On June 14, 1994, approximately 1650 hours Pacific daylight time (pdt), a Hiller/Soloy UH-12L4, N67264, registered to and being flown by James R. Pope, a certificated commercial pilot, was substantially damaged during an autorotation landing to a hillside following a loss of directional control while in cruise approximately 5 miles southwest of Clarkston, Washington. The pilot and two passengers received minor injuries. Visual meteorological conditions existed at the time, and no flight plan had been filed. The flight, which was a post maintenance evaluation, was to have been operated in accordance with 14CFR91, and originated from the pilot's private helicopter base near Clarkston, Washington, approximately 1600. The pilot reported to the Investigator in Charge that while in slow cruise several hundred feet above ground he heard a "bang" and began to lose directional control of the rotorcraft. He attempted to regain directional control by lowering the nose and increasing airspeed. This, however, was unsuccessful and the rotorcraft entered a spiral. He then elected to execute a powered autorotation to a forced landing. The pilot reported that during the flare to sloped terrain the aircraft landed hard and the main rotor blades and tail boom impacted the ground and separated (refer to photograph 01). On site examination by FAA Inspector Tex Gaston revealed that a substantial portion of both tail rotor blades had separated (refer to photograph 02). Further examination revealed that the aft retaining pin which inserts through the side (lateral axis) of the movable, ballast weight bar, was absent. Its retaining wire, which attaches the pin to the tailboom, was observed to be broken. The 17 pound ballast bar, which is used to change the center of gravity of the rotorcraft dependent upon the inclusion of passengers, was then able to drop down vertically a short distance and release from the aft retaining bolt. The ballast bar then, still retained by the forward bolt, could now swing left/ right allowing its aft end to enter the plane of rotation of the tail rotor blade. Scratch marks were observed on the aft end of the ballast bar (refer to photograph 03). The pilot reported to Inspector Gaston that the aft pin had been installed prior to departing on the flight.