CABIN PRESSFAULT OUTFLOW
CONT UNIT SOFTWARE VALVE
LEVEL
MOTOR/VALVE DRIVE CLOSEVW1RATE SELECT
ACA/D
DETECTOR (-)
MOTOR VW2 LDG ALT SET
SOFTWARE HIA/D
TACHX CHANNEL OUT
DEMOD LO AUTO 2
AC POWER OFF
DC GND

CABINDATA
X CHANNEL OUT PRESSAC GND STORAGE
CONTAND
AUTO
+V UNIT
SW
PROCESSOR L ARINC 429
L ADCBARO ALTANEROID SW
A
115V ACBARO COR
SOFTWARE BC
ARINC
STD ALT

-27VPOWER
Pc =9.72 PSIA=B C=0
NOTE:
FAULT SUPPLY
SET POINTR ARINC 429
WOW=1
(MUX) +15V
V REF HIBARO ALT
1 IF, FOLLOWING A POWER INTERRUPTION,
A.B C=1
2 R ADC
BOTH CONTROLLERS ARE PUT IN COMMAND,
115V ACBARO COR
-15V
A
10 |0.02V DCC +5V
A  CONTROLLLER NO. 2 (WITH TIE BREAKER)
B  WILL ASSUME CONTROL AND CONTROLLER
TIE STD ALT AC PWRV REF
NO. 1 (WITHOUT TIE BREAKER) WILL GO
2 SEC
BRKR
OFF 1 TO STANDBY MODE.
V REF LO AUTO 1 CABIN PRESSURE CONTROLLER UNIT
2 FOR AIRPLANES WITH HIGH ALTITUDE AIRPORT CERTIFICATION,AUTO 1 SHOWN, AUTO 2 SIMILARSET POINT = 8.46 PSIPressurization Control System Operation SchematicFigure 7
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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A

(g)

(h)

757
MAINTENANCE MANUAL

The CPU faults the controller and automatically switches
 control to the standby controller, if performance or signal
 faults exist. These faults are:
 1)  Excess Cabin Rate: Excessive cabin rate exists when the controller detects a cabin rate of pressurization 200 FPM greater or less than the cabin rate limit command for a time period when the cabin altitude increases by 250 feet. The system switches to the standby controller. EICAS status and maintenance messages CABIN ALT AUTO 1, or CABIN ALT AUTO 2 are received.
 2)  High Cabin Pressure: Automatic switchover occurs if the cabin-to-ambient differential pressure is greater than 8.75 psi. EICAS status and maintenance messages CABIN ALT AUTO 1 or CABIN ALT AUTO 2 are received.
 3)  AC Power Loss: Loss of AC power for 2 seconds or longer causes automatic switchover to the standby controller. The CABIN ALT AUTO 1 or CABIN ALT AUTO 2 status and maintenance messages are received by EICAS. The selected controller takes control and the EICAS messages disappear when power is restored. The AUTO INOP light comes on and a level B EICAS message appears, CABIN AUTO INOP, if both controllers lose power. The AUTO INOP light and EICAS message remain on when the MAN mode is selected.
 4)  GUN 001-005; If both main AC-power channels are lost, the cabin pressure must be controlled manually.
 5)  GUN 006-999; If both main AC-power channels are lost, power will be supplied by the hydraulic motor-driven generator. Thus, the cabin pressure system will continue to operate automatically.
If the selector panel, outflow valve actuator or selected
 controller have any faults, the standby controller takes
 control and the respective CABIN ALT AUTO 1, or CABIN ALT AUTO
 2 status and maintenance messages are received.
 EFFECTIVITYùùùùùùùùùùùùùùùùùùùùùùùùùùùùùù. ú

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 ALL  ú ú 13 Page 12 ú Jan 28/02
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A

757
MAINTENANCE MANUAL

 (i)  
GUN 001-003, 008-999; If the cabin altitude goes above 10,000 feet an EICAS warning message, CABIN ALTITUDE, is displayed (Ref 21-33-00).

 (j)  
GUN 004-007; The EICAS warning message CABIN ALTITUDE will be displayed if one of these conditions occurs (Ref 21-33-00): 1) The high-altitude-landing switchlight is selected off and

 the cabin altitude goes above 10,000 feet.
 2)  The high-altitude-landing switchlight is selected ON and the cabin altitude goes above 14,500 feet.
 3)  The high-altitude-landing switchlight is selected off when the cabin altitude is above 10,000 feet and the cabin altitude goes below 10,000 feet and then again goes above 10,000 feet.
 (2)  
　
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