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. Boeing 747 Series Aeroplanes AD/B747/337 Upper Chords of the Upper Deck Floor Beams 1/2006 Applicability: Model 747-100, -100B, -100B SUD, 747-200B, 747-300, 747SP, and 747SR series aircraft; as identified in Boeing Alert Service Bulletin 747-53A2452, dated 3 April 2003, or later FAA approved revision. Requirement: Action in accordance with the technical requirements of FAA AD 2005-20-29 Amdt 39-14326. Note: Boeing Service Bulletin 747-53-2349 and Boeing Alert Service Bulletins 747-53A2349 Revision 1 and Revision 2; or later FAA approved revisions, refer. Compliance: As specified in the Requirement document, with a revised effective date of 19 January 2006. This Airworthiness Directive becomes effective on 19 January 2006. Background: Fatigue testing by the manufacturer revealed severed upper chords of the upper deck floor beams due to fatigue cracking. Undetected cracking could result in large deflection or deformation of the upper deck floor beams, resulting in damage to wire bundles and control cables for the flight control system, and reduced controllability of the aircraft. David Villiers Delegate of the Civil Aviation Safety Authority 28 November 2005