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/F50/33 Amdt 1 Landing Gear - Extension/Retraction Control 7/92 Applicability: F27 Mk 050 aircraft Serial Numbers 20103 to 20197 inclusive. Requirement: 1. Connect the DOWN solenoid of the landing gear selector valve to the EMERGENCY DC bus No 2 instead of DC bus No 2 as outlined in Fokker Service Bulletin F50-32-013 dated 16 October 1989, or Note: AD/F50/33 covers Requirement 2 of the RLD Airworthiness Directive, Flight Manual amendment A/ANF 2750/10 has been issued to cover Requirement 1 of the RLD Airworthiness Directive. 2. Replace the Landing Gear Selector Valve P/N 114044002 with a modified Valve P/N 114044003 as outlined in Fokker Service Bulletin F50-32-016 dated 23 December 1991. Compliance with SB F50-32-016 and removal of the Flight Manual amendment A/ANF 2750/10 is an alternative means of compliance with this AD. Note: RLD Airworthiness Directive BLA 89-138 Issue 3 refers. Compliance: The Compliance of the original issue of this Directive was prior to 15 March 1990. This amendment is effective from 25 June 1992. Background: Fokker have found that an inadvertent UP selection of the landing gear selector valve is possible as a result of a leaking pilot valve at the moment the DOWN solenoid is de-energised. The original issue of this Directive required modification to the system wiring to prevent such an occurrence. Amendment 1 is issued to advise of an alternative method of compliance and increases the serial number range of aircraft affected.