Understanding A320 Pressurization Modes: Manual vs Automatic System & How Does the Control Work

The A320 pressurization system is a critical component that ensures a safe and comfortable cabin environment for passengers and crew. This advanced system operates in two primary modes: manual and automatic.

In automatic mode, the system schedules and commands the outflow valve using FMGS and flight-phase inputs (not altitude alone), allowing for optimal cabin pressure levels at high altitudes. It is managed by two Cabin Pressure Controllers (CPCs) that work together to follow a schedule (e.g., pre-press ~400 fpm to ΔP 0.1 psi; max descent 750 fpm; residual dump ~500 fpm after landing).

Conversely, in manual mode, pilots can adjust cabin pressure using manual control of the outflow valve (OFV), allowing for direct intervention if the primary auto system has issues. This flexibility is crucial if automatic control is unavailable; crews can release any residual pressure on the ground and manage cabin rates manually.
Note: in MAN, the OFV does not auto-open at touchdown—verify ΔP = 0 before door opening.

Understanding these modes of operation in the A320 pressurization system is essential for maintaining optimal cabin conditions throughout the flight.

A320 Overview: What the System Does

The Airbus A320 pressurization system maintains a safe and comfortable cabin environment by controlling the OFV and regulating cabin pressure. This system automatically schedules pressure control to maintain cabin altitude within limits and allows manual intervention when necessary.

• Ground: The vent valve fully opens before takeoff and approximately 55 seconds after landing to remove residual pressure.
• Pre-pressurization (takeoff): When thrust is applied, the CPCs close the vent valve to build about 0.1 psi differential at roughly 400 ft/min to prevent a rotation “bump.”
• Climb/Cruise: The system limits cabin altitude to approximately 8,000 ft during cruise and follows a programmed schedule based on FMGS inputs.
• Descent: The system targets landing field pressure (about +0.1 psi shortly before landing) with a maximum cabin descent rate of 750 ft/min.

Pressurization Safety and Backup Features

• Automatic system changeover: The standby CPC takes control 70 seconds after each landing or if the active CPC fails.
• Safety valves: Prevent overpressure or underpressure. They open around +8.6 psi above ambient pressure and protect down to approximately −1 psi below ambient.
• Residual Pressure Control Unit (RPCU): On the ground with engines off, if both CPCs have failed or manual mode is selected and pressure remains, the RPCU automatically opens the outflow valve to release residual pressure.

Automatic Mode (AUTO): Default and Fully Managed

With MODE SEL = AUTO and LDG ELEV = AUTO, the CPCs receive FMGS data (including landing elevation and flight phase information) and automatically command the outflow valve (OFV). If FMGS landing elevation data is unavailable, the pilot can manually set the landing elevation; the system continues to function in AUTO using that value (“semi-automatic” operation).

• ECAM Indications: The CAB PRESS page shows LDG ELEV AUTO/MAN status and which system (SYS 1 or 2) is active.
• Flashing indications: Cabin vertical speed and cabin altitude indications flash when thresholds are exceeded (e.g., V/S ≥ 1,750 ft/min or CAB ALT ≥ 8,800 ft).
• RAM AIR interaction: If RAM AIR is ON and ΔP < 1 psi, AUTO drives the OFV about 50% open. MAN mode does not perform this automatically.

Manual Mode (MAN): When Both Automatic Systems Are Unavailable

If both automatic systems fail or as directed by checklist, select MODE SEL = MAN and use the MAN V/S CTL switch (UP/DN) to command cabin climb or descent by manually moving the outflow valve. Expect a short delay (about 5–10 seconds) on the ECAM for valve movement feedback due to actuation and display update time. In MAN mode, the OFV does not automatically open at touchdown.

Typical crew technique: In MAN mode, target a gentle cabin climb rate of about +500 ft/min and descent rate of about −300 ft/min. Maintain aircraft altitude higher than cabin altitude and confirm differential pressure (ΔP) remains within limits. Ensure ΔP = 0 before door opening.

Semi-Automatic Use Case

If FMGS landing elevation is missing or high-elevation airport operations require it, the crew may manually select LDG ELEV. The controller then uses this setting for its internal schedule while remaining in AUTO mode. An ECAM memo “MAN LDG ELEV” appears when the knob is not in AUTO.

Outflow Valve, Components, and Indications

• Location: Right-hand fuselage, aft of the aft cargo compartment, below the flotation line. The valve is driven by two automatic motors and one manual motor.
• Feedback: OFV position is displayed on the ECAM, driven by the active controller in AUTO or CPC1 backup section in MAN.
• Safety Valves: Open if differential pressure approaches the limit; ECAM may display “SAFETY VALVE OPEN.”
• Active System Annunciation: SYS 1 or SYS 2 status appears on ECAM; MAN mode is clearly indicated.

When to Switch from AUTO to MAN

• CAB PR SYS 1+2 FAULT / EXCESS CAB ALT: Select MAN, command the vent valve DOWN to arrest a cabin climb if required, then control cabin vertical speed toward target values while ensuring ΔP remains within limits.
• OFV not opening on ground: Select MAN and command the valve full UP to open. If unsuccessful, follow ECAM guidance (e.g., turn PACKS OFF) to depressurize.
• High-elevation airports: Crews may manually set landing elevation if FMGS data is unavailable. The system supports ground/climb/descent profiles up to approximately 14,100 ft.

Conclusion

The A320 pressurization system is designed to be hands-off in normal operations yet gives pilots precise control when required. It manages cabin pressure through four phases (ground, takeoff pre-pressurization, in-flight control, and depressurization after landing) using two cabin pressure controllers (CPCs), a single release valve (with two automatic motors and one manual motor), a Residual Pressure Control Unit (RPCU), and two safety valves.

In normal operation, the crew primarily monitors; the system functions automatically. The A320 air pressure control system ensures a safe and comfortable cabin environment by maintaining optimal pressure levels at high altitudes. When operating in manual mode, pilots can adjust cabin pressure using the outflow valve to control the cabin altitude directly.

This manual control allows for pressure management when automatic regulation is not available. In manual mode, the system does not regulate automatically—pilots control cabin vertical speed using the MAN V/S CTL switch. In automatic mode, the controller regulates the OFV through a programmed schedule based on FMGS data, maintaining cabin altitude changes within safe limits.

Understanding the differences between manual and automatic modes in the A320 air pressure control system is essential for maintaining a comfortable cabin environment and ensuring correct procedures when transitioning between modes.

Frequently Asked Questions About Cabin Pressurization

What’s the difference between AUTO and MAN on the A320?

AUTO uses CPCs tied to FMGS data to schedule cabin pressure and drive the release valve. MAN gives the crew direct control of the OFV via MAN V/S CTL; there is no automatic regulation in MAN mode.

Does the A320 pre-pressurize before liftoff?

Yes. On thrust application, the system pre-pressurizes the cabin to approximately 0.1 psi differential at about 400 ft/min to avoid a rotation “bump.”

What protects against over- or under-pressurization?

Two safety valves (open at approximately +8.6 psi and protect down to about −1 psi relative to ambient pressure) and the residual-pressure dump function via the RPCU on the ground.

Disclaimer: This article is for educational purposes only and not an official Airbus or regulatory publication. Always refer to the Airbus FCOM, AFM, and approved procedures for operational use.