747 APU and fuel system

[WebMaximus 372]

Hi,Two questions on the 747:1. After landing I tried to turn on the APU to provide power when shutting down the engines after arriving at the gate but the APU never started, figured it might be because I hadn't any fuel left in the center tanks?2. During flight I received a couple of warnings that read 'Fuel pump 3 aft', 'Fuel pump 3 fwd' and the same for fuel pump 2 and no matter what I tried I couldn't get rid of those messages. What would have been the right procedure in this case?Below is a couple of pics that might help showing my problems.http://forums.avsim.net/user_files/133882.jpghttp://forums.avsim.net/user_files/133883.jpghttp://forums.avsim.net/user_files/133884.jpgTIA,

[744pilot 0]

You realy have no idea how the fuel system works huh??I'll explain. If the APU isn't able to start that's because:A. There is a fault occured some were in the system and then just use the ground power Unit to supply electics.B. There is no more fuel remaining in the MAIN thank #2 (which is your case). The APU never uses fuel from any thank other then #2.All those messages you have got means:-FUEL QTY LOW: Fuel level decreased below 907 KGs in one or more main thanks.->FUEL TANK/ENG: actualy means that you should close crossfeed # 1 & 4, switch off the MAIN OVRD PUMPS # 2 & 3.But in your case you will have a fuel starvation in ENG 2 and 3.So, your'e in the right config right now but this situation (PIC #1) may never happen.-FUEL PUMP 2,3 AFT, FUEL PUMP 2,3 FWD: means that the switches for these fuel pumps are selected off and you should turn them on.

[WebMaximus 372]

So it's that obvious huh...;-)?Actually I haven't invested much time in the 747 yet even though I bought it the day it was released. Have been busy completing the IVAO VFR World Tour in the B190 and also figured I should wait for the upcoming patch for the 747 before I start learning it.So that means that if you're out of fuel in the MAIN tank #2 you will not be able to start the APU in any way?Then you say the situation in pic #1 may never happen, what should I have done to avoid this/what did I do wrong?About the FUEL PUMP messages...I did try turning the fuel pumps on but it didn't make any difference, the messages were still there. Is that because there's no fuel left in the MAIN 2 and 3 tanks?

[744pilot 0]

>So it's that obvious huh...;-)?>Yes indeed. ;)>So that means that if you're out of fuel in the MAIN tank #2>you will not be able to start the APU in any way?>If the PMDG 744 you won't be able to start the APU anymore until refueling occurs. But in the Real thing you still have the Fuel transfer between 1 & 4. Which pumps fuel from MAIN 1 to MAIN 2 and from MAIN 4 to MAIN 3.>Then you say the situation in pic #1 may never happen, what>should I have done to avoid this/what did I do wrong?>Around 52 tons of fuel remaining you will receive the >FUEL TANK/ENG message. At this point you should close crossfeed valves 1 and 4 and switch off the MAIN OVRD PUMPS 2 and 3. This is it. But this, ofcourse, requires that you started in the right fuel config at the first engine start until you get the EICAS message. And for this I would recommend reading the AOM.>About the FUEL PUMP messages...I did try turning the fuel>pumps on but it didn't make any difference, the messages were>still there. Is that because there's no fuel left in the MAIN>2 and 3 tanks?That's correct. As soon as the fuel pumps detect low output pressure it will trigger an EICAS message and a PRESS light in the associated fuel pump switch.Hope it helps you a bit further done the road of flying the Queen. And it's realy worth it!!! :)

[WebMaximus 372]

Thanks alot Ramon for your answers to my questions and yes...I do look forward to start learning the Queen for real in a not too distant future. Funny you mention the 52 tons fuel remaining, I belive that's mentioned in a 747 DVD I own - think I should have another look and really following everything they explain in it and hopefully I will never more have these problems ;-)All the best,

[744pilot 0]

I guess you're refering to the VS19 flight from EGLL to KSFO with in the left hand seat Alan Carter and as F/O Alan Ratigan. :)I own it to.

[WebMaximus 372]

Yep, that's the one :-)