B737 Undifferentiated or Other Model
Flight Crew Air Transport Pilot (ATP)
Flight Crew Last 90 Days 240; Flight Crew Total 23000; Flight Crew Type 11000
Training / Qualification; Troubleshooting; Situational Awareness; Human-Machine Interface
Aircraft Equipment Problem Critical
Flight Crew FLC complied w / Automation / Advisory; Flight Crew Returned To Departure Airport; General Declared Emergency; General Maintenance Action
Aircraft
After a normal takeoff; 25 NM east of the airport; while climbing through 13;000 feet the cabin altitude warning horn went off and the cabin showed 10;100 feet with a pip rate surge from 300 FPM to 1;500 FPM. The flight attendants in the aft galley reported an excessive noise level from the doors. We immediately notified ATC and descended back to 10;000 feet. The AUTOFAIL light was on; but went out back at 10;000 feet and the pip changes were normal; but the noise level only dropped by half in the aft galley according to the flight attendants. Therefore; in the name of safety and with most of the late night trip ahead of us; we decided to divert back into the departure airport for maintenance. The AUTOFAIL light again came on during the final approach phase and since we were out of position for a non-routine landing on 6L; we went around and completed an ILS approach to 6L. The AUTOFAIL light cycled on and off 2 more times. We made a routine safe; smooth overweight landing at 148.0 lbs. and wrote it up along with the auto fail pressurization. We checked the QRH Cabin altitude horn exceedence; AUTOFAIL light on intermittently; Off Schedule Descent and the unpressurized landing procedure; as a precaution; because of the intermittent nature of the pressurization controller/system and warning light. Maintenance was able to resolve the issues on the ground and we departed later and completed a routine flight.
During climb at 13;000 feet; a B737 Cabin Altitude Warning Horn alerted with the cabin at 10;100 feet; so the crew descend to 10;000 feet and with AUTOFAIL light cycling; declared an emergency and returned to the departure airport for an overweight landing.