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PRESSURIZATION CONTROL SYSTEM - MAINTENANCE PRACTICES
1. General
A. Maintenance practices for the pressurization control system consists of an operational test. The pressurization control system operational test provides a method for making periodic quick checks of the pressurization control system ability to switch modes of operation. Although the test does not provide a complete check of the pressurization control system, it does assure that system will switch from automatic to standby and that standby and manual control are available if needed during flight. Refer to Adjustment/Test for a complete functional test of the system.
B. To prevent inadvertent cabin pressurization, an airplane door must be open if air is being supplied to air conditioning packs from a ground cart or APU/ENGINE.
2. Prepare to Operationally Test Pressurization Control System
A. Provide electrical power.
B. Check that following circuit breakers are closed:
(1)
MAN DC (P6)
(2)
STBY DC (P6)
(3)
AUTOMATIC DC (P6)
(4)
AUTOMATIC AC (P6)
(5)
MAN AC (P6)
(6)
STBY AC (P6)
(7)
All CONTROL CABIN LIGHTS module circuit breakers (P6)
(8)
LANDING GEAR LIGHTS (P6)
(9)
On airplanes without SB 21-1119,
No. 1 AIR DATA COMPUTER (P18)
(10)
On airplanes with SB 21-1119,
No. 2 AIR DATA COMPUTER (P6)
C. Move pressurization control system controls as follows:
(1)
Mode selector to AUTO
(2)
FLT/GRD switch to GRD
(3)
CAB ALT counter to 500 feet above field altitude
(4)
Captain and First Officer altimeter to field barometric pressure.
(5)
CABIN RATE selector to pip
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D. Press-to-test following lights:
(1)
AUTO FAIL
(2)
OFF SCHED DESCENT
(3)
STANDBY
(4)
MANUAL
(5)
F OUTFLOW CLOSED
3. Operationally Test Pressurization Control System
NOTE: On airplanes with the CPC 21 controller installed, a 15-minute warm-up time is required. On airplanes with the CPC 22 controller installed, a 5-minute warm-up time is required.
A. Check that lights noted in 2.D. are out.
CAUTION: KEEP HANDS AND TOOLS AWAY FROM THE OUTFLOW VALVE DURING THE TEST. THE OUTFLOW VALVE WILL MOVE, AND CAN CAUSE INJURY TO PERSONS.
B. Attach a KEEP CLEAR tag on or near the outflow valve.
C. Check that VALVE position indicator shows outflow valve to be in open position.
D. Move FLT/GRD switch to FLT and check that outflow valve moves toward close.
NOTE: VALVE position indicator should be monitored to detect outflow valve movement. There will be a delay of approximately 10 seconds before indicator shows movement.
E. Move mode selector to CHECK and observe that following events take place:
(1)
AUTO FAIL light comes on
(2)
STANDBY light comes on
(3)
Outflow valve moves toward open
(4)
F OUTFLOW CLOSED light goes out
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F. Move CAB ALT counter to 500 feet below field level and check that outflow valve moves toward close.
G. Move FLT/GRD switch to GRD and check for the following:
(1)
AUTO FAIL light goes out
(2)
STANDBY light goes out
(3)
Outflow valve moves toward open
H. Allow at least 20 seconds from time mode selector was moved to CHECK, step 3.E., then move FLT/GRD switch to FLT and check for the following:
(1)
AUTO FAIL light stays out
(2)
STANDBY light stays out
(3)
Outflow valve moves toward close
I. Move mode selector to AUTO and check for the following:
(1)
AUTO FAIL light comes on
(2)
STANDBY light comes on
(3)
Outflow valve stays closed
J. Move mode selector to MAN AC and check for the following:
(1)
AUTO FAIL light goes out
(2)
STANDBY light goes out
(3)
MANUAL light comes on
K. Move FLT/GRD switch to GRD.
L. Hold MANUAL switch in OPEN position and check that outflow valve moves toward open.
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