Amateur-built MOSQUITO XET N922RM accident near Angleton, Texas

Probable cause

The pilot’s failure to maintain adequate clearance from trees during a precautionary landing. Contributing to the accident was the pilot’s inadequate preflight inspection during which he failed to detect a loose drive belt, which resulted in an in-flight shudder.

NTSB analysis

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.

Text from the NTSB. Open the NTSB docket for CEN15LA042 for the full record.