On August 11, 2000, an Air Tractor AT-802F (registration N6159F) was involved in an aviation accident near Salmon River, ID. Investigators recorded the probable cause as: Compressor turbine blade failure due to high-cycle fatigue initiating in the surface of the fir-tree root. Factors include unsuitable terrain for an emergency landing. This summary draws on records from the U.S. National Transportation Safety Board (NTSB) historical archive.
An airplane conducting fire suppression operations experienced a loss of engine power and was ditched into a river, resulting in substantial damage. Post-accident examination revealed a fractured compressor turbine blade with fatigue.
Incident
While conducting fire suppression operations, an airplane experienced a loss of engine power during a normal application run over the fire. The pilot reported that the engine power was lost, and due to unsuitable terrain for an emergency landing, the pilot ditched the airplane into a nearby river. The airplane sustained substantial damage as a result of the forced landing.
Post-Accident Examination
A post-accident inspection of the turbine engine was conducted. The examination revealed that a compressor turbine blade was fractured in the first serration of the fir-tree root. Personnel from the Materials Laboratory examined the fracture face of the affected turbine blade and reported that the fracture surface appeared smooth with a curving boundary, typical of fatigue. Fatigue striations and ratchet marks, typical of high-cycle fatigue propagation, were observed. Near the fatigue origin, no surface damage was observed, and no material anomalies were visible on the fracture surface.