Accident Overview
A chartered floatplane carrying the pilot and four passengers departed uneventfully for a fishing lodge. Approximately 45 minutes into the flight, while cruising at about 1,700 feet above rugged terrain and a river, the engine began to lose power. The floatplane descended and the pilot initiated a forced landing to a small lake measuring 1,200 feet in length, located about one mile west of the river.
Sequence of Events
During the approach to the lake, the airplane stalled and impacted swampy terrain at the lake's edge in a steep nose-down attitude. The cargo on board was unsecured.
Examination Findings
An examination of the wreckage determined that the no.1 engine exhaust pushrod had failed in fatigue just below the top (valve) ball end. Further inspection revealed that material had been pushed away from the rod during installation of the ball end. The fatigue crack may have initiated from a score mark produced by the installation. Pushrod life is reduced due to surface scratches; however, the life of the failed pushrod could not be determined. The investigation also found that insufficient information exists in the overhaul manual regarding pushrod life and inspection.
Probable Cause
The probable cause of the accident was a loss of engine power due to the fatigue failure of the no.1 exhaust pushrod. Contributing factors were insufficient information on pushrod inspection and overhaul from the manufacturer, unsuitable terrain available for landing, and the pilot's failure to maintain airspeed during the approach, which led to an inadvertent stall.