Incident Overview
A float-equipped airplane crashed while attempting to cross a mountain pass. The aircraft was following two other company airplanes through the pass. The first two pilots and their passengers reported visibility of five to seven miles, a 700-foot ceiling, clouds hanging on the mountainsides, and misty rain. The route required several turns within the pass. The pilot had not previously flown through the pass in marginal Visual Flight Rules (VFR) weather conditions.
After the first two airplanes successfully transited the pass, they lost radio contact with the accident pilot and did not see or hear from him again. The wreckage was later located at the head of an intersecting canyon, approximately two miles before the correct pass.
Aircraft Modifications and Equipment
The airplane had been modified with a Short Take Off and Landing (STOL) kit. Canadian certification flight tests determined that this modification eliminated the aerodynamic warning of impending stalls, thereby requiring the installation of an audible stall warning system. Company pilots indicated that it was common for the stall warning system to activate at an airspeed 10–15 miles per hour above the actual stall speed.
At the time of the accident, the airplane did not have the ventral fin installed, and a takeoff flaps setting was selected. The audible stall warning circuit breaker was found in the pulled (disabled) position.
Official Findings
The probable cause of the accident was determined to be the pilot's failure to maintain adequate airspeed, which resulted in an inadvertent stall. Factors associated with the accident included the pilot's unfamiliarity with the geographic area, the presence of low clouds, the pilot becoming disoriented, and the blind canyon into which he flew. An additional factor was the intentionally disabled stall warning system.