MEL Dispatch View

Every earlier article in this chapter answered how the electrical system works. This last one answers a different question — with a fault on board, can the aeroplane still be signed out, and on what terms? That is the dispatch view, and it is where the whole chapter's redundancy architecture is finally cashed out into go / no-go decisions. The overview noted that the A330 electrical system has no dedicated chapter in FCOM Limitations; its "limits" live in the degraded procedures and, for the ground decision, in the operator MEL. This article reads the electrical MEL not as a list of items to memorise, but as a way of thinking: redundancy thick enough that a single failure rarely grounds a flight, a survival floor that never discounts, and a strict separation between is the warning there and is the system good.

A note on sourcing: the MEL conditions below are paraphrased from the operator MEL (ATA 24), not quoted, because the dispatch reasoning is the teaching content — the numbers and conditions are reproduced exactly. Where an English manual sentence underpins the reasoning it is quoted verbatim and attributed.

1. The four layers of MEL 24 — how to look something up

The electrical MEL is organised in four layers, and knowing which layer answers which question is half the skill. The sequence below is the lookup you actually run when a caution is latched on the post-flight ECAM:

  Post-flight ELEC caution latched on the ECAM
                    │
                    ▼
   ┌──────────────────────────────────────────────────────┐
   │ ME-24  ECAM warning routing table                     │
   │   col 1  aircraft status  │  col 2  dispatch condition │
   └───────────────┬───────────────────────────────────────┘
        ┌──────────┼─────────────────┬──────────────────┐
        ▼          ▼                 ▼                  ▼
      NO-GO   refer to an MI item   as per the ME item  no additional
                    │
        ┌───────────┴───────────────┬───────────────────┐
        ▼                           ▼                   ▼
   MI-24-01 / -07 / -09        MI-24-22 … -53        MO-24
   panel lights /              system-function       operating
   SD indications /            items — the real      procedures —
   specific ECAM warnings      dispatch body         the (o) actions

• ME-24 (ECAM warning routing table). Two columns: aircraft status and dispatch condition. When an ELEC caution is hung after the flight, this is the first place to look — it tells you whether that warning is a hard stop or points you onward.
• MI-24-01 / -07 / -09 (indications). Panel lights, SD-page indications, and a handful of specific ECAM warnings. These are the lighter, indication-class items — most are Category C and relatively relaxed.
• MI-24-22 … MI-24-53 (system functions). The full spread of generation, transfer, distribution and monitoring functions. This is the real dispatch body for a genuine failure.
• MO-24 (operating procedures). The companion (o) procedures — the crew actions a dispatch carries with it.

[!warning]- Read the two columns the right way round

The dispatch-condition column takes only a small set of values — NO-GO, refer to an MI item, as per the ME item, or no additional condition. The word "none" that appears against many entries is sitting in the aircraft-status column (meaning no additional aircraft status applies), not in the dispatch-condition column. Reading "none" as a dispatch verdict is a classic table-misread: it says nothing about whether you can go.

2. True or false — the warning and the system are two dispatch objects

The single most useful idea in the electrical MEL is that one ECAM warning has two dispatch paths, depending on whether troubleshooting finds the warning real or spurious. Take the IDG disconnect caution:

            ELEC IDG 1(2) DISCONNECTED   (one ECAM warning)
                          │
          ┌───────────────┴────────────────┐
          ▼                                 ▼
   troubleshooting:                  troubleshooting:
   warning is SPURIOUS               warning is TRUE
          │                                 │
          ▼                                 ▼
 ┌───────────────────────┐      ┌──────────────────────────────┐
 │ 24-09-01A             │      │ 24-09-01B → 24-22-01          │
 │ ignore the EWD memo,  │      │ IDG genuinely disconnected;   │
 │ no system downgrade   │      │ the AC main generation system │
 │ (Category C, 2/1)     │      │ is "considered inoperative"   │
 └───────────────────────┘      └──────────────────────────────┘
   "is the warning there?"         "is the system good?"
            two different dispatch objects

Per the operator MEL, the spurious branch (24-09-01A, Category C, 2 installed / 1 required) lets you ignore the EWD indication once troubleshooting confirms it false — no downgrade. The true branch (24-09-01B) routes you to the system item 24-22-01, because now a real generation channel is lost. The same fork appears for the oil-system caution: 24-09-03A treats a spurious OIL SYS FAULT as a Category-C indication item (with a maintenance check — see §6 principle 3), while 24-09-03C treats a true OIL SYS FAULT by requiring the IDG to be disconnected, the IDG fully drained if a leak is confirmed, and the AC main generation system handled under 24-22-01.

The lesson generalises: whether the warning is present and whether the underlying system is healthy are two separate dispatch objects. A latched ELEC caution does not automatically mean a lost function, and a lost function does not always show as the obvious caution. The IDG case is treated in full in Integrated Drive Generator and Generator and IDG Failures.

3. Anatomy of a system item — 24-22-01, the heaviest case

The AC main generation item (IDG, GCU, line contactor) is the model for how a system-function dispatch is built, and the heaviest in the electrical MEL. One main generation system inoperative may be dispatched under 24-22-01, Category C, 2 installed / 1 required, placarded — subject to eleven numbered conditions (per the operator MEL):

1. No ETOPS beyond 180 min.
2. The APU and AC auxiliary generation system operating and used throughout the flight.
3. All busbars energised.
4. The ELEC AC SD page verifies the remaining AC main and AC auxiliary generation indications are operative.
5. No ELEC IDG 1(2) OIL SYS FAULT warning on the EWD for the working AC main generation system.
6. No FUEL APU AFT PUMP FAULT warning on the EWD.
7. When AC main generation 2 is inoperative, check the AC BUS 1 → AC BUS 2 automatic transfer before the first MEL dispatch and daily thereafter.
8. Check the landing-recovery-configuration APU aft fuel-pump shedding function before the first MEL dispatch and weekly thereafter.
9. Check the APU oil quantity is sufficient for the planned flight before each flight.
10. Must be operative for departure from a main base.
11. Must not be inoperative at a high-altitude-airport take-off station.

The logic is clean. Dispatching with one main generator gone leaves the aeroplane on a single main generator; losing one more would drop straight into the electrical emergency configuration. So the MEL requires the APU GEN on line for the whole flight to pre-restore the N-1 redundancy, and it bars ETOPS beyond 180 min — electrical redundancy is the bedrock of ETOPS eligibility.

Because the APU runs the whole flight, the fuel plan must carry its burn, and the MEL gives this as five brackets, not a range (per the operator MEL, MO-24-22):

This is the heaviest MO in the chapter, and it makes a general point: the looser the dispatch relief, the more specific the operating limit attached to it. A one-line "one generator may be inoperative" carries eleven conditions and a five-bracket fuel account behind it.

One economic footnote travels with the same procedure: from a cost standpoint, an IDG should not run in the disconnected mode beyond 50 flight hours (MO-24-22) — the same 50-hour window described, from the safety side, in Integrated Drive Generator.

The companion item 24-23-01 covers AC auxiliary generation (the APU generator, GAPCU and contactors) — the APU-side counterpart of 24-22-01, the dispatch route when the fault sits on the auxiliary source rather than an engine generator (see APU Generator and GAPCU).

4. Redundancy cashed out — choosing a provable path

The chapter's redundancy is not an abstraction at dispatch; it is what gives you a second item to sign against when the first function is lost. Two cases show it.

AC ESS FEED — two independent items. The automatic transfer (24-25-01) and the manual ALTN transfer (24-25-02) are separate dispatch items. If the automatic transfer is unserviceable you can still dispatch on the manual path, and vice versa — the dual-channel design of AC ESS Feed and Transfer paying off at the dispatch level: redundancy means half can be broken and the aeroplane still signs out. The automatic-transfer item (24-25-01, Category C, 1 installed / 0 required, placarded) carries two conditions — the AC ESS FEED pushbutton in its normal position and the three DC TIE contactors operative. That "three DC TIE" requirement is the dispatch-level confirmation of the DC tie pair described in the overview.

Batteries — pick the branch you can prove. The battery dispatch (24-38) is sub-divided into the main BAT channel, the APU battery channel, the BCL and the voltage indication. The APU-battery-channel procedure offers two branches — start the APU on AC power through the APU TR path, or accept "APU considered inoperative" and the capability loss that comes with it (see Batteries and the BCL). The principle behind both cases: dispatch is choosing, within the remaining redundancy, a path you can demonstrate works — not pretending the lost function is still there.

5. The dispatch floor — what carries no margin

Above the system items that can be relieved sits a floor that cannot. Two kinds of entry define it.

Must-be-operative system items. The survival-layer functions are listed with a repair interval of "–", 1 installed / 1 required, must be operative — the strictest form in the chapter. These include:

• 24-24-01 — AC emergency generation (the CSM/G — see Emergency Generator).
• 24-28-01 — static-inverter AC generation (see Static Inverter).

The emergency and last-resort layers — the bottom of the power ladder — have no dispatch margin at all. The reason is exactly the FCTM definition of when they are needed:

"The electrical emergency configuration is due essentially to the loss of all main AC BUS …"

Per FCTM PR-AEP-ELEC. These are the sources that carry the aeroplane after everything above them is gone; you cannot sign out the floor of the safety net.

NO-GO ECAM warnings. A family of ELEC ECAM warnings in ME-24 carry a flat NO-GO in the dispatch-condition column — if one of these is latched after a flight, the aeroplane cannot be signed out until it is repaired. The verified electrical NO-GO list:

These are the protected-bus and essential-conversion faults — the AC/DC essential family, the ESS TR, the APU battery — i.e. the same equipment that, lost in flight, would degrade the aeroplane toward the emergency configuration. The dispatch floor and the failure-chapter floor are the same hardware seen from two sides.

[!warning]- "Indication present" is not the dispatch verdict, and the floor does not discount

Two traps live here. First, a latched memo or a degraded indication is not the same as a failed function (§2) — the dispatch object must be identified before the verdict. Second, do not look for dispatch relief on the survival layer: the emergency generation (24-24-01) and the static inverter (24-28-01) are must-be-operative, and the essential-bus / ESS-TR / APU-battery faults are NO-GO. The bottom of the net is the one place the MEL never bends.

6. Five principles of dispatch thinking

Reading the whole electrical MEL, five working principles fall out.

1. Most repair intervals are Category C (10 days). Electrical redundancy is thick, so a single item failing rarely holds a flight. But stacked dispatch breaks Category-C thinking — if GEN 1 is already dispatched and ECMU 2 then fails, two half-network redundancies are stacked, and you must return to the MEL preamble to judge the interaction, not treat the second item in isolation.

   [!warning]- Two relieved items are not "two Category-C items"

   Each relief is written assuming the rest of the redundancy is intact. Two electrical reliefs that each remove a half-network safeguard can together leave the aeroplane one failure from the emergency configuration. The combined case is a fresh judgement against the MEL preamble — never an arithmetic sum of two independent reliefs.

2. Indication and function are separated. A dead light (MI-24-01 family) is not a dead function — for example the IDG FAULT light may be dispatched 2 installed / 1 required, but only on the condition that the frequency and oil-temperature indications still work on the ELEC AC page (the page substitutes for the light). This is the "lights cannot be trusted on their own" idea of Control Panels and Monitoring and Indication, expressed at dispatch.

3. The (o) and (m) markers are commitments. A dispatch with an (o) crew-operating item or an (m) maintenance item is a promise to perform those actions — for instance the spurious OIL SYS FAULT branch (24-09-03A) commits the operator to a daily sight-glass / oil-loop check (each flight for ETOPS). Signing the dispatch signs the actions attached to it.

4. ETOPS is a hidden threshold. Several items carry "no ETOPS beyond 180 min". Electrical redundancy is the foundation of ETOPS eligibility, so an electrical relief and an ETOPS plan have to be read together, not separately.

5. The survival layer has no dispatch margin (§5). The emergency generation and static-inverter items are must-be-operative and the essential-bus faults are NO-GO — the strictest entries in the chapter. The redundant middle of the system is forgiving; the floor is not.

7. Dispatch scenarios

1. Post-flight ELEC IDG 1 OIL SYS FAULT latched. Run ME-24 → suspect a spurious warning (a history of ground jolting? — see Generator and IDG Failures) → troubleshooting confirms it false → dispatch under the spurious branch (24-09-03A) with the daily oil-check commitment. If it is confirmed true, the route changes: disconnect the IDG, drain it if a leak is confirmed, and handle the AC main generation under 24-22-01 with its eleven conditions, the APU on line throughout, and the five-bracket fuel account.
2. EXT B AVAIL light out. An indication item (MI-24-01 family, Category C) with its companion procedure — on the ground EXT A still feeds, so the function is intact even though the legend is dark (the A-primary / B-secondary picture of External Power).
3. Tomorrow is an ETOPS flight; tonight GEN 2 reports FAULT. Condition 1 of 24-22-01 caps you at 180 min — there is no relief above that. Either swap aircraft or repair; there is no third path.

8. Where this chapter has been

This is the final article of ATA 24. The chapter was built in seven phases, each link below leading into its own treatment:

• Architecture and sources — overview, IDG, GCU, APU generator and GAPCU, external power, emergency generator.
• Network management — ECMU contactor management, network priority, no-break power transfer, AC ESS feed transfer.
• DC and batteries — transformer-rectifiers, DC network transfer, batteries and the BCL, static inverter.
• Distribution and loads — AC distribution and busbars, galley and commercial loads, ground service and maintenance bus, circuit breakers and the CBMU, monitoring and indication.
• Panels and display — control panels, the ECAM ELEC page.
• Failures — automatic reconfiguration, generator/IDG failures, AC bus faults, AC ESS bus fault and shed, DC bus faults, DC ESS bus fault and shed, TR/battery faults and lithium fire, ECMU fault, emergency electrical configuration, battery-only flight.
• Wrap-up — ECAM warnings summary and this dispatch view, which maps every one of those failures onto the ground decision: most relievable in the redundant middle, none on the survival floor. The ME-24 routing table and the ECAM warnings summary are two views of the same warning set — one for can I go, one for what do I do now.

Self-test

[!note]- Q1. What are the four layers of MEL 24, and which is the real dispatch body for a genuine failure?

(1) ME-24 — the ECAM warning routing table, two columns (aircraft status / dispatch condition), the first place to look for a latched caution. (2) MI-24-01 / -07 / -09 — indication-class items (panel lights, SD indications, specific warnings), mostly Category C. (3) MI-24-22 … -53 — the system-function items, the real dispatch body for a genuine failure. (4) MO-24 — the companion operating procedures, the (o) actions a dispatch carries. The dispatch-condition column takes only a few values (NO-GO / refer to an MI item / as per the ME item / no additional); the word "none" you see most often is in the aircraft-status column, not a dispatch verdict.

[!note]- Q2. Walk through the 24-22-01 single-generator dispatch, the redundancy logic, and the APU fuel burn.

One AC main generation system (IDG, GCU, line contactor) inoperative is dispatchable under 24-22-01, Category C, 2 installed / 1 required, placarded, subject to eleven conditions — the load-bearing ones being no ETOPS beyond 180 min, the APU and AC auxiliary generation operating and used throughout the flight, all busbars energised, the SD-page check of the remaining generation, no OIL SYS FAULT on the operating side, no FUEL APU AFT PUMP FAULT, the AC BUS 1→2 transfer checked daily when AC main 2 is the failed side, must be operative for a main-base departure, and not inoperative at a high-altitude-airport take-off station. The logic: after dispatch only one main generator is left, so the APU GEN must run the whole flight to restore N-1, and ETOPS is capped at 180 min. APU fuel burn — ground 215 / 140 kg/h, in flight 130 (FL200) / 65 (FL300) / 55 (FL410) kg/h.

[!note]- Q3. Why are the automatic and manual AC ESS FEED transfers two separate dispatch items, and what does the automatic item require?

Because redundancy is only useful at dispatch if each channel is its own item: with 24-25-01 (automatic transfer to AC BUS 2) and 24-25-02 (manual ALTN transfer) separate, an unserviceable automatic transfer can still be dispatched on the manual path, and the reverse. The automatic item (Category C, 1 installed / 0 required, placarded) requires the AC ESS FEED pushbutton in its normal position and the three DC TIE contactors operative — the dispatch-level confirmation of the DC tie pair.

[!note]- Q4. What sits on the dispatch floor, and what is the verified ME-24 NO-GO list?

The floor is the survival layer with no margin: the must-be-operative system items 24-24-01 (AC emergency generation) and 24-28-01 (static inverter), each listed repair interval "–", 1 installed / 1 required; plus the NO-GO ECAM warnings in ME-24 — ELEC AC BUS 2 FAULT, AC ESS BUS FAULT, AC ESS BUS ALTN, DC BUS 1 FAULT, DC BUS 1+2 FAULT, DC ESS BUS FAULT, DC ESS BUS SHED, ESS TR FAULT, APU BAT FAULT, BUS TIE OFF, EXT PWR A(B) OVERLOAD. These are the essential-bus / essential-conversion / APU-battery faults — the same hardware that, lost in flight, drives the aeroplane toward the emergency configuration.

[!note]- Q5. "A dead light means a dead function." True or false at dispatch?

False. Indication and function are separated. The IDG FAULT light, for instance, may be dispatched 2 installed / 1 required, but only if the frequency and oil-temperature indications still work on the ELEC AC page — the page substitutes for the light. More broadly, is the warning present and is the system good are two dispatch objects: a spurious caution (e.g. IDG DISCONNECTED found false under 24-09-01A) can be ignored with no downgrade, while a true one routes to the system item and its full conditions.

Key takeaways

References

Per the operator MEL, ATA 24 (rev 14 OCT 25; sub-sections eff. 25 JUN 25): ME-24 (ECAM warning routing, the NO-GO list); MI-24-09 (IDG DISCONNECTED and OIL SYS FAULT, true/false branches); MI-24-22 (24-22-01 AC main generation, eleven conditions) and MO-24-22 (APU fuel burn by altitude/configuration, the 50-flight-hour disconnected note); MI-24-23 (AC auxiliary generation); MI-24-24 (AC emergency generation, must be operative); MI-24-25 (AC ESS FEED automatic 24-25-01 and manual 24-25-02, the three DC TIE condition); MI-24-26 (galley and commercial supply); MI-24-28 (static inverter, must be operative); MI-24-38 (DC batteries, the APU-battery-channel branches). The FCTM emergency-configuration cause is quoted from FCTM PR-AEP-ELEC; the "commercial supply has secondary priority" design statement is from FCOM DSC-24-10-10. The four-principle reading of the chapter, the "dispatch floor vs failure floor are the same hardware" synthesis, and the "redundancy = a provable second path" framing are integrative syntheses of the above and contain no facts from outside the library.

Independent study material, not an Airbus publication. Refer to current operator FCOM, FCTM, and QRH for operational use.