What was found
AIRCRAFT DEPARTED, AFTER CLIMBOUT, WHILE TRIMMING FOR CRUISE, THE ACFT DEVELOPED A VIBRATION. PILOT ELECTED TO DIVERT TO INVESTIGATE PROBLEM. UPON LANDING, PILOT DETERMINED THAT THE LT ELEVATOR TRIM TAB WAS LOOSE. SUBSEQUENT INVESTIGATION BY MAINTENANCE PERSONNEL DETERMINED THAT THE TRIM TAB CONTROL ROD HAD BROKEN. MAINTENANCE DETERMINED THAT AT SOMETIME DURING THE AIRCRAFT'S HISTORY SOMEONE HAD DRILLED OUT A TAPER PIN CONNECTING HOLE AND INSTALLED AN AN BOLT. THIS CAUSED THE PART TO FAIL. WE HAVE EXAMINED THE OTHER SIDE OF THIS ACFT AND THE TRIM ACTUATORS ON THE REST OF OUR FLEET AND FOUND NO OTHER INCIDENTS OF THIS TYPE OF IMPROPER REPAIR.