COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 105 CIVIL AVIATION SAFETY AUTHORITY SCHEDULE OF AIRWORTHINESS DIRECTIVES Boeing 747 Series Aeroplanes AD/B747/24 Rear Fuselage Stringers S18 and S19 - Modification 12/80 Applicability: All models listed in Boeing SB 747-53-2114 under groups I and II and those under group III if engines of thrust greater than 50000 lb. are installed. Document: 1. FAA AD 80-20-01 Amdt. 39-3927; or 2. Boeing SB 747-53-2114, Rev. 3. Compliance: Prior to 31 January 1981. As per requirement document No. 1. Background: With installed thrust greater than 50000 lb., failure of an outer engine would require extreme rudder trim, causing excessive loads to be applied to stringers 18 and 19 in the rear fuselage. The Directive requires local reinforcement of these stringers by nesting a radius filler inside.