Educational familiarization only. This original TechOpsBase resource explains system purpose and relationships. It does not reproduce Airbus pages, diagrams, task instructions or controlled maintenance data. Actual aircraft work requires current approved data, correct effectivity, operator procedures, authorization and supervision.
Learning objectives
- Explain the wing-transfer purpose.
- Describe the gravity-head condition required for flow.
- Recognize possible unintended tank-to-tank movement.
1. Purpose
The wing-transfer function opens selected wing and centre tank inlet valves to create a gravity path. It is primarily a manually selected recovery or abnormal-operation function rather than the normal automatic fuel-use sequence.
2. Flow condition
Transfer occurs only when the source fuel level creates sufficient head above the receiving tank. If the centre-tank level is higher, reverse flow toward a wing tank can occur.
If both wing paths are open, fuel can move between wings through the centre tank or refuel gallery when level differences permit.
3. Control and indication
Guarded cockpit controls command the related valves. The FQMS and valve feedback support indication and monitoring. Ground transfer between tanks is handled through the approved refuel/defuel maintenance function.
4. Maintenance awareness
A valve-open command does not guarantee useful flow; tank levels, aircraft attitude, venting and valve position determine the actual result. Unplanned transfer can create imbalance or unexpected tank quantity changes.
5. Abnormal/recovery purpose
Normal A350 fuel management feeds engines directly from the centre and wing tanks. Routine in-flight inter-tank transfer is not required.
Manual wing transfer exists to recover fuel that becomes trapped after both feed-pump pressure sources in one wing tank are unavailable. The fuel can be routed by gravity into the centre tank, where a centre pump or opposite-side feed configuration can make it available.
6. Valve path
For a left-wing transfer, the left wing inlet valve and the corresponding centre-tank inlet valve are commanded open. The right side uses its equivalent pair.
These valves are also part of the refuel/defuel system. The transfer function reuses the refuel gallery and tank inlet architecture.
7. Gravity-head requirement
There is no dedicated wing-transfer pump. Flow depends on the difference in fuel height between the source wing and centre tank.
Transfer can occur only when:
- The selected valves are open
- The source fuel surface is high enough
- The receiving tank has lower fuel head
- Venting permits air displacement
- Aircraft attitude supports the path
If centre-tank fuel height is greater, fuel can move toward the wing. Selection therefore creates a path, not a guaranteed direction.
8. Control and indication
Guarded cockpit pushbuttons provide selection. Discrete command paths drive the valve control through the electrical power-distribution system.
The FQMS and displays provide:
- Selected transfer state
- Valve status
- Tank quantities
- Trapped-fuel information
- Alerts for disagreement
Transfer confirmation comes from quantity trend as well as valve indication.
9. Interaction with engine-feed failure
The transfer is associated with a condition where both pumps on one wing fail and the related engine may be shut down.
The centre-tank pump corresponding to the failed engine side may need to be deselected in the approved operational strategy so it does not continue feeding a damaged line. The public resource should teach the architecture, not reproduce crew procedure.
10. Interaction with jettison
Wing inlet valves must not create recirculation or overflow during jettison. Jettison logic therefore commands a safe valve configuration.
Manual wing transfer has priority. While transfer is selected, FQMS inhibits jettison activation. This prevents competing functions from opening incompatible paths.
11. Both sides selected
If both wing transfer paths are open, fuel can move:
- From each wing to the centre
- From one wing through the centre to the other wing
- Through parts of the refuel gallery
Actual direction depends on head difference. This can create lateral imbalance if not monitored.
12. Failure significance
Failure to initiate transfer can remain hidden because the function is not used during normal daily operation. It becomes significant only when trapped fuel exists.
Loss of transfer indication is less critical because quantities and other indications can confirm movement. The design uses multiple evidence sources.
13. Maintenance reasoning
For no transfer:
- Confirm the abnormal condition requires the function.
- Confirm selection.
- Confirm electrical power to both valves.
- Confirm valve position.
- Compare source and receiving tank levels.
- Confirm tank venting.
- Watch quantity trend.
- Check for an unintended alternate open path.
- Use approved valve and system tests.
The most common conceptual mistake is assuming open valves guarantee gravity flow.
14. Transfer verification
Three independent forms of evidence are useful:
- Valve command and position
- Source and receiving tank quantity trend
- Change in trapped-fuel or availability indication
A quantity decrease in the source without increase in the centre tank can indicate engine consumption, measurement error or another open path. A centre increase with no source decrease can reflect sensor stabilization. Trend must be interpreted with engine feed and crossfeed configuration.
15. Ground transfer is a different function
On the ground, maintenance can move fuel among tanks using the IRP and powered pumps. This is controlled under the refuel/defuel system.
In-flight manual wing transfer is a gravity recovery function. Confusing the two leads to wrong expectations about pump operation and flow rate.
16. Venting dependency
Fuel leaving one tank must be replaced by air, and the receiving tank must release displaced air. A restricted vent path can reduce or stop gravity transfer even when the valves are open.
Venting should therefore be considered when transfer is slow or absent.
17. Structural and balance awareness
Moving fuel changes wing bending relief, lateral balance and centre-of-gravity contribution. The operational function is limited to defined abnormal conditions.
Maintenance ground transfer also requires load-distribution awareness. A tank can reach structural or high-level limits before the total aircraft fuel quantity appears excessive.
18. Scenario example
Both pumps in the left wing lose pressure. The left tank still contains fuel and the left engine is shut down.
The recovery strategy can open a path from the left wing to the centre tank. Gravity moves fuel only if the level difference supports it. Once in the centre tank, an available centre pump or feed configuration can make that fuel available to the operating engine.
The architecture provides an independent recovery path that does not depend on the failed wing pumps.
Key takeaways
- Wing transfer depends on gravity, not a dedicated transfer pump.
- Flow direction can reverse with tank-level difference.
- Opening both sides can create cross-tank movement.
- The function is configuration-sensitive and must follow approved operational data.
Approved-data boundary
This resource is a study aid. It must not be used to determine maintenance steps, limits, dispatch status, component removal criteria or aircraft configuration. Use the current applicable AMM, TSM/FIM, WDM, IPC, CMM, ALS/CDCCL data, operator procedures and task cards for real work.
