On June 25, 2002, at 1245 eastern daylight time, a Sikorsky S-55-QT, N2300Z, registered to Foxtrot Incorporated and operated by a private pilot rolled over on the left side during a maintenance test flight at Sanford Airport, in Orlando, Florida. The maintenance test flight was operated under the provisions of Title 14 CFR Part 91 and visual flight rules. Visual meteorological conditions prevailed at the time of the accident. The helicopter sustained substantial damage, and the private pilot and passenger were not injured. The helicopter was on the second phase of the flight at the time of the accident on June 25, 2002. According to the pilot, during the maintenance check flight two auto-rotations at max gross weight with a neutral center of gravity were conducted. During the second maintenance check flight, on the initial run-up the pilot engaged the rotor clutch and heard a loud "bang". The cyclic control pulled from the pilot's hand, and the pilot rolled the throttle to ground idle to regain control the cyclic control. The helicopter rocked from left to right and rolled over on its side. Examination of the airframe found that the cyclic lateral control rod end bearing on the transmission fractured. There was no prior evidence of a preexisting fracture region or improper material. Scanning electron microscope examination of the fractured surfaces showed both fracture origin features typical of overstress. According to the operator of the helicopter, when the rotor is engaged the hydraulic boost is not effective until the main transmission reaches a speed where it produces sufficient hydraulic pressure to offset the back forces. These back forces are transmitted back to the cockpit flight controls, at this time the cyclic control pulled from the pilot's hand, and the control rod failed. Examination of the main rotor revealed all four main blades were curled from the blade tip to the main rotor. The fuselage displayed buckling in the tail cone section. The tail rotor was also curled inward. No other mechanical or flight control malfunctions were reported by the pilot.