COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 105 CIVIL AVIATION SAFETY AUTHORITY SCHEDULE OF AIRWORTHINESS DIRECTIVES Boeing 747 Series Aeroplanes AD/B747/93 Section 42 Fuselage Frame Web 6/91 Applicability: Model 747 series with line numbers 001 through 045. Requirement: Action in accordance with the technical requirements of FAA AD 91-06-03 Amdt 39- 6923. Compliance: As specified in the Requirement Document with a revised effective date of 13 June 1991 for Australian registered aircraft. Background: The FAA has received reports of multiple cracks in the Section 42 frames. This condition, if not corrected, could result in rapid depressurisation of the aircraft.