A320 Electrical system backup

[redout]

Just a quick question on the A320 electrical system. I was just studying it and wanted to know if you could look at it as follows: APU as the first backup, Emergency gen (RAT) as the secondary backup, then finally the Static inverter. Is that order correct or can it change for different scenario's ?

[dartagnan]

you are correct cuz the RAT deploys automatically.

there is a switch to deploy it anyway.
the batteries are good for 30 minutes and only systems for the captain works. the RAT stalled under a certain speed (120?)

[Dan Winterland]

140 with the olds RATS, 125 with the newer ones. How do you tell? If you have a look at the upper CB panel and if two CBs have yellow collars (D 02 - Anti Ice Pitot 1 and F 07 - ADIRU 1) then it's an old style RAT. These C/Bs are pulled to extend flight time on Batteries only to at least 30 minutes and are only part of the drill for the older aircraft.

[Dusthog]

The "NEW" RAT is available on the A320 from MSN 1045 onwards provided FWC E3 is installed.

[Tail-take-off]

Redout

You are correct except that in the case of a simultaneous double generator failure the recommendation is not to start the APU.


FCOM 3.2.24 ELEC EMER CONFIG
In case of simultaneous engine generator failure, the probability of a successful APU GEN coupling is low. Therefore APU start attempts should be avoided, as this will consequently reduce the flight time on batteries only (by about 3.5 minutes for one start attempt).

This is because in emergency elec config with the older RATs you are left with battery power only when you put the gear down.

You would not want to be flying an electric aircraft on just the battery if it had been depleted by a failed APU start attempt. Our old friend risk assessment again:ok:

[redout]

thanks for that.