COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 105 CIVIL AVIATION SAFETY AUTHORITY SCHEDULE OF AIRWORTHINESS DIRECTIVES Boeing 747 Series Aeroplanes AD/B747/177 Upper Deck Floor Beam at Sta. 980 9/97 Applicability: Model 747-300 and -400 series aircraft with line numbers up to and including 843, and Model 747 series aircraft modified to a stretched upper deck configuration; on which an upper deck cart lift has been installed at station (STA) 980. Requirement: Inspect in accordance with the technical requirements of FAA AD 97-09-13 Amdt 39- 10009. Note: Boeing Service Bulletins 747-53-2327 and 747-53A2400 refer. Compliance: Unless already accomplished, as specified in the requirement document with a revised effective date of 14 August 1997. This airworthiness directive becomes effective on 14 August 1997. Background: The FAA received reports of extensive corrosion at STA. 980. Analysis of the corrosion indicated that fatigue cracking of the floor beam at this area could occur and cause the beam to break, and result in extensive damage to adjacent structure and possible rapid decompression of the aircraft.