This system is closely linked to the Air Conditioning system which we discussed back in episode 2. If you havent listened to it already it may be worth going back and listening to that first.

The main components. The system consists of:
- Two Cabin Pressure Controllers (CPCs)
- One Residual Pressure Control Unit (RPCU) (if fitted)
- One outflow valve, with an actuator that incorporates three motors (two for automatic operation, one for manual operation)
- One control panel
- Two safety valves.

To work out the schedule, the current CPC uses the landing elevation and the QNH we've entered into the perf page of the FMGC, and the pressure altitude from ADIRS.
If FMGC data isn't available, the controller uses the captain BARO reference from the ADIRS and the LDG ELEV selection from the overhead panel.

The system follows a schedule for each flight which consists of four general functions:

• Ground function: It Fully opens the outflow valve on ground
• Pre Pressurisation :During takeoff, it increases cabin pressure to avoid a surge in cabin pressure during rotation (we'll talk about whether this really ever happens later)
• Pressurisation in flight :It Adjusts cabin altitude, and rate of change to provide passengers with a comfortable flight
• Depressurisation :After touchdown, it gradually releases residual cabin overpressure before the ground function fully opens the outflow valve.

Scenario of the Week

You get a call from the Cabin, they are complaining of a loud noise coming from door 2L (at the back).