What was found
THE ELEVATOR TORQUE TUBES HAD UNBONDED CREATING MOVEMENT BETWEEN ELEVATOR TORQUE TUBE & COLLAR. WE HAVE NOTED THIS CONDITION ON AT LEAST 10 DIFFERENT SERIAL NUMBERS OF ACFT. NOTE, THE RUDDER HAS SAME METHOD OF ATTACHMENT & FAILURES HAVE BEEN NOTED AT THAT LOCATION. THE ANODIZING METHOD USED DOES NOT PROMOTE ADHESION BETWEEN PARTS & SEEMS TO BE THE FAILURE POINT. IN ADDITION, INSTRUCTIONS IN REPAIR DOCUMENT (FSI-189) STATES TO APPLY ALODINE CHEMICAL CONVERSION COATING TO THE BONDED SURFACES WHICH IS NOT RECOMMENDED IAW THE LOCTITE HYSOL PREPARATION GUIDE. RESULTING CONDITION DUE TO THIS DEFECT RISKS LOSS OF CONTROL OF THE ACFT DUE TO A BREAKAWAY OF THE ELEVATOR & RUDDER FROM RESPECTIVE BELL CRANKS.