CHI94LA176

The pilot was returning from a maintenance check flight, and entered a long glide to the airport. The conditions were within the area of favorable conditions for carburetor icing at glide power according to the transport Canada carburetor icing chart. When the throttle was advanced, the engine did not produce power and a forced landing was made short of the runway. The airplane struck a ditch. No pre-accident mechanical discrepancies were discovered.

On May 25, 1994, at 1200 central daylight time (CDT), a Snow 600-S2C, N1659S, operated by Farmers Flying Service, Inc., of Bancroft, Wisconsin, impacted a drainage ditch short of the approach end of the runway at the Bancroft East Airport and was substantially damaged. The commercial pilot reported that after an extended glide to descend to the airport, he attempted to increase power, experienced a loss of engine power and made a forced landing. He reported that the propeller was still rotating at impact, but the engine did not produce power. The pilot was not injured.

Visual meteorological conditions existed at the time of the accident and no flight plan was filed. The flight was operated under 14 CFR Part 91 as a maintenance check flight following engine installation. Post-crash inspection of the engine revealed no anomalies except 3 broken gear teeth in the supercharger blower gear reduction section. Metallurgical analysis of these gear teeth revealed that all failed due to ductile overstress. During the forced landing, the pilot reported that the propeller struck the ground.

Ambient conditions were an outside air temperature of 68 degrees, and a dew point of 57 degrees. This combination of temperatures falls within the area labeled "serious icing - glide power" on the Transport Canada Aviation Safety Bureau chart entitled "Conditions Known Favorable For Carburetor Icing."