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Airbus A320ceo / neo · Components

Components by ATA chapter

Every ATA chapter has its own components page. Pick a chapter, then a part: what it is made of, how it works, what it connects to, the numbers that matter, how it fails and how mechanics inspect it.

Unverified — check your manualText on this page is written from general knowledge. Figures marked ✓ are checked against official FAA/EASA data.See verified data

ATA 21 · Air Conditioning & Pressurisation

ATA 21 Air Conditioning & Pressurization

Outflow valve

Controls cabin pressure by regulating how much air leaves the cabin.

Location: Lower aft fuselage, right side.

Outflow valve on the Airbus A320ceo / neo — Outflow valve · illustrative image

Pack bay under the belly with heat exchangers and ducts · *illustrative image*

How it works

Three motors (two automatic, one manual) drive a flap door.

Closing the valve raises cabin pressure; opening it lowers it.

The CPCs schedule cabin altitude from the landing elevation and FMGC data; the valve opens or closes to keep cabin rate within limits.

Safety valves on the aft bulkhead protect against over- and negative pressure.

Construction

Single valve on the lower aft fuselage with two doors (rectangular), driven by three electric motors: two for automatic (one per CPC) and one for manual mode.

Interfaces with other systems

CPC 1 and 2, MODE SEL / MAN V/S CTL, SD CAB PRESS page, ditching pushbutton.

Technical data

Max Δp	8.6 psi (approx.)
Motors	3
Max differential	approx. 8.6 psi
Safety valves	2

Failure modes

Valve stuck	Cabin altitude can't be controlled.
Motor fault	Controller switches motors.
Valve stuck	Use manual mode with MAN V/S CTL.

Inspection

Seal condition.
Actuator function test.
Check door seals and actuator linkage.
Check for blockage around the valve.

Note

In manual mode the toggle moves the valve directly; watch cabin V/S on the SD.

On the ground the valve is fully open.

Educational summary — verify against the component maintenance manual (CMM) and AMM.

All parts in ATA 21

1.Packs (2)

Air-cycle machine: primary heat exchanger, compressor, main heat exchanger, turbine, water separator.

Each A320 has two air-cycle packs mounted in the belly fairing below the wing centre section, fed by bleed air from the engines, APU or ground cart via the pneumatic system. They are the primary source of conditioned and pressurized air for the cabin and cockpit.

How it works

Hot bleed air is cooled in the primary heat exchanger by ram air, compressed by the ACM compressor, cooled again in the main heat exchanger, then expanded across the ACM turbine, dropping temperature sharply.
The turbine drives the compressor on a common shaft, and a water separator downstream removes condensed moisture before mixing with recirculated air.
Pack outlet temperature is modulated by a pack flow control valve and a bypass valve commanded by the zone controller to reach the demanded duct temperature.
Each pack can run in LO, NORM or HI flow depending on bleed pressure, electrical load and cooling demand from the cabin and avionics.

Bleed supply pressure	approx. 30-45 psi
Pack outlet temperature range	approx. 5 to 90 deg C
Max continuous flow	HI flow approx. 100 percent

Failures

Pack fault / overheat: ECAM PACK 1(2) FAULT, pack automatically shuts off, remaining pack and ram air supply cabin
ACM turbine bearing failure: Loss of cooling, possible smoke smell in bleed air, pack isolated

Inspection

Inspect pack bay drains and check valves for blockage
Borescope/visual check of heat exchanger matrices for fouling
Verify pack valve rigging and leak check of ducts

2.Pack flow control valves

Regulate flow (LO/NORM/HI).

Electrically controlled, pneumatically operated valves located at the pack inlet ducting in the belly fairing, one per pack, that set the quantity of bleed air admitted to each air-cycle machine.

How it works

The valve is commanded by the Air Conditioning System Controller (zone controller) to one of LO, NORM or HI flow positions depending on cabin demand and bleed availability.
Flow rate directly affects pack discharge temperature and cooling capacity, so the controller trims it along with the trim air valves to hold selected zone temperatures.
Position feedback is sent back to the controller and displayed on the ECAM BLEED/COND page.
On loss of a pack or bleed source, the opposite pack's flow valve may be driven to HI to compensate.

Flow positions	LO / NORM / HI
Actuation	Pneumatic motor, electrically commanded

Failures

Valve stuck closed: Loss of pack flow, ECAM PACK FAULT, reduced cabin cooling/pressurization margin
Valve stuck open: Excess bleed draw, possible duct over-temperature protection trip

Inspection

Functional check of valve travel and position indication
Inspect actuator linkage and electrical connector for corrosion

3.Mixer unit

Mixes pack air with recirculated air.

A ducting assembly located above the cabin ceiling near the wing box where conditioned air from both packs is combined with cabin recirculated air before distribution to the cockpit and cabin zones.

How it works

Pack discharge air at low temperature mixes with warm recirculated cabin air drawn by two recirculation fans, raising the mix temperature and reducing total fresh-air bleed demand.
The mixed air is then split and passed through trim air valves for each zone to achieve the individually selected temperatures.
A HEPA-equivalent recirculation filter upstream removes particulates and some bacteria from the recirculated portion.
Mix ratio is largely fixed by duct geometry; temperature control is achieved downstream by trim air, not by varying the mix itself.

Recirculation fans	2, electrically driven
Typical recirc fraction	approx. 40-50 percent of total supply air

Failures

Recirculation fan failure: ECAM caution, reduced total airflow, slightly lower cabin temperature uniformity
Mixer duct leak: Loss of conditioned air to distribution, possible uneven zone temperatures

Inspection

Inspect mixer casing and duct joints for leaks
Check recirculation filter condition per maintenance schedule

4.Trim air valves

Add hot air per zone for temperature control.

Small pneumatic valves, one per cabin/cockpit zone, located in the mixer manifold area, that add a controlled trickle of hot (unmixed pack bypass) bleed air to the cold mixed air feeding each zone duct.

How it works

Each zone has its own temperature selector (cockpit, forward cabin, aft cabin); the zone controller compares selected to sensed duct/zone temperature and modulates the trim air valve accordingly.
Opening the valve raises that zone's supply temperature without affecting the other zones, allowing independent temperature control from a common cold air supply.
Hot trim air is tapped from upstream of the pack's cooling turbine so it is still regulated bleed pressure air.
A duct overheat sensor can command the trim valve closed if duct temperature exceeds limits.

Number of zones	3 (cockpit, fwd cabin, aft cabin) typical
Trim air source	pre-cooled bleed air upstream of pack turbine

Failures

Trim valve stuck open: Zone overheats, ECAM duct overheat caution possible
Trim valve stuck closed: Zone cannot be warmed, persistent cold complaint in that zone

Inspection

Functional test of zone temperature selection response
Inspect valve actuator and duct overheat sensor wiring

5.Outflow valve

Rear fuselage; motor-driven by the active CPC.

A single large butterfly-type valve in the lower rear fuselage that is the primary means of controlling cabin pressure by metering the rate at which cabin air is discharged overboard.

How it works

It is driven by two motors, normally controlled automatically by the active Cabin Pressure Controller (CPC) which schedules cabin altitude as a function of flight phase and landing field elevation entered in the MCDU.
The motor positions the valve to balance incoming pack flow against outflow, maintaining a target cabin pressure differential of up to approximately 8.6 psi.
A second CPC and a manual mode allow crew backup control of the valve via a rotary switch on the overhead panel if automatic control fails.
The valve fully opens on the ground via landing gear squat switch logic to equalize cabin pressure before door opening.

Max differential pressure	approx. 8.6 psi
Control	dual CPC, manual backup via overhead switch

Failures

Valve motor failure: ECAM CAB PR FAULT, switch to backup CPC/manual mode
Valve stuck open: Cabin unable to pressurize, emergency descent may be required

Inspection

Visual inspection of valve blade and seals for corrosion/wear
Functional test of automatic and manual operation during pressurization checks

6.Safety valves (2)

Overpressure and negative-pressure relief.

Two spring-loaded pressure relief valves in the aft fuselage pressure bulkhead area, independent of the outflow valve, that protect the fuselage from both over- and under-pressurization.

How it works

Each safety valve opens automatically if cabin differential pressure exceeds the structural limit, venting excess pressure overboard regardless of outflow valve or CPC status.
A negative pressure relief function (sometimes a separate flapper) opens if outside pressure exceeds cabin pressure, preventing structural damage from negative differential.
They are purely mechanical/pneumatic, requiring no electrical power, providing a last-line passive safeguard.
Their setpoints are fixed and not adjustable from the cockpit.

Positive relief setpoint	approx. 8.9-9.0 psi differential
Negative relief setpoint	approx. -1 psi differential

Failures

Valve seized shut: Loss of overpressure protection, airworthiness item if found during check
Valve leaking: Minor unexplained cabin pressure loss, ECAM CAB PR indications

Inspection

Functional pressure test during scheduled maintenance
Inspect valve seat and seal for corrosion or debris

EDUCATIONAL USE ONLY. Content is summarised from manufacturer documentation for learning. It is not approved flight or maintenance data. Always use the current, aircraft-specific POH/AFM, FCOM, QRH, AMM and operator procedures.