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Normal operation of the pressurization system is automatic when the destination airport is programed into the FMS and the
FMS sends the correct landing altitude to the IASC. The crew has the option of manually setting the landing altitude using
the SOURCE SELECT to MAN and setting the landing altitude using the ALT switch.
Pressurization system control indications are displayed on the ECS and SUMMARY synoptic displays. CAB ALT and
CAB RATE are displayed on the captain’s MFD.
COMPONENTS AND OPERATION
INTEGRATED AIR SYSTEM CONTROLLERS (IASC)
Two IASCs control all automatic phases of pressurization. Only one controller is active at a time, with the other controller
in standby. If the operating controller fails, the standby controller automatically takes the active role.
Unless a failure is detected in IASC 1, it becomes the active controller after power up tests are complete. IASC 2 is operated
as a standby mode.
OUTFLOW VALVE
The electrical outflow valve consists of a composite flow body, butterfly plate and electrical double actuator. The actuator
has two motors, one for manual operation and the other for automatic operation.
The outflow valve is located on the bottom of the fuselage. An access panel in front of the wing allows access to the outflow
valve.
In the manual mode, the outflow valve is controlled electrically by the MAN RATE switch on the PRESSURIZATION control
panel. From the control panel, the pilot can manually control the rate at which the cabin altitude climbs (UP) or descends
(DN). To hold a particular cabin altitude, the pilot can command a zero cabin rate of climb.
SAFETY VALVE
Two safety valves located on the aft pressure bulkhead provide overpressure and negative pressure relief.
The safety valves are pneumatically operated and are spring-loaded closed. When cabin differential pressure exceeds normal
limits the safety valves automatically open to relieve excess cabin pressure.
If a negative pressure condition develops (ambient pressure is greater than cabin pressure), the safety valves automatically
open to equalize cabin pressure.
REV 1
AIR CONDITIONING/PRESSURIZATION
Volume 2 Flight Crew Operating Manual Sep 13/2004
02-04-02 CSP 100-6 REV 1
PRESSURIZATION (Cont)
AUTOMATIC PRESSURIZATION MODES
The following automatic pressurization modes are a function of the active IASC:
- Pre-pressurization mode
- Takeoff and return to base sequence
- Climb mode
- Cruise mode
- Descent mode
- Depressurization sequence on ground
PRE-PRESSURIZATION MODE
The pre-pressurization mode is activated on the ground when the thrust levers are advanced for takeoff. Pre-pressurizing
the aircraft will allow the outflow valve to achieve a controlling position prior to takeoff to eliminate any noticeable pressure
changes at takeoff. The cabin is pressurized to 300 ft below actual field elevation.
TAKEOFF AND RETURN TO BASE SEQUENCE
When the aircraft leaves the ground, the takeoff sequence is initiated. The system will maintain the pre-pressurization cabin
altitude of 300 ft below field elevation until the aircraft reaches 6000 ft MSL or differential from takeoff, or 10 minutes has
elapsed. If a descent is initiated the cabin altitude will descent to the takeoff altitude and the landing field elevation does
not have to be reset.
CLIMB MODE
Cabin pressurization is programmed according to selected landing elevation and a theoretical schedule of cabin altitude
versus aircraft altitude. The cabin climb profile varies directly with the aircraft’s climb rate. A typical cabin climb rate is
approximately 300-500 sea level fpm. For light aircraft climbs at the best climb rate, the maximum cabin climb rate is 635
sea level fpm (slfpm).
NOTE: When step climbs are performed at flight altitudes greater than 25 000 ft and at aircraft climb rates greater than
6000 fpm, the cabin climb rate might exceed the max normal limit of 635 sea level fpm for automatic overpressure
protection. For comfortable cabin climb rates during step or zoom climb it is recommended to use a maximum
aircraft climb rate of 6000 fpm.
CRUISE MODE
Cabin pressurization is programmed to activate cruise mode if the aircraft rate of climb is less than 500 sea level fpm for
more than 10 seconds, or the aircraft is climbing at any rate with the aircraft altitude greater than 25 000 ft. The cabin altitude
will be stabilized at a level in accordance with the pressure schedule.
DESCENT MODE
The rate of cabin descent is directly related to the aircraft’s rate of descent. In the case of a high-speed descent, the rate of
cabin descent is increased according to the calculation of remaining flight time. The remaining flight time is calculated from
　
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