{"id":"F2005L01304","name":"AD/JT8D/18 Amdt 2 - Second Stage Turbine Disc","slug":"ad-jt8d-18-amdt-2-second-stage-turbine-disc","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":35043,"registerId":"commonwealth-F2005L01304-current","compilationNumber":null,"startDate":"2026-04-01","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"Pratt and Whitney Turbine Engines - JT8D","sectionType":"division","heading":"Pratt and Whitney Turbine Engines - JT8D Series","content":"### Pratt and Whitney Turbine Engines - JT8D Series\n\n| AD/JT8D/18 Amdt 2 | Second Stage Turbine Disc | 7/2005 |\n| ----------------- | ------------------------- | ------ |\n\n| Applicability: | Pratt and Whitney Aircraft JT8D-15, -17, and -17R turbofan engines.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                |\n| -------------- | -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |\n| Requirement:   | To prevent possible failure of the second stage turbine disk, inspect second stage turbine disk, Part Numbers 676802, 770602, 780502, 786802, and 787302 details, and Part Numbers 676822, 769722, 769832, 786822, and 787232 assemblies for wear and cracking of the snap diameter and at the bottom of the disk air seal groove, repair the disk, and modify the mating third stage turbine inner air seal in accordance with the requirement of FAA Airworthiness Directive (AD) 85-19-51 R1.Note: FAA AD 85-19-51 R1 Amendment 39-5168 refers. |\n| Compliance:    | Unless previously accomplished, as per compliance schedule of the FAA AD85-19-51 R1.                                                                                                                                                                                                                                                                                                                                                                                                                                                               |\n|                | This Amendment becomes effective on 7 July 2005.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   |\n| Background:    | There have been reports of cracking of snap diameter and cracking at the bottom of the disk air seal groove for 2nd stage turbine disks. The inspection and repair requirements of this AD are aimed at prevention of 2nd stage turbine disk failure.The current amendment deletes reference to the manufacturer’s document and refers to the FAA AD as part of the harmonisation with the engine certificating Authority requirements.Amendment 1 of this Directive became effective on 26 December 1985.                                         |\n\n![](image.001.png)  \nJames Coyne  \nDelegate of the Civil Aviation Safety Authority\n\n25 May 2005","sortOrder":0},{"sectionNumber":"AD/JT8D/18 Amdt 2","sectionType":"part","heading":"AD/JT8D/18 Amdt 2","content":"## AD/JT8D/18 Amdt 2","sortOrder":1},{"sectionNumber":"Second Stage Turbine Disc","sectionType":"part","heading":"Second Stage Turbine Disc","content":"## Second Stage Turbine Disc","sortOrder":2},{"sectionNumber":"7/2005","sectionType":"part","heading":"7/2005","content":"## 7/2005","sortOrder":3}],"analysis":{"flash_summary":{"complexity_score":3,"scope_assessment":{"changed":true,"description":"This amendment does not expand the technical scope of the safety action (it still addresses the same second‑stage turbine disk cracking issue for the same JT8D engine variants). Its substantive change is procedural: it deletes the reference to the manufacturer’s document and makes the FAA Airworthiness Directive (FAA AD 85‑19‑51 R1) the operative compliance document (Background; Requirement). That harmonises Australian requirements with the FAA's compliance procedures and schedule but shifts reliance and ongoing technical control to the FAA AD process. In practical terms the safety target is unchanged, but the mechanism for compliance and any future technical updates is altered."},"complexity_factors":["Short, single‑issue instrument focused on one engine family and a small set of actions (inspect/repair/modify).","10 specific engine disk part numbers listed (5 bare disk part numbers and 5 assembly part numbers).","External dependency: mandatory incorporation by reference of FAA AD 85-19-51 R1 for procedures and the compliance schedule — introduces cross‑referencing complexity.","Single conditional phrase ('Unless previously accomplished') that directs operators to defer to prior compliance.","Limited number of internal exceptions or nested conditions — the instrument is procedural rather than heavily conditional."],"plain_english_summary":"**What this instrument does (mechanically)\n\n- Makes mandatory inspections, repairs and a specific part modification for certain Pratt & Whitney JT8D turbofan engines to guard against failure of the second‑stage turbine disk.  (The regulator references an FAA Airworthiness Directive — FAA AD 85-19-51 R1 — for the detailed procedures and the compliance schedule.)\n\n**Who it affects\n\n- Aircraft owners/operators and maintenance organisations that operate Pratt & Whitney JT8D-15, -17 and -17R engines (these are the engines listed under \"Applicability\").\n- Maintenance/repair facilities that inspect and repair the listed turbine disk part numbers or perform the third‑stage inner air seal modification.  Parts suppliers and overhaul shops will be involved where repairs or part replacements are required.\n\n**What you must do\n\n- Inspect second stage turbine disks (listed part numbers) and the corresponding assemblies for wear and cracking at two locations: the snap diameter and the bottom of the disk air‑seal groove.  If defects are found, repair the disk.\n- Modify the mating third‑stage turbine inner air seal as required by the FAA AD referenced in the instrument.\n- Comply according to the timing and procedures set out in FAA AD 85‑19‑51 R1, unless the inspections/repairs have already been done.\n\n**Why the regulator says this matters (stated purpose)\n\n- The instrument records reports of cracking in the snap diameter and at the bottom of the disk air‑seal groove.  Its stated purpose is prevention of second‑stage turbine disk failure (see the Background and Requirement sections).\n\n**How it changes practice and who pays\n\n- Operators must schedule inspections and, where necessary, repairs and a modification.  The cost of inspections, repairs, parts, and any aircraft downtime is borne by the aircraft owner/operator or their maintenance provider (Requirement; Compliance).\n- The civil aviation regulator enforces the requirement and has aligned the Australian instrument with the FAA AD: the FAA document supplies the detailed procedure and compliance timeline (Requirement; Background).  That means Australian compliance follows the FAA’s specified actions and schedule.\n\n**Implementation, incentives and trade‑offs (practical testing of the regulator's claim)\n\n- Implementation burden: operators face inspection and possible repair costs, use of certified maintenance organisations, and potential aircraft downtime while work is done.  These are direct, concentrated costs on operators.\n- Supply and capability risks: repairs or modifications may require specific parts or certified repair processes; if parts or qualified shops are limited, that can extend downtime or increase cost.\n- Regulatory coupling: by making the FAA AD the operative compliance document, CASA reduces duplicate local paperwork but creates an external dependency — future changes to the FAA AD will affect Australian compliance unless CASA issues a separate variation.  This streamlines harmonised compliance but transfers control over technical changes to the FAA AD process (Requirement; Background).\n- Distribution of benefits and costs: benefits (reduced risk of disk failure) are broadly diffused (passenger safety, operator risk reduction), while costs (inspection/repair bills, downtime) are concentrated on operators and their maintenance suppliers.  Parts manufacturers and repair shops may obtain concentrated commercial benefit from required repairs and modifications.\n\n**Operational risks and compliance friction\n\n- If an operator delays inspections, the risk the instrument targets (disk cracking leading to failure) remains.  Enforcement hinges on maintenance records and surveillance by the regulator.\n- Cross‑reference to FAA AD can create ambiguity for operators if the FAA AD is updated; operators must track the FAA AD to remain compliant.\n\n**Short practical summary for an operator**\n- If you operate JT8D‑15, -17 or -17R engines you must follow FAA AD 85‑19‑51 R1: inspect specified second‑stage turbine disk part numbers for cracking/wear, repair as needed, and modify the mating third‑stage inner air seal.  Arrange inspections promptly and budget for repairs and aircraft downtime.\n\n(References in the instrument: \"Applicability\", \"Requirement\", \"Compliance\", and \"Background\" sections; it cites FAA AD 85‑19‑51 R1 as the operative source for procedures and timing.)"},"kimi_summary":{"content_quality":"ok","complexity_score":3,"scope_assessment":{"changed":false,"description":"The legislation maintains its original narrow scope — safety inspection of a specific turbine disk in specific engine models. The 2005 amendment merely updates the reference source (from manufacturer documents to FAA directive) without expanding what must be done or which engines are covered."},"complexity_factors":["Short, single-purpose directive focused on one specific engine component","Only 5 specific part numbers listed for inspection","Clear, direct compliance requirement (follow the FAA AD schedule)","Minimal defined terms — relies on external FAA document for technical details","No nested exceptions or conditional logic — applies to all listed engine models unless already done","Background section explains rationale in plain language"],"plain_english_summary":"This is an **Australian Airworthiness Directive** — essentially a mandatory safety order for aircraft engines. It applies to specific **Pratt & Whitney JT8D turbofan engines** (models -15, -17, and -17R) commonly used in older commercial jets like the Boeing 727 and 737.\n\n**What it does:**\n- **Requires inspection** of a critical engine component called the \"second stage turbine disk\" — a spinning metal disc that takes extreme heat and stress in the engine's core\n- **Checks for cracks and wear** in two specific areas: the \"snap diameter\" (a precision-machined surface where parts fit together) and the bottom of the \"air seal groove\" (a channel that helps manage airflow and cooling)\n- **Mandates repairs** if damage is found, and requires modification of a related part (the third stage turbine inner air seal)\n\n**Why it matters:**\nCracks in turbine disks can lead to **catastrophic engine failure** — potentially causing an uncontained engine breakup where metal fragments pierce the engine casing, endangering the aircraft and passengers. This directive prevents that by catching problems before they become dangerous.\n\n**Key change in this version:**\nThis amendment (from 2005) removes references to the manufacturer's own documents and instead points directly to the **US Federal Aviation Administration (FAA) directive**. This \"harmonisation\" means Australian operators now follow the same rules as the US, simplifying compliance for airlines that fly internationally."},"flash_summary_failed":{"failed":true,"reason":"A positive credit balance is required for all requests, including BYOK, so fallback providers remain available. Add credits at https://vercel.com/d?to=%2F%5Bteam%5D%2F%7E%2Fai%3Fmodal%3Dtop-up to continue.","source":"analysis-cron"}},"importantCases":[],"_links":{"self":"/api/acts/ad-jt8d-18-amdt-2-second-stage-turbine-disc","history":"/api/acts/ad-jt8d-18-amdt-2-second-stage-turbine-disc/history","analysis":"/api/acts/ad-jt8d-18-amdt-2-second-stage-turbine-disc/analysis","conflicts":"/api/acts/ad-jt8d-18-amdt-2-second-stage-turbine-disc/conflicts","importantCases":"/api/acts/ad-jt8d-18-amdt-2-second-stage-turbine-disc/important-cases","documents":"/api/acts/ad-jt8d-18-amdt-2-second-stage-turbine-disc/documents"}}