COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 105 CIVIL AVIATION SAFETY AUTHORITY SCHEDULE OF AIRWORTHINESS DIRECTIVES Fokker F50 (F27 Mk 50) Series Aeroplanes AD/F50/46 Forward Fuselage Skin Dimples 10/91 Applicability: Serial numbers 20103 to 20108 inclusive, 20110 to 20149 inclusive, and 20151 and 20152. Requirement: Action in accordance with the Technical Requirements of RLD AD 89-152, dated 15 December 1989. Note: Fokker Service Bulletin F50-53-018, dated 8 December 1989 refers. Compliance: Prior to exceeding 10 000 pressurisation cycles. Background: During full-scale fatigue testing, cracks were found in the forward fuselage skin, which originated at the rivet hole dimples. To improve the fatigue life of the skin-to- stringer and skin-to-frame connectors, this AD calls for the installation of reinforcement angles.