On October 10, 1998, at 1600 mountain daylight time, a Schweizer 269C, N151KC, operated by a private pilot, collided with the terrain following a loss of control while maneuvering over open land 15 miles east of Oshkosh, Nebraska. The private pilot was not injured. The helicopter was substantially damaged. The 14 CFR Part 91 flight was operating in visual meteorological conditions without a flight plan. The flight originated from Oshkosh, Nebraska, at 1445 mdt. The pilot stated that he was checking cattle while flying over "choppy" terrain at an altitude of 150 to 175 feet above the ground. He stated he was flying to the southeast then made a turn to the northeast (downwind) and had just started a turn back to the southeast when the helicopter began to settle. The pilot reported that because the terrain was uneven the helicopter rolled over to the left when it contacted the terrain resulting in extensive damage to the rotor and tail. He reported the winds were from the south southeast at 20 knots with slight gusts at the time of the accident.