(a)  
With 115 Vac supplied to the airplane, the selected controller enters the standby mode and tests itself for faults. The controller reads the air/ground signal, establishes that the airplane is on the ground and enters the ground mode. If the controller receives conflicting air/ground status data, the EICAS status message AIR/GND DISAGREE will be displayed.

 (3)  
Ground Mode

 (a)  
In the ground mode, the controller drives the outflow valve to the full open position. This is done by setting a 15,000 ft cabin altitude demand (low pressure) and a 2000 FPM pressurization uprate limit. Three seconds after the outflow valve reaches full open, the controller removes the open drive command to prevent actuator heating. A throttle advance signal tells the controller to enter the takeoff mode.

 (4)  
Takeoff Mode

 (a)  
When the throttle is advanced beyond 10.5°, the controller enters the takeoff mode. The controller stores the existing cabin pressure as the takeoff field command. The controller sets the cabin altitude 70 ft below the takeoff field command, and limits the cabin pressurization uprate to 50 FPM while the downrate limit is set at the selected rate limit. During the takeoff roll, the forward door of the outflow valve produces a depressurizing effect around the valve. The valve moves toward close. If positive pressure occurs around the valve because of rotation, the outflow valve moves toward open. At rotation the air/ground signal puts the controller in the flight mode.

 NOTE: The throttle advance switches are part of the Autoflight
____ Microswitch Pack. The microswitches are adjusted per instructions contained in Microswitch Pack Maintenance Practices (MM 22-32-04).
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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A

757
MAINTENANCE MANUAL

Ground and Takeoff Mode
Figure 8

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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A

757
MAINTENANCE MANUAL

 (5)  
Autoschedule (Fig. 9)

 (a)  
The autoschedule is the desired cabin-to-ambient differential pressure, programmed into the controller, over different flight altitudes. The maximum cabin-to-ambient differential pressure is 8.6 psi under normal flight conditions. For normal airplane descent, cabin-to-ambient differential pressure is less than

 8.6 psi. The selected rate of pressurization limits the rate of cabin pressure change.
 (6)  
Climb - Automode (Fig. 10)

 (a)  
Typical takeoff - takeoff altitude lower than autoschedule cruise altitude. 1) At rotation, the controller reads the ambient pressure and

 creates an autoschedule cabin altitude demand. The controller compares the takeoff field altitude with the autoschedule command, and sets the cabin altitude demand to the takeoff field altitude. The cabin holds this takeoff field altitude while the airplane climbs until the autoschedule command intersects the takeoff altitude. The cabin then follows the autoschedule to the cruise altitude.

 (b)
Takeoff altitude higher than autoschedule cabin altitude.

 1)  At rotation, the controller sets the cabin equal to the takeoff altitude. In this case, the takeoff altitude is so high that the autoschedule never reaches the takeoff altitude. Therefore, the cabin remains at the takeoff altitude throughout initial climb until cruise, or until the airplane starts its descent.
 (7)  
Cruise - Automode

 (a)  
When airplane altitude does not change more than |250 ft for 1 minute, the controller enters cruise logic. The autoschedule command is clamped (fixed) and remains unchanged until the airplane climbs or descends 500 feet. Four general cabin altitude profiles occur in cruise. 1) Landing altitude above autoschedule but below takeoff

 altitude (Fig. 11, Detail A).
 a)  At cruise clamp, the controller sets the cabin demand to the landing altitude (landing altitude is higher than autoschedule). The cabin depressurizes to the landing altitude pressure from the takeoff altitude pressure at the selected autorate limit.
　
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