WPR12LA329 · Interplane SKYBOY EX

The pilot had been flying the airplane for about 1 hour before the accident. He landed, shut down the engine, boarded new passengers, and restarted the engine. The total time from shut down to start up was about 5 minutes. He stated that the airplane's engine performed normally during run-up and takeoff. After takeoff, about 300 to 400 feet above ground level, the engine began to lose power. The pilot made a hard right turn and landed in an open field. The airplane impacted a fence post with its right wing during the landing roll. An engine examination revealed that the engine did not have a carburetor heat system installed. The subsequent engine test run on the airframe confirmed that a partial loss of engine power occurred after about 1.5 minutes of operation. The temperature, dew point, and relative humidity were nearly identical during the engine test run and the accident event. A carburetor icing chart indicated the possibility of serious carburetor icing at cruise power at the reported atmospheric conditions. The engine was removed from the airframe, examined, and tested at an engine tech services facility. During the engine test run the engine performed at various power levels for 28 minutes without degraded power output. The atmospheric conditions during this test were significantly different than the conditions at the time of the accident. The engine inspection concluded that there were no anomalies that would have precluded normal operation.

Verbatim NTSB analysis and probable cause from the NTSB dataset