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/F50/86 Skid Control Unit 11/2003 Applicability: Model F.27 Mk050, Mk.0502 and Mk.0604 aeroplanes, all serial numbers, equipped with Aircraft Braking Systems Corporation (ABSC) skid control units with Part Numbers (P/N) 6004125 or 6004125-1. Requirement: 1. Replace skid control units P/N 6004125 or 6004125-1 with P/N 6004125-2 units in accordance with Part 2 Accomplishment Instructions of Fokker Services Service Bulletin (SB) F50-32-038 dated 8 May 2003. Note 1: P/N 6004125 units are pre ABSC SB F50-32-4 and 6004125-1 units are post ABSC SB F50-32-4. Note 2: For modification of the skid control units refer to ABSC SB 6004125-32-01 dated 7 May 200. 2. Modify the skid control unit ground wiring in accordance with Part 2 Accomplishment Instructions of Fokker Services SB F50-32-035 dated 2 August 1999. 3. Skid control units P/N 6004125 or 6004125-1 may not be installed on any aeroplane as a replacement part. Note 3: CAA(NL) BLA 2003-091 (A) refers. Compliance: For Requirement 1: Aeroplanes with skid control unit P/N 6004125 - Before 30 June 2004. Aeroplanes with skid control unit P/N 6004125-1 - Before 30 December 2004. For Requirement 2 - Before or concurrent with Requirement 1. For Requirement 3 - After 30 June 2004. This Airworthiness Directive becomes effective on 30 October 2003. Fokker F50 (F27 Mk 50) Series Aeroplanes AD/F50/86 (continued) Background: Several Fokker 50 (F.27 Mk.050) operators have reported pulsating brake behaviour and loss of braking at low speeds in the normal braking mode. Investigation of this phenomenon has shown that electromagnetic interference (EMI), resulting from failed components in other electronic systems and induced on the wheel speed sensor and/or test inputs of the skid control unit, is the cause of these problems. ABSC, the skid control unit manufacturer, has now developed a modified unit that corrects these problems. This Directive requires the replacement of the affected skid control units with modified units and at the same time requires new ground (earth) connections for the skid control units. Jim Coyne Delegate of the Civil Aviation Safety Authority 19 September 2003 The above AD is notified in the Commonwealth of Australia Gazette on 8 October 2003.