Primary finding
Probable cause
An encounter with a foreign object, which resulted in a loss of control and collision with terrain.
Investigator assessment
Analysis narrative
The pilot was conducting tree trimming operations on a power line right of way that consisted of a 10-blade aerial saw that was slung below the helicopter. During the cutting, a saw blade snagged a 1/2-inch cable that wrapped itself around the lower saw blades. A section of the cable broke off and struck the tail rotor assembly, damaging the stabilizers and tail rotor drive shaft. The helicopter lost all tail rotor authority and began an uncontrolled yaw, impacting the trees as it descended to the terrain where it came to rest on its left side. The impact resulted in substantial damage to the airframe and rotor blades. The operator did not report that there were any preimpact mechanical failures or malfunctions of the helicopter that would have precluded normal operation.