{"id":"F2006B10868","name":"AD/JBK 117/20 - Tail Rotor Transmission/Intermediate Gearbox","slug":"ad-jbk-117-20-tail-rotor-transmission-intermediate-gearbox","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":56369,"registerId":"commonwealth-F2006B10868-current","compilationNumber":null,"startDate":"2026-04-02","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/JBK 117/20 - Tail Rotor Transmission/Intermediate Gearbox","content":"![](image.001.png)\n\nAIRWORTHINESS DIRECTIVE\n\n![](image.001.png)  \n\nFor the reasons set out in the background section, the CASA delegate whose signature appears below issues the following Airworthiness Directive (AD) under subregulation 39.1 (1) of CASR 1998. The AD requires that the action set out in the requirement section (being action that the delegate considers necessary to correct the unsafe condition) be taken in relation to the aircraft or aeronautical product mentioned in the applicability section: (a) in the circumstances mentioned in the requirement section; and (b) in accordance with the instructions set out in the requirement section; and (c) at the time mentioned in the compliance section.\n\n![](image.001.png)  \n\nKawasaki BK 117 Series Helicopters\n\nAD/JBK 117/20 Tail Rotor Transmission/Intermediate\n\nGearbox\n\n  \n13/2003\n\nApplicability: Kawasaki Model BK117 helicopters, except for the C-2 model; incorporating any of the following:\n\n    A tail rotor transmission part number (P/N) 4639003001 or 4639003007 with a serial number (S/N) 900 through 932 inclusive that had been overhauled or repaired in the period 16 July 2001 to 22 May 2003, the effective date of Kawasaki Service Bulletin (KSB) KSB-117-210; or\n\n    b. An intermediate gearbox P/N 4639002001 or 4639002005 with a S/N 902 though 928 inclusive that had been overhauled or repaired in the period 16 July 2001 to 22 May 2003, the effective date of Kawasaki KSB-117-210; or\n\n    c. The tail rotor transmission and/or the intermediate gearbox is fitted with a bearing P/N 4639310006, S/N 3246 through 3598 inclusive; and\n\n    d. The tail rotor transmission and/or the intermediate gearbox have not been inspected in accordance with Paragraph 9 of Kawasaki KSB-117-210.\n\nRequirement: 1. Installed tail rotor transmission and intermediate gearboxes:\n\n    Inspect the magnetic plug of the tail rotor transmission in accordance with Paragraph 9 (3) of Kawasaki KSB-117-210.\n\n    b. Inspect the magnetic plug of the intermediate gearbox in accordance with Paragraph 9 (3) of Kawasaki KSB-117-210.\n\n    2. Unless previously accomplished:\n\nSupply to Kawasaki Heavy Industries (KHI) for inspection by ZF Lufthfahrttechnik, P/N 4639310006, S/N 3246 through 3598 bearings held as spares.\n\n    3. Unless previously accomplished:\n\nInstalled tail rotor transmission and intermediate gearboxes.\n\nKawasaki BK 117 Series Helicopters\n\nAD/JBK 117/20 (continued)\n\n    Remove the tail rotor transmission for an inspection in accordance with Paragraph 9 (2) (c) of Kawasaki KSB-117-210.\n\n    b. Remove the intermediate gearbox for an inspection in accordance with Paragraph 9 (2) (c) of Kawasaki KSB-117-210.\n\n    4. Unless previously accomplished:\n\nSpare tail rotor transmission and intermediate gearboxes:\n\n    Forward the tail rotor transmission for an inspection in accordance with Paragraph 9 (1) b of Kawasaki KSB-117-210.\n\n    b. Forward the intermediate gearbox for an inspection in accordance with Paragraph 9 (1) b of Kawasaki KSB-117-210.\n\nNote: JCAB Airworthiness Directive TCD-6217-2003 refers.\n\nCompliance: 1. Before the first flight of the day pending compliance with Paragraph 9 (2) (c) of Kawasaki KSB-117-210.\n\n    2. Prior to 31 January 2004.\n\n    3. Prior to 31 January 2004.\n\n    4. Prior to installation in a helicopter.\n\nThis Airworthiness Directive becomes effective on 25 December 2003.\n\nBackground: This directive has been issued in response to reports of cracks being found in the cage cover of certain bearings installed in BK117 tail rotor transmissions and intermediate gearboxes. Bearing failure could result in the failure of the tail rotor transmission or intermediate gearbox, causing loss of the control of the helicopter.\n\n![Signature of Jim Coyne Delegate of the Civil Aviation Safety Authority](image.002.png)  \n\nJim Coyne\n\nDelegate of the Civil Aviation Safety Authority 14 November 2003\n\n![](image.001.png)  \n\nThe above AD is notified in the Commonwealth of Australia Gazette on 3 December 2003.","sortOrder":0}],"analysis":{"flash_summary":{"complexity_score":4,"scope_assessment":{"changed":false,"description":"This AD addresses a discrete safety issue (cracked bearing cages in specified tail rotor transmission/intermediate gearbox components) and requires targeted inspections, removals and forwarding of parts/spares. It does not expand beyond that original safety remediation purpose; the requirements are narrowly tied to particular part numbers, serial ranges, overhaul/repair dates, and the inspection procedures in Kawasaki Service Bulletin KSB-117-210."},"complexity_factors":["Multiple applicability conditions combining model exclusion (C-2) with several part numbers and overlapping serial-number ranges","Cross-reference to an external Kawasaki Service Bulletin (KSB-117-210) for the detailed inspection procedures (Paragraph 9 referenced repeatedly)","Four separate requirement blocks with conditional language (\"Unless previously accomplished\") creating staging of actions","Distinct compliance timing rules: immediate daily pre-flight inspection until removal inspection completed, plus fixed calendar deadlines (31 Jan 2004), and pre-installation requirement for spares","Specific routing of spare-bearing inspections to Kawasaki/ZF (narrowing where some work must be done)","Reference to a foreign AD (JCAB TCD-6217-2003) creating another source to consult"],"plain_english_summary":"**What this directive does (mechanical change)\n\n- This Airworthiness Directive (AD) requires owners/operators of certain Kawasaki BK117 helicopter tail rotor transmissions and intermediate gearboxes to have those parts inspected, removed and inspected, or forwarded for inspection, depending on whether they are installed or held as spares.  The inspections must follow the procedures in Kawasaki Service Bulletin KSB-117-210 (see Paragraph 9 references in the AD). (Requirement; Compliance)\n\n**Who it affects\n\n- Applies to Kawasaki BK117 helicopters except model C-2, and to spares, when the parts have one of the specified part numbers and serial-number ranges, and were overhauled or repaired during 16 July 2001 to 22 May 2003, or when a specific bearing part/serial range is fitted. (Applicability)\n\n**Why it matters (safety risk stated)\n\n- The AD was issued because cracks were found in the cage cover of certain bearings fitted to the affected tail rotor transmission and intermediate gearbox assemblies. Bearing failure could allow the transmission or gearbox to fail and lead to loss of helicopter control. (Background)\n\n**What operators must do (plain steps and timing)\n\n- For installed units: inspect the magnetic plug of the tail rotor transmission and the intermediate gearbox as directed in Paragraph 9(3) of Kawasaki KSB-117-210. (Requirement 1)\n- Supply spare bearings with P/N 4639310006 and S/N 3246–3598 to Kawasaki Heavy Industries for inspection by ZF Lufthfahrttechnik, if they are held as spares. (Requirement 2)\n- Remove installed tail rotor transmissions and intermediate gearboxes and carry out the more detailed inspections in Paragraph 9(2)(c) of KSB-117-210, unless already done. (Requirement 3)\n- Forward spare tail rotor transmissions and intermediate gearboxes for inspection in accordance with Paragraph 9(1)(b) of KSB-117-210 before they are installed. (Requirement 4)\n\nTiming (Compliance):\n- The magnetic plug inspection must be done before the first flight of the day until the full inspection required by Paragraph 9(2)(c) has been completed. (Compliance 1)\n- The removals and forwarding of parts/spares for inspection must be completed by 31 January 2004, unless already done. Spare assemblies must be inspected before installation. (Compliance 2–4)\n\n**Who pays and who decides\n\n- Owners/operators pay for the inspections, removals, transport and any repairs. They must comply because CASA (through its delegate) issued the AD under CASR subregulation 39.1(1). Kawasaki and ZF Lufthfahrttechnik perform inspection services for some items (Requirement 2). (Applicability; Requirement)\n\n**Implementation and operational effects (mechanics, costs, incentives and trade-offs)\n\n- Direct costs: labour for inspections and removals, downtime for helicopters while parts are removed/inspected, and transport or inspection fees paid to Kawasaki/ZF for spare bearings. (Requirement; Compliance)\n- Operational constraint: until parts pass the required inspections, affected helicopters may face daily pre-flight inspection requirements and/or grounding while parts are removed for detailed inspection — this imposes short-term availability costs. (Compliance 1 and 3)\n- Supply-chain and capacity risk: sending spare bearings or assemblies to Kawasaki/ZF concentrates inspection demand on those entities; delays in their capacity or in shipping logistics could extend downtime for operators. (Requirement 2)\n- Flow-on effects: maintenance providers and authorised repair stations will perform required work; the AD channels some inspection work to Kawasaki/ZF (explicit for the bearings), which may shift business to those providers. (Requirement 2)\n- Compliance burden: owners must track serial numbers/part numbers and the overhaul/repair history window specified (16 July 2001–22 May 2003), and implement record-keeping and inspection scheduling to meet the AD deadlines. (Applicability; Compliance)\n\n**Cross-references and supporting material\n\n- The AD requires following inspection instructions in Kawasaki Service Bulletin KSB-117-210 (Paragraph 9); it also notes a related Japan Civil Aviation Bureau AD (TCD-6217-2003). Operators must consult KSB-117-210 for the detailed inspection steps. (Requirement; Note)\n\n**Summary sentence**\n- In short: this AD mandates specific inspections, removals and forwarding of certain Kawasaki BK117 tail rotor transmission and intermediate gearbox parts (and related bearings) because of cracked bearing cages; operators must carry out the actions by the stated deadlines and follow KSB-117-210 procedures, with inspection services for spare bearings to be provided by Kawasaki/ZF. (Applicability; Requirement; Compliance; Background)"},"flash_summary_failed":{"failed":true,"reason":"Unauthenticated. Configure AI_GATEWAY_API_KEY or use a provider module. Learn more: https://ai-sdk.dev/unauthenticated-ai-gateway","source":"analysis-cron"},"kimi_summary":{"content_quality":"ok","complexity_score":4,"scope_assessment":{"changed":false,"description":"This AD maintains focused scope on the specific unsafe bearing condition in BK117 helicopter transmissions. The applicability criteria precisely target the affected components without expanding beyond the original safety purpose."},"complexity_factors":["Multiple nested applicability conditions combining part numbers, serial number ranges, dates of overhaul/repair, and inspection history","Four separate requirement paragraphs with different compliance deadlines and conditions ('unless previously accomplished' clauses)","Cross-references to external technical document (Kawasaki Service Bulletin KSB-117-210) for detailed inspection procedures rather than including them in the directive itself","Specific date ranges for overhaul/repair history (16 July 2001 to 22 May 2003) creating conditional applicability","Mixed applicability logic: 'except for C-2 model' combined with inclusive serial number ranges (900-932, 902-928, 3246-3598)","Dual compliance tracks for installed vs. spare components"],"plain_english_summary":"This AD mandates that owners/operators of Kawasaki BK117 helicopters (except C‑2) inspect and, if necessary, replace bearings in the tail rotor transmission and intermediate gearbox after reports of cracked bearing cage covers. Bearing failure could lead to tail rotor or gearbox breakup and loss of control.\n\nIt targets helicopters with affected parts overhauled or repaired between July 2001 and May 2003. Compliance (including daily magnetic‑plug checks and required removals/inspections by the AD deadline) is mandatory before flight."}},"importantCases":[],"_links":{"self":"/api/acts/ad-jbk-117-20-tail-rotor-transmission-intermediate-gearbox","history":"/api/acts/ad-jbk-117-20-tail-rotor-transmission-intermediate-gearbox/history","analysis":"/api/acts/ad-jbk-117-20-tail-rotor-transmission-intermediate-gearbox/analysis","conflicts":"/api/acts/ad-jbk-117-20-tail-rotor-transmission-intermediate-gearbox/conflicts","importantCases":"/api/acts/ad-jbk-117-20-tail-rotor-transmission-intermediate-gearbox/important-cases","documents":"/api/acts/ad-jbk-117-20-tail-rotor-transmission-intermediate-gearbox/documents"}}