Fuel System - Operations 
- Limitations - APU
- Limitations - Engine Fuel System
- Procedure - Ground Transfer of Fuel
Fuelling
Normal fuelling is accomplished through dual fuel nozzle adapters located on the left and right wing leading edge spar at the fuelling stations. All fuelling operations, except fuel pump control, are accomplished at either fuelling station. However, when both left and right stations are being used, the left station has control of all fuel settings and valve positions. Opening the station access door applies DC power to the fuelling system and removes the centre tank pump operating inhibit.
Fuel flows through the dual nozzles to pressurise a fuelling manifold. Fuelling valves control the flow of fuel from the fuelling manifold into each of the three fuel tanks. The fuelling valves may be operated by switches on the fuelling panel. A fuel quantity may be pre-selected for each tank. The fuelling valves close automatically when the pre-selected quantity is reached or when the tank is full (Volumetric Top Off), whichever occurs first.
A tank overspill system is provided to prevent fuel spillage. If any fuel is sensed in the surge tanks during fuelling a signal is sent to close all fuelling valves.
The airplane is filled automatically by hydrant or tank truck pressure. All tanks may be fuelled at the same time. The main tanks may also be fuelled manually through over wing fill ports. There are no over wing fill ports for the centre tank.
Defuelling
Left and right defuelling valves connect their respective engine fuel manifolds with the fuelling manifold.
Fuel can be pumped from any tank to the corresponding engine fuel manifold by operating the tank fuel pumps. Opening the appropriate defuelling valve routes the fuel from the corresponding engine fuel manifold to the fuelling manifold.
For defuelling, the flow in the fuelling manifold is reversed for fuel to flow back into a truck or hydrant.
Suction defuelling can be accomplished by opening the respective defuelling valve and applying an outside suction source to the fuelling nozzles. Suction defuelling, of the centre tank is not possible.
Ground Transfer
On the ground, fuel can be transferred from a source tank to a receiving tank by operating the fuel pumps in the source tank and opening the appropriate Defuelling Valve which pressurises the fuelling manifold. Opening the Fuelling Valve(s) for the receiving tank(s) completes the transfer circuit
The schematic shows fuel being pumped from the centre tanks, via the left and right Defuelling Valves, into the left and right main tanks. Fuel will continue to transfer until either:
- The centre tank is empty.
- The main tanks reach full causing the appropriate refuel valve to close automatically.
- The pre-selected SET amount is reached in the main tank, causing appropriate refuel valve to close.
