COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 105 CIVIL AVIATION SAFETY AUTHORITY SCHEDULE OF AIRWORTHINESS DIRECTIVES Fokker F28 Series Aeroplanes AD/F28/49 Wing Butt Straps and Boundary-Layer Fences 9/85 Applicability: All model F28 with S/Nos 11092, 11093, 11111 to 11203 and 11205 to 11231. Requirement: Fokker SB F28/57-70. Note: Netherlands AD 85-44 refers. Compliance: Prior to 31 December 1985. Air-leakage through butt straps and boundary layer fences has an adverse effect on the aerodynamic behaviour of the wings.