Narrative:

Climbing out; we got a pack trip off on the right side that would not reset. We ran the QRH and determined we were maintaining pressure on one pack; so we continued to climb to FL390. At altitude we tried to reset again. It did reset for a few minutes then the pack tripped off again and wouldn't reset but the cabin altitude was good and remaining so. About 20 minutes later we got a cabin altitude warning light and intermittent horn. We donned oxygen masks; selected 100 percent; and established communications. I directed the first officer to run the qrc for warning horn (intermittent) or warning light and cabin altitude warning. Cabin altitude was uncontrollable; so I began a rapid descent while the first officer continued to complete the qrc and QRH checklists for the pressurization problems. I advised ATC that we were in a descent to 10;000 ft; that we were having an uncontrollable depressurization issue. The first officer then ran the qrc/QRH for rapid descent. Passing through about 20;000 ft; we saw that the cabin pressure was approaching 10;000 ft. At 16;000 ft (with the cabin below 10;000 ft) we came off oxygen and continued the descent to 10;000 ft. We discussed our options and decided to divert to [a nearby alternate]. The first officer had been communicating with the flight attendants from the beginning of the descent. The flight attendant's told us the masks had not dropped in the back and everyone was doing well. We told ATC that we wanted to divert. They gave us direct to the field. We called ops and told them what was going on and requested a patch to dispatch. Dispatch agreed with our plan. We made an uneventful approach and smooth landing. Emergency vehicles accompanied us to the gate. At the gate; maintenance met the aircraft and told us that the aircraft would be out of service for a while; and that the passengers would be put on another flight. Customer service took care of the passengers. I made write ups for the pack trip off; cabin altitude warning/uncontrollable pressurization; and overweight landing. The crew did a self-assessment and determined we were ok to continue with the rest of our crew day. I talked with maintenance control; dispatch; and the chief pilot about the details of the event.

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Original NASA ASRS Text

Title: B737-700 Captain reported diverting to an enroute airport after experiencing a loss of cabin pressure following issues with one of the packs.

Narrative: Climbing out; we got a Pack Trip Off on the right side that would not reset. We ran the QRH and determined we were maintaining pressure on one pack; so we continued to climb to FL390. At altitude we tried to reset again. It did reset for a few minutes then the pack tripped off again and wouldn't reset but the cabin altitude was good and remaining so. About 20 minutes later we got a Cabin Altitude warning light and intermittent horn. We donned oxygen masks; selected 100 percent; and established communications. I directed the FO to run the QRC for Warning Horn (Intermittent) or Warning Light and Cabin Altitude Warning. Cabin altitude was uncontrollable; so I began a rapid descent while the FO continued to complete the QRC and QRH checklists for the pressurization problems. I advised ATC that we were in a descent to 10;000 ft; that we were having an uncontrollable depressurization issue. The FO then ran the QRC/QRH for Rapid Descent. Passing through about 20;000 ft; we saw that the cabin pressure was approaching 10;000 ft. At 16;000 ft (with the cabin below 10;000 ft) we came off oxygen and continued the descent to 10;000 ft. We discussed our options and decided to divert to [a nearby alternate]. The FO had been communicating with the Flight Attendants from the beginning of the descent. The FA's told us the masks had not dropped in the back and everyone was doing well. We told ATC that we wanted to divert. They gave us direct to the field. We called Ops and told them what was going on and requested a patch to Dispatch. Dispatch agreed with our plan. We made an uneventful approach and smooth landing. Emergency vehicles accompanied us to the gate. At the gate; Maintenance met the aircraft and told us that the aircraft would be out of service for a while; and that the passengers would be put on another flight. Customer Service took care of the passengers. I made write ups for the Pack Trip Off; Cabin Altitude Warning/Uncontrollable Pressurization; and Overweight Landing. The Crew did a self-assessment and determined we were OK to continue with the rest of our Crew day. I talked with Maintenance Control; Dispatch; and the Chief Pilot about the details of the event.

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.