On June 10, 1997, at 1830 hours Pacific daylight time, a Bell UH-1B, N888SJ, owned and operated by San Joaquin Helicopters, experienced a partial loss of engine power while spraying a field of tomatoes near Heron, California. The pilot reported that he was flying at a low altitude over the field when power was lost. He autorotated and landed hard in the field. During the touchdown sequence, a main rotor blade severed the tail boom. The helicopter was destroyed by ground fire. The engine continued to operate for between 10 and 12 minutes following touchdown. The commercial pilot was not injured. Visual meteorological conditions prevailed at the time, and no flight plan was filed. The flight originated from the bed of a truck near the field around 1820. According to the Federal Aviation Administration coordinator, no wires or other obstructions were noted in the vicinity of the accident site. The wreckage examination was limited because of extensive fire damage to the helicopter. No findings were noted concerning the loss of engine power.