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 39.001(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. Bombardier (Canadair) CL-600 (Challenger) Series Aeroplanes AD/CL-600/93 Fuel Quantity Gauging System Wiring 3/2008 Applicability: Model CL-600-2B19 aircraft, serial numbers 7003 through 7067, 7069 through 7982. Requirement: Modify the Fuel Quantity Gauging System (FQGS) harness routing according to the Accomplishment Instructions of Bombardier Service Bulletin (SB) 601R-28-059, Revision E, dated 29 October 2007, or later revisions approved by the Chief, Continuing Airworthiness, Transport Canada. Note 1: Modification of FQGS harness routing prior to the effective date of this directive according to the original issue, Revision A, Revision B, Revision C or Revision D of the above noted SB satisfies the requirements of this Directive. Note 2: Transport Canada AD CF-2007-36 refers. Compliance: Within 10 000 hours time in service after the effective date of this Directive. This Airworthiness Directive becomes effective on 13 March 2008. Background: Bombardier Aerospace has completed a system safety review of the CL-600-2B19 aircraft fuel system against new fuel tank safety standards, introduced in Chapter 525 of the Airworthiness Manual through Notice of Proposed Amendment (NPA) 2002-043. The identified non-compliances were assessed using Transport Canada Policy Letter No. 525-001 to determine if mandatory corrective action is required. This assessment showed that the electrical harness of the FQGS is installed in the same routing as the 28 Volts AC, 28 Volts DC and 115 Volts AC electrical harnesses. A chafing condition between these electrical harnesses and the FQGS harness could increase the surface temperatures of fuel quantity probes and high level sensors inside the fuel tank, resulting in potential ignition source and consequent fuel tank explosion. To correct the unsafe condition, this Directive mandates the modification of FQGS electrical harness routing. Charles Lenarcic Delegate of the Civil Aviation Safety Authority 21 January 2008