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'In-flight breakup' could have caused Fort Simpson plane crash: investigators

Plane was found missing left wing and tail section

Investigators with the Transportation Safety Board of Canada have located the wreckage of a plane crash in the N.W.T., and found evidence they say suggests the plane may have fallen apart mid-flight.

On June 25, N.W.T. Fire reported that a plane assisting with wildfire response had crashed the previous evening, killing its three occupants.

The aircraft had been working on a fire identified as FS009 — a naturally-caused fire discovered June 24 in the Martin Hills area near Fort Simpson.

Investigators with the TSB arrived on-site on June 26 to discover the wreckage was missing its left wing and tail section, including the horizontal and vertical stabilizers.

Jonathan Lee, the TSB's regional manager for western Canada, told CBC's The Trailbreaker on Monday that it was an "indication of an in-flight breakup."

A mid-air breakup like that suggests two possible causes, Lee said.

"Number one is the ultimate airload on the aircraft" — the physical forces exerted on the plane by the air flowing over it — "exceeded what it could hold or [is] designed to withstand," he said.

"The other is the materials in the aircraft are fatigued due to corrosion or age."

Lee said "at the moment," it's not clear what was the cause.

Investigators will be interviewing staff at Buffalo Airways, which operated the plane, to understand both the maintenance history of the plane and the training issued to the pilots.

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They will also be returning to the site to extract the wreckage, to have it analyzed by metallurgists in Edmonton.

The missing wing and tail section have still not been located, despite several hours of searching along the flight path, Lee said.

The crash site is "very challenging," Lee noted, because it's in an area of muskeg, with soft ground and lots of creeks and bodies of water nearby which make landing difficult.

The investigation was also stymied by encroaching wildfires, which prompted an evacuation order issued for Fort Simpson on Sunday night.

First wildfire evacuees from Fort Simpson arrive in Yellowknife

"The next step is getting the aircraft recovered," Lee said. "Given the current context with the wildfires, that timeline is unknown."

"Helicopters are going to be required to remove the aircraft, and of course those are in short supply," he said.

As a result, there is currently no timeline for a final ruling on the causes of the crash. The investigation is ongoing.