On May 29, 2002, about 1000 eastern daylight time, a Hughes OH-6A helicopter, N42SD, operated by the Erie County Sheriff's Department, was substantially damaged while landing at a private airstrip near Angola, New York. The certified flight instructor (CFI) and student pilot received minor injuries. Visual meteorological conditions prevailed, and no flight plan was filed for the public use instructional flight conducted under 14 CFR Part 91. According to the CFI, the helicopter departed the Sheriff's Heliport in Hamburg, New York, about 0930, with the student pilot at the controls. The flight proceeded west to a pre-determined training grass strip about 2 miles from the Angola Airport. The CFI instructed the student to perform a high "recon," followed by a low "recon" while in a left hand pattern, in order to inspect the intended practice field. The helicopter was about 1,500 feet above the grass strip, when the CFI requested that the student conduct a normal approach to the runway midfield, and terminate to a hover. The CFI recalled that the gauges were in the normal green range as the student setup for the approach. The approach was into the wind, at an airspeed of 65-70 knots. At the decision height, approximately 75-100 feet above the ground, the CFI observed the student begin to bleed off airspeed by pulling aft on the cyclic. The helicopter then abruptly made an uncommanded yaw to the left, and began to roll. After the CFI observed the rotor tachometer " bleeding off," and did not see the engine needle on the left hand side of it's gauge, he assumed control of the helicopter. The CFI proceeded to lower the collective, and attempted to maintain a glide, while applying forward and right cyclic to counter the left roll. About 30 feet above the ground, he applied aft cyclic to flare, and then forward cyclic to level the skids. The helicopter touched down on the skids, level with the ground, on the side of the grass strip. The helicopter skidded forward about 50 feet, into a culvert ditch, where it came to rest. Inspection of the wreckage by a Federal Aviation Administration (FAA) inspector revealed that the tail boom separated from the fuselage, and substantial damage was sustained to the rotor blades. On June 5 and 6, 2002, the engine and airframe were examined at the Erie County Sheriff's Department maintenance facility, located in Hamburg, New York. The examination did not reveal any pre-impact failures. On July 1, 2002, the engine was examined and tested under the supervision of a FAA Inspector, at the Rolls-Royce Allison Engine Company, Indianapolis, Indiana. The tests on the engine were in accordance with the model 250-T63-A700 production test specifications. With the engine in the standard test configuration, all response times were within limits, and the engine met all performance parameters. The recorded weather at a nearby airport, about the time of the accident, included winds from 200 degrees at 7 knots.