What happened
On November 18, 2020, a Cessna 525 A (registration G-TWOP) was operating a flight from Jersey, Channel Islands, to Brno Tuřany Airport, Czech Republic. While descending through FL 380, the crew and a passenger experienced a rapid change in cabin pressure and an increase in cabin altitude.
At 10:02 UTC, approximately 18 NM south of the VOZ radio beacon, the flight crew declared a PAN-PAN emergency and requested an emergency descent to FL 100. During the descent, the passenger oxygen masks automatically deployed. The crew subsequently descended to FL 130 and eventually to FL 90 to stabilize the cabin environment. The aircraft arrived at Brno Tuřany at 10:28 UTC and landed safely. No injuries were reported, and no damage to the aircraft or third-party property occurred.
The investigation
The ÚZPLN investigation utilized crew statements, operator information, and findings from the maintenance organization that performed subsequent repairs. The investigation examined the aircraft's pressurization system, which is fully automatic and managed by a digital control unit. This unit regulates cabin pressure based on flight management system (FMS) data, including takeoff and landing altitudes.
Post-flight inspections by a maintenance organization identified a technical malfunction within the digital control unit. The investigation also reviewed the crew's adherence to emergency procedures, noting that the crew followed the Flight Manual's abnormal procedures, including the use of oxygen masks and the execution of an emergency descent.
Findings
- The primary cause of the incident was a technical failure of the digital control unit of the cabin pressurization system.
- This failure led to a loss of cabin pressure and a corresponding increase in cabin altitude.
- The crew and passenger correctly utilized oxygen masks following the automatic deployment of the passenger oxygen system.
- The crew's actions were in accordance with the established emergency procedures for the Cessna 525 A.