COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 105 CIVIL AVIATION SAFETY AUTHORITY SCHEDULE OF AIRWORTHINESS DIRECTIVES Short SC7 (Skyvan) Series Aeroplanes AD/SC7/18 Ground/Air Lever Spring Heel Block - Modification 2/81 Applicability: All models SC7, Series 3, 3A and 3M. Document: Shorts SB No. 76-58, Revision No. 1. Compliance: Within 300 hours time in service after 31 March 1981. Background: An improved method of security the retaining pin in the ground/air lever spring heel block has now been developed by the manufacturer. The bulletin has been classified as mandatory by the UK CAA.