APU OFF then ON B737NG
Thread Starter
Join Date: Dec 2006
Location: Casablanca
Age: 53
Posts: 70
Likes: 0
Received 0 Likes
on
0 Posts
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?
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?
Join Date: Jan 2000
Location: FL410
Posts: 860
Likes: 0
Received 0 Likes
on
0 Posts
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.
Thread Starter
Join Date: Dec 2006
Location: Casablanca
Age: 53
Posts: 70
Likes: 0
Received 0 Likes
on
0 Posts
@EGPflyer there is a cool down period of 60 seconds. And when I asked him he said he is used to do it but he couldn’t not find any reference to it. Hence my question
Join Date: Jul 2014
Location: here
Posts: 42
Likes: 0
Received 0 Likes
on
0 Posts
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.
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 Feb 2018 at 06:09.
