On July 24, 1995, an Air Tractor AT-301 (registration N3660U) was involved in an aviation accident near Havre, MT. Investigators recorded the probable cause as: The engine rocker box sustained a fatigue fracture at the point where the rocker pivot bolt passes through the box, leading to a complete loss of engine power. This summary draws on records from the U.S. National Transportation Safety Board (NTSB) historical archive.
During an aerial application flight, the aircraft experienced a complete loss of engine power. One wing caught in tall barley, causing the aircraft to cartwheel and come to rest inverted. Examination revealed a fatigue fracture in the engine rocker box.
Incident Overview
During an aerial application flight, the aircraft experienced a complete loss of engine power. Almost immediately after the power loss, one of the aircraft's wings caught in the tall barley that the pilot was spraying. After the wing made contact with the crop, the aircraft cartwheeled and eventually came to rest in an inverted position.
Engine Examination
A subsequent examination of the engine revealed that a rocker box had sustained a fatigue fracture at the point where the rocker pivot bolt passes through the box. This fracture was identified as the source of the engine failure.
Probable cause
The engine rocker box sustained a fatigue fracture at the point where the rocker pivot bolt passes through the box, leading to a complete loss of engine power.