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/F50/53 Fuselage Skin Above Forward Passenger Door 4/92 Applicability: Serial numbers 20103 - 20108 inclusive, 20110 - 20149 inclusive and 20151 - 20155 inclusive. Requirement: Modify in accordance with Fokker SB F50-53-032 dated 23 July 1990. Note: RLD AD (BLA) 90-090 refers. Compliance: Prior to accumulating 15 000 flight cycles. Background: During full scale fatigue tests, cracks were found in the skin above the passenger door at frame STA.3670. To increase the fatigue life of the fuselage in this area to more than 90 000 flight cycles install a reinforcement plate.