Cabin, Pack-Bay, Battery & Lav/Galley Ventilation — The Other Objects

Avionics Ventilation covered the avionics bay and its single-channel AEVC. This deep-dive opens up the remaining ventilation objects — the cabin, the pack bay, the batteries, and the lavatories/galleys — together with their computer: the Ventilation Controller (VC, 280HN), a dual-CPU hot-standby unit (unlike the single-channel AEVC). Cargo ventilation, the sixth object, is ata-21-16.

1. Six objects, two controllers

   object              air source               control
   ────────────────────────────────────────────────────────
   ① avionics bay      recirculation / packs    AEVC (single-channel)
   ② pack bay          flight: NACA inlet       AEVC
                       ground: turbofan (bleed-driven)
   ③ batteries         venturi (passive)        none (pure mechanical)
   ④ lav & galley      main cabin supply        VC (dual-CPU)
                       + venturi + electric fan (ground)
   ⑤ cabin             pax: recirculation       VC (dual-CPU)
                       freighter: pack 2 direct
   ⑥ cargo (→ -16)     piccolo duct + recirc    VC (dual-CPU)

2. VC vs AEVC

[!warning]- Dual-CPU vs single-channel — not "which is more advanced" but "the failure consequence differs"

An AEVC failure is mild (the extract fan still runs on direct power, the avionics keep basic cooling) → single-channel suffices. A VC failure is severe (cargo + cabin + lav/galley ventilation all depend on it) → multiple sub-systems lost at once → dual-CPU redundancy is required. The redundancy level tracks the failure consequence: the CPC / pack controller / zone controller are dual-channel (life/comfort critical); the VC is dual-CPU (shared sub-systems); the AEVC is single-channel (mild consequence); the battery venturi has no controller (passive). So the VC is one of the A330's key controllers — the same redundancy class as the CPC.

3. The Ventilation Controller (280HN) — dual-CPU hot standby

The ventilation controller 280HN is the computer for: the lower-deck CC ventilation system, the CC heating system ... the cabin-air distribution and recirculation system ... the lavatory/galley ventilation system ... It uses microprocessor electronics to calculate and send the necessary signals to the other systems. It has two Central Processing Units (CPU) to prevent the loss of more than one control function if there is a failure. The CPUs are the same but only one CPU operates at a time, the other is in hot standby mode. The CPUs have a data link between them. The ventilation controller operates during flight and on the ground. — AMM 21-28-00 §6.B

[!note]- The AMM says "two CPUs" for the VC, not "channel/lane" as for the CPC/pack/zone controllers

The CPC, pack controller and zone controller AMM text says "lane 1 / channel 1 + hot standby"; the VC says "two CPUs + hot standby mode". Same concept — a dual-processor industrial controller, one active, one hot standby — different wording (a drafting-era convention). So "the VC's two CPUs" and "the pack controller's two lanes" are the same redundancy design.

The ventilation controller 280HN has interfaces with: the light test system, the Central Maintenance System (CMS), the System Data Acquisition Concentrators (SDACs), the cabin-air distribution and recirculation system, the lavatory/galley ventilation system, the Landing Gear Control and Interface Unit (LGCIU), the Smoke-Detection Control Unit (SDCU), the emergency power system, the zone temperature controller, the lower-deck CC heating system, the proximity switch control-unit. — AMM 21-28-00 §6.B

Eleven interfaces — note the SDCU (smoke detection → close the cargo isolation valves), the emergency-power system (shed the fan relays on emergency power), and the PSCU (door state → stop cargo heating with a door open).

4. Pack-bay ventilation — NACA inlet + bleed-driven turbofan

Ventilation of the pack bay ensures air circulation in order to maintain, on ground and in flight, a mean temperature that is compatible with the structure constraints in the relevant area. In flight, air from the outside flows into the pack bay through a NACA air inlet. On ground, a turbofan provides sufficient airflow. The turbofan is driven by air from the bleed system, which is supplied through the turbofan supply valve. Controlled by the AEVC, the fan operates when the aircraft is on ground. An ECAM warning, associated with an external horn on ground, is triggered in case of failure of the turbofan (supply valve failed closed or turbofan jammed). — FCOM DSC-21-30-70

[!warning]- NACA inlet in flight + a bleed-driven turbofan on the ground — a dual-source switch

In flight the ram air enters the pack bay naturally through the NACA inlet (a flush, low-drag intake) → cooling. On the ground there is no ram air → a turbofan is needed. The turbofan is not electric — it is driven by bleed air (high-pressure bleed spins the impeller). In flight the turbofan need not run (the NACA inlet suffices, and the bleed is prioritised to the packs); on the ground the bleed is plentiful (from the APU), so the turbofan uses bleed without taking electrical power. The AEVC controls it.

[!note]- This is the second part in ATA 21 with an external horn (after the avionics CED)

Like the avionics CED, a pack-bay ventilation failure (supply valve stuck closed or turbofan jammed) triggers an ECAM warning plus an external horn on the ground — so a mechanic is alerted when no one is in the cockpit. ATA 21 has exactly two external-horn parts: the avionics CED and the pack-bay turbofan — both protect heat-critical equipment.

5. Battery ventilation — a passive venturi

A venturi in the aircraft skin draws air from the space around the batteries and vents it overboard. The resulting airflow ventilates the batteries. — FCOM DSC-21-30-40

[!warning]- A pure passive venturi — and the purpose is not cooling, it is preventing H₂ accumulation

A venturi (a converging-diverging shape in the skin) accelerates the airflow as the aircraft moves → the static pressure there drops (Bernoulli) → the battery-bay pressure (cabin pressure) exceeds the venturi pressure → air flows out of the battery bay naturally. Fully passive — no power, fan, or control. The real purpose: batteries produce hydrogen during charge/discharge, which must be continuously vented to avoid reaching an explosive concentration — so the ventilation is about preventing H₂ accumulation, not cooling. Why passive, not an electric fan: a fan failure → ventilation stops → H₂ accumulates → explosion risk; the passive venturi instead matches the need perfectly.

[!note]- The battery ventilation does not work on the ground — by design, not a defect

On the ground stationary, the battery barely works → little H₂. With ground power + charging, the rate is low → slow accumulation offset by natural cabin leakage. The real high-H₂ case is an emergency discharge (the battery as the sole source in flight) → the aircraft is flying → the venturi works → ventilation is normal. A perfect match: the venturi works exactly when ventilation is needed.

6. Lavatory & galley ventilation — cabin supply + venturi + electric fan

The lavatory and galley are ventilated with air from main cabin distribution system. Air is discharged outside through a venturi. On ground, or when ΔP < 1 PSI, it is extracted by an electrical fan controlled by the ventilation controller. — FCOM DSC-21-30-50

[!note]- The lav/galley venturi only works at altitude

ΔP ≥ 1 PSI means the cabin is ≥ 1 PSI above ambient → the airflow accelerates at the venturi → low static pressure → cabin air flows out. On the ground ΔP ≈ 0 → no driving force → the fan is needed. Below 1 PSI the venturi is too weak and the VC starts the fan.

7. GALLEY & LAV FAN pushbutton — OFF for fire/smoke

Normal: The system is running all the time. Note: The Galley and Lavatory system is operational as soon as the aircraft is powered and the GALLEY & LAV FAN pb is activated. CAUTION: In case of fire or smoke alert in the lavatory or galley area, the pilot deactivates the Galley and Lavatory fan by switching the GALLEY & LAV FAN pb to OFF. — FCOM DSC-21-30-65

[!warning]- For fire/smoke you switch the fan OFF, not ON

The intuition is "smoke → boost ventilation → fan to full". The reality is the reverse: running the fan extracts the smoke, but it also carries air past the fire source → feeding the fire (a fire needs oxygen). Switching the fan OFF isolates the affected area → the fire is starved of oxygen → it self-extinguishes; the main cabin distribution still supplies fresh air to the cabin → the passengers are safe. In practice: smell lavatory smoke → GALLEY & LAV FAN pb → OFF → isolate → handle per the smoke procedure.

8. Cabin ventilation — passenger vs freighter

4 ceiling air outlets and 2 floor air outlets provide ventilation in the cabin. In normal mode, the cabin is supplied with fresh air from pack 2, without any recirculation air to avoid any smell from the main deck cargo payload (in particular livestock or perishable goods). In case of pack 2 failure, the cabin is supplied with recirculated air coming from the mixer unit. The air is extracted through openings at floor level at the barrier wall, which are integrated in the lining below the cabin seats. — FCOM DSC-21-30-75 (freighter)

[!warning]- On a freighter variant the cabin uses pack-2 fresh air only, no recirculation — to avoid main-deck cargo odour

A passenger cabin mixes recirculation + fresh pack air (~50/50). On a freighter variant (operated by some operators), the cabin — effectively the supernumerary compartment next to the main-deck cargo — is supplied with pack-2 fresh air direct, with no recirculation air: if it used recirculation, the recirculated air would draw from the main deck → carrying cargo odour (livestock, perishable goods) into the cabin → unacceptable. So pack-2 fresh air supplies the cabin directly, bypassing the mixer recirculation path — the cabin always has fresh air. On a pack-2 failure it falls back to recirculation air from the mixer (accepting the temporary odour risk for continued airflow). A freighter crew seeing PACK 2 FAULT should be aware the cabin air source changes — and brief the supernumeraries about possible odour.

[!note]- Four ceiling + two floor outlets — not evenly distributed

Ceiling outlets blow from overhead, floor outlets at foot level; the air sinks through the cabin and is extracted at floor-level openings at the barrier wall (below the seats). Against the zone controller's trim-air valves, the CIDS programming assigns which outlets belong to which temperature zone.

9. Emergency power — the VC sheds the fan relays

[!note]- On emergency power the VC stops powering the fan relays to save power

When only emergency power is available (RAT / battery / emergency generator), the power is limited — not enough for all the fans. A relay signals the VC, which stops powering the fan relays. The cabin recirculation fans stop, the galley + lavatory fans stop, and cabin ventilation degrades markedly — but the passengers can still breathe (the venturi + the recirculation valves partly closed to protect the avionics). Pilot meaning: dual-engine-out + RAT out → cabin humidity and flow drop sharply but breathable.

10. AEVC / VC co-control

   AEVC (single-channel)              VC (dual-CPU)
     ① avionics ventilation             ① cargo ventilation
     ② pack-bay ventilation             ② cargo heating
     ③ avionics ground cooling          ③ cabin distribution + recirculation
        (incl. pack-bay turbofan)       ④ lavatory + galley ventilation
              └──── zone-controller coordination (ARINC 429) ────┘

Six objects, all controlled: the AEVC ~1.5 (avionics + pack bay), the VC four (cabin + lav/galley + cargo + heating), the battery none (passive). The split mirrors the failure consequence — important objects on the dual-CPU VC, the milder on the single-channel AEVC, the passive on neither.

VC failure: one CPU → the other takes over (no interruption), VC 1 (or 2) FAULT post-flight. Both CPUs → cargo + cabin + lav/galley + cargo heating all lost (the cabin still has pack fresh air but recirculation + lav/galley fans stop) → severe ECAM handling.

Self-test

[!note]- Q1. Is the VC dual-CPU or single-channel? Different philosophy from the AEVC, and why?

Dual-CPU hot standby (one active, one standby, data-linked). Different from the single-channel AEVC. The reason: failure consequence. The VC controls four sub-systems (cargo ventilation + cargo heating + cabin distribution/recirculation + lav/galley) → a VC failure loses several at once → dual-CPU is required. An AEVC failure leaves the extract fan running on direct power → single-channel suffices. The redundancy level tracks the consequence: CPC/pack/zone are dual-channel (critical); the VC is dual-CPU (shared); the AEVC is single-channel (mild).

[!note]- Q2. Why a NACA inlet in flight and a turbofan on the ground? Who controls it?

In flight the ram air enters through the NACA inlet naturally; on the ground there is none, so a turbofan is needed. The turbofan is bleed-driven (bleed spins the impeller) — not electric — so on the ground (plenty of APU bleed) it does not take electrical power; in flight the NACA inlet suffices and the bleed is prioritised to the packs. The AEVC controls it. A failure (supply valve stuck closed / turbofan jammed) gives an ECAM warning + an external horn on the ground — the second external-horn part in ATA 21 after the avionics CED.

[!note]- Q3. Why a passive venturi for the batteries, not an electric fan? What is the real purpose?

The real purpose is preventing H₂ accumulation (an explosion risk), not cooling — batteries produce hydrogen on charge/discharge. Why passive: a fan failure would stop ventilation → H₂ accumulates. The venturi instead matches the need — the aircraft flying = the battery working + producing H₂ = the venturi drawing; the aircraft stationary = the battery idle = no H₂ = no ventilation needed; the high-H₂ case (emergency discharge in flight) = the aircraft flying = the venturi working. Zero maintenance, no moving parts.

[!note]- Q4. Why is the GALLEY & LAV FAN pb switched OFF for fire/smoke, not left ON?

The intuition ("smoke → boost ventilation") is wrong. Running the fan carries air past the fire source → feeding the fire (oxygen). Switching OFF isolates the area → the fire is starved → it self-extinguishes; the main cabin distribution still supplies the cabin → the passengers are safe. In practice: smell smoke → GALLEY & LAV FAN OFF → isolate → handle per the smoke procedure.

[!note]- Q5. Why does a freighter cabin use pack-2 direct, not recirculation? What if pack 2 fails?

The cabin (the supernumerary compartment) is next to the main-deck cargo; recirculation would draw from the main deck → carrying odour (livestock, perishable goods) into the cabin → unacceptable. So pack-2 fresh air supplies the cabin direct, bypassing the mixer recirculation path — always fresh. On a pack-2 failure it falls back to mixer recirculation air (accepting the temporary odour risk for continued airflow). A freighter crew seeing PACK 2 FAULT should expect the cabin air-source change and brief the supernumeraries.

Key takeaways

Common misconceptions

Scope — what this deep-dive covers and defers

References

A330 specifics per FCOM DSC-21-30-40/-50/-65/-70/-75 (the passive battery venturi, the lavatory/galley cabin supply + venturi + electric fan below 1 PSI, the GALLEY & LAV FAN OFF for fire/smoke, the pack-bay NACA inlet + bleed-driven turbofan with its external horn, and the freighter cabin's four ceiling + two floor outlets supplied by pack-2 fresh air without recirculation to avoid main-deck cargo odour with the pack-2-failure fallback) and AMM 21-28-00 §5/§6.B (the Ventilation Controller as a dual-CPU hot-standby microprocessor with its eleven interfaces, controlling the cargo ventilation/heating, cabin distribution/recirculation, and lavatory/galley systems). The redundancy-by-failure-consequence rationale, the H₂-accumulation purpose of battery ventilation, the bleed-not-electric turbofan reasoning, the fire-starving logic of the lav/galley fan, and the emergency-power fan-shedding consequence are integrative syntheses. All engineering detail is from the A330 knowledge base; no cross-type comparison is made, and no fleet tail numbers appear.

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.