22nd January 2013 at 23:59.