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 737 Series Aeroplanes AD/B737/310 Body Station 178 Bulkhead 13/2007 DM Vertical Beam Webs Applicability: Model 737-100, -200, -200C, -300, -400, and -500 series aircraft, as identified in Boeing Service Bulletin 737-53A1225 Revision 1, or later FAA approved revision. Requirement: Action in accordance with the technical requirements of FAA AD 2007-03-03 Amdt 39-14914. Compliance: As specified in the Requirement document, with a revised effective date of 26 October 2007. This Airworthiness Directive becomes effective on 26 October 2007. Background: The FAA received reports of numerous cracks in the vertical beam webs of the body station (BS) 178 bulkhead. Such cracking, unless detected and corrected, could result in loss of structural integrity of the BS 178 bulkhead, and consequently could impair the operation of the control cables for the elevators, speed brakes, and landing gear, or could cause the loss of cabin pressure. David Villiers Delegate of the Civil Aviation Safety Authority 24 October 2007