Incident Summary
During external load operations, the helicopter experienced a loss of engine power. The pilot performed an autorotation and forced landing, during which the helicopter sustained substantial damage.
Witness Report
A witness reported hearing a loud bang, followed by the engine spooling down. The witness also observed smoke coming from the engine as the helicopter descended through trees. The helicopter landed hard on a tree stump located under the pilot's seat area.
Inspection Findings
Postaccident inspection of the turbine engine revealed excessive blending in the web of the first stage turbine wheel. Within the blended area, a notch exhibited a radius sharper than allowed by blend limits. The manufacturer's metallurgists believed the notch was created by a hand-held grinder. It could not be determined whether the manufacturer of the turbine wheel or an overhaul facility made the grinding marks.