{"id":"F2006B06530","name":"AD/RAD/75 - TDR-94/TDR-94D Transponders","slug":"ad-rad-75-tdr-94-tdr-94d-transponders","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":48183,"registerId":"commonwealth-F2006B06530-current","compilationNumber":null,"startDate":"2026-04-02","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"AIRWORTHINESS DIRECTIVE","sectionType":"part","heading":"AIRWORTHINESS DIRECTIVE","content":"# ![](image.001.png)  \nAIRWORTHINESS DIRECTIVE\n\nFor the reasons set out in the background section, the CASA delegate whose signature appears below issues the following Airworthiness Directive (AD) under subregulation 39.1 (1) of CAR 1998. The AD requires that the action set out in the requirement section (being action that the delegate considers necessary to correct the unsafe condition) be taken in relation to the aircraft or aeronautical product mentioned in the applicability section: (a) in the circumstances mentioned in the requirement section; and (b) in accordance with the instructions set out in the requirement section; and (c) at the time mentioned in the compliance section.\n\n![](image.001.png)\n\nRadio Communication and Navigation Equipment","sortOrder":0},{"sectionNumber":"AD/RAD/75 TDR-94/TDR-94D Transponders 5/","sectionType":"part","heading":"AD/RAD/75 TDR-94/TDR-94D Transponders 5/2002","content":"# AD/RAD/75 TDR-94/TDR-94D Transponders 5/2002\n\nApplicability: Rockwell Collins TDR-94 Mode S transponders (Collins part number (CPN) 622- 9352-004) and TDR-94D Mode S transponders (CPN 622-9210-004).\n\nNote 1: These transponders may be installed on, but not limited to, the following series of aeroplanes:\n\nAerospatiale ATR42;\n\ndeHavilland DHC-7 and DHC-8; and\n\nShort Brothers Models SD3-60 and SD3-60 SHERPA.\n\nRequirement: 1. Determine whether the altitude information from any TDR-94 Mode S transponder (CPN 622-9352-004) or TDR-94D Mode S transponder (CPN 622- 9210-004) is derived from a digital air data source or a Gillham (grey code) encoded source. This may be accomplished as specified in Rockwell Collins Service Bulletin (SB) No. 17 (TDR-94/94D-34-17), dated 8 February 1999, SB 17, Revision 1, dated 15 May 2000, or SB 20 (TDR-94/94D-34-20), Revision 1, dated 2 May 2001. Collins Product Information Letter No. 71, dated January 1999, references Service Bulletin 17, dated 8 February 1999.\n\nIf the altitude information from all affected transponders is derived from a digital air data source, this Directive requires no further action.\n\n    2. If the altitude information is derived from a Gillham (grey code) encoded source, modify the unit to prevent erroneous altitude reporting. The modification encompasses converting the TDR-94 transponder from Collins part number (CPN) 622-9352-004 to CPN 622-9352-005 or converting CPN 622-9352- 004/005 to CPN 622-9352-006; and converting the TDR 94D transponder from CPN 622-9210-004 to CPN 622-9210-005 or converting CPN 622-9210-004/005 to CPN 622-9210-006.\n\nModifications are to be accomplished in accordance with either SB 17 (TDR- 94/94D-34-17), SB17 Revision 1or SB 20 (TDR-94/94D-34-20), Revision 1.\n\n    3. TDR-94 Mode S transponder (CPN 622-9352-004) or TDR-94D Mode S transponder (CPN 622-9210-004) may not be installed on any aeroplane if the altitude information is derived from a Gillham (grey code) encoded source, unless the transponder is modified in accordance with Requirement 2.","sortOrder":1}],"analysis":{"flash_summary_failed":{"failed":true,"reason":"A positive credit balance is required for all requests, including BYOK, so fallback providers remain available. Add credits at https://vercel.com/d?to=%2F%5Bteam%5D%2F%7E%2Fai%3Fmodal%3Dtop-up to continue.","source":"analysis-cron"},"kimi_summary":{"content_quality":"ok","complexity_score":3,"scope_assessment":{"changed":false,"description":"This is a standard airworthiness directive maintaining its original scope: addressing a specific unsafe condition in specific transponder models. The scope remains tightly focused on the altitude encoding issue with Gillham/grey code sources and has not expanded beyond this technical safety fix."},"complexity_factors":["Single specific technical issue (altitude encoding error) with clear conditional logic","Only 2 main decision branches (digital source vs. Gillham/grey code source)","Specific part numbers referenced (6 CPNs total) but no extensive defined terms section","References to 3 external service bulletins but with clear hierarchy (SB 17, SB 17 Rev 1, or SB 20 Rev 1)","No nested exceptions or complex cross-referencing between sections","Short document (approximately 300 words) with straightforward applicability, requirement, and compliance structure typical of airworthiness directives"],"plain_english_summary":"This CASA Airworthiness Directive requires owners/operators of aircraft fitted with Rockwell Collins TDR‑94 or TDR‑94D Mode S transponders that receive altitude from older Gillham/“grey code” sensors to stop incorrect altitude broadcasts. Affected operators (e.g., ATR42, Dash 7/8, SD3‑60) must verify their altitude source and modify or replace the transponder as mandated; unmodified units cannot be installed on Gillham-equipped aircraft. This fixes a collision-risking altitude error."},"flash_summary":{"complexity_score":3,"scope_assessment":{"changed":false,"description":"The AD is narrowly targeted to a single safety issue: erroneous altitude reporting from specific Collins TDR‑94/TDR‑94D transponder part numbers when fed by a Gillham (grey code) input. The instrument does not expand beyond that original corrective purpose — it prescribes inspection, a manufacturer‑specified modification where required, and prohibits installation of the unmodified units on aircraft using a Gillham source. There is no indication in the text that the AD broadens its scope beyond that original safety objective."},"complexity_factors":["Short, single‑issue directive (limited length).","Applicability limited to two specific Collins part numbers and an example list of aircraft (Note 1).","Three clear, sequential requirements (inspect, modify if necessary, installation prohibition).","References to three external technical documents (Collins SB 17, SB 17 Rev 1, SB 20 Rev 1) that must be consulted for procedural detail.","Specific part‑number conversion paths (multiple CPNs specified) increase technical specificity.","Technical term requiring identification (Gillham/’grey code’ vs digital air‑data) introduces a factual determination step.","No layered exceptions or ancillary subparts — limited cross‑referencing within the AD itself."],"plain_english_summary":"**What this directive does (mechanically)**\n\n- Applies to Rockwell Collins TDR‑94 Mode S transponders (CPN 622‑9352‑004) and TDR‑94D Mode S transponders (CPN 622‑9210‑004). (Applicability)\n- Requires operators or maintainers to check whether the transponder’s altitude input is taken from a digital air‑data source or from a Gillham (\"grey code\") encoded source. The permitted inspection methods are those described in Rockwell Collins Service Bulletin (SB) No. 17, SB 17 Revision 1, or SB 20 Revision 1. (Requirement 1)\n- If the altitude input is from a Gillham (grey code) source, the transponder must be modified so it cannot report an erroneous altitude. The required modifications are specific part‑number conversions (for example, convert CPN 622‑9352‑004 to 622‑9352‑005 or to 622‑9352‑006, and analogous conversions for the 94D). Modifications must be done in accordance with the Collins service bulletins listed. (Requirement 2)\n- The specified unmodified transponder part numbers may not be installed in any aircraft that uses a Gillham‑encoded altitude source unless the transponder has been modified per Requirement 2. (Requirement 3)\n\n**Who this affects**\n\n- Aircraft operators and owners that have the listed Collins transponder units installed (the AD names several aircraft types as examples but is not limited to them). (Applicability, Note 1)\n- Maintenance organisations and technicians who perform the inspection and the required modification work using the Collins service bulletins.\n- Suppliers of Collins parts and authorised repair stations that supply the conversion parts or accomplish the modification.\n\n**Why it matters (stated purpose and testing that claim against practical effects)**\n\n- The directive’s stated safety purpose is to stop transponders from reporting incorrect altitude when their input comes from a Gillham (grey code) altitude source. The AD implements that by (a) identifying which transponders are affected, (b) requiring those units be checked to see what altitude source they use, and (c) mandating a manufacturer‑specified modification where the unsafe configuration exists. (Requirements 1–3)\n\nPractical implications, trade‑offs and costs:\n\n- Who pays: aircraft operators/owners pay for the inspection and, where needed, the modification (parts, labour and aircraft downtime). (Requirements 1–2)\n- Who decides and how: the CASA delegate issues the AD; compliance is tested/implemented by the operator and maintenance provider following Collins’ service bulletins (the AD explicitly references SB 17, SB 17 Rev 1, and SB 20 Rev 1). Compliance is binary — either the unit is shown to use a digital input (no further action) or it uses Gillham and must be modified. (Requirement 1)\n- Compliance burden: a one‑time inspection for each affected transponder, and for units fed by Gillham code, a hardware/software conversion per the Collins SBs. There is also an installation prohibition to prevent re‑fitting an unmodified affected part where it would be connected to a Gillham source. (Requirements 1–3)\n- Implementation risks and delays: availability of conversion parts or suitably authorised technicians could create aircraft downtime; misidentification of the altitude source could lead to unnecessary work or a missed unsafe condition; aircraft may be unable to return to service until the modification is completed if the transponder is found to be in the prohibited configuration. (Requirements 1–3)\n- Effects on private enterprise and competition: maintenance shops and Collins authorised repair stations will carry out the work; independent maintenance providers can do the work provided they follow the manufacturer SBs. The AD relies on manufacturer documentation for the fix, creating operational dependence on Collins’ technical instructions and parts. (Requirements 2)\n- Concentrated benefits vs. concentrated costs: the safety benefit (accurate altitude reporting for ATC and collision avoidance systems) accrues broadly to airspace users and the public; the direct monetary cost is concentrated on those operators who have the particular transponder fed by a Gillham source. (Applicability, Requirements 1–2)\n\n**Operational notes**\n\n- If the transponder’s altitude input is already derived from a digital air‑data source, no modification is required. (Requirement 1)\n- The AD lists several aircraft models as examples where these transponders are installed (ATR‑42, DHC‑7, DHC‑8, Short SD3‑60 and SD3‑60 Sherpa), but the applicability is defined by transponder part number rather than by airframe model. (Applicability, Note 1)\n\n**Section references**: Applicability; Note 1; Requirement paragraphs 1–3 (as numbered in the AD)."}},"importantCases":[],"_links":{"self":"/api/acts/ad-rad-75-tdr-94-tdr-94d-transponders","history":"/api/acts/ad-rad-75-tdr-94-tdr-94d-transponders/history","analysis":"/api/acts/ad-rad-75-tdr-94-tdr-94d-transponders/analysis","conflicts":"/api/acts/ad-rad-75-tdr-94-tdr-94d-transponders/conflicts","importantCases":"/api/acts/ad-rad-75-tdr-94-tdr-94d-transponders/important-cases","documents":"/api/acts/ad-rad-75-tdr-94-tdr-94d-transponders/documents"}}