Investigators say a fatal crash last April of a small plane on a training flight near Abbotsford, B.C., was likely caused by the pilot not following “best practices” for mountain flying.

The Transportation Safety Board report was issued Wednesday on the crash of the Cessna in the mountains near Chilliwack Lake, in B.C.’s Fraser Valley, killing the instructor and the student onboard.

The investigation showed the plane, operated by Chinook Helicopters, was on a training run when it crashed after slowing down dramatically while making a turn.

Investigators say the pilot did not use “all the lateral space available” in the valley when making the turn, which didn’t completely follow best practices, including flying along one side of the valley to allow for a safer turning radius.

The report says the plane’s speed dropped below the stall threshold during the turn, and flaps were not deployed to improve lift of the aircraft.

The Transportation Safety Board says pilots flying into mountainous areas are responsible for adequately preparing for such conditions, including specific training, as there is no Canadian regulatory requirement for pilots to receive that training.