Incident Overview
The pilot was conducting an approach with an extended downwind leg. The aircraft was in the landing configuration with carburetor heat selected on and power reduced to approximately 13 inches of manifold pressure. As the pilot turned from base to final, the engine began to steadily lose power. Attempts to increase power were unsuccessful, prompting the pilot to perform a forced landing.
Weather and Carburetor Icing Considerations
At the time of the incident, the weather conditions were outside the indicated carburetor icing conditions on the chart. However, a review of literature on carburetor icing indicates the unpredictable nature of this phenomenon. The observed power deterioration in this scenario was consistent with documented examples of carburetor icing.
Pilot Actions and Guidance
The FAA Flight Training Handbook, in the section under 'Descents (Maximum Distance Glides),' notes that during power-off descents, the engine should be cleared periodically to prevent excessive cooling and fouling. The pilot had the carburetor heat on and power reduced, which are typical procedures for descent.
Post-Accident Engine Test
Following the incident, the engine was test run on the airframe. According to the manufacturer's representative, the engine 'startup was immediate, and the engine ran smoothly,' indicating no mechanical issues were found.
Conclusion
The investigation did not identify a definitive cause for the power loss. The engine operated normally during post-accident testing. The incident remains consistent with documented carburetor icing occurrences, though weather conditions were outside the typical icing envelope.