AD/ELECT/75 Amdt 1 - TCM Magneto Impulse Coupling

The instrument pivots on five concrete technical and regulatory concepts, each stated in the directive and implemented through Tables and referenced manufacturer material.

1. Applicability by part number and engine model: The directive applies to TCM magnetos with part numbers listed in Table 1, when installed on Lycoming AEIO‑540, HIO‑540, IO‑540, O‑540 and TIO‑540 series engines (Applicability; Table 1). Table 1 is a partial reproduction of TCM MSB645 (Note 1) and the directive explicitly notes that the listed Lycoming engines are known installations but not necessarily exhaustive for aircraft types (Note 2).

2. Inspection method and source document: Inspections must be carried out using paragraphs 1.2-1.4.5 of the Detailed Instructions in TCM MSB645 (Requirement 1). That ties the substantive inspection standard to the manufacturer’s mandatory service bulletin and makes compliance dependent on following those detailed steps rather than a purely CASA‑written procedure.

3. Differentiated timing by coupling type and hours in service: Initial inspection timing depends on whether the impulse coupling assembly is a riveted or a snap‑ring type and on hours time since new or overhaul (TSN) as of the effective date (Table 2). Repeat inspection intervals are type‑dependent: riveted assemblies require inspection within every 100 hours since the last inspection; snap‑ring assemblies require inspection within every 500 hours since the last inspection (Table 3).

4. Mandatory corrective action and immediate flight‑status effect: Any impulse coupling assembly that fails the inspection must be replaced with a serviceable riveted or snap‑ring assembly, and such replacement must be accomplished before further flight (Requirement 2; Table 3 commentary). This creates a direct link between inspection outcome and aircraft airworthiness status: a failed coupling triggers a grounding action until replacement.

5. Optional terminating modification and data‑plate control: Installing a "Shower‑of‑Sparks" ignition system in place of the magneto system is an optional terminating action for the repetitive inspection requirement; the directive points to TCM SIL648 for details. Additionally, if a snap‑ring coupling is replaced with a riveted coupling, the instruction is to strike out the "A" on the magneto data plate (Requirement 3), which creates an administrative record change tied to the physical modification.

These concepts are expressed through the directive’s tables and notes: Table 1 lists P/Ns, Table 2 prescribes initial inspection timing by type and TSN as of the effective date, Table 3 prescribes repeat intervals, the Requirements set out the operational actions (inspect, replace, mark), and Notes reference the manufacturer and FAA materials that inform the technical rationale (Notes 1, 2, 3, 5; Background). The Background explains that manufacturer data provided to the U.S. FAA showed a need to reduce inspection intervals for riveted impulse couplings on certain Lycoming engines, and that this Amendment narrows applicability and corrects Table 1 accordingly.

The directive assigns duties and triggers costs primarily for a small, concentrated set of actors in aircraft operations and maintenance.

• Aircraft operators and owners who have aircraft with Lycoming AEIO‑540, HIO‑540, IO‑540, O‑540 or TIO‑540 engines that carry TCM magnetos with P/Ns listed in Table 1 are directly affected. The directive’s Applicability and Table 1 specify the relevant magneto part numbers and engine models. Note 2 lists several aircraft manufacturers on which these engines are known to be installed , Cessna, Maule, Mooney, The New Piper, and Raytheon Aircraft Company (formerly Beech) , but the directive expressly states this is not exhaustive.

• Maintenance organisations, certificated aircraft maintenance engineers and other persons authorised to carry out inspections and maintenance must perform the inspections as specified (Requirement 1 referring to MSB645 paragraphs 1.2-1.4.5), carry out replacements where necessary (Requirement 2), and make the prescribed data plate change when a snap‑ring is replaced with a riveted assembly (Requirement 3). The directive prescribes the inspection standard and replacement obligation; it does not itself identify who is qualified to perform the work, but the procedural reference to the TCM MSB implies using the procedures and tooling those instructions require.

• Parts suppliers and TCM (the manufacturer) are indirectly affected. The directive references and relies on TCM MSB645, Service Bulletin 639 and SIL648 and SB643B for technical content and optional terminating action details; operators may need to procure serviceable riveted or snap‑ring impulse coupling assemblies or the optional Shower‑of‑Sparks ignition system, and so availability of parts and retrofit kits matters.

• Regulators and enforcement agents are affected administratively: CASA issued the directive (signed by a CASA delegate), superseding AD/ELECT/68 and narrowing applicability (Background). The directive sets compliance deadlines (e.g. within 10 or 50 hours TIS in certain cases, and "before further flight" for replacements), which the regulator will expect operators to meet.

Who pays. Costs fall first to the aircraft owners/operators and then to maintenance organisations as labour costs. Specific costs include inspection labour, replacement assemblies (purchase and installation), any administrative time to alter data plates and record regulatory compliance, and the capital cost of electing the optional terminating modification (Shower‑of‑Sparks). The directive does not quantify costs; it does identify where work must occur (inspection, replacement, data plate change, or installing terminating action) and when.

Who decides. CASA, through the Directive, decides the required inspections, intervals and corrective steps. Technical detail is outsourced to and incorporated from TCM documents (MSB645, SB639, SIL648, SB643B) and the directive refers to FAA AD 2005‑12‑06 (Note 3) as a related instrument. Individual operators decide whether to perform the optional terminating action (installing the Shower‑of‑Sparks system) or to comply with the recurring inspections and potential replacements. Maintenance providers decide practical intervals, scheduling and labour allocation to meet the "before further flight" and other timing obligations.

Behaviour that changes. Operators must: identify whether their magnetos are covered P/Ns; determine impulse coupling type and TSN/TSI; schedule and perform the required inspections within the deadlines in Table 2; repeat inspections according to Table 3; replace failed assemblies prior to further flight; and, where an administrative change is triggered by replacing a snap‑ring with a riveted assembly, mark the data plate accordingly. Some operators may elect to install the Shower‑of‑Sparks system to terminate repetitive inspections, shifting the cost profile from recurring inspections/replacements to a one‑off modification.

The directive prescribes duties in explicit, technical terms. It does not recite statutory rights or create an appeal path within the text; all duties that carry operational consequences are set out below, with the location in the directive indicated.

Primary duties

1. Inspect the impulse coupling assembly for wear using paragraphs 1.2-1.4.5 of the Detailed Instructions of TCM MSB645 (Requirement 1). This ties the required inspection procedure to the manufacturer’s MSB and makes compliance contingent on following those steps.

2. Initial inspection scheduling (Table 2):

   • Riveted impulse coupling assemblies: if 100 or more hours time since new or overhaul (TSN) as of the effective date, inspect within 10 hours time in service (TIS) after the directive’s effective date; if fewer than 100 hours TSN, inspect before accumulating 100 hours TSN (Table 2).
   • Snap‑ring impulse coupling assemblies: if 450 or more hours TSN as of the effective date, inspect within 50 hours TIS after the directive’s effective date; if fewer than 450 hours TSN, inspect before accumulating 500 hours TSN (Table 2).

3. Repeat inspections (Table 3):

   • Riveted: inspect within 100 hours time since the last inspection (Table 3).
   • Snap‑ring: inspect within 500 hours time since the last inspection (Table 3).

4. Replace failed assemblies (Requirement 2): Replace any impulse coupling assembly that fails the inspection with a serviceable riveted or snap‑ring impulse coupling assembly. Replacement is to be completed before further flight after the inspection (Table 3 commentary).

5. Administrative marking when replacing snap‑ring with riveted (Requirement 3): If a snap‑ring impulse coupling assembly is replaced with a riveted assembly, strike out the "A" on the magneto data plate.

6. Optional terminating action: Installation of a Shower‑of‑Sparks ignition system in place of the magneto system with a riveted or snap‑ring coupling is stated as an optional terminating action for the repetitive inspection requirements; the directive refers to TCM SIL648 for information (second HTML block).

Rights and procedural features apparent from the text

• The directive gives operators a choice whether to adopt the terminating modification (SIL648) or to remain on the inspection/replacement cycle; that is an explicit option in the document text (second HTML block).

• The directive prescribes the inspection procedure by reference rather than rewriting it, which gives operators and maintainers a clear, single technical source to follow (MSB645). That also implies that a right to technical specificity is satisfied by the referenced manufacturer document rather than the directive itself.

• The directive does not state any procedure for seeking an exemption, alternative method of compliance (AMOC), or appeal in its text. It likewise does not state penalties or enforcement mechanisms within the instrument. Those matters, if needed, would be governed by CASA’s broader regulatory instruments and administrative procedures outside this text; the directive itself confines its content to inspection, replacement, marking and the optional terminating action.

Operational implications of duties

• "Before further flight" language for replacements creates immediate operational constraints. A failed inspection creates an obligation to replace the failed assembly before the aircraft may continue to fly. Timing windows in Tables 2 and 3 create additional scheduling obligations that may require short‑notice hangar time and parts availability planning.

• The data plate marking change (strike out "A") creates a permanent record on the magneto that alters the observable configuration history of the unit; maintenance recordkeeping should reflect that physical change and the reason for it.

• Reliance on manufacturer documents (MSB645, SB639, SIL648, SB643B) means operators must source and retain the referenced documents and ensure authorised personnel apply them exactly as written to meet the directive’s requirements.

The directive sets mandatory actions and deadlines, but does not itself specify civil or criminal penalties or an enforcement mechanism in the text provided. The instrument is issued by the Civil Aviation Safety Authority (CASA) and is signed by a CASA delegate (David Villiers, Delegate of the Civil Aviation Safety Authority, dated 22 July 2005), and it sets compliance‑critical timing (e.g. inspect within 10 or 50 hours TIS for initial inspections, "before further flight" for replacement). That language conveys mandatory status and operational consequences; however, the directive does not state in its body what enforcement steps, fines or sanctions apply for non‑compliance.

Consequently, a reader should note two things as a matter of practical compliance risk:

1. The directive’s "before further flight" requirement creates an immediate airworthiness condition. Although the directive text does not itself state a civil penalty, failing to comply with an applicable CASA airworthiness directive will typically have consequences under the broader statutory and regulatory framework that governs civil aviation safety in the jurisdiction. The directive does not set those sanctions out; those are located in CASA’s governing Acts and instrument(s) external to the directive.

2. Enforcement actions, auditing, and verification of compliance are not described in the directive. Operators should expect that CASA or authorised representatives could audit compliance with ADs and require evidence that inspections and replacements were performed, and that data‑plate/method changes were recorded. The directive’s own requirements include inspection procedures and documentation consequences (data‑plate changes), which are the immediate items an inspector would check.

What the directive does specify that bears on enforcement readiness

• Clear compliance deadlines (Table 2, Table 3): These produce a binary compliance test , either the mandated inspections were carried out within the required hours windows and replacements completed before further flight, or they were not.

• Reference to specific external technical documents (MSB645, SB639, SIL648): Compliance is assessed by reference to the manufacturer’s inspection steps; an enforcement assessment will likely require maintenance records showing that the specified paragraphs of MSB645 were followed.

• Data‑plate marking for certain replacements (Requirement 3): This is an observable, physical manifestation of compliance with that requirement and could be inspected.

Given the absence of penalties in the text, regulated parties will need to consult CASA’s regulatory framework outside the directive to understand the precise enforcement tools and penalty regime that apply to non‑compliance. The directive itself imposes mandatory technical and timing obligations but does not set out enforcement mechanisms or sanction schedules.

The directive explicitly cross‑references and interacts with manufacturer service materials and with a United States FAA airworthiness directive. Those interactions shape both technical compliance and the administrative context.

1. Manufacturer documents incorporated by reference

   • TCM MSB645: The inspection method is to be carried out "using paragraphs 1.2 through 1.4.5 of the Detailed Instructions of TCM MSB645" (Requirement 1). Thus, the directive relies on MSB645 for technical detail and inspection criteria.
   • TCM Service Bulletin 639: Paragraphs 2 through 2.6 of MSB645 and TCM Service Bulletin 639 (dated March 1993) "contain information on replacing the impulse coupling assembly" (Requirement 2). That means the replacement procedure and any service limits referenced are to be followed as per those manufacturer publications.
   • TCM Service Information Letter SIL648: The directive identifies installation of a "Shower‑of‑Sparks" ignition system as an optional terminating action and points operators to SIL648 (dated 18 October 1994) for details. Electing this alternative requires following the SIL’s instructions.
   • TCM Service Bulletin SB643B: Note 5 states SB643B provides manufacturer recommended inspection/overhaul periods for TCM magnetos installed on engine types not specifically referenced in this Amendment, but that inspection periods specified in this Amendment supersede those in SB643B for the engines covered here.

   Interaction mechanism: The regulatory duty created by the directive is technically executed by following manufacturer documents noted in the directive. That is a common interaction pattern in aviation where regulators prescribe compliance but rely on manufacturer technical materials for procedures and limits.

2. Relationship to earlier CASA directives

   • The directive supersedes AD/ELECT/68 (Background). That creates an explicit temporal and legal relationship: AD/ELECT/68’s requirements are replaced by this directive. The Background notes that AD/ELECT/68 required repetitive inspections and replacement when worn beyond limits; AD/ELECT/75 Amdt 1 reduces the inspection interval for riveted couplings and narrows applicability to certain Lycoming engines.

3. Relationship to FAA ADs

   • Note 3 references FAA AD 2005‑12‑06 Amdt 39‑14122. The Background explains that manufacturer data was provided to the United States Federal Aviation Administration that showed a need to reduce inspection intervals for riveted impulse couplings used on certain Lycoming engine models; the present Amendment responds to that data. This indicates cross‑jurisdictional technical harmonisation: CASA’s directive is informed by manufacturer data submitted to the FAA and by the FAA AD.

4. Practical interactions with maintenance recordkeeping and airworthiness certification

   • The directive’s requirement to strike out the "A" on the magneto data plate when replacing a snap‑ring with a riveted assembly (Requirement 3) interacts with maintenance logs and data plate records. That physical change and the maintenance entries recording it will be used in future airworthiness assessments and audits.

What the directive does not state about interaction with other legal instruments

• The text does not specify procedures for alternative methods of compliance, delegations, exemptions, appeals, or enforcement penalties; these procedural and legal consequences are left to CASA’s broader legal framework and are not articulated in the directive itself.
• The directive does not purport to change maintenance scheduling rules or other statutory obligations outside its narrow technical scope; those interactions remain within the operating and regulatory context of each operator and CASA oversight.

In sum, the directive functions as a technical, mandatory overlay that depends on manufacturer documents for execution and aligns with a related FAA AD. For practitioners, the relevant interaction points to check are (a) MSB645 and referenced TCM documents for technical execution, (b) AD/ELECT/68 (now superseded) for historical compliance chains, and (c) CASA’s wider regulatory and enforcement framework for procedural matters not specified in the directive text.

The directive text contains an explicit amendment history and related notes. The chronology and mechanical changes are these:

1. Original issue: The original issue of this Directive became effective on 19 July 2005. That original issue required measures to prevent failure of magneto impulse coupling assemblies and possible engine failure (final paragraph of the last HTML block).

2. Amendment 1 (AD/ELECT/75 Amdt 1): This provided corrections and clarifications and became effective on 1 September 2005 (explicit effective date line: "This Amendment becomes effective on 1 September 2005"). The amendment is signed by David Villiers as Delegate of the Civil Aviation Safety Authority on 22 July 2005, indicating the administrative sign‑off.

3. Supersession of AD/ELECT/68: The Amendment expressly supersedes AD/ELECT/68 which is to be cancelled (Background). AD/ELECT/68 had required repetitive inspections of riveted and snap‑ring impulse coupling assemblies and replacement when worn beyond limits. The present Amendment continues those requirements but reduces the inspection interval for riveted assemblies on specified Lycoming engines and limits applicability to those models.

4. Technical corrections and narrowing of applicability: The Amendment corrects Table 1 by limiting the listing to magnetos installed on the specified Lycoming engines and adds a note in the Background indicating where the manufacturer’s recommended maintenance intervals may be found (Background). In short, the Amendment narrows the set of engines to which the listed P/Ns are tied and points to TCM SB643B for broader guidance on other engine types (Note 5).

5. Change in inspection intervals: Compared with the previous directive, the Amendment reduces the inspection interval for riveted impulse coupling assemblies on certain Lycoming engines while leaving the snap‑ring interval unchanged (Background). The precise initial and repeat inspection timings are then set out in Tables 2 and 3.

6. Manufacturer documentation chronology referenced in the Amendment:

   • MSB645 (TCM Mandatory Service Bulletin MSB645 dated 4 April 1994) is explicitly reproduced partially in Table 1 (Note 1).
   • Service Bulletin 639 dated March 1993 is referenced for replacement procedures (Requirement 2).
   • Service Information Letter SIL648 dated 18 October 1994 is referenced for the Shower‑of‑Sparks option (second HTML block).
   • Service Bulletin SB643B dated 6 April 2005 is referenced to provide recommended inspection/overhaul periods for magnetos on engine types not referenced in the Amendment (Note 5).
   • The directive also refers to FAA AD 2005‑12‑06 (Note 3) as a related instrument that informed the change.

What changed substantively and mechanically

• Narrowed applicability: Table 1 corrected to specific Lycoming engines.
• Shorter inspection interval: For riveted impulse coupling assemblies on specified Lycoming engines, initial and repeat inspection intervals were reduced (Tables 2 and 3).
• Administrative note: The Amendment calls out where to find manufacturer guidance for other engine types and states that inspection periods in this Amendment supersede those in SB643B for the engines covered.

For compliance auditors and legal practitioners, the Amendment history establishes (a) that AD/ELECT/75 Amdt 1 is the operative instrument as of 1 September 2005, (b) that AD/ELECT/68 is superseded and cancelled, and (c) that compliance must be assessed against the current directive and the referenced manufacturer documents. The directive itself contains the dates and sources for each of these changes.

The directive text contains no information about litigation, judicial review or contestation. It references administrative materials (manufacturer service bulletins and an FAA AD) and states the date the original issue and the amendment became effective, but it does not record any legal proceedings, appeals, or court decisions concerning the directive. The only signatures and administrative markings are the delegate’s signature (David Villiers) and the effective dates.

Because the instrument does not mention litigation, a researcher seeking litigation history will need to consult external legal databases, tribunal records or CASA administrative files to test whether any party sought relief, review, or an alternative method of compliance after the directive’s publication. The directive itself provides no account of challenges, enforcement actions, or judicial determinations.

Practical consequence for practitioners

• The absence of litigation information in the directive means you cannot assume any judicially defined limits or precedents exist from this source. Where legal risk or contestation is relevant (for example, a dispute about whether a specific maintenance action complied with the directive), counsel should search external records for any CASA decisions, civil proceedings, or administrative reviews after the effective dates provided (original issue 19 July 2005; Amendment effective 1 September 2005). The directive’s text does not supply case names, outcomes, or litigation citations.

The directive contains several practical details and points where misinterpretation or administrative error can create compliance risk. These are explicit in the text and bear close attention.

1. TSN versus TIS and the effect of "as of the Effective Date"

   • Table 2 bases initial inspection timing on "Impulse Coupling Time in Service (TIS) as of the Effective Date of this Directive" (Table 2 heading). The language mixes TSN/TSI conventions in the table rows (it references "time since new or overhaul (TSN) or TSN is unknown" for riveted, and "TSN" for snap‑ring), so operators must carefully determine the correct engine/magneto hours to decide initial inspection timing.
   • The directive uses both "TSN" (time since new/overhaul) and "TIS" (time in service) in its timing language (Table 2 and the compliance instructions). Misreading these can lead to missing the required initial inspection window , for example, treating a riveted assembly with unknown TSN as if it has fewer-than-100 TSN when the table instructs inspection "Within 10 hours TIS after the effective date" if TSN is 100 or more or TSN is unknown. Practitioners should confirm the unit’s TSN and maintain clear records to apply Table 2 correctly.

2. Partial reproduction of Table 1 and limits of applicability

   • Note 1 states Table 1 is a partial reproduction of Table 1 from TCM MSB645 dated 4 April 1994. Operators must not assume that absence of a part number from this partial table means a given magneto is outside the directive; rather the directive limits its applicability to P/Ns in the presented Table 1 and to those P/Ns when installed on the specified Lycoming engines (Applicability). If an operator has a magneto P/N not shown in Table 1, the operator should consult MSB645 and the manufacturer guidance to determine applicability.

3. Data plate marking requirement when replacing snap‑ring with riveted

   • Requirement 3 requires striking out the "A" on the magneto data plate if a snap‑ring assembly is replaced with a riveted assembly. That is a small but permanent physical change and must be reflected in maintenance documentation. Failure to make the data plate change could be a sign of non‑compliance and could cause ambiguity in future inspections or maintenance decisions.

4. Optional terminating action versus recurring inspections

   • Operators can avoid repetitive inspections by installing a Shower‑of‑Sparks ignition system, but the directive refers operators to SIL648 for details. Electing the terminating action shifts costs and affects future compliance obligations. Operators must confirm that installing the terminating action meets all other regulatory and certification requirements for their aircraft; the directive does not describe certification mechanics for that conversion.

5. Parts availability and serviceable assemblies

   • Requirement 2 mandates replacement with a "serviceable riveted or snap‑ring impulse coupling assembly," but the directive does not describe supply or lead times. In practice, long lead times for serviceable parts may complicate the "before further flight" requirement if a coupling fails. Operators should consider stocks and supplier arrangements.

6. Cross‑reference to FAA AD and manufacturer data

   • Note 3 refers to FAA AD 2005‑12‑06. Where operators have aircraft that move between regulatory jurisdictions, they should reconcile CASA AD requirements with FAA and other jurisdictional ADs. Differences in timing or applicability across jurisdictions can create confusion that must be managed proactively.

7. Records of previous inspections

   • Note 4 indicates previous inspections may have been accomplished under AD/ELECT/68 (FAA AD 96‑12‑07). Operators must maintain maintenance histories that clearly show which ADs and which procedures were used for previous inspections to determine whether they fall within the new directive’s repeat intervals.

8. Supersession creates retrospective compliance questions

   • Because AD/ELECT/75 Amdt 1 supersedes AD/ELECT/68, operators whose maintenance schedules were set under the older AD must reconcile past compliance with the new intervals and deadlines. Practical issues can arise where an inspection carried out under AD/ELECT/68 may not have used the exact procedures referenced in MSB645 paragraphs 1.2-1.4.5. Operators should ensure future inspection scheduling aligns with the Amendment’s tables.

9. Unspecified enforcement and AMOC procedures

   • The directive does not describe an alternative method of compliance process or the route to seek exemptions; operators needing such relief must look outside the directive to CASA’s broader administrative framework.

Each of these points is grounded in directive text (Tables 1-3, Requirements, Notes, Background). For compliance professionals and counsel, these are the items that commonly produce audit findings and operational disruption if not handled proactively.

This section sets out a practical compliance checklist distilled from the directive text, with precise references to the directive’s elements. It is structured as a stepwise plan an operator or maintenance organisation can follow.

Step 1 , Identify applicability

• Confirm whether any magnetos installed on your aircraft have part numbers listed in Table 1 and whether they are installed on Lycoming AEIO‑540, HIO‑540, IO‑540, O‑540 or TIO‑540 engines (Applicability; Table 1). Note 1 states Table 1 is a partial reproduction of TCM MSB645 Table 1; if your magneto P/N is not listed, consult MSB645 and the engine installation records to ensure applicability.

Step 2 , Determine impulse coupling assembly type and service hours

• For each magneto in scope, determine whether the impulse coupling assembly is riveted or snap‑ring.
• Establish the impulse coupling’s time since new or overhaul (TSN). If TSN is unknown, follow the guidance in Table 2 that treats unknown TSN for riveted assemblies as requiring immediate inspection within 10 hours TIS (Table 2).

Step 3 , Apply initial inspection timing (Table 2)

• If riveted and TSN is 100 or more or TSN is unknown: inspect within 10 hours TIS after the effective date of the Directive (Table 2).
• If riveted and TSN is fewer than 100: inspect before accumulating 100 hours TSN (Table 2).
• If snap‑ring and TSN is 450 or more: inspect within 50 hours TIS after the effective date of the Directive (Table 2).
• If snap‑ring and TSN is fewer than 450: inspect before accumulating 500 hours TSN (Table 2).

Step 4 , Perform the inspection to the specified standard

• Conduct the inspection "using paragraphs 1.2 through 1.4.5 of the Detailed Instructions of TCM MSB645" (Requirement 1). Obtain and retain a copy of MSB645 and ensure authorised maintenance personnel follow the paragraphs exactly.

Step 5 , Take mandatory corrective action

• If the impulse coupling assembly fails the inspection, replace it with a "serviceable riveted or snap‑ring impulse coupling assembly" (Requirement 2). The directive states replacement must be made before further flight after the Requirement 1 inspection (Table 3 commentary). Use the replacement instructions indicated in paragraphs 2 through 2.6 of MSB645 and TCM Service Bulletin 639 (Requirement 2).

Step 6 , Data plate change where applicable

• If you replace a snap‑ring coupling with a riveted coupling, strike out the "A" on the magneto data plate (Requirement 3). Record this in the maintenance log and any continuing airworthiness records.

Step 7 , Schedule repeat inspections

• For riveted impulse coupling assemblies, repeat the inspection within 100 hours time since the last inspection (Table 3).
• For snap‑ring impulse coupling assemblies, repeat the inspection within 500 hours since the last inspection (Table 3).

Step 8 , Consider the optional terminating action

• Evaluate installation of the Shower‑of‑Sparks ignition system as an optional terminating action for repetitive inspection requirements (second HTML block). Review TCM SIL648 (dated 18 October 1994) for information on that modification. If elected, confirm that the conversion satisfies any additional airworthiness and certification criteria applicable to your aircraft type.

Step 9 , Document and retain records

• Keep records showing: identification of covered magnetos (P/N and engine installation), TSN/TIS calculations and evidence, dates and results of inspections in accordance with MSB645 paragraphs, details of any replacements (including P/Ns of new assemblies), data‑plate changes, and any modification/installations of Shower‑of‑Sparks systems. Because the directive references manufacturer instructions and "before further flight" obligations, precise maintenance entries will be necessary for any audit or regulatory inspection.

Step 10 , Reconcile with previous ADs and other guidance

• If prior inspections were performed under AD/ELECT/68 or other ADs, maintain records that demonstrate timing and conformity so repeat intervals under Table 3 can be correctly scheduled (Note 4). If you operate aircraft in multiple jurisdictions, check related FAA AD 2005‑12‑06 (Note 3) and reconcile any jurisdictional differences.

Operational risk management tips

• Check parts availability before scheduling inspections that could reveal failed assemblies requiring "before further flight" replacement. Stock or supplier arrangements for serviceable assemblies will reduce grounding risk.
• If TSN is unknown for older magnetos, prioritise immediate inspection to avoid regulatory default to the stricter initial deadlines.
• Train maintenance staff on the precise paragraphs in MSB645 required by Requirement 1 and ensure shop procedures and checklists reference those paragraphs.

References in the directive that compliance relies on

• Requirement 1 (inspection using TCM MSB645 paragraphs 1.2-1.4.5).
• Requirement 2 (replacement instructions, referring to MSB645 paragraphs 2-2.6 and TCM Service Bulletin 639).
• Requirement 3 (data plate marking).
• Table 1 (affected P/Ns and engine models).
• Table 2 and Table 3 (timing windows).
• Notes 1-5 and Background for context (including reference to SB643B and FAA AD 2005‑12‑06).

Following these steps will align operations with the Directive’s explicit technical and timing demands; where the directive is silent (for example about appeals or enforcement procedures), consult CASA’s wider regulatory documentation for procedural matters beyond the Directive’s technical scope.