{"id":"F2006B03039","name":"AD/B747/137 - Nacelle - Strut Diagonal Brace","slug":"ad-b747-137-nacelle-strut-diagonal-brace","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":42398,"registerId":"commonwealth-F2006B03039-current","compilationNumber":null,"startDate":"2026-04-01","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/B747/137 - Nacelle - Strut Diagonal Brace","content":"COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 \\- 105 CIVIL AVIATION SAFETY AUTHORITY\n\nSCHEDULE OF AIRWORTHINESS DIRECTIVES\n\n![](image.001.png)  \nBoeing 747 Series Aeroplanes\n\nAD/B747/137 Nacelle \\- Strut Diagonal Brace 5/95\n\nApplicability: All B747 Line No 001 to 781 inclusive except aircraft with PW4000 and GE CF6-80 engines.\n\nRequirement: Inspect the Diagonal Brace for cracks using a detailed visual or a combination of detailed visual and ultrasonic inspection methods. Inspect in accordance with Boeing SB 747-54-2123 Rev 2.\n\nNote: FAA AD 90-20-20 refers.\n\nCompliance: 1. Initially inspect before 10000 flights or within 1000 flights of 27 April 1995, whichever is the later.\n\n    2. Repeat the inspections at intervals not exceeding 1000 flights if only a detailed visual inspection is used. Repeat the inspections at intervals not exceeding 3000 flights if a combination of detailed visual and ultrasonic methods is used.\n\n    3. Replacement of the Diagonal Brace with a new production brace, which has a revised internal and external finish, cancels the inspection requirements of this AD.\n\nBackground: An operator has reported finding a severed diagonal brace. The failure originated at a 0.0025 deep machining mark. Inspection in accordance with this AD on similar production status braces will ensure crack detection before brace failure.","sortOrder":0}],"analysis":{"kimi_summary":{"content_quality":"ok","complexity_score":2,"scope_assessment":{"changed":false,"description":"This is a standard Airworthiness Directive (AD) — a targeted safety bulletin addressing a specific mechanical defect in a specific aircraft type. It has not expanded beyond its original purpose of preventing diagonal brace failures."},"complexity_factors":["Single, specific mechanical component targeted (diagonal brace)","Clear applicability criteria (aircraft serial numbers and engine exclusions)","Straightforward compliance timeline with two simple alternatives","Only one technical reference (Boeing Service Bulletin 747-54-2123 Rev 2)","No nested exceptions or conditional logic beyond the engine type exclusion","Background explanation provided in plain language","Total length: approximately 200 words"],"plain_english_summary":"This safety directive requires operators of most Boeing 747s (S/N 001–781), except those with PW4000 or CF6-80 engines, to inspect the diagonal brace in the nacelle strut for cracking using visual or visual+ultrasonic methods at specified intervals. A replacement brace with improved finish cancels the inspections. It responds to a found complete fracture from a tiny machining defect that could allow engine separation, so the inspections prevent catastrophic failure by catching cracks early."},"flash_summary":{"complexity_score":5,"scope_assessment":{"changed":false,"description":"The directive sets out inspection and replacement requirements for the specified fleet and engine exclusions; nothing in the text indicates the scope has been altered from its stated purpose. It prescribes who must inspect, how often, acceptable methods, and the condition under which inspections are no longer required (Applicability; Requirement; Compliance 1–3; Background)."},"complexity_factors":["Multiple inspection methods with different repeat intervals: detailed visual every ≤1,000 flights vs combined visual+ultrasonic every ≤3,000 flights (Compliance 2).","Initial compliance timing uses a compound threshold (before 10,000 flights or within 1,000 flights of 27 April 1995, whichever is later), which can be operationally awkward to calculate for some fleets (Compliance 1).","Applicability carve-out excludes aircraft fitted with PW4000 and GE CF6-80 engines, requiring operators to verify serial/engine configuration against Line No 001–781 range (Applicability).","Dependence on an external manufacturer document: inspections must follow Boeing SB 747-54-2123 Rev 2, creating reliance on that bulletin's procedures and potential servicing-resource implications (Requirement).","Replacement cancels the inspection requirement only if replaced with a new-production brace having revised internal/external finish; this creates a mitigant option but imposes replacement cost and supply considerations (Compliance 3).","Reference to prior FAA AD (FAA AD 90-20-20) indicates cross-jurisdictional alignment; operators may need to reconcile multiple directives and service instructions (Requirement/Note).","Operational and maintenance burden falls to operators—scheduling inspections at stated flight intervals, arranging ultrasonic capability where chosen, and managing part procurement if replacing braces (Compliance 1–3; Requirement)."],"plain_english_summary":"Requires operators of most Boeing 747s (Line Nos 001–781, excluding PW4000 and GE CF6-80 engine variants) to inspect the nacelle strut diagonal brace for cracks by detailed visual or a combined visual+ultrasonic method, at specified flight-intervals, and to replace the brace with a new-production part to remove the inspection requirement. The directive is designed to catch cracks originating at small machining marks; operators must follow Boeing SB 747-54-2123 Rev 2 and bear inspection and replacement costs."}},"importantCases":[],"_links":{"self":"/api/acts/ad-b747-137-nacelle-strut-diagonal-brace","history":"/api/acts/ad-b747-137-nacelle-strut-diagonal-brace/history","analysis":"/api/acts/ad-b747-137-nacelle-strut-diagonal-brace/analysis","conflicts":"/api/acts/ad-b747-137-nacelle-strut-diagonal-brace/conflicts","importantCases":"/api/acts/ad-b747-137-nacelle-strut-diagonal-brace/important-cases","documents":"/api/acts/ad-b747-137-nacelle-strut-diagonal-brace/documents"}}