{"id":"F2006B03238","name":"AD/B747/58 - Hydraulic Fuse","slug":"ad-b747-58-hydraulic-fuse","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":42662,"registerId":"commonwealth-F2006B03238-current","compilationNumber":null,"startDate":"2026-04-01","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/B747/58 - Hydraulic Fuse","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/B747/58 Hydraulic Fuse 10/87\n\nApplicability: Model 747 series aircraft as listed in Boeing Service Bulletin 747-29-2063.\n\n \n\nRequirement: In accordance with Boeing Service Bulletin 747-29-2063 dated 23 December 1986 or later FAA approved revision.\n\n \n\nCompliance: Prior to 31 July 1989.\n\n \n\nBackground: The installation of a hydraulic fuse in the No. 4 hydraulic system is prompted by the incident in which all four hydraulic systems were lost when failure of the rear pressure bulkhead resulted in loss of the vertical stabiliser.\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\n \n\n \n","sortOrder":0}],"analysis":{"flash_summary":{"complexity_score":2,"scope_assessment":{"changed":false,"description":"The AD does not change scope from its stated purpose: it mandates installation of a hydraulic fuse in the No. 4 hydraulic system on the specified Model 747 aircraft, in line with the stated objective to mitigate the risk arising from the referenced incident. The directive is narrowly targeted and the text provides no indication of an expansion or narrowing of that target beyond the aircraft listed in Boeing Service Bulletin 747-29-2063 and the stated compliance deadline."},"complexity_factors":["Narrow and specific technical scope limited to Model 747 aircraft listed in Boeing Service Bulletin 747-29-2063 (low breadth).","Clear single regulatory requirement: install a hydraulic fuse per a named Service Bulletin or later FAA‑approved revision (straightforward directive).","Hard deadline for compliance (31 July 1989) creates planning constraint but does not add legal complexity.","Dependency on an external technical document (Boeing Service Bulletin) for detailed procedures increases operational complexity for implementers, since the AD itself lacks technical detail.","No allocation of costs, exemptions, or phased implementation in the text increases practical uncertainty for operators (administrative/financial complexity, not legal complexity)."],"plain_english_summary":"What this instrument requires\n\n- This airworthiness directive (AD/B747/58) requires that a hydraulic fuse be installed in the No. 4 hydraulic system of certain Boeing 747 series aeroplanes. The installation must be performed in accordance with Boeing Service Bulletin 747-29-2063 dated 23 December 1986 or a later FAA‑approved revision. (See: \"Requirement\".)\n- The work must be completed by 31 July 1989. (See: \"Compliance\".)\n\nWho is affected\n\n- The AD applies to Model 747 series aircraft as listed in Boeing Service Bulletin 747-29-2063. (See: \"Applicability\".)\n- The directive places an obligation on the operators/owners of those specific aircraft to carry out the specified modification by the compliance date.\n\nWhy the change was ordered (official rationale)\n\n- The AD states that the installation is prompted by an incident in which failure of the rear pressure bulkhead resulted in loss of the vertical stabiliser and a subsequent loss of all four hydraulic systems. The stated purpose is to reduce the risk of a similar total hydraulic loss by fitting a hydraulic fuse in the No. 4 system. (See: \"Background\".)\n\nHow the rule works mechanically\n\n- The AD does not set out detailed installation steps itself; it mandates compliance with the referenced Boeing Service Bulletin (or a later FAA‑approved revision). That means the technical details, parts lists and procedures are contained in the Service Bulletin, and compliance is achieved by following that document. (See: \"Requirement\".)\n- The regulator (the Commonwealth instrument under Civil Aviation Regulations Part 39 — Schedule of Airworthiness Directives) sets the requirement and the deadline; the Service Bulletin provides the technical method. (See: header and \"Requirement\".)\n\nPractical implications, trade-offs and risks (based on what the AD states and what it does not state)\n\n- The AD establishes an operational mandate but does not specify who pays for parts, labour, ferry flights or aircraft downtime. The directive therefore imposes an obligation on the operator/owner to have the installation done by the stated date, but allocation of cost or contractual arrangements between owner/operator, maintenance provider and manufacturer are not addressed in the text. (Implicit from the absence of cost allocation in the AD.)\n- The AD refers to an external technical document (Boeing Service Bulletin 747-29-2063 or later FAA‑approved revision). The compliance burden and schedule impact depend on the Service Bulletin's technical requirements (parts availability, labour hours, need for specialised tooling or facility access). Those specifics are not included in the AD itself. (See: \"Requirement\".)\n- The AD fixes a firm compliance date (31 July 1989). That creates a discrete deadline for operators to plan work, but the AD does not describe any phased compliance or exemptions in the text provided. (See: \"Compliance\".)\n- The safety benefit claimed by the AD is mitigation of the risk of losing all hydraulic systems after a similar structural failure; the text links the requirement directly to that incident. The AD does not quantify the safety benefit or provide a cost–benefit analysis. (See: \"Background\".)\n\nSummary of who decides, who acts and what changes\n\n- Decision authority: the airworthiness directive is issued under the Commonwealth civil aviation framework (Part 39 — Schedule of Airworthiness Directives). (Header.)\n- Action required: operators/owners of the listed Boeing 747 aircraft must install the hydraulic fuse in the No. 4 hydraulic system per the referenced Service Bulletin (or later FAA‑approved revision). (See: \"Applicability\" and \"Requirement\".)\n- Deadline: the work must be done before 31 July 1989. (See: \"Compliance\".)"},"kimi_summary":{"content_quality":"ok","complexity_score":2,"scope_assessment":{"changed":false,"description":"This is a discrete, time-bound safety directive issued in response to a specific incident. It has not expanded beyond its original purpose of mandating hydraulic fuse installation on Boeing 747 aircraft."},"complexity_factors":["Very short document (approximately 150 words)","Only 3 substantive operative provisions: applicability, requirement, and compliance","No defined terms section — uses plain technical language","Single cross-reference to external Boeing Service Bulletin","No nested conditions or exceptions","Straightforward mandatory command structure ('In accordance with...')"],"plain_english_summary":"This is an **Airworthiness Directive (AD)** — essentially a mandatory safety order issued by Australia's Civil Aviation Safety Authority (CASA) for aircraft.\n\n**What it does:**\nIt requires owners and operators of **Boeing 747 aircraft** to install a safety device called a **\"hydraulic fuse\"** in the No. 4 hydraulic system.\n\n**Why it matters:**\nThis rule was created after a catastrophic incident where a Boeing 747 lost all four hydraulic systems because the rear pressure bulkhead (a structural wall at the back of the plane) failed, causing the vertical stabiliser (the tail fin) to break off. Without hydraulics, pilots can't control the aircraft's flight surfaces. The hydraulic fuse acts like a circuit breaker — it shuts off hydraulic flow if there's a major leak, preventing total system failure.\n\n**Who it affects:**\nAnyone operating Boeing 747 series aircraft covered by Boeing Service Bulletin 747-29-2063.\n\n**What had to happen:**\nOperators had to complete this modification **before 31 July 1989**, following the specific technical instructions in Boeing's service bulletin."}},"importantCases":[],"_links":{"self":"/api/acts/ad-b747-58-hydraulic-fuse","history":"/api/acts/ad-b747-58-hydraulic-fuse/history","analysis":"/api/acts/ad-b747-58-hydraulic-fuse/analysis","conflicts":"/api/acts/ad-b747-58-hydraulic-fuse/conflicts","importantCases":"/api/acts/ad-b747-58-hydraulic-fuse/important-cases","documents":"/api/acts/ad-b747-58-hydraulic-fuse/documents"}}