On September 24, 2002, at 1500 central daylight time, a Hughes 269A, N1040S, operated by Iowa Western Community College as a flight training aircraft, was substantially damaged during a hard landing at Council Bluffs Municipal Airport (CBF), Council Bluffs, Iowa. The certified flight instructor and dual student were practicing autorotations. Visual meteorological conditions prevailed at the time of the accident. The 14 CFR Part 91 instructional flight was not operating on a flight plan. The local flight originated from CBF about 1345. The dual student was receiving instruction in preparation for a certificated flight instructor certificate with a helicopter rating. The instructor stated that the day prior to the accident , he and the student had flown 3.2 hours performing various training maneuvers including touchdown autorotations, hovering autorotations, hovering, straight-in, and autorotations with a turn. On the day of the accident, the winds were from 170 degrees at 12 knots with peak gusts of 20 knots. An autorotation was started at 2,200 feet msl, 60 knots and abeam the pad. The instructor described the student's entry as excellent. The collective was reduced with corresponding needle split, the pedals were adjusted to keep the helicopter in trim, the cyclic was adjusted to a 50 knot attitude, and 180-degree turn was initiated. The rotor rpm was within limits through out the turn. About 1,800 feet msl, the turn was completed, the helicopter was aligned with the taxiway, in trim, airspeed slightly less than 55 knots, and the rotor rpm was in the green. At 1,500 msl, the instructor placed his left hand on the throttle and confirmed override. About 50 feet agl and just prior to deceleration, the instructor confirmed that the rotor rpm was in the green. The student started his deceleration by applying aft cyclic. About 8-12 feet agl, the student made his initial application and felt slight forward cyclic to level the helicopter was felt by the instructor. The initial pitch application was at the proper height and the proper descent. They both applied full collective with no results, and the helicopter fell thru and impacted the ground. Inspection of the wreckage revealed a fractured cyclic/mixture support attachment bracket which was sent to the National Transportation Safety Board's Materials Laboratory. Visual examination disclosed that a major portion of the fracture surface contained a very dark discoloration. The discoloration was heavier on the forward side of the fracture, and there were portions of the fracture without discoloration on the aft side of the fracture. Prolonged ultrasonic cleaning in an acetone failed to remove significant amount of this discoloration. The discoloration covered more than 85 percent of the fracture surface. Examination of the fracture surface with a scanning electron microscope after cleaning revealed that the discolored areas had a rounded globular appearance, typical of casting porosity. Features typical of overstress separation were noted in areas without discoloration. The broken arm also contained a secondary crack that extended aft from near the forward edge.