{"id":"F2014L01273","name":"AD/LYC/89 Amdt 4 - Crankshaft Gear","slug":"ad-lyc-89-amdt-4-crankshaft-gear","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":92288,"registerId":"commonwealth-F2014L01273-current","compilationNumber":null,"startDate":"2026-04-02","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"Lycoming Piston Engines","sectionType":"division","heading":"Lycoming Piston Engines","content":"### Lycoming Piston Engines\n\n| AD/LYC/89Amdt 4 | Crankshaft Gear | 20/2014 |\n| --------------- | --------------- | ------- |\n\n| Applicability: | This Airworthiness Directive (AD) applies to all Textron Lycoming direct drive piston engines; excepting the O-145, O-320H,O-360E, LO-360E, LTO-360E, TO-360E, O-435 and TIO-541 series engines.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    |\n| -------------- | --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |\n| Requirements:  | 1. Inspect, and if necessary repair, the crankshaft counter bored recess, the alignment dowel, the bolt hole threads, and the crankshaft gear for wear, galling, corrosion, and fretting in accordance with Lycoming Mandatory Service Bulletin No. 475C dated 30 January 2003 (MSB No. 475C) or later revision approved by the United States of America Federal Aviation Administration (FAA).2. Remove the existing gear retaining bolt and lockplate from service, and install a new bolt and lockplate, in accordance with Lycoming MSB No. 475Cor later revision approved by FAA.3. Do not install into any engine the gear retaining bolt and lockplate removed in compliance with this AD.Note: FAA AD 2004-10-14 Amendment 39-13644 refers. |\n| Compliance:    | 1. The actions in Requirements 1, 2 and 3 must be taken at each removal of the engine following a propeller strike event.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           |\n|                | For the purpose of this AD, a propeller strike event is defined as follows:(a) Any incident, whether or not the engine is operating, that requires repair to the propeller other than minor dressing of the blades.(b) Any incident during engine operation in which the propeller impacts a solid object that causes a drop in revolutions per minute (RPM) and also requires structural repair of the propeller (incidents requiring only paint touch-up are not included). This is not restricted to propeller strikes against the ground.(c) A sudden RPM drop while impacting water, tall grass, or similar yielding medium, where propeller damage is not normally incurred.                                                                  |\n\n|             | (d) The preceding definitions include situations where an aircraft is stationary and the landing gear collapses causing one or more blades to be substantially bent, or where a hanger door (or other object) strikes the propeller blade. These cases should be handled as sudden stoppages because of potentially severe side loading on the crankshaft flange, front bearing, and seal.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            |\n| ----------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |\n|             | The effective date of this AD is 26 September 2014.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   |\n| Background: | This AD was originally issued in December 1991 to require the inspection, rework or replacement of the crankshaft drive gear, and the replacement of the crankshaft drive gear retainer bolt, at each removal of the crankshaft gear.AD/LYC/89 Amdt 1, which became effective on 6 January 1994, was issued to reflect revision B of Lycoming Mandatory Service Bulletin No. 475, which increased the number of engine models applicable.AD/LYC/89 Amdt 2, which became effective on 2 October 2003, was issued to reflect revision C of Lycoming Mandatory Service Bulletin No. 475, which revised details on crankshaft gears.AD/LYC/89 Amdt 3, which became effective on 30 September 2004, was issued to reflect the changes introduced by FAA AD 2004-10-14 Amendment 39-13644, superseding FAA AD 91-14-22 Amendment 39-6916.This AD, AD/LYC/89 Amdt 4, amends the compliance statement to more accurately reflect the circumstances which constitute a propeller strike event. |\n\n![](image.001.png)\n\nMike Higgins  \nDelegate of the Civil Aviation Safety Authority\n\n24 September 2014","sortOrder":0},{"sectionNumber":"AD/LYC/89Amdt 4","sectionType":"part","heading":"AD/LYC/89Amdt 4","content":"## AD/LYC/89  \nAmdt 4","sortOrder":1},{"sectionNumber":"Crankshaft Gear","sectionType":"part","heading":"Crankshaft Gear","content":"## Crankshaft Gear","sortOrder":2},{"sectionNumber":"20/2014","sectionType":"part","heading":"20/2014","content":"## 20/2014","sortOrder":3}],"analysis":{"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"},"flash_summary":{"complexity_score":4,"scope_assessment":{"changed":false,"description":"This amendment (Amdt 4) refines the compliance trigger by clarifying what constitutes a \"propeller strike event\" so the AD applies when specified types of incidents occur. It does not significantly broaden the AD’s substantive scope (inspections, repairs, and bolt/lockplate replacement at engine removal after such incidents) beyond the original purpose; it narrows/clarifies the triggering conditions rather than adding new categories of required work or new engine models."},"complexity_factors":["Event‑driven trigger with a multi‑part defined term: \"propeller strike event\" divided into four subcategories (Compliance definitions a–d).","External technical incorporation: mandatory compliance with Lycoming MSB No. 475C (or later FAA‑approved revisions) — i.e. reliance on an external document for procedural detail. (Requirements)","Cross‑reference to FAA AD 2004‑10‑14 and requirement that later FAA‑approved MSB revisions apply (Note; Requirements)","Engine model exclusions listed in Applicability (several specific series excluded).","Prohibition on reuse of removed parts creates an open‑ended recurring parts obligation (Requirements 3).","Amendment history and prior amendments are noted, increasing interpretive context but not substantive text (Background)."],"plain_english_summary":"**What this Directive does (mechanically)**\n\n- Requires inspection and, if necessary, repair or replacement of the crankshaft counter-bored recess, alignment dowel, bolt hole threads and crankshaft gear whenever the engine is removed after a defined “propeller strike event”. (Requirements 1; Compliance)\n- Requires removal from service of the existing crankshaft gear retaining bolt and lockplate and installation of a new bolt and lockplate, and prohibits reinstalling the removed bolt and lockplate into any engine. (Requirements 2–3)\n- Mandates that the inspections and bolt/lockplate replacement be done in accordance with Lycoming Mandatory Service Bulletin No. 475C (or a later revision approved by the FAA). The AD also refers to FAA AD 2004-10-14. (Requirements; Note)\n\n**Who is affected**\n\n- Owners, operators and maintenance organisations that operate or service Textron Lycoming direct‑drive piston engines, except the listed excluded models (O-145, O-320H, O-360E, LO-360E, LTO-360E, TO-360E, O-435 and TIO-541 series). (Applicability)\n\n**When it applies**\n\n- The required actions must be carried out each time the engine is removed following a \"propeller strike event\". The AD defines that term with four specific categories, which include: repairs other than minor blade dressing; in‑flight or operating impacts causing an RPM drop and structural repair; sudden RPM drops while hitting yielding media (water, tall grass) even if no blade damage occurs; and sudden stoppages caused by events like collapsed landing gear or hanger doors striking blades. (Compliance; definitions (a)–(d))\n\n**Why it matters (official rationale and practical effect)**\n\n- The AD’s stated purpose is to mitigate the risk that crankshaft gears, the gear retaining bolt, and associated components have suffered damage or wear during events that transmit abnormal loads through the propeller to the crankshaft flange (the AD’s background and Requirements). The mechanical effects are: increased inspection and repair work after the specified events, recurring replacement of a specific retaining bolt and lockplate, and a prohibition on re‑using the removed parts.\n\n**Who pays and who decides**\n\n- Cost bearers: aircraft owners/operators and maintenance providers pay for the inspections, any repairs, and replacement bolts/lockplates, plus associated labor and downtime. (Requirements; Compliance)\n- Decision authority: the AD delegates the technical work and compliance decisions to certificated maintenance organisations and mechanics who must follow Lycoming MSB No. 475C (or later FAA‑approved revisions). The Civil Aviation Safety Authority enforces compliance. (Requirements)\n\n**Practical compliance and implementation notes**\n\n- The AD does not mandate calendar‑based inspections; it triggers on engine removal after the defined propeller strike events. That creates an event‑driven compliance obligation rather than routine scheduled work. (Compliance)\n- Compliance requires following an external technical document (Lycoming MSB No. 475C or later FAA‑approved revision). This ties the AD’s technical content to manufacturer guidance and FAA approvals. (Requirements)\n\n**Costs, incentives and trade‑offs**\n\n- Concentrated benefits: the primary beneficiary is the operator whose engine is less likely to suffer undetected crankshaft/gear damage after a propeller strike; inspections may prevent catastrophic failures.\n- Diffuse costs: many operators will incur inspection, repair and replacement costs when engines are removed after the specified events. Costs are intermittent (triggered by events) rather than continuous.\n- Incentives and behaviour: operators may increase conservatism—removing engines for inspection after borderline events—because re‑use of the removed bolt/lockplate is prohibited. That raises parts demand and maintenance downtime.\n- Supply and market effects: recurring replacement of a specific bolt and lockplate increases ongoing demand for those parts, which affects independent maintenance shops and parts suppliers. Compliance depends on availability of FAA‑approved MSB revisions and parts.\n- Compliance burden and implementation risk: reliance on an external service bulletin and FAA approval means changes to the MSB or FAA guidance can alter practical compliance steps; maintenance providers must track revisions.\n\n**Concrete legal mechanics to note**\n\n- The AD cross‑references and incorporates by reference Lycoming MSB No. 475C (or later FAA‑approved revisions) as the technical standard for inspections and repairs. (Requirements)\n- The AD explicitly excludes certain engine models from applicability. (Applicability)\n- The AD forbids reinstalling the removed retaining bolt and lockplate into any engine, creating an irreversible parts‑consumption requirement each triggered event. (Requirements 3)\n\n(References: Applicability; Requirements 1–3; Compliance and propeller‑strike definitions (a)–(d); Note referring to FAA AD 2004‑10‑14.)"},"kimi_summary":{"content_quality":"ok","complexity_score":3,"scope_assessment":{"changed":true,"description":"The original 1991 directive focused on crankshaft gear inspection and bolt replacement at gear removal. Over four amendments (1994, 2003, 2004, 2014), the scope has expanded to: (1) cover more engine models, (2) incorporate updated manufacturer service bulletins, (3) align with US FAA directives, and (4) significantly broaden the trigger conditions for compliance through an expanded definition of 'propeller strike event.' The 2014 amendment specifically adds scenarios like landing gear collapse and hangar door strikes that don't involve traditional 'strikes' during operation, reflecting evolving understanding of damage mechanisms."},"complexity_factors":["Short, single-purpose document (approximately 500 words)","Only 4 defined terms/concepts: 'propeller strike event' with 4 sub-definitions (a)-(d)","Clear conditional logic: compliance triggered only by specific event (propeller strike)","Minimal cross-referencing: references one FAA AD and one Lycoming Service Bulletin","Straightforward structure: Applicability → Requirements → Compliance → Background","No nested exceptions or complex legislative machinery"],"plain_english_summary":"This Airworthiness Directive requires owners and operators of most Textron Lycoming direct‑drive piston engines to inspect and, if needed, repair the crankshaft gear and replace its bolt and lockplate whenever the engine is removed after a propeller‑strike event. It targets aircraft operators and maintenance personnel to prevent in‑flight loss of engine power from hidden crankshaft damage.\n\nThis Amendment 4 clarifies and broadens what counts as a propeller‑strike to capture more scenarios that could harm the crankshaft assembly."}},"importantCases":[],"_links":{"self":"/api/acts/ad-lyc-89-amdt-4-crankshaft-gear","history":"/api/acts/ad-lyc-89-amdt-4-crankshaft-gear/history","analysis":"/api/acts/ad-lyc-89-amdt-4-crankshaft-gear/analysis","conflicts":"/api/acts/ad-lyc-89-amdt-4-crankshaft-gear/conflicts","importantCases":"/api/acts/ad-lyc-89-amdt-4-crankshaft-gear/important-cases","documents":"/api/acts/ad-lyc-89-amdt-4-crankshaft-gear/documents"}}