COMMONWEALTH OF AUSTRALIA (Civil Aviation Safety Regulations 1998), PART 39-105 CIVIL AVIATION SAFETY AUTHORITY SCHEDULE OF AIRWORTHINESS DIRECTIVES Boeing 747 Series Aeroplanes AD/B747/88 CWT Secondary Fuel Barrier 4/91 Applicability: Model 747 series aircraft as listed in Boeing SB 747-57-2253, Revision 1. Requirement: Action in accordance with the technical requirements of FA AD 91-03-13 Amdt 39- 6882. Note: Boeing SB 747-57-2253 Rev. 1 refers. Compliance: As specified in the Requirement Document but with a revised effectivity date of 18 April 1991 for Australian registered aircraft. Background: The FAA has received reports of the secondary fuel barrier not being applied correctly. This condition, if not corrected, could result in fuel or fuel vapours entering the cargo and passenger compartments in the event of failure of a primary seal or crack in the centre wing box structure.