Accident Overview
On July 8, 2018, at approximately 13:35 Japan Standard Time, a privately owned Robinson R22 Beta helicopter, registration JA7980, rolled over during air-taxiing at Fuse Number Three Temporary Helipad near Fuseshita, Kashiwa City, Chiba Prefecture, Japan. The helicopter was occupied by a captain and a passenger; neither sustained injuries.
Flight History
According to statements from the captain and passenger, the helicopter departed from the Fuse In Chiba temporary helipad (the home base) at around 13:30 and headed to the temporary helipad about one nautical mile east, used for training. The captain, who held a private pilot certificate for rotorcraft and had approximately 93 hours total flight time, was in the right seat; the passenger, a commercial pilot, was in the left seat. The flight club did not allow solo flights for pilots whose skills were not fully established, so the captain flew with the passenger's assistance.
The captain judged the wind as about 10 knots from the southeast based on a wind sock. After taking off toward the southeast, the captain reversed the helicopter and entered a traffic pattern at 800 ft and 70 knots. On a 130-degree magnetic approach at 60 knots, the helicopter took a right wind correction angle of about 10 degrees, then flew at 300 ft and 40 knots. The captain again noted a wind of about 10 knots from the southeast at the temporary helipad.
The helicopter landed over to grassland south of a training platform while hovering at about 5 ft AGL. It then climbed to about 10 ft AGL and began air-taxiing at a speed slower than walking toward a circle. Near the edge of the circle, the nose suddenly turned to the right. The captain attempted to correct but could not control as expected. The helicopter suddenly tilted left, the nose turned about 30 degrees to the right, and altitude dropped. The passenger, feeling danger when the control stick moved left, tried to move it right but found the captain still holding it firmly. The passenger raised the collective pitch lever; he did not recall operating the rudder pedals. A low rpm warning sound began ringing. Both pilots were maneuvering simultaneously. The helicopter grounded once, then floated up and rolled over left side down.
Aircraft Damage
The helicopter was substantially damaged. The fuselage frame, main rotor blades, landing gear, and stabilizer were damaged; tail rotor blades and tail rotor drive shaft were broken. The tail cone and lower stabilizer were deformed. Both cyclic sticks were broken from the grip. The engine was running until the rollover. No abnormalities had been noted during pre-flight inspection.
Meteorological Conditions
The captain reported clear weather, good visibility, and wind of about 10 knots from the southeast. Observations from the Abiko meteorological station (about 9 km east-southeast) showed wind speeds that could produce a right wind correction angle of 10 degrees at 60 knots. The calculated wind speed for such a correction was 13.6 knots for south wind (180 degrees) and 10.5 knots for southwest (225 degrees).
Investigation
The Japan Transport Safety Board investigated the accident. Analysis indicated it was highly probable that the helicopter suddenly tilted left, veered right about 30 degrees, and descended while moving backward during air-taxiing. The landing gear contacted the ground once on about a 200-degree heading. It is probable that the tail rotor blade and skid tube then contacted the ground, causing the tail rotor blade to break, the lower stabilizer to deform, and the tail rotor drive shaft to twist off. Once the tail rotor drive shaft failed, directional control became impossible. The helicopter likely rolled over while making a violent right turn, as evidenced by the main rotor blade tip buried in the ground and the left skid broken and buried.
The investigation found that both weather and the pilot were involved in the accident; equipment involvement was determined to be none.