A disintegrated steel spring inside a carbon seal allowed oil to leak and caused smoke to fill the cockpit and cabin of a Nanaimo bound flight in March, according to a Transportation Safety Board (TSB) report.
WestJet Encore flight 3161, on a Bombardier Dash 8 Q400 turboprop, was nearing Nanaimo Airport at about 12:30 p.m. at 2,000 feet from Vancouver when the flight crew noticed smoke in the cockpit, and then smoke appeared in the cabin shortly after.
The TSB says after a teardown and inspection of the plane’s two Pratt & Whitney Canada (PWC) turboprop engines, an inspection revealed a disintegrated wave washer, which allowed oil to leak past the carbon seal and enter the compressor airstream and cabin pressurization system.
The two engines supplied air for cabin pressurize.
The TSB says a significant amount of oil was seen on the outboard side of the left engine and in the engine’s air-intake sections after it landed.
Because of previous 2.5 bearing carbon seal failures, PWC issued a service bulletin in Oct. 2016 and revised it in Jan. 2018, recommending operators replace the seal “with one that has an increased minimum spring load to prevent potential spinning of the air/oil bearing seal ring.”
Operators were recommended to comply to the bulletin when the subassembly was disassembled and there is access to the necessary part, which was not performed on the WestJet plane in Nanaimo since it wasn’t due for an overhaul.
PWC developed a new oil analysis technology to detect any carbon seal failure for operators who have not yet carried out the bulletin recommendation.
The March 20 flight had 56 passengers and four flight crew onboard and they were evacuated onto the runway shortly after landing and no injuries were reported.
The investigation showed the flight crew immediately followed proper procedures, including putting on oxygen masks, declaring an emergency with Air Traffic Services (ATS) and continuing the plane’s approach to Nanaimo.
Data from the flight recorders showed no warnings or alarms were received by the crew, other than a smoke detector in the on-flight bathroom, before or after smoke appeared in the plane.
The flight data recorder showed both engines appeared to be operating normally throughout the flight.
The TSB added ATS and airport personnel also responded in a timely manner, which led to a positive outcome on the ground.