Incident Overview
During a maintenance test flight, the pilot was performing blade tracking procedures when a rotor droop was observed. Subsequently, engine rpm began to decay. The pilot attempted to increase engine power, but the engine did not respond to the power input. An autorotation was initiated from approximately 450 feet above ground level. The helicopter landed hard, and during the landing, the main rotor blades contacted and severed the tail boom.
Inspection Findings
An inspection of the engine revealed that the fuel nozzle filter was completely covered with a dark green/brown colored substance and had collapsed. Additionally, the fuel filter bowl was removed, and a volume of water was present in the fuel drained from the bowl.
Fuel Analysis
Samples of the contaminated fuel were taken and analyzed. The analysis strongly indicated water contamination and possible fungal or bacteria growth in the fuel supply.
Additional Details
The pilot reported that both the fuel supplier and the mobile pick-up truck used for refueling were equipped with filtering devices. The helicopter was not equipped with an external airframe-mounted fuel filter.