COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 105 CIVIL AVIATION SAFETY AUTHORITY SCHEDULE OF AIRWORTHINESS DIRECTIVES Sikorsky S-76 Series Helicopters AD/S-76/26 Amdt 1 Vertical Stabiliser Pylon Leading Edge Skin 11/85 Applicability: All models. Requirement: 1. Sikorsky Alert Service Bulletin No. 76-55-9; or 2. Sikorsky Alert Service Bulletin No. 76-55-11 (Terminating Action); or 3. Sikorsky Customer Service Notice No 76-141B (Terminating Action). Compliance: For para. E(1) of ASB 76-55-9: Within the next 25 hours time in service after 25 March 1983 and thereafter at intervals not exceeding 25 hours time in service. For para. E(2) of ASB 76-55-9: Within the next 100 hours time in service after 25 March 1983 and thereafter at intervals not exceeding 100 hours time in service. Background: Cracks have been found in service in the pylon upper leading edge skin near the tail rotor gear box. This Directive has been amended to provide terminating action for modified helicopters. However, note that CSN 76-141 no longer constitutes terminating action for the requirements of AD/S-76/29. The reason is that forward spar cracks have been found in modified helicopters, although at this stage there have been no reports of L.E. skin cracks. It is expected that an improved modification will be developed by the manufacturer.