AD/CFM56/26 - Low Pressure Turbine Rear Frame Life

The AD operates by invoking a few interlocking technical and regulatory concepts set out in the source text.

• Applicability by engine model and part number. The AD lists specific engine model variants (CFM56‑7B18, ‑7B20, ‑7B22, ‑7B22/B1, ‑7B22/B2, ‑7B24, ‑7B24/B1, ‑7B26, ‑7B26/B1, ‑7B26/B2, ‑7B27, ‑7B27/B1, ‑7B27/B3) and LPT rear frame part numbers (P/N 340‑166‑205‑0 through 340‑166‑210‑0). The Applicability section frames the scope; the AD also notes these engines are installed on, but not limited to, Boeing 737 series aeroplanes (Applicability, Note 1).

• Low Cycle Fatigue (LCF) life limits. The AD requires compliance with LCF life limits as set out in specified chapters of the CFM56‑7B ESM, revision 33 (Requirement, item 1). The AD does not restate numerical life limits; it incorporates the ESM’s substantive limits by reference.

• Damage‑tolerant approach. The Background explains the life limits derive from a "refined damage tolerant approach accounting for crack initiation and propagation" intended to ensure present cracking will not grow to unsafe levels. The AD therefore shifts LPT rear frames from a status of no life limit and no mandatory inspection to a situation governed by a damage‑tolerant life‑limit regime.

• Recordability and unknown history. The AD treats absence of verifiable accumulated cycles since new as a trigger for mandatory physical intervention: remove and replace the LPT rear frame, or perform inspections per CFM service bulletin S/B72‑0579 revision 1 (Requirement, item 2). This establishes the presence or absence of maintenance/operational records as a compliance determinant.

• Interaction with industry documents and NAAs. The AD expressly incorporates CFM documents (ESM revision 33 and Service Bulletin S/B72‑0579 rev 1) but qualifies them by permitting "later NAA approved revision[s]" (Requirement items 1 and 2). The AD also references EASA AD 2007‑0104, indicating linkage with international airworthiness action (Requirement, Note 2).

• Compliance timing and the regulatory turn‑on. The AD specifies short deadlines: actions are required "within 7 days from the effective date of this AD" and "within 300 flight cycles from the effective date" (Compliance). The AD becomes effective 11 May 2007.

These concepts operate together: regulatory incorporation of manufacturer life limits and inspection procedures; short compliance windows; reliance on maintenance record integrity; and NAA approval as an incorporated gate for later revisions. The AD thus translates manufacturer engineering judgement and new ESM content into immediate operator obligations enforceable by the national regulator.

The AD identifies and therefore affects a defined economic and operational population.

• Aircraft operators and owners that operate Boeing 737‑series aeroplanes fitted with CFM56‑7B engines containing LPT rear frames of P/N 340‑166‑205‑0 through 340‑166‑210‑0. The Applicability section lists specific engine variants and P/Ns and explicitly notes that these engines are installed on, but not limited to, Boeing 737 series aeroplanes (Applicability; Note 1). The AD’s Background expressly says the AD is "issued to make sure that all operators are informed" and to ensure they "revise their aircraft maintenance programs accordingly" (Background).

• Maintenance organisations and engineers responsible for engine overhaul, inspection and replacement. The Requirement and Compliance items convert ESM chapters and a CFM Service Bulletin into mandatory instructions. Where cycles since new cannot be established, the AD requires removal and replacement or inspection under CFM56‑7B Service Bulletin S/B72‑0579 revision 1, or later NAA approved revision. Maintenance organisations will therefore carry out the physical inspections, parts changeouts, and paperwork required to demonstrate compliance (Requirement, item 2).

• Records and continuing airworthiness managers. The AD relies on the existence of accurate life‑cycle records. If "the number of cycles accumulated since new by a LPT rear frame ... cannot be established", then mechanical action is mandated; that makes records custodians central to whether invasive corrective action will be necessary (Requirement, item 2).

• National airworthiness authorities (NAAs) and CASA. The AD is issued by a CASA delegate and incorporates CFM documents subject to "later NAA approved revision". That language gives NAAs a role in accepting later revisions to the ESM and service bulletin as compliant with the AD (Requirement items 1 and 2; signed delegate line).

• Suppliers and spare parts providers. Where removal and replacement is required, operators will procure replacement LPT rear frames and associated parts, thereby involving supply chains that support the specific P/Ns listed (Requirement, item 2).

The AD does not list pilots, passengers or other third parties explicitly, but its safety aim and the mechanics of regulatory compliance implicitly affect operational availability, scheduling and maintenance planning for operators and associated service providers. The text does not separately exempt any operator class, nor does it provide alternative compliance beyond the ESM chapters and the cited Service Bulletin (Requirement). The AD also references EASA AD 2007‑0104, which indicates parallel obligations may be in force under other jurisdictions, affecting operators across multiple regulatory regimes (Requirement, Note 2).

The AD establishes mandatory duties; it also creates conditional choices for operators. The source text defines those duties and the limited operator options that flow from them.

Duties

• Comply with LCF life limits in CFM56‑7B ESM chapters 05‑12‑04 and 05‑21‑03, revision 33 dated 15 November 2006, or later NAA approved revision (Requirement, item 1). This duty requires operators to incorporate the ESM life limits into their continuing airworthiness procedures.

• Where accumulated cycles since new cannot be established for an affected LPT rear frame, either remove and replace the LPT rear frame, or perform inspections detailed in CFM56‑7B Service Bulletin S/B72‑0579 revision 1, or later NAA approved revision (Requirement, item 2). This sets out a binary duty: replacement or inspection per the SB.

• Meet the AD’s temporal compliance windows: the AD lists two time markers, "Within 7 days from the effective date of this AD" and "Within 300 flight cycles from the effective date of this AD" (Compliance items 1 and 2). The AD does not map the two time markers to the two requirements in the text; both are listed. Operators must therefore ensure relevant actions occur within these specified timeframes.

• Revise aircraft maintenance programs to reflect the newly mandated LCF life limits and inspection requirements (Background). The AD specifically states it is issued to "make sure that all operators are informed about these LCF life limits ... and revise their aircraft maintenance programs accordingly" (Background).

Rights and limited options

• Choice between replacement or inspection when historical cycles cannot be established. The AD grants operators the option to either remove and replace the LPT rear frame or perform the inspections prescribed in the CFM service bulletin (Requirement, item 2). The AD does not provide additional alternative methods of compliance within the text; it only allows later NAA‑approved revisions of the incorporated documents.

• Ability to rely on later NAA‑approved revisions. Where the ESM or Service Bulletin is amended after the stated revisions, operators may comply with a later revision only if it is "NAA approved" (Requirement items 1 and 2). That leaves discretion to NAAs to accept later changes as compliant.

• Implicit right to consult referenced documents. The AD incorporates external manufacturer material (ESM and SB) by reference; operators have the right and the duty to consult those documents to implement the AD.

The AD does not articulate any appeal mechanism, penalty regime or alternative means of compliance within the text. It also does not state exemptions for particular operators. The only explicit conditional flexibility is the replacement versus inspection choice and the ability to use later NAA‑approved revisions of the incorporated documents.

The source text of the AD does not specify penalties or enforcement mechanisms beyond declaring the mandatory requirements and recording the AD’s effective date and signature. The AD’s stated compliance deadlines and incorporation of ESM and Service Bulletin material create enforceable obligations under CASA’s airworthiness regulatory framework, but the AD itself does not set out sanctions, infringement provisions, or inspection/enforcement processes.

What the text does show regarding enforceability:

• The AD is issued by the Civil Aviation Safety Authority’s delegate, with an effective date (signed by Charles Lenarcic, Delegate of the Civil Aviation Safety Authority, and stating "This Airworthiness Directive becomes effective on 11 May 2007"). The formal issuance and effective date indicate that the requirements are regulatory in nature (signature and effective date lines).

• Compliance timelines are explicit. The AD requires actions "Within 7 days from the effective date of this AD" and "Within 300 flight cycles from the effective date of this AD" (Compliance). Those deadlines create measurable performance targets against which regulator compliance checks can be made.

• The AD incorporates manufacturer technical mandatory content by reference: chapters of the ESM and the Service Bulletin, subject to "later NAA approved revision[s]" (Requirement). That incorporation makes the technical standards enforceable insofar as the AD is enforced by CASA or relevant NAA.

What the AD does not say:

• There is no express provision within the AD text specifying civil penalties, criminal sanctions, or administrative fines for non‑compliance.

• There is no detail on how CASA will monitor compliance, inspect operators, or apply remedial measures such as grounding, suspension of certificates, or mandatory rectification timelines beyond those in the AD.

• The AD does not specify any formal process for alternative methods of compliance besides using later NAA‑approved revisions of the ESM or Service Bulletin.

Practical implication based on the source text: the AD sets out clear, time‑bound obligations and incorporation of manufacturer documents, which in airworthiness regulatory practice become enforceable requirements; however, the AD text itself does not enumerate enforcement tools or sanctions, nor does it provide procedural detail on compliance verification or appeals. Those enforcement mechanisms, if exercised, would arise from the wider regulatory framework administered by CASA or other NAAs, but such mechanisms are not described in this AD.

The AD explicitly links to and incorporates non‑statutory industry documents and references another authority’s AD. The text frames its regulatory effect through those interactions.

• Incorporation of manufacturer documents subject to NAA approval. The AD requires compliance "in accordance with chapters 05‑12‑04 and 05‑21‑03 in CFM56‑7B ESM, revision 33, dated 15 November 2006, or later NAA approved revision" and refers to "CFM56‑7B Service Bulletin S/B72‑0579 revision 1, or later NAA approved revision" (Requirement items 1 and 2). This creates a regulatory dependency: the AD's requirements are defined by manufacturer technical documents, but those documents are effective for compliance only as approved by NAAs where later revisions are used. Thus the AD interfaces with the administrative authority of NAAs to accept updated industry materials.

• Cross‑reference to EASA AD. The AD’s Note 2 states "EASA AD 2007‑0104 dated 17 April 2007 refers." That explicit reference indicates parallel or related regulatory action by the European Union Aviation Safety Agency and suggests alignment or harmonisation between CASA’s AD and the EASA AD. The AD thus functions within an international network of airworthiness directives rather than in isolation.

• Relationship with operators’ maintenance programs. The Background instructs that operators are to "revise their aircraft maintenance programs accordingly" in light of the LCF life limits (Background). This means the AD alters obligations that normally sit inside operators’ compliance with continuing airworthiness requirements and maintenance program approvals under aviation law, linking AD requirements to those programmatic obligations.

• Implied interaction with recordkeeping and continuing airworthiness obligations. Because the AD conditions certain remedies on the absence of established cycles since new ("If the number of cycles accumulated since new ... cannot be established"), it interacts operationally with the legal regime that requires operators and maintainers to keep accurate life‑cycle records. While the AD does not restate recordkeeping law, it elevates the operational importance of those records by making their absence trigger physical interventions.

• Delegation and national enforcement. The AD is signed by a CASA delegate; it therefore sits within national administrative law frameworks that empower CASA to issue airworthiness directives. The AD does not itself recite the statutory delegation basis or enforcement powers; those exist outside the text but the AD’s issuance and effective date signal reliance on the regulator’s statutory authority.

The AD does not mention other statutes, civil aviation regulations, or administrative procedures directly beyond the ESM, SB, and EASA AD references. It therefore primarily interfaces with industry technical documentation, operators’ maintenance program requirements, and international AD actions.

The AD text contains limited but specific information about the origin and integration of the life limits it mandates.

• Temporary Revision TR 05‑0071. The Background states that "before the issue of the CFM56‑7B Engine Shop Manual (ESM) Temporary Revision (TR) 05‑0071, the LPT rear frames were neither subject to a life limit nor a mandatory inspection." That identifies TR 05‑0071 as the initial technical step by CFM to impose life limits and inspection requirements on LPT rear frames (Background).

• Integration into ESM revision 33. The Background continues that TR 05‑0071 "has been integrated into revision 33 of the CFM56‑7B ESM." The Requirement then cites ESM revision 33 dated 15 November 2006 as the document containing the LCF life limits, and also allows later NAA‑approved revisions for compliance (Requirement, item 1).

• CFM Service Bulletin revision 1. For the inspection pathway when cycles since new cannot be established, the AD references "CFM56‑7B Service Bulletin S/B72‑0579 revision 1, or later NAA approved revision" (Requirement, item 2). That indicates the AD relies on at least revision 1 of that Service Bulletin as the operative inspection procedure.

• AD effective date. The AD records that "This Airworthiness Directive becomes effective on 11 May 2007." That is the AD’s effective date and is the legal starting point for its compliance deadlines (Compliance; effective date line).

• External AD reference. Note 2 in the Requirement section references "EASA AD 2007‑0104 dated 17 April 2007." That provides an international AD touchstone contemporaneous with this CASA AD.

The AD does not itself record any subsequent amendments to the AD text, nor does it list amendment numbers for the AD. It does, however, explicitly permit the use of "later NAA approved revision[s]" of the ESM chapters and Service Bulletin as satisfying the AD, which is a form of forward‑compatible amendment mechanism contingent on NAA approvals. No other historical or subsequent amendment details are present in the document beyond the integration of TR 05‑0071 into ESM revision 33 and the referenced EASA AD.

The AD text does not record any litigation history. It contains no references to judicial or administrative litigation, court decisions, appeals, or disputes concerning the AD, the ESM revisions, or the Service Bulletin. The source provides only the regulatory instrument itself, the stated technical background, and the referenced EASA AD; it does not indicate any challenges, stays, or legal proceedings arising from issuance of AD/CFM56/26.

Accordingly, based solely on the provided text:

• There are no reported cases, appeals, or decisions mentioned in the AD that pertain to either the substantive technical requirements or the AD’s legal status.

• The AD contains no language describing a review, stay, injunction, or negotiated settlement. It records an effective date and is presented as a final regulatory instrument in the document.

Where litigators or compliance counsel require information about any subsequent legal challenges or case law, that material is not in the AD text and would need to be sourced from external legal records; it is not possible to infer litigation history from the AD itself.

The AD contains several operational and interpretive features that create practical pitfalls for operators, maintenance organisations and compliance teams. These are drawn directly from the AD text.

• Tight dual compliance windows without explicit mapping. The AD lists two compliance timeframes: "Within 7 days from the effective date of this AD" and "Within 300 flight cycles from the effective date of this AD" (Compliance). The AD does not explicitly map which compliance window corresponds to which Requirement item. That ambiguity creates implementation risk: operators must ensure all required actions are addressed within both timeframes or document why a particular action is intended to fall within one rather than the other.

• Record absence triggers invasive action. If the number of cycles accumulated since new cannot be established for an LPT rear frame, the AD mandates removal and replacement or inspections per the Service Bulletin (Requirement, item 2). Practically, incomplete or missing life‑cycle records will force either replacement or immediate inspection, which can be costly and operationally disruptive. The AD makes recordkeeping quality decisive for whether invasive work is required.

• Reliance on external documents. The substantive life limits are not printed in the AD; they are contained in CFM56‑7B ESM chapters 05‑12‑04 and 05‑21‑03 revision 33 and in Service Bulletin S/B72‑0579 revision 1 (Requirement items 1 and 2). Operators must obtain, read and correctly apply those documents. Errors in interpreting or applying the ESM chapters or Service Bulletin could produce non‑compliance, and the AD conditions acceptance of later revisions on NAA approval.

• NAA approval gate for later revisions. The AD allows later ESM or Service Bulletin revisions only if NAA approved. If an operator attempts to rely on a later revision that lacks NAA approval, the AD text does not authorise that route. This creates administrative dependency and possible delay where CFM issues further revisions but NAA approvals lag.

• Multiple P/Ns and model variants. Applicability lists six P/Ns and many engine variants. Operators must verify P/Ns on installed LPT rear frames precisely; misidentifying a P/N could lead to failing to apply the AD to an affected engine. The Applicability notes the engines are installed on, but not limited to, Boeing 737 series aeroplanes, so operators of other aircraft types must also check.

• Absence of penalty language in the AD. The AD does not state explicit penalties for non‑compliance. That does not mean enforcement will not occur under CASA’s broader statutory regime, but the AD itself provides no enforcement or appeal detail. This may cause confusion about how compliance will be monitored and enforced.

• Timing relative to operational schedules. The AD’s effective date and short deadlines mean scheduled maintenance planning may need immediate adjustments. Operators with aircraft in service close to the effective date must decide quickly whether records suffice or whether to plan removals/inspections that can impact dispatch reliability.

• Assumptions about prior practice. The Background notes that prior to TR 05‑0071 the LPT rear frames were not subject to life limits or mandatory inspection. That historical absence makes it more likely many operators lack clear life‑cycle histories for some frames, potentially triggering the replacement/inspection remedy en masse.

• Interaction with other jurisdictions. The AD references EASA AD 2007‑0104. Operators subject to multiple jurisdictions should reconcile requirements to ensure compliance with all applicable ADs, and need to be aware that the AD text allows later revisions only with NAA approval , potentially different NAAs may take different positions.

Each of these points is grounded in the AD wording and indicates concrete operational risks to manage when implementing the directive.

The AD text provides a direct compliance pathway. The steps below follow the AD wording; they identify required actions, options, time windows and administrative dependencies that operators and maintenance organisations must manage.

1. Confirm applicability immediately.

   • Check whether any installed engine is a CFM56‑7B variant listed in the Applicability section (CFM56‑7B18, ‑7B20, ‑7B22, ‑7B22/B1, ‑7B22/B2, ‑7B24, ‑7B24/B1, ‑7B26, ‑7B26/B1, ‑7B26/B2, ‑7B27, ‑7B27/B1, ‑7B27/B3) and whether the LPT rear frame installed is one of P/N 340‑166‑205‑0, 340‑166‑206‑0, 340‑166‑207‑0, 340‑166‑208‑0, 340‑166‑209‑0 or 340‑166‑210‑0 (Applicability).

2. Obtain the referenced technical documents.

   • Procure CFM56‑7B ESM revision 33 (chapters 05‑12‑04 and 05‑21‑03) dated 15 November 2006, and CFM56‑7B Service Bulletin S/B72‑0579 revision 1. The AD requires compliance "in accordance with" those documents, or with later NAA approved revisions (Requirement items 1 and 2). Review the precise LCF life limits and inspection procedures there.

3. Assess life‑cycle records.

   • For each affected LPT rear frame, determine whether the "number of cycles accumulated since new" can be established. If records are complete and show the component is within the LCF life limit per the ESM, incorporate that data into the maintenance program as required by the ESM chapters (Requirement, item 1; Background).

4. If cycles since new cannot be established, choose and execute the remedial option.

   • Remove and replace the LPT rear frame, or perform the inspections detailed in Service Bulletin S/B72‑0579 revision 1 (Requirement, item 2). The AD gives operators these two alternatives; select the path that is feasible operationally and that satisfies the SB procedures.

5. Meet the AD’s timing obligations.

   • The AD sets two timing requirements: "Within 7 days from the effective date of this AD" and "Within 300 flight cycles from the effective date of this AD" (Compliance). Because the AD does not map those time periods explicitly to specific Requirement items, implementers should take one of two prudent approaches: complete initial applicability checks and necessary record assessments within 7 days, and schedule and complete any required removals, replacements or inspections within 300 flight cycles; or seek clarification from CASA if there is uncertainty. Document actions and rationale.

6. Revise approved maintenance programs.

   • As the Background instructs, revise aircraft maintenance programs to incorporate the ESM LCF life limits and the SB inspection requirements as applicable. Ensure that continued airworthiness documentation and Maintenance Review Board/approved maintenance schedules reflect the mandated life limits (Background).

7. Use later revisions only with NAA approval.

   • If relying on any later revision of the ESM chapters or the Service Bulletin, ensure that the revision is NAA approved before using it to demonstrate compliance with the AD (Requirement items 1 and 2).

8. Record compliance actions and preserve evidence.

   • Maintain records that show applicability checks, life‑cycle record status, removal/replacement or inspection activities, outcomes, and any parts replaced. Because the AD conditions remedial action on the absence of established cycles, contemporaneous records will be critical to demonstrate regulatory compliance.

9. Coordinate across jurisdictions where relevant.

   • Note the AD references EASA AD 2007‑0104. If an operator is regulated by multiple NAAs, co‑ordinate acceptance and implementation of related ADs and any NAA approvals of later revisions to ensure compliance with each applicable authority (Requirement, Note 2).

10. Escalate ambiguous issues to the NAA/CASA.

    • If there is uncertainty about how the AD’s two compliance timeframes map to the Requirement items, or about whether a later ESM/SB revision has been NAA approved, seek clarification or written acceptance from CASA or the relevant NAA.

These steps rest on the AD’s express wording. The AD contains no alternative compliance pathways other than the single inspection vs replacement choice and the ability to use later NAA‑approved revisions; implementers must therefore treat the ESM chapters and Service Bulletin as normative and ensure adherence to the AD’s time limits.