Accident Overview
A flight instructor and a commercial rated pilot were conducting a training session in a helicopter equipped with skid type landing gear. The purpose of the flight was to prepare the pilot for a check ride. During the session, the instructor demonstrated a practice hydraulic failure running landing. As he initially touched down, the helicopter began experiencing ground resonance. The instructor increased power to become briefly airborne and then continued the maneuver to a normal practice hydraulic failure running landing.
Flight Training Activities
After the ground resonance experience, the instructor continued the flight training session for an additional 45 minutes. During this time, they performed another hydraulic failure running landing, several slope landings, and five hovering autorotations. Two of the hovering autorotations were described as rough, with an undesired drift to the front left.
After completing these exercises, the instructor left the airport where they had been practicing and returned to their home base airport. There, they conducted two straight-in autorotations and three 180-degree autorotations, all to a power recovery.
Damage Discovery
After shutdown procedures were completed, the two pilots were surprised when they discovered damage to the helicopter. The helicopter was substantially damaged, with buckling around the full circumference of the forward part of the tail boom and a crack in the skin at the 6 o'clock position. The flight instructor stated that he thought the damage occurred when they were conducting hovering autorotations.
Injuries
Both pilots reported that they were not injured.