Overview
On a training flight over mountainous terrain in British Columbia, a Cessna 172M (registration C-GDPD, serial number 17262636) was destroyed when it struck a hillside during a practice forced approach. The flight, which departed Boundary Bay Airport at 1848 Pacific daylight time, was intended for mountain flying instruction with a flight instructor, a student pilot, and a flight instructor trainee on board.
Accident Sequence
The aircraft flew northeast along its flight-plan route, conducting two practice precautionary approaches at an abandoned airstrip at the north end of Stave Lake and some confined-area turns. After entering the Tretheway Creek valley, the instructor reduced the throttle to idle and suggested a practice forced approach. The student executed a 180-degree turn and descended toward a meadow-like area. The aircraft descended below 500 feet above ground level, at which point the instructor took control to conduct an overshoot. Despite applying full power, selecting carburetor heat off, and fully retracting the flaps, the aircraft continued toward rising terrain. The instructor initiated an evasive left turn, during which the aircraft struck the hillside approximately 24 nautical miles north-northwest of Harrison Hot Springs. The accident occurred at about 1948.
Aircraft and Crew
The student pilot, in the left front seat, held a valid Canadian private pilot licence and had 78 hours of flight experience. The instructor, in the right front seat, held a commercial pilot licence with a Class 2 instructor rating and over 6000 hours, mostly as an instructor in Cessna 150 and 172 series aircraft. The rear-seat occupant, training to become a flight instructor, was observing. Both pilots were appropriately certified. The aircraft was within weight and balance limits, had sufficient fuel, and no mechanical malfunctions were found. The propeller damage indicated the engine was developing significant power at impact. The aircraft was in controlled flight until impact; no stall occurred. A post-crash fire did not occur, partly because the battery was ejected during the breakup.
Injuries and Rescue
The two front-seat occupants sustained serious injuries; the rear-seat occupant received minor injuries and was able to assist. The occupants manually activated the emergency locator transmitter, and a signal was reported at 2230. The aircraft was located by a search aircraft at 0230 the following morning. All three were evacuated by helicopter.
Findings
The Transportation Safety Board determined that the instructor did not brief the student on forced-approach procedures and allowed the descent to continue to a height from which the aircraft could not avoid rising terrain. Additionally, the aircraft was near gross weight, and the combined effects of altitude, outside air temperature, and aggressive manoeuvring degraded climb performance. Shadows and lack of visual cues in the accident area may have affected the pilots' height perception. As a result of the accident, the operator, Pacific Professional Visual Flight Training Ltd., ceased dispatching aircraft into the mountains in the evening and established safe flying limits for mountainous terrain.