CEN15LA042

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.

On November 8, 2014, about 1000 central standard time, a Composite FX Mosquito XET helicopter, N922RM, impacted trees during approach for landing at the Bailes Airport (7R9), Angleton, Texas. The pilot sustained minor injuries and the helicopter was substantially damaged. The helicopter was registered to and operated by the pilot under the provisions of 14 Code of Federal Regulations Part 91 as a personal flight. Day visual meteorological conditions prevailed for the local flight, which departed without a flight plan. According to the pilot, he noticed the helicopter abruptly shudder during the crosswind turn at about 300 feet above ground level. 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 feet. Immediately after the skids cleared these trees, the pilot began a cyclic flare, which resulted in the tail rotor striking a tree. The helicopter began to spin violently and impacted the ground several times, damaging the main rotor and tail boom. The helicopter was examined by Federal Aviation Administration and Composite FX personnel at the kit manufacturer's facility. The belt for the secondary drive reduction unit was observed to be loose, which allowed the teeth of the drive belt to "jump" the drive cogs on the pulley. The loose belt was due to excessive wear on the pulley. The operating manual pre-flight inspection includes a check for tension of this belt, during which the operator should attempt to deflect the belt by about 3/16 of an inch, with an estimated five pounds of finger pressure in the middle of a long, unsupported span of the belt.