NTSB investigators may not have traveled in support of this investigation and used data provided by various sources to prepare this aircraft accident report.
The pilot reported that he noticed the helicopter abruptly shudder during the crosswind turn. The pilot lowered the collective control, entered an autorotation, and turned back toward the airport. As he approached the runway area, the helicopter skids passed over a row of trees by about 5 or 10 ft. Immediately after the skids cleared the trees, the pilot began a cyclic flare, which resulted in the tail rotor striking a tree and a subsequent loss of directional control.
Examination of the helicopter revealed that the belt for the secondary drive reduction unit was loose, which allowed the belt to jump the drive cogs on the pulley. The belt was loose due to excessive wear of the pulley, which resulted in an abrupt in-flight shudder. The helicopter operating manual preflight inspection includes a check for proper belt tension.