Narrative
While performing a visual inspection of a power line support structure, the helicopter was in a stable hover at an altitude of approximately 120 feet above ground level. During this operation, the helicopter experienced a complete loss of engine power. The pilot's ability to maneuver was constrained by the nearby support structure. The pilot attempted to execute an autorotation to achieve a forced landing. However, during this sequence, the helicopter collided with terrain.
Investigation Findings
The investigation focused on the engine failure. It was determined that the engine's fuel nozzle was delivering a nonuniform fuel spray. This condition caused a localized over-temperature in the turbine section of the engine. The excessive heat led to rubbing of the turbine blades. Eventually, a second stage turbine blade failed due to fatigue, resulting in the separation of the blade. This mechanical failure precipitated the complete loss of engine power.
Probable Cause
The probable cause of the accident was the nonuniform fuel spray from the engine's fuel nozzle, which caused a localized over-temperature in the turbine section, leading to turbine blade rub and the eventual fatigue separation of a second stage turbine blade, resulting in loss of engine power.