What happened
On November 21, 2015, a Robinson R2-2 Beta helicopter, registration LN-OZP, was conducting a skill test for a private pilot license at Sandefjord Airport (ENTO). The flight, operated by European Helicopter Center, involved several maneuvers, including autorotations. Following a series of initial exercises, the instructor decided to allow the candidate a second attempt at a simulated engine failure from a low hover.
The aircraft was positioned approximately two to three feet above a grassy area east of taxiway Y south. As the instructor reduced the throttle to idle, the engine RPM dropped. The candidate failed to provide sufficient right cyclic input to counteract the resulting leftward drift. Although the instructor attempted to intervene by applying right cyclic, the left landing gear struck the ground, which was covered in frozen snow and grass. The momentum caused the aircraft to undergo a dynamic rollover, eventually coming to rest on its left side after the main rotor struck the ground.
There were no fatalities and no injuries to the two occupants. However, the aircraft sustained significant damage, including damage to the rotor blades, the tail boom attachment, the rotor head, and structural deformation beneath the main gearbox.
The investigation
The Norwegian Safety Investigation Authority (NSIA) examined the flight maneuvers, the terrain conditions, and the operator's training procedures. The investigation noted that the ground consisted of uneven turf with approximately 15 cm of grass and a 10 cm layer of frozen snow.
Investigators reviewed the company's Training Operations Manual, which specifies that during a hovering autorotation, the pilot must compensate for leftward drift by using right cyclic. The investigation also looked into the operator's practice of performing these specific low-hover maneuvers over grass to reduce wear on the landing gear.
Findings
- The primary cause of the accident was the failure to sufficiently correct the leftward drift with right cyclic input during the engine power reduction.
- The presence of frozen snow and soft turf acted as a pivot point; when the left landing gear penetrated the surface, it prevented necessary lateral movement, facilitating the rollover.
- The instructor's corrective actions were initiated too late to prevent the lateral movement from destabilizing the aircraft.
Safety action
Following the incident, the operator updated its procedures to ensure that hovering autorotation exercises are performed on hard surfaces, such as asphalt or concrete. This change ensures that the aircraft can move laterally upon landing gear contact, reducing the risk of a dynamic rollover.