After the instructor demonstrated a 360° autorotation exercise, his student attempted a similar manoeuvre. At some point during the turn the ‘low rotor rpm’ warning sounded and, although the student further lowered the collective control, the airspeed and height reduced to the point where the instructor intervened by applying power. However the aircraft continued to descend, so he applied full power and pushed the nose down to gain speed. When it appeared that a landing was inevitable he attempted a flare at a height of around 40 ft with the intention of conducting a low speed landing. The landing area was a ploughed field and the skids dug in, causing the rotors to strike the ground, with the helicopter ending up on its right side. The instructor considered that, with a 25-30 kt wind blowing over the area, he had encountered severe windshear in the final stages of the autorotation.