Date: 201304
Local time of day: 0001-0600
Location: ZOA.ARTCC, CA
Flight conditions: VMC
Aircraft: A320
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Cruise
Airspace: Class A ZOA
ATC / advisory: Center ZOA
Aircraft component: Pressurization Control System
Component problem: Malfunctioning
Reporter organization: Air Carrier
Reporter function: Pilot Not Flying; First Officer
Second reporter function: Pilot Flying; Captain
Anomaly: Aircraft Equipment Problem Less Severe
Detector: Automation Aircraft Other Automation; Person Flight Crew
When detected: In-flight
Result: Flight Crew Overcame Equipment Problem; General Declared Emergency
Contributing factors: Aircraft
Primary problem: Aircraft

Narrative: About 30 minutes into the flight we experienced an emergency descent ECAM at FL370. We accomplished the immediate action items; donned oxygen masks and declared an emergency. We initiated a descent to 10;000 FT. As we continued with the ECAM the pressurization stabilized at a normal position. We quickly assessed that the cabin had never exceeded approximately 8;000 FT. Since the aircraft was stable we agreed that there was no need to continue down to 10;000 FT. We coordinated with ATC to level at FL250. We called the flight attendants and they said everything in the cabin was fine and the passengers hardly noticed anything. We then continued with SOP. We referenced the flight manual because the ECAM was complete and we were left with a pressurization system 2 failure. The Flight Manual states that if CPC 2 fails the number 1 system will pick up the load. That appeared to be what happened. After a lengthy discussion and a systems review we agreed that there must have been a system delay in the transfer of CPC control from system 2 to system 1 thereby leading to a partial loss of pressurization resulting in the ECAM. We then discussed the situation with Dispatch and Maintenance. After a lengthy discussion we all agreed that continuation to destination at FL250 was the best course of action. We terminated the emergency with ATC. Finally we made a PA giving a brief description of events to the passengers.


Second narrative: Shortly after level off in cruse an ECAM was annunciated depicting loss of cabin pressure and to initiate emergency descent. Both pilots noticed a small change in cabin pressure in the inner ear but not dramatic. The ECAM warning was silenced and the Captain began the emergency descent profile while the Copilot informed ATC and the cabin. Noting that the Cabin Pressure was still less than 10;000 FT and the situation was not a rapid decompression; a controlled descent was performed and not at maximum IAS. The ECAM steps were completed during the descent at about FL270 and automatic cabin pressure control was regained. Screens indicated a loss of cabin pressure number 2 controller and control was taken over by the number 1 controller. Cabin pressure was noted by the crew to be stable at about 7;000 to 8;000 FT. After checking all cabin pressure systems the crew requested a level off at FL250. A conference call was placed to Dispatch and Maintenance and the decision to continue was made in light of the only item lost was Cabin Press Controller 2. It was assessed that there was a temporary loss of pressure while cabin pressure control was automatically transferred to the number 1 system. Considering the aircraft maintenance status; weather at destination and all en route alternates; and fuel; it was decided to proceed to destination but remain at FL250 as a precaution.


Synopsis: A320 flight crew experiences a cabin pressurization anomaly at FL370 and initiates a descent. With the automated controller switching to CPC 1 and the cabin pressurization remaining below 10;000 FT; the crew elects to continue to destination and land uneventfully.