COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 105 CIVIL AVIATION SAFETY AUTHORITY SCHEDULE OF AIRWORTHINESS DIRECTIVES Boeing 747 Series Aeroplanes AD/B747/129 Fuselage Lower Frames at Body Stations 2200 and 2220 9/94 Applicability: Boeing Model 747 aircraft, Line Numbers 1 to 757 inclusive, SP versions excepted. Requirement: Conduct a detailed visual inspection of the fuselage lower frames at body stations 2200 and 2220 for cracks in accordance with Boeing Service Bulletin 747-53-2302. Note: FAA AD 91-18-04 refers. Compliance: 1. For aircraft with less than 10000 flights as at 18 August 1994, inspect before 10000 flights or within 1000 flights, whichever occurs later. 2. For aircraft which have had the frames replaced in accordance with Boeing Service Bulletin 747-53-2302, inspect within 10000 flights from the date of frame replacement. 3. In all cases, repeat the inspection at intervals not exceeding 2000 flights. 4. If cracks are found as a result of para 1, 2, or 3 inspections, extend the inspection area to include the adjacent frames (BS 2180 and 2240), stringers, skin, skin lap joints and skin adjacent to the outflow valve. Background: This Directive specifies regular visual inspections for cracks in the fuselage frames. If not detected, such cracks could lead to frame failure and sudden decompression of the fuselage.