THE PILOT LIFTED THE HELICOPTER OFF THE HELIPAD AND IT WAS OBSERVED TO TURN TO THE RIGHT. IT THEN CLIMBED TO APPROXIMATELY THIRTY FEET AND NOSE SLOWLY DOWNWARD BEFORE IT ROLLED TO THE RIGHT AND DESCENDED UNCONTROLLED TO IMPACT THE TERRAIN AND SEVERAL CARS IN AN ADJACENT PARKING LOT. THE PILOT WAS THROWN FROM THE COCKPIT WHEN HIS SEATBELT FAILED. HE WAS NOT WEARING A SHOULDER HARNESS. POST-ACCIDENT INVESTIGATION REVEALED THAT COMPANY MAINTENANCE PERSONNEL HAD NOT INSTALLED THE CYCLIC INTERCONNECT TUBE AFTER THE DUAL CONTROLS WERE REMOVED.