{"id":"F2006B11009","name":"AD/JT9D/16 - HPC Variable Stator Synchronising Ring Runner Clearance","slug":"ad-jt9d-16-hpc-variable-stator-synchronising-ring-runner-clearance","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":56609,"registerId":"commonwealth-F2006B11009-current","compilationNumber":null,"startDate":"2026-04-02","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/JT9D/16 - HPC Variable Stator Synchronising Ring Runner Clearance","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/16 HPC Variable Stator Synchronising\n\nRing Runner Clearance\n\nApplicability: JT9D-7R4 D/D1/E/E1/E4 and H1 series engines.\n\n  \n2/87\n\nTX\n\nRequirement: Fit synchronising ring runners having specified clearances to comply at minimum with the requirements of FAA Emergency Telex Airworthiness Directive/TAD/number T86-25-51 dated 12 December 1986. (Revised operating procedures are involved if only minimum levels of compliance are incorporated).\n\nCompliance: To be incorporated into at least one engine per aircraft before further flight after 25 December 1986 and into all engines by 31 December 1987.\n\nBackground: The FAA has determined that clearance between the high pressure compressor case and the variable stator vane synchronising ring runners decreases during operation at take off power and could cause temporary binding in the system during power reduction. An engine deceleration during the take off/climb period can cause the stator vanes to remain open reducing the available surge margin.","sortOrder":0}],"analysis":{"flash_summary":{"complexity_score":3,"scope_assessment":{"changed":false,"description":"No change of scope is indicated in the text. The instrument applies to the specified JT9D engine series and mandates fitting specified synchronising ring runners to meet FAA minimum requirements, with explicit retrofit deadlines (Applicability; Requirement; Compliance; Background)."},"complexity_factors":["Narrow technical scope: affects only JT9D-7R4 D/D1/E/E1/E4 and H1 series engines (Applicability).","Single technical remedy: fitting synchronising ring runners to meet specified clearances (Requirement).","Fixed, phased compliance timeline: one engine per aircraft before further flight after 25/12/1986 and all engines by 31/12/1987 (Compliance).","Cross-reference to FAA Emergency Telex standard — implementers must meet at least that minimum (Requirement).","Safety-critical operational impact: addresses compressor binding and surge margin during takeoff/climb (Background).","Implementation burden on operators: parts, maintenance time and scheduling required to retrofit engines within the deadlines (Compliance)."],"plain_english_summary":"This directive requires operators of aircraft with Pratt & Whitney JT9D-7R4 and H1 series engines to fit synchronising ring runners with specified clearances so the high-pressure compressor variable stator system cannot bind (Requirement; Applicability). The measure responds to an FAA finding that reduced clearances during takeoff can cause temporary binding and lower surge margin; operators must retrofit at least one engine before further flight after 25 Dec 1986 and all engines by 31 Dec 1987 (Background; Compliance)."},"kimi_summary":{"content_quality":"ok","complexity_score":3,"scope_assessment":{"changed":false,"description":"This is a discrete, time-bound safety directive addressing a specific mechanical defect in specific engine models. It has not expanded beyond its original purpose of mandating a hardware modification to prevent compressor stalls."},"complexity_factors":["Single, specific technical requirement (replace/modify one component type)","Limited applicability (6 specific engine sub-models only)","Clear compliance deadline structure (two-tier: immediate partial, then full)","No nested exceptions or conditional logic — applies to all listed engines without carve-outs","Short document (approximately 200 words)","Only one defined term implicitly used ('Compliance' as a defined concept in aviation regulation)","Single cross-reference to external FAA document (T86-25-51) for technical specifications"],"plain_english_summary":"This AD mandates replacing or modifying the synchronising ring runners in certain Pratt & Whitney JT9D-7R series high‑pressure compressors to restore specified clearances. It addresses a takeoff/climb hazard where shrinking gaps can let rings jam, reducing surge margin and risking engine stall or flameout.\n\nIt applies to operators of JT9D-7R4 D/D1/E/E1/E4 and H1 engines (e.g., many 747s) and requires at least one engine fixed before flight after 25 Dec 1986 and all engines by 31 Dec 1987."}},"importantCases":[],"_links":{"self":"/api/acts/ad-jt9d-16-hpc-variable-stator-synchronising-ring-runner-clearance","history":"/api/acts/ad-jt9d-16-hpc-variable-stator-synchronising-ring-runner-clearance/history","analysis":"/api/acts/ad-jt9d-16-hpc-variable-stator-synchronising-ring-runner-clearance/analysis","conflicts":"/api/acts/ad-jt9d-16-hpc-variable-stator-synchronising-ring-runner-clearance/conflicts","importantCases":"/api/acts/ad-jt9d-16-hpc-variable-stator-synchronising-ring-runner-clearance/important-cases","documents":"/api/acts/ad-jt9d-16-hpc-variable-stator-synchronising-ring-runner-clearance/documents"}}