On August 10, 1996, about 1425 central daylight time, a Hughes 269A, N8784F, registered to Joyride Ventures, Inc., crashed at the Helicopter Technologies facility, Cottondale, Florida, while on a Title 14 CFR Part 91 maintenance test flight. Visual meteorological conditions prevailed at the time and no flight plan was filed. The helicopter received substantial damage and the commercial-rated pilot received minor injuries. The passenger received serious injuries. The flight was originating at the time of the accident. The pilot stated the helicopter owner and his pilot had reported the helicopter had a tendency to make a uncommanded roll to the right. On run-up he checked the controls and found nothing unusual. As he lifted the aircraft to a 3 feet hover the aircraft started a vertical vibration which increased to a severe vertical vibration within seconds. The aircraft also started a lateral vibration which increased to a severe lateral vibration. He noticed that one of the blades appeared to jump 12-18 inches from the normal tip path plane. He felt that the helicopter was going to come apart and elected to set it back on the ground. As he set down with the vibration continuing, the helicopter started to come apart and rotate to the right. Review of maintenance records was conducted by an FAA inspector. Records showed the main rotor blade hydraulic friction dampners had been overhauled just before the test flight. Teardown examination of the dampners by an FAA inspector showed the dampners had not been reassembled in accordance with manufacturers maintenance instructions. The maintenance instructions state that improper assembly of the dampners could lead to conditions that could result in ground resonance and destruction of the helicopter. Examination of the helicopter by the FAA inspector showed the failure of the main rotor system and destruction of the helicopter was a result of ground resonance. (See attached FAA inspector statement.)