Zone Controller / Trim Air / Hot Air — Engineering Details

Pack Controller showed how the pack controller drives the pack outlet to a target — but who sets the target, and how does a pilot's knob become the exact temperature at each cabin seat? The answer is the zone controller (FIN 630HK) plus the trim-air system. This deep-dive opens up the zone controller (dual-channel, seven functions), the seven trim-air valves, the trim-air pressure valves, the HOT AIR pb, the basic + optimised regulation philosophy, the four-level demand escalation, the ram-air-inlet close thresholds, and the dual-channel failure behaviour.

Scope notes: cargo trim air (438/448HC, the heaters, the 88/70 °C cargo duct hysteresis) is in Cargo Environmental Control; the pack-internal anti-ice / temperature-control valves are in ACM; the pack controller itself is ata-21-08.

1. The three components — locations

The zone temperature controller 630HK ... is installed in the avionics compartment in the rack 800VU. — AMM 21-63-00 §3.D

The zone controller shares the avionics rack 800VU with the pack controllers but is a separate LRU — pulling the zone-controller card is not pulling a pack-controller card; they are replaced independently. This is why, on a pack-controller failure, the zone controller can still provide a temperature reference and lock the pack to a 20 °C outlet (ata-21-08 §14).

2. The cabin temperature chain — from knob to ceiling

   pilot turns the selector        attendant trims one zone
       670HK / 671HK                    120RH (FAP)
            │                               │
            ▼                               ▼
       [AIR panel cockpit/cabin selectors]
            │  (±3 °C, 0.5 °C steps via FAP)
            ▼
       [CIDS]
            ▼
   ┌────────[Zone temperature controller 630HK]────────┐
   │  avionics rack 800VU, dual-channel hot-standby     │
   │  reads 16 temp sensors 640–656HK (cockpit / 6      │
   │    cabin areas / main-deck cargo)                  │
   │  reads PACK FLOW selector 8HB                      │
   │  computes zone demands → outputs:                  │
   │   ① ARINC 429 → pack controllers (lowest demand)   │
   │   ② trim-air valves 631–637HK (per-zone heat)      │
   │   ③ trim-air shutoff valve 649HK (cross-bypass)    │
   │   ④ APU ECB (pressure demand → APU flow)            │
   │   ⑤ EIVMU (pressure demand → engine idle)           │
   │   ⑥ BMC (temp demand → bleed 200→150 °C)            │
   │   ⑦ E/WD + SD COND page display                    │
   └────────────────────────────────────────────────────┘
            │
   bleed (hot) → [pack 1/2] → mixing unit → cabin zones
            │ (pack outlet = cold conditioned air)
            └→ hot-air manifold (bleed bypass)
                  ▼
       ┌──[Trim-air pressure valve 639HK (pack 1)]──┐
       │  holds cabin + 0.276 bar (4 PSI)           │
       │  HOT AIR 1 pb controls the solenoid        │
       └────────────┬───────────────────────────────┘
                    ▼ trim-air supply 1
       [Trim-air check valve 5631HK]  (+ pack-2 line 638HK / 5632HK)
                    │
       [Trim-air shutoff valve 649HK]  normally closed; opens if one line fails
                    ▼
       [Hot-air manifolds] → [7 trim-air valves 631–637HK] → per-zone heat
                    ▼
            cabin distribution → ceiling / floor outlets

Sources: AMM 21-63-00 §3/§6 + FCOM DSC-21-10-30.

3. Seven trim-air valves

The trim air valves 631HK, 632HK, 633HK, 634HK, 635HK, 636HK and 637HK add an adjustable quantity of hot trim air to the cooled conditioned air from the mixer unit. The zone temperature controller 630HK controls the position of the trim air valves. The trim air valves are installed in the ducts to the cockpit and the six cabin areas. — AMM 21-63-00 §3.F

The cabin is divided into 3 temperature control zones: FWD, MID and AFT. The length of the three zones is, as far as practicable, adapted to the individual cabin class arrangement by respective programming of the CIDS. — FCOM DSC-21-10-30

Seven valves: 631HK → cockpit; 632–637HK → six cabin areas. But the FCOM sees only three zones (FWD / MID / AFT) plus the cockpit — the CIDS decides which physical areas fall in FWD / MID / AFT, so the zone boundaries differ by cabin-class layout. (The freighter configuration has six valves: cockpit + supernumerary + main-deck cargo, no six cabin areas.)

4. The zone controller — dual-channel architecture

The zone temperature controller 630HK ... has two digital-microprocessor control systems. They are the same and operate in "Hot-Standby" mode. They are called channel/lane 1 and channel/lane 2. The channels operate independently without loss of performance. In normal operation one channel/lane is active and the other channel/lane is in Hot-Standby mode. If a failure of the primary channel/lane occurs, the zone controller operates the other channel. — AMM 21-63-00 §6.B

Same design philosophy as the pack controller: both sit in avionics rack 800VU, both are dual-channel industrial controllers, both talk over ARINC 429, both have BITE + CMS logging, both have "a single-channel failure has no effect". Differences: there are two pack controllers (one per pack, 531HH/532HH) but only one zone controller (shared, 630HK); the zone controller controls trim-air valves + the trim-air shutoff valve (outside the pack), the pack controllers control PFCV + temperature-control / ram-air / anti-ice valves (inside the pack).

5. Seven functions

Per AMM 21-63-00 §3.D, the zone controller: ① keeps the four zones (cockpit + FWD + MID + AFT) at the temperatures set on panel 225VU / FAP 120RH / AAP; ② computes and sends demand signals (ARINC 429) to the pack controllers; ③ sends the pressure demand (ARINC 429) to the APU ECB (59KD) when the APU supplies bleed; ④ sends the engine pressure demand (ARINC 429) to the EIVMUs when bleed pressure is low; ⑤ sends the bleed-temperature demand to the BMC; ⑥ controls the seven trim-air valves; ⑦ controls the trim-air shutoff valve.

BLEED TEMPERATURE DEMAND. If the cooling demand cannot be satisfied, the zone controller signals the Bleed Monitoring Computer (BMC) to decrease the bleed temperature from normal (200 °C) to reduced setting (150 °C). This reduction is inhibited, if the wing-anti ice is ON. — FCOM DSC-21-10-30

[!warning]- Counter-intuitive: with wing anti-ice ON, bleed cannot drop 200 → 150 °C

Wing anti-ice heats the leading edge with bleed — the bleed temperature must stay at 200 °C for enough heating power. So in icing conditions with wing anti-ice on, the cooling system's last resort (lowering bleed temperature) is disabled, and the cabin may run a little warm. If it does, the crew can select LO flow (smaller flow, larger temperature drop) or lower the selector — but must not turn off wing anti-ice for cabin comfort: anti-ice priority >> comfort.

6. Three-level temperature selection

On ground, prior to flight: The cabin temperature selector in the cockpit (AIR panel) should be set to about the 10 o'clock position (21.5 °C/70.7 °F) ... The zone correction should be set to zero by pressing the «RESET TO COCKPIT SELECTED TEMP» soft key on the cabin temperature page of the PIM. An individual zone correction up to +/– 3 °C (5.4 °F) can be selected for the FWD, MID or AFT cabin zones in steps of 0.5 °C (0.9 °F). — FCOM DSC-21-10-30

Final zone target = cabin master + zone correction + altitude correction (programmable, default 0).

[!note]+ Crew / attendant practice (from the FCOM)

Set the cockpit master once before flight, do not change it often in flight; if the pilot does change it, tell the cabin crew (there is no cabin-end indication of it). Attendants trim ±0.5 °C at a time, not large frequent changes; allow 20 minutes to stabilise after a change (10 min air-conditioning response + 10 min lining/panel thermal balance); the FCOM says attendants should judge by feel, not by the PIM display value.

7. The 16 temperature sensors — dual thermistor

Each temperature sensors 640HK ... 656HK have two thermistors in the tubular body. One thermistor is for the temperature control in channel/lane 1 and one for the temperature control in channel/lane 2. — AMM 21-63-00 §6.F

[!note]- Counter-intuitive: cabin "actual temperature" is measured in the lavatory/galley extract path, not the cabin centre

The FCOM states the actual temperature is measured by sensors in the cockpit and in the lavatory extract circuit and galley ventilation. Why not the cabin centre: the centre swings with passenger body heat, sunlight, and individual overhead outlets; the lavatory/galley extract path is where the average cabin airflow collects — a steadier, more representative temperature. Operational meaning: a front-cabin "I'm cold" complaint may not move the controller (the extract-path sensor still reads 21 °C, averaged by the steady aft value) — which is why attendants trim the FAP by feel, as the FCOM says.

8. Trim-air valves — stepper motor + 75° butterfly

The trim air valves 631HK ... have an actuator with an electrical connector and a valve body. The actuator has a stepper motor, a reduction gearbox with mechanical end stops and two micro switches to sense the end position. A shaft goes from the actuator through the valve body to turn the valve flap. The butterfly shape valve flap has an angle of approximately 75 degrees to the direction of the air flow. Outside the body at the lower end of the valve shaft is a manual lever. — AMM 21-63-00 §6.D

[!note]- Stepper motor + step-counting position feedback (same as the new temperature-control-valve design)

Like the new-part-number temperature control valve (ata-21-08 §10), the zone controller counts the stepper steps to infer the valve position — no separate feedback wire. Advantages: high precision (each step = a fixed angle), no potentiometer wear, no feedback wire. Risk: lost steps → the software thinks the valve is at X when it is at Y → temperature drifts; it re-zeros each power-up / reset against the microswitch end position. The 75° angle (the flap at ~75° to the flow when fully open — near-perpendicular but leaving 15° so the flow is not directly impacted, reducing noise). The external manual lever lets maintenance force the valve position (test / ferry / deactivation — MMEL 21-63-02C allows a trim-air valve to be deactivated for dispatch).

9. Trim-air pressure valves — cabin + 4 PSI

The trim-air pressure valves 639HK (638HK) keep the pressure in the trim air supplies to 0.276 bar (4.00 psi) above the cabin pressure. They are installed upstream of the trim-air check valves ... In usual operation they operate pneumatically. You can use the trim-air pressure valves to shut off a trim air supply. ... If there is no electrical power to the solenoid, the butterfly valve closes fully. — AMM 21-63-00 §3.G / §6.E

[!warning]- Counter-intuitive: the trim-air pressure valve is not the trim-air switch — it is a pressure regulator

Pilots tend to think "HOT AIR 1 pb OFF = trim air off = no more cabin heating". Partly right, partly wrong. Right: HOT AIR 1 pb OFF → solenoid de-energised → the trim-air pressure valve closes fully → the pack-1 trim-air supply is cut. But the pack-2 trim-air supply still flows (if HOT AIR 2 pb is ON) — the cabin can still be heated, now entirely from the pack-2 line. Wrong: the HOT AIR pb is not a temperature valve — it is a master gate switch. The trim-air flow is set by the pressure valve holding cabin + 4 PSI, self-adjusting as the downstream pressure changes; the pilot does not directly control the trim-air pressure (the pneumatic logic does). The 4 PSI is the driving pressure that pushes trim air into the cabin; the solenoid closing fully on power loss is fail-safe to no flow (better than uncontrolled trim air).

10. HOT AIR 1 / HOT AIR 2 pb (2HK1 / 2HK2)

The HOT AIR 1 pushbutton switch 2HK1 is installed on the panel 225VU ... You can use it to close the trim air pressure valve 639HK. If there is a heater installed in the line behind the trim air pressure valve, the heater will also stop operation. — AMM 21-63-00 §3.B / §3.C

HOT AIR 1 pb controls the pack-1 trim-air pressure valve (639HK); HOT AIR 2 pb controls the pack-2 valve (638HK). pb ON = solenoid energised = the valve regulates normally (holding pressure); pb OFF = solenoid de-energised = the valve closes fully = that line's trim air is cut. On the freighter, the HOT AIR pb also gates cargo heating (see ata-21-05).

[!note]- HOT AIR pb FAULT triggers (integrative reasoning — the FCOM does not list them explicitly)

The knowledge base does not give an explicit HOT AIR FAULT trigger list; synthesising AMM 21-63-00 §3.G/§6.E/§5: a hot-air pressure anomaly (the hot-air pressure switches 681/682HK change state), a trim-air-pressure-valve position disagreement, a downstream duct overheat (the same hysteresis philosophy as the 88/70 °C cargo duct), or a trim-air supply leak/loss. To be confirmed against FCOM PRO-ABN-AIR "HOT AIR FAULT" when writing the abnormal article.

11. Hot-air pressure switches (681HK / 682HK)

The hot-air pressure switches 681HK (682HK) have: A hermetically sealed microswitch, A stainless steel diaphragm, A snap action disk spring ... At a set pressure the disk spring moves across and pushes the microswitch. When the pressure decreases to a set pressure, the disk spring returns to the normal position and the microswitch opens. — AMM 21-63-00 §6.K

They monitor whether the hot-air supply pressure is in range and signal the zone controller on an anomaly. The snap-action disk spring gives a discrete switch (not a continuous analogue), preventing chatter near the threshold.

12. Trim-air shutoff valve (649HK) — cross-bypass

The trim-air shutoff valve 649HK opens if there is a failure in a trim air supply or if one pack is switched off. Then all of the cabin areas and the cockpit get trim air from the other trim air supply. The zone temperature controller 630HK controls the position of the trim-air shutoff valve. It is installed between the two trim air supplies. ... two positions, fully open and fully closed. In normal operation the butterfly valve is fully closed. — AMM 21-63-00 §3.K / §6.G

[!note]- Counter-intuitive: the trim-air shutoff valve is normally closed

The "shutoff" valve sits between the two trim-air supplies and normally keeps them separated (each line independent). It opens when either line fails or either pack is switched off — then both lines' areas draw from the surviving supply (like the ATA 29 PTU "one side feeds the other"). Triggers: any trim-air supply failure, any pack off (PACK pb OFF / PACK FAULT cutting that line), or the zone controller commanding it. The pilot does not operate 649HK — the zone controller handles it; so after a PACK 1 OFF the whole cabin still gets trim air via 649HK from the pack-2 line.

13. Trim-air check valves (5631HK / 5632HK)

The trim-air check valves 5631HK (5632HK) prevent reverse flow if there is a pack failure. They are installed in the trim air supplies at frame 40. — AMM 21-63-00 §3.N

If pack 1 fails, pack 2's trim air does not back-flow into the pack-1 line — a standard spring-loaded one-way flap.

14. Basic + optimised regulation

The zone controller computes a temperature demand, depending on the selected temperature and the actual temperature. ... A signal corresponding to the lowest demanded zone temperature goes to the pack controller, which then makes both packs produce the required outlet temperature. OPTIMIZED TEMPERATURE REGULATION. The zone controller optimizes temperature by acting on the trim air valves. — FCOM DSC-21-10-30

   pilot sets: cockpit 25 / cabin master 23  (FWD 23 / MID 24 / AFT 22 actual)
            ▼
   zone demands:  cockpit 0 / FWD 0 / MID −1 (warm) / AFT +1 (cold, needs heat)
            ▼
   BASIC: pick the lowest demand = AFT's 23 °C
          → demand ~22 °C to the pack controller
          → packs deliver ~22 °C cold air to the whole cabin
            ▼
   OPTIMISED: each zone's trim-air valve adds heat
          cockpit: valve 631HK open  → heated to 25 °C
          FWD:     valve 632HK open  → heated to 23 °C
          MID:     valve 633HK near-closed → ~22 °C
          AFT:     valve 634HK closed → 22 °C (target met)
            ▼
   Result: each zone gets its exact temperature

[!warning]- Counter-intuitive: to cool a zone the pack must deliver cold; to warm it, trim air heats — the pack cannot heat

The core physical fact of cabin temperature control: the pack is a cold source (outlet usually 5–20 °C); the trim air is the heat source (bleed bypass, ~200 °C, mixed in). The zone-controller logic: to cool a zone → close its trim-air valve more (less heat); to warm a zone → open it more (more heat); the pack outlet follows the coldest zone's demand, and every other zone is heated up to its own target. If all zones want cold → pack as cold as it can + all trim-air valves closed; if all want warm → pack still cold (per the coldest zone) + all trim-air valves open. Design philosophy: pack always cools, trim air always heats — simple, and the cabin always has ventilation flow even when no zone needs cold air.

15. Four-level demand escalation

When the cooling demand cannot be met, the response escalates:

   cooling demand not met (cabin/zone too hot)
        ▼
   ① PACK FLOW auto-managed (AUTO per MCDU pax; or selected; HI forced on
       single-pack / APU bleed)
        ▼ (still short)
   ② engine pressure demand → ARINC 429 → EIVMU → raise minimum idle →
       bleed pressure up → pack inlet pressure up
        ▼ (still short, APU supplying)
   ③ APU flow demand → ARINC 429 → APU ECB 59KD → raise APU flow output
        ▼ (still short)
   ④ bleed temperature demand → BMC → bleed 200 → 150 °C
       (inhibited if wing anti-ice ON) — the last resort

The pilot can influence level ① (select HI manually); levels ②③④ are automatic and invisible — the pilot only sees the cabin slowly cool or not.

16. ACM anti-stall + the LO advisory

To protect the Air Cycle Machine (ACM) from a stall in case of LO flow selection and strong heating cases (high bleed air bypass around the ACM), the flow can be increased automatically to NORM by the Zone Controller. If the crew selects LO flow and the temperature demand cannot be satisfied, the zone controller generates an ECAM advisory message to inform the crew to manually select NORM flow. — FCOM DSC-21-10-30

[!warning]- Counter-intuitive: LO + heavy heating cannot coexist — the zone controller auto-raises to NORM to stop an ACM stall

The stall physics: LO flow = PFCV throttled = little bleed into the pack; heavy heating = the temperature-control / anti-ice valves bypass much bleed around the ACM = even less bleed actually enters the ACM → below a critical value → the turbine cannot self-sustain → ACM stall (stops) → the pack drops into bypass mode (ata-21-07 §12) → cooling collapses. Protection: the zone controller detects LO + heavy heating → auto-raises the PFCV to NORM → more bleed into the pack → no stall. The pilot sees: LO selected but the ECAM shows NORM flow — normal protection, not a fault. Separately, LO + unmet demand generates an ECAM advisory to select NORM manually (e.g. long-cruise LO for fuel/noise, a few zones run warm).

17. Ram-air-inlet close thresholds

The ram air inlet and outlet flaps close during takeoff and landing to avoid ingestion of foreign objects. ... During takeoff, the ram air inlet and outlet flaps close when the thrust lever is at or above CL detent. During landing, they close as soon as the landing gear is compressed, when the speed is at or above 70 kt. They open, when the speed is below 70 kt, with a 10 s delay. — FCOM DSC-21-10-30

[!note]- "CL detent" is the CLIMB detent, not "climb thrust"

The A330 thrust levers have IDLE / CL / FLEX / TOGA detents (ATA 22 / 72). The "CL detent" is the CLIMB detent — after takeoff the crew pulls the levers back to CL to continue climbing. So: takeoff roll at TOGA (or FLEX) → at/above CL → inlets closed; after liftoff back to CL → still at/above CL → still closed; end of climb, levers below CL (cruise) → inlets reopen.

18. Zone-controller single / dual failure + reset

ZONE CONTROLLER. CHANNEL 1 OR 2 FAILURE. A Channel 1 or 2 failure has no effect on zone temperature regulation. CHANNELS 1 AND 2 FAILURE. Optimized and backup temperature regulation are lost. The packs deliver a fixed pack outlet temperature of 20 °C (68 °F). A Channel 1 and 2 failure removes all information from the COND SD page, which then displays "PACK REG". Flow selection from the PACK FLOW selector is lost. — FCOM DSC-21-10-40

[!warning]- Counter-intuitive: a dual zone-controller failure locks the whole cabin at 20 °C — the pilot cannot adjust temperature at all

Worse than a pack-controller dual failure (which still trims 9–15 °C via the anti-ice valve): no trim-air heating (the zone controller cannot drive the trim-air valves), no pack-outlet adjustment (locked 20 °C), no PACK FLOW selector (LO/NORM/HI inert), no zone correction (the FAP does nothing). The whole aircraft = 20 °C (cabin / cockpit / main-deck cargo). 20 °C is the design fallback — cooler than the comfortable 22–24 °C but neither freezing nor scalding. Crew action (integrative + FCOM PRO-ABN-COND, detailed in ata-21-23): try a zone-controller reset (3HK ≥ 1 s); if it fails, accept the 20 °C lock and write it up for an LRU change.

Reset (per AMM 21-63-00 §8.D): hold the 3HK switch on reset panel 262VU for ≥ 1 s; during the reset the E/WD shows COND ZONE REGUL FAULT, MASTER CAUT + single chime, and the AIR COND SD page shows amber XX on the cabin/cockpit temperatures, duct temperatures, cabin/cockpit trim-air valve positions, HOT AIR 1/2 valve positions, and the shutoff valve position. After a few seconds the XX clears and the controller resumes. This is not a routine flight action — most pilots never use 3HK; it is used when maintenance BITE finds a non-critical fault or when COND ZONE REGUL FAULT persists. Avoid resetting at a sensitive cruise moment (all valve positions are lost during the reset, so cabin temperature can wobble briefly).

19. Trim-air valve failure

TRIM AIR VALVE FAILURE. Failed closed: Optimized temperature regulation of half of the corresponding zone is lost. Failed open: Corresponding hot air valve closes. Optimized temperature regulation of half of each zone is lost. — FCOM DSC-21-10-40

[!warning]- A trim-air valve failed open closes the corresponding hot-air valve — preventing that zone overheating

The zone controller's protection: any trim-air valve failed open → that zone runs continuously hot → the controller detects the anomaly → closes that line's trim-air pressure valve (HOT AIR 1 or 2 auto-off) → the whole line's trim air is cut → optimised regulation of half the zones is lost (the other line serves everyone). The crew sees: HOT AIR 1 (or 2) FAULT + the hot-air valve shown closed — the root cause being a trim-air valve stuck open.

Self-test

[!note]- Q1. Where is the zone controller, and is it the same as the pack controller?

In avionics rack 800VU — the same rack region as the pack controllers but a separate LRU. There is one zone controller (630HK) for the whole aircraft; there are two pack controllers (531HH/532HH, one per pack). Both are dual-channel and talk over ARINC 429. The zone controller controls outside the pack (trim-air valves, trim-air shutoff valve, trim-air pressure valves via the HOT AIR pb); the pack controllers control inside the pack.

[!note]- Q2. How many trim-air valves (passenger layout), which zones, and what feedback?

Seven (631–637HK): cockpit + six cabin areas. Feedback: stepper motor with the zone controller counting steps (no separate feedback wire, same as the new temperature-control-valve design), re-zeroed each power-up against a microswitch end position. The flap is a 75° butterfly; an external manual lever lets maintenance force the position (test / ferry / deactivation).

[!note]- Q3. Is the trim-air pressure valve the same as the trim-air valve? Which does the HOT AIR pb control?

Different parts. The trim-air pressure valve (638/639HK) is a pressure regulator holding the trim-air supply at cabin + 0.276 bar (4 PSI). The HOT AIR pb controls the trim-air pressure valve — OFF → solenoid de-energised → the valve closes fully → that line's trim air is cut. The trim-air valve (631–637HK) is the per-zone temperature valve, driven by the zone controller (stepper). Layer: HOT AIR pb → pressure valve → whole-line supply on/off; zone controller → trim-air valve → per-zone heat.

[!note]- Q4. Do "cooler" and "warmer" use different chains, and why can the pack not heat?

Different chains. Cooler: the pack cools (air-cycle physics) → cold pack outlet → mixing unit → cabin. Warmer: the pack still delivers cold air (controlled to the coldest zone's demand) + trim air heats (bleed bypass mixed in). The pack cannot heat — the air cycle is a cooling cycle (the turbine outlet is cold) and the pack has no heating element. Philosophy: pack always cools + trim air always heats → simple design + ventilation flow in every case (even all-warm: the pack runs to the coldest zone, trim air brings each zone up).

[!note]- Q5. What happens on a dual zone-controller failure, what is the pack outlet, and can the pilot adjust it?

The pack locks at a fixed 20 °C (68 °F); the PACK FLOW selector is inert; trim air cannot adjust; the FAP zone correction does nothing — the whole aircraft is 20 °C. The pilot can try a 3HK reset (≥ 1 s); if it fails, accept the 20 °C lock and write it up for an LRU change. ECAM: COND SD page all lost, showing "PACK REG" (all data XX).

Key takeaways

Common misconceptions

Scope — what this deep-dive covers and defers

References

A330 specifics per FCOM DSC-21-10-30 (three zones + CIDS, three-level selection 18–30 °C / ±3 °C / 0.5 °C, the four-level demand escalation including the 200→150 °C bleed reduction inhibited by wing anti-ice, the basic + optimised regulation, the ACM anti-stall LO→NORM, the LO advisory, the ram-air-inlet close thresholds, the pre-flight 21.5 °C / 10-o'clock and 20-minute stabilisation guidance) and DSC-21-10-40 (zone-controller single/dual-channel failure and the 20 °C / "PACK REG" lock, the trim-air valve failed-closed/open behaviour). The zone-controller and trim-air engineering per AMM 21-63-00 §3/§6/§8 (location in rack 800VU, the dual-channel architecture, the seven functions, the 16 dual-thermistor sensors, the stepper-motor 75° trim-air valves, the cabin+4 PSI trim-air pressure valves, the HOT AIR pbs, the hot-air pressure switches, the normally-closed trim-air shutoff valve, the trim-air check valves, and the 3HK reset) — the English AMM being the fact source where the Chinese FCOM carries no AMM content. The HOT AIR FAULT trigger synthesis, the lavatory/galley sensor rationale, the CIDS zone-mapping, and the trim-air-shutoff active-command logic are integrative syntheses. All engineering detail is from the A330 knowledge base; no cross-type comparison is made.

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.