<< >> NASA ASRS Report 1347886, April 2016

B737 crew reported loss of pressurization shortly after level off. Crew executed an emergency descent; complied with procedures; and returned to departure airport.

Attributes
ACN	1347886
Time
Date	201604
Local Time Of Day	0601-1200
Place
Locale Reference	ZZZ.Airport
State Reference	US
Environment
Light	Daylight
Aircraft 1
Make Model Name	B737 Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Flight Phase	Cruise
Flight Plan	IFR
Component
Aircraft Component	Pressurization System
Person 1
Function	Captain Pilot Flying
Qualification	Flight Crew Air Transport Pilot (ATP)
Person 2
Function	First Officer Pilot Not Flying
Qualification	Flight Crew Air Transport Pilot (ATP)
Events
Anomaly	Aircraft Equipment Problem Critical

Narrative:

Shortly after level off at FL310; heard audible cabin altitude warning horn; accompanied by red cabin altitude annunciator. Ca and first officer immediately donned oxygen masks; established communications; and [advised ATC]. Ca executed an emergency descent to 10;000 ft MSL per qrc procedures while first officer performed cabin altitude warning/rapid depressurization qrc procedures. Upon level off at 10000 ft cabin stabilized (regained pressurization) in standby mode. Entered hold to burn off gas; run appropriate checklists; make additional PA to passengers; communicate with flight attendant's in what's format; advise dispatch of intentions; contact ops; get current ATIS; reset nav equipment; & returned to land. No illnesses or injury reported. After communicating with maintenance control post event; it is believed to be either a pressurization mode controller malfunction or an indicator fault.

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Original NASA ASRS Text

Title: B737 crew reported loss of pressurization shortly after level off. Crew executed an emergency descent; complied with procedures; and returned to departure airport.

Narrative: Shortly after level off at FL310; heard audible cabin altitude warning horn; accompanied by red cabin altitude annunciator. CA and FO immediately donned oxygen masks; established communications; and [advised ATC]. CA executed an emergency descent to 10;000 ft MSL per QRC procedures while FO performed cabin altitude Warning/Rapid Depressurization QRC procedures. Upon level off at 10000 ft Cabin Stabilized (regained pressurization) in Standby Mode. Entered hold to burn off gas; run appropriate checklists; make additional PA to passengers; communicate with FA's in What's format; advise Dispatch of intentions; contact ops; get current ATIS; reset nav equipment; & returned to land. No illnesses or injury reported. After communicating with Maintenance Control post event; it is believed to be either a Pressurization Mode Controller malfunction or an indicator fault.

Data retrieved from NASA's ASRS site and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.