{"id":"F2006B10993","name":"AD/JT8D/4 - Sixth Stage Compressor Disc and Blades","slug":"ad-jt8d-4-sixth-stage-compressor-disc-and-blades","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":56583,"registerId":"commonwealth-F2006B10993-current","compilationNumber":null,"startDate":"2026-04-02","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/JT8D/4 - Sixth Stage Compressor Disc and Blades","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 - JT8D Series\n\n \n\nAD/JT8D/4 Sixth Stage Compressor Disc and Blades 8/70\n\nApplicability: All JT8D series engines incorporating sixth stage compressor discs P/Ns 483506, 494906 and 586906.\n\n \n\nRequirement: 1. Using a suitable borescope, inspect the rear of the sixth stage compressor blade dovetail roots and disc slots for any evidence of cracking. Any sixth stage compressor blade or disc found cracked shall be removed from service before further flight.\n\n \n\nNote: Pratt & Whitney SB No. 1133, Rev. 3 gives details of a modification for incorporating suitable borescope inspection ports in the compressor casing.\n\n \n\nor\n\n \n\n2. AD/PW-T/27A.\n\n \n\nCompliance: At intervals not exceeding 500 hours time in service, after 31 August 1970.\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, targeted safety directive focused on a specific known defect in specific engine part numbers. It has not expanded beyond its original purpose of preventing sixth stage compressor disc failures in JT8D engines."},"complexity_factors":["Very short document (approximately 200 words)","Only 3 defined part numbers (P/Ns 483506, 494906, 586906)","Simple binary compliance structure (two alternative methods)","Single cross-reference to another directive (AD/PW-T/27A)","No nested exceptions or conditional logic","Clear, unambiguous time-based compliance requirement (500 hours)","Technical but straightforward mechanical inspection requirement"],"plain_english_summary":"This CASA Airworthiness Directive mandates repeated inspections of the sixth-stage compressor disc and blades on Pratt & Whitney JT8D engines (specific P/Ns) because cracking can lead to catastrophic engine failure. Affected operators and maintenance organisations must inspect every 500 flight hours — either by borescope (with blade/disc replacement if cracks are found; service bulletin guidance exists for adding inspection ports) or by complying with the cited alternative AD. It prevents in‑flight engine damage and loss of control."},"flash_summary":{"complexity_score":3,"scope_assessment":{"changed":false,"description":"The directive applies only to JT8D engines fitted with the three listed sixth-stage compressor disc part numbers and prescribes inspection intervals and removal requirements. The text does not expand or narrow that applicability beyond those parts or change the nature of the obligation."},"complexity_factors":["Technical specificity: targets a precise component (sixth stage compressor disc and blade dovetail roots) with specific part numbers (P/Ns 483506, 494906, 586906).","Recurring compliance: mandates inspections at fixed intervals (<=500 hours TIS), creating ongoing scheduling and record-keeping obligations.","Alternative compliance path: permits compliance by following AD/PW-T/27A, requiring cross-referencing another directive.","External modification reference: points to Pratt & Whitney SB No.1133 Rev.3 for installing borescope ports, adding a mechanical modification step before inspections are practicable.","Immediate operational consequence: cracked items must be removed before further flight, creating potential unscheduled removals and replacement costs."],"plain_english_summary":"Requires borescope inspection of the rear of sixth-stage compressor blade dovetail roots and disc slots on JT8D engines that use discs P/Ns 483506, 494906 or 586906; any cracked blade or disc must be removed from service before further flight. Inspections must occur at intervals not exceeding 500 hours TIS after 31 August 1970; alternatively an operator may comply with AD/PW-T/27A. Pratt & Whitney SB No.1133 Rev.3 describes adding borescope ports. Operators and maintenance organisations pay for inspections, casing modifications and part removals; the regulator sets the mandatory interval and removal requirement."}},"importantCases":[],"_links":{"self":"/api/acts/ad-jt8d-4-sixth-stage-compressor-disc-and-blades","history":"/api/acts/ad-jt8d-4-sixth-stage-compressor-disc-and-blades/history","analysis":"/api/acts/ad-jt8d-4-sixth-stage-compressor-disc-and-blades/analysis","conflicts":"/api/acts/ad-jt8d-4-sixth-stage-compressor-disc-and-blades/conflicts","importantCases":"/api/acts/ad-jt8d-4-sixth-stage-compressor-disc-and-blades/important-cases","documents":"/api/acts/ad-jt8d-4-sixth-stage-compressor-disc-and-blades/documents"}}