Incident Overview
A helicopter experienced a loss of engine power while in cruise flight. The aircraft was en route to a rugged area to rescue a person. According to the pilot, the engine-out warning system activated, and after determining that manual control of the engine power was not possible, he initiated an autorotation to a creek. The landing was performed in a steep and highly vegetated area.
Post-Accident Engine Examination
Following the incident, an examination of the engine revealed that the turbine section had sustained hot corrosion (sulfidation) damage. This damage reduced the cross-sectional area of the airfoils. The degree of hot corrosion indicated that multiple over-temperature events had occurred over a number of flights. The reduced cross section led to the liberation of one or more airfoils in tensile overload. The failure of these airfoils caused secondary over-temperature and failure of other airfoils in the turbine section, eventually resulting in turbine seizure.
Thermocouple Findings
Examination of the turbine outlet temperature (TOT) thermocouples found that three of the four leads were broken. However, it could not be determined when these fractures occurred during the operation.
Conclusion
The loss of engine power was attributed to hot corrosion damage in the turbine section, which initiated a cascade of airfoil failures and eventual turbine seizure. The pilot executed an autorotation landing following the engine failure.