{"id":"F2016L00368","name":"AD/RAD/47 Amdt 4 - Periodic Testing of ATC Transponders","slug":"ad-rad-47-amdt-4-periodic-testing-of-atc-transponders","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":94345,"registerId":"commonwealth-F2016L00368-current","compilationNumber":null,"startDate":"2026-04-02","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"Radio Communication (including Emergency","sectionType":"division","heading":"Radio Communication (including Emergency Transmitters and Navigation Equipment)","content":"### Radio Communication (including Emergency Transmitters and Navigation Equipment)\n\n| AD/RAD/47 Amdt 4 | Periodic Testing of ATC Transponders | 7/2016 |\n| ---------------- | ------------------------------------ | ------ |\n\n| Applicability: | All Air Traffic Control transponders fitted to aircraft to which Part 42 of CASR 1998 applies. |\n| -------------- | ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |\n| Requirement: | 1. For all transponders, perform a system test in accordance with the requirements of United States of America 14 CFR (Federal Aviation Regulations) Part 43, Appendix F.2. For transponders utilising electron tube technology (ETT) perform the following tests to confirm:a. the duration of all reply pulses (pulse width) is between 0.35 to 0.55 microseconds; andb. the amplitude variation between one reply pulse and any other reply pulse is not greater than 1 dB.For Requirements 1 and 2: Mode A code 2100 is to be used when carrying out transponder tests.For Requirement 2 only: ETT means the technology that utilises physical and electrical characteristics of a physical body to oscillate and amplify a signal at its resonant frequency for subsequent broadcast. This includes thermionic valves, klystrons or cavity oscillators etc. As these components age, the characteristics which provide the signal stability vary, which affects the output signal. Transponders utilising ETT include, but are not limited to, Honeywell (Bendix-King) KT76A, Narco AT150 and ARC RT859.3. Repair or replace any transponder that fails any of the Requirement 1 or 2 tests. |\n| Compliance: | For Requirements 1 and 2: Within 24 calendar months after the effective date of this AD or within 24 calendar months after a system test was last accomplished in accordance with AD/RAD/47 Amdt 2, whichever occurs first, and thereafter at either:a. intervals not exceeding 24 calendar months; orb. intervals in accordance with an approved maintenance program for the aircraft under regulation 42.140 of CASR 1998. |\n| | Note: Generic guidance on the testing of transponders is available in AWB 34-013 and AWB 34-09.For Requirement 3: Before further flight after the Requirement 1 or 2 tests. |\n| | This AD commences on 23 March 2016. |\n| Background: | AD/RAD/47 was originally issued to introduce a procedure additional to the transponder self-check prescribed in paragraph (4) (k) of section 5 of Schedule 5 of the Civil Aviation Regulations 1988 (CAR 1988), and to align with the requirements of overseas civil aviation authorities.Amendment 1 advised of a new code, compatible with air traffic control requirements, that was to be used when testing transponder systems.Following the deployment of new Mode S radar interrogators in Australia, it was discovered that variation in the height of reply pulses transmitted by the transponder could be misinterpreted by the interrogator and this may cause the Mode A code to appear to spontaneously change during flight. This may generate short term conflict alerts to be displayed to air traffic controllers.Amendment 2 introduced serviceability checks to confirm that transponders utilising ETT are performing to the specifications to which they were originally certified.Amendment 3 was issued to limit the applicability of the AD to Part 42 aircraft only.Amendment 4 is issued to update a regulatory reference in the compliance section from regulation 42M of CAR 1988 to regulation 42.140 of CASR 1998. This AD will be repealed after the requirements are incorporated into a future amendment of the Part 42 Manual of Standards. |\n\n![DAVID_W](image.001.png)\n\nWilliam M. David \nDelegate of the Civil Aviation Safety Authority\n\n18 March 2016","sortOrder":0},{"sectionNumber":"AD/RAD/47 Amdt 4","sectionType":"part","heading":"AD/RAD/47 Amdt 4","content":"## AD/RAD/47 Amdt 4","sortOrder":1},{"sectionNumber":"Periodic Testing of ATC Transponders","sectionType":"part","heading":"Periodic Testing of ATC Transponders","content":"## Periodic Testing of ATC Transponders","sortOrder":2},{"sectionNumber":"7/2016","sectionType":"part","heading":"7/2016","content":"## 7/2016","sortOrder":3}],"analysis":{"flash_summary":{"complexity_score":5,"scope_assessment":{"changed":true,"description":"The AD’s scope was narrowed by Amendment 3 to apply only to aircraft subject to CASR Part 42 (Background). Amendment 4 itself updated a regulatory cross‑reference from CAR 1988 to CASR 1998 (regulation 42.140) without expanding applicability. The instrument is transitional pending incorporation into the Part 42 Manual of Standards (Background)."},"complexity_factors":["Technical test standards reference an external foreign rule set (US FAR Part 43, Appendix F) rather than only domestic technical specs (Requirement 1).","Additional precise laboratory measurements for ETT transponders: pulse width 0.35–0.55 μs and amplitude variation ≤1 dB increase measurement and tooling needs (Requirement 2).","Applicability limited to aircraft to which CASR Part 42 applies, producing a scope boundary that operators must determine (Applicability; Background: Amendment 3).","Two compliance pathways: fixed 24-month interval or timing under an approved maintenance program, creating administrative choice and recordkeeping (Compliance).","Immediate operational consequence on failure: 'repair or replace' and 'before further flight' requirement creates potential grounding and direct operator costs (Requirement 3; Compliance note).","Regulatory cross-reference update (from CAR 1988 to CASR 1998, regulation 42.140) and a stated plan to fold requirements into the Part 42 Manual of Standards introduce a transitional regulatory state (Background).","Enforcement and approval discretion sits with CASA and approved maintenance program holders, creating delegated decision points for intervals and acceptance (Compliance: regulation 42.140 reference)."],"plain_english_summary":"This AD requires periodic system tests of all ATC transponders on aircraft subject to CASR Part 42, using US FAR Part 43 Appendix F procedures; transponders with electron-tube technology (ETT) must also meet pulse-width and amplitude limits, and failures must be repaired or replaced. It aims to reduce misinterpretation by Mode S interrogators that can cause apparent Mode A code changes and conflict alerts. Compliance is every 24 calendar months or under an approved maintenance program (operators pay for testing/repairs; maintenance providers perform tests; CASA enforces via regulation 42.140)."},"kimi_summary":{"content_quality":"ok","complexity_score":4,"scope_assessment":{"changed":true,"description":"The original AD/RAD/47 was issued to introduce additional testing procedures beyond basic self-checks. Over four amendments, the scope has narrowed significantly: Amendment 1 changed test codes; Amendment 2 added specific ETT testing after new radar deployment revealed safety issues; Amendment 3 restricted applicability to Part 42 aircraft only (excluding simpler aircraft); and Amendment 4 updates regulatory references. The directive has evolved from a broad additional testing requirement to a targeted safety fix for aging technology (electron tubes) interacting with modern radar, with limited applicability. The document also notes this AD will be repealed once requirements are absorbed into the Part 42 Manual of Standards, indicating temporary scope pending broader regulatory integration."},"complexity_factors":["Multiple amendment layers (Amendment 4) with historical context requiring understanding of previous versions (Amendments 1-3)","Dual applicability structure: general requirements for all transponders PLUS specific technical requirements for electron tube technology (ETT) subset","Nested compliance timelines: 24-month baseline with alternative compliance via approved maintenance programs","Technical specifications requiring specialized knowledge (microseconds, decibels, Mode A codes, Mode S radar)","Cross-references to external regulations: US 14 CFR Part 43 Appendix F, CASR 1998 Part 42, regulation 42.140, AWB 34-013 and 34-09","Conditional logic: 'whichever occurs first' calculations for initial compliance dates","Defined term (ETT) with technical explanation embedded within requirements section rather than interpretation section"],"plain_english_summary":"This CASA Airworthiness Directive mandates periodic testing of aircraft ATC transponders—particularly older electron-tube models—to prevent garbled returns that can mimic identity changes and trigger false collision alerts. It affects aircraft with transponders under Part 42 maintenance rules and requires system checks every 24 months, additional performance checks for tube-based units, and immediate repair or replacement if tests fail.\n\nAmendment 4 only updates a regulatory reference; the testing requirements remain unchanged."},"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"}},"importantCases":[],"_links":{"self":"/api/acts/ad-rad-47-amdt-4-periodic-testing-of-atc-transponders","history":"/api/acts/ad-rad-47-amdt-4-periodic-testing-of-atc-transponders/history","analysis":"/api/acts/ad-rad-47-amdt-4-periodic-testing-of-atc-transponders/analysis","conflicts":"/api/acts/ad-rad-47-amdt-4-periodic-testing-of-atc-transponders/conflicts","importantCases":"/api/acts/ad-rad-47-amdt-4-periodic-testing-of-atc-transponders/important-cases","documents":"/api/acts/ad-rad-47-amdt-4-periodic-testing-of-atc-transponders/documents"}}