Fuel management system of B747-400, A330-300

[StudentATP]

hello,

I would like to ask you all professional pilots about the fuel system of those airliners.

If I am not mistaken, the B744 first draws fuel from centre tank, then stab tank, then inboard tanks no.2 & 3 and finally tank 1 & 4.

With the A333, fuel usage is squenced in the following,
1. Centre tank
2. Inner wings no. 2 & 3 to a certain level
3. stab tank
4. Outer wings no. 1 & 4
5. inner wings again

*on departure after passing certain FL, the FCMCs will transfer fuel to stab tank automatically (do they call it trim tank or stab tank?) the CG will move aft and thus reduces the aerody. load on the tail and thus less trim drag and thus less fuel burn.

Thank you in advance.

[Tinwacker]

A333 in our fleet does not have a centre tank but the -200 does.

So then once settled in the climb/cruise fuel is transferred to the trim tank for C of G purposes.
Centre if avail is used then inner tank 1 and 2.
Trim tank moves fuel fwd incrementally to tanks 1 and 2 as C of G moves.
Outer tanks move fuel to inner tanks 1 and 2 when any inner reaches 3500kg incrementally.
Approx 35 mins to touchdown all remainder, if any left in trim tank, is moved fwd.
Now using inner 1 and 2 only.

TW

PS Someone will now be exacting but this is good for student level.

[Tinwacker]

B744
Almost there...
After climb approx
Centre tank
Tanks 2 and 3
Stab tank moves fwd when space avail
Tanks 1,2,3 and 4 together when levels equal.
Tanks 2 and 3 continue after reserve tanks transferred when space avail
Back to tanks 1,2,3 and 4 together when levels equal again.

TW

[SMOC]

744

Fuel supply varies from start up till CLB/CRZ this is very basic as some conditions require a slight change in order.

If fullish on departure the order is, (all approx figures)

1. CWT
(@ 36.5 T Stab transfers forward to CWT) then

2. Main 2 & 3
(@ 18.2T in either tank, RES 2 & 3 transfer to M2 & 3) then @ 13.6T in M2 or M3

3. Main 1,2,3 & 4
(known as "tank to engine" each tank should have approx 13.6T)

The Stabiliser tank and RES tanks don't supply the engines, they just top up the Centre tank and Main 2 & 3 respectively.

[leewan]

A333s do not have center tanks, only the A332s have them.

[Tinwacker]

Leewan,

A333 in our fleet does not have a centre tank but the -200 does.

I mentioned that in my reply, but then there is always someone who knows somebody with an A330-300 aircraft in the desert that is the only one converted with a centre tank - such is life....

Cheers TW

[Joetom]

Excuse the drift.

Does any operator ever put fuel in the CWT on the A332/what flight time is needed to place fuel in the CWT for departure ?

[bvcu]

747-400 stab tank is a fuel tank , not for c.g control as in airbus , hence none on freighters [up til now ?] . Only time i've put centre tank fuel in 332 was tankering from middle east to europe in the week or so that some routes had pax figures in single numbers after 9/11. Even then we only put a few tons in , so be interested to know if anyone using it properly on a regular basis. Think with that capacity its going to be an awesome tanker !!!!

[Swedish Steve]

There are also some pax B744 without a stab tank. BA has four aircraft.
The B744 fuel system just uses the fuel in the correct order. It is not very clever, uses point sensors to initiate fuel transfer as required, and commands the pilots to close the cross feed valves at the right time.
The A330 is clever. It moves the fuel back during the climb, then fwd in small doses, and sometimes will move the fuel back a second time (if centre tank fuel used).
One thing confuses me as an engineer on the B744 is why different airlines start using the stab tank at different fuel qtys. If you let the aircraft refuel itself, stab tank starts to be used at around 129000 kgs, but BA starts using it a lot later. What is the reasoning behind this?

[SMOC]

One thing confuses me as an engineer on the B744 is why different airlines start using the stab tank at different fuel qtys. If you let the aircraft refuel itself, stab tank starts to be used at around 129000 kgs, but BA starts using it a lot later. What is the reasoning behind this?

I believe it has to do with standard fuel loads for C of G calculation when the stab is used with certain SGs.

Our company avoids standby loads between 125 -132T which I think allows for all SGs, meaning you could end up with fuel in the stab with loads as low as 125T and no fuel with loads as high as 132T

As you said at 129T you should end up with 16.8T in the CWT & 3.2T in the HST based on an SG of 0.785, I believe the problem lies with when you try to top it up to say 131T the system has a problem of adding 1.7T to the CWT and 0.7T to the HST, I think it chucks it all in the CWT which results in a non standard fuel load which requires a loadsheet change for the non standard C of G.

I've never had the chance to see how it loads fuel. With 129T entered and an SG of 0.785 does it fill all tanks at the same time or in a certain order, does it put 16.8T in the CWT and then 3.2T in the HST or does it fill them together?

[Swedish Steve]

SMOC
Sorry can't help you. The B744 I have fuelled have usually been around 125-130 tons of fuel. I set up 125T on the refuel panel and leave the stab switch off. I then come back towards the end and do the last bit manually. What I was always careful of was an initial figure of say 128T (no fuel in the stab) followed by a final figure of 132T (about 4 T in the stab) and you could get too much in the centre. But I usually asked the crew and they were always willing to put 132T with no stab fuel. OK as long as the dispatcher knows!

[SMOC]

Swedish Steve,

That makes sense, I assume our company does it to avoid problems of guys not being careful when loading the final fuel, must have caused enough problems to come up with a blanket rule.

[Joetom]

Set the 744 refuel panel to auto at say 145T and tail selected, all tanks fill at the same time, the tail is a slow filling tank, guess small pipes to keep weight down.

From memory most airlines use 129T approx for tail fuel, some airlines use 138T, guessed it just suits that airlines config and saves a bit of fuel for them.