19980427016069A

(.4) The instructor and student were performing an autorotation with both pilots on the controls. As the power recovery progressed the aircraft continued to descend. The aircraft contacted the ground and slid into soft mud. The toes of the skids sunk into the ground and the aircraft rocked forward onto its nose and then fell on its right side. Both the instructor and student were able to exit the aircraft through the left cabin door without assistance. The instructor attributed the unintended descent to high temperature and humidity near the surface. According to the manufacturer, Robinson helicopter safety notice SN-22 was issued in 1986 and revised in 1994. The document states that rate of descent, trim, and airspeed are also factors that effect the aircraft's ability to transition to a hover. By not reducing the rate of descent but instead reducing forward airspeed and then raising collective and attempting to flare to stop the rate of descent, the aircraft flares in its own downwash. This sequence increases the power and collective pitch required to arrest the descent. The aircraft begins to enter the vortex ring state and a hard landing occurs. This can occur during a steep, power off approach. (-23) CFI and student practiced an enroute autorotation. CFI attempted to recover the maneuver with power. Aircraft contacted the ground during which time the aircraft hit a soft spot and the right skid caught and the aircraft rolled. No injuries to CFI and student.