TR and Battery Faults; Lithium Battery Fire

This article gathers the fault family of the DC "source" hardware — the four transformer-rectifiers (TRs) and the three batteries — and pairs it with a modern cabin threat that shares the word battery but almost nothing else: a portable-device lithium fire (QRH 24.05A). The DC layer is derived, not generated (see the overview), so its faults are mostly quiet — the network reconfigures itself and the procedures carry few action lines. The lithium fire is the opposite: a hands-on, time-critical drill where the most counter-intuitive instruction in the whole chapter — pour water on the burning device — is exactly right.

One distinction must be fixed before anything else, because the two events both say "battery" and are handled in completely different ways.

[!warning]- Aircraft NiCd thermal runaway and a passenger lithium fire are two different worlds

A main or APU aircraft battery is nickel-cadmium; its thermal runaway is caught by the Battery Charge Limiter and handled through the BAT FAULT procedure (§2, and the chemistry/protection in Batteries and the BCL). A passenger lithium device (phone, tablet, power bank, laptop) is a different chemistry, in the cabin or cockpit, handled through the SMOKE / FIRE FROM LITHIUM BATTERY procedure (§4). Same word, different cell chemistry, different handling — do not let "battery" blur them together.

By the end of this article you should be able to answer five questions:

1. The TR FAULT procedure tells you to switch the APU battery off — what loss is that step stopping, and what does it protect?
2. The BAT FAULT procedure says the contactor opening "must be manually confirmed open" — if the BCL has already opened it, what does pressing OFF add?
3. Which combination of failures produces APU START NOT AVAIL, and which version of it is recoverable?
4. A lithium fire has two phases (flames / no flames) — what changes between them?
5. Can you pour water on a burning lithium device?

This is the last of the DC fault articles; it follows DC ESS Bus Fault and Shed.

1. TR faults — ELEC TR 1(2) / APU TR / ESS TR FAULT

All four TRs share one ECAM caution family. The trigger is simply the loss of the unit (any of the TR's own protections — overheat / overcurrent / minimum current / open-or-short — latching its contactor open; see Transformer-Rectifiers):

"The ELEC TR 1(2) FAULT alert triggers when the TR 1(2) is failed. The ELEC ESS TR FAULT alert triggers when the ESS TR is failed. The ELEC APU TR FAULT alert triggers when the APU TR is failed."

Per FCOM PRO-ABN-ELEC. One inhibition note is worth holding, because it is asymmetric across the family:

"Note: (a) Alert inhibited in flight phase 9 for TR 1(2) or ESS TR FAULT only."

Per FCOM PRO-ABN-ELEC. Flight phase 9 is the landing roll — a TR 1(2) or ESS TR fault is suppressed there so it cannot distract during the rollout; the APU TR fault is not inhibited in phase 9 (it is not flight-critical and its handling is a deliberate housekeeping choice, below).

1.1 The only action line — and the loss it stops

The procedure carries a single crew action, and only for the APU TR:

"In case of an APU TR fault: IF APU NOT REQUIRED: APU BAT ... OFF"

Per FCOM PRO-ABN-ELEC. The reasoning runs through the DC network transfer logic (see DC Network Transfer): with the APU TR lost, the APU start/charge bus (309PP) is picked up by the APU battery. While the APU is not needed, that pick-up is pure, pointless discharge. Switching APU BAT OFF stops the bleed and preserves the APU battery's capacity for a later start. The STATUS keeps the books for exactly that later moment:

"If APU TR fault, and APU BAT off: FOR APU START: APU BAT ... ON"

Per FCOM PRO-ABN-ELEC. So the sequence is deliberate: switch APU BAT off now to save charge, and if you decide later that you want the APU, set APU BAT back on — the battery then starts the APU on its own (the dedicated APU-start function of Batteries and the BCL).

1.2 The autoland bookkeeping

A TR 1 or TR 2 failure costs an autoland category even though the supply is never actually lost:

"if TR 1 or 2 is failed: CAT 3 SINGLE ONLY [...] INOP SYS: TR 1(2) or APU TR or ESS TR [...] CAT 3 DUAL (if TR 1 or 2 is failed)"

Per FCOM PRO-ABN-ELEC. The opposite main TR takes over through the DC BAT BUS automatically (the symmetric recovery of Automatic Reconfiguration), so the DC buses stay powered — but the redundancy that backs a CAT 3 DUAL autoland is gone, and the capability drops to CAT 3 SINGLE ONLY. The lesson: a successful reconfiguration is not a free lunch; the network can hold the load while still shedding a layer of redundancy.

1.3 The silent ESS TR case

For an ESS TR fault there is no action line at all. That is not an omission — it is the point. With TR2 available, the DC ESS and DC SHED ESS buses are recovered automatically by TR1 through the DC BAT BUS and DC BUS 1; only if TR2 is also gone do those buses drop (the precondition and the overcurrent-linked variant are worked through in Transformer-Rectifiers and DC ESS Bus Fault and Shed). A caution that informs you but asks nothing of you — a "silent reconfiguration" — is itself a thing to recognise on the ECAM.

2. Battery faults — ELEC BAT 1(2) / APU BAT FAULT

The BAT FAULT caution has a sharp, specific trigger:

"This alert triggers when the charging current increases at an abnormal rate."

Per FCOM PRO-ABN-ELEC. This is the annunciation-level face of the thermal-runaway criterion built up in Batteries and the BCL — the charging current climbing and continuing to climb. The procedure then gives one conditional action:

"In case of thermal runaway or short circuit: BAT (AFFECTED) ... OFF. Battery contactor is automatically opened by Battery Charge Limiter, but the automatic opening must be manually confirmed open."

Per FCOM PRO-ABN-ELEC.

[!warning]- "Manually confirmed open" is not redundant — it latches the door shut

The BCL's automatic protection (commanding the battery contactor open) is the first line of defence; it has already acted. Pressing OFF does not re-open an open contactor — it latches that open state, removing any path by which the BCL's reset logic could re-close the contactor and re-energise a runaway cell. Nickel-cadmium thermal runaway is a positive-feedback process; the design philosophy is "once it has run away, never give it a second chance" — the same no-retry principle established in Batteries and the BCL.

2.1 APU START NOT AVAIL — read which state you are in

APU START NOT AVAIL can be reached two different ways, and only one of them is recoverable. Work out which state you are in before concluding the APU is gone:

APU START NOT AVAIL — which state?
   ┌──────────────────────────────────┬──────────────────────────────────┐
   │ APU BAT OFF  +  APU TR fault      │ APU BAT FAULT  +  APU TR FAULT    │
   │ (you switched the APU battery     │ (a genuine double loss of the     │
   │  off in the §1.1 step)            │  battery itself and the TR)       │
   ├──────────────────────────────────┼──────────────────────────────────┤
   │ RECOVERABLE                       │ NOT recoverable                   │
   │ STATUS gives the way back:        │ Both the battery start path AND   │
   │   FOR APU START: APU BAT ... ON   │ the TR start path are gone — no   │
   │ (the battery path picks the       │ source is left to start or feed   │
   │  start up again)                  │ the APU                           │
   └──────────────────────────────────┴──────────────────────────────────┘

"If APU BAT and APU TR FAULT: APU START NOT AVAIL"

Per FCOM PRO-ABN-ELEC. The left column is the housekeeping state of §1.1 — you chose to switch the APU battery off, and FOR APU START: APU BAT ... ON undoes it. The right column is the true double loss (the battery start path and the TR start path both gone), cross-confirmed by DC Network Transfer and Batteries and the BCL.

2.2 The cross-system reach of a BAT 2 FAULT

A "battery" fault is not always confined to the DC layer. The BAT 2 FAULT STATUS carries two extra lines and an aileron:

"In case of BAT 2 FAULT: FUEL CONSUMPT INCRSD [...] FMS PRED UNRELIABLE [...] INOP SYS: BAT 1(2) or APU BAT, L OUTR AIL"

Per FCOM PRO-ABN-ELEC. Depending on the combination of failures, a BAT 2 FAULT can take the left outer aileron (L OUTR AIL) with it; the resulting drag drives FUEL CONSUMPT INCRSD, which in turn makes the FMS fuel predictions unreliable. The footnote tells you how to recover the fuel figure by hand:

"Disregard FMS fuel predictions and Refer to QRH/OPS Fuel Penalty Factors/ECAM Alert Table in order to find the applicable Fuel Penalty Factor."

Per FCOM PRO-ABN-ELEC. So FMS PRED UNRELIABLE is an instruction, not just a warning: disregard the FMS prediction and work the fuel penalty from the QRH table.

3. The three "lightweight" battery cautions

Beside the BAT FAULT above, three further battery cautions sit at the crew-awareness level — none is a thermal event, and it is easy to confuse them with BAT FAULT. Each has its own distinct trigger.

ELEC BAT 1(2) SYS FAULT — the BCL itself has failed:

"The ELEC BAT 1(2) SYS FAULT alert triggers when the BCL of BAT 1(2) is failed."

Per FCOM PRO-ABN-ELEC. This is the charge limiter failing, distinct from §2's BAT FAULT (abnormal charging current). The battery is still backed up by the other side and by the system, but its charge management is degraded; dispatch is handled through the operator MEL 24-38 (the failure face of the BCL's functions in Batteries and the BCL). The procedure does allow one reset attempt, deferred so it never happens at a busy moment:

"BAT 1(2) ... OFF THEN ON. This action line is displayed in cruise (flight phase 6) at the first occurrence of the alert if the BAT SYS failure occurred during the take-off phases (flight phases 3, 4, or 5)."

Per FCOM PRO-ABN-ELEC. A single OFF THEN ON reset, held back to cruise if the fault arose during take-off.

ELEC APU BAT SYS FAULT — the APU battery's BCL has failed:

"The ELEC APU BAT SYS FAULT alert triggers when the BCL of the APU is failed."

Per FCOM PRO-ABN-ELEC. The same logic for the APU battery. Combined with an APU TR fault it is yet another route into APU START NOT AVAIL ("If APU BAT SYS FAULT and APU TR fault: APU START NOT AVAIL", per FCOM PRO-ABN-ELEC).

ELEC BAT 1(2) or APU BAT OFF — a pushbutton left off:

"This alert triggers when the BAT 1(2) pb-sw is abnormally set to OFF."

Per FCOM PRO-ABN-ELEC. A pushbutton inadvertently in the OFF position — crew-awareness level, and the handling is simply to set it back on.

4. Smoke or fire from a lithium battery (QRH 24.05A)

This is the one hands-on drill in the article, for a portable electronic device (PED) lithium battery in the cockpit. The FCTM states the mechanism that makes the whole procedure make sense:

"Fire or smoke from lithium battery is due to thermal runaway in the battery cells. It is important to know that fire extinguishers are efficient on flames but cannot stop thermal runaway. The treatment for thermal runaway of lithium battery is to cool the battery by pouring water or non-alcoholic liquid on the device."

Per FCTM PR-AEP-SMOKE. The extinguisher knocks down flames; only cooling stops the cell-to-cell propagation. The QRH lays the drill out as a branching flow:

┌────────────────────────────────────────────────────────────────┐
│  SMOKE / FIRE FROM LITHIUM BATTERY  (QRH 24.05A)                 │
└────────────────────────────────────────────────────────────────┘
   (If necessary) transfer control to the pilot seated on the
   side AWAY from the fire
        │
        ▼
   CKPT / CAB COM ............................. ESTABLISH
   STORAGE AFTER Li BAT FIRE cabin procedure .. REQUEST INITIATION
        │
        ▼
   ┌─ If FLAMES ──────────────────────────────────────────────┐
   │    CREW OXY MASK (PF) ............. USE / 100% / EMER      │
   │    PBE (PM) ...................... USE                     │
   │    FIRE EXTINGUISHER ............. USE                     │
   └───────────────────────────────────────────────────────────┘
        │
        ▼
   ┌─ If NO FLAMES, or when flames extinguished ──────────────┐
   │    • not possible to remove device from cockpit:          │
   │        WATER or NON-ALCOHOLIC LIQUID . POUR ON DEVICE      │
   │        DEVICE ........................ MONITOR             │
   │    • possible to remove device from cockpit:              │
   │        DEVICE ........................ TRANSFER TO CABIN   │
   └───────────────────────────────────────────────────────────┘
        │
        ▼
   ┌─ At ANY TIME of the procedure ───────────────────────────┐
   │    SMOKE becomes the GREATEST THREAT                      │
   │        ► REMOVAL OF SMOKE / FUMES procedure ... CONSIDER   │
   │    situation becomes UNMANAGEABLE                         │
   │        ► IMMEDIATE LANDING .................... CONSIDER   │
   └───────────────────────────────────────────────────────────┘

Per QRH 24.05A. Three points carry the drill.

[!warning]- Yes — pour water on it, and keep pouring

Water on an electrical fire is the reflex this procedure deliberately overrides. The Halon extinguisher only suppresses flames; lithium thermal runaway propagates by the cells heating one another, and "fire extinguishers [...] cannot stop thermal runaway" (FCTM PR-AEP-SMOKE). Continuously pouring water or a non-alcoholic liquid cools the cells and breaks the propagation chain — hence POUR ON DEVICE followed by a standing MONITOR. The danger is reignition: do not pack up because "the fire is out".

Fixed division of labour. The two roles do not swap mid-drill:

"the PF must wear the oxygen mask and the PM must wear the smoke hood."

Per FCTM PR-AEP-SMOKE — the PF protects flying with the oxygen mask, the PM fights the fire with the PBE (smoke hood) and the extinguisher.

Two "any time" exits outrank the flow. The branches SMOKE becomes the GREATEST THREAT → REMOVAL OF SMOKE / FUMES and situation UNMANAGEABLE → IMMEDIATE LANDING are not the end of the list — they apply at any time. Situational judgement overrides completing the steps in order.

4.1 No cabin crew, and the "removable" test

The procedure assumes the cabin can take over the device. The FCTM covers the case where it cannot — a ferry or all-cargo flight:

"If there is no cabin crew on board (e.g. ferry flight, etc.), the PM must apply the steps of the CCOM procedure."

Per FCTM PR-AEP-SMOKE. And the CCOM storage procedure that the cabin (or the PM) carries out is simply to immerse the device:

"This CCOM procedure specifies that the cabin crew must fill a container with water or non-alcoholic liquid and must immerse the device in it."

Per FCTM PR-AEP-SMOKE. One practical test for "removable": if the device is on a cable that cannot be quickly disconnected, treat it as not removable and pour on it in place —

"If the device is attached to a cable that cannot be easily disconnected, then the device must be considered not removable from the cockpit, and water or non-alcoholic liquid must be poured on it. The device must then be regularly monitored to ensure that the thermal runaway is successfully stopped."

Per FCTM PR-AEP-SMOKE.

5. Flight-deck scenarios

1. Cruise, ELEC ESS TR FAULT alone. No action line. Confirm on the ELEC DC page that the DC ESS bus has reconfigured onto the TR1 chain (the silent recovery of §1.3). If DC ESS turns amber at the same time, this is the overcurrent-linked variant of Transformer-Rectifiers — proceed to the DC ESS Bus Fault and Shed procedure.
2. BAT 1 FAULT. BAT 1 ... OFF to latch the contactor open; make no recovery attempt afterwards. Re-evaluate the battery margin and the bridging capability on a single remaining battery (see Battery-Only Flight).
3. Passenger tablet smoking in the cockpit. Transfer control to the far-side pilot → flames phase: PBE + extinguisher (PF on oxygen mask) → after flames out: pour water to cool and keep monitoring — do not stop because the flame is gone, since reignition is the lithium signature → if it can be removed, hand it to the cabin under the STORAGE procedure.

Self-test

[!note]- Q1. Why does the TR FAULT procedure switch the APU battery off?

With the APU TR lost, the APU start/charge bus (309PP) is picked up by the APU battery; while the APU is not required this is pointless discharge. APU BAT ... OFF stops the bleed and preserves capacity. The STATUS reminds you of the way back: if you later want the APU, FOR APU START: APU BAT ... ON — the battery then starts the APU on its own. (A TR 1 or 2 failure separately downgrades the autoland to CAT 3 SINGLE ONLY, even though the opposite TR keeps the DC buses powered.)

[!note]- Q2. What does "manually confirmed open" mean in the BAT FAULT procedure?

The BCL has already commanded the battery contactor open (the automatic protection). Pressing OFF does not re-open an open contactor — it latches that open state, removing any path by which the BCL could re-close it and re-energise the cell. Nickel-cadmium thermal runaway is positive feedback, so it is given no second chance — the no-retry principle.

[!note]- Q3. Which combination produces APU START NOT AVAIL, and which version is recoverable?

APU BAT FAULT + APU TR FAULT is the genuine double loss — both the battery start path and the TR start path are gone, and it is not recoverable. It must be distinguished from APU BAT OFF + APU TR fault, which is the housekeeping state you created in the TR-fault step and is recoverable via FOR APU START: APU BAT ... ON. (An APU BAT SYS FAULT plus an APU TR fault is a third route to the same APU START NOT AVAIL.)

[!note]- Q4. What are the two phases of a lithium battery fire, and what changes between them?

Flames present: suppress with the FIRE EXTINGUISHER, PF on CREW OXY MASK / 100% / EMER, PM on the PBE. No flames, or flames extinguished: if the device cannot leave the cockpit, WATER or NON-ALCOHOLIC LIQUID — POUR ON DEVICE and MONITOR to cool the cells and stop the thermal runaway; if it can leave, TRANSFER TO CABIN for immersion under the STORAGE procedure. The extinguisher stops flames; only cooling stops thermal runaway and beats reignition.

[!note]- Q5. What are the two "any time" exits, and how do they rank against the flow?

SMOKE becomes the GREATEST THREAT → REMOVAL OF SMOKE / FUMES, CONSIDER and situation UNMANAGEABLE → IMMEDIATE LANDING, CONSIDER. They apply at any time of the procedure and outrank completing the steps — situational judgement over step completion.

Key takeaways

References

Per FCOM PRO-ABN-ELEC (ELEC TR 1(2)/APU TR/ESS TR FAULT — triggers, phase-9 inhibition note, the APU BAT OFF action, FOR APU START and the CAT 3 SINGLE ONLY / CAT 3 DUAL INOP bookkeeping; ELEC BAT 1(2)/APU BAT FAULT — abnormal-charging-rate trigger, "manually confirmed open", APU START NOT AVAIL combinations, BAT 2 FAULT FUEL CONSUMPT INCRSD / FMS PRED UNRELIABLE / L OUTR AIL and the Fuel Penalty footnote; ELEC BAT 1(2) SYS FAULT / APU BAT SYS FAULT / BAT or APU BAT OFF — BCL-failed and pb-off triggers and the OFF THEN ON reset); QRH 24.05A (the full SMOKE / FIRE FROM LITHIUM BATTERY drill); FCTM PR-AEP-SMOKE "Lithium Battery Fire in the Cockpit" (thermal-runaway mechanism, "extinguishers cannot stop thermal runaway", cooling by pouring water, PF oxygen mask / PM smoke hood, the no-cabin-crew ferry case, the CCOM immersion step and the cable/removable test); the operator MEL 24-38 (BAT SYS dispatch). Cross-references to Transformer-Rectifiers, DC Network Transfer, Batteries and the BCL, Automatic Reconfiguration, DC Bus Faults, DC ESS Bus Fault and Shed, Battery-Only Flight, ECAM Warnings Summary and MEL Dispatch View. The "latched-open / no-retry" reading, the "silent reconfiguration" framing, and the "knock down flames then cool" summary 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.