What happened
On July 8, 2018, a privately owned Robinson R22 Beta, registration JA7980, was performing training maneuvers at a temporary helipad in Kashiwa City, Chiba Prefecture. The flight, consisting of a captain and a passenger, had departed from the Fuse helipad for a series of touch-and-go training exercises.
During the approach to the temporary landing site, the aircraft was air-taxiing at a low altitude of approximately 10 feet AGL at a walking pace. As the helicopter moved toward the landing circle, a sudden gust of wind from the right triggered a strong weathercock stability effect. This caused the nose of the helicopter to veer approximately 30 degrees to the following right, while the aircraft simultaneously tilted to the left and began to lose altitude.
In an attempt to manage the sudden movement, the occupants engaged in conflicting maneuvers. The passenger attempted to correct the tilt by moving the control stick to the right, but was unable to do so because the captain was holding the stick firmly. The aircraft's landing gear made contact with the ground, causing the tail rotor blades to break and the tail rotor drive shaft to twist off. The momentum of the aircraft led to a violent rollover on its left side, resulting in significant damage to the airframe, rotor blades, and landing gear.
The investigation
Investigators examined the meteorological conditions, the flight controls, and the pilot's actions during the incident. The investigation focused on the discrepancy between the captain's perceived wind conditions and the actual wind speeds present at the time. Analysis of local meteorological data from a nearby observatory suggested that while the captain estimated a 10-knot southeast wind, actual instantaneous gusts may have reached up to 26 knots, potentially exceeding the limitations specified in the flight manual.
The investigation also reviewed the mechanical state of the Robinson R22 Beta and the physical evidence at the site, including the broken tail rotor components and the deformed fuselage. Furthermore, the investigators looked into the flight club's administrative procedures regarding landing permissions, noting that while permission for the site had been obtained, the specific pilot's credentials were not included in the original application.