Accident Description
During a mountain flying instructional flight, the aircraft, with a flight instructor and two pilots aboard, lifted off approximately halfway down a 4,903-foot runway. After lift-off, the aircraft failed to climb sufficiently to clear a perimeter fence located on higher terrain about 1,560 feet from the runway. The fence was at an elevation about 60 feet above the departure end of the runway. The airplane came to rest in a field approximately 140 feet from the fence.
Investigation Findings
No aircraft or system failure or malfunction was found. Evidence indicated that the fuel boost pump was on during takeoff, although the engine-driven pump was operating normally. During a test run, the engine operated normally with the boost pump off. However, with the boost pump set to low boost, there was a 500 to 700 rpm loss; at high boost, the engine quit running.
The investigation revealed that the location and design of the boost pump switch were non-standard, having been moved during an STC aircraft alteration. The switch was located next to the throttle, where it could be inadvertently operated, and it had no safeguard to prevent such operation.
Boost Pump Switch and Leaning Issues
The switch's placement near the throttle increased the risk of inadvertent activation due to the lack of a guard or protective feature. Additionally, the investigation found that no leaning procedures were incorporated in the pilot manual. The flight instructor had briefed the pilots to lean the engine by using the rpm gauge. However, the manufacturer reported that the engine could not be properly leaned by using the rpm gauge because it was equipped with a constant speed propeller.