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/F50/52 Cockpit Window Post Attach Angles 4/92 Applicability: F27 Mk 50 series serial numbers: 20103 to 20108 inclusive; 20110 to 20149 inclusive; and 20151 and 20152. Requirement: Modify in accordance with Fokker Service Bulletin F50-53-029 dated 1 August 1990. Note: RLD AD (BLA) 90-084 refers. Compliance: Required before accumulating 30 000 flight cycles. Background: During a full scale fatigue test of the forward fuselage, five of the attachment angles at the upper and lower ends of the window posts showed fatigue cracks at 45 000 simulated flight cycles. To extend the fatigue life of the window posts the 16 existing aluminium alloy angles are replaced by corrosion resistant steel angles.