B747-400 min fuel for hydraulic cooling
 

On a 737-400 min fuel in a wing tank is 1657lbs to cool the hydraulic A and B system fluid.
What is the min fuel for a 747-400(F) in order to adequately cool the hydraulic fluid of the respective systems?
I can't find it in FCOM2....:(
If anybody knows the answer can you provide the reference also pls?
Thanks ;)

My old, possibly outdated, copy of the 744 AMM in Ch. 71 Ground Running states the following fuel is required to cover the heat exchangers.
Tanks 1/4 - 953 kg
Tanks 2/3 - 2450 kg
This is the mininum amount required in tanks after completing the ground run, not the starting amount.

So total min fuel would be 3400kgs divided over the tanks as per above?
6800kgs being min landing fuel?
Was afraid I couldn't go to sleep tonight without knowing that ;)
Thank you for looking that up for me.

(6) Do a check to determine the amount of fuel in the fuel tanks.

NOTE: If there is sufficient fuel in the applicable tank, there is no time limit on the operation of the hydraulic pump. If there is less fuel than the quantities below, then the hydraulic pump operation is limited to 15 minutes.

NOTE: The fuel weight values given below are found on a specified fuel density of 6.7 pounds for a gallon (0.802 Kg for a liter).

(a) For system No. 1, there must be 2000 pounds (900 KG) of fuel in the No. 1 main tank.

(b) For system No. 2, there must be 5400 pounds (2450 KG) of fuel in the No. 2 main tank.

(c) For system No. 3, there must be 5400 pounds (2450 KG) of fuel in the No. 3 main tank.

(d) For system No. 4, there must be 2000 pounds (900 KG) of fuel in the No. 4 main tank.

We regularly land with less than 9800KG (4x2450) of fuel.
Didn't know there was a hydraulic pump operation time limit with 9800KG remaining fuel.
No word about it in OM-B V1 Limitations either...

Well the limit is obviously 900kgs but it's probably pump position in the tank which warrants 2450kgs in the (much) larger #2 and #3 tank.
#1 and #4 hydraulic system are heavier loaded then #2 and #3.

B2N2,


"it's probably pump position in the tank"........close but no banana, try hydraulic heat exchanger position in tanks. Hydraulic pumps are not located in the fuel tanks.

No, the 747-400 normally lands with equal quantities in each wing tank, so as 747-8 Driver says, total fuel would be 9800Kgs (4x2450).

But you may run the APU for a while lowering fuel in one tank. I think most issues of this sort are during maintenance. Running an engine with no worry of what your landing fuel will be.

@747-8driver: Yes, some may call your landing fuel a bit low, the tank and hyd. pump on 748(F?) may be very different from the 744. I've never accessed the 748 books and I don't know. If you are within Boeing and company SOPs, and have enough to reach a weather alternate, go for it. For the long legs that you probably fly, you need most of that fuel simply to arrive at TOD. If the older 15 min rules still apply to your fancy new Big Bird, work-arounds learned on older aircraft may be of help. I don't see a problem.
(Visited LUX multiple times and if the work is OK, you've already gone to Heaven!)

I suppose if you don't have any fuel in the CWT, APU fuel usage will not be offset by CWT fuel scavenging (where an electric CWT scavenge pump is fitted).

On 744s with hydromechanical scavenge pumps, is APU fuel usage a problem? Both 2/3 tank aft boost pumps are turned on during ground operations to feed the APU, but I heard somewhere that APU has a preference for tank 2 (fuel from tank 3 has to travel much further to get to the APU)

I stand corrected.
Case of fingers faster then the brain.