What happened
On June 30, 2000, an Airbus A321-231 operating a scheduled flight from Düsseldorf to Antalya experienced a serious cabin pressure malfunction while cruising at flight level 330. The event began with minor pressure fluctuations in the cabin, which were shortly followed by a rapid drop in pressure. This depressurization caused the cabin altitude to rise above 14,000 feet, triggering the automatic deployment of passenger oxygen masks.
The flight crew initiated an emergency descent procedure to reach a safe altitude. The aircraft subsequently diverted and landed safely at Vienna-Schwechat Airport. There were no injuries among the 214 passengers or the seven crew members on board, and the aircraft sustained no damage.
The investigation
The investigation focused on the malfunction of the cabin pressure regulation system. It was established that a faulty Cabin Pressure Controller (CPC) from the -9 series failed to properly manage the outflow valve (OFV). This malfunction caused the outflow valve to move into a fully open position, leading to the rapid loss of cabin pressure.
Investigators reviewed technical documentation, including Service Bulletins from Airbus Industrie and Nord Micro. The findings revealed that the -9 series CPCs were known to be prone to such failures, and a global retrofit program to replace them with the -10 series was already underway. Furthermore, the investigation examined the implementation of Airbus Operations Engineering Bulletin (OEB) 139/1, which provided specific procedures for managing this known issue.
Findings
- The primary cause of the depressurization was a malfunctioning Cabin Pressure Controller.
- The aircraft was still equipped with the older -9 series controller and had not yet been upgraded to the more reliable -10 series.
- The crew did not attempt to rectify the malfunction through manual intervention, despite manufacturer-recommended procedures.
- The specific procedures outlined in OEB 139/1 for addressing this failure were not sufficiently known within the airline or by the flight crew.
Safety action
Following the investigation, the BFU issued safety recommendation 06/2000. The recommendation stated that until the retrofit of the Cabin Pressure Controller to the -10 series is completed for A319, A320, and A321 models, the procedures described in Airbus Operations Engineering Bulletin 139/1 should be formally integrated into the relevant aircraft checklists.