On October 7, 1999, at 2005 hours Pacific daylight time, a McDonnell Douglas 369E helicopter, N991SD, was substantially damaged during a forced landing at Moreno Valley, California, following an in-flight loss of directional control. The commercial pilot and two observer crewmembers were not injured. The helicopter was operated by the Riverside County Sheriff's Department under the provisions of 14 CFR Part 91 as a public-use aircraft. Visual meteorological conditions prevailed and no flight plan was filed for the local area patrol flight, which originated from Hemet, California, at 1950. According to the Sheriff's Department report, it was a dark night and the winds aloft were northerly at 20 to 25 knots, at 500 feet agl, as the pilot orbited over ground based law enforcement activity. In accordance with department operating procedures, the pilot had identified a school athletic field as a suitable emergency landing site. He was attempting to shine the helicopter's spotlight on a vehicle; however, the northerly wind kept blowing the aircraft well south of the location on each of the first two orbits. On the third orbit, he inadvertently allowed the helicopter to slow below translational lift speed and the helicopter yawed 180 degrees to the right uncontrollably. The pilot momentarily recovered directional control of the helicopter but then the right yaw resumed. He made several more attempts to recover directional control of the helicopter but when he saw the altitude becoming low, he flew to the pre-selected landing zone where the helicopter landed hard while in a right yawing spin. During the landing the main rotor blades severed the tail boom and the helicopter came to rest on its right side.