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CPCS
Cabin pressure control system
Can operate in normal or automatic mode. Consists of 1 of each of the following:
- cabin pressure controller
- cabin outflow valve (closes at 14,500')
- negative pressure relief valve (spring loaded, on the rear bulkhead, opens when differential pressure <-0.5psi)
- positive pressure relief valve (pneumatically driven, on the rear bulkhead, opens when differential pressure >8.6psi)
- static port (electrically heated, on the rear bulkhead, senses outside pressure in order to determine differential pressures)
Cabin pressure controller
Has 2 identical channels. In AUTO mode, 1 channel is command and the other is standby. In MAN mode, both channels are in standby, and the outflow valve position is controlled directly by the pilots. Manual mode has protection for differential pressure, but not cabin altitude, and it will not automatically depressurise on the ground. With the mode selector in LFE, the controller remains in AUTO mode. Note that landing field elevation is normally set using the MCDU. Uses the FADEC, ADC, and FMS to determine the flight mode.
Cabin differential pressure is 7.8psi below 37,000', and 8.4psi above. Maximum cabin altitude is 8,000'.
DUMP button
Used to depressurise the cabin at 2,000fpm to a maximum of 12,400' cabin altitude for smoke removal or an emergency evacuation. Above 12,400', cabin altitude continues to rise due to natural leak. Deactivates ECS packs and recirculation fans. If the button is pressed a second time, the system returns to normal operation.
Flight modes
| Mode | Config |
| Ground | on the ground |
| Taxi | doors closed and both engines running, N2 >60% |
| Takeoff | in takeoff run |
| Climb | climbing |
| Cruise | constant altitude |
| Descent | descending |
| Abort | flight aborted, returning to takeoff field |
EICAS messages
CABIN ALTITUDE HI - cabin altitude >9,700', or >500' above takeoff field elevation, whichever is higher