Defuelling and Ground Transfer

Getting fuel out of an A330 — or just moving it between tanks on the ground — reuses the refuel plumbing in reverse, with one crucial difference: most of the refuel protections don't work backwards. Defuelling is therefore a procedure-guarded operation, not a computer-guarded one. This article covers the two defuel methods (pressure and suction), the centre tank's separate pressure-defuel path, and the ground-transfer configurations — plus the interlocks that decide which tank may empty when.

A pilot rarely runs these; a pilot does sign the aircraft after them — and the flight-deck check is the same as after refuelling: panel switches back, door closed, no REFUEL memo.

1. Pressure defuel — wing tanks, aircraft pumps pushing

"The pressure defuel cannot start unless all the wing inlet valves are closed. This prevents the possibility of a tank overflow, because the inner tanks have no fuel hi-level sensor protection during a defuel. It is only possible to pressure defuel the inner fuel tanks. To defuel the other fuel tanks, their fuel must first be moved to the inner tanks."

The configuration: MODE SELECT to DEFUEL, TRANSF VALVE switch OPEN, then the aircraft's own main/standby pumps push inner-tank fuel through the aft transfer valves (B/D) into the refuel gallery and out of the coupling to the defueller. Pumps 1/2 running opens the LH valve, pumps 3/4 the RH valve.

The aft transfer valve's permission list is the procedure in miniature — it will not open unless all of:

• a main or standby pump on its side is running;
• the trim tank is empty;
• the surge-tank sensors are dry;
• the outer-tank inlet valves are closed;
• (six-tank) the centre-tank inlet valve is closed;
• the inner-tank inlet valves are closed.

As an inner tank empties, automation lends one hand: at 3 500 kg the intertank transfer valves open and the outers drain inboard, joining the defuel (main transfer — same latched valves). And on six-tank aircraft a quiet guard: "During the defuel, the center-tank restrictor valve will stay closed. This will prevent operation of the center-tank burst disc" — gallery pressure must not reach the centre tank's 5–7 psi relief threshold (tank venting).

One hose detail with a placard behind it: when only one adapter on a coupling is used for defuelling, it must be the one labelled "USE THIS ADAPTOR TO DEFUEL".

2. Centre-tank pressure defuel — a separate path with the guards off

The wing procedure cannot touch centre fuel. Six-tank aircraft have a second pressure-defuel mode: MODE SELECT to DEFUEL and the centre transfer pumps ON — they push centre fuel directly out through the gallery. Two things make this the most supervised case of all:

[!warning]- In centre defuel, the automatic shut-offs are disconnected In this configuration the defuel-isolation relay stays de-energised, which means "the fuel hi-level indication relays cannot automatically shut the inlet valves when wet" and "the surge-tank overflow indication relays cannot automatically shut the isolation valves when wet". The overfill protections that guard every refuel are out of the loop — the operation runs on eyes and procedure. (One automatic guard remains: a surge-tank sensor wetting stops the transfer pumps.)

Trim fuel rides along the same path: set a forward transfer and the trim tank drains into the centre tank as the centre is pumped off — tail to centre to bowser in one chain.

3. Suction defuel — the defueller does the work

"It is possible to suction defuel all of the fuel tanks. To do this: the MODE SELECT switch 3QU is set to DEFUEL ‐ the necessary fuel-tank inlet valves are set to OPEN."

The ground rig pulls; fuel leaves each opened tank backwards through its refuel diffusers and inlet valves. Quieter and gentler than pressure defuel — but with its own dependencies: the FCMS level-sense function must be operating, and if the full FCMS is powered the valves follow the panel switches (NORM = closed). One interlock stands guard:

"If the trim tank contains fuel, then fuel-system interlocks prevent a suction defuel of the inner tanks."

Emptying the inners while tonnes sit in the tail would walk the CG aft on the ground — the interlock makes the order non-negotiable: tail before wings.

4. Ground transfer — moving fuel without removing it

After maintenance, after an overwing refuel, or to correct a bad distribution, fuel is moved tank-to-tank on the ground through the refuel gallery.

From an inner tank (all aircraft): MODE SELECT REFUEL · TRANSF VALVE OPEN · receiving tanks' switches OPEN · standby (or main) pumps ON · crossfeed valves OPEN. The TRANSF VALVE switch carries a protective subtlety: it opens each side's aft transfer valve only if a pump on that side is actually running — "this function prevents a loss of fuel pressure to the APU when it is supplied through the forward APU fuel pump". An open valve with no pump behind it would bleed the APU's feed line.

From the centre tank (six-tank): MODE SELECT REFUEL · receiving switches OPEN · TRANSF VALVE OPEN (the aft transfer valves do not open in this mode — the switch simply puts the inlet valves into refuel logic) · main pumps OFF · transfer pumps ON. The centre pumps push; the gallery distributes.

Destination note from the AMM: fuel left in the centre tank after maintenance should be transferred to the inners — that restores "the correct configuration for an automatic pressure refuel".

(Ground transfer to the trim tank is a maintenance-procedure-only operation — normal ground transfers exclude it.)

5. The flight-deck face

The EWD memo logic watches the panel throughout (controls and ECAM): the not-in-flight-position warning shows with the door closed if MODE SELECT is in REFUEL/DEFUEL, any valve switch is out of NORM, the TRANSF VALVE switch is OPEN, or panel power is on BAT; REFUEL IN PROCESS shows for the same switch states or an open door. After any defuel or ground transfer, the pre-departure state is binary: every switch normal, door shut, memos gone.

Self-test

[!note]- Q1. Why must all wing inlet valves be closed before a pressure defuel can start? Because during defuel the inner tanks have no high-level sensor protection — an open inlet valve could overflow a tank with nothing to stop it.

[!note]- Q2. List the aft transfer valve's opening conditions for pressure defuel. Side pump running · trim tank empty · surge sensors dry · outer inlets closed · (six-tank) centre inlet closed · inner inlets closed — all simultaneously.

[!note]- Q3. What is uniquely risky about the centre-tank pressure defuel? The high-level and overflow relays cannot automatically close the valves in this configuration — overfill protection is procedural, not automatic (only the surge-sensor pump-stop remains).

[!note]- Q4. Why won't the aircraft suction-defuel the inners while the trim tank has fuel? A fuel-system interlock blocks it: draining the wings first would shift the ground CG aft with tonnes still in the tail. Tail empties first.

[!note]- Q5. In an inner-tank ground transfer, why does the TRANSF VALVE switch check for a running pump before opening the aft valve? An open aft transfer valve without pump pressure behind it would let the APU's feed pressure bleed away into the gallery — the gate protects the APU supply.

Key takeaways

References

• AMM 28-25-00 Description and Operation §7.B/C/D (defuel modes, permission lists, ground transfer, relay logic) and §7.E (EWD message conditions).
• FCOM DSC-28-10-110 (panel functions).
• The risk framing of centre defuel and the interlock rationales are integrative synthesis from the cited logic.

Independent study material, not an Airbus publication and not endorsed by the manufacturer. Always defer to the current operator FCOM, FCTM, and QRH for operational use.