On August 14, 1998, at 1026 central daylight time, a Hiller UH-12E, N88782, operated by a commercial pilot, received substantial damage on impact with terrain during a forced landing near Shelton, Nebraska. The aircraft experienced a total loss of engine power while maneuvering during agricultural spraying. Visual meteorological conditions prevailed at the time of the accident. The 14 CFR Part 137 local flight was not operating on a flight plan. The pilot received serious injuries. The flight originated at a field located approximately four miles northwest of Shelton, Nebraska. The pilot reported that he had arrived at the field to be sprayed with his helicopter loaded on a truck at approximately 1015. The helicopter was loaded with chemicals and departed with 20 gallons of fuel. Three chemical dispensing passes were performed prior to initiating another "ag" turn at the edge of the field. During the "ag" turn, the engine sputtered in the stall point of the turn and then quit. The aircraft was in a 45 degree banked turn when the pilot turned the helicopter into the wind. With an airspeed of 0 knots, an altitude of 25'-50' agl and the helicopter in a descent, the pilot nosed the aircraft over in an attempt to increase airspeed. The pilot realized that he was not going to achieve enough airspeed to execute a normal auto rotation so he leveled the helicopter through the application of collective pitch to cushion the impact. The pilot recalled the left skid impacting first. An employee of the pilot stated that he had found that the electrical fuel pump was running after the accident. He also reported that all normal switches were in their correct positions according to how the pilot always selected them. Examination of the engine by a Federal Aviation Administration Inspector showed the engine to rotate and to have compression in all cylinders. Electrical continuity was established from the magnetos and through the harness. There was no fuel found in the fuel line connecting the fuel tank to the engine driven pump. The engine driven and electric fuel pumps rotated and were then disassembled but no damage was found on the impeller of the fuel pumps. The carburetor bowls contained 1/3 fuel. Approximately three gallons of fuel was drained from the helicopter fuel tank with no external leakage visually present. The fuel tank port is located at the forward end of the fuel tank. The Hiller UH-12E Flight Manual states, "Operating with fuel indicator in the yellow arc during sideward or rearward flight may result in loss of power". The yellow arc indicates a fuel range from 0 to 2.9 gallons, 0 to 11 liters, 0-17 lbs of fuel. The Hiller UH-12E Flight Manual Supplement states, "Consideration should be given to hoisting loads off the ground vertically as pulling or dragging loads off in other than a vertical direction can cause the helicopter to exceed the certified normal flight body-angle and unusable fuel envelope".