Packs on APU or Packs OFF
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capt. solipsist,
That's to stop engine exhaust being ingested by the APU due to some air flow in that general direction at low speed / stopped. During the take off roll and flight - the APU inlet is in clean air - else they would have had to redesign it.
the same reason why we turn OFF APU Bleed just after engine start, or turn ON APU Bleed just before shutdown (after PARK BRK On):
Last edited by rudderrudderrat; 16th Oct 2011 at 08:59. Reason: quoted text
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APU failure during takeoff roll is a very remote possibility and should not play any part in the decision to go packs off or APU bleed on.
Having flown A1 powered Airbi and needing that extra thrust we always go APU bleed on when needed. Actually we use it more on the 321.
Normal preference is FLEX, then TOGA, then APU bleed on. Packs off is only used when APU is on MEL. There is also a certain level of passenger discomfort with an unpressurized T/O, which is what a packs off condition gives you. Now I will admit that there have been a few done when the F/O has inadvertently shut the APU down on the afterstart flow before checking the numbers.
Having flown A1 powered Airbi and needing that extra thrust we always go APU bleed on when needed. Actually we use it more on the 321.
Normal preference is FLEX, then TOGA, then APU bleed on. Packs off is only used when APU is on MEL. There is also a certain level of passenger discomfort with an unpressurized T/O, which is what a packs off condition gives you. Now I will admit that there have been a few done when the F/O has inadvertently shut the APU down on the afterstart flow before checking the numbers.
