A
757 MAINTENANCE MANUAL
(h)
GUN 004-007; If the cabin altitude reaches 14,500 ft, the controller automatically closes the outflow valve to increase cabin pressure.
(i)
The landing altitude initiate switch overrides the existing cabin altitude demand and sets it to the landing field altitude command. The cabin depressurizes at the full depressurization rate limit, until it reaches the landing altitude. The maximum cabin-to-ambient pressure ratio (P = 8.6 psi) limits the depressurization rate. The landing initiate function is used for rapid descent from cruise or flight from high to low altitudes.
B. BITE (Fig. 5)____
(1)
Each controller includes built-in test circuitry to monitor system operation, detect critical faults, and identify the faulty line replaceable units (LRU's) by means of a fault display. The controller contains switches and indicator lamps on the controller face for initiating fault isolation, system checks and fault display.
(2)
The PRESS TEST switch serves as a lamp-test function. When pressed, all fault indicator lamps come on. If no lights come on, this indicates no ac power to the controller, selector panel switch is not in the appropriate position, or a defective controller.
(3)
When the BIT switch is pressed, the controller will display any faults previously recorded. If no faults are present, the NO FAULT lamp will come on for 30 seconds and then go out. If a fault exists in memory, the appropriate lamp will come on for 30 seconds and then go out.
(4)
The VERIFY switch is used to determine if any faults still exist in the system. When the VERIFY switch is pressed on the selected controller, the VERIFY MODE lamp will light and remain on while the test is being preformed. If any faults are detected, the applicable fault light comes on for 30 seconds. If no faults are detected, the NO FAULT light comes on for 30 seconds. The faults in the verify selection are taken from a temporary memory. It is possible that an intermittent fault that occurred in flight, but no longer exists, would not show up in the verify mode. Pressing the BIT switch would display any intermittent fault. If the VERIFY switch is pressed on a nonselected controller, the VERIFY MODE light will flash. This indicates that the verify mode is not being performed. If the cabin pressure selector is moved from the correct to incorrect selection while the VERIFY MODE lamp is on, the test will be terminated. The VERIFY MODE lamp will go out. The VERIFY switch overrides the BIT switch.
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21-31-00
ALL ú ú 13 Page 7 ú May 28/00
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
757
MAINTENANCE MANUAL
CABIN PRESSURE PRESS
TEST
BITE INSTRUCTIONS
CABIN PRESSURE CONT (2)
SEE A
COMPONENT STATUS
THROTTLE
CONTROLLER NO FAULT
POSITION
AC MOTOR AC POWER OFF
SWITCHES
SELECTOR LOW INFLOW SEE B
LDG GEAR SW VERIFY MODE
BIT VERIFY RESET
A
S17 LOAD SHED/PRESSURE CONTROL (THROTTLE POSITION)
ELECTRICAL
CONNECTORS
MICROSWITCH
PACK ASSEMBLY
S18 LOAD SHED/PRESSURE
SEE C CONTROL
(THROTTLE POSITION)
AUTOTHROTTLE DRIVE ASSEMBLY
B
C
Cabin Pressure Cont
Figure 5
EFFECTIVITYùùùùùùùùùùùùùùùùùùùùùùùùùùùùùù. ú
21-31-00
ALL ú ú 01 Page 8 ú Sep 20/88
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
757
MAINTENANCE MANUAL
(5)
The RESET switch is used to erase the memory and set the controller in an operable mode. The switch must be pressed while the VERIFY MODE light is on. If the RESET switch is pressed before the VERIFY switch, nothing will occur.
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