Porter Airlines is replacing door seals on De Havilland Canada Dash 8-400 turboprops to address the type of rapid cabin decompression on 17 July, the Toronto-based airline says.
The cause of that decompression differs from a cargo door handle issue that has caused inflight depressurisations of several other Dash 8-400s recently, Porter adds.
The July depressurisation involved a Porter Q400 headed from Toronto to Boston. After the cabin lost altitude, the pilots descended to 10,000ft, determined the aircraft had no structural damage and continued to Boston, where they landed safely, according to an incident report from the Transportation Safety Board of Canada.
An inspection determined the aircraft's "aft baggage blowout panel was loose", the report says.
"This situation related to an imperfection in the door seal, which caused the panel to move," Porter tells FlightGlobal. "The system worked as intended to equalise pressure in different areas of the aircraft."
Porter "has a proactive programme to replace door seals, although there is no required timeframe for doing so," the airline adds. "The failure rate is extremely low."
The airline describes the door seal replacement work as a part of its normal, ongoing maintenance practices, not a response to a single incident.
De Havilland says the incident's "root cause was found to be a damaged aft cargo door seal, which would have been replaced."
"We are supporting Porter to resolve these technical issues, recommending a pressure decay check and have suggested regular inspections of the door seals to ensure they are in good condition in order to minimise events such as these," De Havilland adds.
Canadian aviation regulatory Transport Canada "is aware of the recent occurrence on a Porter Airlines Q400, and is working with the manufacturer to determine if an unsafe condition is present," it tells FlightGlobal.
Porter says that Transport Canada has not issued directives related to the door seal issue.
Porter stresses the 17 July incident "is different" from a cargo door handle issue that has caused inflight depressurisations of at least three other Dash 8-400s, including two Porter and one WestJet Encore aircraft, in the last year.
Porter and WestJet have said they are making modifications to their fleets to address the cargo door handle issue.
Story updated on 6 August to note that Porter's door seal replacement work is a part of its established Dash 8-400 maintenance programme. The door seal replacement work has been ongoing, and did not come in response to the 17 July depressurisation.