On December 6, 1997, about 1400 Pacific standard time, N171HH, an Enstrom F-28F helicopter, operated by the owner/pilot, impacted terrain during a forced landing near John Day, Oregon, and was substantially damaged. The forced landing was precipitated by a loss of engine power while manuevering. The airline transport pilot, the sole occupant, was not injured. Visual meteorological conditions prevailed and no flight plan had been filed. The aerial application flight departed from John Day about one hour prior to the accident and was conducted under 14 CFR Part 137. In a written statement, the pilot reported that he had just returned from seeding about 20 acres, and landed to refill the seed bucket. The pilot stated that after the bucket was filled, he lifted off and headed downhill towards the working area. The pilot stated that he "noticed some rotor droop and lowered the collective and twisted on some more throttle to get the rpm back." The pilot stated that nothing happened and the "throttle hit the stop." The pilot stated that he was aware that he was going to impact the terrain and slowed the forward speed. The seed bucket swung forward and the helicopter landed on top of the bucket. The helicopter bounced twice downhill and subsequently came to rest on its left side. Two Federal Aviation Administration (FAA) aviation safety inspectors from the Portland Flight Standards District Office, Hillsboro, Oregon, inspected the engine. The inspectors reported that the engine was prepared for a test run. After the preparation, the engine was started and ran for about five to ten minutes without any noted problems before it was shut down. Fuel samples were taken and filters were checked with no contaminants found. The fuel mixture was checked and found okay. Control continuity was established throughout the aircraft. The pilot provided his calculations for the weight of the helicopter at the time of the accident. The calculations indicated that the helicopter's weight was approximately 76 pounds under the maximum gross weight of 2,600 pounds.