COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 105 CIVIL AVIATION SAFETY AUTHORITY SCHEDULE OF AIRWORTHINESS DIRECTIVES Fokker F27 Series Aeroplanes AD/F27/121 Flight Controls - Elevator Trim System 2/91 Applicability: F27 aircraft with S/No's 10102 to 10684 inclusive, 10686, 10687 and 10689 to 10692 inclusive. Requirement: Action in accordance with the technical requirements of Netherlands AD BLA 90-106. Note: Fokker SB F27/27-130 refers. Compliance: As specified in the Requirement document with effective date 5 October 1990. Background: Country of origin AD. To modify the elevator and trim tab systems so that they are considerably more resistant to flutter and easier to maintain.