B737-700
Flight Crew Air Transport Pilot (ATP)
Flight Crew Last 90 Days 128; Flight Crew Type 10000
Aircraft Equipment Problem Critical
Air Traffic Control Issued New Clearance; Flight Crew Diverted; Flight Crew Landed As Precaution; General Maintenance Action; General Declared Emergency
Aircraft
Cabin Altitude Warning horn at FL390; cabin altitude climbed to 14;000 FT after initiating emergency descent. Step-down altitudes coordinated with Center and with communication being lost at 10;000 FT. Relay aircraft passed frequency and communication reestablished. QRH Checklist accomplished with little to no control of pressurization system. Cabin altitude began coming down on emergency descent passing FL280. Divert decision due to proximity to ZZZ and unknown/uncontrollable nature of problem/pressurization.
We had a Cabin Altitude Warning horn at FL390. We had been at cruise altitude for several minutes. There were no associated warning lights. Cabin altitude showed climbing above 10;000 FT. We donned our oxygen masks; accomplished the appropriate memory items; declared an emergency; and initiated an emergency descent. Cabin Altitude Warning Horn Checklist was unable to stabilize the cabin altitude or regain the system. Once we were level at 10;000 FT; continued troubleshooting; seemed to indicate a left engine bleed valve malfunction. We decided to divert to ZZZ; as it was the closest major airport and were still uncertain as to the entire nature of the problem. Flight attendants and passengers were notified and updated; time permitting; throughout the emergency. The Captain accomplished the approach and landing. Fire crews confirmed no damage to the aircraft.
B737-700 flight crew experiences a cabin altitude warning horn at FL390 followed by an emergency descent and diversion to a suitable airport.