Incident Details
On the morning of 25 March 2023, a Link Airways Saab 340B aircraft departed Canberra Airport for the first flight of the day. During the climb towards cruising altitude, the flight crew observed a cabin altitude of 6,500 ft, which was higher than normal. In response, the crew descended the aircraft and maintained an altitude below 10,000 ft for the remainder of the flight to Sydney Airport.
Investigation Findings
The Australian Transport Safety Bureau (ATSB) investigation determined that after the last flight on 24 March 2023, a broken section of the door seal seat was found. However, due to an incorrect assessment that the broken section was merely a piece of cosmetic trim, the off-going flight crew inappropriately applied the company’s non-safety of flight defect deferral process during a phone consultation with the continuing airworthiness maintenance organisation representative and a licenced aircraft maintenance engineer.
On the following morning, 25 March 2023, the on-coming flight crew noted an additional section of broken door seal seat. This was misidentified as the previously deferred defect, and the aircraft was assessed as serviceable for flight. The combined effect of the two sections of broken door seal seat resulted in the aircraft’s pressurisation system being unable to maintain normal cabin altitude in flight.
The ATSB noted that while a piece of door cosmetic trim would be considered a deferrable defect, the door seal seat defect adversely affects aircraft airworthiness and is therefore not eligible to be deferred under the non-safety of flight defect (NSOFD) process. It was found that the existence of a second defect was not understood by the on-coming flight crew and was not identified until after the incident flight. The specific level of contribution of each broken section could not be determined, but it is likely that their combined effect was greater than either individual piece.
Corrective Actions
Following the occurrence, Link Airways provided retraining and guidance to the involved parties on the importance of accurate identification of cosmetic trim, including terminology and the level of detail required when raising defects. The internal investigation report was distributed to flight operations and maintenance personnel as a reminder to be aware of the risk of communication errors.
Safety Recommendations
The ATSB highlighted that communication between aircrew and maintenance engineers is critical to continuing airworthiness. Issues often arise due to differences in technical knowledge or language, time pressures, and remote communications. It recommended that aircrew and maintenance engineers remain vigilant of potential misunderstandings and use confirming techniques such as follow-up questioning, demonstration, or photos or video to ensure accurate communication. Additionally, they should include as much detail as practical when recording defects in technical logs to minimise ambiguity.