AD/LYC/89 Amdt 4 - Crankshaft Gear

The instrument establishes several discrete regulatory concepts and linkage points to manufacturer guidance and a foreign airworthiness authority. First, it mandates inspection and repair actions that must be performed according to Lycoming Mandatory Service Bulletin No. 475C dated 30 January 2003, or a later FAA‑approved revision (Requirements 1; Requirements 2). The AD therefore does not provide its own technical detail for the inspection and repair steps; instead it incorporates the MSB by reference as the required technical standard. Second, it mandates a parts replacement and retirement rule: the existing gear retaining bolt and lockplate must be removed and replaced with a new bolt and lockplate as specified by Lycoming MSB No. 475C, and any removed bolt and lockplate may not be reinstalled into any engine (Requirements 2-3). Third, the AD defines the trigger for mandatory compliance narrowly by reference to engine removal following a propeller strike event (Compliance). The AD supplies an inclusive, operational definition of "propeller strike event" in four sub‑parts that captures situations that do not always show obvious propeller damage: (a) incidents requiring propeller repair beyond minor dressing; (b) in‑flight propeller impacts causing an RPM drop and structural repair; (c) sudden RPM drops while impacting yielding media (water, tall grass) even without prop damage; and (d) sudden stoppages caused by events such as landing gear collapse or hanger door strikes that bend blades and impose severe side loading (Compliance (a)-(d)). Fourth, the AD ties domestic compliance to FAA approval by permitting only later revisions of the MSB that are approved by the United States FAA, and it references FAA AD 2004‑10‑14 (Note). Fifth, the AD is presented as an amendment (Amdt 4) to a continuing safety measure first issued in December 1991, reflecting a continuing process of adaptation to manufacturer guidance and FAA mandates (Background). These elements combine to make compliance contingent on (1) engine removal after specified events; (2) following the MSB technical procedure as it stands subject to FAA approval; and (3) permanent retirement of certain fasteners removed because of the event.

The AD directly affects owners, operators and maintenance organisations that operate, maintain or overhaul Textron Lycoming direct drive piston engines within the AD's applicability scope. The AD applies to "all Textron Lycoming direct drive piston engines" except the specifically excluded series (O‑145, O‑320H, O‑360E, LO‑360E, LTO‑360E, TO‑360E, O‑435 and TIO‑541) (Applicability). That means aircraft with engines inside the applicable range , including private owners, commercial operators, maintenance, repair and overhaul (MRO) providers, and entities performing engine removals , must comply when the compliance trigger occurs. The compliance trigger is removal of the engine following a propeller strike event (Compliance); therefore, parties who decide to remove an engine after such an event (for inspection, repair or overhaul) will be required to carry out the inspections and replacements mandated by the AD. Maintenance organisations performing the inspection, repair and bolt replacement will need to follow Lycoming MSB No. 475C or a later FAA‑approved revision for the technical procedure (Requirements 1-2). The AD also constrains parts management: any gear retaining bolt and lockplate removed in accordance with this AD must not be reinstalled in any engine (Requirements 3). That imposes an obligation on maintainers to quarantine and retire removed hardware and on operators to ensure replacement hardware is installed in accordance with the MSB. The AD further affects those responsible for event classification because compliance is tied to whether an occurrence meets the AD's definition of a propeller strike event; owners and maintenance personnel must apply the AD's multi‑part definition (including incidents that produce sudden RPM drops even where propeller damage is not apparent) to determine if the AD's requirements are triggered (Compliance (a)-(d)). The AD does not list penalties or enforcement mechanisms in its text, so readers should note the document establishes mandatory maintenance obligations without setting out sanctioning language in this instrument (see Penalties and enforcement). The AD also links domestic compliance to FAA approval of MSB revisions, so impacted parties who rely on later revisions must confirm FAA approval status (Requirements 1-2; Note).

Duties imposed by this AD are procedural and mechanical duties tied to a defined event and to a manufacturer technical document. The primary duties are: (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, strictly in accordance with Lycoming Mandatory Service Bulletin No. 475C dated 30 January 2003, or later revision approved by the United States FAA (Requirements 1). (2) Remove the existing gear retaining bolt and lockplate from service and install a new bolt and lockplate in accordance with Lycoming MSB No. 475C or later FAA‑approved revision (Requirements 2). (3) Do not reinstall any gear retaining bolt and lockplate removed under this AD into any engine (Requirements 3). The timing duty is explicit: these actions must be performed at each removal of the engine following a propeller strike event, with that triggering event defined in four express categories (Compliance; Compliance (a)-(d)). Rights, as such, are not framed in the AD; however the document creates predictable procedural rights for operators insofar as it invites reliance on an established technical document (the MSB) and FAA approvals for any later revisions (Requirements 1-2). Practically, that means an operator or maintenance organisation may elect to use a later revision of Lycoming MSB No. 475 only if it is a revision that has FAA approval, thereby creating a compliance path that depends on the status of FAA approval. The AD also creates a constraint on inventory and parts reuse: removed bolts and lockplates must not be reused, which reduces options for operators who might otherwise reuse removed hardware after inspection (Requirements 3). The AD does not specify waivers, alternative methods of compliance (AMOCs) or an approval process within its text; it instead references FAA approval for MSB revisions and notes FAA AD 2004‑10‑14 (Note). The Background indicates the AD has been subject to prior amendments and that this amendment refines the compliance statement to more accurately describe what constitutes a propeller strike event (Background). The AD’s duties therefore combine a procedural trigger (engine removal after a defined event), mandatory technical standards (the MSB), a parts retirement rule, and a specific prohibition on reuse of removed components.

The AD text does not include explicit penalty provisions, fines or administrative sanctioning mechanisms. The instrument sets mandatory maintenance actions and an effective date (26 September 2014), and is issued by a delegate of the Civil Aviation Safety Authority (signature block and date). The AD therefore establishes regulatory obligations; enforcement of those obligations is not specified within the AD’s text provided here. Because the AD is issued by the Civil Aviation Safety Authority (CASA) delegate, enforcement in practice would be expected to occur under CASA’s wider regulatory powers and surveillance activities; however, the AD itself contains no internal provision stating the form of sanctions, infringement notices, suspension/withdrawal of approvals, or criminal offences for non‑compliance. The AD does reference FAA AD 2004‑10‑14 (Note) and requires adherence to MSB revisions only where those revisions are approved by the United States FAA (Requirements 1-2), but that cross‑reference is procedural rather than a statement of enforcement consequence. Readers should therefore note the following, grounded in the source text: the AD creates mandatory duties (inspection, repair, replacement and permanent retirement of certain parts) and an effective compliance trigger, but it does not state penalties or enforcement procedures in the printed AD text. Parties seeking the enforcement regime applicable to non‑compliance will need to consult the Civil Aviation Safety Authority’s broader regulatory framework, enforcement policies or applicable aviation law; those documents are not reproduced or referenced in any enforcement detail in this AD. The AD’s Background shows it is part of a continuing series of amendments and interactions with FAA ADs and Lycoming service bulletins, which implies it sits within a broader compliance and oversight ecosystem, but explicit sanctioning mechanisms are beyond this AD’s textual content.

This AD interacts directly with manufacturer technical guidance and with foreign airworthiness directives, as reflected in its own text. The AD incorporates Lycoming Mandatory Service Bulletin No. 475C dated 30 January 2003 by reference as the technical standard for inspection, repair and bolt replacement, but qualified so that only later revisions of the MSB approved by the United States FAA may be relied on (Requirements 1-2). That creates an explicit dependency: the domestic regulatory obligation is satisfied only by following a manufacturer MSB as approved by the FAA. The AD also expressly references FAA AD 2004‑10‑14 Amendment 39‑13644 (Note). The Background explains this AD is an amendment to earlier ADs that were issued to reflect revisions of Lycoming MSB No. 475 and to reflect changes introduced by FAA AD 2004‑10‑14 (Background). Consequently, compliance under this AD requires practitioners to consider not only the MSB text but its FAA approval status and to be aware of related FAA ADs. The AD does not itself quote or reproduce broader statutory aviation law, nor does it state how it affects certificates, approvals, or licences beyond the specified inspection and parts rules. It does, however, sit within CASA’s regulatory output (the delegate’s signature block is included) and is therefore an element of the domestic regulatory regime that interfaces with international/foreign airworthiness directives. In practice, operators and maintenance organisations must reconcile this AD with other maintenance obligations, continuing airworthiness requirements and any record‑keeping or certification duties imposed by domestic aviation law; those external obligations are not delineated in this AD text. The AD’s reliance on FAA approval for MSB revisions and its reference to FAA AD 2004‑10‑14 signals that changes in FAA guidance or FAA ADs can influence the applicable technical standard under this AD. The AD does not establish its own conflict resolution rule; where another instrument imposes a contradictory requirement, the AD text does not state how that conflict is to be resolved.

The AD includes a short, explicit amendment history in its Background. The measure was originally issued in December 1991 to require inspection, rework or replacement of the crankshaft drive gear and replacement of the crankshaft drive gear retainer bolt at each removal of the crankshaft gear (Background). AD/LYC/89 Amdt 1 became effective on 6 January 1994, and was issued to reflect revision B of Lycoming Mandatory Service Bulletin No. 475, which increased the number of engine models applicable (Background). AD/LYC/89 Amdt 2 became effective on 2 October 2003, and was issued to reflect revision C of Lycoming Mandatory Service Bulletin No. 475, which revised details on crankshaft gears (Background). AD/LYC/89 Amdt 3 became effective on 30 September 2004 and 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 (Background). The current document, AD/LYC/89 Amdt 4, amends the compliance statement to more accurately reflect the circumstances which constitute a propeller strike event (Background). The effective date for Amdt 4 is 26 September 2014, as stated in the AD (Effective date). The AD text also includes a Note that explicitly refers readers to FAA AD 2004‑10‑14 Amendment 39‑13644, and the Requirements refer to Lycoming MSB No. 475C dated 30 January 2003 as the technical standard, with the possibility of using later revisions only if those revisions have FAA approval (Requirements; Note). The amendment history therefore records successive iterations that track Lycoming MSB revisions and FAA AD changes, culminating in the present amendment that clarifies the AD’s compliance trigger definition. The AD’s Background explicitly ties each amendment to either a manufacturer MSB revision or to a corresponding FAA AD update.

The AD text contains no litigation history, no court decisions, and no references to legal disputes. The only external document explicitly named is FAA AD 2004‑10‑14 Amendment 39‑13644 (Note), which is referenced for technical context; the Background mentions prior AD amendments but does not identify any judicial review, appeals, or litigation concerning the AD or its application (Background; Note). Therefore, on the basis of the instrument provided, there is no enclosed record of cases, injunctive proceedings, administrative appeals or other litigation arising from the AD’s issuance or enforcement. Practitioners seeking case law or disputes that interpret or challenge this AD will need to consult external judicial and administrative records outside this AD text; none are reproduced or summarised here. The AD’s Background does show an administrative amendment trajectory (original AD, Amdt 1, Amdt 2, Amdt 3, and the present Amdt 4), which indicates ongoing regulatory attention, but the text does not report any contested proceedings. Where parties have sought legal relief or judicial review in relation to this AD, such records would be found in court or tribunal databases, or in CASA administrative records; they are not part of the instrument as presented.

Several concrete implementation pitfalls and compliance‑sensitive points appear directly from the AD’s text. First, the AD’s applicability excludes specific Lycoming series engines (O‑145, O‑320H, O‑360E, LO‑360E, LTO‑360E, TO‑360E, O‑435 and TIO‑541), so operators must confirm the engine series precisely; misidentifying engine type could lead to unnecessary parts replacement or missed compliance (Applicability). Second, compliance is not on a fixed calendar schedule; it is triggered by engine removal following a propeller strike event. The AD supplies a wider definition of propeller strike event than operators might expect: it captures incidents requiring propeller structural repair beyond minor dressing, in‑flight impacts causing RPM drops and structural repair, sudden RPM drops while impacting yielding media where prop damage is not normally incurred, and sudden stoppages caused by events such as landing gear collapse or hanger door strikes that bend blades , each of these triggers mandates the inspection and bolt replacement at the next engine removal (Compliance (a)-(d)). That means an engine removal that follows an otherwise subtle event (for example, sudden RPM drop in tall grass or a bent blade from a hanger door while stationary) still obliges operators to perform the AD’s actions. Third, the AD incorporates Lycoming MSB No. 475C dated 30 January 2003 as the technical standard, but allows only later revisions that are approved by the United States FAA. Operators and maintainers must verify the approval status of any MSB revision before relying on it for compliance; using an unapproved MSB revision would not meet the AD’s stated condition (Requirements 1-2). Fourth, the AD contains a parts‑retirement obligation: any gear retaining bolt and lockplate removed in accordance with this AD must not be reinstalled into any engine (Requirements 3). That is an irreversible parts management duty that affects inventory and could increase parts procurement costs. Fifth, the AD does not include explicit alternate methods of compliance (AMOC) or waiver language within the text, nor does it set out enforcement mechanisms or penalties; parties requiring an alternative technical procedure or an enforcement interpretation will need to seek direction from CASA or consult other regulatory documents (Penalties and enforcement). Finally, the AD’s history shows multiple earlier amendments that tracked MSB and FAA AD changes, so operators should be attentive to future MSB or FAA revisions that could alter the technical method approved for compliance (Background; Note).

The AD specifies a clear, event‑triggered compliance pathway; adherence requires three concrete actions performed at the next removal of the engine following a propeller strike event. Step 1: Determine whether the removal follows a propeller strike event as defined by the AD. Apply the four‑part definition: (a) any incident requiring propeller repair beyond minor dressing; (b) any in‑operation impact causing an RPM drop and structural propeller repair; (c) a sudden RPM drop while impacting a yielding medium (water, tall grass), even if propeller damage is not normally incurred; and (d) sudden stoppages where stationary events bend blades or impose severe side loading (for example, landing gear collapse or hanger door strikes) (Compliance (a)-(d)). If the removal is not following such an event, the AD’s actions are not triggered by its own terms. Step 2: If the AD is triggered, perform the inspection and any necessary repair of the crankshaft counter bored recess, alignment dowel, bolt hole threads, and crankshaft gear for wear, galling, corrosion and fretting strictly in accordance with Lycoming Mandatory Service Bulletin No. 475C dated 30 January 2003, or a later revision that has been approved by the United States FAA (Requirements 1). Ensure that the MSB revision used is FAA‑approved; the AD conditions compliance on FAA approval status for later revisions. Step 3: Remove the existing gear retaining bolt and lockplate from service, and install a new bolt and lockplate in accordance with Lycoming MSB No. 475C or later FAA‑approved revision (Requirements 2). Step 4: Permanently retire and do not reinstall the removed bolt and lockplate into any engine (Requirements 3). Step 5: Record the inspection, repair and parts replacement in the aircraft and engine maintenance logbooks or records required by applicable maintenance regulations, noting the AD reference and MSB revision used; the AD itself does not prescribe record content but the maintenance records will be the primary evidence of compliance. Step 6: Confirm that the engine model is within the AD’s applicability (i.e. not among the excluded series listed) before applying the foregoing steps (Applicability). Practical notes for implementers include verifying MSB and FAA approval status before relying on any later MSB revision, ensuring procurement and availability of replacement bolts and lockplates so removed parts are not reinstalled, and training line and base maintenance personnel on the AD’s propeller strike definition so they correctly identify when the AD is triggered. If an operator believes an alternative approach is necessary, the AD contains no AMOC language; therefore operators should contact CASA for approval of any alternative method or for guidance on acceptance of different technical procedures. Finally, the AD became effective on 26 September 2014, so records of events and maintenance after that date should be reviewed to confirm whether the AD applied at the time of any engine removal.