On February 14, 2005, about 1520 Pacific standard time, a Robinson R44, N44NG, experienced a dynamic roll over and collided with terrain while practicing a pinnacle approach near Lake Arrowhead, California. Flight Development, Inc., was operating the helicopter under the provisions of 14 CFR Part 91. The certified flight instructor (CFI) sustained minor injuries; the commercial pilot undergoing instruction (PUI) and two passengers were not injured. The helicopter sustained substantial damage. The cross-country instructional flight departed Big Bear, California, about 1500, with a planned destination of Torrance, California. Visual meteorological conditions prevailed, and no flight plan had been filed. The primary wreckage was at 34 degrees 33 minutes north latitude and 117 degrees 25 minutes west longitude. The CFI stated that the airplane had no mechanical failures or malfunctions during the flight. In the written statement attached to Pilot/Operator Aircraft Accident Report (NTSB form 6120.1/2), the CFI stated that he was demonstrating a pinnacle approach. The CFI selected a suitable landing spot with the intent not to land but to go around. Approximately 150 feet above the ground, the helicopter began to sink and it did not respond as he added collective to compensate. He felt that they were in a vortex ring state. Choosing not to risk losing his preferable landing spot by lowering the nose to gain airspeed, the CFI opted to set down there, and attempted to cushion the landing using the collective. After a hard landing and bouncing two or three times, the helicopter came to rest with the right landing skid on a rock approximately 12-14 inches high. The CFI then attempted to lift the helicopter off the rock and set it down on level ground. The helicopter balanced on the rock with the right skid, and the left skid was in the air. The helicopter rolled left, the left skid contacted the ground, and the helicopter experienced a dynamic roll over. Once outside the helicopter, the CFI reported that the winds shifted 180 degrees several times. He felt that this contributed to his encountering the vortex ring state, and the dynamic rollover.