MEL Dispatch

The previous eleven articles cover how the system works and how it is handled; this one returns to the ground for the practical question: with this fire-protection item unserviceable, can the aircraft still be dispatched? The dispatch logic hides two elegant asymmetries that test your grasp of the earlier mechanics — and both fall straight out of the system articles rather than out of rote.

[!warning]- This article is generalised — always use the current operator MEL Minimum-equipment relief is operator-specific (each operator's MEL is derived from the manufacturer MMEL and approved by its authority). The verdicts below describe the typical structure and reasoning that follow from the system mechanics; specific items, conditions, placards and time limits vary by operator. For any real dispatch, apply the current operator MEL entry itself.

1. How a fire-protection MEL is organised

A fire MEL is indexed by ECAM alert: each alert maps to a "dispatch condition" — either a flat "no dispatch", or a pointer to a detailed item (a 26-XX-XX entry) carrying the specific operational/maintenance conditions. A useful four-layer view of the verdicts:

  Fire-protection item degraded
   ┌───────────────┬───────────────┬───────────────┬───────────────┐
  active FIRE/SMOKE  detection lost   single loop      bottle fault
  (warning active)   (DET FAULT)     (LOOP FAULT)     (BTL FAULT)
   │                 │               │                │
  no dispatch     depends on zone   dispatchable     conditional
                  eng/avionics/all  (OR logic)       (per item)
                  = no dispatch
                  APU/cargo = OK

In one line: a live fire cannot fly; total detection loss depends on the zone (engine and avionics are strictest); a single loop still walks on one leg; a missing bottle usually flies.

2. An active fire or smoke warning — never dispatched

The most direct layer: a warning that is active cannot be dispatched. An active ENG FIRE, APU FIRE or CARGO/AVNCS SMOKE is a no-dispatch item.

[!warning]- Not a truism — the MEL manages inoperative equipment, and an active warning is the opposite The MEL governs whether an unserviceable item may be dispatched; an active fire warning means the equipment is working and has found a real threat. It is not "broken", it is "doing its job and reporting a fire" — a system actively reporting a fire has only one dispatch answer. On the ground, first establish whether it is real or spurious (a ground cargo SMOKE can be humidity, article 11), but while the warning is valid, do not dispatch.

3. Total detection loss (DET FAULT) — the verdict depends on the zone

Both loops failed is a DET FAULT (articles 02/04). The same "detection fully blind" outcome yields opposite dispatch verdicts by zone:

No dispatch: engine fire DET FAULT; avionics smoke DET FAULT; a total SMOKE DET FAULT.
Dispatchable (per item): APU fire DET FAULT; cargo, crew-rest and broadband smoke DET FAULT.

[!warning]- The chapter's crowning asymmetry — engine detection fully blind is no-go, APU is go Reasoned from articles 02/04/05:

Engine fire is the most critical fire on the aircraft (thrust, fuel, ability to hold altitude); with detection fully blind, a fire would be invisible and the ENG FIRE procedure impossible to run (the ground version of article 09's "FIRE became DET FAULT — the fire burned the detectors"). This blind spot is unacceptable — no dispatch.

The APU is non-critical in flight (engines supply power and air) with ground auto-extinguishing (article 04); even with detection lost, a real APU fire can be shut down and, on the ground, self-extinguished — the risk is bounded, so dispatch with conditions is possible.

The avionics bay sits with the engine at "no dispatch": it is detect-only (article 05), so detection is the only line — losing it means an avionics fire is both invisible and un-fightable, a double failure.

Whether total detection loss can fly depends on how lethal that blind spot is — engine (most lethal) and avionics (detect-only) cannot fly; APU and cargo (bounded or secondary) can. This is the same logic family as ATA-36's "wing-leak detection fault = no dispatch, APU-loop fault = dispatchable": whether a lost detection path can dispatch turns on how critical what it guards is, and whether an alternative exists.

4. Single loop (LOOP FAULT) — still one leg, flies

A single loop failed is a LOOP FAULT; the system falls to OR logic and still detects (articles 02/04) — so an engine or APU LOOP FAULT is dispatchable per item.

[!warning]- Single-loop dispatchable but engine dual-loop no-go — the line is "is there still a leg that detects fire?" Article 02's "AND demotes to OR, one loop failed still detects, dispatchable" lands here as an MEL verdict: a single loss is reduced sensitivity with capability intact → dispatch per item; a dual loss (engine) is capability gone → no dispatch. Mechanics decide dispatch, not memorised clauses — this is the cleanest weld of the system (article 02) to the dispatch decision (this article).

5. Extinguishing degraded (BTL FAULT) — usually conditional dispatch

A bottle low-pressure or fault is a BTL FAULT; dispatch depends on whether the other hold / bottle is also affected (e.g. an aft-cargo bottle fault is dispatchable per item if the forward bottle is not also faulted).

[!warning]- Detection is stricter than extinguishing — the eyes are worth more than the hands Reasoned: detection is the "eyes" — blind (especially engine/avionics) and you cannot even find the fire, the most dangerous state. Extinguishing is the "hands" — one bottle short, there is still another bottle or path (article 06: two shared bottles, FWD/AFT dual outlets); unless both holds' bottles are dead, dispatch with conditions is usually possible. So MEL relief runs "a lost eye (detection) is dearer than a lost hand (extinguishing)": the most critical zone's blind eye cannot fly, a missing hand often can. BTL FAULT conditions typically require the other hold's bottle intact plus an operational/maintenance procedure — apply the specific item.

6. Using the MEL — the read flow

  fire-protection ECAM warning on the ground
   1  active FIRE / …SMOKE?           -> yes: no dispatch (first distinguish real vs spurious)
   2  DET FAULT (detection lost)?     -> engine / avionics / total SMOKE: no dispatch; APU / cargo / others: item 26-XX
   3  LOOP FAULT (single loop)?       -> item 26-12/26-13 (dispatch with conditions)
   4  BTL FAULT (bottle)?             -> depends on the other hold -> item 26-23 (conditional)
   -> a pointer to "item 26-XX-XX" = read that item's detailed dispatch conditions (o/m procedures, limits)

Freighter: the MDCC (article 07) has its own MEL items by configuration (no extinguishing system, so its detection-degrade entries stand alone) — apply the freighter-specific MEL.

Reminder: this article is the verdict-level pattern (no dispatch / see item). The specific items carry the operational and maintenance procedures, time limits and additional restrictions — for real dispatch, read that item, not the category.

Self-test

[!note]- Q1. Why is an active fire/smoke warning always no-dispatch, and why does the MEL even list it? The MEL manages inoperative equipment; an active warning means the equipment is working and reporting a real threat — the only answer is no dispatch.

[!note]- Q2. Why do engine FIRE DET FAULT and APU FIRE DET FAULT give opposite verdicts? Why is avionics with the engine? Engine fire is the most critical and blind detection makes the procedure impossible → no dispatch; the APU is non-critical with ground auto-extinguishing → dispatchable. Avionics is detect-only, so lost detection means invisible and un-fightable → no dispatch.

[!note]- Q3. Why is a single LOOP FAULT dispatchable but an engine dual-loop DET FAULT not? Which article's mechanism is this? OR logic still detects on the surviving loop (article 02); both lost means capability gone.

[!note]- Q4. Why is detection dispatch generally stricter than extinguishing? Detection is the eyes — blind, you cannot find the fire (most dangerous). Extinguishing is the hands — one bottle short, another path usually remains.

[!note]- Q5. A single cargo bottle (BTL FAULT) — dispatch depends on what? Whether the other hold's bottle is also faulted, plus the operational/maintenance conditions of the specific item.

Key takeaways

Point	Detail
Indexed by ECAM alert	each alert → no dispatch, or a pointer to a 26-XX item's conditions
Active warning	never dispatched (equipment working, reporting a real threat)
DET FAULT	engine / avionics / total SMOKE = no dispatch; APU / cargo / others = dispatchable per item
Crowning asymmetry	engine detection blind = no-go; APU = go (non-critical + ground auto); avionics = no-go (detect-only)
LOOP FAULT	single loop dispatchable (OR still detects) — mechanics decide, not clauses
BTL FAULT	usually conditional (other hold intact) — detection is stricter than extinguishing
Freighter	MDCC has its own configuration-specific items

References

Operator MEL (chapter 26) — dispatch verdicts by ECAM alert; operator-specific, apply the current operator entry. The reasoning above is derived from the system mechanics and generalised, not quoted from any operator publication.
FCOM DSC-26-20-10 / AMM 26-12-00, 26-13-00 — AND→OR dispatchability and the DET FAULT mechanism (articles 02/04) that underpins the verdicts.

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