{"id":"F2006B03138","name":"AD/B747/24 - Rear Fuselage Stringers S18 and S19 - Modification","slug":"ad-b747-24-rear-fuselage-stringers-s18-and-s19-modification","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":42510,"registerId":"commonwealth-F2006B03138-current","compilationNumber":null,"startDate":"2026-04-01","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/B747/24 - Rear Fuselage Stringers S18 and S19 - Modification","content":"---\nmeta-content-style-type: text/css\nmeta-content-type: application/xhtml+xml; charset=utf-8\nmeta-generator: Aspose.Words for .NET 22.10.0\n---\n\n?xml version=\"1.0\" encoding=\"utf-8\" standalone=\"no\"?>\n\nCOMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 105 CIVIL AVIATION SAFETY AUTHORITY\n\nSCHEDULE OF AIRWORTHINESS DIRECTIVES\n\n \n\n![](image.001.png)  Boeing 747 Series Aeroplanes\n\n \n\nAD/B747/24 Rear Fuselage Stringers S18 and S19 - Modification 12/80\n\nApplicability: 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.\n\n \n\nDocument: 1. FAA AD 80-20-01 Amdt. 39-3927; or\n\n \n\n2. Boeing SB 747-53-2114, Rev. 3.\n\n \n\nCompliance: Prior to 31 January 1981. As per requirement document No. 1.\n\n \n\nBackground:  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.\n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n","sortOrder":0}],"analysis":{"kimi_summary":{"content_quality":"ok","complexity_score":2,"scope_assessment":{"changed":false,"description":"This is a discrete, time-limited airworthiness directive with a single, specific purpose. It has not expanded beyond its original intent of reinforcing two specific structural elements on a defined subset of Boeing 747 aircraft."},"complexity_factors":["Very short document (under 200 words)","Only 4 defined applicability groups (Groups I, II, III, and the thrust exception)","Single compliance requirement with fixed deadline","No cross-references to other legislation beyond the cited FAA AD and Boeing Service Bulletin","No conditional logic or nested exceptions — straightforward mechanical modification","Technical aviation terminology present but explained in context (stringers, radius filler, thrust ratings)"],"plain_english_summary":"**What this is:** An airworthiness directive (a mandatory safety order) for Boeing 747 aircraft.\n\n**What it requires:** Airlines and aircraft operators must reinforce two specific structural parts of the plane's rear fuselage (body) — called \"stringers S18 and S19\" — by fitting a strengthening piece inside them. This must be done before 31 January 1981.\n\n**Who it affects:** All Boeing 747 models covered by Boeing Service Bulletin 747-53-2114, specifically:\n- Groups I and II (all engines)\n- Group III, but **only if** the aircraft has engines producing more than 50,000 pounds of thrust\n\n**Why it matters:** If an outer engine fails on a high-thrust 747, the pilot needs to apply extreme rudder (the steering fin at the back) to keep the plane straight. This puts dangerous stress on stringers 18 and 19. Without reinforcement, these parts could fail — potentially causing structural damage or worse. The fix is relatively simple: inserting a \"radius filler\" (a curved reinforcing piece) inside the existing stringers.\n\n**The bottom line:** This is a one-off safety fix to prevent structural failure after engine failure on powerful 747s. It's old (from 1980) and was time-limited, so compliant aircraft would have been modified decades ago."},"flash_summary":{"complexity_score":4,"scope_assessment":{"changed":false,"description":"Scope remains consistent with the directive's original technical aim: reinforce stringers S18 and S19 on specified 747 models and configurations (groups I & II, and group III only if engines >50,000 lb). The instrument prescribes the modification method via the FAA AD or Boeing Service Bulletin and sets a firm compliance date; it does not expand or narrow the set of affected aircraft beyond those criteria."},"complexity_factors":["Conditional applicability tied to SB groupings and engine thrust (>50,000 lb) increases scope-check complexity (Applicability).","Requirement references external documents (FAA AD 80-20-01; Boeing SB 747-53-2114) so compliance depends on following detailed external procedures (Document).","Technical nature of the modification (local reinforcement by nesting a radius filler) requires specialised structural work and skilled labour.","Fixed compliance deadline (prior to 31 January 1981) creates scheduling and operational-disruption pressure for operators (Compliance).","Regulatory enforcement is prescriptive (a mandatory modification), limiting operator discretion on alternative mitigations (Compliance/Background).","Potential need to verify affected serials/models against the service bulletin grouping increases administrative burden for operators and maintenance organisations (Applicability/Document)."],"plain_english_summary":"Requires operators of affected Boeing 747s (those listed in Boeing SB 747-53-2114 groups I & II, and group III when engines exceed 50,000 lb thrust) to reinforce rear fuselage stringers S18 and S19 by nesting a radius filler to reduce overload risk after an outer‑engine failure. Aircraft owners/operators must arrange and pay for the work under the FAA AD or Boeing Service Bulletin method and complete it by 31 January 1981. The airworthiness directive mandates compliance; it changes maintenance action and scheduling for affected fleets."}},"importantCases":[],"_links":{"self":"/api/acts/ad-b747-24-rear-fuselage-stringers-s18-and-s19-modification","history":"/api/acts/ad-b747-24-rear-fuselage-stringers-s18-and-s19-modification/history","analysis":"/api/acts/ad-b747-24-rear-fuselage-stringers-s18-and-s19-modification/analysis","conflicts":"/api/acts/ad-b747-24-rear-fuselage-stringers-s18-and-s19-modification/conflicts","importantCases":"/api/acts/ad-b747-24-rear-fuselage-stringers-s18-and-s19-modification/important-cases","documents":"/api/acts/ad-b747-24-rear-fuselage-stringers-s18-and-s19-modification/documents"}}