The pressurization control system controls the pressure in the flight, passenger, and baggage compartments during the flight and the ground operations. The galley and lavatory have the same pressure altitude as the passenger compartment. The compressed air comes from the air conditioning system. A part of the air is recirculated into the passenger compartment and the rest goes out through the outflow valves of the cabin pressure control system.

The cabin-pressure control system controls the pressure altitude of the pressurized compartments. The cabin-pressure control system has two modes of operation, automatic mode and manual mode. A safety system overrides the two modes if the pressure becomes too large. There are two cabin pressure controllers, two outflow valves, two safety valves and a PRESSURIZATION control panel.

Cabin-Pressure Control System

The cabin-pressure control system has two automatic modes available from two fully electrical and automatic control systems. The two systems are the same and operate independently. In the two automatic modes the cabin pressure controller controls the cabin pressure through the two outflow valves. Only one automatic mode is in operation while the other automatic mode is in standby. If a malfunction occurs in the active system, a smooth transfer from one automatic mode to the other will automatically occur. The cabin pressure controller drives the two electrical outflow valves through the automatic drive mechanism of the outflow valve actuator.

In the manual mode, cabin pressure is manually controlled with the MAN ALT switch on the PRESSURIZATION control panel. The switch directly controls the two outflow valves. The manual drive mechanism of the outflow valve actuator controls each outflow valve. When the two automatic modes are defective, the AUTO/MAN switch/light on the PRESSURIZATION control panel must be set to MAN. The MAN ALT switch then controls the pressure.

The safety system operates as follows:

• Overpressure relief is controlled pneumatically by the two safety valves that override the operation of the two automatic modes and the manual mode
  
  
• Negative relief is controlled pneumatically by the two safety valves that override the operation of the two automatic modes and the manual mode
  
  
• Cabin altitude limitation overrides the operation of the two automatic and the manual modes. Two cabin altitude limitation functions are provided, each one is related to one outflow valve. Each cabin altitude limitation is done from the indicator module included in the cabin pressure controller. It directly moves the related electrical outflow valve to the closed position through the manual drive mechanism of its actuator
  
  
• Ditching is controlled through an automatic sequence in the two automatic modes and through a manual sequence in manual mode
  
  
• Emergency depressurization is controlled in the two automatic modes and in manual mode. This function occurs independently of the controller. When the EMERG DEPRESS switch/light is pressed the two electrical outflow valves open