What happened
During a training session at Ashland Airport, a dual-student and an instructor performed several maneuvers, including hovering exercises, hovering autorotations, and loss of tail rotor effectiveness (LTE) maneuvers. The flight also included stuck-pedal exercises on a parallel taxiway and a series of run-on landings to runway 30. The final maneuver was a full-down autorotation to runway 30, initiated at approximately 300 feet above ground level with the flare starting at 50 feet.
Both the student and the instructor reported that the flare and touchdown were performed correctly and without incident. However, as the helicopter slid down the runway for approximately 150 feet, the left skid sank into soft tar on the runway surface just before the aircraft reached a normal stop speed of about five knots. This caused the helicopter to veer abruptly to the left and roll over onto its right side. The occupants were not injured.
The investigation
Upon exiting the aircraft, the crew observed that the tar in the area where the rollover occurred was thick, soft, and sticky. The instructor noted that while the runway surface did not appear problematic during earlier run-on landings, imprints from previous skid contacts were visible on the surface during subsequent maneuvers. The instructor also reported that the temperature at the time of the accident was just over 90 degrees Fahrenheit, following two previous days with temperatures reaching approximately 100 degrees. The runway surface, composed of chip-seal (a mixture of tar and crushed rock), was found to be inconsistent, with varying amounts of tar and rock across different areas.