What happened
On 25 March 2023, a Link Airways Saab 340B, registered VH-VEZ, was performing a commercial passenger flight from Canberra to Sydney. During the initial climb, the flight crew observed the cabin altitude rising to 6,500 ft, significantly higher than normal. While the pressurisation system was correctly configured and no specific warnings were triggered, the cabin manager reported a loud whistling noise emanating from the forward left door.
To manage the situation, the crew leveled the aircraft at 12,000 ft and eventually requested a descent to 10,000 ft to maintain a stable cabin altitude. To mitigate passenger discomfort caused by the whistling noise, the crew also reduced the airspeed to a maximum of 200 kts. The flight landed safely at Sydney Airport with 0 fatalities and 0 injuries.
The investigation
The investigation focused on why the aircraft's pressurisation integrity was compromised. It was established that on the evening of 24 March 2023, a 15 cm section of the door seal seat had broken away. The terminating captain misidentified this component as a piece of cosmetic door trim. Using the company's non-safety of flight defect deferral process, the crew consulted with maintenance via telephone, and the defect was officially deferred for up to 120 days.
On the morning of the incident, the incoming crew discovered an additional 10 cm section of the broken door seal seat. They mistakenly believed this was the same piece of trim that had been previously deferred and therefore deemed the aircraft serviceable. The investigation found that the combined effect of these two separate broken sections of the seal seat prevented the aircraft from maintaining normal cabin pressure.
Findings
- The primary cause was the misidentification of the cabin door seal seat as cosmetic door trim, which led to the incorrect application of the defect deferral process.
- A second broken section of the seal seat was misidentified as the previously deferred item, contributing to the failure of the pressurisation system.
- Communication gaps between the flight crew and maintenance engineers regarding the nature of the defect allowed an unserviceable aircraft to fly.