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/B747/53 Amdt 3 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. Boeing 747 Series Aeroplanes AD/B747/53 Amdt 4 Longitudinal Skin Lap Joint and 14/2010 Body Frame Corrosion and Cracking Applicability: B747 aircraft line numbers 1 to 200. Requirement: Conduct an external visual inspection of the lower fuselage lap joints for corrosion in accordance with Boeing Service Bulletin (SB) 747-53A2267, dated 28 March 1986 or later FAA approved revision. Note: FAA AD 86-09-07 R1 refers. Compliance: Inspect in accordance with the requirement before 12,000 hours time in service or before 100 hours time in service after 30 October 1986, whichever is the later. Re-inspect at intervals not to exceed 4000 hours time in service or 15 months, whichever is the sooner if no corrosion was found at the last inspection. If corrosion was found re-inspect at intervals not to exceed 1000 hours time in service. Inspect until modified in accordance with Boeing SB747-53A2267, dated 28 March 1986. This Amendment becomes effective on 19 July 2010. Background: Corrosion and fatigue cracking of fuselage skin lap joints has been reported on many B747 aircraft. The initial issue of this AD required visual inspections for corrosion and cracking. Amendment 1 allowed an optional terminating modification. Amendment 2 referenced FAA AD 86-09-07. Amendment 3 required inspection after modification in accordance with FAA AD 94-17-01, which is no longer considered to be terminating. The inspection requirement is dependent on the SB revision at the time of installation. The modification is now mandatory before 20 years of service. This Amendment retains the requirement to visually inspect for corrosion mandated by FAA AD86-09-07 R1 whilst the requirements for ECI to the upper row of fasteners in the lap joints mandated by FAA AD 94-17-01 have been superseded by State of Design FAA AD 2010-14-10. David Punshon Delegate of the Civil Aviation Safety Authority 6 July 2010