What happened
On May 3, 2023, at approximately 15:32 JST, a privately owned Robinson R22 Beta, registration JA7875, was performing a familiarization flight in Toyama City, Toyama Prefecture. The flight, which included a pilot and one passenger, involved a round trip from the Yamafuji Temporary Operation Site (referred to as the "Old Operation Site") to Noto Airport.
During the return leg, as the helicopter approached the Old Operation Site from the south, it encountered significant wind conditions. Although the pilot was aware of high wind velocities from previous communications, the aircraft encountered a strong westerly wind during the final approach. As the helicopter descended toward the paved area near a hangar, the nose direction swung sharply to the and the aircraft began a rapid spin to the right. In an attempt to stabilize the aircraft, the pilot applied right pedal and the passenger attempted to assist using the cyclic control. However, the aircraft's attitude could not be recovered. The main rotor made contact with steel wires from nearby grapevine shelves, causing the helicopter to roll over and sustain substantial damage to the airframe, including the tail rotor system and fuselage.
The investigation
The Japan Transport Safety Board (JTSB) examined the flight history, surveillance camera footage, and the physical state of the aircraft. The investigation focused on the meteorological conditions at the time of the accident and the suitability of the landing site. Investigators reviewed the aircraft's flight path and noted that the pilot was approaching from the south to avoid power lines.
Crucially, the investigation established that the landing took place at the "Old Operation Site," which was not the officially approved location. The approved site was located approximately 150 meters to the east. The JTSB also analyzed the presence of obstacles, specifically the grapevine shelves, which protruded into the transition and approach surfaces required for safe operations.
Findings
- The primary cause of the accident was a sudden unanticipated yaw occurring as the helicopter transitioned from low-speed flight to a hover, triggered by changing wind direction and velocity.
- The pilot's radical pedal and collective inputs during this unstable phase contributed to a rapid rightward spin.
- The aircraft's main rotor struck steel wires from the eastern grapevine shelves, leading to the rollover.
- The use of an unauthorized landing site meant that the approach path was not properly cleared of obstacles, as the grapevine shelves encroached upon the required transition surfaces.
- The passenger's attempt to assist with the cyclic control during the instability further complicated the aircraft's attitude control.