What happened
The instructor pilot and the rated helicopter pilot were conducting training exercises focused on touchdown autorotations. Following a landing and subsequent ground slide, both crew members observed unusual vibrations in the aircraft. They proceeded to shut down the engine and exited the helicopter to inspect the damage.
Upon examination, it was determined that the main rotor blades had struck the tailboom. This impact resulted in the severing of the tail rotor driveshaft. The wind conditions at the time of the incident, recorded at 1450 CST, were from 140 degrees at 16 knots with gusts reaching 22 knots.
The investigation
The physical inspection of the helicopter revealed that the main rotor blades had made contact with the tailboom. This collision caused catastrophic failure of the tail rotor driveshaft, which was severed by the impact. No other mechanical failures were noted prior to the event.
Findings
The vibrations observed by the crew were directly attributable to the structural damage sustained during the incident. The wind conditions did not appear to be a contributing factor to the initial landing, but the sequence of events led to the specific damage pattern observed.