{"id":"F2006B11013","name":"AD/JT9D/20 - Diffuser Case Strut Inserts","slug":"ad-jt9d-20-diffuser-case-strut-inserts","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":56613,"registerId":"commonwealth-F2006B11013-current","compilationNumber":null,"startDate":"2026-04-02","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/JT9D/20 - Diffuser Case Strut Inserts","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 \\- JT9D Series\n\nAD/JT9D/20 Diffuser Case Strut Inserts 8/89\n\nApplicability: JT9D-3A, \\-7, \\-7A, \\-7AH, \\-7H, \\-7F, \\-7J, \\-20 engines.\n\nRequirement: Install strut insert assembly Part Number 804698-01 into both the number 4 and number 7 diffuser case struts, in accordance with the Accomplishment Instructions of Pratt and Whitney Service Bulletin No. 5730.\n\nNote: FAA AD 89-10-07 refers.\n\nCompliance: At the next disassembly of the high compressor case from the diffuser case at \"K\" flange, but no later than 31 August 1991.\n\nBackground: This Directive requires compliance with P & W SB No. 5730. The Requirement reflects concern regarding reported No. 3 bearing compartment fire events in certain JT9D models. The Requirement requires installation of strut insert assembly P/N 804698-01 to provide a physical restraint to strut collapse, and to provide an airflow path separate from 15th stage air.","sortOrder":0}],"analysis":{"flash_summary":{"complexity_score":3,"scope_assessment":{"changed":false,"description":"The directive's mandated action aligns with the stated corrective purpose in the background (to address No. 3 bearing compartment fire events) by requiring installation of the specified strut insert assemblies into two diffuser case struts for the listed engine models. The instrument does not expand applicability beyond the listed JT9D models nor impose additional inspection or operational restrictions beyond the installation and its timing requirement. (Applicability; Requirement; Background; Compliance)"},"complexity_factors":["Single prescriptive technical action: installation of one specific part (P/N 804698-01) into two named struts reduces procedural complexity. (Requirement)","Limited applicability: only affects a defined list of JT9D engine models, which narrows scope. (Applicability)","Compliance timing uses a simple conditional rule (at next disassembly of the high compressor case from the diffuser case at \"K\" flange) plus an absolute calendar deadline, which is straightforward to administer but creates scheduling implications. (Compliance)","Dependency on an external technical document (Pratt & Whitney Service Bulletin No. 5730) for the detailed steps adds procedural dependency and requires maintenance organisations to possess and follow that bulletin. (Requirement)","Cross-reference to another regulator's AD (FAA AD 89-10-07) introduces potential coordination or record-keeping complexity for operators operating under multiple jurisdictions. (Note)"],"plain_english_summary":"Owners, operators and maintenance organisations of specified Pratt & Whitney JT9D engines must install strut insert assembly P/N 804698-01 into the No.4 and No.7 diffuser case struts per Pratt & Whitney Service Bulletin No. 5730. Compliance is required at the next K‑flange disassembly or by 31 August 1991.  \n\nThe change—paid for by operators—aims to reduce No.3 bearing compartment fire risk by restraining strut collapse and providing an alternate airflow path."},"kimi_summary":{"content_quality":"ok","complexity_score":2,"scope_assessment":{"changed":false,"description":"This is a discrete airworthiness directive addressing a specific safety defect in specific engine models. It has not expanded beyond its original purpose of mandating a particular hardware modification to prevent bearing compartment fires."},"complexity_factors":["Single, specific technical requirement with clear part number (P/N 804698-01)","Limited applicability to 8 specific engine models only","Straightforward compliance deadline with one conditional trigger (next disassembly) and one absolute deadline","No defined terms section, no cross-references to other legislation beyond a single FAA AD reference","Background explanation provided in plain language","Short document (approximately 150 words)"],"plain_english_summary":"This is a **safety order for aircraft engines**. It applies to specific Pratt & Whitney JT9D engines used in planes like the Boeing 747.\n\n**What it does:**\n- Requires airlines and maintenance crews to install a specific metal part (a \"strut insert assembly\") into two particular locations in the engine (the number 4 and number 7 diffuser case struts).\n- This part acts like a safety brace to prevent the struts from collapsing, and helps manage airflow to reduce fire risk.\n\n**Why it matters:**\n- There had been **fires in the No. 3 bearing compartment** of these engines — a dangerous situation that could lead to engine failure.\n- This fix prevents those struts from collapsing and creating conditions where fires can start or spread.\n\n**Who must comply:**\n- Anyone operating or maintaining JT9D-3A, -7, -7A, -7AH, -7H, -7F, -7J, or -20 model engines.\n\n**When to do it:**\n- By 31 August 1991 at the latest, or sooner if the engine is being taken apart for maintenance anyway (specifically when separating the high compressor case from the diffuser case at the \"K\" flange)."}},"importantCases":[],"_links":{"self":"/api/acts/ad-jt9d-20-diffuser-case-strut-inserts","history":"/api/acts/ad-jt9d-20-diffuser-case-strut-inserts/history","analysis":"/api/acts/ad-jt9d-20-diffuser-case-strut-inserts/analysis","conflicts":"/api/acts/ad-jt9d-20-diffuser-case-strut-inserts/conflicts","importantCases":"/api/acts/ad-jt9d-20-diffuser-case-strut-inserts/important-cases","documents":"/api/acts/ad-jt9d-20-diffuser-case-strut-inserts/documents"}}