A check airman was giving the pilot in command a night vision goggle (NVG) annual check ride in the emergency medical service helicopter. After a satisfactory slope landing, the pilot in command repositioned the helicopter to a flat area and performed a hovering autorotation which resulted in a hard landing. The check airman then demonstrated a second hovering autorotation and the pilot in command performed a third hovering autorotation which was satisfactory. The check airman continued the annual check ride. After the flight, during a post flight inspection, substantial damage was discovered to the tail boom and the aft portion of the fuselage. The damage was consistent with a hard landing, presumably incurred during the first hovering autorotation in which the helicopter landed hard. In a statement provided to the NTSB, the check airman said that he should have guarded the collective more to limit the amount of control input during the practice autorotation maneuvers.