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/F50/71 Wings - Bottom Skin Access Covers 8/96 Applicability: Model F.27 Mk 050 Serial numbers 20103 to 20263. Requirement: Action in accordance with Fokker SB F50-57-015. Note: RLD BLA 1996-042(A) refers. Compliance: Prior to the accumulation of 24,000 flight cycles since new. This Directive has effect from 18 July 1996. Background: The heads of some countersunk screws used to attach access panels P/N 923AB and 924AB have been found not to be seating properly. This condition may result in unequal loads and cause fatigue cracking in the rabbets of the centre wing bottom skin.