AIRWORTHINESS DIRECTIVE On the effective date specified below, and for the reasons set out in the background section, the CASA delegate whose signature appears below revokes Airworthiness Directive (AD) AD/F50/84 and issues the following AD under subregulation 39.1 (1) of CASR 1998. The AD requires that the action set out in the requirement section (being action that the delegate considers necessary to correct the unsafe condition) be taken in relation to the aircraft or aeronautical product mentioned in the applicability section: (a) in the circumstances mentioned in the requirement section; and (b) in accordance with the instructions set out in the requirement section; and (c) at the time mentioned in the compliance section. Fokker F50 (F27 Mk 50) Series Aeroplanes AD/F50/84 Amdt 1 Fuel - Ventilation Float Valve & Sniffle Valve 13/2004 Applicability: Model F.27 Mk.050, 0502 and 0604 aeroplanes with serial numbers 20103 to 20204 and 20206 to 20212. Requirement: 1. Replace Ventilation Float Valves Part Number (P/N) 29000 and P/N 29000-1 with improved units P/N 29000-3 in accordance with Part 2 of Accomplishment Instructions of Fokker Services Service Bulletin (SB) F50-28-020 dated 15 April 2003 or SB F50-28-022 dated 23 August 2004 as is applicable. 2. Replace Sniffle Valves P/N 2770002-101 with P/N 2770002-103 in accordance with Part 2 of Accomplishment Instructions of Fokker Services SB F50-28-021. 3. No Ventilation Float Valves P/N 29000 or P/N 29000-1 or Sniffle Valves P/N 2770002-101 may be installed on any aircraft. Later CAA NL approved revisions of the referenced service bulletins may be used in lieu of those detailed in the requirements section of this Directive. Note: CAA NL AD 2003-090/2 and EASA Approval No 2004-10037 dated 30 September 2004 refers. Compliance: For Requirement 1: For P/N 29000 valves, remains unchanged as within 24 months after 17 September 2003. For P/N 29000-1 valves, within 10 calender months from the effective date of this Directive. For Requirement 2: Remains unchanged as; Within 10 months after 17 September 2003. For Requirement 3: After the effective date of this Directive. This Amendment becomes effective on 23 December 2004. Fokker F50 (F27 Mk 50) Series Aeroplanes AD/F50/84 Amdt 1 (continued) Background: Operators have reported four occurrences of fuel collector tank implosion caused by insufficient ventilation of the fuel tanks. It is thought that freezing (or failure) of both the ventilation float and sniffle valves are the reason for reduced ventilation. The intent of this Directive is to correct an unsafe condition by replacing both valves with those of an improved design. Further testing has identified another ventilation float valve that has similar problems to those valve detailed in the original issue of this Directive. The original issue of this Directive became effective on 15 September 2003. James Coyne Delegate of the Civil Aviation Safety Authority 9 November 2004 The above AD is notified in the Commonwealth of Australia Gazette on 1 December 2004.