AD/ARRIEL/20 - Digital Engine Control Unit - Torque Measurements

This AD is built on a small set of technical and legal concepts stated in the instrument and the Turbomeca MSB it mandates. The AD ties together these concepts: applicability by serial number, production DECU measurement accuracy, use of a prototype DECU as a comparator, conformation resistance values, torque conformation box recalibration, and compliance timing.

Applicability by serial number. The AD limits its reach to "Arriel 2S1 turboshaft engines whose Module 01 serial number is listed in Turbomeca Mandatory Service Bulletin (MSB) A 292 72 2816." That makes the precise scope contingent on the MSB's list of Module 01 serial numbers. The AD does not attempt to list the serial numbers itself. This creates a two-document test for applicability: the AD plus the MSB.

Production DECU vs prototype DECU. The central technical concept is that the production Digital Engine Control Unit (DECU) can produce torque indications that differ from a prototype DECU used as a reference. The AD instructs that the torque measurements made by the production DECU be checked and compared "to those obtained from a prototype DECU, installed in parallel with the production DECU." The AD therefore presumes that a prototype DECU can be installed in parallel for comparative measurement. The AD does not define what constitutes a prototype DECU beyond naming it.

Conformation resistance values and torque conformation box. The AD requires recalculation of "the new conformation resistance values" and recalibration of "the torque conformation box." Those terms appear without definition in the AD; the procedural detail is delegated to Turbomeca MSB A 292 72 2816. The AD therefore operates as a directive to carry out specific measurement, calculation and calibration tasks in the MSB.

Quantified error and operational consequences. The AD provides quantified error information from DGAC: "a possible overestimation up to 27 N.m (3.0% torque) of the indicated torque compared to the real torque of the engine." It further links that measurement error to two operational consequences stated by DGAC: "a possible overestimation of the power margin during the Power Assurance Check as specified in the aircraft flight manual" and "a possible power limitation below the minimum declared levels of the 'OEI 30s', 'OEI 2min' and 'OEI continuous' ratings in a limited part of the flight envelope." Those passages anchor the AD's prescribed technical remedy in identified safety and performance concerns.

Mandation by reference. The AD mandates performance "in accordance with MSB A 292 72 2816." The AD does not reproduce the MSB procedures; it makes the MSB the operative technical standard. In drafting terms, this is a mandation by reference: the AD prescribes behaviour and refers to an external technical document for the specific method and steps. The AD also notes a linked foreign directive: "DGAC AD F-2004-192 (EASA approval 2004-12118) refers." That signals regulatory alignment with DGAC/EASA findings.

Timing and legal effect. The AD contains two dates: its effective date ("This Airworthiness Directive becomes effective on 17 February 2005") and a compliance deadline ("Before 31 January 2006"). The signature date in the document is 6 January 2005. The AD makes compliance mandatory for engines within applicability prior to the compliance deadline.

Delegated issuing authority. The AD is signed by a named delegate of CASA, which establishes the issuer and the issuing authority in the Australian regulatory context, as reflected in the document: "David Punshon, Delegate of the Civil Aviation Safety Authority."

In summary, the document is a targeted, serial-number-limited technical mandation by reference to a manufacturer MSB, triggered by quantitative measurement error in DECU torque indication that has quantified potential effects on indicated torque and certain OEI ratings, with specific timelines for compliance.

The AD identifies a narrow set of affected parties through its applicability language and the nature of the required work. The direct affected stakeholders are:

• Owners and operators of Arriel 2S1 turboshaft engines whose Module 01 serial numbers are listed in Turbomeca MSB A 292 72 2816. The AD's applicability line makes these engines the subject of mandatory corrective action. Where an engine's Module 01 serial number appears on the MSB list, the operator must comply "Unless previously accomplished."

• Maintenance organisations and licensed engineers who perform engine bench work and DECU installations. The AD requires installation of a prototype DECU "in parallel with the production DECU" for comparative torque measurements, and recalculation and recalibration tasks. That implies bench capability to mount a prototype DECU and perform comparative measurement and recalibration of the torque conformation box in accordance with the manufacturer MSB.

• Aircraft operators and flight crew who rely on torque and power margin indications for operational checks. The AD records a quantified overestimation of indicated torque "up to 27 N.m (3.0% torque)" and flags a "possible overestimation of the power margin during the Power Assurance Check" and "a possible power limitation below the minimum declared levels" of certain OEI ratings. These statements indicate potential operational impacts on performance assessments and OEI margins for operators who have affected engines installed in aircraft.

• Compliance and airworthiness managers responsible for regulatory conformity. They must determine engine applicability by cross-referencing the MSB list of Module 01 serial numbers and schedule the required MSB work prior to the compliance deadline of "Before 31 January 2006."

• Turbomeca as manufacturer. Although the AD is an instruction to operators, the underlying MSB is a manufacturer document; Turbomeca will be the source of the detailed corrective procedure and the list of affected Module 01 serial numbers in MSB A 292 72 2816. The AD explicitly instructs work "in accordance with MSB A 292 72 2816," which places procedural responsibility with the manufacturer's published process.

• Regulatory and technical approvers. The AD notes that the DGAC AD F-2004-192 (EASA approval 2004-12118) refers, signalling that French/EASA authorities had identified the same issue. CASA's delegate issued this domestic AD, and staff within CASA and possibly other oversight bodies will be involved in verifying compliance filings or records as appropriate.

Who pays. The AD does not state costs or funding arrangements. Practically, the owners and operators of the affected engines will pay for the work required by the MSB (the AD instructs performance of MSB work), including any parts, prototype DECU procurement or loan, labour, bench time, and aircraft downtime. Maintenance organisations will incur labour and facility costs to perform the checks and recalibrations.

Who decides applicability and exemption. The AD says applicability is determined by Module 01 serial numbers listed in the MSB, and the phrase "Unless previously accomplished" creates an exemption for engines where the MSB work has already been performed. Therefore the operator, in conjunction with maintenance records and the MSB list, decides whether an engine falls within the AD and whether the work has been previously accomplished.

Who enforces. The instrument is an Airworthiness Directive issued by CASA (signed by the delegate). The AD imposes mandatory corrective steps for the named engines. The AD itself does not specify sanctions; enforcement remains a regulatory matter inferred by issuance of an AD and CASA's oversight role as reflected in the document signature.

The AD imposes narrow, technically specific duties and leaves procedural detail to the referenced Turbomeca MSB. The obligations and the limited expressions of rights in the text are as follows.

Key duties:

• Determine applicability. Operators must determine whether the engine's Module 01 serial number appears on the list in Turbomeca MSB A 292 72 2816. The AD explicitly sets applicability as "Arriel 2S1 turboshaft engines whose Module 01 serial number is listed in Turbomeca Mandatory Service Bulletin (MSB) A 292 72 2816." That requires access to and review of the MSB list.

• Perform comparative torque checks. For applicable engines not already done, the operator must "Check the torque measurements made by the production Digital Engine Control Unit (DECU) installed on the engine and compare them to those obtained from a prototype DECU, installed in parallel with the production DECU." The duty requires physical installation of a prototype DECU in parallel for comparative measurement.

• Recalculate and recalibrate. The AD requires the operator to "Recalculate the new conformation resistance values and recalibrate the torque conformation box." These calculation and calibration steps must follow the MSB procedures.

• Follow the MSB. All the required work is framed "in accordance with MSB A 292 72 2816." The duty therefore extends to following the methods, tolerances, recording and procedural steps set in the MSB.

• Meet the compliance deadline. Operators must accomplish the required work "Before 31 January 2006." The AD also states it "becomes effective on 17 February 2005"; compliance must be completed within the period the AD establishes.

Rights and procedural points reflected or implied in the AD:

• Exemption for previously accomplished work. The duty is conditional: "Unless previously accomplished, perform the following..." That creates an explicit exemption for engines on which the MSB-mandated checks and recalibration have already been performed. The operator is responsible for establishing that prior accomplishment.

• Use of manufacturer procedure. The AD delegates technical detail to the manufacturer MSB. Operators have the right to perform the required work by following the MSB's steps. The AD does not offer an alternate technical procedure; it directs compliance "in accordance with MSB A 292 72 2816." The operator's practical right is to use the MSB's specified method; there is no alternative process provided in the AD.

• Reference to foreign approval. The AD notes "DGAC AD F-2004-192 (EASA approval 2004-12118) refers." That indicates the operator may consult the DGAC/EASA material for background or corroboration, but the AD does not create a duty to follow the foreign AD separately from the MSB method directed by this instrument.

• No penalty text in the AD. The AD contains no explicit statement of penalties, remedial enforcement procedures or administrative sanctions. The directive is prescriptive and time-limited, but the text does not set out consequences within the instrument itself for failure to comply.

Operational duties implied in the AD text:

• Production of records. While the AD does not set record-keeping requirements directly, the conditional exemption "Unless previously accomplished" and the requirement to follow an MSB logically require operators and maintenance organisations to maintain, and be ready to show, maintenance records demonstrating compliance.

• Downtime scheduling. The AD's work requires bench procedures and DECU installation in parallel. Operators must schedule maintenance windows and accept aircraft or engine downtime to perform the comparative measurements and recalibrations.

• Equipment and parts sourcing. The requirement to use a prototype DECU in parallel implies the operator or maintenance organisation must source or borrow a prototype DECU compatible for the bench or installation. The AD does not specify who supplies the prototype DECU; the MSB may set out procurement or loan procedures, but the AD itself imposes the duty to perform the comparison.

Who decides sufficiency of work and compliance. The AD assigns the method and scope of the work to Turbomeca's MSB; the operator must follow the MSB. Verification of sufficiency would be subject to CASA oversight or normal maintenance record review practices, but the AD does not set an administrative verification process within the text.

The AD text contains no explicit penalties, monetary sanctions, administrative fines or criminal sanctions. The instrument prescribes required work and a compliance deadline but does not itself set out enforcement mechanisms or penalties. The only enforcement signalled in the document is its nature as an Airworthiness Directive issued by CASA (signed by a CASA delegate), which creates a mandatory regulatory obligation for those engines to which the AD applies.

What the AD states about timing and legal effect:

• Effective date and compliance deadline. The AD states "This Airworthiness Directive becomes effective on 17 February 2005." It sets a compliance deadline: "Before 31 January 2006." These dates are explicit; the AD therefore creates a window in which the required work must be completed.

Absence of expressed sanctions. Because the AD text does not specify penalties, there is no instrument-internal penalty regime to cite. The AD is silent on the consequences for non-compliance in statutory or administrative terms. The text does not, for example, mention any licence suspension, grounding, fines or other remedial measures.

Enforcement implications implied by the document. Although the AD does not specify enforcement mechanisms, an Airworthiness Directive functions as a mandatory regulatory measure. The text itself indicates CASA as the issuing authority via the signature of its delegate, "David Punshon, Delegate of the Civil Aviation Safety Authority." Issuance by CASA indicates that the directive is an official regulatory instrument. The AD’s mandatory wording, identification of affected engines by serial number in the MSB, and the compliance deadline, together create an obligation the regulator expects to be performed. The AD does not describe the administrative process CASA will use to monitor compliance, nor does it detail any remedial action CASA will take in the event of non-compliance.

Record-keeping and proof of compliance. The AD’s conditional exemption ("Unless previously accomplished") and the requirement to follow MSB A 292 72 2816 imply that operators must be able to establish that the required MSB work has been performed. The AD does not specify what documentary proof suffices. Any monitoring, audit or inspection process and the associated enforcement consequences are not detailed in the AD.

Reference to foreign approval. The AD notes "DGAC AD F-2004-192 (EASA approval 2004-12118) refers." That records correspondent foreign regulatory action but does not itself create enforcement procedures within this AD.

In short, the AD prescribes mandatory technical work and a deadline, identifies the issuing authority, and omits explicit penalty language. Enforcement practice and the consequence of non-compliance are not specified in the text of the AD and would be matters for CASA procedure or other regulatory instruments beyond this document.

The AD explicitly links to a manufacturer service bulletin and to a foreign airworthiness directive; other statutory or regulatory interactions are not set out in the text. The AD’s text enables these interactions:

• Mandation by reference to a manufacturer MSB. The AD instructs operators to perform the specified actions "in accordance with MSB A 292 72 2816." That creates a direct operational connection between the regulatory instrument and the manufacturer's technical procedures. The AD therefore operates by incorporating the MSB as the operative technical standard for the corrective work. Legal interaction in practice means that regulatory compliance is measured not by the AD text alone but by the AD together with the Turbomeca MSB.

• Cross-reference to DGAC/EASA action. The AD states "Note: DGAC AD F-2004-192 (EASA approval 2004-12118) refers." That records alignment with a DGAC AD that had EASA approval. The presence of that note suggests that the issue was already addressed in DGAC/EASA channels and that CASA's AD is cognate with that foreign regulatory instrument. The AD does not formally incorporate the DGAC AD; it simply refers to it.

• Applicability determined by manufacturer serial-number list. The AD’s applicability criterion depends on the serial-number list in the manufacturer MSB. That creates a dependency: the regulatory obligation is co-extensive with a manufacturer document. Interaction with other laws therefore flows through the MSB: for instance, any operator’s duty to keep maintenance records or to maintain an airworthy aircraft under civil aviation law will intersect with the AD insofar as completing the MSB work is necessary to maintain airworthiness.

• No explicit interaction clauses with other domestic statutes. The AD contains no express statements about its relation to other Australian statutes, administrative processes, or penalty provisions. It does not, for example, invoke a specific statutory power or cite an enabling Act within the text. The instrument is an Airworthiness Directive issued by CASA; the linkage to enabling legislation or the administrative rules under which CASA acts is not reproduced in the AD text itself.

• Record and prior accomplishment clause. The AD’s phrase "Unless previously accomplished" interacts operationally with maintenance-record requirements under general airworthiness rules. If an operator claims prior accomplishment, that claim must be supportable by whatever maintenance-recording rules apply elsewhere. The AD, however, does not specify what constitutes adequate evidence or how to resolve disputes.

• International regulatory alignment. By noting DGAC AD F-2004-192 (EASA approval 2004-12118), the AD situates itself within an international safety information chain. This interaction is primarily informational in the AD, indicating that the same technical issue was recognised by France/EASA and that CASA’s AD is consistent with that recognition.

• No express treatment of operational flight rules or flight manual amendments. The AD notes that the DECU inaccuracy can affect the "Power Assurance Check as specified in the aircraft flight manual" and can affect declared OEI ratings in a part of the flight envelope. However, the AD does not require flight manual amendments or operational limitations; rather, it requires measurement checks and recalibration. Any consequent changes to flight operations or flight manual entries would be matters for the operator and potentially further regulatory action, but such changes are not mandated in the text of the AD.

In sum, the AD’s explicit interactions are with the Turbomeca MSB and the DGAC/EASA AD. It does not itself mention or reproduce enabling legislation, enforcement powers, or other domestic regulatory instruments; those connections lie outside its text and would be handled by CASA policy or broader regulatory frameworks.

The AD text contains internal date stamps and a signature date but shows no textual amendments or subsequent variations within the document itself. The document provides the following dates and references:

• Signature and delegate date: "David Punshon, Delegate of the Civil Aviation Safety Authority" dated "6 January 2005."

• Effective date of the Airworthiness Directive: "This Airworthiness Directive becomes effective on 17 February 2005."

• Compliance deadline: "Before 31 January 2006."

• AD identifier and date: "AD/ARRIEL/20 | Digital Engine Control Unit - Torque Measurements | 2/2005."

• Reference to related foreign AD approval: "DGAC AD F-2004-192 (EASA approval 2004-12118)."

The document repeats the AD identifier and the title in multiple lines. There is no textual indication in the AD itself of any prior or subsequent Australian amendment to AD/ARRIEL/20. The AD does not contain an amendment log or a history section describing changes, nor does it present an insert of amended clauses.

"Unless previously accomplished" is a temporal carve-out in the operative instruction, not an amendment. It permits engines for which the MSB procedures have already been performed to be treated as compliant; it is not framed as an amendment to the AD itself.

The AD refers to MSB A 292 72 2816 for the procedural details and to DGAC AD F-2004-192 (EASA approval 2004-12118) as a related foreign action. Any amendment history to the technical method, the MSB, or to DGAC/EASA actions would be recorded in those documents, not in this AD. The AD does not state whether the MSB itself was amended, nor does it reproduce MSB revision numbers or dates in the text supplied.

Therefore, based on the text of this AD alone, there is no recorded amendment history within the AD. The dates given describe signature, effectiveness and compliance windows, and the AD’s cross-reference to the manufacturer MSB and a DGAC AD. Any later amendments, superseding ADs, revocations, or modifications are not present in the supplied document.

The supplied AD text contains no reference to litigation, court decisions, notices of dispute, administrative reviews or legal challenges. There are no case names, judgments, or administrative rulings mentioned in the instrument. The AD records the technical issue discovered by DGAC and the corrective action required; it does not record any legal proceedings arising from the issue or from the AD.

The only legal-technical references in the AD are to Turbomeca MSB A 292 72 2816, and to "DGAC AD F-2004-192 (EASA approval 2004-12118)." Neither of those is a court decision. The AD is issued by CASA and signed by a delegate, but no litigation or dispute resolution process is described or mentioned.

Therefore, as to litigation history, the document itself records none. Any litigation touching this AD, the MSB, the DECU manufacturer, or the engines would fall outside the AD text and is not captured here.

The AD contains a number of practical traps and points requiring attention; these are stated or implied in the text and deserve careful reading:

• Applicability depends on an external list. The AD's applicability is "Arriel 2S1 turboshaft engines whose Module 01 serial number is listed in Turbomeca Mandatory Service Bulletin (MSB) A 292 72 2816." The serial-number list is not reproduced in the AD. An operator must consult the MSB to determine whether an engine is captured. Failing to consult the MSB or misreading the serial-number list could lead to non-compliance or unnecessary work.

• "Unless previously accomplished" is an operational trigger. The AD exempts engines on which the specified MSB work has already been performed. That requires accurate historical maintenance records proving the MSB work was done, aligning with the MSB's method and scope. Operators relying on claimed prior accomplishment must ensure records corroborate the required actions as stated in the MSB.

• Requirement for a prototype DECU installed in parallel. The AD requires comparative measurements "to those obtained from a prototype DECU, installed in parallel with the production DECU." Practical issues arise: access to a prototype DECU, compatibility, mounting in parallel, and whether the prototype must be sourced from the manufacturer or can be provided by the operator. The AD does not prescribe who supplies the prototype DECU or the chain of custody and calibration status of that prototype unit. That logistical detail is likely contained in the MSB, but the AD's plain text makes the availability of a prototype DECU a prerequisite step.

• Recalculation and recalibration task boundaries. The AD requires recalculating "the new conformation resistance values" and recalibrating "the torque conformation box." The AD does not define acceptable tolerances, calibration standards, or record formats. The MSB is the source of those technical parameters; operators must rely on the MSB's procedural detail to ensure the recalculation and recalibration meet the AD's intent.

• Timeline may create maintenance scheduling pressure. The AD's compliance deadline is "Before 31 January 2006," with an effective date of "17 February 2005." That gives a limited compliance window. Operators must plan bench time, parts, prototype DECU availability and any aircraft downtime to meet that deadline.

• Possible operational effects already present. The AD notes that the DECU inaccuracy "can lead to an overestimation of the torque" up to "27 N.m (3.0% torque)" and that this can cause "a possible overestimation of the power margin during the Power Assurance Check" and "a possible power limitation below the minimum declared levels" of certain OEI ratings "in a limited part of the flight envelope." Those two possible operational effects are distinct: one is an overestimation of margin in checks, which may create complacency in maintenance or flight assurance checks; the other is an actual power limitation relative to declared OEI performance in a limited flight envelope, which could affect operational performance. Operators must consider both implications when assessing operational safety and scheduling corrective work.

• Reference to DGAC/EASA action. The AD notes the DGAC AD F-2004-192 (EASA approval 2004-12118). Operators dealing with multinational fleets or cross-registered aircraft should be aware that the issue has been addressed by other authorities; the practical consequence is that similar technical procedures and approvals may exist elsewhere, which could create different record-keeping or compliance expectations across jurisdictions.

• No penalties or enforcement detail in the AD. The absence of express penalties in the AD does not relieve operators of the obligation to comply. However, because enforcement procedures and consequences are not set out in the AD, operators should not infer the existence or absence of penalties; instead, they should treat the AD as a mandatory corrective measure whose enforcement is governed by CASA processes outside this text.

• The AD does not require flight manual changes. The AD notes adverse performance implications that touch flight manuals ("Power Assurance Check as specified in the aircraft flight manual" and OEI ratings), but it does not itself mandate changes to flight manuals or operational limitations. Operators considering temporary operational mitigations pending corrective work must note the AD does not provide such instructions; any operational changes would be separate actions.

• Document redundancy in the text. The AD reproduces its own header and title lines multiple times. That repetition does not alter the operative instructions but may create minor confusion during record extraction.

• The MSB is the operative technical standard. Operators must obtain and follow Turbomeca MSB A 292 72 2816 exactly to perform the corrective steps required by the AD. The AD is not a substitute for the MSB's detailed procedure.

These "gotchas" are directly grounded in the AD's text and the consequences of its structure and requirements. Operators and maintenance organisations should confirm MSB details, availability of prototype DECU equipment, and the sufficiency of maintenance records showing prior accomplishment.

Compliance under this AD requires a sequence of actions grounded in the AD's operative clauses and in Turbomeca MSB A 292 72 2816. The AD sets out the required tasks; the MSB will contain the procedural specifics. The following is a pragmatic compliance checklist based on the AD text. Each step is grounded in the AD's language.

1. Determine applicability. Obtain Turbomeca Mandatory Service Bulletin A 292 72 2816 and check whether the engine's Module 01 serial number is listed. The AD's applicability is explicit: "Arriel 2S1 turboshaft engines whose Module 01 serial number is listed in Turbomeca Mandatory Service Bulletin (MSB) A 292 72 2816." If the serial number is not listed, the AD does not apply to that engine.

2. Verify prior accomplishment. If the MSB work has been previously performed, document the prior accomplishment. The AD conditions the duty with "Unless previously accomplished." Therefore, assemble and retain maintenance records that demonstrate the MSB procedure was completed previously, including dates, work orders, part numbers, torque measurements and calibration records per the MSB.

3. Schedule the MSB work before the compliance deadline. The AD requires completion "Before 31 January 2006." Plan bench time, facilities and logistics to complete the work within that timeframe. Note the AD's effective date "17 February 2005" and plan accordingly.

4. Procure or arrange for a prototype DECU and resources. The AD requires comparing the production DECU torque measurements to those "obtained from a prototype DECU, installed in parallel with the production DECU." Ensure access to a prototype DECU meeting the MSB's requirements, and confirm compatibility and calibration status. If the MSB specifies supply or loan arrangements with Turbomeca, follow those instructions.

5. Perform the comparative torque check in accordance with the MSB. The AD instructs: "Check the torque measurements made by the production Digital Engine Control Unit (DECU) installed on the engine and compare them to those obtained from a prototype DECU, installed in parallel with the production DECU." Follow the MSB for set-up, test procedures, data logging, environmental conditions, and permissible tolerances. Record all measurement data as required.

6. Recalculate conformation resistance values. The AD requires operators to "Recalculate the new conformation resistance values." Use the computational method, formulas, and reference parameters specified in MSB A 292 72 2816. Capture the input values and calculation outputs in the maintenance record.

7. Recalibrate the torque conformation box. After recalculation, perform recalibration steps for the torque conformation box as specified in the MSB. Ensure calibration standards and instruments meet the MSB-specified criteria.

8. Complete and retain records. Although the AD does not set forth explicit record-keeping language, the exemption for prior accomplishment and the compliance requirement imply that operators should prepare, retain and be able to present complete records of the comparative measurements, recalculation worksheets, recalibration certificates, parts used, and sign-off by authorised personnel. The records should identify the engine Module 01 serial number, the MSB reference, dates, and the person/organisation performing the work.

9. Update maintenance and airworthiness documentation where appropriate. The AD notes that the inaccuracy could affect "Power Assurance Check" results and OEI ratings. If the recalibration or findings require any adjustments to operational procedures or documentation, follow the applicable airworthiness and operator procedures for updating flight manuals, maintenance logs, or operational checks, in accordance with regulatory and operator requirements. The AD itself does not mandate flight manual changes, so any such changes should follow the operator’s normal amendment process and any applicable regulatory approvals.

10. Confirm closure with CASA/oversight body if required. The AD is issued by CASA; if CASA requires formal notification or submission of completion records for ADs, follow the regulator’s established processes for AD compliance reporting. The AD text does not specify a reporting mechanism, so operators should rely on CASA’s standard procedures and guidance for AD compliance reporting.

11. Address any non-standard findings. If comparative measurements show anomalies beyond the ranges addressed by the MSB, follow the MSB’s instructions for reporting, additional corrective actions or contacting Turbomeca. The AD does not provide alternative corrective measures beyond the MSB.

12. Maintain traceability for future audits. Keep the MSB, the AD text, measurement logs, recalculation worksheets and calibration certificates as part of the engine’s maintenance record package to demonstrate compliance and support any future inspections.

Who performs the work and who pays. The operator or owner is responsible for ensuring the work is done and will bear the costs of parts, prototype DECU access, maintenance labour and aircraft or engine downtime. The work must be performed "in accordance with MSB A 292 72 2816" by appropriately authorised personnel and maintenance organisations.

Key practical checks before starting work. Confirm the MSB revision/version that contains the serial-number list and the procedural details. Confirm that the prototype DECU is the unit identified in the MSB. Ensure authorised signatures and sign-off procedures are in place to record compliance. Confirm the planned completion date will meet the "Before 31 January 2006" deadline.

In all steps, operators must follow the exact methods and tolerances in MSB A 292 72 2816 to ensure that the AD’s requirements are satisfied. The AD is the regulatory trigger, and the MSB contains the technical instructions needed to comply.