The pilot took off on a flight to York, PA to refuel the helicopter and to demonstrate it to a prospective buyer while en route. Witnesses observed the helicopter shortly after departure. Two of four witnesses heard a change in the sound of the helicopter, two witnesses saw the helicopter swinging from side to side prior to crashing, and two of the witnesses saw the main rotor assembly separate from the main rotor drive shaft. One witness, who saw the helicopter flying toward his position, reported that it started to 'swoop' down, then turned upward, and then the main rotor assembly and two other pieces separated. The helicopter then turned over and crashed. The first person to arrive at the crash site said the pilot did not have a seat belt on. An exam of the wreckage revealed that the main rotor mast had separated adjacent to the main rotor system static stops. All fuselage and flight control separations were examined and found typical of overload failures. The tail cone had been severed by the main rotor.