{"id":"F2006B03277","name":"AD/B747/99 - Differential Protection Current Transformers - Wiring","slug":"ad-b747-99-differential-protection-current-transformers-wiring","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":42714,"registerId":"commonwealth-F2006B03277-current","compilationNumber":null,"startDate":"2026-04-01","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/B747/99 - Differential Protection Current Transformers - Wiring","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\n# AD/B747/99 Differential Protection Current Transformers - Wiring\n\nApplicability: As specified in the requirement document.\n\n \n\nRequirement: Action in accordance with the Boeing Service Bulletin 747-24-2154.\n\n \n\nNote: FAA AD 91-18-05 also refers.\n\n \n\nCompliance: Prior to 18 March 1992.\n\n# 12/91\n\n \n\nBackground: This AD is issued following a 747 Safety Assessment which demonstrated that the potential exists for a single fault to cause the loss of all normal sources of aircraft power. Compliance with this AD requires re-routing and adding shielded wiring associated with the differential protection current transformers in the P6 panel.\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 safety directive with a narrow technical scope (wiring modification for one aircraft type). It has not expanded beyond its original purpose of addressing the specific power loss vulnerability identified in the 747 Safety Assessment."},"complexity_factors":["Extremely short document — only 4 substantive paragraphs","No defined terms section; relies entirely on external Boeing Service Bulletin for technical specifications","Single unconditional requirement with fixed deadline","No nested exceptions, conditional logic, or cross-references to other legislation beyond a single note about a related FAA directive","Minimal regulatory machinery — essentially a pointer to an external technical standard"],"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 modify the electrical wiring in a specific panel (the P6 panel) that houses \"differential protection current transformers.\" These are safety devices that monitor electrical current to prevent dangerous power faults.\n\n**The specific fix:**\nTechnicians must **re-route and add shielded wiring** to these transformers, following instructions in a Boeing technical document called Service Bulletin 747-24-2154.\n\n**Why it matters:**\nA safety assessment found that a single electrical fault in this system could potentially **knock out all normal power sources** on the aircraft — a serious flight safety risk. This directive closes that vulnerability.\n\n**Who must comply:**\nAnyone operating Boeing 747 series aircraft in Australia (as specified in the underlying Boeing document).\n\n**Deadline:**\nThe work had to be completed before **18 March 1992**.\n\n**Key point:** This is a **retrospective safety fix** — it doesn't change how new planes are built, but mandates repairs to existing aircraft already in service."},"flash_summary":{"complexity_score":4,"scope_assessment":{"changed":false,"description":"Based on the text provided, the AD implements a targeted technical mitigation (re-routing and shielding wiring of differential protection current transformers in the P6 panel) to address a single-fault loss-of-power risk identified in the 747 Safety Assessment (\"Background\"). The requirement to follow Boeing Service Bulletin 747-24-2154 (\"Requirement\") aligns with that stated intent and does not, in the text supplied, widen the scope beyond that mitigation. Applicability is delegated to the requirement document (\"Applicability\"), so the AD's scope as shown here is consistent with the stated original intent."},"complexity_factors":["Reliance on an external technical document (Boeing Service Bulletin 747-24-2154) for the required work (\"Requirement\").","Applicability not specified in the AD text provided — the directive defers to the requirement document for which aeroplanes are covered (\"Applicability\").","Technical nature of the mandated change: wiring re-routing and addition of shielded wiring in a specific electrical panel (P6) is safety-critical and technically detailed (\"Background\", \"Requirement\").","Firm compliance deadline adds scheduling and operational complexity for fleet operators (\"Compliance\").","Cross-reference to FAA AD 91-18-05 introduces coordination with foreign regulatory material and potentially additional technical requirements to consider (\"Note\")."],"plain_english_summary":"This AD mandates re‑routing and shielding of differential protection current‑transformer wiring in the P6 panel of specified Boeing 747s, to be done per Boeing Service Bulletin 747‑24‑2154 by the compliance date. It affects listed operators, shifts cost and scheduling onto them, and aims to remove a single‑fault vulnerability that could cause loss of normal aircraft power."}},"importantCases":[],"_links":{"self":"/api/acts/ad-b747-99-differential-protection-current-transformers-wiring","history":"/api/acts/ad-b747-99-differential-protection-current-transformers-wiring/history","analysis":"/api/acts/ad-b747-99-differential-protection-current-transformers-wiring/analysis","conflicts":"/api/acts/ad-b747-99-differential-protection-current-transformers-wiring/conflicts","importantCases":"/api/acts/ad-b747-99-differential-protection-current-transformers-wiring/important-cases","documents":"/api/acts/ad-b747-99-differential-protection-current-transformers-wiring/documents"}}