AC pumps for the APU

[JD396 37]

If I'm sitting on the ground with the APU running for a while, is it "proper" to run two AC pumps, from both the left and the right tanks? I notice it works just fine to prevent potentially having to deal with a fuel imbalance later. There's no fuel config warnings in the cockpit or anything about it, and nothing I could find in the FCOM tells me NOT to do this, but it doesn't tell me TO do it either. I guess I'm wondering, is that something that ever happens in the RW?

[VIPERGTSR01 22]

You can I guess but I don't think it is something normally done as the APU will use it's own DC pump if it needs, a fuel imbalance is something easy to fix later rather than run AC pumps for long periods of time when not needed.

[JD396 37]

You can I guess but I don't think it is something normally done as the APU will use it's own DC pump if it needs, a fuel imbalance is something easy to fix later rather than run AC pumps for long periods of time when not needed.

Yeah, it doesn't take more than a couple minutes to solve a fuel imbalance, and you have to run it for a good long while to actually get an imbalance big enough to trigger the warning. The FCOM suggests running one of the AC pumps for "extended APU operation" on the ground... kinda vague.

[Spin737 102]

If I'm sitting on the ground with the APU running for a while, is it "proper" to run two AC pumps, from both the left and the right tanks? I notice it works just fine to prevent potentially having to deal with a fuel imbalance later. There's no fuel config warnings in the cockpit or anything about it, and nothing I could find in the FCOM tells me NOT to do this, but it doesn't tell me TO do it either. I guess I'm wondering, is that something that ever happens in the RW?

RW, use one pump at a time. The planes come from Boeing with an option for a DC pump that will suction feed from the left main tank. To prevent fuel imbalance, use the center tank fuel by switching the left pump on. If you don't have center tank fuel, switch between the main tanks by turning on one of the aft pumps. If you use the right tank, you must also open the cross feed valve.

[badderjet 174]

Correct. IRL I see Main tank #1 aft pump operating for APU 99% of the time. Doesn't seem to be a problem.