Air Tractor Inc AT-502 N1022N accident near Lewistown, Montana

Probable cause

The fatigue fracture and separation of the fuel bypass line, which resulted in a total loss of engine power.

NTSB analysis

The pilot reported that while in cruise flight about 800 feet above ground level, the engine lost power, and he initiated a forced landing to an area of open, uneven terrain. During the landing roll, the left wing struck the ground and the airplane ground looped. Postaccident examination revealed that the fuel bypass line was fractured and had separated from the fuel control unit.

Metallurgical analysis revealed that the fuel bypass line fractured near a ferrule at the edge of the braze filler metal fillet. Striations on the fracture surface were consistent with a fatigue crack originating on the outside surface of the tube and propagating toward the inside surface and circumferentially around the tube wall. No maintenance records for the airplane were recovered during the course of the investigation, and, therefore, the amount of time and maintenance history on the line was undetermined.

Text from the NTSB. Open the NTSB docket for WPR11LA288 for the full record.