What happened
During a flight through a mountain pass, a float-equipped aircraft was following two other company planes. The flight conditions were characterized by misty rain, low ceilings of approximately 700 feet, and visibility limited to between five and seven miles, with clouds obscuring the mountainsides. The flight path through the pass necessitated several turns. The pilot of the aircraft involved had no prior experience navigating this specific pass under such marginal Visual Flight Rules (VFR) weather conditions.
After the leading two aircraft successfully navigated the pass, they lost all radio communication with the third aircraft. The wreckage was subsequently discovered at the head of a canyon that intersected the intended route, located approximately two miles short of the correct pass.
Findings
Investigations into the wreckage revealed that the aircraft had been fitted with a Short Take Off and Landing (STOL) kit. Previous Canadian certification testing indicated that this specific modification removed aerodynamic indicators of an impending stall, necessitating a functional audible warning system. It was noted by company pilots that the stall warning system frequently triggered at speeds 10 to 15 miles per hour above the actual stall speed.
At the time of the crash, the aircraft was missing its ventral fin and was configured with a takeoff flaps setting. Crucially, the circuit breaker for the audible stall warning system was found in the pulled position, meaning the stall warning system was disabled.