Flight and Landing
While en route to his original destination, the pilot diverted to his home airport. During the diversion, he found that he could not achieve the desired indicated airspeed using the throttle settings that he usually employed. Upon arrival, the pilot opted to land on a runway with an approximate 10-knot tailwind, following local takeoff and landing terrain avoidance procedures. Believing the engine was malfunctioning and producing reduced thrust, he selected only 20 degrees of flaps on final approach. As he crossed the runway threshold, he recognized that his ground speed was excessive, but chose not to execute a go-around. This decision was based on the suspected engine problem and the risk of impacting trees on rising terrain beyond the departure end of the runway. The aircraft touched down roughly halfway down the wet runway. Despite applying maximum braking, the pilot could not stop the aircraft before it departed the far end of the runway and went over an embankment.
Post-Accident Findings
A post-accident inspection of the engine determined that it had not malfunctioned. However, multiple contaminants were found in the pitot system mast and lines. The size and structure of these contaminants were such that they interfered with the correct display of the aircraft's indicated airspeed.