COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 105 CIVIL AVIATION SAFETY AUTHORITY SCHEDULE OF AIRWORTHINESS DIRECTIVES Fokker F100 (F28 Mk 100) Series Aeroplanes AD/F100/15 Centre Section Frame Strips 4/99 Applicability: F.28 Mk.0100 aircraft, serial numbers 11244 through 11371. Requirement: Install two reinforcement plates each at fuselage STA.14911 and STA.17011 in accordance with Fokker Service Bulletin (SB) F100-53-072 dated 12 March 1993. Note: RLD BLA 93-037(A) refers. Compliance: Unless previously accomplished, before accumulating 24,000 flight cycles since new. This Airworthiness Directive becomes effective on 22 April 1999. Background: During fatigue tests on the F.28 Mk.0100, cracks were discovered in the frame strips at fuselage STA.14911 and STA.17011. This AD requires a modification to increase the crack initiation threshold beyond 90,000 flight cycles.