Boeing 747-400 Using Fuel tank logic

[Mr.Vortex]

Hi to all of the members,

Recently I'm study about the B747-400 and I'm heard someone show me a
schematics of how B744 using fuel from different tank for different phase of
flight like takeoff or landing.
[Excluding the logic that the CWT and Stab trim tank will be used first]

Thanks to all of your reply.

Best Regards

PS. if there're the same thread that's similar to this, I'm apologize for that but
I'm search it and couldn't find it.

[NSEU]

It depends on fuel levels. If there is usable fuel in the CWT, when the flaps are extended to the takeoff range during taxy out (plus 40 second delay), the #2 and #3 crossfeed valves automatically close. Then:

The CWT feeds the outboard engines (The HST can't be used on the ground or with the flaps extended)
The (EDIT) inboard tanks (2 & 3) feed the inboard engines.

In the air, with flaps up, the CWT will resume feeding all 4 engines. If the flaps are re-extended, the logic won't allow the fuel feed to go back into the takeoff configuration. To re-arm this logic, the airplane has to land and the flaps go back to the takeoff range.

After fuel has been used in the CWT and HST, the pumps for these tanks are manually deselected at the appropriate times. Then, all four engines are fed by the inboard wing tanks until the inboard tanks are down to the same level as the outboard tanks. Then, the override jett pumps in the inboard tanks are turned off.

Then, the outboard tanks feed their respective engines and the inboard tanks feed the inboard engines (not quite "(1)tank to (1)engine")

I've skipped a few things, but I assume you know the rest?

[TopBunk]

The CWT feeds the outboard engines (The HST can't be used on the ground or with the flaps extended)
The outboard tanks (1 & 4) feed the inboard engines.

Surely that is the other way round, ie CWT feeds inboard and outboard wing tanks feed outboard engines.

[mustafagander]

Fuel feed logic for T/O is, with CWT usable fuel, inbd x-feeds close as stated hence CWT pumps over ride #1M & #4M pumps so feeding the outboard engines and #2M & #3M feed their individual engines.

It's actually the same as the B747 Classic except the FEO isn't there to set it up.

After cruise sensed - not sure of the deck angle, but that's the driver - HST pumps selected on and HST (stab) fuel feeds to CWT when CWT less than about 37 tons.

Then CWT burnt down to about 1,200Kg and feed is #2m & #3M to all. #2R & #3R transfer into #2M & #3M respectively and CWT scavenge pump - on older airframes, later A/C use a jet pump system which actually works - attempts to scavenge the CWT into #2M usually missing about 200 - 300Kg.

When #2M = #3M and they roughly equal #1M and #4M obrd x-feeds closed and inbd over ride/jettison pumps off. This gives tank to engine effectively.

[eckhard]

Quote:
The CWT feeds the outboard engines (The HST can't be used on the ground or with the flaps extended)
The outboard tanks (1 & 4) feed the inboard engines.


Surely that is the other way round, ie CWT feeds inboard and outboard wing tanks feed outboard engines.

I reckon it's neither of these! During take-off with CWT fuel (above 7.7.Tonnes) the CWT will feed engines 1 and 4 and the mains 2 and 3 will feed engines 2 and 3.

[NSEU]

Mustavagander

Thanks for the correction. You are right of course.

Re: When #2M = #3M and they roughly equal #1M and #4M obrd x-feeds closed and inbd over ride/jettison pumps off. This gives tank to engine effectively.

Normally, yes, but there is still a pathway for the fuel to cross feed should pumps fail in one tank. The 2 & 3 crossfeed valves remain open.

Re: After cruise sensed - not sure of the deck angle, but that's the driver - HST pumps selected on and HST (stab) fuel feeds to CWT when CWT less than about 37 tons.

This is new to me. Is this crew procedure or airline-specific?

[Mr.Vortex]

Thanks to all of your reply.

So to sum it up.

- If plane on ground + Flap takeoff range = the CWT feed the outboard engine
to keep fuel on the outer wing part as many as possible to reduce wing
bending moment and the inboard tank feed it engine. Is that right? Also the
HST doesn't feed because it need to keep the CG in the envelop is that
right?

- If CWT is less than 37 ton, the HST will fill the CWT.

- If CWT is below 2000KG. The Scavenge pump is activated and move the fuel
to the no 2 tank.

- If CWT is empty, the inboard tank will feed all engine.

- If inboard and outboard tank is equal, then the tank will feed their engine.

Is there any configuration beside the above?

Thanks for all of your reply.

Best Regards

[spannersatcx]

If CWT is below 2000KG. The Scavenge pump is activated and move the fuel to the no 2 tank.

That used to be so with an electric pump most now use 4 hydromechanical pumps and scaveng fuel to both 2 & 3 main tanks.

[mustafagander]

Actually Vortex, the scavenge pump first run was triggered by the CWT Over ride/jett pump LP warning at quite low fuel levels - 600 - 700Kg if I remember correctly. It is triggered again by the transfer of fuel from the R tanks. Electric scavenge pumps move fuel to #2M, but later aircraft have jet pumps which scavenge to both #2M and #3M and actually empty the CWT.

The stab fuel is left there for T/O and climb to ensure that the CG remains always predictable AFAIK.

Just BTW, the pumps are selected to make the fuel feeds so, it is not automatic in the main but the system does give us EICAS messages.

[JammedStab]

Mustavagander

Thanks for the correction. You are right of course.

Re: When #2M = #3M and they roughly equal #1M and #4M obrd x-feeds closed and inbd over ride/jettison pumps off. This gives tank to engine effectively.

Normally, yes, but there is still a pathway for the fuel to cross feed should pumps fail in one tank. The 2 & 3 crossfeed valves remain open.

Re: After cruise sensed - not sure of the deck angle, but that's the driver - HST pumps selected on and HST (stab) fuel feeds to CWT when CWT less than about 37 tons.

This is new to me. Is this crew procedure or airline-specific?


Have not seen anything to do with pitch for the stab Tank. Only the Center Wing Tank where if it happens to decrease to 3.2 tons with pitch above 5 degrees such as during the climb, you are directed to select those pumps off. Later when the pitch decreases below 5 degrees such as when levelling off(if more than 1.8 tons in CWT), you are directed to select pumps on again. Then soon after you are directed to turn them off again when the fuel quantity is low.

I guess at high pitch angles, the minimum fuel for CWT pumps operating is greater than at low pitch angles.

[NSEU]

Have not seen anything to do with pitch for the stab Tank.

In my old airline's operations manual, there was a flow chart specific to EIU IDS-503 Software. In one of the flow chart boxes for HST operations, there was the question "Is aircraft in cruise? (Y/N)". There was a footnote relating to this which said "Cruise flight is automatically determined by aircraft pitch attitude less than 5deg for 10 minutes".