A320-Red flag on standby horizon with AC1 fail?

[bloggs99]

Anyone know why a red flag appears on the standby horizon with an AC1 fail on the A320? Cannot see why this should occur since it is powered by the DCESS

Even though flagged it seems to work ok though?

Any ideas?

[captainpaddy]

Hi bloggs!

If you have not yet selected the AC ESS feed pushbutton to ALTN, then you will have lost both AC and DC ESS busses. Therefore you will have lost the supply to the Standby Horizon. It will still continue to work for a while though until it loses RPM.

The AC ESS feed pb transfers AC ESS bus to AC BUS 2. The DC ESS bus is powered from the AC ESS via the ESS TR!

If you have already selected the AC ESS feed and you still have the red flag in the AI then I'm afraid I'm stuck too!

[bloggs99]

Yes I see that now. the scenario I was 'playing' with in the sim was a DMC2 fail with a subsequent AC1. This means you lose all screens until the ACESS feed selected. Since no ECAM couldn't look at electrical config (which would have answered the question). Very scary scenario since DMC2 in flight is a pretty innocuous failure but then with an AC1 you lose pretty much everything and no clues to get you out of stum (just an amber on the ACESS feed being perhaps a clue) unless you had looked at the MEL which warns of this failure and advises on the action. I cannot understand why airbus do not have an automatic transfer of the ACESS or at least put the drill for this in the QRH since no ECAM.

Anyway, that answers my question, many thanks.