A320 BCL1 Fault APU START

[Bkdoss]

Hi everyone,

In case of BCL1 fault on the A320, the FCOM says APU BAT START not available. The Capt. who I happened to fly with, was of the opinion that APU was inop, whereas I contended that only APU start with the aircraft on BAT power was inhibited as the ECB is supplied by DC BAT BUS and as this is supplied by the normal electrical network, APU could in fact be started. The Capt. then went on to show (on a different aircraft with no BCL fault) that actually during the APU start, BAT1 and BAT2 gets connected to the DC BAT BUS momentarily due to the huge surges in requirement for APU start and hence APU should not be started. I contended that being the case, AIRBUS should have said APU START not available and not BAT START not available. Can anyone throw light on this ?

[dream747]

You need the batteries to start the APU. The batteries pb must be in the auto position to start the APU even if external power is connected. Otherwise it will not start. And there is no fire protection.

Also, refer to the MEL for the said fault directs you to start the engines with external power and do not start the APU.

[Bkdoss]

You need the batteries to start the APU. The batteries pb must be in the auto position to start the APU even if external power is connected. Otherwise it will not start. And there is no fire protection.

Also, refer to the MEL for the said fault directs you to start the engines with external power and do not start the APU.

But the BAT are in AUTO position, even after the fault triggers. In fact the fault has no ECAM actions. It is just crew awareness. Secondly my understanding of the MEL was because it allows you to operate with APU inop for 10 flights, the manufacturer doesn't want you to drain your batteries by starting the APU every time. Last of all, according to the MEL preamble you're supposed to only use the MEL procedure which is valid for that phase of the flight. Since the procedure Don't start the APU is a part of Flight preparation in MEL, and you being already in the flight phase you're not required to adhere to it.

Can you please specify where in the FCOM does it say that there is no fire protection with the BCL not working ?

[Lantirn]

It actually refers to DC BAT BUS fault. Not in single BCL faults.

This is the reason why you should test the batteries one by one when apu is running.

APU can be started if needed, but shouldn't for the purpose of MEL. If it's started, maintenance action is due. Of course if you need it, it's there

[RUMBEAR]

This was a discussion recently in my company. The fault in question was a BAT 1 Fault however the status Page was the same. The "APU BAT START ONLY" status message is displayed as a limitation. Can confirm from the simulator that the APU start is available in flight, however the end result of our discussions was that the BAT start was not available due to BAT performance ( also the same reason why both BAT 1 + 2 must be selected to AUTO prior to APU start at pre flight. Even though the APU will start with only one BAT selected to AUTO.).

If you have a DC BAT BUS fault then APU start/operation is not available as the APU ECB is not powered. Having said that the status page also shows "APU BAT START NOT AVAIL" as a limitation, however can again confirm that with APU operating and before engine start if the DC BAT BUS fault is simulated the APU will shutdown due to APU ECB not being powered.

[Bkdoss]

This was a discussion recently in my company. The fault in question was a BAT 1 Fault however the status Page was the same. The "APU BAT START ONLY" status message is displayed as a limitation. Can confirm from the simulator that the APU start is available in flight, however the end result of our discussions was that the BAT start was not available due to BAT performance ( also the same reason why both BAT 1 + 2 must be selected to AUTO prior to APU start at pre flight. Even though the APU will start with only one BAT selected to AUTO.).

If you have a DC BAT BUS fault then APU start/operation is not available as the APU ECB is not powered. Having said that the status page also shows "APU BAT START NOT AVAIL" as a limitation, however can again confirm that with APU operating and before engine start if the DC BAT BUS fault is simulated the APU will shutdown due to APU ECB not being powered.

Thanks Rumbear. You have confirmed my conviction. Besides when I referred the FCOM again only in DC BAT BUS fault does the APU fire extinguisher become inop. So I guess as you say we can start the APU in Flight with BcL fault or one of the BAT off.

[dream747]

Make sense guys. I stand corrected.