COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 105 CIVIL AVIATION SAFETY AUTHORITY SCHEDULE OF AIRWORTHINESS DIRECTIVES Pilatus Porter PC-6 Series Aeroplanes AD/PC-6/39 Wing Spar and Lift Strut Fatigue Lives 7/93 Applicability: All PC-6 series aircraft. Requirement: Retire the main spar and lift strut on each wing. Compliance: Retire each component before it achieves10000 hours time in service. Note: Operation beyond 10000 hours may be permitted if the components are inspected in accordance with a Supplemental Structural Inspection Program (SSIP) approved by the Authority. Background: The life limits are based on the limited available fatigue data. There may be scope for the Authority to approve an increase after receipt of further analysis of worldwide fleet data and development of a SSIP.