Fuel Management in Operations
The chapter closes where every flight actually lives: not in failures, but in the running discipline that catches them early and the decision ladder that governs a shrinking fuel state. Almost everything here is one habit and one escalation: keep the conservation books every half hour, and know the exact words that change your priority with ATC.
1. The standing habit — conservation bookkeeping
The FCTM's rule, already met in the overview:
"Fuel checks should be performed when the aircraft overflies a waypoint, or at least every 30 min. Any difference should alert the flight crew... For any message or alert related to the fuel quantity or imbalance, the flight crew should consider a fuel leak as a possible cause."
The check itself is three numbers: FOB + fuel used = departure FOB (within the gauge tolerances of fuel quantity indication). Less than the departure figure and falling — the leak reflex (fuel leak); more than the departure figure — the overread reflex (quantity and level faults); on target — note it and fly on. The FWC runs the same sum continuously (the 3 500 kg DISAGREE line), but the half-hourly human check exists because the FWC's threshold is a coarse net: the crew's trend-reading catches what the comparator cannot.
Alongside the conservation sum, the EFOB trend on the FMS flight-plan page is the forward-looking book: each waypoint's predicted remainder, drifting down faster than planned = the same three suspects (burn, plan, or leak) before any alert fires.
2. The minimum lines
- Takeoff: 5 200 kg minimum and no wing-tank low-level alert displayed (overview — the LIM-FUEL hard lines).
- Destination: the FMS holds the crew-entered MIN DEST FOB; predictions falling below it turn the destination EFOB amber — the planning-level warning that precedes any tank-level alert by a long margin.
- The tank-level floor: the LO LVL alerts (1 100–2 520 kg per side) — by which point the situation is no longer about planning (quantity and level faults).
The deliberate redundancy: the plan warns first (amber EFOB), the tanks warn last (LO LVL). A crew that manages by the first line should rarely meet the second.
3. The declaration ladder
When the destination arithmetic tightens, standard phraseology changes the operational machine around the aircraft (ICAO framework as reflected in operator documentation):
| State | Words | Meaning |
|---|---|---|
| Committed, any further delay unacceptable | MINIMUM FUEL | not an emergency — a notification that the crew can accept no further delay; ATC owes information, not priority |
| Calculated landing fuel below final reserve | MAYDAY MAYDAY MAYDAY FUEL | an emergency — priority handling; landing below final reserve is now predicted |
The ladder's value is its bright line: minimum fuel is a planning statement; MAYDAY FUEL is triggered by one computable condition (predicted landing fuel below final reserve). Crews who know the trigger compute it early and declare without agonising — the declaration is arithmetic, not bravado.
In the fuel-failure procedures of this chapter, the same arithmetic appears as the usable-fuel recomputation: trapped trim fuel, a written-off centre tank, gravity-feed dead fuel — each procedure's "unusable" figure subtracts from the FOB before any of the lines above are assessed. The half-boxed FOB (controls and ECAM) is the display doing this subtraction visually; the crew's plan must do it numerically.
4. Flying cheaper — the system's contribution
Two threads from this chapter convert directly into fuel economy:
- the aft-CG optimisation (aft-CG transfer) runs automatically — but only as well as its inputs: a correct ZFW/ZFCG entry is worth real fuel (wrong or absent data costs a 1.5 % forward target correction and its drag);
- transfer-fault penalties are part of diversion economics: the ~1 % burn penalty of an open trim-line transfer, the cost of flying with the CG stuck forward after an AFT XFR FAULT — small percentages that matter on long sectors and belong in the re-planning whenever a transfer procedure has run.
The habit-level summary of the whole chapter: enter the weights carefully, check the books every half hour, treat anomalies as leaks, recompute usable fuel after any failure, and know your two declarations cold.
Self-test
[!note]- Q1. What three numbers make the half-hourly fuel check, and what do the two failure directions mean? FOB + fuel used vs departure FOB. Short and falling = suspect a leak; over = suspect overread. The FWC's 3 500 kg comparator backs the habit but is coarser than a trend-reading crew.
[!note]- Q2. Order the warning lines from earliest to last. Amber destination EFOB (planning) → minimum-fuel/declaration arithmetic (crew) → wing-tank LO LVL alerts (tanks). Managing by the first line should keep you off the last.
[!note]- Q3. What exactly triggers MAYDAY MAYDAY MAYDAY FUEL? The calculated landing fuel at the intended airport falling below final reserve — a computable condition, distinct from MINIMUM FUEL (a no-further-delay notification, not an emergency).
[!note]- Q4. After a trim-fuel-unusable declaration, which FOB do the declaration lines use? Usable fuel — FOB minus the trapped quantity. The half-boxed FOB shows the issue; the crew's arithmetic must subtract it before assessing minima.
[!note]- Q5. Name two crew actions in this chapter that directly buy fuel economy. Accurate ZFW/ZFCG entry (protects the aft-CG optimisation from the 1.5 % conservative correction) and prompt, correct transfer-fault handling (limits the ~1 % class penalties).
Key takeaways
| Point | Value |
|---|---|
| Habit | conservation check every waypoint / 30 min; anomalies = leak first |
| Warning order | amber EFOB → declaration arithmetic → LO LVL |
| Declarations | MINIMUM FUEL = no further delay; MAYDAY FUEL = landing below final reserve predicted |
| Hard lines | 5 200 kg + no LO LVL alert for takeoff |
| After failures | recompute usable fuel before assessing minima |
| Economy | correct weights protect the CG optimisation; transfer penalties belong in re-planning |
References
- FCTM PR-AEP-FUEL (fuel checks, leak-first discipline); FCOM LIM-FUEL (takeoff minimum); FMS documentation (MIN DEST FOB, EFOB display logic).
- ICAO-framework fuel declarations as reflected in operator documentation.
- The warning-order framing and economy threads are integrative synthesis of the cited chapters.
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.