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/F50/18 Door Mechanism Gearbox Cover 5/89 Applicability: Model F27 Mark 050 with serial numbers 20103 through 20108 and 20110 through 20145. Requirement: Action in accordance with Fokker 50 SB No F50-52-005. Note: RLD AD BLA 88-96 refers. Compliance: Prior to 31 August 1989. Background: The manufacturer has determined that the operating mechanism gearbox of the passenger, cargo, and service/emergency doors, can collect water as a result of condensation; which may freeze at low temperatures and prevent the mechanism from operating correctly.