B737NG Fuel Pumps & APU

[RohanThePilot]

Hi guys,

In the absence of a GPU, the APU must be started to support the batteries so my question is that for extended APU ops should all fuel pumps be turned on or should only one of the left wing tanks be turned on? I ask because I have observed that a small imbalance develops between the port and starboard wing tanks when one wing tank pump is turned on.

I know that in the first officers pre-flight procedures, all pumps are turned on but by the time this is done an imbalance has already developed. So I basically want to know if it's okay to turn on all fuel pumps once battery dependent electrical power is established. I tried doing this in a full flight simulator and there was no imbalance because center tank fuel was used.

Since I noticed this on a full flight sim I'm not too sure how it works in the real world depending on airline SOPs and all. Input will be appreciated.

Cheers!

[BOAC]

You may wish to look at http://www.pprune.org/tech-log/48026...p-apu-ops.html.

for extended APU ops should all fuel pumps be turned on or should only one of the left wing tanks be turned on?

as per Boeing, yes, one of the left, centre with fuel, or right with crossfeed.

I ask because I have observed that a small imbalance develops between the port and starboard wing tanks when one wing tank pump is turned on.

- most unlikely, and if it is the APU causing the 'imbalance' (40kg per hour - you must have very good eyesight!!) then it happens pumps on or off.

. So I basically want to know if it's okay to turn on all fuel pumps once battery dependent electrical power is established.

- no reason why not but they will not run as they are AC. However, since it is generally my policy to be kind to aeroplanes (with a few exceptions....) I would leave them off so when you put generator power on there is no surge of demand

[RohanThePilot]

Thanks for your reply mate.

most unlikely, and if it is the APU causing the 'imbalance' (40kg per hour - you must have very good eyesight!!) then it happens pumps on or off.

I'm a little picky and try to be a perfectionist. I guess an imbalance of 6 to 8 kg is nothing to be worried about. This is when using the AFT1 pump.
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One more question. If the amount of fuel in the CTR tank exceeds 5,000 kg, are the CTR tank pumps turned off prior to takeoff?

[BOAC]

That should have been 80kg /hour, sorry.

Centre tanks pumps (NG) off below 453kg for modified a;/c or 2400kg un-modified.

http://www.pprune.org/tech-log/47728...gnd-737ng.html