Amateur-built WAIEX N12YX accident near Fond Du Lac, Wisconsin

Probable cause

A partial loss of engine for reasons that could not be determined during an examination of the engine.

NTSB analysis

Shortly after takeoff on an instructional flight, the pilots heard a sudden change in engine noise. The instructor scanned the engine instruments and observed that the engine rpm was lower than expected. The instructor took control of the airplane and attempted to return to the airport. The airplane was not able to maintain altitude, and the instructor could not restore engine power to full. Unable to reach the airport, the instructor initiated a forced landing to a field. During the approach, the airplane collided with a power transmission line and impacted terrain. An examination of the engine found that the Nos. 1 and 2 exhaust valves displayed excessive wear. While such wear will result in a loss of engine power, it could not be determined what caused the sudden change in noise and engine power that the pilots experienced on the day of the accident.

Text from the NTSB. Open the NTSB docket for CEN16LA302 for the full record.