On February 13, 1998, at 1130 hours Pacific standard time, a Hiller UH-12E, N4027Z, owned and operated by Chico Aerial Applicators, Chico, California, experienced a total loss of engine power during an aerial application flight. The pilot reported that he was too low to enter an autorotation, and the helicopter touched down hard in an open field a few miles from the Chico Airport. The helicopter was substantially damaged, and the commercial pilot was not injured. Visual meteorological conditions prevailed. The flight originated from Chico at 1100. The pilot verbally stated that seconds prior to experiencing the loss of engine power he heard two loud "bang" sounds and then the engine failed. In the pilot's completed report, he reported that the engine lost power at 40 feet above ground level while he was spraying an orchard. The pilot further reported that an examination of the helicopter revealed it was out of fuel. According to the pilot, prior to and following the mishap, the fuel quantity gage indicated 12 gallons remained in the tank and evidently the fuel float had become stuck in the tank. According to the Federal Aviation Administration (FAA) coordinator, the fuel tank quantity gage and its associated erroneous reading was examined and the discrepancy that the pilot reportedly observed could not be duplicated during the postimpact examination. The FAA reported that, however, during the examination when the fuel quantity sender arm was manipulated the float could be induced to hang up vertically. Then, when lowered to the bottom of the tank, the fuel quantity would read 12 gallons. All other system circuitry and component tests were negative. No specific mechanical defect was established.