Messerschmitt-Bolkow-Blohm BK 117 B-2 N370SS accident near Rochester, New York

Probable cause

An unintentional movement of the cyclic control before takeoff, which resulted the main rotor blades contacting the fixed wire cutter.

NTSB analysis

After the pilot of the air medical helicopter landed, the medical crew boarded and he prepared the helicopter for takeoff. The pilot stated that he was adjusting a light switch while his right hand was on the cyclic control when he heard a loud “bang.” He subsequently noticed that the rod from the airframe-mounted wire cutter was bouncing back and forth. The pilot then shut down the engines and the crew exited the helicopter. A postaccident examination of the helicopter revealed substantial damage to the main rotor blades that was consistent with them having contacted the wire cutter. The examinations otherwise did not reveal evidence of any anomalies of the flight control system that would have precluded normal operation. Based on this information, while the pilot indicated that he was holding the cyclic control at the time of the event, given the damage to the helicopter and the lack of anomalous findings with the flight control system, nor the existence other external influences like substantive wind, it is likely that he inadvertently moved the cyclic, which resulted in the main rotor briefly moving into a position where it contacted the wire cutter.

Text from the NTSB. Open the NTSB docket for ERA22LA229 for the full record.