Incident Overview
A Hiller UH-12E helicopter suffered a total loss of engine power while maneuvering during an agricultural spraying operation. The aircraft subsequently impacted terrain during a forced landing.
Engine Examination
A Federal Aviation Administration Inspector examined the engine. The engine rotated and demonstrated compression in all cylinders. Electrical continuity was established from the magnetos and through the harness. No fuel was found in the fuel line connecting the fuel tank to the engine-driven pump. The engine-driven and electric fuel pumps rotated and were disassembled; damage was observed on the impeller of the fuel pumps. The carburetor bowls contained one-third fuel.
Fuel System Findings
Approximately three gallons of fuel was drained from the helicopter's fuel tank. No external fuel leakage was visually apparent. The fuel tank port is located at the forward end of the fuel tank.
Flight Manual Information
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, or 0 to 17 pounds 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."