Dual Pack Failure — RAM AIR & Emergency Descent

This article covers PACK 1+2 FAULT — the A330 air-conditioning system's most serious failure — and its linked emergency ram-air system and descent procedure. It is the only ATA 21 failure that mandates a descent.

1. The trigger — "one off, the other failed"

This alert triggers when one pack is off, and the other is failed. — FCOM PRO-ABN-AIR

[!warning]- The trigger is "one OFF + one failed", not "both failed"

Intuitively a dual failure means "both packs broken". The FCOM wording is precise: one OFF (not delivering, whether crew-selected or fault-closed) + the other failed. This covers every "the cabin has lost all air-conditioning supply" case: pack 1 fault-closed then pack 2 fails; pack 1 crew-selected OFF (e.g. during an OVHT procedure) then pack 2 fails; or both failing at once (rare — a power loss or dual bleed loss). The detection logic is "neither pack is supplying air", regardless of cause. Teaching line: dual pack failure = "the cabin has no air-conditioning supply", cause-agnostic.

2. Three immediate consequences

An emergency ram air inlet ventilates the cockpit and cabin, if both packs fail. The outflow valves open about 50 %, provided that they are under automatic control and ΔP is less than 1 PSI. — FCOM DSC-21-10-20

The descent altitude: FL 100 (no cabin oxygen needed below it) or MEA-MORA (terrain), whichever is higher. The FCOM states MAX FL ... 100/MEA-MORA — mountainous MEA FL 130 → MAX FL 130; flat MEA FL 040 → MAX FL 100.

3. The emergency ram-air system

The emergency ram-air inlet is on the lower fuselage aft of the cockpit (near FR 40), independent of the pack ram-air inlets — a purely airspeed-driven vent (no pump).

[!warning]- RAM AIR ON with ΔP > 1 PSI does nothing

Even with the RAM AIR pb ON and the door physically open, if the cabin-to-ambient ΔP > 1 PSI, the check valve does not open and no air flows.

If ΔP is greater than 1 PSI, the check valve, located downstream the ram air door, will not open. No airflow will then be supplied. — FCOM DSC-21-10-20

The check valve is pushed open by pressure; the external pressure (lower than the cabin at altitude) cannot open it. The ΔP must first be released below 1 PSI (by the outflow valves) before the external static pressure can open it. So in cruise (ΔP ~8 PSI), RAM AIR ON opens the door but admits no air — useless. The FCOM procedure says WHEN DIFF PR < 1 PSI AND FL BELOW 100: RAM AIR ON.

[!warning]- RAM AIR ventilates only — it does not pressurise or condition

Capability	RAM AIR	Pack
Fresh-air flow	✓	✓
Pressurise the cabin	✗ (the outflow valves open 50 %)	✓
Condition (heat/cool)	✗ (ambient enters directly)	✓
Trim air	✗	✓

RAM AIR is emergency ventilation — fresh outside air to avoid hypoxia, not air-conditioning, not pressurisation. With it open, the cabin temperature drifts to ambient, the pressure equals ambient (cabin altitude = aircraft altitude), and the flow is well below a normal pack flow but enough to keep the occupants breathing.

[!note]- Why the outflow valves auto-open 50 %

With both packs failed + RAM AIR ON, the airspeed-driven flow needs an exit. If the outflow valves stayed nearly closed, the flow would be trapped and the RAM AIR flow tiny. Opening them ~50 % gives the ram air a large exit, ensuring the cabin air-change rate. The 50 % is a CPC software command — only in automatic mode. If the CPC was switched to manual control earlier, the auto-50 % does not act and the pilot must open the valves manually (ata-21-23).

[!note]- DITCHING inhibits RAM AIR

The DITCHING pb closes all external openings (including RAM AIR) to keep water out — so the RAM AIR pb opens the valve only if ditching is not selected (ata-21-28).

4. The PACK 1+2 FAULT procedure

   If one door not locked closed on ground:  PACKS INHIB BY DOORS (check doors closed)
   In all other cases:
     PACK (AFFECTED) ............... OFF      ← switch off the failed pack
     DESCENT TO FL 100/MEA-MORA              ← start the descent
       Note: closing the CARGO ISOL VALVES (if the freight permits) minimises the cabin-altitude rise
     WHEN PACK OVHT OUT (if the fault was an overheat):  PACK (AFFECTED) ... ON
     WHEN DIFF PR < 1 PSI AND FL BELOW 100:  RAM AIR ... ON
     MAX FL ........................ 100/MEA-MORA

[!tip]- "PACK (AFFECTED) OFF" — the already-OFF one is not touched again

One pack is OFF (selected or auto), the other failed → PACK 1+2 FAULT. The procedure switches off the AFFECTED one (the failed one, FAULT light on); the already-OFF one stays. The point: put the failed pack to OFF too, to stop the controller retrying / the PFCV oscillating.

[!important]- "DESCENT TO", not "EMER DESCENT"

The FCOM says "DESCENT TO" (a normal descent), not "EMER DESCENT". The difference: an emergency descent (the FCTM template — speedbrakes, autopilot, max-speed) is for excess cabin altitude / a loss of pressurisation; a "descent to" is a normal descent. The pilot's judgement: if PACK 1+2 FAULT appears with the cabin altitude already climbing / past 9550 ft (ata-21-20) → link the EXCESS CAB ALT procedure = start the emergency descent; if the cabin altitude is still stable (the outflow valves intact) → a normal descent to FL 100.

[!note]- Closing the CARGO ISOL VALVES slows the cabin-altitude rise

The cargo ventilation draws cabin air through the cargo and overboard (ata-21-16). Closing the CARGO ISOL VALVES stops the cargo ventilation → reduces cabin leakage → slows the cabin-altitude rise, giving a longer decision window. The cost: the cargo temperature may become uncontrolled — so the FCOM says "if the cargo freight permits" (not for livestock / perishables / temperature-sensitive goods). The pilot checks the cargo manifest.

[!warning]- "WHEN DIFF PR < 1 PSI AND FL BELOW 100" — both conditions (AND)

RAM AIR needs both: ΔP < 1 PSI (so the check valve opens) and FL < 100. Not OR — the pilot must not press RAM AIR "just before FL 100" or "at altitude because ΔP is already low". High but ΔP low → still wait for FL 100; low but ΔP high → wait for the outflow valves to release the ΔP.

5. ECAM EMERGENCY RAM AIR — five states

EMERGENCY RAM AIR inlet indication: Crossline - Green: The flap is normally closed. In Transit - Amber: The flap is partially open. Inline - Amber: If open on ground, or if the flap position disagrees with the position of the RAM AIR pushbutton (OFF). Inline - Green: The flap is fully open. Crossline - Amber: The flap is closed, and the RAM AIR pushbutton is in the ON position. — FCOM DSC-21-10-50

The common "counter-intuitive" indication: RAM AIR pb ON but a Crossline-amber display → the ΔP has not fallen below 1 PSI, the check valve has not opened, the flap is closed. Wait for the outflow valves / the descent — do not press the pb repeatedly.

6. Operations

Timeline (ideal)

Dual pack failure + smoke

[!warning]- Multiple emergencies stacked

PACK 1+2 FAULT may come with smoke (an electrical fire / bleed leak / cargo fire). Then the pilot runs the PACK 1+2 procedure (descend + RAM AIR) and in parallel the smoke procedure + crew oxygen + smoke removal; a cargo fire links the ATA-26 fire procedure + an immediate diversion. The stacked priority: (1) fly the aircraft, (2) crew oxygen, (3) start the descent, (4) the ECAM procedure, (5) communicate. The PACK 1+2 procedure is at step 4 — do not press RAM AIR before steps 1–3.

When RAM AIR cannot be opened

(1) In cruise (ΔP > 1 PSI) — the check valve will not open. (2) DITCHING selected — all external vents are closed. (3) Flight phase 1/2 (ground/roll) — the RAM AIR memo goes amber ("should not be open in this phase"). Confirm none applies before RAM AIR ON.

Dispatch

PACK 1+2 FAULT cannot be reset-and-continued on landing — maintenance is required (PRO-ABN-AIR has no "WHEN OUT → continue" branch, unlike PACK OVHT). The MEL does not dispatch a dual pack failure (ata-21-29).

Self-test

[!note]- Q1. Is the PACK 1+2 FAULT trigger "both packs broken"?

No — "one pack OFF + the other failed", where OFF can be crew-selected or auto-closed. It covers every "the cabin has lost all pack supply" case, not only both faulting.

[!note]- Q2. In cruise at FL 350, the pilot presses RAM AIR ON after PACK 1+2 FAULT — what happens?

Nothing (for now). The door may open, but the check valve does not (ΔP ~8 PSI > 1 PSI), so no air flows; the ECAM shows Crossline amber. The ΔP must first be released below 1 PSI (descend + the outflow valves) before the check valve opens. The FCOM gates it: WHEN DIFF PR < 1 PSI AND FL BELOW 100.

[!note]- Q3. With RAM AIR working, is there air-conditioning? Pressurisation?

Neither. RAM AIR ventilates only: the temperature drifts to ambient, the pressure equals ambient (cabin altitude = aircraft altitude, the outflow valves open 50 %), and the flow — lower than a pack but enough — keeps the occupants from hypoxia.

[!note]- Q4. DESCENT TO FL 100/MEA-MORA — what if the MEA is FL 130?

MAX FL = 100/MEA-MORA, the higher. MEA FL 130 → MAX FL 130 (terrain forbids FL 100). At FL 130 the ΔP may still be > 1 PSI → RAM AIR still cannot open. In practice: route over flatter terrain + request a path down below FL 100.

[!note]- Q5. What does closing the CARGO ISOL VALVES achieve, and when is it not allowed?

It stops the cargo ventilation → slows the cabin-altitude rise → a longer decision window. Not allowed when the freight is temperature-sensitive (livestock, fresh flowers/produce, some pharma/chemicals marked "ventilation required"). The pilot checks the cargo manifest; ordinary baggage/cargo → it can be closed.

Key takeaways

Common misconceptions

Scope — what this article covers and defers

References

A330 specifics per FCOM PRO-ABN-AIR (the PACK 1+2 FAULT trigger "one off, the other failed", and the procedure — PACK AFFECTED OFF, DESCENT TO FL 100/MEA-MORA, the CARGO ISOL VALVES note, the WHEN-PACK-OVHT-OUT restoration, the WHEN-ΔP<1-PSI-AND-FL-BELOW-100 RAM AIR ON, and MAX FL 100/MEA-MORA), FCOM DSC-21-10-20 (the emergency ram-air inlet ventilating the cockpit and cabin, the outflow valves opening ~50 % under automatic control with ΔP < 1 PSI, the downstream check valve not opening above 1 PSI, and the ditching inhibit), and FCOM DSC-21-10-50 (the five EMERGENCY RAM AIR states). The cabin-oxygen decision-window timing is an integrative synthesis (the FCOM gives no figure); the DESCENT-vs-EMER-DESCENT boundary and the stacked-emergency priority are integrative. All engineering detail is from the A330 knowledge base; the procedures are presented generically without operator-specific SOP or effectivity tail numbers, 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.