What happened
During a flight instruction session, a flight instructor was performing a demonstration of an autorotation from 50 feet Above Ground Level (AGL) into a grassy area. The helicopter initially touched down with the skids level. To maintain a straight ground track and keep the aircraft skids light on the ground, the instructor increased the collective pitch.
After traveling approximately 70 feet at a speed of about 20 knots, the aircraft suddenly pitched forward and to the right. The instructor reported feeling at least three severe impacts against the aircraft before it came to a complete stop. There were no injuries reported in the incident.
The investigation
Mechanical examination of the helicopter revealed significant structural damage. Both the left and right skid tubes had fractured, and the right skid had become detached from its front and rear gear dampers. Additionally, the main rotor blades had sheared off the tailboom and the tail rotor.
Further inspection of the landing gear components showed that the bottom of the right skid tube was worn beyond manufacturer tolerances. An FAA inspector determined that a certified A&P mechanic had failed to adhere to the inspection procedures specified in the work card and the Manufacturer Maintenance Manual.