AD/RAD/89 - Funwerk Avionics GmbH TRT800A and TRT800H Transponders

The central concept is an Airworthiness Directive (AD). Under the Australian regulatory system for civil aviation, an AD is a legally enforceable notice issued by CASA mandating inspection, modification, or replacement of an aircraft component or system to correct an identified unsafe condition. Non-compliance renders the aircraft unairworthy, meaning it may not be operated legally under the Civil Aviation Act 1988 and the Civil Aviation Regulations 1988 (CAR) or Civil Aviation Safety Regulations 1998 (CASR). ADs are part of a broader system of continuing airworthiness management that includes service bulletins, maintenance manuals, and mandatory reporting. Here, the AD is adopted from an equivalent EASA directive, illustrating the principle of regulatory harmonisation: Australia often adopts foreign ADs for components certified by overseas authorities, particularly when the same aircraft types operate under Australian registration. The directive concerns a Mode-S transponder. A transponder is an airborne radio transmitter-receiver that responds to interrogations from ground-based Secondary Surveillance Radar (SSR). Mode-S is an advanced SSR protocol that provides selective addressing of individual aircraft, allowing more precise identification and data exchange (altitude, call sign, flight ID) compared to older Mode A/C systems. The failure specifically reported was an intermittent loss of detection, meaning the transponder would stop replying to ground interrogations for periods, causing the aircraft to disappear from ATC screens. The directive ties compliance to a Service Bulletin (SB TRT800-A-H-1 Revision 1.04). A service bulletin is a manufacturer-issued document describing a modification or inspection procedure, but it is not itself mandatory until adopted by an AD or other regulatory requirement. By referencing the SB, the directive gives it legal force. The SB revision must be approved by EASA, not by CASA, reflecting the cascading approval structure. The concept of Mod-Index 10 is also important. This marking signifies that the transponder has already been modified to address the fault, likely through a previous version of the SB or a different revision. Units so marked are excluded from the AD, which creates an incentive for owners to check the marking before undertaking expensive removal. The directive distinguishes between two compliance obligations: requirement 1 (remove or replace existing installations by a deadline) and requirement 2 (prohibit new installations of unmodified units after that deadline). This bifurcated structure is typical for ADs that address both retroactive and prospective safety risks. The concept of effective date versus compliance date is key. The AD becomes effective on 7 May 2009, meaning it is legally in force from that day, but the actual physical compliance is not due until later. This gives time for parts procurement, maintenance scheduling, and labour allocation. However, if an unmodified transponder fails between the effective date and the compliance date, the aircraft cannot operate unairworthy; the AD imposes no obligation to proactively remove until the compliance date, but a failure might be considered a known unsafe condition.

The directive directly affects any person or entity that owns, operates, or maintains an aircraft registered in Australia and fitted with a Funkwerk TRT800A or TRT800H transponder falling within the specified serial number ranges. This includes private aircraft owners, flying schools, charter operators, aerial work operators, and corporate flight departments. The affected aircraft types listed in the directive’s note span a range of light aircraft and small general aviation airframes from manufacturers such as APEX (Robin) - DR1050, DR250, DR350, DR400 series; Cessna (including Reims) - 150, 172, 182, 210, T303, 337 series; Diamond Aircraft - DV20; Extra - EA300 series; Grob - G109B powered sailplane and G115 series; Mooney - M20J; Piper - PA28 series; Scheibe - SF25C powered sailplanes; and True Flight Holdings (Grumman/American) - AA5B. However, the note says these are “known to be installed on, but not limited to” those types, so the actual population may be broader. The directive indirectly affects maintenance organisations that carry out the replacement or modification. They must source the modified units or perform the SB modification, which requires access to the manufacturer’s instructions and possibly special tooling or training. The directive also affects importers and distributors of avionics equipment, as they can no longer sell unmodified affected transponders for installation in Australian aircraft after the cut-off date, unless they are for spare parts for already modified systems or for export. The directive’s background acknowledges that very few TRT800 transponders are known to be in Australia. This is a critical economic qualifier. If only a handful of units are affected, the compliance burden on the Australian fleet is small, but the cost per affected unit may be high because fixed costs of retrieval, modification, and reinstallation are spread over few units. For an owner of a single Cessna 172 with a TRT800A, the cost could easily exceed A$2,000 to A$5,000 depending on labour, shipping to an authorised repair station, and replacement cost if the unit is beyond economical repair. The directive does not provide any compensation or subsidy. The compliance chain also involves the manufacturer, Funkwerk Avionics, which has produced the SB and presumably supplies modification kits. If the company no longer supports the product line, owners may be forced to replace with a different brand transponder, incurring additional certification costs (e.g., supplementary type certificate) if the replacement is not identical. EASA is indirectly affected as the approval body for the SB revision; any delay in approval could affect compliance if owners wait for a later revision. The Civil Aviation Safety Authority itself is affected only as the issuer and enforcement body; the directive imposes no direct cost on CASA except for potential follow-up audits or enforcement actions. Crucially, the directive does not exempt aircraft operating VFR outside controlled airspace or other low-risk operations; the obligation is absolute regardless of where the aircraft flies. This means that even a glider or ultralight that happens to have an affected transponder is caught, although in practice such aircraft may not carry Mode-S transponders at all.

The primary duty imposed by the directive is on the aircraft owner or the operator (whoever is responsible for continuing airworthiness). By 19 November 2010, any affected transponder installed on the aircraft must be replaced with a unit that has been modified per SB TRT800-A-H-1 Rev 1.04 or later. After 18 November 2010, no affected transponder may be installed on any aircraft unless it has been so modified. This duty extends to any person who carries out an installation, including maintenance organisations and owners returning an aircraft to service after maintenance. The duty is strict: ignorance of the defect or lack of notification from CASA or the manufacturer is not a defence. The operator must also ensure that the transponder is correctly identified by model, part number, and serial number. The directive provides no remedy for owners who have already replaced the transponder voluntarily or who have had to replace it due to other failures before the compliance date; the duty is simply to not operate with an unmodified unit. There is a right (implicit) to use a different modification path, but only if approved by CASA via a separate exemption. The text of the directive does not mention that process, so it would fall under general regulatory provisions. Owners also have the right to trust the Mod-Index 10 exclusion. If a transponder is marked Mod-Index 10, the owner may rely on that marking as proof of compliance with the AD, without needing to obtain a separate modification. However, if the marking is incorrect or falsified, the owner could still be liable. The directive creates a right to operate the aircraft with a modified transponder once the modification is recorded in the aircraft maintenance records. That recording should reference the SB revision and the compliance date. The directive does not create any right to compensation from the manufacturer, EASA, or CASA for the cost of compliance. It also does not limit the owner’s right to remove the transponder entirely if the aircraft can legally fly without it (e.g., if the aircraft operates only outside Mode-S airspace). However, if the aircraft is required to carry a transponder under other rules (e.g., in controlled airspace), removal may not be a practical option. The directive does not impose a duty on the manufacturer to supply modification kits; if the manufacturer ceases support, the owner must source a replacement. The right to contest the directive through administrative review exists under general administrative law, but the directive itself is a legislative instrument and would be difficult to challenge on safety grounds. The duty is not ongoing once compliance is achieved; there is no periodic inspection requirement. But if the transponder later fails or is replaced with a new unit that is affected, the duty re-arises.

The directive does not specify penalties on its face; instead, it relies on the enforcement framework under the Civil Aviation Act 1988 and the Civil Aviation Regulations 1988 (CAR) or Civil Aviation Safety Regulations 1998 (CASR). Under regulation 39 of CAR, or equivalent provisions in CASR, failure to comply with an Airworthiness Directive is a breach of the condition of the aircraft’s certificate of airworthiness. Operation of an aircraft that does not comply with an applicable AD is unlawful and may result in the aircraft being grounded. Penalties for operating an unairworthy aircraft can include civil penalties of up to A$11,000 for an individual and A$55,000 for a body corporate per offence under the Civil Aviation Act, as well as potential criminal prosecution for reckless behaviour (s 20A of the Act). Moreover, the pilot in command and the owner may both be held liable. In practice, CASA may issue a direction to ground the aircraft or revoke or suspend the certificate of airworthiness until compliance is shown. Enforcement is risk-based: given the small number of affected units in Australia, it is unlikely that CASA will conduct targeted surveillance sweeps, but if an aircraft is subjected to a ramp inspection and the transponder is found to be within the suspect serial numbers, the inspector will check for compliance. A finding of non-compliance would lead to an immediate airworthiness directive non-compliance report, possible grounding, and a requirement to rectify before further flight. If the compliance deadline has passed, the owner cannot receive an extension from the inspector; only CASA head office might grant an exemption in exceptional circumstances, but the directive itself does not contain an exemption clause. There is also potential liability for maintenance organisations that certify an aircraft as airworthy with a known non-compliant transponder; they may face action under CAR 1988 regulation 42ZZJ or CASR Part 145 maintenance organisation certification. The note that the directive references EASA AD 2008-0183 does not create additional penalties under EASA regulations for Australian operators, but if the aircraft also operates in EASA member state airspace, both regulators could take action. The directive’s effective date of 7 May 2009 means any installation attempted after that date of an unmodified affected transponder (for Requirement 2, which only applies after 18 November 2010) may be considered a breach from that later date. However, if a transponder is fitted between 7 May 2009 and 18 November 2010, it is not a breach of Requirement 2 but still must be replaced before the compliance date. This creates a transitional trap: an owner could install a new old-stock unmodified unit in 2009, only to have to replace it in 2010. The penalties do not consider economic hardship; they are strictly liability-based.

The directive explicitly references EASA AD 2008-0183 as the originating directive. This reflects a hierarchy: EASA determined the unsafe condition for European-registered aircraft; CASA adopted the same condition for Australian-registered aircraft under its own regulatory powers. This interaction means that an operator maintaining aircraft to both EASA and CASA requirements will find identical compliance standards, reducing duplication. However, the Australian directive is a separate legal instrument; it is not simply a republication of the EASA AD. If EASA later revises its AD (e.g., to extend compliance dates or include new serial numbers), the Australian AD remains unchanged unless CASA issues an amendment. The directive interacts with the Civil Aviation Safety Regulations (CASR), particularly Part 39 (Airworthiness Directives) if the aircraft is classified as a large aeroplane or complex type, or with CAR 1988 regulation 39 for other aircraft. Under these provisions, an AD must be complied with as a condition of the aircraft’s airworthiness certificate. The directive also interacts with regulations concerning the installation of avionics: CASR Part 21 (certification of products and parts) and Part 43 (maintenance). The modification described in the SB must be carried out by a person authorised to perform maintenance on avionics, typically a licensed aircraft maintenance engineer (LAME) with an appropriate avionics rating. The maintenance release required after the modification must state that the AD has been complied with. There may be interactions with the Civil Aviation Orders, such as Civil Aviation Order 20.18 (equipment for IFR operations), which may require a transponder for flight in controlled airspace. If an aircraft is not required to carry a transponder, the owner could simply remove the unit entirely rather than modify it, which would achieve compliance without the cost of modification. But if the aircraft normally flies in transponder-mandatory airspace, removal may not be practical. The directive does not address privacy or data handling aspects of Mode-S, which may intersect with communications surveillance laws, but that is likely irrelevant. The directive also interacts with the manufacturer’s service bulletin as a contractual document; if the modification is carried out by the manufacturer or an authorised service centre, it will be governed by the terms of the service bulletin, which itself may require specific training or parts. There is no interaction with state or territory laws, as aviation safety is a Commonwealth matter. The directive does not incorporate the text of the SB, so operators must obtain the SB from the manufacturer or from EASA’s website. This creates a practical interaction with intellectual property law: the SB is a proprietary document, and the owner must acquire it legally. The directive does not create any interaction with the Competition and Consumer Act 2010; it does not affect consumer guarantees or product liability, as it is a safety regulation. However, if the transponder defect was due to manufacturing fault, an owner may have a separate claim against Funkwerk under consumer law, but that is beyond the directive’s scope.

The directive document itself, AD/RAD/89 dated 26 March 2009 and effective 7 May 2009, does not contain any record of amendments. It is presented as a standalone instrument. There is no indication that it replaced an earlier AD or that it has been subsequently amended by CASA. However, the directive references EASA AD 2008-0183, which may have its own amendment history. The directive also references Funkwerk Avionics Service Bulletin TRT800-A-H-1 Revision 1.04 dated 17 October 2008, and allows for later revisions approved by EASA. This means that the compliance standard can change without an amendment to the Australian AD, provided the later revision is approved by EASA and the owner chooses to use it. But the directive itself remains static unless CASA issues a new instrument. The note states “EASA AD 2008-0183 refers”, but does not incorporate it by reference into the Australian AD; it is merely a reference. Therefore, if EASA AD 2008-0183 is amended (e.g., to include new serial numbers or extend rework intervals), those amendments do not automatically apply in Australia. Operators must continue to comply with the Australian directive as written until CASA issues a new AD. In practice, CASA may issue a follow-up AD or a variation, but none is recorded in this document. The directive became effective on 7 May 2009. The compliance deadlines (19 November 2010 and 18 November 2010) were set approximately 18 months and 19 months respectively from the effective date. Those dates have long since passed, so for any aircraft still operating with an unmodified TRT800A or TRT800H transponder today (2025), the AD is now retrospective and ongoing: the transponder should have been modified long ago. The lack of amendment history suggests that CASA did not extend the deadlines or alter the scope. One can infer from the small quantity of affected units in Australia that CASA may have considered the urgency low, but the compliance dates are fixed. For a practitioner researching whether a specific transponder is compliant, the only relevant amendment is the revision of the underlying service bulletin. If the owner used Revision 1.05 or later, they must confirm that EASA approved that revision. The AD does not require that the SB revision be incorporated by reference into the aircraft’s maintenance data. The absence of an amendment history also means that there is no known relaxation of the directive for non-Mode-S airspace or for aircraft operated solely in visual flight conditions outside controlled airspace. The directive applies universally.

The directive document does not reference any court cases or tribunal decisions. No litigation is mentioned. In Australia, litigation over airworthiness directives is relatively rare because aviation safety regulations are typically not challenged on their merits; operators comply or face enforcement. However, there is a background of potential disputes that could arise from this directive. First, if an owner alleged that the defect was not actually safety-critical and that CASA exceeded its power, judicial review under the Administrative Decisions (Judicial Review) Act 1977 might be theoretically available, but given the scientific and operational basis (ANSP reports and flight trials), such a challenge would face a high threshold. Second, an owner might seek compensation from the Commonwealth for a taking of property (the transponder having to be replaced at owner’s cost) under paragraph 51(xxxi) of the Constitution. Australian courts have consistently held that safety regulations are not acquisitions of property; there is no right to compensation for being forced to fix a defective part. Third, there could be contract disputes between the owner and a maintenance organisation if the modification was botched; but that is private litigation, not about the AD itself. Fourth, if a foreign regulatory authority (e.g., EASA) later finds that Funkwerk’s transponder defect caused an accident, there could be product liability litigation, but that would occur in overseas courts. None of this is recorded in the directive. CASA itself is a delegate of the Minister and is immune from civil liability under the Civil Aviation Act for actions taken in good faith, so tort claims against CASA for issuing the AD are unlikely. The only recorded litigation history that might affect this directive is a general pattern of few challenges to ADs in Australia. The Federal Court has heard cases on other ADs (e.g., relating to fuel tanks or engine components), but not on this specific directive. The absence of litigation does not mean the directive is uncontroversial; it simply means no recorded case exists. For compliance professionals, the lack of litigated interpretation means the directive’s black-letter text is the final word. Courts have not needed to interpret the phrase “intermittent loss of detection” or whether a transponder that fails only 1% of the time is covered. The directive is self-executing. If a dispute did arise, it would likely be over whether a particular serial number falls within the range (e.g., if the serial number is missing or illegible) or whether a transponder marked Mod-Index 10 genuinely complies. These are factual disputes, not legal ones.

Several aspects of this directive could catch an unwary aircraft owner or compliance officer. First, the serial number cut-offs are absolute, but the format of the serial numbers is not described beyond the numbers “40539908” for TRT800A and “30250007” for TRT800H. If a transponder has a serial number with alpha prefixes or suffixes, the owner must determine whether a sequential logic applies. The directive says “up to and including” those numbers, but if Funkwerk used a different convention (e.g., date codes or batch letters), an exact reading might be impossible without manufacturer support. Second, the Mod-Index 10 exclusion is critical. A transponder that has been modified in the field might not have that marking on its label; the owner cannot rely on the exclusion unless the marking is physically present. A maintenance organisation that installs a used transponder without verifying the marking could inadvertently install a non-compliant unit. Third, the directive does not state that a transponder with a later serial number (above the cut-off) is automatically compliant. It only says transponders within the stated ranges are affected. But if later serial numbers have the same design defect, they are not covered by this AD; however, they may be subject to a different AD. Do not assume high numbers are safe. Fourth, the compliance dates have passed, but the obligation to comply is ongoing. An aircraft that has not flown since 2009 but is now being returned to service must still have its transponder modified or replaced before flight. Many owners may forget this and think the issue is obsolete. Fifth, the directive applies to transponders “manufactured by Funkwerk Avionics GmbH (formerly Filser Electronic GmbH)”. Company name changes can cause confusion: the part may be labelled “Filser Electronic” but is still caught. Sixth, the directive allows use of a later revision of the SB if approved by EASA, but it does not create a register of approved revisions. The owner must check EASA’s website or contact the manufacturer to know which revisions are current. If a later non-approved revision is used, compliance is not achieved. Seventh, the note listing aircraft types is illustrative, not exhaustive. The directive applies regardless of the aircraft model, so even a helicopter or a large turbo-prop fitted with this transponder must comply. Eighth, the effective date of 7 May 2009 means that any installation of a new transponder of the affected types after that date is not illegal until 18 November 2010, but it might be considered poor practice. An owner might inadvertently install a brand new old-stock unit in 2009 and then have to replace it the following year, wasting money. Ninth, the directive does not provide for a ferry flight exemption. If the transponder is found to be affected during a pre-purchase inspection after the compliance date, the aircraft cannot be flown for repair unless it is operated outside Mode-S airspace and transponder requirements, or a special CASA exemption is obtained. Tenth, the directive is an Australian AD, but if the aircraft is registered in another country and imported into Australia, the Australia only applies after import and registration. The foreign owner must check the local equivalent AD. Finally, the directive is short and contains no compliance schedule for parts availability or reporting. Owners who wait until the last minute may find that modification kits are backordered or that repair stations are fully booked, leading to an expensive grounding.

Compliance with AD/RAD/89 requires a systematic, documented process. Step one: identify all aircraft in the fleet that are equipped with a Funkwerk Avionics TRT800A or TRT800H transponder. This includes checking the aircraft records, the current installed equipment list, and physically inspecting the transponder faceplate for model and serial number. If the serial number is less than or equal to 40539908 for TRT800A, or less than or equal to 30250007 for TRT800H, the unit is suspect unless it carries a Mod-Index 10 marking. If the marking is present, the unit is excluded and no further action is required, though it is wise to photograph or log the evidence. Step two: if the unit is within the affected range and not excluded, determine if it has already been modified per SB TRT800-A-H-1 Rev 1.04 or later. Check the maintenance logbooks for an entry referencing the service bulletin. If there is no such entry, assume non-compliance. Step three: for affected units installed before the compliance date (19 November 2010), the owner must have the unit removed and either replaced with a modified compliant unit or sent to an authorised repair station for modification. In practice, given the passage of time, it is likely that any affected unit still in service has either been modified or is non-compliant. The modification involves installing a kit and possibly updating software. The work must be performed by a licensed aircraft maintenance engineer (LAME) with avionics certification. The modification must follow the SB exactly; deviations invalidate the compliance. After modification, the unit should be marked with a new part number or modification identifier; the maintenance release must cite SB TRT800-A-H-1 Rev 1.04 and the AD number. Step four: for new installations after 18 November 2010, ensure that the transponder being installed is not within the affected serial number ranges unless it has been modified. Sourcing a transponder from stock requires checking its serial number and, if in the range, verifying the modification status. It may be simpler to purchase a different brand or model that is not covered by the AD. Step five: maintain records. The aircraft log book entry should reference the AD number (AD/RAD/89), the effective date (7 May 2009), the compliance date (19 November 2010 for removal, 18 November 2010 for installation ban), the SB used, and the part number/serial number of the transponder. If the modification was done at the manufacturer or a repair station, a Form 1 (EASA Form 1 or equivalent) should be obtained. Step six: after compliance, continue to check during routine inspections that the transponder remains in the modified configuration. If the unit is replaced in the future with another affected unit, the compliance cycle restarts. There is no need to report compliance to CASA unless specifically asked; the records are proof. An owner may wish to voluntarily notify CASA if the aircraft is part of a fleet that was previously non-compliant, to avoid enforcement action. Finally, if the transponder is not required for the aircraft’s operations (e.g., aircraft that never enters controlled airspace requiring Mode-S), the owner may remove the unit entirely and install a blank plate or a non-transponder system. This achieves compliance because the AD only restricts installation and operation of transponders; it does not require a transponder to be present. However, if the aircraft’s weight and balance or other systems depend on the unit, removal must be logged accordingly. If the aircraft is to be sold internationally, the seller should disclose the AD and provide evidence of compliance to the buyer.