{"id":"F2006B06395","name":"AD/PW4000/4 - Low Pressure Turbine Stage 4 Disk","slug":"ad-pw4000-4-low-pressure-turbine-stage-4-disk","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":47707,"registerId":"commonwealth-F2006B06395-current","compilationNumber":null,"startDate":"2026-04-02","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/PW4000/4 - Low Pressure Turbine Stage 4 Disk","content":"COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 \\- 106 CIVIL AVIATION SAFETY AUTHORITY\n\nSCHEDULE OF AIRWORTHINESS DIRECTIVES\n\n![](image.001.png)  \nPratt and Whitney Turbine Engines \\- PW4000 Series\n\nAD/PW4000/4 Low Pressure Turbine Stage 4 Disk 10/99\n\nApplicability: PW4000 series engines with a Low Pressure Turbine (LPT) Stage 4 disk as specified in FAA AD 99-15-01.\n\nRequirement: Replace affected LPT Stage 4 Disks in accordance with the technical requirements of FAA AD 99-15-01.\n\nNote: Pratt and Whitney Service Bulletins PW4ENG 72-657 and PW4G 100-72-105 also refer.\n\nCompliance: At periods detailed in the Requirement document.\n\nThis Airworthiness Directive becomes effective on 7 October 1999.\n\nBackground: This Directive is prompted by advice that a change in cooling hole geometry on affected LPT disks results in a reduction in cooling air flow to the disk and higher stresses. Higher than normal stress could result in an uncontained disk failure.","sortOrder":0}],"analysis":{"kimi_summary":{"content_quality":"ok","complexity_score":2,"scope_assessment":{"changed":false,"description":"This is a standard, narrow Airworthiness Directive that addresses a specific technical defect in a specific engine component. It has not expanded beyond its original safety purpose."},"complexity_factors":["Very short document (under 200 words)","Only 1 defined term implicitly referenced (LPT = Low Pressure Turbine)","Single, clear compliance requirement (replace the disk)","No nested exceptions or conditional logic — applies straightforwardly to all affected engines","Cross-references only to external FAA document and service bulletins, not to other sections of Australian law","No interpretive provisions or deeming clauses"],"plain_english_summary":"**What this is:** This is an Airworthiness Directive (AD) — essentially a mandatory safety order issued by Australia's Civil Aviation Safety Authority (CASA). It requires specific maintenance action on certain aircraft engines.\n\n**What it does:**\n- **Targets:** Pratt & Whitney PW4000 series jet engines (used on large commercial aircraft like Boeing 747s and 777s)\n- **The problem:** The Low Pressure Turbine (LPT) Stage 4 disk has a design flaw — the cooling holes were changed in a way that reduces airflow, causing the metal disk to run hotter and experience higher stress than designed\n- **The risk:** If left unchecked, the disk could crack and break apart catastrophically (an \"uncontained failure\" — where engine parts fly out through the engine casing, potentially damaging the aircraft or injuring people)\n- **The fix:** Airlines must replace the affected disks following the technical instructions in the referenced US Federal Aviation Administration (FAA) directive (AD 99-15-01)\n\n**Who it affects:** Airlines and aircraft operators in Australia using PW4000 engines with these specific disks, plus maintenance organisations that service these engines.\n\n**Why it matters:** This is a critical safety measure. Uncontained engine failures have caused fatal accidents in aviation history. The directive forces operators to fix the problem before it causes an accident, rather than waiting for something to go wrong."},"flash_summary":{"complexity_score":4,"scope_assessment":{"changed":false,"description":"The AD does not indicate a change in scope from any prior instrument within the text provided. It applies specifically to PW4000 series engines with the affected LPT Stage 4 disk as described in FAA AD 99-15-01 and requires replacement of those disks in accordance with that FAA AD (\"Applicability\", \"Requirement\")."},"complexity_factors":["Delegation to an external technical document (FAA AD 99-15-01) for specific procedures and compliance timing","Safety-critical part replacement requiring coordination between operators, maintenance providers and manufacturer","Cross-references to manufacturer service bulletins (additional documents to consult)","Operational impacts (aircraft downtime, parts procurement) that vary by operator and are not specified in the AD","Regulatory enforcement by CASA with technical detail supplied by another authority (creates reliance on external rulemaking)"],"plain_english_summary":"This AD requires owners/operators to replace certain Low Pressure Turbine (LPT) Stage 4 disks in Pratt & Whitney PW4000 engines, following the technical steps and timing in FAA AD 99-15-01; it takes effect 7 October 1999.  \n\nIt affects operators, maintenance organisations and Pratt & Whitney. It responds to a cooling‑hole geometry change that raises disk stress and risk of uncontained failure, shifting compliance costs and technical direction to the FAA requirements and referenced P&W service bulletins."}},"importantCases":[],"_links":{"self":"/api/acts/ad-pw4000-4-low-pressure-turbine-stage-4-disk","history":"/api/acts/ad-pw4000-4-low-pressure-turbine-stage-4-disk/history","analysis":"/api/acts/ad-pw4000-4-low-pressure-turbine-stage-4-disk/analysis","conflicts":"/api/acts/ad-pw4000-4-low-pressure-turbine-stage-4-disk/conflicts","importantCases":"/api/acts/ad-pw4000-4-low-pressure-turbine-stage-4-disk/important-cases","documents":"/api/acts/ad-pw4000-4-low-pressure-turbine-stage-4-disk/documents"}}