787 Flight Crew Operations Manual
DO NOT USE FOR FLIGHT
Air Systems Chapter 2
Pressurization System Description Section 30
Copyright © The Boeing Company. See title page for details.
D615Z003-TBC 2.30.1
2.30 Air Systems-Pressurization System Description
Air Systems30 Pressurization System DescriptionPressurization System Description
Introduction
Cabin pressurization is controlled by regulating the discharge of conditioned cabin
air through the outflow valves.
Two outflow valves are installed: one forward and one aft. Normally, the outflow
of cabin air is split equally between these two outflow valves. Cabin altitude and
full ventilation rates can be maintained by either valve.
Positive and negative pressure relief valves protect the fuselage against excessive
pressure differential.
The pressurization system has automatic and manual operating modes. Other than
accomplishing normal procedures for entering FMC data, no specific flight crew
action is required for fully automatic operation.
Pressurization System Automatic Operation
In flight, the Cabin Pressure Control System (CPCS) operates in a climb mode, a
cruise mode, or a descent mode.
The pressurization system uses ambient pressure and flight plan data from the
FMC to calculate a cabin pressurization schedule. The schedule provides a
comfortable cabin climb to cruise altitude.
For takeoff, the system supplies a small positive pressurization prior to rotation to
cause a smooth cabin altitude transition to the cabin altitude climb schedule.
In climb mode, cabin altitude increases on a schedule related to the airplane climb
rate and flight plan cruise altitude. When the FMC climb path has a planned level
segment, it is included in the total time required for the airplane to reach the top
of climb. Cabin altitude continues to increase during the planned level segment.
For unplanned level segments or when VNAV is disengaged, cabin altitude
remains constant as long as airplane altitude is not changing. When the airplane
climb flight path is above the FMC climb path and maximum cabin pressure
differential is reached during the climb, cabin rate then becomes a function of
airplane climb rate so maximum cabin differential pressure is not exceeded.
If cruise altitude is unavailable from the FMC in AUTO, the default cruise altitude
is 43,000 feet.
In the cruise mode, maximum cabin altitude is no more than 6,000 feet. The
pressurization system enters descent mode after airplane descent has been
initiated.
February 13, 2009
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