AIRWORTHINESS DIRECTIVE For the reasons set out in the background section, the CASA delegate whose signature appears below issues the following Airworthiness Directive (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/F50/83 Grimes Aerospace Passenger Service Units 6/2003 Applicability: Model F.27 Mk.050 and F.27 Mk.0502 aeroplanes, all serial numbers (S/N), with Grimes Aerospace Passenger Service Unit (PSU) Part Number (P/N) 10-1178-XX (XX may be any number) installed. Requirement: 1. Unless previously modified in accordance with either Grimes Aerospace Company Service Bulletin (SB) 10-1178-33-0140 dated 15 October 1993 or Revision 1 dated 25 March 1996, modify the Grimes Aerospace PSUs P/N 10- 1178-XX (XX may be any number) in accordance with SB 10-1178-33-0040 Revis ion 1. 2. Apply sealant to the aft air-conditioning duct ends in accordance with the Accomplishment Instructions of Fokker Services SB F50-25-055 dated 17 March 2003. Note 1: Aeroplane S/N 20306, 20307, 20309, 20310 and 20312 had the air- conditioning duct sealant modification incorporated before delivery. Note 2: CAA(NL) BLA 2003-035 (A) refers. Compliance: For Requirements 1 and 2 - Within three years after the effective date of this Directive. This Airworthiness Directive becomes effective on 12 June 2003. Background: Over the years Fokker 50 operators have reported incidents of smoke in the aft passenger compartment during flight, apparently due to overheating of a PSU. Investigation has shown the overheating to occur due to water leakage onto the PSU electrical connector. To address this problem, Fokker Aircraft issued a SB which recommended a one-time inspection of the PSU panels and, if leakage was detected, the cleaning of the connector and modification of the PSU panel. As the smoke problems appeared to be minor and were not considered hazardous at the time, the inspection and modification were not made mandatory. As a result, only few operators accomplished the inspection/modification on affected PSU panels. Fokker F50 (F27 Mk 50) Series Aeroplanes AD/F50/83 (continued) Since the unsafe condition is still likely to exist or develop on other aircraft of the same type design, this Directive requires the modification of all PSU panels and the application of sealant on the aft air-conditioning duct ends. Jim Coyne Delegate of the Civil Aviation Safety Authority 29 April 2003 The above AD is notified in the Commonwealth of Australia Gazette on 21 May 2003.