AD/APU/23 - Saphir 2 Exhaust Thermal Insulation

This directive is organised around a short list of technical-conformity and safety-control concepts.

• Applicability: The AD applies to Microturbo SA Saphir 2 Model 016 APUs in which the exhaust thermal insulation has been replaced since 1 January 1995. The instrument identifies, by part number, the specific insulation components thought to be affected: 016-33-01 (Inner Thermal Insulation), 016-33-02 (Outer Thermal Insulation), and 016-33-03 (EGT Sensor Thermal Insulation). The AD also records a known installation context (Dassault Falcon 20 aeroplanes) but does not limit applicability to that airframe.

• Inspection regime: The AD requires an immediate inspection (Requirement 1) and recurrent inspections (Requirement 2) for signs of deterioration. The initial inspection must be completed within 10 APU operating hours; repeat inspections must not exceed intervals of 10 APU operating hours. The inspections are for signs of deterioration of the exhaust thermal insulation and are the primary preventive mechanism mandated by the AD.

• Corrective and compulsory replacement actions: If deterioration is detected, Requirement 3 prescribes replacement of the exhaust thermal insulation in accordance with Microturbo Alert Service Bulletin 49-11A76 Revision 1, dated 6 September 2007. Independently of whether deterioration is observed, Requirement 4 requires replacement of the exhaust thermal insulation in accordance with the same Service Bulletin within 50 APU operating hours from the effective date of the AD.

• Technical standard reference and revision path: The AD specifically mandates conformity with Microturbo Alert Service Bulletin 49-11A76 Revision 1 (6 September 2007) and allows the use of later approved revisions of that document for compliance, creating an explicit path for technical updates to be incorporated into compliance work.

• Safety rationale: The stated safety risk is a manufacturing quality-control lapse that may have produced exhaust thermal insulation not meeting approved design standards, with the consequence that the insulation may deteriorate or break down. The chain of harm described is loss of insulation efficiency, exposure of the hot APU exhaust section and risk of fire.

• Cross-reference to external regulator: The AD records that EASA AD 2009-0100 dated 4 May 2009 is referred to (Note 2). The AD therefore links the CASA action to an earlier European Aviation Safety Agency directive for the same condition.

Mechanically the AD transforms a manufacturer-originated Service Bulletin and an identified manufacturing defect into binding operational obligations: inspection within a narrow time window, frequent re-inspections, and either immediate or time-limited replacement actions tied to a specific technical publication.

The AD names a precise set of equipment and circumstances, which defines the affected parties and the locus of the required activity.

• Primary affected parties: Operators and maintainers of Microturbo SA Saphir 2 Model 016 APUs on which the exhaust thermal insulation has been replaced since 1 January 1995. The AD’s applicability statement makes the replacement-since-1995 criterion the threshold for relevance. These operators will include aircraft owners and operators whose aircraft have those APUs installed, and maintenance organisations responsible for APU inspections and component replacement.

• Secondary affected parties: The maintenance providers who carry out inspections and replacements, and parts suppliers that can provide the specified insulation parts or the materials and kits required by Microturbo Alert Service Bulletin 49-11A76 Revision 1. The AD’s instruction to use the Microturbo Service Bulletin for replacement will draw activity to whichever vendors or approved maintenance organisations can implement that Bulletin.

• Geographic and regulatory scope: The directive is issued by the Civil Aviation Safety Authority (CASA) and becomes effective in Australia on 2 July 2009. It refers to EASA AD 2009-0100, indicating that the defect and responses have international regulatory attention; however, the directive itself imposes obligations on operators subject to CASA’s jurisdiction.

• Aircraft types that may be affected: The AD notes that affected APUs are known to be installed on, but not limited to, Dassault Falcon 20 aeroplanes. The qualification “not limited to” means that any aircraft type with a subject APU replaced since 1995 falls within scope; the AD does not confine applicability to specific airframes.

• Who decides and enforces compliance: The document is signed by a CASA delegate (James Coyne) and is an Airworthiness Directive, which in aviation regulatory practice typically creates mandatory obligations for continuing airworthiness. The AD text itself sets out the technical obligations and timelines, but does not in this text specify penalty mechanisms or the enforcement process; that responsibility sits with CASA as the issuing authority.

• Operators’ decision space and obligations: Affected operators must schedule and fund the inspections and replacement work within the stated time intervals. The AD requires the replacement to be carried out in accordance with the Microturbo Alert Service Bulletin cited, with later approved revisions acceptable, which constrains how replacement work is performed and by whom (that is, organisations capable of meeting the Service Bulletin instructions).

• Scope exclusions: The AD explicitly limits the affected population by the date of the insulation replacement (parts replaced since 1 January 1995) and by part number. Parts that pre-date that replacement threshold are not described as affected in this instrument.

In short, the AD’s immediate costs and administrative burden fall on operators and maintenance organisations responsible for Saphir 2 Model 016 APUs with insulation replaced since 1995, with knock-on effects for parts suppliers and maintenance scheduling.

The AD imposes discrete duties on operators and provide limited procedural discretion; it does not, within the text provided, spell out compliance penalties or appeals processes. The key duties and interactions are described below, with direct references to the AD’s expressed requirements.

• Duty to inspect: Operators must perform an initial inspection of the exhaust thermal insulation for signs of deterioration (Requirement 1). The compliance deadline is explicit: this initial inspection must be performed within 10 APU operating hours from the AD’s effective date. After that, operators must perform repeat inspections at intervals not exceeding 10 APU operating hours (Requirement 2). The AD thereby sets a high-frequency inspection regime.

• Duty to replace if deterioration is detected: If deterioration is detected in an inspection, operators must replace the exhaust thermal insulation in accordance with the accomplishment instructions in Microturbo Alert Service Bulletin 49-11A76 Revision 1, dated 6 September 2007 (Requirement 3). The timing requirement for this act is strict: any detected-deterioration replacement must be completed before operating the APU again. That imposes an immediate operational stop-start constraint where deterioration is observed.

• Duty to replace within fixed time even if no deterioration is detected: Separately from the conditional replacement in Requirement 3, Requirement 4 requires replacement of the exhaust thermal insulation in accordance with the same Service Bulletin within 50 APU operating hours from the AD’s effective date. This creates a time-limited mandatory replacement irrespective of inspection findings.

• Technical standard duty: The AD identifies a single technical standard document , Microturbo Alert Service Bulletin 49-11A76 Revision 1 , as the required method for replacement work and permits later approved revisions of that document for compliance. Operators are therefore required to follow that manufacturer-originated procedure, or a later approved revision, when performing replacements.

• Rights regarding approved revisions: The AD expressly states that the use of later approved revisions of Microturbo Alert Service Bulletin 49-11A76 Revision 1 is acceptable for compliance. That creates a limited right for operators to adopt updated technical instructions, subject to those revisions being “approved” (approval process not defined in the AD text).

• Obligation timing and operation restriction: The AD’s Requirement 3 imposes an operational restriction: where deterioration is detected, the APU must not be operated again until replacement is completed. The combination of frequent inspection intervals and the pre-operation replacement requirement creates an immediate operational contingency for affected aircraft.

• Documentation and traceability: The AD itself does not state specific record-keeping duties, but by mandating actions in accordance with a Service Bulletin it implies that operators must be able to show compliance with the Service Bulletin instructions and the AD’s timing requirements if inspected by CASA or otherwise audited. The AD accepts later approved revisions of the Service Bulletin, which implies any operator invoking a later revision must be able to show that the later revision was approved.

• Delegated decision-making: The AD is signed by a CASA delegate, identifying the issuing authority within CASA. The AD’s allowance for later approved revisions introduces delegated technical decision-making (approval of later revisions), but the AD text does not specify who grants such approvals or the approval criteria.

• Limited explicit exemptions: The AD contains no express exemptions, alternative methods of compliance, or special flight permits in the text provided. It does, however, reference a specific Service Bulletin and EASA AD as part of the compliance context.

To summarise, duties created by the AD are operationally immediate and procedural: short-deadline inspections, frequent re-inspections, conditional and mandatory replacements tied to a named Service Bulletin, and a narrow ability to rely on later approved revisions of that Service Bulletin. The AD does not, in its text, enumerate rights such as appeal routes, alternative compliance procedures, or penalty frameworks.

The AD text sets operational obligations but does not, within the provided material, specify penalties, sanctioning mechanisms, or the routine enforcement process. The following points summarise what the instrument does say and where it is silent.

• Enforcement authority and signature: The AD is an instrument issued under the authority of the Civil Aviation Safety Authority (CASA) and is signed by a CASA delegate (James Coyne, 22 May 2009). This identifies the regulatory author as the issuing and enforcing body in practice; CASA is the organisation that promulgates and enforces airworthiness directives. The AD itself, however, contains no text setting out penalty amounts, prosecution provisions, or enforcement steps.

• No penalties in text: The AD’s printed requirements, compliance times and reference to Service Bulletin instructions do not include any clause describing criminal or civil penalties for non-compliance, or the administrative enforcement actions CASA may take. The document does not provide an enforcement schedule, notice-and-comment process, or administrative review mechanism in the text supplied.

• Implied enforcement mechanisms outside the AD: In aviation regulatory practice, an AD creates mandatory continuing airworthiness requirements enforceable by the regulator under aviation safety legislation and regulations. While that is standard context, the AD as provided does not quote or reference specific legislative provisions that describe available enforcement tools (for example, grounding aircraft, revoking certificates, issuing fines). Therefore, any claim about specific criminal or civil penalties, or the precise enforcement steps CASA would use, would be beyond the document’s text.

• Operational compliance as the immediate control: The instrument’s immediate mechanism to reduce risk is procedural: inspections and replacement tied to a Service Bulletin, with specified time windows. The AD creates compliance obligations that, if met, should mitigate the stated safety hazard. The document itself leaves the question of enforcement mechanisms to the broader regulatory framework under which CASA operates, which is not recited in this text.

• Record-keeping and audit implications: The AD requires actions that are typically subject to audit by a regulator. While the AD does not specify records to be kept, the technical linkage to an approved Service Bulletin implies that operators should maintain records demonstrating that the inspection and replacement work was performed in accordance with the Service Bulletin and within the AD’s stated time limits. Again, the AD itself does not define sanctions for lack of records.

• Cross-reference to EASA AD: The AD notes EASA AD 2009-0100 (4 May 2009) as a related document. That cross-reference indicates multi-jurisdictional regulatory attention to the defect; however, the AD text does not state whether CASA will coordinate enforcement action specifically in line with EASA procedures.

In sum, the AD creates binding technical and timing duties but does not themselves detail penalty provisions or enforcement procedures within the text provided. The enforcement and penalty mechanisms that could be applied for breach of these duties are therefore not set out in this AD and sit elsewhere in the regulatory system.

The AD explicitly interacts with a manufacturer’s Service Bulletin and references an equivalent foreign regulator’s directive, but within the text supplied it does not cite other domestic statutes, regulations, or penalty regimes. The interactions that are stated are set out below.

• Microturbo Alert Service Bulletin as the technical norm: The AD requires replacement actions “in accordance with the accomplishment instructions in Microturbo Alert Service Bulletin 49-11A76 Revision 1, dated 6 September 2007” (Requirements 3 and 4). The AD also states “The use of later approved revisions of this document is acceptable for compliance with the requirements of this AD.” This creates a direct normative link between the AD (a regulatory instrument) and a manufacturer-originated technical document. Practically, compliance with the AD thereby requires adherence to that Service Bulletin or an approved later revision.

• Cross-reference to EASA AD 2009-0100: Note 2 in the AD states that “EASA AD 2009-0100 dated 4 May 2009 refers.” This records that the European Aviation Safety Agency issued a parallel or antecedent AD covering the same condition, and signals that CASA’s action is consistent with (or at least informed by) EASA’s prior measure. The AD does not include the text of the EASA AD nor does it adopt EASA’s enforcement mechanisms; it merely references it.

• No explicit domestic statutory citations in the AD text: The provided AD does not quote or list specific provisions of Australian aviation safety legislation or regulations that create the legal basis for the AD, or that spell out associated enforcement powers. The absence of express statutory citations in the text means that the AD relies on the reader’s knowledge of CASA’s enabling legislation for the legal basis; the AD itself does not reproduce that material.

• Interplay with maintenance certification and approved data: By directing compliance with a Service Bulletin and permitting later approved revisions, the AD interacts with the broader rules and practices concerning approved data and airworthiness maintenance standards. The AD makes the Service Bulletin the method of compliance, which intersects with the processes by which revisions to Service Bulletins are approved for regulatory compliance. The AD text does not, however, set out the approval process for later revisions, leaving that interaction to other administrative procedures.

• Implications for contractual relations: The AD imposes obligations that affect operator-maintenance provider contracts and parts-supply arrangements. While the AD does not address contractual law or procurement rules, it forces private parties subject to the AD to make decisions about who will perform the required inspections and replacements, and which approved revisions of the Service Bulletin to follow. Those private contractual adjustments occur within the broader legal framework (contract law, consumer and business law), but the AD does not specify interactions with those bodies of law.

• No mention of airworthiness certificates or flight permits: The AD does not state whether aircraft can be flown to a maintenance facility under special flight permits or whether the airworthiness certificate is affected in specific ways by non-compliance. Those typical regulatory interactions are not addressed in the text provided.

Overall, the AD interacts directly with manufacturer technical instructions and references an EASA directive, but does not itself reproduce or expressly tie into particular domestic statutory penalty or procedural provisions; those interactions must be inferred from the broader regulatory context outside the text of this AD.

The AD’s own revision history in the provided text is limited but includes several dated references which together form the documentary lineage relevant to compliance.

• Effective date of the AD: The AD states that it “becomes effective on 2 July 2009.” It was signed on 22 May 2009 by James Coyne, Delegate of the Civil Aviation Safety Authority. Those two dates are the primary temporal markers for the AD itself.

• Manufacturer Service Bulletin referenced: The AD mandates compliance with Microturbo Alert Service Bulletin 49-11A76 Revision 1, dated 6 September 2007. That Service Bulletin is the technical document whose content the AD adopts as the method of accomplishing the required replacement actions. The AD allows the use of later approved revisions of that Service Bulletin for compliance, opening an amendment channel by which updated Service Bulletin revisions, if approved, can substitute for Revision 1.

• Prior regulatory action referenced: Note 2 refers to EASA AD 2009-0100 dated 4 May 2009. That date is earlier than the CASA AD’s effective date and appears to be the EASA counterpart or antecedent document that CASA relied upon or referred to when issuing this AD. The AD therefore sits in a chain of regulatory responses, with EASA’s AD dated 4 May 2009 and CASA’s AD effective 2 July 2009.

• Parts replacement date threshold: The AD’s applicability includes only APUs “on which the exhaust thermal insulation has been replaced since 1 January 1995.” That historical cut-off (1 January 1995) is an element of the AD’s applicability history and indicates the population targeted by this directive is limited to replacements made from that date forward.

• Acceptance of later approved revisions: The AD explicitly states that “The use of later approved revisions of this document [Microturbo Alert Service Bulletin 49-11A76 Revision 1] is acceptable for compliance with the requirements of this AD.” That language institutionalises a process for the Service Bulletin to be updated after the AD’s issuance, provided later revisions carry the necessary approvals. The AD does not define the approvals process or identify the approving authority in the AD text.

• No subsequent amendments in the provided text: The AD document supplied does not include any further amendments, revocations, or superseding notices. It does not show a revision table for the AD itself, and it does not include later dates indicating that the AD was amended or withdrawn. Any later changes to the AD or to the Service Bulletin beyond those noted would not be visible in the text provided.

In summary, the AD’s amendment history as contained in the supplied text is comprised of: the Service Bulletin revision date (6 September 2007), the EASA AD date (4 May 2009), the CASA delegate signature date (22 May 2009), and the AD effective date (2 July 2009). The AD opens the option to use later approved revisions of the referenced Service Bulletin for compliance but does not itself document later amendments or revocations.

The provided AD text does not record any litigation history. It contains no references to court decisions, administrative appeals, or legal challenges to the directive. The document lists the technical requirements, timing and the Service Bulletin to be used, and it cites EASA AD 2009-0100 as a related regulatory document. There are no named cases, no reference to judicial review outcomes, and no mention of enforcement proceedings or contested enforcement actions in the text supplied.

Given the absence of litigation references in the AD, the following are points that can be stated from the instrument itself and not beyond it:

• The AD does not identify any precedents or court rulings as the basis for the actions required. There is no legal argumentation in the AD text that draws on litigation outcomes.

• The AD does not indicate that it was issued in response to a litigation case or as the subject of an ongoing administrative appeal. It stands as a regulator-issued safety directive with technical instructions and compliance timelines.

• Any litigation history that may exist in respect of this AD, the manufacturer's Service Bulletin, or the underlying manufacturing quality-control issues is not contained in the supplied text. If a practitioner needs to know about court decisions, administrative appeals, or enforcement litigation connected to this AD, they would need to consult external sources such as CASA records, court databases, or legal reporting that are not included in this AD’s text.

Therefore, based solely on the supplied instrument, there is no litigation history to summarise.

The AD text contains several concrete features that can create traps for operators and maintenance providers if they are overlooked. The following items are drawn directly from the AD’s language and timing requirements.

• Applicability is time-limited by past work (replacement since 1 January 1995): The AD applies only to APUs for which the exhaust thermal insulation was replaced since 1 January 1995. Operators who assume that “all Saphir 2 Model 016 APUs” are covered will misapply the AD; you must verify whether the insulation on a given APU was replaced on or after the 1 January 1995 threshold. The AD lists the affected part numbers (016-33-01, 016-33-02, 016-33-03), so record checks against maintenance histories and part numbers are necessary to confirm applicability.

• Short inspection windows: The initial inspection must be completed within 10 APU operating hours from the AD’s effective date, and repeat inspections must occur at intervals not exceeding 10 APU operating hours. Those are tight windows that can be missed if an operator does not immediately schedule inspections. If the AD’s effective date is 2 July 2009, the initial inspection deadline is 10 APU hours after that date; operators must translate “APU operating hours” into their operational tracking systems and not rely on flight hours alone if those differ.

• Replacement requirement even if no deterioration is found: Requirement 4 mandates replacement of the exhaust thermal insulation within 50 APU operating hours from the AD’s effective date regardless of inspection outcomes. Operators who perform the initial and repeated inspections but assume replacement is only conditional on deterioration will be non-compliant unless they also complete the 50-hour replacement.

• Immediate grounding potential where deterioration is detected: If deterioration is detected during any inspection, the AD requires replacement prior to operating the APU again. This creates an operational grounding risk: an aircraft may be prevented from further flight with that APU until replacement is complete. Operators must plan for potential APU replacement downtime and logistics.

• Dependence on a specific Service Bulletin and approval of later revisions: The AD requires replacement “in accordance with the accomplishment instructions in Microturbo Alert Service Bulletin 49-11A76 Revision 1, dated 6 September 2007,” and allows later approved revisions. Operators must ensure they use either Revision 1 or a later revision that is actually approved for compliance. Using an unapproved revision or an informal repair method would not meet the AD’s stated compliance method.

• Parts identification: The AD identifies three part numbers as affected. Maintenance records must be checked against those part numbers. Failure to check could result in unnecessary replacement or, conversely, failure to replace an affected part.

• Geographical and regulatory assumptions: The AD notes that affected APUs are “known to be installed on, but are not limited to, Dassault Falcon 20 aeroplanes.” Operators must not assume that only Falcon 20s are affected; any aircraft with a Saphir 2 Model 016 APU whose exhaust thermal insulation was replaced since 1995 falls within scope. Broad-brush filtering by aircraft type would be a compliance gotcha.

• Records and proof of compliance: While the AD does not itself list record-keeping requirements, compliance will typically be demonstrated to the regulator by maintenance logs and Service Bulletin compliance records. Operators should not assume that simply having performed work is sufficient; they should document that the inspection and replacements were done in accordance with the named Service Bulletin and within the AD’s deadlines.

• Overlooking cross-reference to EASA AD: The AD notes EASA AD 2009-0100. Operators who operate in multiple jurisdictions should not assume the CASA AD is the sole or final regulatory directive; cross-jurisdictional operators may need to reconcile the CASA AD with the EASA AD.

• Timing mismatch between inspections and replacement window: The requirement to inspect every 10 APU hours and to replace within 50 APU hours creates multiple inspection points before the mandatory replacement. Operators need to track cumulative APU operating hours to ensure that the replacement is completed within 50 hours even if no deterioration is detected earlier.

These “gotchas” are all directly traceable to the AD’s content: the applicability clause, the four named requirements, the specified compliance times, the identification of affected parts, and the reliance on a named Service Bulletin and on later approved revisions.

The AD sets a short, prescriptive compliance pathway. Below is a practical, source-grounded checklist and sequencing that follows the AD’s requirements and timelines exactly.

1. Confirm applicability to each APU

   • Check maintenance and parts records for each Microturbo Saphir 2 Model 016 APU installed in your fleet.
   • Verify whether the exhaust thermal insulation was replaced since 1 January 1995. The AD applies only to those APUs where replacement occurred on or after that date.
   • Confirm the part numbers for the insulation present in the APU: 016-33-01 (Inner Thermal Insulation), 016-33-02 (Outer Thermal Insulation), and 016-33-03 (EGT Sensor Thermal Insulation). If these part numbers are present and the replacement date criterion is met, the AD applies.

2. Schedule and perform the initial inspection (Requirement 1)

   • The initial inspection for signs of deterioration must be completed within 10 APU operating hours from the AD’s effective date (the AD becomes effective on 2 July 2009). Translate “APU operating hours” into your maintenance tracking system and schedule the inspection immediately if the required hours are near.
   • The inspection purpose is to identify any signs of deterioration of the exhaust thermal insulation. Follow your approved maintenance procedures to assess physical condition, noting any evidence of breakdown, loss of insulation integrity, or related defects.

3. Establish and conduct repeat inspections (Requirement 2)

   • Repeat inspections must occur at intervals not exceeding 10 APU operating hours. Set up a monitoring and scheduling process to ensure continuing inspections at the prescribed frequency until replacement is complete.
   • Record inspection findings in maintenance logs and link entries to the applicable APU serial number and part numbers.

4. If deterioration is detected, replace before further operation (Requirement 3)

   • If any inspection reveals deterioration, immediately arrange replacement of the exhaust thermal insulation.
   • Replacement must be performed “in accordance with the accomplishment instructions in Microturbo Alert Service Bulletin 49-11A76 Revision 1, dated 6 September 2007.” Obtain and follow that Service Bulletin’s accomplishment instructions precisely.
   • Do not operate the APU again until the replacement work specified in the Service Bulletin has been completed and verified.

5. Complete mandatory replacement within 50 APU operating hours (Requirement 4)

   • Even if none of the inspections reveal deterioration, you must replace the exhaust thermal insulation within 50 APU operating hours from the AD’s effective date.
   • This replacement must also be carried out according to the Microturbo Alert Service Bulletin 49-11A76 Revision 1 instructions, or a later revision that has been approved for compliance.

6. Use approved revisions where applicable

   • The AD allows the use of later approved revisions of Microturbo Alert Service Bulletin 49-11A76 for compliance. If you intend to use a later revision, confirm that the later revision is formally approved for compliance with this AD. The AD text does not specify the approval process, so obtain confirmation from the relevant approval authority or CASA guidance.

7. Documentation and evidence of compliance

   • Although the AD does not explicitly list record-keeping requirements, maintain contemporaneous maintenance records showing the dates, APU operating hours on which inspections and replacements were carried out, the parts used (including part numbers), and the Service Bulletin revision applied.
   • Record the exact APU operating hours at which the initial inspection, each repeat inspection, any detected-deterioration replacement, and the mandatory 50-hour replacement were performed to demonstrate compliance with the AD’s timing requirements.

8. Coordinate logistics and parts procurement

   • Plan for potential lead times for parts that match the part numbers identified (016-33-01, 016-33-02, 016-33-03) and for a competent maintenance facility capable of accomplishing the replacement in accordance with the Service Bulletin.
   • Because the AD requires replacement within a tight window, arrange parts and maintenance capacity as early as possible to avoid operability constraints.

9. Manage operational impacts

   • If deterioration is found and replacement is required before further operation, deploy contingency planning for aircraft availability, alternative dispatch options, or ferry arrangements as necessary. The AD’s requirement to not operate the APU again until replacement is completed means that affected aircraft may be grounded for repair.

10. Coordinate with CASA and review related regulatory documents

    • The AD references EASA AD 2009-0100 dated 4 May 2009. If you operate across jurisdictions or under different regulatory regimes, reconcile the CASA AD requirements with any applicable EASA directive or other foreign ADs.
    • If questions remain about acceptable later revisions to the Service Bulletin or about alternative methods of compliance, seek clarification from CASA or the delegated approval authority; the AD itself allows later approved revisions but does not describe the approval process.

Following the AD’s exact wording,inspection within 10 APU hours, inspections every 10 APU hours, immediate replacement where deterioration is found before further operation, and mandatory replacement within 50 APU hours using the named Service Bulletin or a later approved revision,constitutes compliance as described in the instrument. Maintain clear records showing the work was done in accordance with the Service Bulletin and within the AD’s specified timeframes.