APU OFF then ON B737NG
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Joined: Dec 2006
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From: Casablanca
APU OFF then ON B737NG
Hi everyone, was a bit puzzled by a FO practice yesterday and im looking for some answer. Parked at the gate, GPU connected, we turned APU OFF. 20 after that, GPU just was not delivering anymore for some reason. At that point, FO positionned APU switch to ON and reconnected the busses. I never saw or heard of this procedure. Looked for it in our manuals and found nothing. I understand the logic of being in the automatic cooling period but it still puzzled me. Anyone with some reference on that?
Joined: Jan 2001
Aviation Qualifications: ATPL
Posts: 1,710
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From: UK
Been a long time since I flew the 737 but does the APU run for a while after turning it off? If so and it’s selected back on in this period then it can be used again to supply the busses.
In a separate note, if you are the captain and your FO is doing something that you don’t understand, isn’t it a good idea to ask them what they’re up to?
In a separate note, if you are the captain and your FO is doing something that you don’t understand, isn’t it a good idea to ask them what they’re up to?
Joined: Jan 2000
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From: FL410
Yes, had to do this once as well after putting the switch to OFF then realised we needed the APU for take off. While the APU is in its cooldown cycle (60 seconds), carefully replacing the switch to ON will illuminate the GEN OFF BUS light again and cancels the shutdown.
Joined: Jul 2014
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From: here
Not B737 but 787
The EICAS memo message APU COOLDOWN is displayed. At any time during the cooldown period, the APU may be returned to its running condition by placing the APU selector back to ON.
Joined: Jun 1999
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From: Oztrailia
777 did the same, as does the A330.
APU slows to about 82% during the cooldown, switch it back on and up it goes back to 100%.
During the 85 second cooldown you have the opportunity to switch it back on.
Note: if you weren’t using the bleed air there isn’t a cooldown, it shuts down after 15 seconds ( A330 )
APU slows to about 82% during the cooldown, switch it back on and up it goes back to 100%.
During the 85 second cooldown you have the opportunity to switch it back on.
Note: if you weren’t using the bleed air there isn’t a cooldown, it shuts down after 15 seconds ( A330 )
Last edited by ACMS; 18th February 2018 at 06:09.
