Incident Overview
During a training flight, an instructor and student performed an autorotation with both pilots on the controls. As power was recovered, the helicopter continued to descend, contacted the ground, and slid into soft mud. The skids' toes sank into the mud, causing the aircraft to rock forward onto its nose and subsequently fall onto its right side.
Occupant Actions
Both the instructor and the student were able to exit the helicopter through the left cabin door without assistance.
Instructor's Observations
The instructor attributed the unintended descent to high temperature and humidity near the surface.
Manufacturer's Guidance
According to the manufacturer, Robinson Helicopter Safety Notice SN-22 was issued in 1986 and revised in 1994. The notice states that rate of descent, trim, and airspeed affect the aircraft's ability to transition to a hover. It describes a scenario where, instead of reducing the rate of descent, forward airspeed is reduced and collective is raised while attempting to flare. This causes the aircraft to flare in its own downwash, increasing the power and collective pitch required to arrest the descent. The aircraft then begins to enter the vortex ring state, resulting in a hard landing. The notice notes that this can occur during a steep, power-off approach.
Conclusion
The incident involved a hard landing and rollover following an autorotation training maneuver, with no injuries reported.