Narrative
While conducting a fire patrol flight, the pilot encountered weather and decided to return to the departure airport. After initiating a turn toward the airport, the engine began to run rough and lose RPM. The pilot checked all pertinent systems and applied carburetor heat, which had a limited effect. While searching for a suitable landing area, engine power dropped from 2,000 RPM to 400–800 RPM. The pilot then performed a forced landing on a logging road approximately 45 nautical miles west of Presque Isle, Maine.
Examination
Post-accident examination of the airplane revealed no mechanical deficiencies. Fuel drained from the wing tanks and fuel sump was free of debris and water, indicating no fuel contamination issues.
Carburetor Icing Conditions
Interpolation of a carburetor icing probability chart indicated that conditions at the time were conducive to moderate icing at cruise power and serious icing at glide power. This suggests that carburetor icing may have been a factor in the engine power loss.