AD/DA42/3 Amdt 2 - Engine Control Unit Back-Up Batteries

Several technical and regulatory concepts are central to understanding this Directive. Full Authority Digital Engine Control (FADEC) is the engine management system on the TAE125‑01 and TAE125‑02‑99 engines approved for installation on the DA42. A FADEC system relies on a steady electrical power supply for its digital control unit. The Directive’s Background explains that these engines “are not totally independent from the aircraft electrical power supply.” During the incident that triggered the Directive, a significant voltage drop caused a simultaneous reset of the FADEC on both engines, leading to automatic feathering of the propeller blades. The ECU backup battery is a dedicated power source for the engine control unit intended to prevent such transient voltage drops from causing FADEC resets. The modification effectively decouples the ECU power supply from the aircraft’s main battery during high‑demand events such as landing gear retraction.

Mandatory Service Bulletin (MSB) is a document issued by the manufacturer (DAI) that contains instructions for a modification or inspection that the manufacturer considers essential for continuing airworthiness. An MSB is made mandatory when referenced in an Airworthiness Directive. Optional Service Bulletin (OSB), by contrast, is a manufacturer‑issued bulletin that is not mandatory on its own but can become an alternative method of compliance if approved by the airworthiness authority. The Directive provides that compliance with DAI OSB 42‑050/1 (a later optional bulletin) is an acceptable alternative to the MSB‑based modification. This creates two possible compliance paths with potentially different costs and complexity.

Temporary Revision (TR) is a document inserted into an Aircraft Flight Manual or Aircraft Maintenance Manual to provide interim instructions until the permanent revision of the manual incorporates the changes. The Directive requires the insertion of specific TRs and permits their removal once the permanent revision is published. This involves a record‑keeping burden for operators: the TR must be physically inserted, and later removed only when confirmed that the permanent revision includes the same information.

Alternative Method of Compliance (AMOC) is a regulatory concept allowing the airworthiness authority to approve a different means of satisfying an AD requirement. In this case, EASA approved DAI OSB 42‑050/1 as an AMOC for the requirements of AD 2007‑0183 R2, and the Directive accepts that same AMOC for its own requirements. The Directive does not specify the technical differences between the MSB and OSB modifications. Operators must therefore make their own assessment of which path is more feasible given parts availability, labour skill, and documentation compatibility.

Voltage drop is the physical phenomenon at the root of the Directive. When the main landing gear is retracted, the electrical system experiences a transient high current draw. If the main battery is inadequately charged, the voltage dips sufficiently to disrupt FADEC operation. The Directive prescribes a hardware solution (backup batteries) but does not alter the underlying operator behaviour that the German accident investigation identified as the primary cause (violation of AFM procedures regarding battery charge). This creates a regulatory asymmetry: the cost of the fix is borne by all owners, while the root behavioural cause may or may not be corrected by other means.

The Directive directly applies to registered owners and operators of Diamond DA42 series aeroplanes within a defined range of serial numbers. The listed serial numbers are: 42.004, 42.006, 42.009 through 42.156, 42.158 through 42.176, 42.178 through 42.190, 42.192 through 42.233, 42.235 through 42.246, 42.248 through 42.254, 42.256 through 42.261, 42.263 through 42.269, and Canadian production line aeroplanes S/N 42.AC001 through 42.AC109. The Directive does not explain why aeroplanes outside this range are not affected; presumably either later serial numbers incorporated the backup battery modification at manufacture, or the TAE engine type is not fitted to aircraft outside the range. Operators of aeroplanes with serial numbers just below or above the listed ranges have no compliance obligation under this AD but may still face pressure from insurers or lessors to adopt the modification voluntarily.

The Directive’s requirements impose duties on multiple parties. Aircraft owners bear the ultimate financial and legal obligation to ensure that the modification is performed on time and that the manuals are amended. They must procure the MSB or OSB kit and pay for labour, which may involve specialised maintenance organisations because the work involves modifications to the engine electrical system. Maintenance organisations that hold approvals under Part 145 of the Civil Aviation Safety Regulations (or equivalent under Part 42 or Part 66) must have the capability to install ECU backup batteries in accordance with the approved instructions. They must also be able to insert temporary revisions into the maintenance manual and update the operator’s maintenance program. Pilots are affected indirectly: they must fly with an AFM that includes the temporary revision, which may contain new procedures or limitations. The mandatory manual update may affect flight operations such as pre‑flight checks or emergency procedures related to the FADEC system. Regulatory bodies include CASA as the issuing authority, EASA as the approval body for the referenced documents, and the German investigation agency (BFU) whose report formed the background rationale. The Directive also interacts with the Canadian regulator because Canadian production line aeroplanes are within the applicability, suggesting that CASA’s AD is recognised or reciprocated internationally.

Lessors and financiers are indirectly affected because an unmodified aircraft would fail to comply with airworthiness requirements, potentially grounding the asset and reducing its lease or resale value. The Directive thus imposes a cost on capital‑intensive assets that must be borne by the operator in the short term, but ultimately may be passed through to lessors or purchasers through lease terms or asset valuation adjustments. The Directive does not provide any compensation mechanism for this regulatory imposition, consistent with the general approach under the Civil Aviation Act that airworthiness directives are uncompensated.

The Directive creates a hierarchy of duties on the operator. The primary duty is to perform the modification mandated in Requirement 1: “Modify the engine electrical system by installing additional engine control unit (ECU) backup batteries” in accordance with DAI MSB 42‑042, as amended by later EASA‑approved revisions. This is an absolute obligation; there is no carve‑out for aircraft that are about to be retired, sold, or operated in limited conditions. If the aircraft is within the applicabile serial number range, the duty attaches regardless of whether the operator believes the voltage drop risk is acceptable.

The second duty is to amend the DA 42 Aircraft Maintenance Manual by inserting the specified Temporary Revision and updating the operator’s maintenance programme so that the aircraft is maintained in accordance with the revised manual. This is not merely a paperwork exercise; it imposes a continuing obligation on the operator to keep the maintenance program current with the TR, and to ensure that all future maintenance tasks are performed in accordance with the revised procedures. Similarly, the third duty requires inserting a copy of the AFM TR into the Aircraft Flight Manual, which must then be carried on board and used by flight crew. Pilots must follow any new procedures or limitations contained in that TR.

The Directive also confers certain rights on the operator. Most significantly, the operator has the right to choose an alternative method of compliance: modification in accordance with DAI OSB 42‑050/1, which has already been approved by EASA as an alternative to the original MSB requirement. This gives operators flexibility to select a compliance path that may be cheaper, more readily available, or more convenient, provided the associated documents referenced in the OSB are followed. The Directive does not specify what those associated documents are, so operators must acquire and review the OSB and its cross‑references.

The operator also has the right to remove the Temporary Revisions from the AMM and AFM “when the information contained in the TR is incorporated in the manual during the normal revision process.” This means that the operator does not need to permanently carry the TR once the manufacturer issues a permanent revision to the manual that includes the same content. However, the operator must verify that the permanent revision indeed incorporates the TR information; premature removal could lead to non‑compliance.

A further implied right is the ability to seek CASA approval for an alternative method of compliance that is not already approved by EASA. The Directive explicitly defines OSB 42‑050/1 as an acceptable alternative, but it does not close the door to other deviations. In practice, an operator could petition CASA for a separate AMOC under the general provisions of the Civil Aviation Act or regulations, though the Directive does not address this directly.

The duties are time‑sensitive. Compliance must be achieved within 200 hours time in service after the original effective date (27 July 2007), but no later than 30 November 2007. This creates a hard deadline that is earlier than the 200‑hour limit for most aircraft that fly at a high utilisation rate. For an aircraft flying 50 hours per month, the 200‑hour limit would fall around November 2007 anyway, so the calendar deadline is the binding constraint for aircraft with lower utilisation. The short compliance window imposes a significant operational burden on operators who must schedule the modification during already tight maintenance slots.

Although the Directive itself does not recite penalty provisions, it is issued under the authority of the Civil Aviation Act 1988 (Cth) and the Civil Aviation Safety Regulations 1998 (CASR). Non‑compliance with an Airworthiness Directive constitutes a breach of section 20AA of the Civil Aviation Act (maintaining an aircraft in an airworthy condition) or regulation 42. of CASR, depending on the exact regulatory framework at the time of issuance. The Civil Aviation Act provides that operating an aircraft that does not meet airworthiness requirements is an offence that can be prosecuted in the Commonwealth magistrate’s court. Penalties for individuals can include fines of up to 200 penalty units (currently $27,500 per offence, but indexed to inflation) and for bodies corporate, up to 1,000 penalty units ($137,500) or more under the Criminal Code and the Regulatory Powers (Standard Provisions) Act 2014.

Enforcement is primarily the responsibility of CASA’s enforcement arm. CASA has a range of enforcement tools beyond prosecution: it can issue a written direction under section 29 of the Civil Aviation Act requiring an operator to ground the aircraft until the AD is complied with; it can suspend or cancel the aircraft’s Certificate of Airworthiness for non‑compliance; it can impose a “maintenance grounding” under Part 42, Subpart 42.O; and it can issue a show‑cause notice. The practical consequence for most operators is that an annual Certificate of Airworthiness renewal inspection will check compliance with applicable ADs. An unmodified DA42 will fail that inspection and the aircraft will be grounded until the AD is satisfied.

The Directive’s compliance deadline creates an implicit enforcement sequence. The original compliance date (30 November 2007) has long passed for current operators, but the Directive remains effective for any aircraft that may have been out of service at that time and is now being brought back into active use. For such aircraft, the modification must be performed before the aircraft can be legally flown. CASA may also audit operators to ensure that the AMM and AFM Temporary Revisions are present. In practice, the primary enforcement mechanism is the periodic maintenance and certification chain, not active surveillance.

The Directive does not provide for a grace period or for partial compliance. The modification, manual amendment, and AFM insertion are all mandatory; omitting any one of them would render the aircraft non‑compliant despite full performance of the other two. The alternative method of compliance (OSB 42‑050/1) must be followed exactly as described; a partial or variant installation that deviates from the OSB’s instructions would not be accepted unless separately approved as an AMOC. Enforcement may therefore focus on checking that the modification matches the approved MSB or OSB instructions, not merely that some backup batteries have been installed.

The Directive explicitly cross‑references EASA AD 2007‑0183 R2, the European Airworthiness Directive that first mandated the ECU backup battery modification for the same aircraft type. The Background notes that the original issue of the CASA Directive “mandated the installation of additional ECU backup batteries,” a requirement already imposed by the EASA AD. The interaction creates a situation where an Australian‑registered DA42 operating internationally must meet both the CASA AD and the EASA AD, although in practice the requirements are identical because the CASA AD directly references the same DAI MSB. The CASA Directive explicitly states that performance of OSB 42‑050/1 is “acceptable as an alternate method of compliance for this Directive,” noting that OSB 42‑050/1 was already approved by EASA as an alternative to AD 2007‑0183 R2. This means that an operator who follows the OSB path will have simultaneously satisfied the EASA AD (if applicable to the aircraft’s registry) and the CASA AD.

The Directive also interacts with the general regulatory framework for aircraft maintenance. Under the Civil Aviation Safety Regulations, maintenance must be performed in accordance with an approved maintenance program. The Directive requires the operator to “update the operator’s maintenance programme” to reflect the insertion of the AMM TR. This makes the TR part of the approved maintenance basis for the aircraft. If the operator fails to update the program, they may be in breach not only of the Directive but also of regulation 42.120 (which requires maintenance to be performed in accordance with the maintenance program) or equivalent rules for aircraft operating under Part 42 or Part 91.

The Directive’s requirement to amend the AFM interacts with the rules governing flight manual carriage and use. Under Civil Aviation Regulation 257 (or equivalent provisions in CASR Part 91), the aircraft must be operated in accordance with the AFM. Inserting a TR changes the approved flight manual, thereby altering the operational limitations that pilots must follow. A pilot who operates the aircraft without the TR inserted (or who removes it before the permanent revision is published) would be flying without a current AFM, potentially in breach of the operation‑specific regulations.

The Directive is silent on the interaction with the Australian Consumer Law or product liability. However, the forced modification may limit the manufacturer’s exposure: if a voltage drop incident occurs on an unmodified aircraft after the AD took effect, the owner’s ability to bring a product liability claim against Diamond or Thielert may be reduced because the AD made the modification mandatory and provided a clear standard. Conversely, the owner could argue that the AD’s requirement itself acknowledges a design defect, potentially strengthening a claim for compensation from the manufacturer in jurisdictions that allow such actions.

There is no explicit discussion of state‑by‑state application because aviation is a Commonwealth‑regulated field under the Constitution section 51(i) and (xxix). The Directive therefore overrides any state or territory airworthiness requirements that might conflict.

The Directive is marked “AD/DA42/3 Amdt 2,” designating it as the second amendment to the third Airworthiness Directive on the DA42 type. The original issue of this Directive became effective on 27 July 2007. It mandated the installation of ECU backup batteries and the insertion of AFM and AMM Temporary Revisions. Amendment 1 (released after the original issue but before September 2007) continued all original requirements but allowed compliance in accordance with later EASA‑approved revisions of the referenced documents. This provided operators with the ability to use updated versions of MSB 42‑042 or its associated work instructions if EASA approved newer versions, without needing a further amendment to the CASA Directive.

Amendment 2 (the subject of this document) introduces two significant changes. First, it explicitly approves an alternative method of compliance: DAI Optional Service Bulletin 42‑050/1 dated 15 October 2007, along with its associated documents. This OSB had already been accepted by EASA as an alternative to AD 2007‑0183 R2. Second, Amendment 2 extends the compliance deadline by an additional 100 hours time in service and sets a final calendar date of 30 November 2007. The original compliance period had been “the next 200 hours time in service after the effective date of the original issue … but not later than 30 November 2007.” Since the original effective date was 27 July 2007, that gave at most four months. Amendment 2 appears to have relaxed the requirement slightly (or perhaps the 200‑hour period was running out), but the calendar deadline remained the same (30 November 2007). The Background text states: “This Amendment continues the requirements of Amendment 1 but introduces an optional alternate method of compliance … and extends compliance by an additional 100 hours time in service until 30 November 2007.” This phrasing suggests that the original 200‑hour limit was replaced with a 300‑hour limit, but the calendar deadline (30 November) did not change for aircraft already approaching that date.

A curious inconsistency appears in the effective date. The table at the top of the document reads: “This Amendment becomes effective on 16 November 2007.” Yet the Background paragraph at the bottom of the page states: “This Amendment becomes effective on 7 September 2007.” The document is signed on 13 November 2007 by David Punshon, Delegate of CASA. It is possible that the 7 September date applies to Amendment 1, but the formatting places it directly under “This Amendment continues the requirements of Amendment 1 …” without clear separation. The document is labelled “Amdt 2” so the effective date of Amendment 2 should be 16 November 2007, which would make sense for a signature date of 13 November with a three‑day delay. The 7 September date likely refers to Amendment 1. This ambiguity is a classic “gotcha” and should be resolved by the operator by checking the official CASA registry for the correct effective date.

The directive is numbered “1/2008 TX” in the top right corner, likely a CASA internal tracking number indicating it relates to the 2008 transmission series. This has no operational significance.

The source document does not reference any court proceedings or litigation related to the Directive. Airworthiness directives are generally not directly litigated in Australia unless there is a challenge to the validity of the directive (for example, on procedural grounds such as failure to consult, or on jurisdictional grounds). The Commonwealth Administrative Appeals Tribunal can review certain CASA decisions under the Administrative Appeals Tribunal Act 1975, but an Airworthiness Directive is a legislative instrument rather than a reviewable decision, so it would be difficult to challenge directly. Judicial review under the Administrative Decisions (Judicial Review) Act 1977 is also limited because ADs are legislative in character.

There is no record of a test case involving DA42 modification costs. In the United States, airworthiness directives have been challenged on cost‑benefit grounds (e.g., U.S. v. Tilton), but Australian courts have generally deferred to CASA on safety matters. The lack of litigation history means that the Directive’s requirements have not been subject to judicial interpretation, so terms like “sufficiently charged” (from the Background) have no operative legal meaning in the AD itself. The Directive neither creates a statutory duty of care nor provides a right of action for damages. If an operator incurs costs due to a faulty modification kit or due to delays in the manual revision process, they would need to rely on contract or product liability law rather than any remedy under the Directive.

The absence of litigation also means that the Directive has not been tested against the principle of proportionality or the implied freedom of political communication, as might be raised if an operator argued that a mandatory hardware modification for a pilot‑error incident was unnecessary. Such a challenge would be unlikely to succeed given the broad safety powers delegated to CASA. The Directive’s background reference to an accident investigation does not incorporate the investigation’s conclusions as binding findings of fact.

The Directive contains several traps for the unwary operator, maintainer, or regulator.

Inconsistent effective dates. The document displays two different effective dates for Amendment 2: the table states “16 November 2007,” while the Background states “7 September 2007.” If an operator relied on the later date and performed the modification after 7 September but before 16 November, they might be non‑compliant according to the narrower reading. Conversely, if CASA intended the later date, anyone who performed the modification between 7 September and 16 November based on the Background text would have been early, but not necessarily in breach. The safest approach is to treat the document as effective on the date stated in the formal table (16 November 2007), since that appears in the official action box. However, the compliance deadline in that same table refers to “the effective date of the original issue of this Directive” (27 July 2007), not the amendment effective date, so the two‑effective‑dates issue does not affect the compliance calculation for Requirement 1-3. It only matters for knowing when Amendment 2 itself became law, which could affect the availability of the alternative method of compliance or the extension of time.

Alternative method of compliance reliance. The OSB alternative (OSB 42‑050/1) is approved only “as an alternate method of compliance for the requirements of AD 2007‑0183 R2” and “is also acceptable as an alternate method of compliance for this Directive.” The Directive does not say that the OSB automatically satisfies the CASA Directive; it says the EASA’s approval of the OSB as an alternative to the EASA AD is accepted by CASA for this Directive. That is a one‑step chain: CASA adopts EASA’s AMOC determination. If at any point EASA withdraws its approval of OSB 42‑050/1 (for example, because a defect is found in the OSB instructions), the CASA acceptance would likely fall away too, and operators who used that path could be non‑compliant without notice. The Directive does not address this scenario.

Serial number ranges. The applicability lists serial numbers with gaps (e.g., 42.004, 42.006, skipping 42.005, 42.007, 42.008). It is critical for owners to check the exact serial number against the list. A typographical error or an owner’s assumption that their serial number is covered could result in unnecessary compliance costs, or worse, incorrect assumption of non‑coverage leading to flying an unmodified aircraft that is in fact subject to the AD. The Canadian production line numbers are also specifically listed (42.AC001 through 42.AC109). Aircraft with serial numbers outside this range, even if identical in design, are not subject to the Directive, but they may be subject to other ADs or manufacturer recommendations.

TR Removal Pitfalls. The Directive permits removal of the AFM and AMM Temporary Revisions when the information they contain “is incorporated in the manual during the normal revision process.” This requires active monitoring by the operator. The manufacturer may issue a permanent revision that does not incorporate every detail of the TR; the operator must check the revision against the TR content before removal. If a critical procedure or limitation is omitted from the permanent revision, removing the TR could render the manual incomplete and the aircraft non‑compliant.

Compliance deadline for aircraft in deep storage. The Directive sets compliance within 200 hours time in service after 27 July 2007, but no later than 30 November 2007. An aircraft that was in long‑term storage on both dates (zero hours flown) would still be required to comply by 30 November 2007. If the storage facility missed the AD, the aircraft could not be flown after that date without first performing the modification. This could trap owners of stored aircraft who neglect to monitor ADs.

No compensation for early compliance. Owners who had already performed the modification before the original AD was issued (e.g., voluntarily in response to the accident investigation) are not entitled to any credit or refund. The AD does not recognise prior compliance; the modification must still be accomplished in accordance with the specific MSB or OSB documents, which may differ from any earlier work.

Document procurement cost. The referenced MSB and OSB documents are proprietary to Diamond Aircraft and may require purchase from the manufacturer or an authorised distributor. The Directive does not require CASA to supply these documents free of charge. Operators must budget for document acquisition costs as well as hardware and labour.

Compliance with AD/DA42/3 Amdt 2 requires a sequence of steps, preferably documented in a log and tracked against both the serial number and the compliance deadline. The following procedure adheres to the Directive’s requirements and the alternative method provision.

1. Verify applicability. Check the aircraft’s serial number against the list in the Directive. If the serial number is not in the range, no compliance is required, though owners should check for other ADs that may apply. For serial numbers in the range, proceed.

2. Choose a compliance path. Two paths are available: (a) the mandatory service bulletin path (MSB 42‑042 and associated work instruction); or (b) the optional service bulletin path (OSB 42‑050/1, including its associated documents, which are referenced in the OSB but not listed in the Directive). Obtain the chosen bulletin from Diamond Aircraft Industries or an authorised distributor. For the OSB path, ensure that the OSB is the revision dated 15 October 2007 or a later EASA‑approved revision.

3. Procure modification kit. The MSB or OSB will specify a kit containing ECU backup batteries, wiring harness, mounting hardware, and installation instructions. Order the correct kit for the specific DA42 serial number. Kits are likely to be part‑specific to the aircraft’s engine variant (TAE125‑01 or TAE125‑02‑99). Verify compatibility.

4. Schedule modification and manual updates. Arrange for an appropriately rated maintenance organisation to perform the following in the same maintenance event:

   • (i) Install the ECU backup batteries in accordance with the MSB or OSB instructions.
   • (ii) Insert the AMM Temporary Revision (DAI‑AMM‑TR‑MÄM‑42‑240 dated 17 June 2007 or later EASA‑approved revision) into the DA 42 Aircraft Maintenance Manual. If using the OSB path, the OSB may come with its own AMM instructions; check whether the OSB references different TRs. The Directive states that the OSB path “includes [the] associated documents referenced therein,” so any TR required by the OSB must be inserted.
   • (iii) Insert the AFM Temporary Revision (AFM TR‑MÄM‑42‑240) into the Aircraft Flight Manual, or the OSB‑equivalent if different.
   • (iv) Update the operator’s maintenance programme to reflect the AMM revision. This may involve adding a new task card or inspection interval related to the ECU backup batteries (e.g., periodic battery replacement).

5. Record compliance. The maintenance organisation must make a logbook entry referencing this Directive and the specific bulletin used. Enter the aircraft hours at the time of compliance. Retain a copy of the installed bulletins and TRs for future reference.

6. Monitor compliance deadline. Ensure the work is completed within 200 hours time in service after 27 July 2007, but in any event no later than 30 November 2007. For aircraft that have low utilisation, the calendar deadline is binding. If the aircraft exceeded the 200‑hour limit before the deadline, the earlier limit applied.

7. Post‑compliance actions. After compliance, the aircraft may be flown only with the amended AFM. If the permanent manual revisions are later published, the operator may remove the TRs but only when verified that the permanent revision incorporates all TR content. Update the maintenance programme to the permanent revision at that time. The TRs themselves should be retained in the aircraft records to demonstrate the compliance history.

8. For aircraft in storage. If the aircraft was in storage on the compliance date, the modification must be performed before the aircraft is returned to service. The storage period does not suspend the AD obligation; the aircraft is non‑airworthy until compliance.

9. Document retention. Keep copies of the AD itself, the used bulletin (MSB or OSB), the work order, logbook entries, and the TRs (or evidence of permanent revision) for the life of the aircraft. These documents may be required for future AD compliance audits or aircraft transfers.