At a glance
FCOM DSC-21-10-10 P 1 · DSC-21-20-10 P 1 · DSC-36-10-10 P 1
- Air sources
- Engine bleed, APU load compressor, HP ground connection
- Bleed control
- Two bleed monitoring computers (BMC), one per engine
- Packs
- Two, each fed through its own pack flow control valve
- Zones
- Cockpit, forward cabin, aft cabin
- Temperature control
- Two controllers (ACSC), or a zone controller and two pack controllers, depending on the aircraft
- Pressure control
- Two cabin pressure controllers (CPC), one active at a time
- Outflow valve
- One, with two automatic motors and one manual motor
- Safety valves
- Two, on the rear pressure bulkhead
Bleed air
FCOM DSC-36-10-20 P 4–13 · DSC-36-10-30 P 1 · DSC-36-10-40 P 1 · DSC-36-10-50 P 1 · PRO-ABN-AIR · LIM-APU
- Packs
- APU bleed: Both on APU air, HI flow selected automaticallyEngine 1 bleed lost: Both on engine 2. PACK FLOW LO with wing anti-ice offLeft side leak: Pack 1 lost, pack 2 on engine 2
- Crossbleed
- APU bleed: Opens in AUTOEngine 1 bleed lost: OPEN, selected by the crewLeft side leak: Closes automatically, except during engine start
- Wing anti-ice
- APU bleed: Never from APU bleedEngine 1 bleed lost: Available. With it on, affected pack OFFLeft side leak: OFF, avoid icing conditions
- Also
- APU bleed: Engine bleed valves close. Air conditioning up to 22,500 ft on one pack, 15,000 ft on twoEngine 1 bleed lost: Trigger: above 57 PSI, or 257 °C for 55 s, 270 °C for 15 s, 290 °C for 5 sLeft side leak: APU bleed valve closes too. Trigger: wing loop above 124 °C, pylon above 204 °C
- IP stage normally. The HP valve opens at low engine speed.
- The bleed valve regulates to about 45 PSI (42 to 50 PSI on some engines). The precooler cools it to about 200 °C.
- Crossbleed shut: each engine feeds its own side.
Packs and temperature
FCOM DSC-21-10-20 P 1–5 · DSC-21-10-30 P 1–3 · DSC-21-10-40 P 1–2 · DSC-21-10-50 P 1–6
- PACK FLOW LO / NORM / HI
- 80 / 100 / 120 %
- HI automatically
- Single-pack operation or APU bleed supply
- LO selected
- Rises to NORM if a zone cannot be cooled
- NORM, on ground, both engines running
- Limited to 85 or 90 %, depending on the aircraft
- Zone selectors
- 18 to 30 °C, 24 °C at 12 o'clock
- Pack demand
- The coldest zone demand sets both pack outlets
- Trim air
- Hot air from upstream of the packs, one trim valve per zone
- Ram air inlet flaps
- Closed for take-off and landing, reopen 20 s after slowing below 70 kt
- Pack valve closes for low pressure, compressor overheat, engine start, ENG FIRE or DITCHING.
- Engine start with crossbleed shut closes only the starting side pack valve. With crossbleed open, both close.
- One controller lane fails: the other lane takes over. Both lanes: that pack is lost and the hot air valve closes.
- Hot air valve closed: pack 1 controls the cockpit, pack 2 the cabin at the mean selection.
Pressurisation
FCOM DSC-21-20-10 P 1–2 · DSC-21-20-20 P 1–2 · DSC-21-20-30 P 1–5 · DSC-21-20-40 P 1–4 · LIM-AIR P 2
| Mode | What the active controller does |
|---|---|
| Ground | Outflow valve fully open, before take-off and 55 s after landing |
| Take-off | Pre-pressurises at 400 ft/min up to ΔP 0.1 PSI |
| Climb | Cabin follows a schedule based on the aircraft climb rate |
| Cruise | Holds the cabin target, 8,000 ft maximum |
| Descent | Reaches landing field pressure + 0.1 PSI just before touchdown |
| Abort | Returns to take-off field pressure + 0.1 PSI if the aircraft descends before 5,000 ft AAL or 8,000 ft |
- Maximum ΔP
- 9.0 PSI positive, −1.0 PSI negative
- Safety valves open
- 8.6 PSI above, 1 PSI below ambient
- Controllers swap
- 70 s after each landing, or when the active one fails
- Inputs
- FMGS landing elevation and QNH, ADIRS pressure altitude
- LDG ELEV knob
- −2,000 to +14,000 ft, used instead of the FMGS value
- High airfields
- Cabin up to 14,500 ft on ground, climb and descent
- Cabin descent rate
- Up to 750 ft/min, lower on some aircraft
- Outflow valve: right side, behind the aft hold, below the flotation line. Safety valves sit above it.
- MAN mode: the MAN V/S CTL switch drives the manual motor. The valve does not open by itself at touchdown.
- Cabin above 9,550 ft: CAB PR EXCESS CAB ALT. Above FL 160 that means EMER DESCENT.
Ventilation
FCOM DSC-21-30-20 P 1–18 · DSC-21-30-40 P 1 · DSC-21-30-50 P 1 · DSC-21-40-20 P 1–2 · LIM-AIR P 1
| Avionics configuration | When |
|---|---|
| Open circuit | On ground before take-off thrust, when warm. Outside air in, out overboard |
| Closed circuit | In flight, and on ground when cold. Air loops through the skin heat exchanger |
| Intermediate | In flight with a hot skin. Partly open to outside air |
| One pushbutton in OVRD | Closed circuit, plus air conditioning air |
| Smoke (both OVRD) | Air conditioning air through the bay, then overboard. Blower stops |
- Skin threshold, ground
- 12 °C rising, 9 °C falling
- Skin threshold, flight
- 35 °C rising, 32 °C falling
- T.O CONFIG on ground
- Closes the skin valves for 10 min
- Ground power, OAT above 49 °C
- Time limited: 2 h, down to 0.5 h above 60 °C
- Lavatory and galley
- One extraction fan, always on, exhausts near the outflow valve
- Cargo, where fitted
- Extraction fan. Forward hold: ΔP alone above 1 PSI in flight
- Cargo heating, where fitted
- Hot bleed air through a trim valve. Overheat at 88 °C
- The blower and extract fans run whenever the aircraft has electrical power.
Failures
FCOM PRO-ABN-AIR P 1–4, 16–19, 41–43, 51–60 · PRO-ABN-CAB_PR P 2–4, 11–13 · PRO-ABN-COND P 8–10 · PRO-ABN-VENT P 2–4
| Alert | Main actions |
|---|---|
| PACK 1(2) FAULT | Affected PACK OFF. The other pack goes to HI flow |
| PACK 1(2) OVHT | Compressor outlet above 260 °C. PACK OFF, back ON once it cools |
| PACK 1+2 FAULT | Both PACKS OFF, descend to FL 100 or MEA-MORA, RAM AIR ON once ΔP is below 1 PSI |
| ENG 1(2) BLEED FAULT | ENG BLEED OFF, X BLEED OPEN, PACK FLOW LO |
| ENG 1(2) BLEED LEAK, L(R) WING LEAK | ENG BLEED OFF, X BLEED SHUT, wing anti-ice OFF. Left side: APU BLEED OFF |
| ENG 1+2 BLEED FAULT | Bleeds OFF then ON. If that fails: descend to FL 100 or MEA-MORA, or use APU bleed at or below FL 200 |
| CAB PR EXCESS CAB ALT | Crew masks, descent to FL 100 or MEA-MORA. Passenger masks MAN ON if cabin above 14,000 ft |
| CAB PR SYS 1+2 FAULT | MODE SEL MAN. Cabin 500 ft/min up, 300 ft/min down, V/S CTL full up on final |
| VENT BLOWER or EXTRACT FAULT | Pushbutton to OVRD. Blower fault with DC ESS BUS fault: land ASAP |
- Excess cabin altitude: above 9,550 ft, or 1,000 ft above the airfield in climb and descent if higher.
- One engine bleed lost with wing anti-ice on: one pack only.
Overhead panel
FCOM DSC-21-10-50 P 1–7 · DSC-21-20-40 P 1–4 · DSC-21-30-60 P 1 · DSC-36-20 P 1–2
| Pushbutton | FAULT light |
|---|---|
| ENG 1, ENG 2 BLEED | Overpressure, overheat, onside wing or pylon leak, valve open during engine start or with APU bleed on |
| APU BLEED | APU leak |
| PACK 1, PACK 2 | Valve not in the selected position, compressor or pack outlet overheat |
| HOT AIR | Duct overheat at 88 °C. Goes out below 70 °C once OFF is selected |
| MODE SEL | Both automatic systems failed |
| BLOWER | Low pressure, duct overheat, computer power lost, smoke |
| EXTRACT | Low pressure, computer power lost, smoke |
- X BLEED in AUTO opens with APU bleed, and closes for a wing, pylon or APU leak. OPEN and SHUT are manual.
- RAM AIR is guarded. With ΔP below 1 PSI, the outflow valve opens about 50 % in automatic mode.
- DITCHING closes the outflow valve, ram air inlet, avionics inlet and extract valves, and pack valves.
ECAM pages
FCOM DSC-21-20-40 P 5–10 · DSC-21-10-50 P 15–21 · DSC-36-20 P 9–12
- Cabin altitude
- Pulses from 8,800 ft, red at 9,550 ft
- Cabin V/S
- Pulses from 1,750 ft/min
- ΔP amber
- −0.4 PSI or less, or 8.5 PSI or more
- Outflow valve amber
- More than 95 % open in flight, automatic mode
- Precooler inlet pressure amber
- Below 4 PSI, or overpressure from 57 to 60 PSI
- Precooler outlet temperature amber
- Overheat, or below 150 °C with wing anti-ice on
- Pack outlet amber
- 90 °C or more
- Pack compressor outlet amber
- 260 °C or more
- Zone duct amber
- Above 80 °C
- CAB PRESS page: PACK 1(2) turns amber when its valve is closed with the engine running.
- BLEED page: a valve turns amber when it disagrees with its command.
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Questions about A320 air conditioning and pressurisation
When does the A320 select HI pack flow by itself?
With only one pack running, or with APU bleed air, the packs deliver HI flow whatever the PACK FLOW selector shows. With LO selected, flow also rises to NORM when a zone cannot be cooled.
What is the maximum cabin differential pressure on the A320?
9.0 PSI positive and 1.0 PSI negative. The two safety valves open at 8.6 PSI above or 1 PSI below ambient pressure.
When does the crossbleed valve open in AUTO?
It opens when the APU bleed valve opens. It closes when the APU bleed valve closes, or when a wing, pylon or APU leak is detected, except during engine start.
What happens if both A320 cabin pressure controllers fail?
CAB PR SYS 1+2 FAULT. The crew selects MODE SEL to MAN and drives the outflow valve with the MAN V/S CTL switch, targeting about 500 ft/min cabin climb or 300 ft/min cabin descent, then full up on final approach.