B. FUEL SYSTEMS

b) CG control
The following profile describes the CG control system behavior throughout the flight:
SYSTEMS

The CG control function is active once the aircraft has reached FL 255. It is deactivated when the aircraft flies below FL 245 or when time-to-destination from the FMGS is less than a given value, which depends on the aircraft type and on whether a trim tank pump is fitted and operative.
CG control starts with an aft transfer to the trim tank when all the following conditions are met:
. The landing gear is up and the slats are retracted
. The trim tank is not full
. The aircraft CG is not on the target
. Each inner tank quantity is above 6250kg (6000 kg for A340-500/-600)
. The Flight Level is above FL 255
Normally only one aft transfer is generated during the flight. However, it can happen that an additional aft transfer occurs when both the CG position is 2% forward the target value and the trim tank reaches a low level.
An aft transfer ends if one of these conditions is fulfilled:
. The computed CG reaches Target CG - 0.5%
. The trim tank is full
. The inner tank quantity reaches 6250kg (4000 kg for A340-500/-600)
. The crew requests a manual fuel transfer (forward trim transfer or transfer from
the center or outer tanks to the inner tanks).
. Jettison is selected
B. FUEL SYSTEMS

SYSTEMS

Then, during the normal fuel burn, center tank and inner tanks depletion brings the CG further aft. Automatic forward transfers from the trim tank (and also from the RCT on A340-500) keep the CG position within the CG control band. These transfers occur in each of the following circumstances:
.  The Calculated CG position reaches the target CG. The transfer stops when the calculated CG reaches CG Target -0.5%
.  The fuel quantity in one of the inner tanks decreases down to 4000 kg (or 5000 kg depending on the aircraft). The transfer stops when the level reaches 5000 kg (or respectively 6000 kg).
.  The FMGS sends a time-to-destination signal or the aircraft is in descent below FL245. In this case, the fuel transfer is continuous and stops only if the inner tanks are overflowing.
These transfers take into account potential tank imbalance that can be encountered during the flight. In case the inners are unbalanced by more than 500 kg, either forward transfer is directed to the lightest tank or aft transfer is stopped on the lightest tank.
c) CG target possible shifts during flight
During the flight all the fuel transfers are based on the CG position determined by the FCMC,
these positions are linked to the ZFW and ZFCG values input by the pilot before flight in the
MCDU.
An independent CG determination is made by the FMGC. If the CG position computed by the
　
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本文鏈接地址：Getting to Grips with Aircraft Weight and Balance(29)