On April 13, 2013, about 1215 mountain daylight time, a Robinson R-44 II helicopter, N424DP, serial number 11036, was substantially damaged after impact with terrain near Buffalo, South Dakota. The commercial pilot and three passengers did not report any injuries. The helicopter was registered to Double D Choppers LLC and operated under the provisions of 14 Code of Federal Regulations Part 91 with no flight plan filed. Day visual meteorological conditions prevailed for the flight, which originated from private land near Buffalo, South Dakota, about 1210. While maneuvering on a sightseeing flight at 100-150 feet above ground level and 50 knots airspeed, the pilot reported that he reversed course from the southeast to the northwest. After making this turn, he noticed that the low rotor speed horn activated. The pilot lowered the collective and executed an immediate landing into uneven terrain, during which the tail boom and landing gear were separated from the fuselage of the helicopter. The weather station at Harding County Airport (K2WX), Buffalo, South Dakota, located 14 nautical miles south of the accident site, reported the following conditions at 1156: wind 120 degrees at 22 knots with gusts to 28 knots, 10 miles visibility, temperature 8 degrees Celsius (C), dew point minus 2 degrees C, altimeter setting 29.46 inches of mercury. Following the accident, the engine was functionally tested on the accident helicopter. The engine started without hesitation and ran continuously at different power settings, including idle and 100 percent rpm. During the engine test, no anomalies were noted with the engine or its associated engine controls. Postaccident examination of the airframe and engine revealed no evidence of mechanical malfunctions or failures that would have precluded normal operation. The pilot was an experienced fixed-wing agricultural spray pilot. At the time of the accident, he reported a total flight experience of 12,020 hours; of which, 306 hours were flown in a helicopter and 89 hours were flown in this make and model of helicopter. On April 5, 2012, he was the pilot of a Robinson R-22 helicopter accident, which also involved a low rotor RPM condition and forced landing. Review of Robinson Safety Notice SN-18 revealed: OVERCONFIDENCE PREVAILS IN ACCIDENTS A personal trait most often found in pilots having serious accidents is overconfidence. High-time fixed-wing pilots transitioning into helicopters and private owners are particularly susceptible. Airplane pilots feel confident and relaxed in the air, but have not yet developed the control feel, coordination, and sensitivity demanded by a helicopter. Private owners are their own boss and can fly without discipline, enforced rules, or periodic flight checks and critique by a chief pilot. A private owner must depend on self-discipline, which is sometimes forgotten. When flown properly and conservatively, helicopters are potentially the safest aircraft built. But helicopters are also probably the least forgiving. They must always be flown defensively. The pilot should allow himself a greater safety margin than he thinks will be necessary, just in case.