Amateur-built BAKENG N39796 accident near Garden Valley, Idaho

Probable cause

A mechanical failure of the oil cooler, which resulted in a complete loss of oil and engine power.

NTSB analysis

In the days just preceding the accident, the owner-pilot made several uneventful flights in the experimental amateur-built airplane, which was equipped with an aircraft engine and an automotive performance/racing oil cooler. On the morning of the accident, the owner's brother joined him at a remote turf airstrip in mountainous terrain to conduct a flight. The brother, who was also a pilot, took the aft cockpit seat, which was the primary pilot position in the airplane. The owner took the forward cockpit seat. The brother conducted the engine start, taxi-out, run-up, and takeoff, which were all normal. During the climbout, the owner realized that the airplane was not performing as it should, and, when he asked his brother about it, his brother reported that the engine was losing power. The owner took control of the airplane and began a turnback to the airport, and the engine lost total power shortly thereafter. An attempt to restart the engine was unsuccessful, and the airplane landed short of the runway.

Examination of the airport revealed an oil spray trail on the turf that began at the parking location and extended along the taxi route and through the takeoff path. Postaccident examination of the airplane revealed a significant oil streak on the exterior side of the airplane that emanated from the oil cooler. The engine was also devoid of oil. Detailed examination of the oil cooler revealed deformation of its containment frame and damage to some of the unit's oil tubes, which included separation of the cooling fins from the tubes and several holes in the tubes that permitted oil to escape the cooler. The damage signatures were not consistent with preaccident or postaccident impact or other structural deformation damage. The damage signatures were somewhat, but not completely, consistent with an internal overpressure of the oil cooler; however, the reasons for the internal overpressure could not be determined during postaccident examination.

Text from the NTSB. Open the NTSB docket for WPR13LA304 for the full record.