Incident Summary
The pilot reported that while overflying wooded terrain at 1,000 feet mean sea level (MSL), the helicopter's engine lost power. The pilot executed an autorotation to a hilly field. During the landing, the rotor blade separated the tailboom from the helicopter.
Fuel System Findings
According to the pilot, the fuel low warning light did not illuminate before the power loss occurred. Subsequent examination of the helicopter revealed that both fuel tanks were empty. Additionally, the fuel emergency vent valve had malfunctioned. As a result of this malfunction, the fuel cell decavitated and collapsed. This collapse held the fuel quantity probe in a position that indicated approximately one-quarter tank of fuel remaining, despite the tanks being empty.
Sequence of Events
The empty fuel tanks and the false indication from the fuel quantity probe meant the pilot did not receive a timely low-fuel warning. The power loss occurred due to fuel exhaustion, forcing the autorotation that resulted in the tailboom being severed by the rotor blade during landing.