On April 11, 2008, about 0900 Pacific daylight time, a Bell 47G-3B-1, N24SD, made a hard landing on hilly terrain about 25 miles south of Denio, Nevada. Following impact, the helicopter's skids collapsed, the main rotor blades severed the tail boom, and the substantially damaged helicopter rolled over. Neither the commercial pilot nor the passenger was injured during the aerial observation flight. The helicopter was operated by Helicopter Roundup Service, LLC, Nephi, Utah. Visual meteorological conditions prevailed at the time, and no flight plan was filed. The flight was performed under the provisions of 14 Code of Federal Regulations Part 91, and it originated from a private ranch near Denio, about 0700. The pilot reported to the National Transportation Safety Board investigator that the purpose of the flight was predator control, and the passenger-gunman had just shot a coyote. The pilot opined that a mechanical malfunction occurred as he was circling the injured coyote about 20 feet above ground level, and while nearly in a hover. According to the pilot, while maneuvering he heard a grinding noise emanating from the transmission, which was immediately followed by a loss of power to the main rotors. Prior to hearing the noise, there had not been any problem with the helicopter. The pilot stated that, at the time, the helicopter's airspeed was about 15 miles per hour, and he was unable to perform a successful autorotative descent. The helicopter was recovered from the accident site and examined by Federal Aviation Administration (FAA) and Bell Helicopter personnel. In pertinent part, the swashplate and centrifugal clutch for the main rotor system showed no indication of failure, the engine and turbocharger rotated freely, the tail rotor drive shaft and tail rotor gear box rotated freely, and no signs of abnormal wear or failure were found. No evidence of any abnormal wear, failure, or anomalies with the transmission was found. The FAA noted that the only discrepancy that was possibly pertinent to the pilot's report of hearing unusual noise may have related to the fact that one of the helicopter's two cooling fan drive belts was not found seated; although it was found at the accident site. The FAA reported that the belt may have rolled over on its pulley and made a noise that the pilot heard just before it broke.