AIRPLANE
OPERATIONS
MANUAL
PNEUMATICS
AIR CONDITIONING
AND PRESSURIZATION
JANUARY 21, 2002
2-14-15
Page
1
Code
01
PRESSURIZATION SYSTEM
The Cabin Pressure Control System (CPCS) controls the cabin
pressure by regulating the cabin air exhaust rate supplied by the
ECUs.
The CPCS comprises two subsystems:
- One digital electropneumatic subsystem(automatic mode).
- One pneumatic subsystem (manual mode).
Both subsystems comprise a digital controller, a manual controller, an
electropneumatic outflow valve, a pneumatic outflow valve, an air filter,
two pressure regulator valves, an ejector pump, two static ports, and a
Cabin Pressure Acquisition Module (CPAM).
Both outflow valves receive static pressure signals from static ports for
overpressure relief and negative pressure relief functions, actuating
pneumatic devices to inhibit airplane structural damage or injury in
case of improper system operation. The safety devices provide the
following features:
− Positive cabin differential pressure relief: 8.2 psi maximum.
− Negative cabin differential pressure relief: - 0.3 psi.
− Cabin altitude limitation (when in the auto mode): 15000 ft maximum.
The system is normally operated in the automatic mode. The manual
mode is used in case of automatic mode failure.
The cabin air filter is provided to prevent nicotine and dust to enter the
outflow valve chamber.
Indications of cabin altitude, cabin differential pressure, and cabin
altitude rate of change are presented on the EICAS.
A caution message is presented on the EICAS in case of automatic
mode failure, requiring the crew to select the manual mode.
The CPAM and CPCS have internal tolerances of
± 100 ft and ± 200 ft,
respectively. Then, depending on these tolerances accumulation, the
displayed cabin altitude may be increased up to 300 ft. Although
displayed in the amber range for airplanes equipped with EICAS
version up to 16, it may not be considered an abnormal condition if
cabin altitude indication remains stabilized at or below 8300 ft.
If, however, the cabin altitude indication continuously increases and the
system is out of its normal range of operation, causing a cabin
depressurization, the CPAM sends a signal to the aural warning
system to alert the crew when cabin altitude is above 9900 ± 100 ft.
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