.
DC – outflow valve operates from DC power

.
all auto and standby circuits bypassed

CHECK – Tests auto failure function of auto system.

Flight /Ground Switch
AUTO mode –
.  
GRD – on the ground, drives the pressurization outflow valve full open at
a controlled rate and depressurizes the airplane. After takeoff, inhibited;
functions the same as FLT position

.  
FLT – on the ground, pressurizes the cabin to approximately (-200ft)
below airport elevation. After takeoff, cabin pressure is automatically
controlled in climb and descent as a function of airplane altitude. In
cruise, cabin pressure is held constant.

STANDBY mode –
.  
GRD – on the ground, drives outflow valve open at the rate selected by
the Cabin Rate Selector. After takeoff, inhibited; functions the same as
FLT position

.  
FLT – pressurizes the airplane at a rate selected by the Cabin Rate
Selector to the cabin altitude selected on the Cabin Altitude Indicator
(normally -200ft below takeoff field elevation).

Cabin /Flight Altitude (CAB ALT)(FLT ALT) Placard
Used to determine setting for cabin altitude when operating in standby and manual modes.
Air Systems -Controls and Indicators

Cabin Pressurization Panel (Airplanes with DCPCS)

AUTO FAIL Light
Illuminated (amber) – automatic pressurization system failure detected:
.
indicates a single controller failure when ALTN light is also illuminated

.
indicates a dual controller failure when illuminated alone.

OFF Schedule (SCHED) DESCENT Light
Illuminated (amber) – airplane descended before reaching the planned cruise altitude set in the FLT ALT indicator.

Flight Altitude (FLT ALT) Indicator
.
indicates selected cruise altitude

.
set before takeoff.

Copyright . The Boeing Company. See title page for details.
2.10.10  December 7, 2001

Air Systems -Controls and Indicators 737 Operations Manual

Flight Altitude Selector
Rotate – set planned cruise altitude (-1,000 ft. to 37,000 ft. in 500 ft. increments).

Landing Altitude (LAND ALT) Indicator
.
indicates altitude of intended landing field

.
set before takeoff.

Landing Altitude Selector
Rotate – select planned landing field altitude (-1,000 ft. to 14,000 ft. in 50 ft. increments).

MANUAL Light
Illuminated (green) – pressurization system operating in the manual mode.

Alternate (ALTN) Light
Illuminated (green) – pressurization system operating in the alternate automatic mode:
.  
Illumination of both ALTN and AUTO FAIL lights indicates a single
controller failure and automatic transfer to ALTN mode

.
pressurization mode selector in ALTN position.

Outflow VALVE Position Indicator
. indicates position of outflow valve
. operates in all modes.

Outflow Valve Switch (spring–loaded to center)
CLOSE – closes outflow valve electrically with pressurization mode selector in MAN position
OPEN – opens outflow valve electrically with pressurization mode selector in MAN position.

Pressurization Mode Selector
AUTO – pressurization system controlled automatically
ALTN – pressurization system controlled automatically using ALTN controller
MAN –
.
pressurization system controlled manually by outflow valve switch

.
both auto controllers bypassed.

Air Systems -Controls and Indicators 737 Operations Manual

Cabin /Flight Altitude (CAB ALT)(FLT ALT) Placard
Used to determine setting for cabin altitude when operating in manual mode.
Air Systems Schematic
TO LEFT
SIDEWALL RISER
FROM
RECIRC

TO RIGHT
FAN

CONDITION:
ENGINES OPERATING BLEED AIR & SUPPLYING AIR CONDITIONED AIR CONDITIONING PACKS
Copyright . The Boeing Company. See title page for details.
2.10.12  December 6, 2002

737 Operations Manual

Introduction
Air for the bleed air system can be supplied by the engines, APU, or an external air cart/source. The APU or external cart supplies air to the bleed air duct prior to engine start. After engine start, air for the bleed air system is normally supplied by the engines.
The following systems rely on the bleed air system for operation:
.
Air conditioning/pressurization

.
Wing and engine thermal anti-icing

.
Engine starting
　
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