Getting to Grips with Aircraft Weight and Balance(28)

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As described previously, engines are only fed from the inner tanks and so, all the fuel from the other tanks have to be transferred to the inner in order to be burnt.
Besides, the fuel burn sequence for long-range family aircraft and the associated fuel transfers are in accordance with the basic structural constraints (wing root stress).
As for refueling data, the following depletion sequence is applicable to FCMS 9.0 standard :
a) A330-200/-300 and A340-200/-300
. 1/ ACT (if applicable) fuel transferred to the center tank . 2/ Center tank (if applicable) fuel transferred to the inner tanks . 3/ Inner tanks down to a given level (ie 4000 or 5000 kg in each inner tank
depending on the aircraft) . 4/ Trim tank fuel transferred to the inner tanks . 5/ Inner tanks is emptied down to a second given level (ie 3500 or 4000 kg in
each inner tank)
. 6/ Outer tanks fuel transferred in the inner tanks
. 7/ Inner tanks (until empty)

b) A340-500/A340-600
.  1/ Center tank fuel transferred to all inner tanks until center tank fuel quantity reaches 17000 kg
.  2/ Center tank fuel transferred to inner tanks 1 and 4, to maintain full quantity, until all inner tanks are balanced (approximately 18000 kg per inner tank)
. 3/ Rear center tank (if applicable) fuel transferred to the center tank when the center tank quantity reaches 1000 kg . 4/ Center tank fuel transferred to all inner tanks, cycling the inner tanks
quantities between 17200 and 18200 kg, until the center tank is empty . 5/ Inner tanks down to 4000 kg per inner . 6/ Trim tank fuel transferred to the inner tanks . 7/ Inner tanks is emptied down to 2000 kg per inner . 8/ Outer tanks fuel transferred in the inner tanks . 9/ Inner tanks (until empty)
All the transfers mentioned here are managed automatically by the fuel system.
The fuel burn sequence is a reference vector, which is not strictly followed in flight as the CG position is modified by the CG control system.
SYSTEMS

B. FUEL SYSTEMS

SYSTEMS

3.4.2. CG control system
The position of the aircraft CG during the flight has an impact on the fuel consumption. Indeed, an aft CG position reduces the drag and then implies fuel savings. That is the reason why a CG control system has been introduced on long-range family aircraft.
a) CG target
In flight, the FCMC controls the position of the center of gravity. It calculates the CG position and compares it to a target value, which depends on the aircraft weight. According to this calculated CG position compared to the target, the FCMC determines the fuel quantity that needs to be transferred aft or forward.
The graph below is published in FCOM 1.28.10 and provides with the target CG expressed in %MAC as a function of the aircraft weight:

AFT CG Target -A340-300
The FCMC determines the fuel quantities to be transferred to maintain the aircraft CG in a control band limited by the CG target position and CG target position . 0.5%.
　
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