Cessna 337 stalls and crashes in British Columbia mountain bowl

Casualties unknown • S almo, British Columbia, 11 nm SE, CA

A fire-patrol Cessna 337 crashed into a mountainside in British Columbia, resulting in two fatalities after the aircraft stalled during a steep turn.

What happened

On a summer afternoon in British Columbia, a Cessna 337 was conducting a scheduled fire-patrol mission for the provincial Forest Service. The flight, crewed by a pilot and an observer, was tasked with monitoring the southeast region for signs of smoke or wildfire. The aircraft had departed from Nelson earlier that day and was flying a route designed to detect potential threats.

At approximately 15:11 PDT, the pilot radioed the Fire Centre dispatcher to report the aircraft's position near Salmo. Shortly thereafter, witnesses observed the aircraft climbing through a valley at a low altitude. As the aircraft reached the end of the valley, it attempted a steep left turn around a knoll. During this maneuver, the aircraft struck the side of a steep mountain bowl at the 5,800-foot level. The impact was severe, causing the aircraft to flip onto its back and resulting in two fatalities. There was no fire at the crash site.

The investigation

The investigation examined the terrain, aircraft performance, and the pilot's flight path. Investigators analyzed the topography of the accident site, noting that the valley's shape created a visual illusion where the path appeared to continue around a knoll, masking the steep mountain walls of the bowl until the turn was nearly complete.

Technical assessments focused on the aircraft's performance under the prevailing environmental conditions. On the day of the accident, temperatures were high, reaching approximately 30°C. Investigators calculated that the aircraft's maximum rate of climb was significantly reduced due to the combination of high altitude and high ambient temperature. Furthermore, the investigation reviewed the pilot's experience and the aircraft's maintenance history, finding no evidence of mechanical failure or system malfunction prior to the crash.

Findings

  • The terrain features created a visual illusion that a safe exit route existed through the end of the valley.
  • High ambient temperatures and the aircraft's operating altitude resulted in reduced climb performance.
  • The pilot entered a steep bank to avoid the rising terrain, which increased the aircraft's stall speed.
  • The aircraft stalled during the turn at an altitude that provided insufficient margin for recovery before striking the mountainside.

Probable cause

The aircraft stalled during a steep maneuver to avoid rising terrain at an altitude that left the pilot with no opportunity to recover, a situation exacerbated by reduced climb performance due to high temperature and altitude.

Frequently asked questions

What happened in the 1997-08-03 Cessna 337D Super Skymaster C-FYOC accident near S almo, British Columbia, 11 nm SE, CA?

A fire-patrol Cessna 337 crashed into a mountainside in British Columbia, resulting in two fatalities after the aircraft stalled during a steep turn.

What aircraft was involved and where did it happen?

The accident on 1997-08-03 involved a Cessna 337D Super Skymaster C-FYOC, operated by Nelson Mountain Air Limited, at S almo, British Columbia, 11 nm SE, CA.

What was the probable cause of the accident?

The aircraft stalled during a steep maneuver to avoid rising terrain at an altitude that left the pilot with no opportunity to recover, a situation exacerbated by reduced climb performance due to high temperature and altitude.

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