brs planespotter
24th Mar 2009, 12:05
i have often noticed that when a a/c is waiting for its slot that the apu is obviously running for engine start.am i right in thinking that the airconditioning is supplied by the apu and that the electrics by the a/c battery?when your doing your fuel figures do you allow for the use of the apu?i guess its cheaper using a gpu than the apu?many thanks in advance:ok:
Bullethead
24th Mar 2009, 12:38
The APU is used on the ground for airconditioning and to power the aircraft's electrical system and also for engine starting.
Although the APU fuel usage is not a lot in the overall scheme of things the use of GPUs for electrical power and ground conditioned air is becoming more popular for extended turnarounds due to the fuel costs.
On some aircraft the APU can be started and used airborne for electrical power in case of generator problems.
There is an allowance for APU fuel usage in the flight plan calculations.
Regards,
BH.
SNS3Guppy
24th Mar 2009, 12:54
On my last aircraft, we figured 1,200 lbs of fuel per hour for the APU.
When the fuel costs began rising, we were directed to shut down the APU whenever in the blocks, and use ground power. The APU was for use prior to engine start and for taxi. It wasn't approved for inflight use. I've flown a few aircraft in which the APU was available in flight, but in most aircraft it's not.
APU's power electrical systems, heat and cool the aircraft, and in some airplanes also provide hydraulic power.