{"id":"F2006B11017","name":"AD/JT9D/24 - HPC Turbine Drive Shafts","slug":"ad-jt9d-24-hpc-turbine-drive-shafts","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":56619,"registerId":"commonwealth-F2006B11017-current","compilationNumber":null,"startDate":"2026-04-02","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/JT9D/24 - HPC Turbine Drive Shafts","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/24 HPC Turbine Drive Shafts 8/91\n\nApplicability: JT9D-7R4 series engines.\n\n \n\nRequirement: Action in accordance with the Technical Requirements of FAA AD 91-03-03 Amdt 39-6838.\n\n \n\nCompliance: As detailed in Requirement Document with a revised effective date of 8 August 1991.\n\n \n\nBackground:  This Directive requires initial and repetitive inspection of certain high pressure compressor (HPC) turbine drive shafts. This requirement follows advice of circumferential cracks found in the thread area of the HPC drive shaft which mates with the number three bearing retainer nut.\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":{"kimi_summary":{"content_quality":"ok","complexity_score":2,"scope_assessment":{"changed":false,"description":"This is a standard, narrow airworthiness directive focused on a specific mechanical defect in a specific engine series. It has not expanded beyond its original safety purpose."},"complexity_factors":["Very short document (approximately 150 words of substantive content)","Only 1 defined applicability criterion (JT9D-7R4 series engines)","Single requirement referencing an external FAA document rather than setting out detailed technical steps","No nested exceptions, conditional logic, or cross-references to other Australian legislation","Straightforward compliance structure with a single effective date"],"plain_english_summary":"This is an **Airworthiness Directive** — a mandatory safety order issued by Australia's Civil Aviation Safety Authority (CASA) that requires specific maintenance actions on aircraft engines.\n\n**What it does:**\n- Requires owners and operators of **Pratt & Whitney JT9D-7R4 series jet engines** to inspect the **high pressure compressor (HPC) turbine drive shafts** for cracks.\n- The inspections must follow the exact technical requirements set out in a US Federal Aviation Administration (FAA) directive (AD 91-03-03).\n- These inspections are **repetitive** — meaning they must be done more than once, not just a one-off check.\n\n**Why it matters:**\n- Cracks were discovered in the threaded area where the drive shaft connects to a bearing retainer nut. If left unchecked, these cracks could cause **catastrophic engine failure**.\n- This directive prevents potential accidents by catching fatigue damage before it becomes dangerous.\n\n**Who it affects:**\n- Airlines and aircraft operators using JT9D-7R4 engines (commonly found on older Boeing 747 and Airbus A300/A310 aircraft).\n- Maintenance organisations servicing these engines.\n\n**Key deadline:**\n- The directive took effect on **8 August 1991**, with compliance timelines set by the referenced FAA document."},"flash_summary":{"complexity_score":3,"scope_assessment":{"changed":false,"description":"The Directive enforces initial and repetitive inspections for JT9D-7R4 HPC turbine drive shafts by mandating compliance with FAA AD 91-03-03 and specifying the revised effective date (Applicability; Requirement; Compliance). It does not expand or narrow the population of affected engines beyond the stated applicability, nor does it add additional substantive obligations beyond adopting the FAA AD’s technical requirements. Therefore the scope has not changed from the Directive’s stated purpose of requiring inspections prompted by observed cracks (Background)."},"complexity_factors":["Narrow applicability: only JT9D-7R4 series engines (Applicability)","Primary technical content is referenced externally (FAA AD 91-03-03), not reproduced in the Directive (Requirement)","Repetitive inspection regime implies ongoing compliance tracking and maintenance scheduling (Requirement; Compliance)","Regulatory enforcement via Part 39 means limited domestic discretion but relies on the FAA document’s definitions (header; Requirement)","Effective date and revised Requirement Document introduce a fixed compliance timeline that operators must follow (Compliance)"],"plain_english_summary":"This Airworthiness Directive adopts FAA AD 91-03-03 for Pratt & Whitney JT9D-7R4 engines, requiring operators and maintenance organisations to perform the referenced inspections and corrective actions on HPC turbine drive shafts to detect circumferential thread-area cracks. It makes the FAA’s technical requirements mandatory in Australia, shifting costs and compliance responsibility to operators and removing discretion to ignore the referenced AD."}},"importantCases":[],"_links":{"self":"/api/acts/ad-jt9d-24-hpc-turbine-drive-shafts","history":"/api/acts/ad-jt9d-24-hpc-turbine-drive-shafts/history","analysis":"/api/acts/ad-jt9d-24-hpc-turbine-drive-shafts/analysis","conflicts":"/api/acts/ad-jt9d-24-hpc-turbine-drive-shafts/conflicts","importantCases":"/api/acts/ad-jt9d-24-hpc-turbine-drive-shafts/important-cases","documents":"/api/acts/ad-jt9d-24-hpc-turbine-drive-shafts/documents"}}