Event Summary
A local sightseeing flight was underway when the pilot, cruising at approximately 2,500 feet with the engine at cruise RPM, noted a sudden change after crossing a dam. The engine's RPM dropped to idle and began running roughly. The pilot identified a dirt road as a potential landing site and turned toward it. During the final turn, the engine regained partial power, prompting the pilot to initiate a go-around. However, as the go-around began, the engine lost power again. The pilot then elected to land on a roadway. During the final approach, the left wing struck the ground first, causing the airplane to cartwheel.
Investigation Findings
The subsequent investigation revealed that the aircraft's primary and main venturi was of a two-piece design. The primary venturi had become loose, which directly caused the loss of engine power. Additionally, two service bulletins had not been performed; these bulletins would have replaced the two-piece venturi design with a one-piece venturi, preventing the loosening that led to the power loss.
Maintenance History
The aircraft had received its annual inspection approximately three months before the accident. In the time since that inspection, the aircraft had accrued 20 flight hours. The investigation did not indicate whether the annual inspection included a review of the venturi or compliance with the applicable service bulletins.