COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 105 CIVIL AVIATION SAFETY AUTHORITY SCHEDULE OF AIRWORTHINESS DIRECTIVES Fokker F100 (F28 Mk 100) Series Aeroplanes 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 CAR 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. AD/F100/43 Anti Skid Control Box 4/2001 Applicability: F.28 Mk.0100 series aeroplanes. Requirement: Either: a. Modify all Skid control boxes having Part Number (P/N) 6004272-3, 6004272-4, 6004272-5 and 6004272-6 in accordance with ABS Corporation Service Bulletin (SB) Fo100-32-83 dated 30 October 2000; or b. Replace all Skid control boxes having P/N 6004272-3, 6004272-4, 6004272-5 and 6004272-6 with improved units having P/N 6004272-7 in accordance with Fokker Services SB F100-32-123 dated 15 November 2000. Note: RLD AD 2000-149 (A) refers. Compliance: Within the next 24 calendar months after the effective date of this Directive. This Airworthiness Directive becomes effective on 19 April 2001. Background: During 1999 the Dutch Rijksluchtvaartdienst (RLD) received a report concerning an incident with a Fokker 100, where during an approach, the liftdumpers inadvertently deployed. Preliminary investigation revealed that the outboard wheelspeed signal was induced to 'high' by electromagnetic interference (EMI), but the liftdumper arming test did not detect the signal because it was not transmitted until the skid control box was 'powered up' on landing gear DOWN selection. RLD considered that two separate design safety features were not effective. Analysis of the liftdumper system protection against EMI led RLD to mandate certain modifications on the affected aircraft to achieve a configuration, which is significantly less susceptible to EMI on the wheelspeed signals. The RLD issued BLA 1998-100/2 (AD/F100/33) to require modification of the grounding to the shielding of the Wheelspeed Sensor wiring and in addition, the installation of new electrical grounds for the Wheelspeed Sensor Channel of the Anti-Skid Control Box. A modified Skid Control Box was then developed to improve the resistance of the skid control system against unknown sources of EMI, the installation of which was subsequently mandated by BLA 1999-127 (AD/F100/39). COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 105 CIVIL AVIATION SAFETY AUTHORITY SCHEDULE OF AIRWORTHINESS DIRECTIVES ABS Corporation, which supplies the Skid Control Box, has developed another modification, which renders the Skid Control Box even less susceptible to EMI signals during power-up and power-down transients. Since a potentially unsafe condition has been identified that may still exist or develop on other aircraft of the same type design, this Directive requires the modification or replacement of currently installed Skid Control Boxes with improved units. Prior compliance with AD/F100/39 is not considered compliance with this Directive. Eugene Paul Holzapfel Delegate of the Civil Aviation Safety Authority 8 March 2001 The above AD is notified in the Commonwealth of Australia Gazette on 21 March 2001.