Definition

A Fuel Control and Management Computer (FCMC), a component on certain Airbus aircraft, calculates the aircraft's centre of gravity (CG) from various parameters including fuel tank contents.

Description

The FCMC continuously calculates the aircraft's CG in flight. Based on this calculation, the FCMC decides the quantity of fuel to be moved forward or aft to maintain CG limits. According to Airbus guidance, one initial aft fuel transfer is usually carried out late in the climb to keep CG within the accepted range. During flight, there are usually several smaller forward adjustments as fuel burns off. On the A330, if the actual CG differs from the desired CG by more than a half percent, and the aircraft is above 25,500 feet, a corrective transfer takes place. If an inner tank quantity drops below 4,000 kg, a forward transfer occurs to maintain fuel in the inner tanks between 4,000 and 5,000 kg. Finally, a forward transfer is usually made as the aircraft nears its destination to bring CG within landing limits.

The system works by transferring fuel either to or from a trim tank. Adding fuel to the trim tank moves the CG aft. Taking fuel from the trim tank moves the CG forward. These automatic fuel transfers optimize CG to save fuel by reducing drag.