Incident Summary
Before takeoff, the helicopter was fueled with 100LL aviation gasoline, an approved alternate fuel provided that the boost pump is used in flight. During the flight, the engine lost power. The pilot executed an autorotation into an area with tall vegetation. However, during the landing, the main rotor blades struck and severed the tail boom.
Post-Accident Inspection
Following the accident, an inspection of the fuel system revealed no evidence of contamination. The pneumatic system was pressure-tested and no leaks were found. Attempts to start the engine were unsuccessful until the fuel system was purged of air. Once purged, the engine started and ran normally for approximately five minutes.
Fuel System Examination
The fuel pump was found to be unserviceable, with worn seals and bearings. A bench test showed that the pump had a flow rate of 700 pounds per hour at 600 psi, well below the required minimum flow rate of 1,269 pounds per hour. Additionally, the power turbine governor was found to be slightly out of adjustment, and the fuel nozzle exhibited excessive streaks and voids in its spray pattern.
Manufacturer Assessment
Personnel at the manufacturer believed that the engine may have lost power due to a combination of the worn fuel pump and the use of 100LL fuel on a 94-degree Fahrenheit day, or possibly from vapor lock.