(a)  
After detecting a 1000 foot airplane descent, the controller unclamps the autoschedule. The cabin pressure rate descends with the airplane descent schedule or at the selected autorate limit, whichever is less.

 (b)  
When the cabin reaches the landing altitude minus 100 ft, (the controller reads the landing (field) altitude as 100 ft below the actual landing altitude selected at the pressurization control panel), the cabin holds that altitude and waits for the airplane to touchdown.

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MAINTENANCE MANUAL

 (9)  
Landing and Ground Test - Automode

 (a)  
On-ground signals from the air/gnd relays put the controller in the landing mode. Conflicting air/ground inputs will signal EICAS to display the status message AIR/GND DISAGREE. In the landing mode, the cabin depressurizes at 500 FPM, by setting the cabin pressure demand 1000 ft above the selected landing (field) altitude. The system remains in the landing mode for 40 seconds to allow for complete thrust reversal and to allow the outflow valve to reach the full-open position. The selected controller then enters the ground test mode and relinquishes control to the standby controller for approximately 30 seconds. During this 30 second period, the selected controller determines if a critical fault has been registered in the EAROM, and if EAROM check is successful the controller resumes control and enters the ground mode. The standby controller enters the ground test mode during the same 30 second period that it assumed control from the selected controller and tests the entire system for faults. The outflow valve moves toward the close position 2 seconds after the standby controller enters the ground test mode. This regulates the cabin rate to 300 fpm for 12 seconds (equivalent to 60 ft altitude decrease). The system then returns to the ground mode. This drives and holds the outflow valve open. The standby controller then releases control of the system back to the selected controller.

 (10)
 Manual Mode (Fig. 13)

 (a)  
If both controllers fail, the cabin pressurization system can be manually controlled from the flight deck. Placing the mode selector switch to MAN allows a momentary contact switch to directly control the outflow valve. In the manual mode, the 28 vdc motor powers the outflow valve. The outflow valve position indicator monitors valve movement.

 (b)  
Turning the momentary switch toward DESCEND closes the outflow valve and increases cabin pressure. Turning the switch toward CLIMB, opens the outflow valve and decreases cabin pressure.

 (c)  
GUN 001-003, 008-999; The manual mode circuit also contains a 11,000 ft aneroid switch. If the cabin altitude reaches 11,000 ft with the system in the manual mode, the aneroid switch closes. This allows 28 vdc to flow to the close windings of the outflow valve motor and automatically closes the valve.

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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
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CABIN PRESSURE SELECTOR PANEL
14,500 FT SWITCH FOR AIRPLANES WITH HIGH ALTITUDE AIRPORT CERTIFICATION
AIRPLANES WITH CABIN PRESSURE SELECTOR PANEL P/N S210T160-42,-52, OR -62
AIRPLANES WITH CABIN PRESSURE SELECTOR PANEL P/N S210T160-72
Manual Pressurization Operation Schematic Figure 13
A73157
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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
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MAINTENANCE MANUAL

 (d)  GUN 004-007; The manual mode circuit also contains a 14,500 ft aneroid switch. If the cabin altitude reaches 14,500 ft with the system in the manual mode, the aneroid switch closes. This lets 28 vdc flow to the close windings of the outflow valve motor and automatically closes the valve.
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