Amateur-built RV4 N7765X accident near Butler, Pennsylvania

Probable cause

The pilot's improper decision to fly the airplane with a known engine problem and his improper modification of the engine control unit fuel delivery software, which led to the engine running too lean and resulted in a total loss of engine power during climb.

NTSB analysis

Shortly after takeoff on an extended crosswind leg about 800 ft mean sea level, the engine lost total power. The private pilot continued ahead and landed the airplane in a field. During the landing, the airplane impacted a wire fence and brush, which resulted in substantial damage to the fuselage and wings.

During postaccident interviews, the pilot reported that this was the first flight after he had made maintenance repairs to the automobile-converted engine due to an engine failure 1 month before the accident. He stated that he installed an aftermarket engine control unit and modified the fuel delivery software, which resulted in the engine running too lean for flight and likely caused detonation and piston damage to occur. During the run-up before the accident flight, the pilot was aware that the engine was not producing power as it should. However, he decided to depart with a known engine problem, and his decision to do so led to the accident.

Text from the NTSB. Open the NTSB docket for ERA18LA163 for the full record.