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. Learjet 45 Series Aeroplanes AD/LJ45/11 Engine Firewall 11/2007 Applicability: Model 45 aircraft, as identified in Bombardier Service Bulletin 45-54-3 Revision 2, or later FAA approved revision. Requirement: Inspect the engine pylon trailing edge for unsealed gaps, and clean and seal any unsealed gap in accordance with Bombardier Service Bulletin 45-54-3 Revision 2, or later FAA approved revision. Note: FAA AD 2007-17-17 Amdt 39-15175 refers. Compliance: Within 12 months after 25 October 2007, unless already accomplished. This Airworthiness Directive becomes effective on 25 October 2007. Background: The FAA received a report of unsealed gaps (penetration points) of the engine firewall that were discovered during production. Such a condition, unless corrected, could allow penetration of flammable liquids or fire through the engine firewall into the engine pylon, which could lead to fire inside the aircraft. David Villiers Delegate of the Civil Aviation Safety Authority 10 September 2007