1 FUEL SYSTEM
The fuel system is one of the major systems of the Airbus A320. This system, controls the entire
fuel flow and fuel reservoir on board the aircraft. The primary use of the system is to supply fuel
to then engine and the APU. It also contributes in the balancing of the center of gravity of the
aircraft during flight. On Board the A320, the essential characteristics of the fuel system are: fuel
pressurization, Engine Feed, Fuel Transfer, Defuel and Refuel. The fuel system uses a pump feed
system to move the fuel in the desired location (tank, engine…).
1.1 FUEL TANKS AND PUMPS
The fuel tanks are integrated into the center fuselage area and the wings. The center wing tanks are part of
the center wing box. The wing tanks are divided into inner and outer cells as seen in Figure 1-1:Fuel tanks
SchematicFigure 1-1. To reduce structural loads, the fuel in the outer cells is not used until the fuel in the
inner cells decreases to a low level [1]. There is a vent surge tank outboard of the outer tank in each wing.
Figure 1-1:Fuel tanks Schematic [1]
The main fuel pump system supplies fuel from the center tank or the inner wing tanks to the engines [2].
The system has six main fuel pumps, two are installed in the center thank and two are installed in each
wing tank inner cell [1]. All wing tank pumps remain active throughout the flight. They are fitted with
pressure relief sequence valves; these valves give priority to center tank pump to supply fuel until it is
low [3].
A specific fuel pump supplies the APU when tank pumps are not operating. This fuel pump is connected
to the left supply line. This fuel line is critical at the procedure of engine starting [3].
1.2 FUEL SYSTEM VALVES
The fuel system is run by a pressurized line made of pumps, pipes and valves. Valves play the roll of
regulating the fuel flow and fuel directions. There exist 4 types of valves on board of the Airbus A320.
1.2.1 Transfer Valves
Two electrical transfer valves are mounted in each wing to permit fuel transfer from outer to inner tank as
seen in Figure 1-2 [2]. They turn active when the fuel reaches low level in the inner cells. The use of
transfer valve instead of cross feed valves is due to the nature of transfer valves, transfer valves allow one
way transfer of fluid instead the cross feed valve allows two ways of fluid movement.
1.2.2 Cross Feed Valve
A cross feed valve controlled by a double motor allows both engine to be fed from one side or one engine
to be fed from both sides. The cross-feed valve is normally inactive [2]. The activation of the cross-feed
valve is temporary and allows the shortest route of fuel to flow. It is kept inactive throughout most of the
flight, it is usually activated to balance the aircraft, or an engine is lost.
1.2.3 Engine Low Pressure Valves
The low-pressure valve isolates the engines or APU from the fuel supply. This valve manages the fuel
flow to the engine and APU. The Valve is active when the engines or APU system are running, it
deactivates when the engine or APU is shut down or when FIRE pushbutton is released out [2].
1.2.4 Suction Valves
The suction valves are inactive in normal conditions, they allow the engines to be fed by gravity if the
inner tank pumps fail. The center tank is not equipped with suction valves therefore in case of pump
failure, the engines cannot be fed from the center tank [2].
1.2.5 Sequence Valves
Pressure relief sequence valves are integrated on the wing tank pumps as see in Figure 1-2, to give
priority to center tank pump to supply fuel. The sequence valves give priority by limiting the wing tank
pumps output pressure [3]. Sequence valves have external drain port to keep from trapping leakage oil.
The sequence valves have the option to be internally pilot-operated, controlling fluid passing through fuel
pumps. Sequences valves have some disadvantages; once a high pressure at a certain level is reached
sequence valves switch to relief the pressure however, the actuator positioning cannot be known, the only
information given when sequence valves are activated is that there is a high pressure in the fluid but the
cause is unkown.
Figure 1-2:Detailed Fuel Line Schematic [3]
1.3 REFUELING AND DEFUELING SYSTEM
Refuel panels are located on the fuselage and wings as see in Figure 1-3. The refuelling system is
Automatic, the refueling procedure starts by the outer cells. If the selected fuel loads exceed the wing tank
capacity, the center tank is refuelled simultaneously. As the outer cells are being refuelled, fuel flows to
the inner cell though a spill pipe. Refuel Valves close automatically when the tanks contain the
preselected fuel loads [2].
Figure 1-3:Refuel Panel Locations [2]
1.4 FUEL RECIRCULATION SYSTEM
The fuel recirculation system is used to cool down the engines. The fuel supplied to each engine goes
from the high-pressure fuel line through the integrated drive generator (IDG) in which it releases the
absorbs heat, to the fuel return line as seen in Figure 1-4. This operation ensures that the IDG cooler is
operating when the oil temperature is high or when at low engine power [2].
Figure 1-4: Fuel Recirculation System [2]
Figure 1-5:Fuel System Architecture [2]
Figure 1-6: ECAM Display [1]
Fuel Sensors are installed in the Fuel tank to detect the quantity of fuel left in the tank, it is programmed
to be triggered when the fuel system reaches 750 Kg. At this stage the Low Fuel sensor sends commands
to the FQI Computer as seen in Figure 1-5 and the FQI sends signals to the ECAM Fuel Page Figure 1-6 to
trigger the ‘LO LVL’ warning.
[1] AIRBUS S.A.S., "T1-28-Fuel," Airbus Training & Flight Operations Support and Services, Toulouse ,
2005.
[2] AIRBUS, "28-Fuel System," AIRBUS Training manuals, 2006.
[3] AIRBUS, "ATA 28: Technical Training Manual," AIRBUS, Blagnac , 2000.