Electrical Power Supply Split A320/321
 

In the event of a single generator failure on A320/A321, landing cat is downgraded to Cat 3 single. This is the case even when the APU is supplying the affected side. I've been told that the FMGC doesn't recognise the APU as an "independent" power supply (as it does on the A330), but as I can't find the answer in the FCOM's could someone please tell me why ?

According to Airbus:

The power supply split function, that monitors the electrical segregation of the FMGCs, does not consider the APU generator
as an independent electrical source. As a consequence, when an engine generator is lost the capability is automatically downgraded to CAT 3 SINGLE. The electrical power supply split function monitors:
- The two BUS TIE contactors and
- The DC TIE contactor (between DC BUS 2 and DC BAT BUS).
When one of the above contactors is closed, the FMGC considers that the power supply split is lost (independently of the APU generator).

I have been told that the A330 does not have this restriction. Since the probability of this limitation impacting a flight operation is so low, I doubt if a retrofit to the A320 electrical system could be economically justified. I am not sure why this information is not included in the FCOM. Maybe if AI gets enough questions about this subject, they could make an addtion to the manual.

Regards,
The Kid

Thanks AK,