Story updated on 29 January to note that Porter Airlines is also modifying its Q400s and on 7 February to include more comments from the TSB.
WestJet is making modifications to its Bombardier Q400 turboprop fleet to prevent an issue that has caused at least three recent in-flight Q400 depressurisations.
One of those incidents involved a WestJet Encore aircraft and two involved Porter Airlines' Q400s, and all three apparently stemmed from cargo door handles not being properly stowed.
"Bombardier has released a recommended modification to fix the issue," WestJet tells FlightGlobal. "WestJet Encore is completing this modification to the fleet and to-date more than half of our fleet has been modified."
WestJet's regional unit Encore operates 47 Q400s, according to Flight Fleets Analyzer.
"Although this was human error, it is a known issue on the Bombardier Q400," WestJet adds. "Transport Canada has determined that there is no risk to safety and the decision to complete the modification is at each company’s discretion."
WestJet declines to provide more details about Bombardier's recommendations, such as when Bombardier issued them.
The Montreal airframer did not immediately respond to questions about the recommendations, but says three recent depressurisations involved cargo door "handles that were not stowed properly and popped open."
"The door seal would deflate as if someone was opening the cargo door, as the system was designed," Bombardier says. "No problems were noted with the door handle in any of these three cases."
Transport Canada is "evaluating the situation. The department will not hesitate to take action should a safety concern be identified", the regulator says.
The most recent in a string of similar events happened on 17 January and involved an Encore Q400 that had not yet undergone WestJet's modifications, the airline says.
"Flight 3265 from Calgary to Kelowna did experience a loss of pressure due to [an] incorrectly stowed door handle," WestJet says.
During cruise, pilots of that Q400 (registration C-FWEP) received a "fuselage door warning light", says the Transportation Safety Board of Canada's daily aviation incident report. "Subsequently, a loud bang was heard and pressurisation was lost during the descent."
After declaring an emergency and landing safely, maintenance personnel "found the lateral door handle in the extended position," the TSB says. "The door handle had not been secured properly."
That event followed two similar 2018 incidents involving Porter Q400s. In August last year a Porter Q400 depressurised at 4,000ft, and in October 2018 a Porter Q400 depressurised at 12,000ft, the TSB has reported.
"This situation occurs periodically, always during the climb stage of flight in our experience," Porter told FlightGlobal last year. "It is considered to be primarily an operational and passenger inconvenience, but not a significant safety issue."
"Our maintenance team will replace door handles, if deemed necessary, and door operation procedures for ground staff are consistently emphasised," the airline added.
Bombardier adds that the "Q400 aircraft has been designed to be robust and reliable in consideration of the high-cycle demands of regional airlines, and was designed to comply or exceed all airworthiness certification requirements".
Update: Porter tells FlightGlobal on 29 January it is also making Q400 modifications.
"We are in the process of modifying the door handles as outlined in the recommendation. The work began this month," the carrier says. "The work will be completed across our 29 aircraft during scheduled maintenance intervals in the coming weeks."
Update on 7 February: The TSB says 19 incidents involving similar Q400 cargo door handle issues have occurred since 2005, or roughly 1.4 annually. "All these events are very similar in nature, in that the baggage door handle was not stowed properly," the TSB says, adding that Bombardier documents say the incidents required no maintenance actions. When the issue occurs, the Q400 has a system that depressurises the aircraft for safety reasons.