Amateur-built HIGHLANDER N707KM accident near Oshkosh, Wisconsin

Probable cause

The reported uncommanded retraction of the flaps while on short final for unknown reasons, which resulted in a hard landing.

NTSB analysis

The pilot reported that when the airplane was on short final to land on a grass airstrip, close to the ground, the wing flaps retracted from 40° to 0° uncommanded, and the airplane started to sink. The pilot added engine power to arrest the descent; however, the airplane landed hard. The pilot taxied the airplane without further incident. A postlanding examination of the airframe revealed substantial damage to the fuselage on the right side.

After the accident, the flaps were manipulated in and out of the fully extended flap position using the flap actuator handle. The flap controls were continuous and extended and retracted as designed. The flap actuator handle always remained secure in the detent. Investigators were unable to duplicate the uncommanded retraction of the flaps from 40° to 0°. There were no mechanical anomalies with the airplane or related systems that would have precluded normal operations.

Text from the NTSB. Open the NTSB docket for CEN24LA282 for the full record.