What happened
On an evening flight departing Boundary Bay Airport, British Columbia, a Cessna 172M, registration C-GDPD, was conducting mountain flying instruction. The crew consisted of a flight instructor, a student pilot, and an observer. After performing practice maneuvers near Stave Lake, the aircraft entered the Tretheway Creek valley.
During the flight, the instructor reduced the throttle to idle to simulate an engine failure, prompting the student to perform a practice forced approach. The aircraft descended toward a meadow-like area at a height significantly below 500 feet above ground level. When the instructor took control to execute an overshoot, the aircraft was unable to clear the rising terrain. Despite applying full power and retracting flaps, the aircraft struck a hillside approximately 24 nautical miles north-northwest of Harrison Hot Springs. The impact destroyed the aircraft, though no fire occurred. The two occupants in the front seats sustained serious injuries, while the rear occupant suffered minor injuries.
The investigation
The investigation established that the aircraft was within weight and balance limits and had sufficient fuel for the planned mission. No mechanical failures or engine power losses were identified; in fact, propeller damage suggested the engine was producing significant power at the moment of impact. The aircraft appeared to be in controlled flight until it struck the terrain.
Investigators noted that the student pilot had been trained in forced-approach techniques on non-mountainous terrain, where the procedure involved descending until the instructor called for an overshoot. Because no specific briefing for mountain flying procedures was provided for this flight, the student followed that previous pattern. Furthermore, the investigation looked into environmental factors, such as the lack of visual cues in the shadowed, non-forested area and the impact of altitude and temperature on climb performance.
Findings
- The instructor failed to brief the student on specific forced-approach procedures for mountain terrain and did not intervene to prevent the student from gliding the aircraft toward rising terrain.
- The aircraft's ability to out-climb the terrain was degraded by its high weight, the altitude, and the outside air temperature, as well as aggressive maneuvering during an evasive turn.
- Shadows and a lack of distinct visual landmarks, such as trees, likely hindered the pilots' ability to accurately judge their height above the ground.
Safety action
Following the accident, Pacific Professional Visual Flight Training Ltd. implemented new safety protocols, including a prohibition on dispatching aircraft into mountainous regions during the evening and the establishment of specific safe flying limits for mountain operations.