AD/RAD/91 - Rockwell Collins TDR-94/94D Transponder - Air/Ground Discrete Inputs

The Directive rests on three technical and regulatory concepts stated in the source.

1. Air/Ground discrete inputs and reply inhibition: The TDR‑94/TDR‑94D transponders have two Air/Ground discrete inputs that may be connected to the aeroplane Weight‑On‑Wheels (WOW) system. The Directive explains that a connection to Air/Ground discrete #2 implements inhibition of ATCRBS, ATCRBS/Mode‑S All‑Call and Mode‑S Only All‑Call replies when the aeroplane is on the ground, while a connection to Air/Ground discrete #1 does not implement on‑ground reply inhibition. This differential behaviour is the root technical fault the AD addresses.

2. A‑SMGCS operational requirement and ICAO standard: The background links reply inhibition to the operation of Advanced Surface Movement Guidance & Control Systems (A‑SMGCS). The source records that Airservices Australia and other ANSPs have implemented A‑SMGCS to improve on‑ground surveillance and control, and that, to ensure proper and effective A‑SMGCS operation, “transponder replies to Air Traffic Control Radar Beacon System (ATCRBS) and All‑Call interrogations must be inhibited when the aeroplane is on ground.” The AD notes that an aeroplane exhibiting the transponder interface problem “does not meet the specifications of International Civil Aviation Organisation (ICAO) Annex 10 Volume IV Amendment 77 Section 3.1.2.10.3.10 , Inhibition of replies”, and that failure to inhibit could “lead to degradation of the functioning of the A‑SMGCS” with attendant ATC effects and runway incursion risks.

3. Compliance pathway and exclusions: The Directive’s required action is a verification against a manufacturer’s Service Information Letter (SIL) Table 1 (Rockwell Collins SIL TDR‑94 SIL 07‑1 dated 25 May 2007). If wiring is not compliant, the AD requires corrective modification “in accordance with approved aeroplane modification instructions”. The AD also lists specific Service Bulletins and embodied modifications (per Note 2 a-d) that, if already incorporated, render the Directive not applicable to that aeroplane. The document also cross‑references EASA AD 2009‑0097.

These concepts show the technical mechanism (which discrete pin is wired to WOW), the operational rationale (A‑SMGCS requires reply inhibition on ground), and the remediation channel (verify against SIL Table 1; if non‑compliant, modify per approved instructions), together with discrete exemptions for aircraft already modified per listed SBs or mods.

The Directive affects operators, owners, maintainers and approved modification organisations responsible for aeroplanes that have Rockwell Collins TDR‑94 or TDR‑94D Mode S transponders of the listed part numbers (P/Ns). Table 1 in the Directive lists the affected transponder P/Ns for TDR‑94 and TDR‑94D (for example, TDR‑94 P/Ns including 622‑9352‑004 through 622‑9352‑408 in various suffixes; TDR‑94D P/Ns including 622‑9210‑004 through 622‑9210‑408). The Directive states “Applicability: Rockwell Collins Mode S Transponders identified by type and Part Number (P/N) in Table 1.”

The AD also identifies a non‑exclusive set of aircraft types on which these transponders are known to be installed. Note 1 lists, among others: ATR 42 and ATR 72 (all models); a set of Bombardier CL‑600 variants; DHC‑8 (all models); Dassault Falcon variants (Mystère‑Falcon 50, Falcon 900, Falcon 2000 series); Gulfstream G‑IV; Hawker Beechcraft 200 and 400 series; SAAB SF340A and SF340B. Because the listing is said to be “known to be installed on, but not limited to” these models, any aircraft with the listed P/N transponder is in scope regardless of model, and operators of the listed models should check serial numbers and P/N.

Who pays: the Directive requires verification and corrective modification “in accordance with approved aeroplane modification instructions” if wiring is non‑compliant. The source does not state who bears cost, but the required actions fall on the party responsible for maintaining the aeroplane’s airworthiness , practically, the owner/operator and their approved maintenance organisation , since they must perform the verification and any modifications. The AD does specify the compliance timeframe ("within 12 months after the effective date"), which imposes a scheduling and downtime obligation on operators.

Who decides: CASA issued the Directive (delegate signature dated 15 March 2010); the technical compliance check is against Rockwell Collins SIL Table 1, and any modification must be performed “in accordance with approved aeroplane modification instructions.” That means the technical method of remediation will come from approved modification instructions (manufacturer or approved design authority), and operators will decide when and how , subject to that approval , to schedule the work within the compliance window.

Who need not act: Aeroplanes that have already incorporated specified Service Bulletins or modifications (listed in Note 2 a-d, e.g., ATR SB ATR42‑34‑0164 or ATR72‑34‑1093 modification n° 05602; Bombardier SB 601R‑34‑146 for CL‑600‑2B19; MODSUM IS8Q2450012 for DHC‑8‑100/200/300; various Dassault SBs and modification numbers) are identified as not applicable for the Directive.

Duties imposed by the Directive:

• Identification duty: Operators must identify whether the installed transponder is one of the listed TDR‑94/TDR‑94D part numbers set out in Table 1 of the Directive. The AD states applicability is to the transponders “identified by type and Part Number (P/N) in Table 1.”

• Verification duty: For affected transponders, operators must verify that the transponder Air/Ground discrete input connections are installed in accordance with Table 1 of Rockwell Collins SIL TDR‑94 SIL 07‑1 dated 25 May 2007 (document reference 523‑0809129‑001000). The Directive’s Requirement section specifies this verification.

• Corrective duty: If the wiring installation is not compliant with the SIL Table 1, operators must modify the aeroplane Air/Ground discrete input connections “in accordance with approved aeroplane modification instructions.” The AD makes modification conditional on verification outcomes.

• Timing duty: Compliance is required within 12 months after the effective date of the Directive. The AD makes this explicit under Compliance.

Rights and carve‑outs stated in the Directive:

• Exemption/Not applicable right: The AD lists circumstances where the Directive does not apply. Note 2 provides that the Directive is not applicable to aeroplanes that have complied with certain Service Bulletins or have had specific modifications embodied. The AD lists these SBs and modification references in items a-d and cross‑references EASA AD 2009‑0097.

• Use of approved instructions: The Directive channels remedial action through “approved aeroplane modification instructions,” meaning that modification work must follow design approval processes and instructions as approved by the relevant authority or design organisation. The AD does not prescribe exactly which approved instructions must be used; it requires their use for the modification.

The Directive does not set out administrative appeal rights, enforcement mechanisms, or penalty scales in the text provided. It does, however, set an effective date (26 March 2010) and a compliance period (12 months). The AD implicitly places the responsibility for scheduling, performance and recordkeeping of verification/modification on the operator/maintainer because they are the ones who must ensure the required wiring is correct or corrected per approved instructions.

The Directive itself specifies the compliance deadline and effective date, but it does not specify civil penalties, criminal sanctions, or the enforcement procedures in the text provided. Concretely, the AD states the action required (verify wiring against Rockwell Collins SIL Table 1; if non‑compliant, modify per approved aeroplane modification instructions), the compliance timeframe (“within 12 months after the effective date”), and the effective date (“26 March 2010”). The Directive was signed 15 March 2010.

The source does not describe how CASA will monitor or enforce compliance, nor does it articulate any administrative process for enforcement, suspension of operations, fines or other sanctions for non‑compliance. It also does not set out whether compliance is recorded via maintenance release entries, logbook entries, or approval certificates. Because the Directive requires actions be carried out “in accordance with approved aeroplane modification instructions,” the AD imposes a substantive technical requirement; however, the specific enforcement modalities or penalties are not stated in this document.

The Directive does frame the safety rationale and regulatory baseline: it declares that an aeroplane that retains the transponder interface problem “does not meet the specifications of International Civil Aviation Organisation (ICAO) Annex 10 Volume IV Amendment 77 Section 3.1.2.10.3.10” and sets out that the problem “could affect the ATC functions … increase the risk of undetected runway incursions and endangering the aeroplane, its occupants and persons on the ground.” Those statements indicate the safety rationale that underpins the Directive’s mandatory nature but do not themselves outline penalties. Practitioners will need to consult CASA’s regulatory framework or ancillary guidance (not included in this text) for the formal enforcement regime and administrative consequences of non‑compliance.

The Directive references and interacts with two external regulatory or standards instruments within the source text.

1. ICAO Annex 10 Volume IV Amendment 77: The AD states that an aeroplane with the transponder interface problem “does not meet the specifications of International Civil Aviation Organisation (ICAO) Annex 10 Volume IV Amendment 77 Section 3.1.2.10.3.10 , Inhibition of replies.” That is an explicit normative baseline: the AD treats compliance with that ICAO specification as part of the functional requirement for transponder behaviour on the ground. The Directive therefore operates to bring affected Australian‑registered aeroplanes into alignment with that ICAO standard as interpreted by CASA in this AD.

2. EASA AD 2009‑0097 and manufacturer/airframe SBs: The AD expressly refers to EASA AD 2009‑0097 in Note 3 and lists a set of Service Bulletins and modifications (Note 2 a-d) which, if already embodied on the aeroplane, render the CASA Directive not applicable. The Directive therefore coordinates with both EASA’s AD and specific manufacturer Service Bulletins. Practically, an aeroplane modified in accordance with the listed SBs or mods is treated as already meeting the requirement; the CASA AD does not require duplicate action where those SBs or mods have been applied.

The Directive also prescribes verification against a Rockwell Collins Service Information Letter (SIL TDR‑94 SIL 07‑1 dated 25 May 2007), and instructs corrective action to be performed “in accordance with approved aeroplane modification instructions”. That language connects the AD to the design approval and modification approval processes: the method of corrective action must be approved as an aeroplane modification instruction. The source does not specify which approval authority must give those instructions, but the phrasing implicates the existing airworthiness modification approval framework.

Beyond these explicit cross‑references, the source does not set out interactions with aviation safety criminal or administrative law, commercial laws, or insurance regimes. The Directive is framed as a technical airworthiness requirement tied to international standards (ICAO) and to EASA and manufacturer publications; for broader legal interactions (liability, insurance, enforcement), the source itself is silent.

The document provided does not record any subsequent amendments to AD/RAD/91; it is presented as issued on 15 March 2010 and effective on 26 March 2010. The Directive itself cites earlier or external documents which form part of its context:

• Rockwell Collins Service Information Letter: TDR‑94 SIL 07‑1 dated 25 May 2007 (document reference 523‑0809129‑001000). This SIL contains the wiring Table 1 that the AD directs operators to use for verification.

• EASA AD 2009‑0097: The Directive notes “EASA AD 2009‑0097 refers.” That EASA AD pre‑dates CASA’s AD and is referenced as related authority; the CASA AD also lists specific Service Bulletins and modifications that, if embodied, create an exclusion to the CASA AD.

The AD includes a “Note 2” list of Service Bulletins and modification references that were available at the time the CASA AD was issued. Those references indicate manufacturer remediation pathways that some operators may already have incorporated. The AD does not itself record later changes to those SBs, nor does it document any amendments, supersessions, or withdrawal of AD/RAD/91.

Because this source is a single AD text, the absence of an explicit amendment log in the document means practitioners should treat the AD as a snapshot effective 26 March 2010 and verify whether later amendments, superseding ADs, or related CASA instruments have been issued after that date by consulting CASA’s official AD registry or aeronautical information publications. The Directive as provided does not contain that subsequent administrative history.

The source document contains no litigation history. It does not name any judicial proceedings, appeals, or case law arising from issuance of AD/RAD/91. The text is a technical mandatory directive and the only legal references in the document are to international and foreign regulatory materials: ICAO Annex 10 Volume IV Amendment 77 and EASA AD 2009‑0097.

Because the AD itself does not record disputes, judicial review, enforcement actions or successful challenges, this Directive as provided has no litigation history in the text. Practitioners seeking cases about enforcement or challenges to this AD will need to search external legal and regulatory records; the Directive itself offers no court citations, no appeal processes, and no record of legal contestation in the provided material.

Several practical pitfalls are visible in the Directive text that can cause operators or maintainers to misjudge scope, compliance requirements, or exemption status.

• Wrong discrete pin wiring is subtle but safety‑critical: The core technical issue is that the transponder’s two Air/Ground discrete inputs behave differently. Connection to Air/Ground #2 implements inhibition of ATCRBS and Mode‑S all‑call replies on the ground; connection to Air/Ground #1 does not. An installer who assumes either discrete is interchangeable will leave the aeroplane in a state that fails to inhibit ground replies, with consequences to A‑SMGCS performance described in the AD. The mechanical wiring difference is the fundamental “gotcha”.

• Applicability is by transponder P/N, not solely by aircraft model: The Directive applies to specific transponder part numbers listed in Table 1. The AD warns that the transponders are known to be installed on certain aeroplane models “but not limited to” those models. An operator cannot rely solely on aircraft model to determine applicability; they must inspect the installed transponder’s P/N and serial numbers against Table 1.

• Exemption reliance requires careful verification of SB/mod embodiment: Note 2 lists specific Service Bulletins and modification numbers which render the AD not applicable. Operators who assume exemption because they have a broadly similar SB must confirm that the exact SB number and modification number match those listed (for example, ATR SB ATR42‑34‑0164 or SB ATR72‑34‑1093 modification n° 05602; Bombardier SB 601R‑34‑146; MODSUM IS8Q2450012 for certain DHC‑8s; and specific Dassault SB/modification numbers). A mismatch in SB version, incomplete embodiment, or incorrect modification number would not create the exemption listed in Note 2.

• The required standard for verification is the Rockwell Collins SIL Table 1: The AD requires verification “in accordance with Table 1 of Rockwell Collins Service Information Letter TDR‑94 SIL 07‑1 dated 25 May 2007 (document reference 523‑0809129‑001000).” If maintenance personnel do not use the correct version of the SIL or the wrong table, the verification may be invalid.

• Approved aeroplane modification instructions are required for corrective work: The AD does not permit any ad hoc wiring correction; it requires modification in accordance with approved aeroplane modification instructions. Operators must therefore ensure the modification method is approved, which can involve design authority input and administrative lead times. Assuming a simple rewiring without obtaining or following approved instructions would not satisfy the AD’s stated requirement.

• Time window and operational scheduling: The compliance window is “within 12 months after the effective date,” the AD being effective 26 March 2010. Operators who miscalculate the compliance deadline or delay planning may face compressed maintenance scheduling. The source does not state whether continued operation is permitted during the compliance period, so operators should not assume indefinite flyable status without verifying with CASA or maintenance control.

• Recordkeeping and proof: The AD does not specify the recordkeeping format for demonstrating compliance (e.g., maintenance log entry text or form). Operators should not assume that any informal note suffices; instead, they should preserve verification records, SIL references and modification approvals per their normal airworthiness documentation standards. The AD’s silence on recordkeeping is itself a risk point.

• Cross‑jurisdictional differences: The AD references EASA AD 2009‑0097. Operators with international operations or maintenance carried out in different regulatory environments must ensure the correct combination of SBs, modifications and approvals match what CASA requires. A modification accepted under another authority might not be identical to the modification references listed in Note 2.

The Directive sets a contained compliance pathway. The steps below rest on the Directive’s text and reference the specific documents it names.

1. Identify installed transponder P/N and serial number:

   • Check the installed transponder’s type and Part Number against Table 1 of the Directive. The AD’s Applicability section makes applicability conditional on the transponder being one of the listed TDR‑94 or TDR‑94D P/Ns (e.g., TDR‑94 P/Ns 622‑9352‑004 through 622‑9352‑408 variants; TDR‑94D P/Ns 622‑9210‑004 through 622‑9210‑408 variants). This is the starting gate: if the unit is not a listed P/N, the AD as written does not apply to that unit.

2. Confirm whether Note 2 exclusions apply:

   • Before performing verification or work, check whether the aircraft has already complied with one of the specific Service Bulletins or embodied modifications listed in Note 2 (ATR SB ATR42‑34‑0164 or SB ATR72‑34‑1093 modification n° 05602; Bombardier SB 601R‑34‑146 for CL‑600‑2B19; MODSUM IS8Q2450012 for certain DHC‑8s; Dassault SBs and corresponding modification numbers listed). If the precise SB/modification listed in the AD has been incorporated, the AD states it is not applicable to that aeroplane.

3. Obtain Rockwell Collins SIL TDR‑94 SIL 07‑1 (25 May 2007, doc ref 523‑0809129‑001000):

   • The AD requires verification “in accordance with Table 1 of Rockwell Collins Service Information Letter TDR‑94 SIL 07‑1 dated 25 May 2007.” Obtain the exact SIL and confirm you are using Table 1 referenced in the AD. Use that table as the benchmark for correct Air/Ground discrete input wiring.

4. Perform verification:

   • Have qualified maintenance personnel verify the Air/Ground discrete input connections against the SIL Table 1. The verification must determine whether the Air/Ground discrete connected to the Weight‑On‑Wheels (WOW) system is the correct input (Air/Ground #2) that implements on‑ground inhibition. Note the AD’s technical statement: connection to Air/Ground #2 implements inhibition; connection to Air/Ground #1 does not.

5. If wiring is non‑compliant, plan modification per approved instructions:

   • The AD requires that where the wiring installation is not compliant with SIL Table 1, the aeroplane Air/Ground discrete input connections be modified “in accordance with approved aeroplane modification instructions.” Obtain the relevant approved modification instructions for the specific aeroplane type and transponder installation. Ensure those modification instructions are formally approved per the applicable design approval process.

6. Schedule and execute the modification:

   • Schedule the modification work within the compliance window: the AD requires action “within 12 months after the effective date,” with the Directive effective 26 March 2010. Practically, that gives till 26 March 2011 to complete verification and any required modification. Arrange for downtime, qualified personnel and documentation capture to evidence the corrective action.

7. Record compliance:

   • Although the AD does not specify a recordkeeping format, document the verification results, the SIL revision used, any modification instructions and approvals, and the maintenance action performed. Retain serial number and P/N evidence that the effected transponder unit was subject to the AD, and enter appropriate maintenance logbook entries consistent with normal airworthiness practice.

8. Coordinate with relevant stakeholders:

   • Notify the operator’s continuing airworthiness management organisation, maintenance provider and relevant authority contacts as necessary. If maintenance is carried out under a third party with delegated approval, ensure the modification instructions used are the “approved aeroplane modification instructions” required by the AD.

9. For international maintenance or leased aircraft:

   • If the aircraft is maintained or modified outside the registering state, confirm that the approved modification instructions and embodiment meet the CASA AD’s requirements and that the exact SBs or modifications listed in Note 2 are the ones applied if relying on an exemption.

10. If in doubt, obtain authoritative clarification:

• The AD references Rockwell Collins SIL and approved aeroplane modification instructions. If there is ambiguity as to whether a given wiring, SB, or mod constitutes compliance, obtain clarification from the design approval holder, the modification approver, or CASA. The AD itself does not give an administrative appeal or clarification procedure in its text.

Following these steps will align the maintenance action with the Directive’s stated requirements: identify applicability via Table 1, verify against Rockwell Collins SIL Table 1, and, if non‑compliant, carry out approved modifications within the specified 12‑month compliance window.