Fuel consumtion in tank 1 without APU running

[snalz 0]

-Aircraft ordered 05, August-Hotfixes installed: Hotfix No. 3 Hi, actually fired up FSX, loaded 737-800WL, standard preload panel state is "NGX SHORT". Inside the cockpit i decided to change panel state load in MCDU menue - changed now "STATE LOAD" to "NGX CLDDRK" for cold & dark conditions. All is fine in cockpit, all systems are completely off. Now i went through the "FUEL" page to insert my TOPCAT calculated fuel load. First i realized that tank 1 and tank 2 of each wing have a maximum capacity of 3911 kg. So i manually entered 3911 kg for tank 1. Tank 2 still had its full level of 3911 kg. I continued to fill center tank while realizing a permanent decreasing fuel load in tank 1. It seems that there is a "ghost"- APU running uses fuel. I hope to get that patched after changing panel state to C&D. Nicolas B.

[henkie 0]

So how much fuel was in tank 1 before you filled it up?What is the fuelflow of tank1 with the apu off?Kind regards,Daniel Verhaal

[snalz 0]

So how much fuel was in tank 1 before you filled it up? What is the fuelflow of tank1 with the apu off? Kind regards, Daniel Verhaal

Hi, at about 3989 kg in tank 1, this margin to 3911 kg was burned fuel of APU from pre loaded panel state before. This panel state was active for a couple of minutes until i changed panel state to C&D condition, but the fuel burn -out of tank 1- continued in C&D without running APU. regards

[snalz 0]

Hi, at about 3989 kg in tank 1, this margin to 3911 kg was burned fuel of APU from pre loaded panel state before. This panel state was active for a couple of minutes until i changed panel state to C&D condition, but the fuel burn -out of tank 1- continued in C&D without running APU. regards

Correction of first part of my post: " at about 3889 kg in tank 1", ....

[Big_Les 1]

I observed similar behavior but with tank2. At cruise I accelerated to x4 time compression for a while and then noticed a fuel unbalanced warning with tank 2 about 1000 kg below tank 1. APU was off, center tank was empty and pumps were off, cross-feed was closed. had to re balance fuel before landing. I wasn't sure at the time if it was a fuel leak (random serviced based failures on)

[snalz 0]

Ok, for the moment i do not use random failures, so a fuel leak is impossible. There was also no cross flow of fuel possible, X Valve was closed. Strange that you had a misterious additional fuel consuption out of tank 2. But 1000 kg fuel imbalance would be a realistic amount of a running APU during a whole flight.I seems that some logic "behind" the systems has an hang up, so that in different situations or panel state changes there is a simulated fuel consumption of the APU - independent if that generator runs or not.

[davierosoft 13]

There is a problem... try to load again, or try to load cold and dark from the beginning of the simulation.Try also to see if there is a "logic" in this fuel consuption, turn on one the right pumps, center rh (if there is fuel), fwd rh or aft rh, crossfeed open, and see if quantity on the relative tank changes with tank 1 no more used.If there is "a logic" it means that the simulation consider the APU still running.Try also anoter way to stop the fuel flow:Extract the APU fire handle (do not rotate) it must stop the fuel flow.Sometimes the simulation create a random "error", I did Y/D and overwing door problem, problems not linked to the failures, but pmdg error. Load and try again. PS: 1000Kg of unbalance is very dangerous, in my memory maximum allowed unbalance between wings is 300kgs. Few things about APU fuel, each of the 6 pumps can feed the APU (with DC pump we have 7), normally all uses the FWD LH pump, this pump, in this way, wears more than the others. It is possible to use the AFT LH tank pump, OR, LH CTR tank pump (if there is fuel). Or, with the crossfeed, the other pumps.The only important thing is that the LH FWD pump is used also for center tank fuel scavenge system.This system is used to transfer the fuel remaining in the center tank wen the pumps are in low pressure (low fuel in the tank)By turning off the center tank pumps, with FWD LH ON, the scavenge system will come on and transfer fuel from center to wing tank. The rate is not very high, on classics it is around 120/200kgs in 22 minutes.Why there is a scavenge only on the left side? To compensate the APU consuption.

[Dankovic 39]

I observed similar behavior but with tank2. At cruise I accelerated to x4 time compression for a while and then noticed a fuel unbalanced warning with tank 2 about 1000 kg below tank 1. APU was off, center tank was empty and pumps were off, cross-feed was closed. had to re balance fuel before landing. I wasn't sure at the time if it was a fuel leak (random serviced based failures on)

I had the same problem yesterday. But I was not using time acceleration. I can say for sure that CDU did not report any failures.BTW what is correct procedure fot balancing fuel? I have turnd the one side pump off and opened cross.feed. Regards,Danko

[Cristi_Neagu 134]

You could try that scenario again, and when you see the fuel level decreasing with APU off, start the APU and then turn it off. What does that do to the fuel?

[davierosoft 13]

I had the same problem yesterday. But I was not using time acceleration. I can say for sure that CDU did not report any failures.BTW what is correct procedure fot balancing fuel? I have turnd the one side pump off and opened cross.feed. Regards,Danko

Crossfeed OPENPumps of the tank wit less fuel OFFJust wait and ceck for fuel balance. EDIT: as you know, the crossfeed will not transfer fuel, it is used to feed both engines from the same tank.