{"id":"F2006B03081","name":"AD/B747/18 - Lower Cargo Doorway Lower Sill Truss and Latch Support Fitting - Inspection","slug":"ad-b747-18-lower-cargo-doorway-lower-sill-truss-and-latch-support-fitting-inspection","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":42440,"registerId":"commonwealth-F2006B03081-current","compilationNumber":null,"startDate":"2026-04-01","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/B747/18 - Lower Cargo Doorway Lower Sill Truss and Latch Support Fitting - Inspection","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/B747/18 Lower Cargo Doorway Lower Sill Truss\n\nand Latch Support Fitting - Inspection\n\n\n11/79\n\n \n\nApplicability:   All models.\n\n \n\nDocument: 1. FAA AD 79-17-02, Amdt. 39-3526;\n\n \n\n2. (Boeing SB 747-53-2200 refers). Compliance:   As per requirement document No. 1.\n\nBackground:  Overseas it has been found that the 7079-T6 truss and related 7079-T6 latch support fittings on the lower sill of forward and lower cargo doorways can exhibit corrosion, cracking and blocked drainage paths.\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\n \n","sortOrder":0}],"analysis":{"flash_summary":{"complexity_score":3,"scope_assessment":{"changed":false,"description":"The AD, as presented, preserves the original scope of requiring inspections of the specified lower sill truss and latch support fittings for corrosion, cracking and blocked drainage paths and applies to all Boeing 747 models. The instrument achieves this by mandating compliance with the referenced FAA AD and citing the Boeing Service Bulletin for technical procedures (Applicability; Document: 1; Document: 2; Background; Compliance)."},"complexity_factors":["Reference to external technical documents (FAA AD 79-17-02 and Boeing SB 747-53-2200) places technical detail outside the AD text","Technical subject matter (metal alloy 7079-T6 fittings, structural truss and latch supports) requiring specialist maintenance knowledge","Applicability to all Boeing 747 models increases operational scope for affected operators","AD text defers inspection intervals and corrective-action detail to the referenced documents, creating reliance on third-party publications"],"plain_english_summary":"What this instrument does (mechanically)\n\n- Requires inspection of the lower sill truss and latch support fittings on the forward and lower cargo doorways of Boeing 747 series aeroplanes for corrosion, cracking and blocked drainage paths. (Background)\n- The inspections must be carried out in accordance with the referenced FAA airworthiness directive. (Document: 1. FAA AD 79-17-02; Compliance)\n- The Boeing Service Bulletin 747-53-2200 is cited as the Boeing technical reference. (Document: 2. Boeing SB 747-53-2200)\n\nWho this affects\n\n- Operators and maintenance organisations of Boeing 747 series aeroplanes, because the AD is applicable to all models. (Applicability: All models)\n- The Civil Aviation Safety Authority enforces the AD as part of the Australian Schedule of Airworthiness Directives. (header: PART 39)\n\nWhy it matters (stated purpose and practical implications)\n\n- The stated purpose is to address findings that the 7079-T6 alloy truss and related 7079-T6 latch support fittings on the lower sill of forward and lower cargo doorways can show corrosion, cracking and blocked drainage paths. The AD directs inspections to detect those conditions. (Background)\n\nWho pays, who decides, and what changes in behaviour\n\n- Who pays: aircraft operators bear the direct costs of carrying out the inspections, any required cleaning, repairs or part replacements, and any resulting aircraft downtime. (Compliance; Background) \n- Who decides: the AD makes compliance contingent on the referenced FAA AD (Document: 1). The FAA AD and the Boeing Service Bulletin specify the technical inspections and corrective actions; CASA enforces the requirement by issuing this AD. (Document: 1; Document: 2; Compliance)\n- Behaviour changes required of operators: schedule and perform the inspections specified in the FAA AD/Boeing SB, clear blocked drainage paths where found, and repair or replace corroded or cracked fittings as required by the referenced documents. (Compliance; Document: 2; Background)\n\nCosts, incentives and trade-offs (mechanisms, not value judgments)\n\n- Direct compliance cost mechanism: inspections consume maintenance labour hours and may require parts and repairs if defects are found; aircraft may be out of service while work is completed. The AD text ties required actions to an external technical requirement rather than listing detailed tasks itself, which shifts technical detail to the referenced FAA AD/Boeing SB. (Compliance; Document: 1; Document: 2)\n- Incentives: operators are incentivised to detect and correct corrosion/cracking to meet the AD and maintain airworthiness; failing to comply risks regulatory enforcement. (Applicability; Compliance)\n- Trade-offs and opportunity cost: maintenance capacity used for these inspections and repairs is not available for other tasks; operators must allocate resources accordingly. (Background; Compliance)\n\nImplementation risk, compliance burden and administrative discretion\n\n- Implementation risk: the AD requires following an external FAA AD and a Boeing Service Bulletin. If those documents are unclear, unavailable, or require interpretation, practical implementation may be more burdensome. (Document: 1; Document: 2; Compliance)\n- Compliance burden: the AD applies to all 747 models, so it potentially covers the entire operator fleet of that type in Australia; the AD text itself does not set inspection intervals or steps but defers to the FAA AD, which creates reliance on that document for operational detail. (Applicability; Compliance)\n- Administrative discretion: this AD prescribes compliance by reference to specific documents rather than leaving technical detail to CASA—CASA retains enforcement authority but the technical content is primarily determined by the FAA AD and Boeing SB. (Document: 1; Document: 2; Compliance)\n\nSubstitution effects and limited scope observations\n\n- Substitution effects: operators may choose from corrective options set out in the referenced FAA AD/Boeing SB (for example, repair versus replacement) where those documents allow alternatives; the AD text itself does not specify alternative methods. (Document: 1; Document: 2)\n- The AD addresses a defined structural area and specific fittings (7079-T6 truss and latch support fittings on the lower sill of forward and lower cargo doorways). It does not in this text broaden obligations beyond inspection and remediation per the referenced documents. (Background; Applicability; Compliance)\n\nCitations to the instrument\n\n- Applicability: \"All models.\" (Applicability)\n- Compliance: \"As per requirement document No. 1.\" (Compliance)\n- Documents referenced: \"1. FAA AD 79-17-02, Amdt. 39-3526; 2. (Boeing SB 747-53-2200 refers).\" (Document)\n- Background statement of the identified problem: corrosion, cracking and blocked drainage paths in 7079-T6 truss and latch support fittings on the lower sill of forward and lower cargo doorways. (Background)\n"},"kimi_summary":{"content_quality":"ok","complexity_score":2,"scope_assessment":{"changed":false,"description":"This is a discrete, targeted safety directive focused specifically on Boeing 747 cargo door inspections. It has not expanded beyond its original purpose of addressing corrosion and cracking in specific structural components. The scope remains precisely as intended when first issued (November 1979)."},"complexity_factors":["Very short document (approximately 150 words of substantive content)","Only 1 defined term implicitly used ('Applicability' refers to aircraft models)","No nested conditional logic or exceptions","Single cross-reference to external FAA AD and Boeing Service Bulletin (compliance delegated entirely to external documents)","No internal definitions section or interpretation clauses","Straightforward command structure: identify aircraft → inspect specific part → follow external standard"],"plain_english_summary":"**What this is:** This is an **Airworthiness Directive (AD)** — a mandatory safety order issued by Australia's Civil Aviation Safety Authority (CASA) that requires specific inspections or repairs on aircraft.\n\n**What it does:** It orders owners and operators of **all Boeing 747 models** to inspect the **lower cargo doorway structures** — specifically the metal truss (support frame) and latch support fittings made from a particular aluminium alloy (7079-T6). These parts sit at the bottom of the forward and aft cargo doors.\n\n**Why it matters:** Overseas investigations found these parts can suffer from **corrosion (rust-like deterioration)**, **cracking**, and **blocked drainage paths** (which lets water pool and cause more damage). If these problems aren't caught, the cargo door could fail in flight — potentially leading to explosive decompression or loss of cargo.\n\n**What must be done:** Operators must follow the inspection procedures set out in **FAA Airworthiness Directive 79-17-02** (the American aviation safety regulator's equivalent order) and Boeing's Service Bulletin 747-53-2200. The exact timing and method of inspection comes from those documents.\n\n**Who it affects:** Anyone who owns, operates, or maintains Boeing 747 aircraft in Australia — including airlines, cargo operators, and maintenance organisations."}},"importantCases":[],"_links":{"self":"/api/acts/ad-b747-18-lower-cargo-doorway-lower-sill-truss-and-latch-support-fitting-inspection","history":"/api/acts/ad-b747-18-lower-cargo-doorway-lower-sill-truss-and-latch-support-fitting-inspection/history","analysis":"/api/acts/ad-b747-18-lower-cargo-doorway-lower-sill-truss-and-latch-support-fitting-inspection/analysis","conflicts":"/api/acts/ad-b747-18-lower-cargo-doorway-lower-sill-truss-and-latch-support-fitting-inspection/conflicts","importantCases":"/api/acts/ad-b747-18-lower-cargo-doorway-lower-sill-truss-and-latch-support-fitting-inspection/important-cases","documents":"/api/acts/ad-b747-18-lower-cargo-doorway-lower-sill-truss-and-latch-support-fitting-inspection/documents"}}