On August 26, 1994, at 1745 hours central daylight time, a Bell BH-47 Mark-6 helicopter, N19JM, operated by Northland Helicopter, Inc., of Stacyville, Iowa, impacted in a crop field 4 miles south of Lake City, Minnesota, and was substantially damaged. The commercially certificated pilot was uninjured and no fire occurred. Visual meteorological conditions existed at the time of the accident and no flight plan was filed. The flight operated under 14 CFR Part 137 as an agricultural application aircraft, and the flight had originated from a tending vehicle near the accident site at 1530 hours CDT. The pilot reported that after making an application turn, rotor RPM decayed and he was unable to maintain level flight or regain the rotor rpm. The temperature was 74 degrees Farenheit, the humidity was described by the pilot as high, the elevation was 1300 feet above mean sea level, and the density altitude was at least 2000 feet. Post crash inspection of the helicopter and powerplant failed to reveal any discrepancies.