{"id":"F2006B11005","name":"AD/JT9D/12 Amdt 1 - Fifteenth Stage Compressor Discs","slug":"ad-jt9d-12-amdt-1-fifteenth-stage-compressor-discs","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":56601,"registerId":"commonwealth-F2006B11005-current","compilationNumber":null,"startDate":"2026-04-02","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/JT9D/12 Amdt 1 - Fifteenth Stage Compressor Discs","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 - 106 CIVIL AVIATION SAFETY AUTHORITY\n\nSCHEDULE OF AIRWORTHINESS DIRECTIVES\n\n \n\n![](image.001.png)  Pratt and Whitney Turbine Engines - JT9D Series\n\n \n\nAD/JT9D/12\n\nAmdt 1\n\n\nFifteenth Stage Compressor Discs 9/89\n\n \n\nApplicability: JT9D-3A, -7, -7A, -7H, -7AH, -7A(SP), -7F, -7J, -20, -20J.\n\n \n\nRequirement: Inspect 15th stage compressor discs P/N 658615 and 672915 in accordance with the requirements of PWA SB No.4908 Rev.1.\n\n \n\nCompliance: As detailed in the Requirement document.\n\n \n\nBackground: This Directive has been amended to reflect the manufacturers latest revision to S.B.\n\n4908. The revision, in part, reduces the initial inspection requirement from 6,500 cycles to 3,500 cycles.\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":true,"description":"The AD amends the previous directive by adopting the manufacturer’s latest Service Bulletin (PWA SB No.4908 Rev.1) and, specifically, reduces the initial inspection threshold for the 15th-stage compressor discs from 6,500 cycles to 3,500 cycles. The amendment thus narrows the interval between first operation and mandatory inspection for the listed parts, while otherwise continuing to require inspections per the referenced Service Bulletin. [Background; Requirement]"},"complexity_factors":["Reference to an external technical document (PWA SB No.4908 Rev.1) that contains the detailed inspection procedures and intervals","Multiple engine variants listed in the applicability, requiring operators to identify affected assets precisely","Change in inspection interval (from 6,500 to 3,500 cycles) which affects maintenance scheduling and record-keeping","Mandatory regulatory nature (Airworthiness Directive) leaves limited operational discretion and requires conformity or an approved alternative","Potential operational coordination across operators and maintenance organisations to implement the SB procedures"],"plain_english_summary":"What this instrument does (mechanical change)\n\n- Requires inspection of the 15th-stage compressor discs, part numbers 658615 and 672915, on specified Pratt & Whitney JT9D engines. The inspections must be carried out in accordance with Pratt & Whitney Aircraft Service Bulletin No. 4908 Revision 1. [Requirement]\n- The directive replaces the prior inspection timing by adopting the manufacturer’s latest service bulletin, which reduces the initial inspection threshold from 6,500 cycles to 3,500 cycles. [Background]\n\nWho is affected\n\n- Aircraft operators, owners and maintenance organisations that operate or service JT9D engines of the listed variants (JT9D-3A, -7, -7A, -7H, -7AH, -7A(SP), -7F, -7J, -20, -20J). [Applicability]\n- Maintenance providers and parts suppliers who perform the mandated inspections or supply replacement discs. [Requirement]\n\nWhy it matters (official rationale and practical implications)\n\n- Official rationale: the directive follows the manufacturer’s updated service bulletin and reduces the initial inspection interval from 6,500 cycles to 3,500 cycles. The change is presented as aligning the regulatory requirement with the manufacturer’s latest inspection specification. [Background; Requirement]\n\nPractical mechanics, incentives and costs\n\n- Who pays: aircraft operators/owners are responsible for complying with the inspection requirement and for any subsequent repair or replacement costs that arise from findings during inspection. The AD mandates compliance with the manufacturer’s service bulletin, so the direct cost of inspection and any parts or labour falls to the operator or its maintenance contractor. [Requirement; Compliance]\n- Behaviour change required: operators must schedule and perform the inspections described in PWA SB No.4908 Rev.1; where the initial threshold is now 3,500 cycles instead of 6,500, inspections for some engines will occur sooner. [Requirement; Background]\n- Implementation and compliance burden: operators must follow the detailed procedures and intervals set out in the referenced Service Bulletin. That creates record‑keeping and maintenance scheduling obligations and may increase aircraft downtime or maintenance frequency for some engines. The directive refers operators to the SB for specifics. [Requirement; Compliance]\n- Who decides and where discretion lies: the Civil Aviation Safety Authority issues the Airworthiness Directive and references the manufacturer’s Service Bulletin; operators have limited discretion other than to comply with the AD and the SB’s requirements or to seek an alternative approved method of compliance from the regulator. [Schedule header; Requirement; Compliance]\n\nTrade‑offs, incentives and market effects to note (mechanism‑based)\n\n- Increased inspection frequency (lower initial cycle threshold) raises near‑term maintenance activity and costs for affected operators; maintenance providers that perform the inspections may receive additional business. [Background; Requirement]\n- The directive substitutes a mandatory regulatory inspection requirement for whatever inspection practice operators previously followed; it therefore shifts the incentive from operator choice to compliance with the SB as adopted by the AD. [Requirement; Compliance]\n- The text of the AD is procedural: it mandates inspection per the SB rather than prescribing non‑inspection remedies. Implementation risk lies in correct execution of the SB procedures and in operators’ timely scheduling of inspections. [Requirement; Compliance]\n\nReference to the instrument text\n\n- Applicability: lists the affected JT9D engine variants. [Applicability]\n- Requirement: mandates inspection of P/N 658615 and 672915 in accordance with PWA SB No.4908 Rev.1. [Requirement]\n- Compliance: directs operators to the Requirement document for compliance detail. [Compliance]\n- Background: states the AD was amended to reflect the manufacturer’s SB revision and that the revision reduces the initial inspection requirement from 6,500 cycles to 3,500 cycles. [Background]"},"kimi_summary":{"content_quality":"ok","complexity_score":2,"scope_assessment":{"changed":false,"description":"This amendment maintains the original scope (inspection of 15th stage compressor discs on JT9D engines). The change is purely an update to inspection intervals based on new technical data, not an expansion of the directive's coverage."},"complexity_factors":["Very short document (under 200 words)","Only 2 defined part numbers and 10 engine models listed","Single operative requirement referencing an external technical document (PWA SB No.4908 Rev.1)","No nested conditions, exceptions, or cross-references to other legislation","Straightforward compliance structure (follow the manufacturer's bulletin)","Minimal legal drafting — essentially a technical instruction with regulatory force"],"plain_english_summary":"This is an **Airworthiness Directive** — a mandatory safety order issued by Australia's Civil Aviation Safety Authority (CASA). It requires airlines and aircraft operators to inspect specific parts on certain Pratt & Whitney jet engines.\n\n**What it does:**\n- Orders inspection of the **15th stage compressor discs** (critical rotating parts inside the engine) on specific JT9D engine models\n- These discs have part numbers 658615 and 672915\n- The inspection must follow the manufacturer's Service Bulletin 4908, Revision 1\n\n**Who it affects:**\n- Operators of aircraft using JT9D-3A, -7, -7A, -7H, -7AH, -7A(SP), -7F, -7J, -20, or -20J engines\n- This includes many older Boeing 747, 767, and Airbus A300 aircraft\n\n**Why it matters:**\n- Compressor discs spin at extreme speeds; if they crack or fail, they can destroy the engine and endanger the aircraft\n- This amendment makes inspections **more frequent** — reducing the allowed flight cycles before first inspection from 6,500 to 3,500\n- This reflects new safety data suggesting the parts may develop problems sooner than previously thought\n\n**Key change in this version:**\n- Updated to match the manufacturer's latest guidance\n- **Critical safety improvement:** Earlier detection of potential disc failures through more frequent inspections"}},"importantCases":[],"_links":{"self":"/api/acts/ad-jt9d-12-amdt-1-fifteenth-stage-compressor-discs","history":"/api/acts/ad-jt9d-12-amdt-1-fifteenth-stage-compressor-discs/history","analysis":"/api/acts/ad-jt9d-12-amdt-1-fifteenth-stage-compressor-discs/analysis","conflicts":"/api/acts/ad-jt9d-12-amdt-1-fifteenth-stage-compressor-discs/conflicts","importantCases":"/api/acts/ad-jt9d-12-amdt-1-fifteenth-stage-compressor-discs/important-cases","documents":"/api/acts/ad-jt9d-12-amdt-1-fifteenth-stage-compressor-discs/documents"}}