If I turn on the left center fuel pump before starting the APU (which is the recommended procedure - Bulfer 737 cockpit companion page 44), will the APU run and deplete fuel from the center tank?

Well, I tested, and even though I only put on the left center tank pumps, the APU still drew fuel from tank 1.I got the impression that the reason to activate the left center pump was to avoid a fuel imbalance when running the APU. If I'm wrong in how the system operates, please let me know. If I'm right in how the real aircraft works, please put it on your bug list (way down 'cause it's not that critical).

Maybe Ian Riddell knows the answer - the Aussies should be waking up soon (then again, Friday night is Pub and BBQ night, I believe... :)).Cheers,Gosta.http://hifi.avsim.net/activesky/images/wxrebeta.jpg

Hello Tim, I looked all the way back in this forum's archives for your info on the CFG changes required for Markers to be heard. Came up empty handed. Would it be too much to ask for you to send it to me via email? [email protected] YouBlais Klucznik

"Maybe Ian Riddell knows the answer - the Aussies should be waking up soon (then again, Friday night is Pub and BBQ night, I believe... :))."Er... no... Gosta... Unfortunately, too stuffed after an 11.5 hour day at work *:-* One would assume that fuel would be drawn out of the tank which has the pump running. In this case it should not balance out the fuel. An APU of this size, however, should not draw massive amounts of fuel, so there shouldn't be an imbalance of more than a few hundred kilos... even running for an hour or two (A 747-400 APU only draws about half a tonne per hour... and that is a LOT bigger... Think V8 vs lawnmower engine :-lol).Normally I would write a mini-tutorial on this kind of stuff, but I think it's past my bedtime ;-)Cheers.Ian.

>One would assume that fuel would be drawn out of the tank>which has the pump running. In this case it should not balance>out the fuel. An APU of this size, however, should not draw>massive amounts of fuel, so there shouldn't be an imbalance of>more than a few hundred kilos... even running for an hour or>two (A 747-400 APU only draws about half a tonne per hour...>and that is a LOT bigger... Think V8 vs lawnmower engine>:-lol).>>Normally I would write a mini-tutorial on this kind of stuff,>but I think it's past my bedtime ;-)>>Cheers.>Ian.As I read the fuel schematic and the 737 cockpit companion, the APU suction pickup is in the #1 (left) tank. But Bulfer states to turn on the left center fuel pump to prevent a fuel imbalance when running the APU - so I assumed it had a connection to the main fuel plumbing that feeds the left engine as well.It's not that important - as you note, it doesn't draw much fuel.I just wanted to know in my tutorial which pump to turn on for the APU start - for now, I'm putting a little extra fuel in the left tank and turning on the number 1 aft pump for APU start.

Well Tim your not required to turn on a fuel pump on the NG prior to starting it, there is a DC fuel pump that is energized at apu start.The DC fuel pump is actually optional ,suction alone from the apu fuel control will feed it, Although its recommended to run the left center AC pump on versions without the DC pump to extend life of the apu fuel control.Running the left center tank AC pump will force the fuel from the center tank and thus keep your wings balanced (have not tried this on the PMDG 737)

>Well Tim your not required to turn on a fuel pump on the NG>prior to starting it, there is a DC fuel pump that is>energized at apu start.>>The DC fuel pump is actually optional ,suction alone from the>apu fuel control will feed it, Although its recommended to run>the left center AC pump on versions without the DC pump to>extend life of the apu fuel control.>>Running the left center tank AC pump will force the fuel from>the center tank and thus keep your wings balanced (have not>tried this on the PMDG 737) It doesn't work on the PMDG, and I think that is due to limitations in the way MSFS models fuel systems. So no complaint on my end, and I won't use a pump at all if the PMDG doesn't require it.I'm glad to know I was not crazy, and that the real aircraft does operate as described.