What happened
On 20 September 2017, a Cessna 525A Citationjet CJ2, registration G-SONE, was conducting a commercial passenger flight from Bristol Airport to Paderborn Lippstadt Airport, Germany. While the aircraft was climbing through FL200, the flight crew received a master warning indicating that the cabin altitude had exceeded 10,000 ft.
In response to the warning, the crew donned oxygen masks and began emergency procedures. Although the aircraft was initially cleared to descend to FL170, the cabin altitude continued to rise. Once the cabin altitude reached 12,500 ft, the onboard oxygen masks deployed automatically for the passengers. The crew subsequently declared an emergency to Air Traffic Control and descended the aircraft to FL080. The flight concluded with a safe landing back at Bristol Airport, with no injuries reported to the two crew members or six passengers.
The investigation
Following the event, the operator performed ground tests and a maintenance flight to investigate the pressurisation system. However, these examinations failed to identify any underlying fault, and the aircraft was subsequently returned to service.
Investigators also noted that the Cockpit Voice Recorder (CVR) did not contain a recording of the incident. This was due to a failure to take immediate action to preserve the data following the occurrence. Under relevant aviation regulations, the commander is responsible for ensuring that CVR and FDR records are preserved following a reportable incident.
Findings
- The aircraft experienced a loss of cabin pressure control during the climb.
- Post-flight maintenance and testing could not replicate or identify the specific cause of the pressurisation malfunction.
- The CVR recording was unavailable because the data was not preserved following the incident.