AD/HS 125/161 Amdt 1 - Oxygen System

The Directive rests on a small set of interlocking technical and administrative concepts. First, the physical problem: cadmium‑plated cone caps and fittings in parts of the oxygen plumbing can undergo a reaction leading to cadmium flaking. The source states that flaking could block valves and thereby impair oxygen system function in an emergency (Background). The AD therefore targets the discrete components identified by Raytheon SBs for replacement with “improved” cone caps or fittings and requires inspection of the removed items and mating parts.

Second, the action hierarchy in the AD: replace, inspect, clean and test, repair. For each model group the AD sets out three parallel obligations:

• a. Replace the cadmium‑plated item with an improved part and perform a detailed visual inspection of the removed item and adjacent plumbing (Requirement 1.a and corresponding items for Requirements 2-4).
• b. If flaking or corrosion is found on inspection, clean the affected tee‑piece, sleeve or pipe connections and then perform an oxygen system flow check in accordance with the SB (Requirements 1.b, 2.b, etc.).
• c. If the flow check shows a discrepancy, repair the system in accordance with the SB, except where the SB specifies to contact the manufacturer , in that case the AD requires repair in accordance with a method approved by the Manager, Technical Specialists Section, Certification Standards Branch, CASA (Requirement paragraphs and following text).

Third, the AD anchors compliance to OEM documentation: the Service Bulletins are the operative technical standard for both the replacement parts and for the flow check and repair procedures. The AD explicitly names the SB numbers and dates for each model group, thereby incorporating those SB procedures by reference (Applicability table). That makes the SBs the central source of technical detail; the AD prescribes timelines and the fallback approval process when the SB requires manufacturer disposition.

Fourth, inspection standardisation: the Directive defines “detailed visual inspection” for the purposes of this AD (Note 1). The definition requires an intensive visual examination, with supplemental direct lighting as appropriate, and allows inspection aids such as mirrors and magnifying lenses; it notes that surface cleaning and access procedures may be necessary. That definition raises the qualitative standard for the inspection step and sets expectations about inspector competence and tools.

Fifth, temporal constraints and operational effect. The AD distinguishes two time bands: the replacement work must be completed within six months of the Directive’s effective date (Requirement a. items for treatments 1-4), while any remedial cleaning, flow checks and repairs identified by inspection must be completed before further flight (Requirements b. and c.). This sequencing makes the initial replacement a scheduled maintenance event; any defects found convert to immediate grounding or restriction until resolved.

Sixth, administrative exception and escalation: where the SB instructs to contact the manufacturer for repair disposition, the AD requires an alternative repair method be approved by the Manager, Technical Specialists Section, Certification Standards Branch, CASA (the AD provides that office’s postal and facsimile contact details). That creates a defined administrative pathway for non‑SB dispositions and places decision authority for such exceptions within CASA’s Certification Standards Branch.

Finally, the AD cross‑references FAA action: Note 2 refers to FAA AD 2000‑02‑35 Amendment 39‑11553. The Amendment 1 corrects a typographical error in the FAA AD reference (Background). Thus the AD functions within an established international airworthiness coordination framework, translating an FAA/OEM problem report and SB response into Australian mandatory action.

Together these concepts produce a regulatory instrument that takes an OEM diagnosis and SB remedy and makes it compulsory for Australian‑registered aircraft of the listed models, with specified timing and with CASA oversight where the SB requires manufacturer contact.

The Directive directly affects owners and operators of the listed BAe 125 series aeroplanes and specified Hawker models identified in the Applicability table. The text lists model groups and the associated Raytheon SBs; for example it covers DH.125, HS.125, BH.125 series 1A, 1B, 3A, 3B, 400A, 400B, 401B, 403A, 403B, 600A, 600B, 700A and 700B under SB 35‑3169 (September 1998), BAe.125 series 800A (C‑29A) under SB 35‑3171, BAe.125 series 800A/800B and Hawker 800 under SB 35‑3034 or SB 35‑3170, and BAe.125 series 1000A/1000B and Hawker 1000 under SB 35‑3167 or SB 35‑3168 (Applicability table). Any aircraft not listed in those model groups is not covered by this particular AD as written.

Those directly affected include:

• Aircraft owners and operators who must schedule and pay for the replacement of cadmium‑plated fittings with improved parts within the stated six‑month window (Compliance section).
• Maintenance organisations and certificated maintenance engineers who must perform the detailed visual inspections, cleanings, oxygen system flow checks and repairs in accordance with the appropriate SBs; they must also be capable of meeting the defined standard for a “detailed visual inspection” (Note 1).
• Parts suppliers and manufacturers of the “improved” cone caps or fittings, since the Directive requires replacement with improved parts specified in the SBs.
• Raytheon Aircraft (the SB issuer) because the AD incorporates and enforces their SBs as the operative technical specification and because the AD references Raytheon’s field survey and report as the source of the identified problem (Background).

Indirectly affected parties include aircraft operators’ flight crews and passengers because the AD addresses a failure mode that could impair oxygen delivery in emergency conditions; and insurers, lease holders and financiers where aircraft grounding or mandatory modifications affect operational availability and asset condition.

The Directive also assigns decision authority to CASA’s Manager, Technical Specialists Section, Certification Standards Branch where the SB specifies contacting the manufacturer for repair disposition. That makes CASA personnel active decision‑makers for any repair paths not strictly outlined in the SBs (see the paragraph providing the CASA contact details for approval).

Finally, the AD’s compliance requirements create time and capability demands on operators and maintenance providers: the six‑month replacement window is a scheduled obligation, while any required cleaning, flow testing and repair must be completed before further flight, which can impose immediate grounding and associated commercial consequences. Those obligations fall on the operator as the compliant party; the Directive does not shift primary responsibility for compliance to the OEM or to third parties.

Key duties imposed by the AD are explicit and procedural. The primary duties are:

• Replace cadmium‑plated cone caps or fittings with improved cone caps or fittings as specified in the applicable Service Bulletin. This is Requirement 1.a (and the equivalent a. paragraphs for Requirements 2, 3 and 4). The replacement for each affected model group must follow the indicated SB (for example SB 35‑3169 for the DH.125 family; SB 35‑3171 for the series 800A C‑29A; SB 35‑3034 or SB 35‑3170 for certain 800 series and Hawker 800 models; SB 35‑3167 or SB 35‑3168 for 1000 series and Hawker 1000).

• Conduct a “detailed visual inspection” of the removed items and relevant adjacent plumbing (tee‑piece, sleeve or pipe connections) for flaking or corrosion, immediately after removal during the replacement activity. Note 1 defines the standard and required aids for such inspection.

• Where flaking or corrosion is present, clean the affected tee‑piece, sleeve or pipe connections and perform an oxygen system flow check in accordance with the applicable SB (Requirement b. for each model group).

• If the flow check reveals a discrepancy, effect repairs in accordance with the SB. Where the SB specifies contacting the manufacturer for repair disposition, the AD requires repair in accordance with a method approved by the Manager, Technical Specialists Section, Certification Standards Branch, CASA; the AD provides the postal address and facsimile number for that office (Requirement c. and the paragraph addressing manufacturer repair disposition).

Timing duties are also explicit:

• The replacement step (the a. items) must be done within six months of the Directive’s effective date.
• Any cleaning, flow check and repairs triggered by inspection must be completed before further flight (Compliance section).

Rights and administrative processes set out by the AD include:

• The right to seek an alternative, CASA‑approved repair method where the SB instructs to contact the manufacturer for repair disposition. The AD identifies the Manager, Technical Specialists Section, Certification Standards Branch, CASA as the approving authority and gives contact details. That provides a defined procedure for obtaining regulatory approval of non‑SB repair methods where the SB directs consultation with the manufacturer.

• Implicitly, operators and maintainers have the right to use the SBs as the technical standard for the prescribed works because the AD directs repairs and checks “in accordance with the SB.” The SB therefore functions as an incorporated technical contract between operator/maintainer and regulator.

The Directive places no express procedural burden on Raytheon other than its SBs being the operative technical references and the background citation that Raytheon reported the issue to the FAA (Background). The AD does not allocate liability or indemnity in its text.

Recordkeeping is not specified in the Directive, nor are appeals or dispute mechanisms set out within the AD itself. However, the AD’s requirement that repairs be in accordance with the SB or approved by CASA means that operators have an administrative pathway to seek approval for alternative repair methods through the CASA Certification Standards Branch contact identified in this AD.

Finally, the AD corrects a typographical error in a referenced FAA AD (Background). That correction is administrative but clarifies the international cross‑reference on which the AD’s background rests.

The text of this AD does not specify civil or criminal penalties, nor does it set out an enforcement procedure or sanctions schedule. The Directive is issued by the Civil Aviation Safety Authority (the document is signed by a CASA delegate) and sets mandatory technical and timing requirements for specified aircraft, but the AD itself contains no clause imposing fines, licence suspensions or similar penalties within its own text.

Operational enforcement is manifest, however, through the compliance timings and “before further flight” conditions. The AD requires that where a detailed inspection reveals flaking or corrosion, and where flow checks reveal discrepancies, repairs must be completed before further flight (Requirement b. and c., Compliance section). That requirement creates an immediate operational constraint: an aircraft with such a discrepancy must be restored to compliance before it is permitted to fly. The Directive therefore creates an immediate ground‑for‑action in practical terms, even though it does not itemise legal penalties in the document.

Where the SB advises contacting the manufacturer for repair disposition, the AD requires any non‑standard repair to be approved by the Manager, Technical Specialists Section, Certification Standards Branch, CASA (the AD provides address and facsimile details). That creates an administrative control point through which CASA may authorise or deny alternative repair methods. The AD does not describe the criteria or process CASA will use to grant approvals, nor does it specify timelines for those approvals.

Because the AD does not itself state enforcement mechanisms, affected parties who need clarity on legal consequences should consult the broader CASA regulatory framework and relevant civil aviation safety legislation and regulations for enforcement mechanisms applicable to non‑compliance with CASA ADs. The Directive’s Background and Compliance sections indicate the AD’s effective date and the original AD’s effective date, and the Amendment is signed by a CASA delegate, which evidences that the Directive is an instrument issued under CASA authority. The AD does not mention judicial review or appeals of CASA decisions, nor does it reference administrative penalty provisions within its own text.

In practice, the operational consequence of the “before further flight” requirement is that an operator cannot continue operations with a known flaking or flow‑check discrepancy, thereby enforcing corrective maintenance by preventing flight until the required remedial action is completed. Where an operator disagrees with CASA’s approval decision for an alternative repair method, the AD does not describe an internal dispute resolution process; those procedures (if any) would be found in the administrative framework under which CASA operates and are not included in this Directive’s text.

The AD explicitly integrates and cross‑references non‑Australian materials, and by its nature is an instrument that sits in a network of technical and regulatory instruments. The Directive refers to Raytheon Aircraft Service Bulletins (SBs) as the operative technical standards for the replacement, inspection, flow test and repair procedures; the AD therefore operationally incorporates those SBs into the Australian regulatory requirement for the listed aeroplane models (Applicability table; Requirement paragraphs). Because the SBs are the specified technical standards, the AD makes compliance with those SBs necessary for compliance with the Directive.

The AD also cross‑references an FAA Airworthiness Directive: Note 2 and the Background correct the FAA AD reference to FAA AD 2000‑02‑35 Amendment 39‑11553. The Background expressly states that the FAA advised Raytheon and that Raytheon received reports of the cadmium reaction. That places the Australian AD in an international safety coordination context: the AD implements in Australia the safety response that originated in OEM/FAA reporting and SB issuance. The AD does not, however, incorporate the FAA AD text into its own obligations; it merely cites the FAA AD as a cross‑reference and corrects the citation.

The AD names the CASA Certification Standards Branch, Manager, Technical Specialists Section as the approving authority for alternative repair methods where the SB specifies contacting the manufacturer. That sets an administrative linkage: the CASA office referenced is the decision maker for alternative repair dispositions. The AD supplies that office’s postal and facsimile contact details, making an administrative interface explicit. The AD does not, however, reproduce CASA’s wider regulatory powers or prescribe the criteria for approval; those would be dependent on CASA’s broader legislative and regulatory frameworks that are not contained in the AD text itself.

The Directive interacts implicitly with an operator’s continuing airworthiness obligations. By setting “before further flight” and “within six months” compliance requirements, the AD creates operational constraints that will intersect with maintenance scheduling regulations and operational permission regimes; the AD does not cite the underlying statutory provisions that give CASA the authority to issue ADs, nor the enforcement mechanisms for non‑compliance. Thus, the technical obligations in the AD will be enforced through CASA’s normal administrative and regulatory apparatus, which is external to this particular document.

Because the AD mandates repair in accordance with SBs, it also interacts commercially with the Service Bulletin author (Raytheon) and with aftermarket parts suppliers who provide the improved fittings. The AD makes the SBs the normative technical standard; vendors and maintenance organisations will follow the SBs to satisfy CASA’s requirement. That means the AD functions as a point of regulatory incorporation of private technical guidance.

Lastly, the AD’s correction of the FAA AD citation (Background) is an instance of formal harmonisation of international safety documentation. The AD does not alter other Australian legal instruments but is part of the broader regulatory architecture in which CASA adopts or mandates technical measures that arise from OEM reporting and foreign authority ADs.

This instrument is labelled AD/HS 125/161 Amendment 1 and dated 19/2013. The Amendment 1 is explicit in its stated purpose: it corrects a typographical error in Note 2 of the Requirement Section, changing the FAA AD reference from the incorrectly cited FAA AD 2000‑03‑35 to the correct FAA AD 2000‑02‑35 (Background). The Amendment 1 does not change the substance of the original airworthiness requirements; the Background expressly states “There is no change to initial requirements of the AD.” In other words, Amendment 1 is a technical correction, not a substantive revision to the compliance obligations.

The effective date for Amendment 1 is stated as 10 September 2013 (Compliance; effective date line), and the document bears the signature of a CASA delegate, Mike Higgins, dated 5 September 2013. The Directive also records the original issue date: the original AD became effective on 23 March 2000 (Background). The AD therefore has an initial issuance in 2000 and a narrow amendment in 2013 correcting an FAA AD cross‑reference.

The amendment log in the AD is limited to this single correction and an associated note about the FAA AD reference. The AD’s Background section describes the technical genesis of the Directive,namely FAA advisement and Raytheon reporting of cadmium flaking in oxygen fittings,which predates the SBs that are dated September 1998. The SBs themselves are the OEM technical responses, and the AD implements those SBs as mandatory requirements for the listed aircraft in Australia. The Amendment 1 does not add models, change SB references, alter timing, or modify inspection or repair requirements.

There are no other amendment entries, rescissions or superseding ADs recorded in the provided text. The AD therefore appears as an original AD (effective 23 March 2000) with a single narrow Amendment 1 (effective 10 September 2013) addressing a typographical error in the FAA AD reference. The AD states that there is no change to the initial technical requirements, which is consistent with the correction being limited to cross‑reference accuracy.

For historical or compliance searches, the SB numbers and dates (September 1998) remain central because the AD continues to mandate compliance with those SBs. Operators should note that the AD text points to those specific SBs as the operative technical standards and should ensure they source the correct SB versions referenced in the AD when executing the required maintenance.

The AD as provided contains no litigation history and does not reference any judicial decisions or administrative appeals. The document includes no mention of legal challenges, court proceedings, or contested administrative decisions relating to the AD or to its subject matter. The Background and amendment notes reference technical reporting by Raytheon and the FAA, but there is no record in the Directive of disputes or litigation arising from the AD’s issuance or implementation.

Because the text does not state any litigation outcomes or ongoing disputes, there is nothing in this Directive to analyse in terms of case law or judicial interpretation. The AD also does not set out an appeal process or judicial review mechanism within its own text; matters of dispute over CASA approvals, denial of alternative repair methods, or alleged non‑compliance would need to be pursued, if at all, under the general administrative and judicial frameworks applicable to CASA decisions, which are not described in the AD.

Practitioners seeking precedent on enforcement or disputes arising from this type of AD will need to consult external sources,CASA enforcement records, relevant administrative tribunal or court decisions, or other case law relating to CASA ADs. The Directive itself contains no litigation record or cross‑references to judicial determinations. In short, the provided AD includes no litigation history to cite or analyse.

Several practical and legal pitfalls are embedded in the AD’s text and structure; these are concrete operational and administrative considerations that can catch operators or maintainers if overlooked:

• Model and SB specificity. The AD does not apply to all BAe 125 variants by generic name; applicability is defined by specific model lists paired with specific SB numbers. Operators must match their aircraft to the exact model series and the SB number/date listed. For example, DH.125/HS.125/BH.125 series are tied to SB 35‑3169, while certain 800 series or Hawker models are tied to SB 35‑3034, SB 35‑3170, SB 35‑3171, or the 1000 series to SB 35‑3167/35‑3168 (Applicability table). Failure to identify the correct SB for a given tail number could lead to non‑compliance.

• “Detailed visual inspection” has a heightened standard. Note 1 defines “detailed visual inspection” as intensive, with supplemental lighting and allowance for inspection aids, surface cleaning and elaborate access procedures. Maintenance personnel who treat this as a cursory examination may miss the required standard. The AD’s definition increases labour time and possibly access costs because removable panels or disassembly may be required to attain the “detailed” standard.

• Timing split: scheduled versus immediate. Replacement of cadmium parts must be completed within six months, but any required cleaning, flow checks and repairs identified during or after inspection must be completed before further flight (Compliance). An operator may schedule the replacement within six months, but if an inspection during that work reveals flaking and a flow check shows discrepancy, the requirement to repair before further flight could ground the aircraft until repairs are effected. That creates a risk of unexpected downtime.

• SB dependence and scope of repairs. The AD requires repairs “in accordance with the SB,” except where the SB specifies contacting the manufacturer for repair disposition. Where the SB directs manufacturer contact, the AD requires a CASA‑approved method. Operators must therefore examine the SB language carefully: if the SB expressly requires manufacturer consultation, the repair path requires CASA approval of any alternative. That can create administrative delay and uncertainty.

• Contact and approval pathway. The AD provides a single CASA contact for approval of alternative repair methods (Manager, Technical Specialists Section, Certification Standards Branch) with a postal address and fax number. The AD does not provide email, turnaround times, or criteria for approval. Relying on fax and postal pathways can create operational delay in urgent situations, and the AD does not set out emergency procedures or interim relief.

• Parts supply and “improved” parts. The AD requires replacement with “improved” cone caps or fittings as specified by the SBs. Operators must source those improved parts. The AD does not discuss authorised sources, parts numbering, or aftermarket approvals; hence operators must ensure the parts used match the SB specifications to avoid non‑compliance.

• Recordkeeping and proof. The AD does not include a recordkeeping clause specifying what records must be kept or for how long, nor does it identify an inspection certificate or log entry requirement. That absence does not negate the practical need to keep clear evidence of compliance because the AD imposes technical obligations that CASA may require proof of; operators should therefore anticipate the need to document replacement, inspection and flow checks even though the AD does not describe record formats.

• Correction is narrow: typographical only. Amendment 1 corrects an FAA AD reference but does not change the technical or timing requirements (Background). Operators should not assume Amendment 1 relaxes or changes obligations.

• International coordination. The AD references FAA AD 2000‑02‑35 as corrected. For operators involved in international operations or with foreign registries, differences in AD wording, SB revisions, or later FAA/CASA actions may complicate compliance strategies; the AD does not integrate any subsequent SB revisions or later FAA ADs.

• No penalty text. The AD itself contains no penalty text. That is not the same as absence of enforceability; however, the lack of explicit penalty provisions increases the importance of understanding CASA’s broader enforcement framework to assess legal risk of non‑compliance.

• Potential for mis‑matching SB versions. All SBs cited are dated September 1998. Operators must ensure they apply the exact SB revision referenced by the AD; later SB revisions may exist but are not automatically incorporated by this AD unless the AD is amended to reference them.

These “gotchas” translate into concrete operational steps: verify the exact model and SB applicability for each aircraft; use maintenance personnel competent in “detailed visual inspection” procedures; allow contingency time and budget for immediate repairs that may be required before further flight; ensure improved parts are available and meet the SB specification; and use the CASA approval pathway where the SB directs manufacturer contact, accounting for potential administrative delay.

To comply with AD/HS 125/161 Amdt 1, follow a structured, evidence‑based workplan that tracks the AD’s explicit steps, timing and approval pathways. The AD itself provides the operative requirements; the following is a practical sequence distilled from the Directive text.

1. Confirm applicability.

• Identify each aircraft by model/series and confirm whether it appears in the AD’s Applicability table. Cross‑check against the SB numbers referenced (for example SB 35‑3169 for DH.125/HS.125/BH.125 series; SB 35‑3171 for BAe.125 series 800A (C‑29A); SB 35‑3034 or SB 35‑3170 for certain 800 series and Hawker 800; SB 35‑3167 or SB 35‑3168 for 1000 series/Hawker 1000).
• Only aircraft listed against an SB in the Applicability table are covered by this AD as written.

2. Obtain the applicable Service Bulletin(s).

• Acquire the exact Raytheon SB(s) referenced by the AD (all SBs cited are dated September 1998). The AD mandates actions “in accordance with the SB,” so having the correct SB text is necessary to perform the required replacement, inspection, flow check and repair procedures.

3. Plan the replacement within the six‑month window.

• The AD requires the replacement step (Requirement a. items) be completed “within 6 months after the effective date of this Directive.” The Amendment effective date is 10 September 2013; for compliance planning, use the AD’s effective date relevant to your fleet and registration circumstances (see Compliance timings).
• Schedule the replacement during a maintenance slot within that six‑month window, accounting for potential additional tasks that may arise from inspections.

4. Perform replacement and detailed visual inspection.

• Replace the cadmium‑plated cone caps or fittings with the improved parts as specified in the applicable SB (Requirement a.).
• Immediately after removal, perform a “detailed visual inspection” of the removed cone caps or fittings and of the tee‑piece, sleeve or pipe connections for flaking or corrosion, following the AD’s Note 1 definition: intensive visual examination, supplemented lighting, use of inspection aids such as mirrors and magnifying lenses, and surface cleaning and access procedures as required.

5. Where flaking or corrosion is found, clean and flow‑check.

• If the inspection identifies flaking or corrosion, clean the affected tee‑piece, sleeve or pipe connections, and perform an oxygen system flow check in accordance with the SB (Requirement b.). The flow check procedure will be detailed in the SB.

6. Repair any discrepancies before further flight.

• If the flow check reveals any discrepancy, repair the oxygen system in accordance with the SB (Requirement c.). Repairs must be completed before further flight. Do not return the aircraft to service with unresolved discrepancies revealed by the flow check.

7. If the SB directs manufacturer contact, obtain CASA approval for repair method.

• Where the applicable SB specifies that the manufacturer must be contacted for repair disposition, the AD requires repair according to a method approved by the Manager, Technical Specialists Section, Certification Standards Branch, CASA. The AD provides the contact details: Manager, Technical Specialists Section, Certification Standards Branch, Civil Aviation Safety Authority, GPO Box 2005 Canberra ACT 2601, Facsimile (02) 6217 1914.
• Prepare and submit the technical repair disposition documentation to CASA if the SB so directs, and do not proceed with an alternative repair method until CASA has approved it.

8. Document the work.

• Although the AD does not prescribe a recordkeeping format, retain traceable evidence of compliance: SB revision used, replacement parts (part numbers/serials where applicable), inspection findings (with photographs if appropriate), flow check reports, description and evidence of any repairs, and any CASA approvals obtained for alternative repair methods. Documentation will be essential to demonstrate compliance in the event CASA requests evidence.

9. Coordinate parts procurement and maintenance resources.

• Source the “improved” cone caps or fittings according to SB specifications. Confirm part numbers and ensure authorised parts are procured. Coordinate maintenance personnel who are competent to perform the “detailed visual inspection” and oxygen flow testing as specified in the SB.

10. Manage operational risk and scheduling.

• Plan for contingencies: an initial replacement within six months may still uncover flaking that triggers “before further flight” repairs. Allocate sufficient labour time and possible spare parts, and consider scheduling the replacement during a maintenance downtime to reduce the commercial impact of any unexpected grounding.

11. Review for SB revisions or subsequent ADs.

• The AD references specific SBs and a corrected FAA AD reference. Confirm there have been no later ADs or SB revisions that amend the required procedures or parts list relevant to your aircraft; the AD itself does not incorporate later SB revisions unless the AD is amended to do so.

12. Legal and compliance advisory.

• If there is uncertainty about whether a repair method complies with the SB, or if manufacturer contact is required by the SB, engage with the CASA Technical Specialists contact provided in the AD and obtain written approval for any alternative repair disposition. Keep a clear record of communications with CASA for auditability.

Following this sequence aligns maintenance work with the AD’s explicit steps: replacing the cadmium‑plated parts per the SB within the six‑month period, applying a high‑standard “detailed visual inspection,” cleaning and flow testing when flaking is found, and repairing any discrepancies before further flight in accordance with the SB or CASA‑approved method where required. The AD’s explicit compliance timings and CASA approval pathway are the operative constraints; adhering to them and maintaining documentary evidence of performance will support regulatory compliance.