Narrative:

This was the aircraft's first revenue flight after undergoing a heavy maintenance check in tampa. During preflight, some minor maintenance was required on some previous mco's as well as some new write-ups. Preflight, taxi, takeoff, climb, and leveloff were normal. A few mins after leveloff at FL350, the master caution light and the overhead light on the master caution enunciator panel illuminated. The passenger oxygen 'on' light on the overhead panel was found to be illuminated. Cabin altitude was found to be approximately 15000 ft, with the cabin climbing at approximately 300 FPM. The automatic fail light on the pressurization control panel was illuminated. The cabin altitude warning horn failed to sound at 10000 ft cabin altitude. The standby light on the pressurization control panel was not illuminated until the pressurization controller was switched to the standby mode. An emergency was declared, and all applicable checklists were performed. During descent, a return to dfw was coordinated with ATC. An attempt was made to contact the dispatcher through atl radio, but we were unable to contact atl radio. After leveling off at 7000 ft, the right pack air mix valve was observed to be in the warm position and would not respond to temperature control inputs. The left pack was put in high and the right pack was shut off in order to control cabin temperature. During the return to dfw, the approach, landing, and taxi were normal. The dfw chief pilot met the crew at the gate and cleared us to continue the trip. Supplemental information from acn 564711: after leveling at FL350, the automatic mode of the cabin pressurization controller failed. An emergency was declared and emergency descent and automatic pressurization failure checklists were accomplished.

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Original NASA ASRS Text

Title: A B737-300 CREW, AFTER LEVELING AT FL350, EXPERIENCED A LOSS OF CABIN PRESSURE, AND INITIATED AN EMER DSCNT TO 7000 FT AND A RETURN TO DFW.

Narrative: THIS WAS THE ACFT'S FIRST REVENUE FLT AFTER UNDERGOING A HVY MAINT CHK IN TAMPA. DURING PREFLT, SOME MINOR MAINT WAS REQUIRED ON SOME PREVIOUS MCO'S AS WELL AS SOME NEW WRITE-UPS. PREFLT, TAXI, TKOF, CLB, AND LEVELOFF WERE NORMAL. A FEW MINS AFTER LEVELOFF AT FL350, THE MASTER CAUTION LIGHT AND THE OVERHEAD LIGHT ON THE MASTER CAUTION ENUNCIATOR PANEL ILLUMINATED. THE PAX OXYGEN 'ON' LIGHT ON THE OVERHEAD PANEL WAS FOUND TO BE ILLUMINATED. CABIN ALT WAS FOUND TO BE APPROX 15000 FT, WITH THE CABIN CLBING AT APPROX 300 FPM. THE AUTO FAIL LIGHT ON THE PRESSURIZATION CTL PANEL WAS ILLUMINATED. THE CABIN ALT WARNING HORN FAILED TO SOUND AT 10000 FT CABIN ALT. THE STANDBY LIGHT ON THE PRESSURIZATION CTL PANEL WAS NOT ILLUMINATED UNTIL THE PRESSURIZATION CONTROLLER WAS SWITCHED TO THE STANDBY MODE. AN EMER WAS DECLARED, AND ALL APPLICABLE CHKLISTS WERE PERFORMED. DURING DSCNT, A RETURN TO DFW WAS COORDINATED WITH ATC. AN ATTEMPT WAS MADE TO CONTACT THE DISPATCHER THROUGH ATL RADIO, BUT WE WERE UNABLE TO CONTACT ATL RADIO. AFTER LEVELING OFF AT 7000 FT, THE R PACK AIR MIX VALVE WAS OBSERVED TO BE IN THE WARM POS AND WOULD NOT RESPOND TO TEMP CTL INPUTS. THE L PACK WAS PUT IN HIGH AND THE R PACK WAS SHUT OFF IN ORDER TO CTL CABIN TEMP. DURING THE RETURN TO DFW, THE APCH, LNDG, AND TAXI WERE NORMAL. THE DFW CHIEF PLT MET THE CREW AT THE GATE AND CLRED US TO CONTINUE THE TRIP. SUPPLEMENTAL INFO FROM ACN 564711: AFTER LEVELING AT FL350, THE AUTO MODE OF THE CABIN PRESSURIZATION CONTROLLER FAILED. AN EMER WAS DECLARED AND EMER DSCNT AND AUTO PRESSURIZATION FAILURE CHKLISTS WERE ACCOMPLISHED.

Data retrieved from NASA's ASRS site as of July 2007 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.