Pump Failures and Gravity Feed

Pump alerts run a clean escalation: one main pump is a non-event (the standby already took over), one standby pump is a dispatch problem, a whole side's pumps is a fork in the road (leak or no leak?), and at the very bottom waits the unpowered floor — gravity feed, with altitude ceilings instead of pumps. This article walks the ladder alert by alert, then the gravity-feed regime in full.

1. Single main pump — FUEL L(R) PUMP 1(2) LO PR

The standby pump starts by itself the moment a main pump's pressure drops (main fuel pumps). The ECAM procedure is accordingly one line:

PUMP (AFFECTED) ............ OFF

The engine never noticed. Dispatch afterwards: a single main pump inoperative is a conditioned MEL item (fuel margin, ETOPS restrictions by position) — the working layer of redundancy was spent, not the last one.

2. Standby pump — FUEL L(R) STBY PUMP LO PR

Same one-line drill (pump OFF), very different bill on the STATUS page: FUEL AFT XFR and the standby itself inoperative — the standby drives the wing-tank water scavenge and underwrites several transfer paths. And the dispatch line is absolute: both standby pumps must work; there is no relief. The understudy gets no understudy.

3. Centre pumps (six-tank) — one, then both

One centre pump (FUEL L(R) CTR PUMP LO PR): switch it off; the other carries the centre transfer.

Both (FUEL L + R CTR PUMPS LO PR) — the centre tank has lost its muscle:

L + R CTR PUMPS ............ OFF
WHEN EITHER INR < 17 T:
  CTR TANK XFR ............. MAN
CTR TK XFR BY GRVTY
CTR TK UNUSABLE IF < 15 T

The fallback is gravity transfer from centre to inners — but gravity only moves what sits above the outlet's level: with less than 15 tonnes in the centre tank, the remainder is unusable. The fuel-remaining arithmetic changes on the spot: usable = FOB − (centre quantity below 15 t). Trim fuel reroutes too — with the centre path degraded, forward transfer delivers directly to the inners. STATUS: centre pumps and aft transfer inoperative.

4. The fork — FUEL L(R) WING PUMPS LO PR

A whole side losing pump pressure is the alert with two opposite procedures, and the first decision is not a switch but a question: is this a feedline rupture?

◆ failure due to an engine feedline rupture:
    → the FEEDLINE BURST regime: WING X FEED — DO NOT OPEN,
      pumps OFF, gravity ceilings ([fuel leak / feedline burst](./ata-28-21-fuel-leak-feedline-burst.md))
◆ no fuel leak:
    WING X FEED ................ ON      ← the other side rescues
    PUMPS (AFFECTED SIDE) ...... OFF
    STBY PUMP (AFFECTED) ....... OFF
    → L(R) FUEL GRVTY FEED ONLY
    GRVTY FEED PROC ............ APPLY

[!warning]- Same alert, opposite crossfeed actions No leak → open the crossfeed and let the healthy side's pumps feed both engines. Rupture → the crossfeed is forbidden (it would pump the good side's fuel into the break). The leak question comes first, every time — it decides which procedure you are in.

One protection underneath: if the opposite side's main pumps are already inoperative, the ECAM logic will not ask you to switch off this side's pumps — no scenario is allowed to leave both sides unpowered at once.

5. The floor — gravity fuel feeding

Engines do not strictly need pumps: at low enough altitude, tank head pressure alone feeds them. The QRH regime:

ENG START selector .............. IGN          ← relight protection
AVOID NEGATIVE G FACTOR                        ← gravity is the only pump left
MAX ALTITUDE: GRAVITY FEED CEILING
   20 000 ft  — flight time from takeoff > 30 min
   15 000 ft  — flight time from takeoff < 30 min
    7 000 ft  — JP4 / JET B, flight time < 30 min
WHEN AT THE CEILING:
   WING X FEED ................. CLOSE         (exception: EMER ELEC config —
                                                crossfeed stays as set)
INR UNUSABLE IF < 2 000 kg (4 400 lb)

The ceiling logic is dissolved-air physics: fuel at altitude holds gas in solution; without pump pressure, climbing (or staying high) lets it come out of solution in the feed lines and vapour-lock the flow. Fuel that has been airborne longer than 30 minutes has already outgassed — hence the higher ceiling; volatile fuels (JP4/JET B) get the lowest. Continuous ignition stands guard against the flame-outs that vapour slugs can cause, and negative g is forbidden because the head pressure is the feed.

The quantity bill: each gravity-fed inner tank's last 2 000 kg is unusable — the head runs out before the tank does. Two tanks on gravity = 4 t written off the usable figure.

[!warning]- Gravity feed is an altitude decision, not just a checklist The procedure's real content is the descent: you are committing to FL200 or below (often FL150), with the range and terrain consequences that brings. The pumps failed; the strategy is altitude.

Self-test

[!note]- Q1. Why is a single main-pump failure a one-line procedure? The standby pump started automatically on the pressure drop — by the time the alert shows, the feed is already restored. The line just secures the dead pump.

[!note]- Q2. Why does the standby pump get zero dispatch tolerance when a main pump gets relief? The main has a backup (the standby); the standby is the backup — and it also drives wing water scavenge and supports transfer paths. Its loss is not compensable.

[!note]- Q3. Both centre pumps are gone with 18 t in the centre tank. How much of it can you use? Gravity transfer moves it until the centre is down to 15 t — about 3 t usable, the remaining 15 t unusable unless pumps return. Plan fuel as FOB minus the trapped amount.

[!note]- Q4. What single question splits the WING PUMPS LO PR procedure? Whether the failure is due to a feedline rupture. No leak → crossfeed ON (rescue); rupture → crossfeed forbidden, gravity regime on that side.

[!note]- Q5. Explain the three gravity ceilings. Outgassing: >30 min airborne = fuel already de-aerated → 20 000 ft; <30 min → 15 000 ft; volatile JP4/JET B <30 min → 7 000 ft. Less dissolved gas, higher safe ceiling.

Key takeaways

Point	Value
Escalation	main pump (non-event) → standby (no dispatch) → centre pair (15 t trap) → side group (fork) → gravity
The fork	leak? crossfeed forbidden : crossfeed ON
Cross-side guard	logic never de-powers both sides at once
Gravity regime	IGN, no negative g, ceilings 20 000/15 000/7 000 ft
Crossfeed at ceiling	CLOSE (except EMER ELEC)
Quantity bills	gravity: 2 t per inner unusable; centre gravity: <15 t unusable

References

FCOM PRO-ABN-FUEL (pump LO PR family, WING PUMPS fork, GRVTY FEED) and QRH gravity fuel feeding.
FCOM DSC-28-10-40 (automatic standby); STATUS/INOP listings per procedure.
Some operators' MEL (pump items).
The outgassing physics and "altitude strategy" framing are integrative synthesis.

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.