This Topic is relevant to the whole fleet

GENERAL

The trim tank transfer system controls the center of gravity (CG) of the aircraft. When the aircraft is in cruise the system optimizes the CG position to increase the fuel economy by reducing the drag of the aircraft.

The system transfers fuel to the trim tank (aft transfer) or from the trim tank (forward transfer).

This movement of fuel changes the CG of the aircraft. Normal operation is automatic but the crew can manually select forward fuel transfer.

The fuel control and management computer (FCMC) calculates the CG of the aircraft and compares the result to a target value which depends on the aircraft actual weight as shown below. From this calculation the FCMC decides the quantity of fuel to be moved aft or forward in flight (usually only one aft fuel-transfer is carried out during each flight).

AFT CG TARGET

NORMAL OPERATION

Automatic control of CG begins in climb at FL 255 and stops in descent at FL 245 or when FMGS time to destination is below 35 minutes (or 75 minutes if the trim tank transfer pump fails).

1. The trim pipe isolation valve and the trim tank isolation valve are closed at takeoff and for landing. Reopening is possible when landing gear is up and slats are retracted (or when the MODE SEL switch is set at REFUEL on the REFUEL panel).

2. If the CG detected by FMGC is too far aft then the target will be automatically moved 1.5 % forward.

   Target also moves 1.5 % forward in case of degradation of FQI data, or in the event of ZFCG or ZFW modification in flight (through the MCDU).

   Note that these CG target alterations should be added together.

 

AFT TRANSFER

The FCMC only starts an aft fuel transfer when all of these conditions are met:

	the landing gear is retracted.
	the slats are retracted.
	the trim tank is not full.
	fuel quantity in an inner tank is above 6 250 kg.
	the aircraft is above FL 255.
	aircraft CG is not on target.

Normally only one aft transfer occurs per flight. However if in cruise the CG is forward of the target by more than 2 % and the trim tank quantity is below 3 000 kg, a further aft transfer is carried out.

The aft transfer is terminated when:

	computed CG = target CG - 0.5 % or,
	trim tank high level sensor becomes wet or,
	the fuel quantity in an inner tank reaches 6 250 kg or,
	the T TANK pushbutton is selected FWD or,
	the flight crew manually selects transfer from outer tanks to inner tanks.

The inner tanks provide fuel for trim tank aft transfer through the engines feed pumps.

If during transfer the inner tanks are out of balance by more than 500 kg, transfer is stopped on the lightest side by automatic closure of the related aft transfer valve until the fuel balance is recovered.

ECAM indication




FOR INFO




AFT TRANSFER

 

AUTOMATIC FORWARD TRANSFER

The FCMC sends a forward fuel transfer signal if one of the following conditions occurs :

	The calculated CG = the target. (It stops when the calculated CG = the target CG minus 0.5 %)
	The fuel contents of one of the two inner tanks decreases to 4000 kg (5000 kg*). (It stops when 5000 kg (6000 kg*) are reached). * in case of trim tank forward transfer pump failure.
	The FMGS sends a time to destination signal or the aircraft descends below FL 245. (In this case transfer is continuous but controlled by the inner tank high levels to prevent overflow).

Fuel is transferred from trim to inner tanks. If an inner tank reaches the high level the related inlet valve closes to prevent tank overflow. It reopens when inner tank quantity reaches

2000 kg below the high level.

In normal operation the trim tank transfer pump performs the forward transfer.

The pump starts to operate when the landing gear and the slats are retracted provided there is fuel in the trim tank, and continuously runs during the flight until the trim tank is empty or T TANK FEED selector is selected to ISOL.

In the event of pump failure, forward transfer is performed by gravity through the trim tank non return valve. The FCMC inhibits the forward transfer by closure of the TRIM PIPE ISOL VALVE when the aircraft attitude exceeds 3.4° for more than 1 minute and reinitiates it when the aircraft attitude is lower than 3.4° for more than 1 minute.

MANUAL FORWARD TRANSFER

When the T. TANK MODE pushbutton is pressed, FWD light comes on white and :

	the TRIM TK ISOL valve, the AUX FWD XFR valve and the TRIM PIPE ISOL valve open,
	the LH and RH INR TK INLET valves open,
	the two AFT XFR valves close.

The fuel is transferred from the trim tank to the inner tanks through the forward transfer pump.

When the pushbutton is released, the system reverts to normal.

Inner tank overflow must be manually prevented by releasing the pushbutton when either inner tank is full.

ECAM indication

AUTOMATIC FORWARD TRANSFER

FOR INFO







MANUAL FORWARD TRANSFER