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/F50/54 Fuselage Skin to Stringer and Skin to Frame Connections Applicability: Serial numbers 20103 - 20108 inclusive and 20110 - 20149 inclusive. Requirement: Modify in accordance with Fokker SB F50-53-037 dated 14 May 1991. Note: RLD AD (BLA) 91-044 refers. Compliance: Prior to accumulating 24 000 flight cycles. 4/92 Background: During full scale fatigue tests, cracks were found in the outside skin of the forward fuselage section (AD/F50/46 was issued to cover this subject). The centre fuselage section frame-to-stringer connections are similar to those in the forward section, so, to improve the fatigue life of these connections, this Directive requires the installation of additional reinforcement angles.