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 21-33-00
 ALL  ú ú 02 Page 2 ú Sep 20/89 
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details. 
A 
757 
MAINTENANCE MANUAL
STATIC PRESSURE SENSOR 
Cabin Pressure Indication System 
Figure 2
EFFECTIVITYùùùùùùùùùùùùùùùùùùùùùùùùùùùùùù. ú
 21-33-00
 ALL  ú 
 ú  02  Page 3 
 ú  Dec 20/87 
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details. 
A
757 
MAINTENANCE MANUAL
CABIN PRESSURE
Cabin Pressure Warning System
Figure 3 (Sheet 1)
EFFECTIVITYùùùùùùùùùùùùùùùùùùùùùùùùùùùùùù.
 GUN 001-003, 008-999 ú 21-33-00
 ú ú 03 Page 4 ú Sep 20/89 
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details. 
A 
757 
MAINTENANCE MANUAL
HIGH ALTITUDE LANDING SWITCH/LIGHT 
Cabin Pressure Warning System Figure 3 (Sheet 2) 
EFFECTIVITYùùùùùùùùùùùùùùùùùùùùùùùùùùùùùù. GUN 004-007 ú
 21-33-00
 ú ú 02 Page 5 ú Mar 20/93 
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details. 
A
757 
MAINTENANCE MANUAL
 A. GUN 001-003, 008-999;
_____________________
 Altitude Warning System
_______________________
 (1)  
If the cabin altitude climbs to 10,000 feet, the altitude switch closes, which supplies a ground to cause the high-cabin-altitude-warning signals to occur. If the cabin altitude goes below 10,000 feet, the altitude switch opens and the high-cabin-altitude-warning signals will go off. The high-cabin-altitude-warning signals are:
 (a)  
The CABIN ALTITUDE light on the P5 panel comes on.
 (b)  
The CABIN ALT light on the captains instrument P1 panel comes on.
 (c)  
A level A EICAS message, CABIN ALTITUDE, appears.
 (d)  
The aural warning siren sounds.
 NOTE: The aural warning siren can be silenced by pressing
____ the Master-Warning-and-Caution switch/light.
 B. GUN 004-007;
____________
 Altitude Warning System
_______________________
 (1)  
If the cabin altitude climbs to 10,000 feet, the altitude warning switch closes to supply a ground for the warning system. If the high-altitude-landing switchlight is selected off, the high-titude-sel/inop relay is relaxed to complete the circuit and cause the high-cabin-altitude-warning signals to occur.
 (2)  
If the high-altitude-landing switchlight is selected on, 28v dc power and ground are supplied through the switchlight to energize the high-altitude-sel/enable relay. When the sel/enable relay is energized, power is supplied to energize the sel/inop relay. When the sel/inop relay is energized, power is supplied to the cabin-high-altitude-warning switch. In this condition, if the cabin altitude goes above 14,500 feet, the switch will close to complete the circuit and cause the high-cabin-altitude-warning signals to occur.
 (3)  
If the cabin altitude is above 10,000 feet and the high-altitude-landing switchlight is selected off, the high-altitude-sel/enable relay will stay energized. When the sel/enable relay is energized, the high-cabin-altitude-warning signals will only occur if the cabin altitude goes above 14,500 feet. The sel/enable relay will stay energized as long as the cabin-altitude-warning switch supplies a ground (cabin altitude is above 10,000 feet). When the cabin altitude goes below 10,000 feet, the cabin-altitude-warning switch will open to cause the sel/enable relay to relax. With the sel/enable relay relaxed, the high-cabin-altitude-warning signals will occur when the cabin altitude goes above 10,000 feet.
 
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