What happened
While entering the downwind leg of the traffic pattern, the engine of the unspecified aircraft began to misfire. In an attempt to rectify the issue, the pilot applied carburetor heat and increased engine power to 1,500 RPM; however, the misfire persisted. Despite further increases in engine power, there was no improvement in performance.
During the base leg of the pattern, the pilot turned off the carburetor heat and reduced the engine power to idle in preparation for landing. At that moment, the engine ceased producing power entirely. The pilot executed a shallow right turn to line up with a field for an emergency landing. Although the pilot was aware of a row of power lines located before the field and successfully flew under them, the right main landing gear struck a small tree, causing it to be sheared off.
The aircraft subsequently landed in the field and experienced a ground loop. The pilot was not injured.
The investigation
Investigators examined the engine and the airframe's fuel system. The engine was run using the airplane's own fuel system, at which point it started immediately and operated normally. The onboard fuel was found to be sufficient in quantity and was free of any debris or contamination. A mechanical examination of both the engine and the aircraft revealed no mechanical malfunctions.