{"id":"F2006L04102","name":"AD/S-92/4 - Tail Gear Box","slug":"ad-s-92-4-tail-gear-box","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":61033,"registerId":"commonwealth-F2006L04102-current","compilationNumber":null,"startDate":"2026-04-02","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"Sikorsky S-92 Series Helicopters","sectionType":"division","heading":"Sikorsky S-92 Series Helicopters","content":"### Sikorsky S-92 Series Helicopters\n\n| AD/S-92/4 | Tail Gear Box | 2/2007 TX |\n| --------- | ------------- | --------- |\n\n| Applicability: | Sikorsky Model S-92A helicopters, with a gear box output housing, part number (P/N) 92358-06109-043, installed.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                |\n| -------------- | -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |\n| Requirement:   | 1. Unless previously accomplished, replace each tail gear box output housing, P/N 92358-06109-043, with 600 or more hours time-in-service (TIS) with an airworthy tail gear box housing with less than 600 hours TIS.Note 1: Sikorsky Maintenance Manual SA S92A-AWL-000, Airworthiness Limitations and Inspection Requirements, Chapter 4, dated March 3, 2005, contains the limitation for the tail gear box output housing.2. Unless previously accomplished, revise the Airworthiness Limitations section of the maintenance manual by reducing the life limit of the tail gear box output housing from 4500 hours TIS to 600 hours TIS.Note 2: FAA AD 2005-13-13 Amdt 39-14150 dated 10 June 2005 refers. |\n| Compliance:    | Before further flight after the effective date of this AD.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     |\n|                | This Airworthiness Directive becomes effective on 18 December 2006.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            |\n\n| Background: | This AD requires, before further flight, replacing tail gear box output housing, part number (P/N) 92358-06109-043, that has 600 or more hours TIS with an airworthy gear box output housing with less than 600 hours TIS. Also, this AD revises the Airworthiness Limitations section of the maintenance manual by reducing the life limit of the tail gear box output housing from 4500 hours TIS to 600 hours TIS. This is prompted by the premature failure of the tail gear box output housing during fatigue testing by the manufacturer. The follow-on investigation indicated the manufacturing process created an oxide skin defect in the housing, making it necessary to reduce the life limit of the gear box housing from 4500 hours TIS to 600 hours TIS. The manufacturer is reviewing its processes on the output housing to determine methods, including a material change, to prevent the oxide skin defect. |\n| ----------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ |\n\n![](image.001.png)  \nJames Coyne  \nDelegate of the Civil Aviation Safety Authority\n\n13 December 2006","sortOrder":0},{"sectionNumber":"AD/S-92/4","sectionType":"part","heading":"AD/S-92/4","content":"## AD/S-92/4","sortOrder":1},{"sectionNumber":"Tail Gear Box","sectionType":"part","heading":"Tail Gear Box","content":"## Tail Gear Box","sortOrder":2},{"sectionNumber":"2/2007 TX","sectionType":"part","heading":"2/2007 TX","content":"## 2/2007 TX","sortOrder":3}],"analysis":{"flash_summary":{"complexity_score":3,"scope_assessment":{"changed":false,"description":"This AD is narrowly targeted to correct a safety defect identified in fatigue testing of a specific part. It reduces the approved life limit for that part and mandates replacement where the new limit is exceeded. Those changes alter the operational life of the component compared with earlier guidance (reducing from 4,500 to 600 hours), but they do not expand the AD’s subject matter beyond the original safety purpose (addressing premature failure of the tail gear box output housing). Therefore the instrument has not grown beyond its original safety-focused intent; it tightens and accelerates corrective action rather than adding unrelated obligations."},"complexity_factors":["Short, single-issue directive focused on one part number (P/N 92358-06109-043).","Two clear mandated actions: immediate part replacement for housings with >=600 hours TIS, plus a one-time maintenance manual life-limit revision (nested but limited).","Immediate compliance timing: \"before further flight\" (no phased compliance), which raises operational complexity though not textual complexity.","Cross-references to external documents: Sikorsky Maintenance Manual and FAA AD 2005-13-13 are cited (adds cross-reference complexity).","Relatively few defined terms and no long schedule of inspections or conditional exceptions."],"plain_english_summary":"**What this instrument does (mechanically)**\n\n- Applies to Sikorsky Model S-92A helicopters that have a tail gear box output housing with part number P/N 92358-06109-043 installed (Applicability).\n- Requires immediate action: any helicopter with that specific housing that has accumulated 600 or more hours time-in-service (TIS) must have the housing replaced with an airworthy housing that has less than 600 hours TIS before the helicopter can fly again (Requirement; Compliance).\n- Requires a change to the maintenance manual: the Airworthiness Limitations section must be revised to shorten the approved life limit of that same housing from 4,500 hours TIS to 600 hours TIS (Requirement).\n- The effective date for the directive is 18 December 2006; compliance is required before further flight after that date (Compliance).\n\n**Who this affects**\n\n- Operators and owners of Sikorsky S-92A helicopters that have tail gear box output housing P/N 92358-06109-043 installed.\n- Maintenance organisations and engineers who keep aircraft records and update the maintenance manual.\n- Manufacturers and parts suppliers to the extent replacement housings are needed.\n\n**Why it matters (stated reason and practical implications)**\n\n- Stated reason: fatigue testing found premature failure of the tail gear box output housing caused by an oxide skin defect originating in the manufacturing process; the manufacturer is reviewing processes and possible material changes (Background).\n- Practical effect: the allowable service life of the specified housing is cut from 4,500 hours to 600 hours (Requirement). Any helicopters already at or beyond 600 hours for that part must have that part replaced before the next flight (Compliance). This imposes immediate workload and replacement-parts demand on operators and maintenance providers.\n\n**Who pays, who decides, and what changes**\n\n- Who pays: operators/owners are responsible for arranging and funding the replacement of housings and for updating the maintenance manual entries (Requirement; Compliance). The AD does not include any funding or compensation mechanism.\n- Who decides: the regulator (the Civil Aviation Safety Authority delegate issued the AD) sets the mandatory requirement; operators and approved maintenance organisations implement it and certify compliance.\n- What behaviour changes: operators must track the TIS of that part, remove and replace any housings at or above 600 TIS, and amend maintenance documentation to reflect the shorter life limit.\n\n**Costs, incentives and trade-offs**\n\n- Direct costs: replacement parts, labour, and possible aircraft downtime while parts are procured and installed. If many helicopters are affected simultaneously, parts supply constraints could extend downtime and increase costs.\n- Incentives for the manufacturer: the AD’s background says the manufacturer is reviewing its process and materials; the manufacturer has an incentive to redesign or change production to eliminate the oxide defect and reduce future replacement frequency (Background).\n- Opportunity costs: operators may face lost revenue from grounded aircraft and diversion of maintenance capacity from other work.\n- Implementation risk and compliance burden: accurate TIS records for the part and prompt manual updates are necessary to show compliance. The directive’s “before further flight” timing leaves little discretion for operators facing part shortages.\n\n**Mechanisms for safety and enforcement**\n\n- The AD achieves risk reduction by (a) removing housings that have accumulated 600 or more hours TIS and (b) imposing a much shorter life limit going forward (Requirement). The enforceable deadline is immediate: no further flight with affected parts after the effective date (Compliance).\n\n**References within the AD**\n\n- The action required is in the AD’s Requirement and Compliance sections; the Applicability section specifies the exact part number to which the AD applies. The Background explains the manufacturing-origin oxide skin defect and the manufacturer’s ongoing review (Applicability; Requirement; Background)."},"kimi_summary":{"content_quality":"ok","complexity_score":2,"scope_assessment":{"changed":false,"description":"This AD maintains its original narrow scope — addressing a specific manufacturing defect in a single aircraft component. The directive precisely targets the identified safety risk without expanding into broader operational or maintenance requirements."},"complexity_factors":["Single, clearly defined applicability (one helicopter model, one specific part number)","Two straightforward requirements with no conditional exceptions or nested logic","No cross-references to other legislation or complex regulatory frameworks","Simple compliance deadline ('before further flight')","Plain language background explanation included","Total length is approximately 300 words of substantive content"],"plain_english_summary":"CASA has issued an Airworthiness Directive requiring immediate replacement of a specific tail gearbox output housing (P/N 92358-06109-043) on Sikorsky S‑92A helicopters after testing found a manufacturing \"oxide skin\" flaw that can cause premature failure.\n\nAny S‑92 with that part at or above 600 flight hours must be grounded until the housing is replaced and records updated to the new 600‑hour life limit—affecting offshore, oil & gas, and emergency‑service operators because tail‑rotor failure risks catastrophic loss of control."},"flash_summary_failed":{"failed":true,"reason":"A positive credit balance is required for all requests, including BYOK, so fallback providers remain available. Add credits at https://vercel.com/d?to=%2F%5Bteam%5D%2F%7E%2Fai%3Fmodal%3Dtop-up to continue.","source":"analysis-cron"}},"importantCases":[],"_links":{"self":"/api/acts/ad-s-92-4-tail-gear-box","history":"/api/acts/ad-s-92-4-tail-gear-box/history","analysis":"/api/acts/ad-s-92-4-tail-gear-box/analysis","conflicts":"/api/acts/ad-s-92-4-tail-gear-box/conflicts","importantCases":"/api/acts/ad-s-92-4-tail-gear-box/important-cases","documents":"/api/acts/ad-s-92-4-tail-gear-box/documents"}}