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/F50/28 Stringer 18 Between Stations 4875 and 5325 13/89 Applicability: F27 Mark 50 aircraft serial numbers 20103 through 20108 and 20110 through 20123. Requirement: Action in accordance with Fokker Service Bulletin F50-53-017, dated 30 June 1989. Note: RLD BLA 89-077 dated 12 July 1989 refers. Compliance: Prior to accumulating 10000 flights. Background: During full-scale fatigue testing, cracks were found in the skin, near the intercostal of the toilet wash-water tank. These cracks were found to initiate at the dimpled rivet holes in the skin-to-stringer connection. To improve the fatigue life of this connection, inspection and reinforcement of the affected skin is required.