Document ID: chunk:federal_register_of_legislation:F2008L03494:body:0:p2
Version: federal_register_of_legislation:F2008L03494
Segment Type: other
Provision Reference: 
Character Range: 2807–3945

occurrence of unusual vibrations during the start phase of the main rotor on one helicopter.  These vibrations stopped after the application of torque.  The troubleshooting accomplished by the maintenance personnel showed that six of the eight attachment screws of the lower hub-shaft bearing support had loosened.  After inspection of the affected operator's fleet, the attachments screws of the lower hub-shaft bearing support were found loosened on the main transmissions of two additional helicopters.  The lower hub-shaft bearing consists of a ball bearing and a roller bearing.  The outer race of the roller bearing is fixed to the housing with screws.  Should all attachment screws become loose, the outer race of the roller bearing might separate, which would constitute an unsafe condition.  In such case, however, the axial guidance of the rotor hub-shaft would still be ensured.

             For the reasons described above, this AD requires the inspection of the main transmission attachment hardware and installation of locking washers.

Charles Lenarcic
Delegate of the Civil Aviation Safety Authority

17 September 2008