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/F50/13 Accessory Bay Ventilation Air Outlet 5/89 DM Applicability: S/No. 20103 to 20108 and 20110 to 20134 inclusive. Requirement: Action in accordance with Fokker S.B. F50-54-004. Note: RLD AD 89-021 refers. Compliance: Prior to 31 May 1989. Background: Cold air moisture and rainwater can enter the aircraft through the ventilation air outlet. This has caused ice buildup on control cable systems at high altitude, low OAT and during high humidity conditions.