Summary
On 21 November 2015, a Robinson Helicopter Company R22 Beta (registration LN-OZP) operated by European Helicopter Center AS experienced a rollover during a training flight at Sandefjord Airport Torp (ENTO). The helicopter was conducting a skill test for a Private Pilot License (Helicopter) candidate. The two occupants, an examiner and the candidate, were not injured. The helicopter sustained substantial damage to rotor blades, tail boom, and structure.
The Accident
The flight included several elements, including autorotations to taxiway 'Y south'. After those, the instructor intended to simulate a complete power loss from a low hover. The helicopter was established in a hover 2-3 feet above flat, grass-covered terrain east of the taxiway. The examiner asked the candidate if ready, counted down from three, and then reduced the throttle to idle. Engine rpm dropped, and the candidate did not apply sufficient right cyclic, causing a leftward drift. The examiner took the cyclic and corrected to the right but could not stop the movement before the left skid contacted the frozen, snow-covered grass. The helicopter then rolled over onto its left side. The main rotor struck the ground a few rotations before the helicopter came to rest on its side. No fire occurred.
Investigation Findings
The terrain consisted of soft, uneven peat with approximately 15 cm long grass and about 10 cm of frozen snow on top. According to the operator's training manual, the hovering autorotation exercise is intended to simulate landing from a hover with complete power loss. The manual states that rolling off the throttle causes a left drift, which must be compensated with right cyclic. The operator stated that such exercises were performed on grass to reduce undercarriage wear, but as an immediate post-accident measure, they changed to hard surfaces to allow sideways movement upon ground contact.
Probable Cause
According to the accident investigation board, the corrective reaction from the examiner came too late to prevent the helicopter from drifting left while descending to the ground. When the left skid contacted the snow and grass, further lateral movement was prevented, and the helicopter's kinetic energy caused it to rotate left until it rolled over—a phenomenon known as dynamic rollover.