Factual Information
The accident involved a Robinson R22 Beta II helicopter, registration HB-ZGH, operated by Heli-West AG. On 27 February 2006 at approximately 16:05 local time, the helicopter was conducting a VFR training flight at Neumatt, municipality of Bätterkinden/BE, about 9 km south-south-west of Solothurn. The crew consisted of a flying instructor and a pilot. Both occupants sustained minor injuries, and the helicopter was considerably damaged.
History of the Flight
The pilot and flying instructor met at Grenchen regional airport to perform a required annual check flight. After briefing and weather consultation, the pilot took off at 15:46 LT under the instructor's supervision. They flew to the model aircraft aerodrome at Neumatt. Following two reconnaissance overflights, the pilot landed on the grass area. The instructor then planned a simulated engine failure while hovering. The pilot brought the helicopter to a hover at about one metre above ground. The instructor reduced the engine to idle after counting to three. The pilot applied right pedal to prevent yaw, lowered the collective pitch, then immediately raised it. The helicopter shifted left, the left skid contacted the ground, and it began tipping left. Both crew members lowered the collective fully but could not prevent the helicopter from tipping over.
Meteorological Information
Meteorological conditions around the accident time included a north-easterly wind of 8 to 10 knots, gusting to 15 knots. Visibility was about 20 km. The air temperature was 0 °C with a dew point of -9 °C. Turbulence due to the 'bise' wind was not excluded. The sun azimuth was 235° with an elevation of 18°.
Aircraft Information
The Robinson R22 Beta II is a two-seat light helicopter with a piston engine and landing skids. It features a semi-articulated two-blade main rotor rotating counter-clockwise (viewed from above) and a twin-blade tail rotor for torque compensation. The low-mass rotor system provides limited kinetic energy reserve, requiring rapid pilot reaction during engine failure. The manufacturer's pilot operating handbook (POH) specifies the following procedure for power failure below 8 feet AGL: apply right pedal as required to prevent yawing, allow the aircraft to settle, and raise collective just before touchdown to cushion the landing.
Analysis
No technical defects or restrictions were found that could have influenced the accident. Flight preparation and mission discussion were diligent. During the simulated engine failure, the application of right pedal reduces tail rotor thrust, causing the helicopter to drift left. The observed leftward movement likely resulted from this effect. When the left skid contacted the ground, the helicopter began to tip. Raising the collective increased main rotor thrust, and the line of action of the lift force produced a torque that accelerated the rollover. Lowering the collective would have reduced thrust and could have arrested the roll, but it was applied too late. The crew's procedure deviated from the POH: they lowered the collective immediately after power reduction, which is not prescribed.
Probable Cause
Loss of control during touchdown following a simulated engine failure in hover, and application of an emergency procedure not in accordance with manufacturer's specifications.