Accident Overview
On 9 April 2009, a Robinson R22 Beta II helicopter, registration HB-ZGR, was destroyed when it struck the grass runway during an autorotation demonstration at Bern-Belp Airport (LSZB). The flight was a training mission with a flight instructor and a student pilot. The aircraft was operated by Mountain Flyers 80 Ltd. and owned by MR Flugbetriebs AG.
Flight History
The flight began at 10:10 LT when the crew requested start clearance from Helipad 1. After a flyover to the grass runway west of the main runway, traffic pattern training commenced at 10:14. The student flew four circuits and approaches from about 2100 ft AMSL, followed by nine normal straight-in autorotations from approximately 2400 ft AMSL (about 700 ft AGL). The student had coordination difficulties typical for his training level.
The Demonstration Maneuver
The instructor planned to demonstrate a special autorotation maneuver: reducing speed to zero, yawing 180 degrees with right pedal, then rebuilding speed and transitioning into a normal flare. The briefing covered rotor rpm loss during yaw. The instructor stated he chose right yaw due to less rpm loss. After a preflight inspection, the helicopter was fueled with 18 US gallons.
During the final (14th) exercise, the student initiated autorotation at about 2800-2900 ft AMSL. The instructor reduced throttle below 80% and took control, with the student following controls. First, the instructor flared to reduce airspeed nearly to zero while maintaining rotor rpm above 102%. The helicopter descended vertically with slight backward motion, reaching about 2500 ft AMSL (800 ft AGL). Then he accelerated to about 60 kt.
At approximately 2000 ft AMSL, the instructor executed the planned maneuver: a nose-up attitude of about 15° with collective applied to maintain rpm and altitude. At 15 kt, he yawed right using pedal. During the yaw, rotor rpm dropped, so he lowered collective fully. After the 180° turn, rpm was above 102%. The helicopter was at roughly 2000 ft AMSL, about 300 ft AGL. The instructor was aware that altitude was at the lower limit for the maneuver.
The student was surprised that the instructor performed a 180° turn (not 360°) because they were already close to the ground. During subsequent acceleration for the flare, rotor rpm dropped to about 95%, triggering the low RPM warning (active below 97%). The instructor was surprised by the high sink rate. He estimated airspeed before the flare at 50 kt and altitude at about 10 m AGL when he initiated the flare and opened throttle fully. Realizing ground contact was imminent, he told the student it would not be enough. He held the helicopter level to possibly use ground effect, then pulled collective fully up just before impact.
The helicopter struck the grass runway hard, bounced, and began rotating clockwise. The engine revved high, and the main rotor appeared to be normally driven. After two to three rotations, the helicopter tipped sideways, and rotor blades contacted the ground.
Injuries and Damage
One occupant (the student) sustained minor injuries; the other (the instructor) was not injured. The helicopter was destroyed. Minor grass damage occurred to the runway.
Probable Cause
The accident occurred because the helicopter made violent contact with the grass runway during a failed autorotation demonstration. Contributing factors were the lack of planning of a safety altitude and the non-interruption of the demonstration.