Flight Crew Air Transport Pilot (ATP)
Aircraft Equipment Problem Critical
Flight Crew FLC complied w / Automation / Advisory; Flight Crew Returned To Departure Airport
Aircraft
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.
[Report narrative contained no additional information.]
B737 crew reported loss of pressurization shortly after level off. Crew executed an emergency descent; complied with procedures; and returned to departure airport.