The AD uses a set of aviation-specific technical and regulatory concepts. Understanding these concepts is necessary to map the AD’s requirements to concrete compliance steps and to anticipate operational consequences.

Affected hardware and configurations

• Transponder models and P/Ns: The AD identifies Rockwell Collins TDR-94 and TDR-94D transponders and lists specific current part numbers in Table 1 (622-9352-007, -008, -108 for TDR-94; 622-9210-007, -008, -108 for TDR-94D). The AD prescribes either modification (per Rockwell Collins Service Bulletins in Tables 2 and 3) or replacement with listed new P/Ns (622-9352-309 or -409, and 622-9210-309 or -409).
• ADC link and Selected Altitude: Applicability is conditional on the Honeywell AZ800 or AZ810 ADC providing Selected Altitude via the data bus interface to the transponder. The AD targets installations where the ADC is the source of the Selected Altitude parameter for the Mode S transponder.

Mode S Selected Altitude parameter

• The Mode S Selected Altitude is a transponder parameter transmitted in label 102, with a Motion Bit (Selected Altitude in Motion) that the AD says can be mismatched between ARINC and GAMA specifications, producing potentially incorrect transmitted values. The AD’s corrective measures focus on ensuring correct encoding and/or preventing transmission of incorrect Selected Altitude.

Two remediation routes (technical compliance options)

• Modify existing transponder per Rockwell Collins SBs (Requirement 1.a, Tables 2 and 3). Tables identify the Rockwell Collins SB references (for example TDR-94/94D-34-505, -506, -507 “as in force from time to time”) and map current P/Ns to new P/N options.
• Replace transponder with specified new P/N under an approved aeroplane modification (Requirement 1.b). The AD requires that replacement be effected “in accordance with an approved aeroplane modification”.

ADS-B functionality control

• Note 2 imposes a direct functional control: where operators install transponders with P/N 622-9352-409 (TDR-94) or 622-9210-409 (TDR-94D), they must disable ADS-B on those units unless they can demonstrate compliance with EASA AMC 20-24 (or CS-ACNS) or FAA 14 CFR 91.225 and 91.227. The AD therefore links avionics hardware choices to aviation surveillance capabilities and to external certification standards.

Installation prohibition and spares management

• Requirement 3 prohibits installation of affected transponders in aeroplanes with Honeywell AZ800/AZ810 ADC providing Selected Altitude unless the transponder has been modified per Requirement 1.a. That prohibition affects the use of spare/rotable units and maintenance inventory practices.

Exemptions tied to original aircraft architecture

• Notes 3 and 4 provide carve-outs for ATR 42/72 and certain DHC-8 aircraft where, on original architecture, Selected Altitude is not supplied by the ADC. The exemptions do not apply if the aircraft have been modified to enable a digital link between the ADC and transponder.

Document currency and versioning requirement

• The AD repeats the phrase “as in force from time to time” for Rockwell Collins SBs and EASA/FAA references (Note 2), explicitly requiring the operator to use the most recent version of referenced documents. This creates an ongoing obligation to use updated SBs and standards when carrying out the modification.

Schedule and enforcement modality

• The AD sets a primary compliance window of 60 days for Requirement 1 from commencement (Commencement: 10 September 2021; Compliance: within 60 days), requires ADS-B disabling (Requirement 2) to be concurrent with the modification, and forbids certain installations immediately after commencement (Requirement 3, “After the commencement date”). The AD does not state penalty amounts but is an enforceable safety directive issued by CASA’s delegate.

Source-linked cross-reference to EASA

• The AD expressly states it is based on EASA AD 2009-0173R1 (Note 5), and it pulls in outside certification standards as the gating documents for continued ADS-B operation. Hence compliance is not purely about following a local SB; it may require demonstrating interoperability with international surveillance and certification criteria.

Together, the AD maps a technical interoperability error (Selected Altitude motion bit mismatch) into a discrete set of hardware-modification or replacement decisions, operations-affecting controls on ADS-B, and inventory/installation constraints. The key mechanisms are: (a) either apply a vendor SB or (b) install a listed replacement P/N under approved modification; (c) disable ADS-B on certain replacement P/Ns unless broader certification criteria are met; and (d) ban reinstallation of unmodified units where ADC supplies Selected Altitude.

The AD allocates costs, duties and decision rights across a set of actors. Primary and secondary affected parties are:

Aircraft operators (airlines, charter operators, corporate operators)

• Directly affected when their aeroplanes have Rockwell Collins TDR-94 or TDR-94D transponders (listed P/Ns) installed in combination with Honeywell AZ800/AZ810 ADCs that provide Selected Altitude. Operators are the parties responsible for ensuring compliance within the 60-day window for Requirement 1 and for taking the concurrent ADS-B actions required by Requirement 2. Operators pay for parts, labour, maintenance facility time, and operational downtime.
• Operators also face an installation prohibition (Requirement 3): they must not reinstall affected transponders in the specific ADC-connected configuration unless the units are modified per Requirement 1.a.

Maintenance organisations and approved maintenance engineers

• Approved maintenance organisations (AMOs), Part 145 organisations, and licensed maintenance engineers will execute the modifications or replacements. They must source the correct Rockwell Collins Service Bulletins, apply the latest revisions (“as in force from time to time”), and perform the aeroplane modification in an approved manner. They bear operational risk if they fail to apply the correct SB version or do not perform the required post-modification documentation.

Design approval holders and engineering authorities (CAMOs, design organisations)

• Where replacement is effected “in accordance with an approved aeroplane modification” (Requirement 1.b), design approval holders or organisations authorised to carry out approved modifications must produce the approved change. They are responsible for the engineering substantiation of the replacement and for ensuring that the new P/N+installation meets certification and continuing airworthiness obligations.

Spare parts suppliers and supply chain participants

• Suppliers holding inventory of the affected P/Ns (622-9352-007, -008, -108, 622-9210-007, -008, -108) must note that those units may not be reinstalled in certain configurations (Requirement 3). Operators and operators’ parts managers must assess rotables pools and parts exchanges to prevent inadvertent non-compliant installations.
• Suppliers of replacement units (622-9352-309, -409, 622-9210-309, -409) are in commercial position to benefit from replacement demand; however, selection of P/N 409 carries the technical consequence in Note 2 (ADS-B disablement unless compliance with the listed standards is demonstrated).

Air navigation service providers and air traffic management stakeholders

• Disabling ADS-B on some units (Note 2) reduces (or changes) ADS-B-derived surveillance data from affected aircraft. Where ADS-B is disabled, operators or ATC may need alternative surveillance sources (radar, SSR). The AD does not itself mandate airspace-level restrictions, but ADS-B disabling is operationally relevant to ANSPs and may affect an operator’s access to ADS-B required airspace.

Regulator and compliance authority (Civil Aviation Safety Authority)

• CASA (through its delegate who signed the AD) is the issuing authority. Operators must meet the AD’s requirements; CASA enforces airworthiness directives under its regulatory framework. The AD itself does not list monetary penalties but is an enforceable instrument in the CASA oversight regime.

Aircraft types and model-specific operators

• The AD lists examples of aircraft models on which the affected combinations are known to be installed (Table 1 and Note 1): ATR 42/72 series, Bombardier CL-600 variants, DHC-8 series 100/200/300, Dassault Mystère-Falcon 900, Gulfstream G-IV, and others. Operators of these models should check their installations against the Applicability statement.
• The AD also gives exemptions (Notes 3 and 4) for ATR 42/72 and certain DHC-8 aircraft where the aircraft’s original architecture does not supply Selected Altitude from the ADC; these operators may be unaffected unless their installation has been modified to provide a digital link between ADC and transponder.

Manufacturers and service bulletin authors

• Rockwell Collins (transponder manufacturer) and Honeywell (ADC manufacturer) are implicated because the AD requires Rockwell Collins Service Bulletin work and depends on the ADC/transponder interface. The AD compels operators to follow Rockwell Collins SB instructions and to use the most recent version.

Legal and commercial consequences by role

• Who pays: aircraft operators incur direct costs for parts, labour and downtime. Maintenance organisations may incur costs to source and apply SBs and to schedule work. Parts suppliers may shoulder inventory-management costs. Who decides: the operator or its CAMO chooses between modification per SB or replacement under approved modification, subject to availability of parts, maintenance capacity and operational needs. CASA decides enforcement and may respond to non-compliance.

Concentrated versus diffuse impact

• The burden is concentrated on operators that actually have the specific P/Ns in the specified ADC configuration. The cost is diffuse across parts suppliers, AMOs and potentially ANSPs if surveillance capability is affected. For operators without the identified hardware or without the ADC-provided Selected Altitude architecture, the AD imposes little or no direct cost.

Information and documentation obligations

• The AD requires using the most recent SBs and references to EASA/FAA standards “as in force from time to time” (Note 2). This creates an ongoing evidence obligation: operators and maintainers must hold the current SB version used to demonstrate compliance and, where ADS-B is to remain enabled on replacement P/N 409 units, must hold documentary evidence of compliance with the referenced EASA or FAA standards.

Timing and urgency

• The 60-day window from the commencement date (10 September 2021) is a short compliance timeline. Operators must triage aircraft, parts and maintenance availability quickly to meet this schedule.

In short, practical actors who must mobilise compliance are aircraft operators, their CAMOs, maintenance organisations, and design approval holders. The AD’s specific P/N list concentrates impact on a subset of fleets and gives manufacturing/service bulletin-based remediation routes and constraints on ADS-B functionality that translate into operational and commercial decisions.

The AD spells out discrete duties for operators, maintenance organisations and design approval holders. It does not set out rights in the human-rights sense but establishes procedural obligations that confer certain implementation choices. This section lists the duties and the practical scope of each.

Duties imposed by the AD

1. Identify applicability and affected units (duty to assess)

• Operators must determine whether their aeroplanes have the specified Rockwell Collins TDR-94 or TDR-94D transponders (P/Ns listed in Table 1) and whether a Honeywell AZ800 or AZ810 ADC provides Selected Altitude to the transponder. This assessment is the prerequisite to compliance because the AD’s requirements are conditional on that configuration (Applicability and Table 1).

2. Remediate affected transponders within 60 days (Requirement 1, Compliance)

• Primary duty: within 60 days after the AD commencement (commencement 10 September 2021), an operator must either: a) modify the transponder in accordance with the applicable Rockwell Collins Service Bulletin listed in Tables 2 and 3 (Requirement 1.a), or b) replace the transponder with the listed TDR-94/TDR-94D P/Ns (622-9352-309/-409 or 622-9210-309/-409) under an approved aeroplane modification (Requirement 1.b).
• The AD requires use of the Rockwell Collins SB instructions “as in force from time to time” (Note 2), so the most recent SB revision must be applied.

3. Disable ADS-B on specified replacement P/Ns unless compliance demonstrated (Requirement 2 / Note 2)

• If an operator uses replacement P/N 622-9352-409 or 622-9210-409, the AD requires disabling the ADS-B function on those units unless the operator can demonstrate compliance with one of the listed standards: EASA AMC 20-24, EASA CS-ACNS, or FAA 14 CFR 91.225 and 91.227. Compliance with the “as in force from time to time” version of those documents is required.

4. Prohibit installation of unmodified units in affected ADC installations (Requirement 3)

• After the commencement date, the AD bars installation of the transponders identified in the Applicability statement in an aeroplane equipped with Honeywell AZ800/AZ810 ADC providing Selected Altitude unless the transponder has been modified in accordance with Requirement 1.a. This affects use of spares and rotables.

5. Use current versions of referenced documents (Note 2)

• The AD’s repeated “as in force from time to time” language creates an ongoing duty: when performing the SB-based modification or demonstrating compliance for ADS-B enablement, the operator/organisation must use the most recent versions of the relevant SBs and EASA/FAA documents.

6. Concurrent action on ADS-B (Compliance for Requirement 2)

• Requirement 2 must be completed concurrently with the accomplishment of the Requirement 1 modification of the aeroplane. This synchronisation duty means ADS-B disablement (or compliance demonstration) must be addressed at the time of the hardware change.

7. Verify exemption applicability where claimed (Notes 3 and 4)

• Operators seeking to rely on the ATR or DHC-8 exemptions must verify that their aircraft retain the original architecture in which the Selected Altitude is not supplied by the ADC. The exemption does not apply if a modification has enabled a digital link between the ADC and transponder.

Rights, choices and decision paths (practical implications)

1. Choice of remediation path

• The AD gives a clear choice: modify the existing transponder per SBs (1.a) or replace the transponder under an approved aeroplane modification (1.b). The operator decides which route to follow based on cost, parts availability, maintenance scheduling and operational needs.

2. Choice regarding replacement P/N that affects ADS-B

• The operator can choose replacement P/N 309 or 409 where both are listed as “new P/N (options)”. The practical difference is that if the operator chooses the 409 option they must disable ADS-B unless they can demonstrate compliance with the EASA or FAA standards (Note 2). That creates a trade-off the operator can control.

3. Ability to rely on exemptions where applicable

• Operators of ATR 42/72 and certain DHC-8 aircraft may rely on the AD’s Notes 3 and 4 exemptions if the aircraft’s original architecture does not supply Selected Altitude via ADC. That grants relief to particular operators but requires verification. The right is conditional and revocable if the aircraft has been modified to enable a digital link.

4. Duty to obtain approved aeroplane modification for replacement

• The replacement route is explicitly constrained to “approved aeroplane modification”. The operator’s right to replace is therefore not unconditional; it requires obtaining or using an already approved modification and performing the work through appropriate authority.

5. Duty to maintain records and evidence of compliance

• Although not stated as a specific paperwork list, the AD’s reliance on the most recent SBs and on demonstrating compliance with EASA/FAA criteria implies that operators must retain documentary evidence of the SB revision used and any certificates demonstrating ADS-B compliance. This is a de facto duty implied by the “as in force from time to time” language and the requirement to demonstrate compliance to the referenced standards.

Limitations and scope of duties

• The AD governs only the specified transponder/ADC combinations and does not require action where the ADC does not supply Selected Altitude or where the aircraft is exempt by original architecture. The AD’s duties are precise and confined to the named P/Ns and configurations.

Implementation delegations

• The AD anticipates implementation by maintenance organisations under CAMO/approved change processes. It requires “approved aeroplane modification” for replacements, which delegates technical design responsibility to the authorised modification approval process.

Summary

• Duties are concrete: (i) identify applicability; (ii) perform modification or replacement within 60 days; (iii) address ADS-B disablement or demonstrate compliance with listed standards; (iv) do not install unmodified units in affected configurations; and (v) use current SBs and standards. Rights are limited to the choice of remediation route and to relying on listed exemptions where the original aircraft architecture qualifies. The AD places documentary and procedural obligations on operators and maintenance/design organisations rather than open-ended policy mandates.

The AD itself sets mandatory remedial actions and a timeline for compliance but does not specify monetary penalties or a detailed enforcement procedure within the text provided. The document is an airworthiness directive issued by the Civil Aviation Safety Authority (signed by David Punshon, Delegate of CASA) and therefore sits within CASA’s regulatory instrument set. The following are the enforcement-relevant features that can be read from the AD and the practical enforcement implications they create.

What the AD states about enforcement

• The AD prescribes mandatory actions (Requirements 1-3) and compliance timelines (Compliance and Commencement sections). It is an issuing instrument of CASA, which is the competent airworthiness authority. The AD does not itself enumerate sanctions or fines in the text provided; it instead states technical requirements, compliance dates and the organisational authority that issued it.

Operational enforcement mechanisms (practical and inferred, grounded in the function of ADs)

• Airworthiness directives like this AD are enforceable through the aviation regulatory system. Practically, enforcement mechanisms include:
  • Continued Airworthiness oversight and audit: CASA may verify compliance through oversight of operators’ continuing airworthiness management systems and through audits or inspections.
  • Grounding or operational limitations: In the event of observed non-compliance with an AD, CASA or an airworthiness authority could impose grounding, airworthiness limitations, or conditions on operations pending compliance. The AD’s Requirement 3 explicitly prevents installation of unmodified units; installation contrary to that prohibition would leave the aircraft non-compliant with its airworthiness requirements.
  • Enforcement action under CASA’s regulatory regime: CASA maintains administrative and enforcement powers (not set out in the AD text) to address breaches of regulatory obligations, including potential enforcement notices, prohibition orders, and other regulatory measures. The AD itself does not list specific penalty amounts or steps.

Evidentiary expectations

• To satisfy an AD, operators will typically be expected to maintain records showing the work performed, the SB revision used, approvals for any aeroplane modification, and,if relevant,evidence of compliance with the listed EASA/FAA standards that permit retaining ADS-B functionality on certain replacement P/Ns. Lack of such documentation may be treated as a failure to comply in an audit or inspection.

Consequences of ADS-B disabling or non-compliance

• The AD’s Note 2 requires disabling ADS-B on some P/Ns unless a demonstration of compliance is made. From an enforcement perspective, an operator that continues to operate an ADS-B-enabled 409 unit without the documented demonstration may be out of step with the AD and thus non-compliant. CASA would likely treat that as a continuing airworthiness non-compliance issue.

Scope of CASA authority (as inferred)

• The AD is issued by a CASA delegate and is therefore enforcing CASA’s airworthiness oversight. The AD does not itself specify the procedural route for requesting deviations or extensions. Operators needing relief (e.g., time extension) would generally apply to CASA through existing channels (not specified within the AD text). The AD’s content implies that compliance is binary (modified/replaced/ADS-B disabled as required).

Practical enforcement steps operators should expect

• CASA may require evidence of compliance in the form of maintenance release documents, logbook entries, SB compliance records, and approved modification paperwork. Operators should be prepared to present such documentation during oversight activities.

Limitations in the AD text

• The AD does not state fines, penalty amounts, or the precise administrative penalties applicable for breach. It does not explain CASA’s process for granting approvals, deviations or extensions. These matters fall under broader CASA enforcement and administrative rules, not under the AD’s text itself.

In sum, the AD imposes enforceable mandates but leaves the details of sanctions and procedural enforcement to CASA’s broader regulatory machinery. For compliance purposes, operators should treat the AD as a binding technical requirement and prepare documentary evidence of fulfilment of the AD’s Requirements and use of the referenced current SBs and certification documents.

The AD is a technical regulatory instrument inside the aviation regulatory framework; it interacts with external certification standards and operational rules referenced in the AD text. This section maps the AD’s explicit cross-references and the likely legal interfaces that an operator must consider.

Direct cross-references in the AD

• EASA AD 2009-0173R1: The AD expressly states that EASA AD 2009-0173R1 is the basis for this AD (Note 5). That ties the domestic AD to a prior European airworthiness directive and implies that the technical rationale and remedial measures align with EASA’s findings.
• Rockwell Collins Service Bulletins: The AD mandates modification per Rockwell Collins Service Bulletins (Tables 2 and 3), using the most recent SB versions (“as in force from time to time”). The SBs are manufacturer technical publications that often form part of the approved means of compliance for airworthiness actions.
• EASA AMC 20-24 / CS-ACNS and FAA 14 CFR 91.225 and 91.227: Note 2 requires a demonstration of compliance with these documents to avoid disabling ADS-B on transponders with new P/Ns 622-9352-409 and 622-9210-409. These are external certification standards governing surveillance and ADS-B performance and interoperability.

Interface with continuing airworthiness and design approval regimes

• Approved Aeroplane Modification: Requirement 1.b requires replacement “in accordance with an approved aeroplane modification”. That invokes the domestic processes for design change approval and continued airworthiness compliance; operators must go through the approved modification pathway (CAMO/design approval holder/approved engineering processes) under CASA policy or delegated approvals.
• Maintenance and logbook requirements: Work to satisfy the AD will need to be recorded in the aircraft’s maintenance records and logbooks, as required by domestic continuing airworthiness rules. The AD’s “as in force from time to time” requirements for SBs mean that operators must apply the current permissible methods and retain documentary proof.

Relation to ADS-B and operational rules

• ADS-B regulatory context: The AD’s Note 2 ties ADS-B enablement to EASA or FAA standards. In jurisdictions where ADS-B carriage or operation is mandated by airspace rules, disabling ADS-B may have operational consequences under those rules. Operators must therefore coordinate the AD’s technical requirement with airspace/operational obligations (e.g., ADS-B carriage mandates, route and airspace access rules). The AD itself does not amend those operational rules but imposes a technical constraint that may interact with them.

Interaction with spares distribution and sales law

• The installation prohibition (Requirement 3) affects parts management. Legal obligations under sale/lease agreements and warranty terms could be implicated if unmodified units are transferred or installed contrary to the AD. The AD requires that unmodified units not be installed in affected ADC configurations after commencement, which requires parts custodians to implement controls. Contractual terms that allowed transfer of spare transponders would need to be read against this operational constraint.

International equivalence and foreign-registered aircraft

• The AD applies in the Australian domain (CASA). Foreign-registered aeroplanes operating in Australia or Australian-registered aeroplanes operating overseas may have to align with both this AD and foreign authorities’ directives. The reference to EASA and FAA standards for ADS-B compliance emphasises cross-jurisdictional interplay: an operator may rely on demonstration under EASA/FAA criteria to retain ADS-B functionality, but it must document that demonstration to the Australian regulator.

Regulatory enforcement framework

• Although the AD does not itself list sanctions, it sits within CASA’s enforcement framework. Non-compliance with an AD is typically treated as a breach of continuing airworthiness obligations and could lead to regulatory action under CASA’s broader enforcement powers.

Key legal interface considerations for operators

• Ensure aeroplane modifications comply with the domestic approved modification processes.
• Be aware that disabling ADS-B to comply with the AD could create conflicts with operational rules that require ADS-B; coordinate with CASA and ANSPs as needed.
• Use current SB versions and retain documentary proof; reliance on older SB versions will fail the AD’s “as in force from time to time” requirement.
• For international operations, ensure that compliance paths are consistent with other authorities’ ADs or that equivalence is demonstrated.

In summary, the AD interacts with manufacturer service bulletins, EASA and FAA certification documents, domestic approval processes for aeroplane modification and continuing airworthiness rules, and with operational ADS-B requirements. Operators must map the AD’s technical requirements to these other legal and regulatory instruments to ensure comprehensive compliance.

The AD text itself summarises an internal amendment history and its lineage to EASA AD 2009-0173R1. The AD is presented as AD/RAD/92 Amdt 2. The Background section of the AD records the history in narrative form.

Recorded amendment sequence in the AD

• Original Directive: The initial (original issue) version of this AD identified the underlying problem , a mismatch between ARINC and GAMA specifications for the Selected Altitude motion bit causing incorrect transmission of the Mode S Selected Altitude parameter , and required modification or replacement of affected transponders and prohibited reinstallation of unmodified units.
• Amendment 1: Amendment 1 continued the requirements from the original AD and supplied relief for operators of some DHC-8 aircraft. Specifically, Amendment 1 seems to have implemented exemptions (now reflected in Note 4) for certain DHC-8 Series 100/200/300 aircraft where the original architecture does not provide Selected Altitude via the ADC, thereby exempting those aircraft from the AD’s requirements unless modified.
• Amendment 2 (this document): The AD as presented is Amendment 2. Amendment 2 “removes obsolete references and makes minor editorial changes to reflect current requirements.” The AD is titled AD/RAD/92 Amdt 2 and carries the Commencement date of 10 September 2021 and signature date 27 August 2021.

External lineage

• EASA AD 2009-0173R1 is explicitly identified as the basis for this AD (Note 5). That indicates that the Australian AD tracks the EASA corrective action that first identified the fault and set out comparable remedial measures.

Versioning of Service Bulletins and external standards

• The AD repeatedly requires compliance with Rockwell Collins Service Bulletins “as in force from time to time” (Tables 2 and 3, Note 2). The AD thereby binds the operator to use current service bulletin revisions and to account for updates that may occur after the AD’s issuance.
• Similarly, the AD ties the ADS-B functional outcome to the most recent versions of EASA AMC 20-24, EASA CS-ACNS, or FAA 14 CFR 91.225 and 91.227 “as in force from time to time” (Note 2). That creates a dynamic component to compliance: an operator must conform to the current external standards when demonstrating ADS-B compliance for P/N 409 replacements.

Practical consequence of the amendment history

• Amendment 1 adjusted the scope and allowed relief for certain operators; Amendment 2 made editorial updates and removed obsolete references. For users, the key practical effect is that the AD’s current text, including the exemptions and the “as in force from time to time” language, is the operative instrument. Historical versions are relevant only insofar as work may have been performed under a previous issue; the Compliance section recognises that pre-existing actions done in accordance with a previous issue of the AD may count as satisfying the current requirement.

Record-keeping and traceability requirements

• Because the AD requires use of current SB revisions and references prior amendment changes (Amendment 1 relief, Amendment 2 editorial updates), operators should retain records showing which AD issue and which SB revision were used to demonstrate compliance. The AD’s Compliance section acknowledges that earlier compliance in accordance with a previous issue of this AD counts, making traceable evidence of earlier compliance events important.

In essence, the AD is the second amendment to AD/RAD/92, it continues the original technical requirements, applies limited relief for specific aircraft types via Amendment 1, and has been editorially updated in Amendment 2. The document’s linkage to EASA AD 2009-0173R1 shows its international origin and technical pedigree.

The AD document provided contains no litigation history. It cites EASA AD 2009-0173R1 as its basis and records internal amendment steps (original issue, Amendment 1, Amendment 2), but it does not reference any court proceedings, disputes, enforcement litigation, or legal challenges.

What the absence of litigation history in the AD means for practitioners

• The AD is a regulatory technical instrument and typically enforcement and compliance issues are resolved administratively by the regulator and by operators through maintenance and modification activities. The lack of litigation references in the AD means there are no judicially recorded disputes cited within the AD text to inform interpretation or contested application.
• Where operators seek relief (extensions, alternative methods of compliance), they ordinarily liaise with the regulator (CASA) through administrative processes rather than through litigation. If disputes arise about enforcement action taken by CASA (for example, grounding or penalties), those enforcement actions could become the subject of litigation, but none are recorded in the AD text.

Advice for counsel or compliance teams

• Because there is no litigation history referenced, practitioners should treat the AD as a primary technical regulatory requirement and expect compliance issues to be settled in the administrative oversight context first. If enforcement action follows non-compliance, litigation could ensue as with other regulatory enforcement matters, but the AD text itself does not provide precedent or case law to guide outcomes.
• Documentation proving timely and correct performance of the required modification or replacement (including the SB revision used and the approved modification paperwork) is the primary line of defence against enforcement scrutiny; the AD’s “as in force from time to time” language emphasises the need to show current-document compliance.

In short, the AD contains no litigation history to draw upon. Any litigation arising from non-compliance or disputed enforcement measures would be external to the text and is not recorded here.

This AD contains several practical pitfalls and traps for the unwary. They derive from the specificity of part numbers, the interplay with ADS-B functionality, the “most recent version” language, and exemptions that are conditional rather than absolute. Below are concrete “gotchas” with the textual hooks cited.

1. “As in force from time to time” creates versioning risk (Tables 2 & 3; Note 2)

• The Rockwell Collins Service Bulletins and the EASA/FAA documents are required “as in force from time to time”. Using an older SB revision or an outdated standard to claim compliance will not meet the AD. Practitioners must procure and apply the current SB revision at the time of modification and retain documentary evidence of which revision was used. Failure to do so risks non-compliance.

2. Choosing replacement P/N 409 may force ADS-B disablement unless you can demonstrate compliance (Note 2)

• Table 2 and Table 3 list new P/N options including the 409 variants. Note 2 explicitly requires disabling the ADS-B function on transponders with P/N 622-9352-409 and 622-9210-409 unless EASA AMC 20-24 or CS-ACNS, or FAA 14 CFR 91.225/91.227 compliance is demonstrated. Practically, this means that selecting a P/N 409 replacement can lead to reduced surveillance capability if the operator cannot produce the required demonstration. Operators that rely on ADS-B for operational access need to factor this trade-off into procurement decisions.

3. Prohibition on installing unmodified units affects rotables and spare management (Requirement 3)

• After the commencement date, transponders identified in the Applicability may not be installed in aeroplanes where the ADC provides Selected Altitude unless modified in accordance with Requirement 1.a. If operators maintain inventories of spare transponders or do on-wing swaps, they must ensure unmodified units are not reinstalled in affected installations. Inventory controls, tagging and staff training are essential to avoid inadvertent non-compliant installations.

4. Exemption is conditional on original architecture; modifications can revoke exemption (Notes 3 and 4)

• The ATR and DHC-8 exemptions relate to original architecture where Selected Altitude is not provided by the ADC. If the aircraft has been modified to enable a digital link between the ADC and the transponder, the exemption does not apply. Operators who rely on an exemption must verify their aircraft configuration and maintain records proving that the ADC does not supply Selected Altitude. Failure to recognise a prior modification that enabled the digital link could leave the operator non-compliant.

5. Time pressure: 60-day compliance window from commencement (Compliance; Commencement)

• The AD requires remediation for Requirement 1 within 60 days of commencement (commencement 10 September 2021). This is a short window. Operators must prioritise affected aircraft, secure parts and maintenance slots quickly, and coordinate approved aeroplane modifications where replacements are chosen. Delay or supply-chain constraints will create operational disruptions if compliance cannot be accomplished in time.

6. Concurrent ADS-B action requirement (Compliance for Requirement 2)

• Requirement 2 must be addressed concurrently with the implementation of Requirement 1. Practically, when you're modifying or replacing a transponder you must address the ADS-B enablement/disabling choice at the same time. Scheduling work without accounting for the ADS-B outcome could result in repeated shop visits or operational lapses.

7. “Approved aeroplane modification” is not a vending-machine option (Requirement 1.b)

• Replacement must be effected “in accordance with an approved aeroplane modification”. This requires either using an existing approved modification or obtaining one. Engineering approvals, minor/major change classification, and design documentation may be needed. Time and cost associated with obtaining approval and executing the modification are often underestimated.

8. Cross-jurisdictional compliance demonstration for ADS-B (Note 2)

• The AD permits ADS-B to remain enabled on certain replacement P/Ns only if the operator demonstrates compliance with EASA or FAA documents “as in force from time to time”. Demonstrating compliance may be non-trivial, may require independent testing, certification evidence, or manufacturer attestations, and must be preserved for audit. Operators that operate internationally must ensure the demonstration is acceptable to all relevant authorities.

9. Multiple P/N mapping complexity (Tables 2 & 3)

• The tables map various current P/Ns to possible new P/Ns and specific SB references. Mistyping or misreading P/Ns during procurement or maintenance can lead to incorrect parts being fitted. Scrupulous part-number verification is needed.

10. Potential mismatch between operational ADS-B requirements and AD-imposed disablement

• If an operator is required by airspace rules to carry ADS-B (in certain regions), disabling ADS-B to comply with the AD may create a separate operational compliance issue. The AD does not modify airspace ADS-B carriage rules; operators must coordinate with CASA/ANSPs if disabling ADS-B would affect operations.

11. No explicit extension procedure in the AD text

• The AD does not lay out a mechanism to seek an extension of the 60-day deadline. Operators who cannot comply within 60 days should be proactive in engaging CASA to request relief or to document mitigating circumstances; doing nothing risks administrative enforcement.

12. Documentation and audit evidence expectations

• Because the AD references SBs and external standards, operators should anticipate documentary review by CASA. Failure to retain records (SB revision used, maintenance release, approved modification paperwork, ADS-B compliance evidence) will leave the operator exposed during oversight.

These are concrete operational risks embedded in the AD’s text. Mitigation requires close inventory control, fast scheduling with AMOs, clear selection among P/N options (and the ADS-B consequences), and rigorous documentary practice.

This section gives a practical, stepwise compliance checklist grounded in the AD’s text. It does not substitute for engineering or regulatory advice but translates the AD’s requirements into action items that operators, CAMOs and maintenance organisations should follow.

Step 0 , Read and map applicability

• Consult the AD’s Applicability and Table 1. Confirm whether any aeroplane in your fleet has a Rockwell Collins TDR-94 or TDR-94D transponder with the listed current P/Ns (622-9352-007, -008, -108; 622-9210-007, -008, -108) and is equipped with a Honeywell AZ800 or AZ810 ADC that provides Selected Altitude to the transponder via the data bus interface. If the ADC is not supplying Selected Altitude, review Notes 3 and 4 to determine whether an exemption applies (honour the caveat that modifications enabling a digital link revoke the exemption).

Step 1 , Prioritise affected aircraft and create a compliance plan (timebox)

• The AD requires compliance for Requirement 1 within 60 days of commencement (commencement 10 September 2021). For each affected aircraft, create a slotting plan that identifies:
  • whether you will pursue modification per Rockwell Collins SBs (Requirement 1.a) or replacement under an approved aeroplane modification (Requirement 1.b),
  • parts procurement lead times for the chosen P/N,
  • maintenance facility capacity and available dates,
  • necessary approvals for aeroplane modifications (if replacement chosen),
  • the need to address ADS-B function concurrently (Requirement 2 / Note 2).

Step 2 , Choose remediation route and document rationale

• Option A , Modify per Rockwell Collins Service Bulletin (Requirement 1.a)

  • Obtain the Rockwell Collins Service Bulletins referenced in Tables 2 and 3 that correspond to your current P/N. The tables identify SB references (e.g., TDR-94/94D-34-505, -506, -507) and map current to new P/N options. Remember the AD requires the SB “as in force from time to time” , obtain and record the current revision.
  • Schedule the SB work with an approved maintenance organisation and document SB revision, maintenance release, and logbook entries.

• Option B , Replace with listed new P/N under approved aeroplane modification (Requirement 1.b)

  • Confirm available approved aeroplane modifications that authorise installation of P/N 622-9352-309/-409 or 622-9210-309/-409. If none exists, engage your design approval holder/CAMO to develop an approved modification.
  • If choosing 409 variants, prepare to address Note 2: ADS-B must be disabled on P/N 409 units unless you can demonstrate compliance with EASA AMC 20-24 or CS-ACNS or FAA 14 CFR 91.225 and 91.227. If you need ADS-B enabled, document and assemble the required demonstration evidence (testing, manufacturer attestations, certification evidence).
  • Schedule procurement and installation, and ensure maintenance release and approved modification paperwork are completed and retained.

Step 3 , Address ADS-B concurrently

• Requirement 2 requires action on ADS-B concurrent with the modification.
  • If you are installing P/N 622-9352-409 or 622-9210-409 and do not have the necessary demonstration, ensure the ADS-B function is disabled at the time of the modification.
  • If you intend to keep ADS-B enabled, gather the necessary evidence that demonstrates compliance with the listed EASA or FAA standards; document the method of demonstration and retain records for inspection. Confirm with CASA that your demonstration approach is acceptable if necessary.

Step 4 , Implement installation prohibition controls for spares (Requirement 3)

• After commencement, unmodified units identified in the Applicability must not be installed in affected ADC installations. Put inventory controls in place:
  • Tag/segregate unmodified transponders that must not be installed in the specified ADC configuration.
  • Update maintenance procedures and provide staff training and job cards to ensure unmodified spares are not mistakenly fitted.
  • Record the modification status of each transponder serial number and P/N in the maintenance records.

Step 5 , Verify exemptions where claimed (Notes 3 and 4)

• If you seek to rely on the ATR or DHC-8 exemptions:
  • Maintain documentation proving the original architecture does not supply Selected Altitude via the ADC (design drawings, type design notes, modification histories).
  • If the aircraft has later modifications that enable a digital link between ADC and transponder, do not claim the exemption; comply with the AD.

Step 6 , Record evidence and update continuing airworthiness documentation

• For every action undertaken, retain:
  • SB revision used and maintenance release documents,
  • logbook entries recording the work and P/N changes,
  • approved aeroplane modification paperwork if replacement route used,
  • evidence of ADS-B compliance demonstration where relevant,
  • records showing the date of compliance relative to the AD’s commencement and the 60-day window.
• Update CAMO records and continuing airworthiness documentation to reflect the change.

Step 7 , Operational planning for ADS-B impact

• If ADS-B is disabled on affected aircraft or transponders, coordinate with operations and route/airspace planning teams to confirm whether that affects access to routes or airspace that require ADS-B surveillance. If necessary, coordinate with ANSPs and CASA to identify mitigations (alternative surveillance or procedural measures).

Step 8 , Engage CASA proactively if you cannot meet the deadline

• The AD does not set out an extension mechanism. If you foresee inability to comply within 60 days due to parts shortage, maintenance capacity or other constraints, proactively contact CASA to request guidance, relief or to document mitigating steps. Maintain written evidence of your communications and remediation plan.

Step 9 , Post-compliance surveillance and maintenance

• Monitor the behaviour of modified or replacement transponders in service, and maintain records for potential follow-up (e.g., if a newer SB revision supersedes the current one). Because the AD ties SB and standards to “as in force from time to time”, operators should track further SB revisions and relevant EASA/FAA updates that could affect continued compliance or ADS-B enablement status.

Step 10 , Audit readiness

• Prepare for CASA oversight by assembling a compliance dossier per aircraft showing:
  • identification of affected units,
  • the remediation route selected and why,
  • SB and modification documentation,
  • maintenance release and logbook references,
  • ADS-B compliance evidence or proof of disablement,
  • inventory controls preventing reinstallation of unmodified units.

Concise checklist for a single aircraft

1. Verify whether ADC provides Selected Altitude to the transponder. If not, verify exemption documented.
2. If affected, decide: modify per SB (1.a) or replace under approved modification (1.b).
3. If replacing with 409 P/N, determine whether you can demonstrate compliance with EASA/FAA ADS-B criteria; if not, plan to disable ADS-B.
4. Schedule maintenance within 60 days; obtain current SBs; perform work and record SB revision.
5. Update logbooks, CAMO records and parts inventory; ensure unmodified units cannot be reinstalled.
6. Retain evidence for CASA audit.

Following these steps aligns an operator’s processes with the AD’s textual requirements and helps demonstrate compliance in a way CASA is likely to expect.