A320 APU Usage

[Jack1985]

Hi everyone! I'm just wondering what is the normal day to day operation of the APU on an A320? I'm a ground handler and with my experience of A320's at Cork it seems the APU's are always running as you can hear it and see the heat from the exhaust, are APU's always running during turnarounds to keep the cabin warm etc? And for example after ground power is connected do they keep the APU running simply for cabin comfort?

Any responses appreciated! :)

[Sue Ridgepipe]

APUs can be used on the ground for cabin comfort (heating or cooling) but they also provide the air for starting the engines. So if it's not required for cabin comfort, and you use ground power during the turn around, you're going to have to turn it on anyway just before pushback because you need it for the start.

The engines can also be started using a ground air cart instead of the APU, but it's a lot easier and takes less time to use the APU.

[BARKINGMAD]

Does anyone have a minimum running time for a typical APU before it is shutdown again?

A previous company used to start the "rocket" approaching the stand and it was running down again within 4 minutes.

I always thought back to my basic aero groundskule which stressed thermal creep and stabilised running conditions and can't help thinking such a short cycle had a detrimental effect on the APU.

The chief trainer of that outfit would not consider the practice of shutting down #2 on a twin turbofan so's the ext power could be plugged in safely, so we continued to potentially abuse the rocket as it was considered "safer". :confused:

[heggo48]

There isn't any limitation published for minimum time before shut down because the APU has an electronic control box that ensures thermal stabilization of the APU before shutting down, so even if you push the master push button to off, it will continue running till the APU cools down then shuts down, however there is a minimum time for consequent starts....3 start attempts and then wait 60 minutes before attempting another 3 starts and so on....
They probably do that to make sure that they have a pneumatic source readily available while engine shutdown, in order to deal with any engine tailpipe fire that might happen during shutdown(though its not a very common thing to happen)......It is sure though that by shutting the APU so fast after starting is a waste of APU starter....and it would be better to have a GPU and an ASU ready at the stand while shutting down the engines, unless of course they don't own the ground equipment and they have to pay for using it, in that case a starter replacement every once in a while doesn't sound so bad.