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/CL-600/66 and issues the following 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-600/66 Amdt 1 Rudder Balance Spring Assembly 3/2006 Applicability: Bombardier Inc. Models: CL-600-1A11 - Serial numbers 1004 through 1085. CL-600-2A12 - Serial numbers 3001 through 3066. CL-600-2B16 - Serial numbers 5001 through 5194. CL-600-2B16 - Serial numbers 5301 through 5564. Requirement: Modify the rudder balance spring assembly; and perform the rigging of the adjustable rudder balance spring assembly in accordance with the instructions of the applicable Service Bulletin (SB) listed below, or later Transport Canada approved revisions. Applicable Service Bulletins: CL-600-1A11 (CL-600) SB 600-0714 dated, 04 April 2003 CL-600-2A12 (CL-601) SB 601-0549 dated, 04 April 2003 CL-600-2B16 (CL-601-3A/3R) SB 601-0549 dated, 04 April 2003 CL-600-2B16 (CL-604) SB 604-27-013 dated, 04 April 2003 Note: Transport Canada AD CF-2005-21R1 refers. Compliance: Before the 29 September 2006, unless previously accomplished. This Amendment becomes effective on 16 March 2006. Background: The rudder balance spring assembly, which is intended to position the rudder close to its neutral position in case of a rudder aft linkage disconnect, may not have the correct pre-load on some aircraft. Excessive rudder deflections may occur, reducing controllability of the aircraft. No in-service problems have ever been reported with rudder aft linkage disconnect. A new adjustable balance spring assembly is being introduced to correct this potential problem. This amendment changes the applicability of the CL-600-2B16 (CL-604) by serial number. The original issue of this Airworthiness Directive became effective on 29 September 2005. James Coyne Delegate of the Civil Aviation Safety Authority 1 February 2006