Accident Summary
During an instructional flight, a helicopter performed autorotations with a certified flight instructor (CFI) and a dual student seeking a CFI certificate present. The helicopter landed hard despite the application of cyclic control.
Investigation Findings
Examination of the wreckage identified a fractured cyclic/mixture support attachment bracket. The fracture surface exhibited a very dark discoloration covering more than 85 percent of the area, with heavier discoloration on the forward side and portions without discoloration on the aft side. Prolonged ultrasonic cleaning in acetone failed to remove a significant amount of the discoloration.
Scanning electron microscope analysis revealed that the discolored areas had a rounded globular appearance, typical of casting porosity. Features consistent with overstress separation were observed in areas without discoloration. Additionally, a secondary crack extended aft from near the forward edge of the broken arm.