What happened
During an instructional flight, a certified flight instructor and a student pilot were practicing autorotations. During the maneuvers, the helicopter landed hard despite the pilot applying cyclic input. There were no fatalities or injuries reported in the incident.
The investigation
An inspection of the wreckage focused on the control components. Investigators discovered a fractured cyclic/mixture support attachment bracket. A significant portion of the fracture surface, covering more than 85 percent of the area, exhibited a very dark discoloration. This discoloration was heavier on the forward side of the fracture, while some portions on the aft side remained without discoloration.
Following the discovery, the component underwent prolonged ultrasonic cleaning in acetone, which failed to remove the significant amount of dark discoloration. Subsequent examination using a scanning electron microscope revealed that the discolored areas possessed a rounded, globular appearance characteristic of casting porosity. In areas where no discoloration was present, features typical of overstress separation were observed. Additionally, the broken arm contained a secondary crack extending aft from near the forward edge.