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/F50/12 Engine Anti-Ice Control Unit 3/89 Applicability: F27 Mark 050 aircraft. Requirement: Replace engine anti-ice control units in accordance with the requirements of Fokker SB F50-30-003. Note: RLD AD BLA No. 88-105 refers. Compliance: Forthwith. Background: Following a number of flight tests which revealed ice formation in the engine intake duct, the manufacturer has released a new anti-ice control unit which increases the protection of the intake duct against ice formation. Fokker SB F50-30-003 details the procedure for replacement of the anti-ice control unit.