(b) Ground 1) Ground mode is active when both air/ground signals indicate airplane on ground and the system has not entered takeoff mode.
 2)  In ground mode, the outflow valves and the forward overboard valve are driven most of the way open to maintain cabin pressure approximately at ambient pressure.
 (c)  
Takeoff 1) The CPCS switches from ground mode to takeoff mode when the FMC indicates that groundspeed is greater than 65 knots.

 2)  In takeoff mode, the forward overboard valve is shut and the outflow valves are positioned to pressurize the cabin slightly.

 (d)  
Climb

 1)  Climb mode is entered from ground or takeoff mode when one or both of the air/ground signals indicate that the airplane is in the air. Climb mode is entered from other modes whenever the airplane ascends more than 500 feet.
TAKEOFF ALTITUDE

LANDING ALTITUDE

TAKEOFF BEGIN BEGIN  TOUCHDOWN
CRUISE DESCENT
GROUNDSPEED
>65 KNOTS

TIME

AIRPLANE
ALTITUDE

CABIN ALTITUDE

Example Flight Profile
Figure 3

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A
747-400
MAINTENANCE MANUAL

OUTFLOW VALVES LR OP

CL
MAN AUTO

CABIN PRESSURE SYSTEM:
CAB ALT 5000 RATE 125 LDG ALT 3000 AUTO ~P 7.0 CPC IN CONTROL A
OUTFLOW VALVES LR
0.45 0.45
MAN AUTO
ECS - AIR SUPPLY AND
CABIN PRESSURE SYSTEM
MAINTENANCE PAGE

AUXILIARY EICAS DISPLAY (2 PAGES SHOWN)
Cabin Pressure Control System EICAS Displays Figure 4
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747-400
MAINTENANCE MANUAL

(E1-3)

TIME FOR CLIMB, TIME FOR DESCENT, TIME TO START OF DESCENT,
CRUISE ALTITUDE, LANDING ALTITUDE, AUTOPILOT MODE,
VNAV MODE, FMC MASTER, GROUNDSPEED >65 KTS

CABIN ALTITUDE, LANDING ALTITUDE, AIRPLANE ABOVE 25,000 FT,
AIRPLANE ABOVE 15,000 FT, CRUISE CLAMP, DESCENT DETECT,
TWO HOURS BEFORE INITIAL DESCENT, MAINTENANCE DATA,
SRU FAULT TRANSFER

CPCS-DADC, FMC, CMC, and EIU Interface Schematic Figure 5
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MAINTENANCE MANUAL

L35041
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MAINTENANCE MANUAL

NOTE: LEFT OUTFLOW VALVE COMPONENTS SHOWN. V91 LEFT
SELECTOR PANEL (P5) RIGHT OUTFLOW VALVE COMPONENTS SIMILAR. OUTFLOW VALVE
Cabin Pressure Control System Manual Mode Schematic Figure 7
L32046
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 (e)
(f)
A
747-400 MAINTENANCE MANUAL
 2)  Climb mode normally operates in external climb, when data from the FMC's are available to the CPCS. Cabin pressure is targeted against a schedule based on ambient pressure.
　
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