ask26
27th Sep 2011, 23:43
Just wondered in hot conditions, whether Airbus has anything similar to Boeing's Isolated Pack Operation. I know it's just a few minutes but in the Middle East every second counts. Having read the FCOM and in our procedures wondered if there was a reason why this is not in place.
albertofdz
30th Sep 2011, 10:04
On Airbus´you start engine 1 first, mainly due to the fact that the parking brake is pressurized by blue hydraulic.
The APU bleed is on the left hand side of the cross bleed valve.
In order to do an isolated pack operation you need to close the cross bleed valve. So if engine 1 is started first, and then you manually close the cross bleed, you will find that you have no bleed source to start engine 2.
Of course, you can start engine 2 first as long as the brake accumulator is pressurized at the time of start. So this point may lead us to think that an isolated pack operation could be applied via engine 2......
This discussion could go on and on, however, Airbus also recommends (SUP-PRO) that the cabin should be air-conditioned when passengers have been on board for 20 minutes due to the fast reduction of cabin air quality... I believe that this recommendation on its self sorts out the temperature problem.
Taking into account that engine starting is relatively fast, and that the pneumatic system is fully automatic, you may find that the cabin will not be cooled for a period of 2, maybe 3 minutes.... Even in the hottest desert conditions it seams that cooling will be re-gained in little time with little impact on passenger and crew comfort.
It is very true however, that many airports impose very strict noise regulations, and the authorities will not allow us to use the APU for air-conditioning purposes, except for a very short period of time between the closure of the doors, removal of ground power and finger, push back and engine start..... Instead the ground staff will connect a low air pressure pre-conditioned tube which will work in some places, and at others it will make a lot of noise and offer no cooling at all....... But thats the crazy bull s.... world we live in!
I hope a helped a little!
Safe flights.