B737 Cabin Pressurization Panel

Cabin Altitude & Cabin Pressure Control Panel

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.

Note: A panel failure detected after a DC power interruption will result in the display of “88888” or all dashes. If cabin altitude and cabin rate are normal, automatic control of cabin pressure is not affected by the failure.

Note: FLT ALT indicator failure may result in the display of non-numbers or a blank display. If the indicator cannot be changed by rotating the flight altitude selector, it may be necessary to monitor the pressurization system to ensure normal operation, especially during climb and descent.

Flight Altitude Selector

  • Rotate – set planned cruise altitude. (-1,000 ft. to 42,000 ft. in 500 ft. increments).

Landing Altitude (LAND ALT) Indicator

  • Indicates altitude of intended landing field,
  • Set before takeoff.

Note: A panel failure detected after a DC power interruption will result in the display of “88888” or all dashes. If cabin altitude and cabin rate are normal, automatic control of cabin pressure is not affected by the failure.

Note: LAND ALT indicator failure may result in the display of non-numbers or a blank display. If the indicator cannot be changed by rotating the landing altitude selector, it may be necessary to monitor the pressurization system to ensure normal operation, especially during climb and descent.

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.

Cabin / Flight Altitude (CAB ALT) (FLT ALT) Placard

  • Used to determine setting for cabin altitude when operating in manual mode.

CABIN Altimeter (ALT) / Differential Pressure (DIFF PRESS) Indicator

  • Inner Scale – indicates cabin altitude in feet.
  • Note: The CABIN ALT indicator can show a cabin altitude of less than 0 feet and reach the upper end of the cabin altitude scale. This can occur under the following conditions:
    • on the ground at airports close to or below sea level.
    • in flight when the cabin is pressurized below sea level.
  • Outer Scale – indicates differential pressure between cabin and ambient in psi.

CABIN Rate of CLIMB Indicator

  • Indicates cabin rate of climb or descent in feet per minute.

Altitude (ALT) HORN CUTOUT Switch

  • Push –
    • cuts out intermittent cabin altitude warning horn
    • altitude warning horn sounds when cabin exceeds 10,000 feet altitude.