Accident Sequence
The pilot departed at 1805 with 150 pounds of fuel remaining, intending to fly to Beckley, West Virginia for refueling. After leveling off at about 3,000 feet MSL for three to four minutes, the pilot noticed an unusual jerk or vibration originating from the rear of the helicopter. Suspecting a possible tail rotor problem, he lowered the collective and turned toward an open area. Shortly after, he noted that the engine had lost power. During the subsequent autorotative landing, the helicopter touched down hard without sufficient rotor RPM to cushion the impact.
Investigation Findings
Examination of the fuel system found approximately 20 gallons of fuel remaining in the tanks. The engine and fuel pumps operated normally during bench testing. Further inspection revealed that when the fuel in the aft tank dropped below the standpipe level, fuel would leak to the front tank. Additionally, there was virtually no induced flow in the left transfer system.
Fuel System Examination
Disassembly of the fuel system components identified two anomalies. The standpipe in the aft tank was not properly aligned, resulting in an improperly seated O-ring that allowed a leak. Also, a piece of masking tape was found lodged in the inlet to the left transfer pump. As the front tank neared empty during operation, air was entrained into the fuel, leading to the loss of engine power.