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/F100/7 Vertical Stabiliser 4/99 Applicability: F.28 Mk.0100 aircraft, serial numbers 11244, 11245, 11250 through 11256 and 11268 through 11273. Requirement: Inspect the vertical stabiliser and install three reinforcement doublers in accordance with Fokker Service Bulletin (SB) F100-55-011 dated 1 October 1991. Note: RLD BLA 91-117 refers. Compliance: Unless previously accomplished, before accumulating 6,500 flight cycles since new. This Airworthiness Directive becomes effective on 22 April 1999. Background: Fatigue tests on the F.28 Mk.0100 have revealed cracks in the skin of the vertical stabiliser at rib 5.0 near intermediate spars I and II, and in the underlying structure. This AD requires a modification to prevent cracks and to improve the fatigue life of the vertical stabiliser.