On July 19, 2004, about 1634 Pacific daylight time, an Agusta A119 (Koala), N928KR, impacted mountainous terrain during a low altitude maneuver about 10.7 nautical miles south-southeast of Big Bear City, California. Agusta Aerospace Corporation, Philadelphia, Pennsylvania, operated the helicopter, and it was substantially damaged. The commercial pilot was not injured. Five of the six passengers received minor injures, and the sixth passenger was not injured. Visual meteorological conditions prevailed, and no flight plan had been filed for the sales demonstration flight. The flight was performed under the provisions of 14 CFR Part 91, and it originated from the Rialto Municipal Airport, Rialto, California, about 1615. In the demonstration pilot's completed "Aircraft Accident Report," he indicated that the purpose of the flight was for him to provide the San Bernardino County Sheriff's Department (the potential customer) with an evaluation flight to verify the helicopter's usefulness in the sheriff's patrol and reconnaissance missions. The demonstration pilot reported that his total rotorcraft flying experience and pilot-in-command flying experience in the accident model of helicopter was 12,347 and 397 hours, respectively. The sheriff's pilot verbally reported to the National Transportation Safety Board investigator that he chose the route of flight, and the demonstration pilot found it satisfactory. To facilitate the evaluation, the demonstration pilot allowed the sheriff's pilot to handle the controls and to maneuver the helicopter over high mountainous terrain about 50 feet above the trees. The sheriff's pilot's total rotorcraft flying experience and pilot-in-command flying experience in the accident model of helicopter was 11,058 and 0 hours, respectively. According to the sheriff's department, its pilot was not qualified to perform as pilot-in-command of the accident helicopter. The demonstration pilot reported to the Safety Board investigator that the entire flight had been uneventful until the sheriff's pilot slowed the helicopter from 40 to 20 knots indicated air speed (KIAS) while making a left turn. At this time, the helicopter's airspeed decreased below that required for effective translational lift, and the main rotor rpm decreased. The demonstration pilot reported that he then joined the sheriff's pilot on the flight controls and used the remaining main rotor energy to direct the descending helicopter toward a small semi-level area for the impending impact. The demonstration pilot also stated that the sheriff's pilot had been flying with his permission, but that continued flight was not possible under the ambient +20 degrees Celsius condition, over the 8,800-foot mean sea level (msl) rising terrain. The demonstration pilot indicated that he could not arrest the descent prior to impacting the ground while descending between 300 and 500 feet per minute. During a post-accident interview by a sheriff's investigator, the sheriff's pilot indicated that during the final seconds of flight "there was insufficient power available to continue flying," and the sheriff's pilot heard the low rotor audible warning alert. The sheriff's pilot indicated that they had not experienced a mechanical malfunction or failure during the accident flight. Based upon the reported 8,800-foot msl accident site elevation and the estimated +20 degrees Celsius outside air temperature, the Safety Board investigator calculated that the density altitude was over 11,000 feet. According to the sheriff's investigator who totaled the weights of the occupants in the helicopter and also accounted for the fuel burn off during the accident flight, when the crash occurred the helicopter's weight was about 2,715 kg. The Agusta "Hovering Ceiling Out of Ground Effect" performance chart for the helicopter indicates that under the aforementioned density altitude condition, the helicopter was capable of hovering out of ground effect at a maximum weight of 2,200 kg.