The 747-400 has eight fuel tanks, with a combined capacity of 57,164 gallons of Jet-A fuel. This amount weighs in excess of 380,000 pounds. (Pilots normally discuss fuel in terms of weight rather than volume.) The distribution of fuel among these tanks has a profound effect on how the aircraft performs. In particular, during a long trip, it is important that the fuel in some tanks be burned off before using the fuel in other tanks. Otherwise, the aircraft can become unbalanced.Fuel management in the 747-400 is largely automated, but there are still certain actions that are required from the crew. We will discuss them below.
Activate the fuel diagnostic screen on the lower EICAS panel by pressing the button labeled "Fuel" on the right hand side of the "Mode Control Panel" on the glare shield. Assuming the aircraft is fully powered, this will display a diagram of the aircraft's fuel tanks and pumps. At the top of the screen, you will see the total fuel on board displayed by weight. In the diagram, you will also see how much fuel is in each tank, and which fuel pumps, if any, are turned on.
Locate the fuel pump controls on the overhead panel. They consist of several groups of buttons located near the center of the panel. Across the top of this section of the panel, you will see buttons for the fuel cross-feed valves, labeled "Fuel X Feed." Below this row of buttons you will see buttons for the 12 fuel pumps and the four override pumps.
Look at the upper EICAS screen and check to see if there are any yellow messages pertaining to the fuel system. If there are none, then the fuel system is properly configured. If there is one, consult the Abnormal Procedures Guide in the operator's handbook, for instruction on correcting the anomaly.
Configure the fuel tanks for departure by verifying that the fuel pumps for each tank containing fuel are on. To do this, compare the fuel diagnostic screen with the fuel tank controls on the overhead panel. For all tanks with fuel, there should be a green light showing on the respective button. For any tanks that are empty, be sure that no lights are showing on those buttons.
Configure the cross-feed valves as follows:1. If the fuel quantity in tank #2 is more than that in tank #1, AND the fuel quantity in tank #3 is more than in tank #4: THEN all cross-feed valves should be on.2. If the fuel quantity in tank #2 is equal or less than in tank #1, AND the fuel quantity in tank#3 is equal or less than in tank #4; THEN Cross-feed valves #1 and #4 should be off.
Configure the Override pumps as follows in relation to the Cross-feed configuration in Section 2: Step 2:If the Cross-feed configuration matches situation #1, then all override pumps should be ON. If the Cross-feed configuration matches situation #2, then Override pumps #2 and #3 should be switched off.
Watch the EICAS for fuel messages in flight. If you departed with a large fuel load, you may need to reconfigure the tanks as fuel burns off during the flight. If you departed with a smaller fuel load, for a shorter trip, then no further crew action will required.
Switch off the fuel pumps for any fuel tanks that run empty during flight. Typically, these will be the stabilizer tank, the reserve tanks, and the center wing tank in that order.
Watch for the EICAS message: "XFEED CONFIG." This message indicates that fuel has burned off and the fuel tanks need reconfiguration. Continue to Step 3.
Switch off Override pumps #2 and #3.
Turn off cross-feed valves #1 and #4.
Generally speaking, the fuel quantity in the tanks in the main wing tanks should closely match each other. However, a small discrepancy is tolerable and will often be seen if the APU was used while the aircraft was on the ground. This is because the APU only draws fuel from tank #2. If the disparity between right and left ever becomes too large, you will see a warning message on the EICAS that says "FUEL IMBALANCE." This is a potentially serious situation and must be dealt with promptly. Refer to the respective section of the "Abnormal Procedures Guide" for the aircraft.