What happened
On July 25, 2010, a Eurocopter AS365N3, registered JA31TM, was engaged in a high-stakes rescue operation in the mountainous Otaki region of Chichibu City, Saitama Prefecture. The aircraft, operated by Honda Airways Co. Ltd. for the Saitama Prefect/Government, had been dispatched to assist a gorge climbing party after a member had fallen into a waterfall pool.
After conducting a reconnaissance flight and coordinating with local firefighters at a temporary helipad, the crew returned to the rescue site to perform a hoist operation. Two rescuers—one from the Saitama Disaster Prevention Aviation Unit and one from the Chichibu Fire Brigade—were lowered via the aircraft's hoist. As the rescuers reached the ground, the aircraft attempted to adjust its position to better align with the target area.
During this maneuver, the aircraft's tail rotor assembly made contact with nearby trees. This impact led to a loss of yaw control and a subsequent strike by the main rotor blades against the terrain. The aircraft crashed into a steep bank, causing the destruction of the airframe. Of the seven people on board, five fatalities were recorded, including the pilot in command, the second pilot, and three rescue personnel.
The investigation
The Japan Transport Safety Board (JTSB) conducted an investigation involving on-site inspections, examination of the aircraft's electronic control units, and analysis of imagery retrieved from the aircraft’s hoist camera. The investigation also included interviews with the two survivors and eyewitnesses at the scene. Investigators examined the physical damage to the fuselage, the fractured main rotor blades, and the damaged Fenestron tail rotor assembly to reconstruct the sequence of events.