Following completion of the helicopter's annual inspection, the aircraft mechanic/pilot departed Clover Field in Houston for the R22's home base in Austin, TX. One witness observed the helicopter in cruise flight, then saw a large piece separate from the helicopter. Other witnesses heard a loud noise and observed pieces falling from the helicopter. The main wreckage came to rest on the south side of Highway 290 and exhibited evidence that a main rotor blade had contacted the tail boom. The tail boom and tail rotor were located on the opposite side of Highway 290. No evidence of preimpact failure of the engine or flight controls could be identified. Visual meteorological conditions were reported with winds from 130 degrees at 12 knots. Multiple electrical lines that cross Highway 290 revealed no evidence of being struck by the helicopter. No abrupt maneuvers were observed by witnesses. Damage to the main rotor hub suggested low main rotor RPM when the main rotor struck the tail boom.