AD/CL-600/106 - Auxiliary Fuel Tanks

The central concept is an Airworthiness Directive (AD), a regulatory instrument issued under the Civil Aviation Safety Regulations. An AD is a legally enforceable notice that requires operators to inspect, modify, or take other action on aircraft to correct an unsafe condition. AD/CL-600/106 is a specific AD covering auxiliary fuel tanks on a particular aeroplane type. The AD is issued by a delegate of CASA, in this case James Coyne, signalling that the authority to mandate such action is delegated under the Civil Aviation Act.

The second concept is the auxiliary fuel tank system itself. The tanks are not OEM equipment; they are installed under a Supplemental Type Certificate (STC) ST00365NY or ST00365NY-D, issued by PATS Aircraft, LLC. An STC allows modification of a type-certified aircraft through a supplementary approval, subject to continued airworthiness oversight. The AD targets only those tanks and specifically excludes tanks installed with “Configuration 5”, which presumably was a later modification that addressed the unsafe condition. The AD does not explain what Configuration 5 entails, but the exemption suggests that CASA considers that version safe, or that FAA AD 2008-22-01 already addressed it.

Deactivation is distinct from removal. The AD requires rendering the tanks inoperative, not physically taking them out of the aeroplane. This distinction matters because deactivation can be done without major structural work, but leaving components in place creates ongoing weight and balance considerations. The deactivation procedure must be approved by CASA in advance, not merely notified after the fact. The guidance in Appendix A sets out minimum criteria that the procedure should address, but the AD makes clear that the operator may include additional steps deemed necessary. This gives operators some flexibility to tailor the deactivation to their specific configuration, but at the cost of having to design and seek approval for a bespoke procedure.

The “unsafe condition” described in the background relates to potential ignition sources inside fuel tanks. This is a classic fuel tank flammability risk, similar to the issues that led to the TWA Flight 800 investigation and subsequent US regulations on fuel tank inerting. However, the AD does not identify the specific ignition source mechanism for the PATS tanks. It states only that fuel system reviews by the manufacturer identified unsafe conditions and that the manufacturer has not provided corrective actions. This is significant: the manufacturer’s inaction forced the regulator to intervene. Without a manufacturer-issued service bulletin or modification, operators cannot rely on an OEM fix; they must develop their own deactivation procedure. That increases the compliance burden relative to a scenario where the manufacturer provides an approved kit and instructions.

The reference to FAA AD 2008-22-01 highlights coordination between US and Australian regulators. That FAA AD likely applies to US-registered aircraft, but because Australian operators may have aeroplanes originally certificated under FAA type certification, CASA adopts a parallel directive. This avoids regulatory gaps where an aircraft that moves between registries might be subject to inconsistent requirements.

The concept of “continued airworthiness” appears several times. The secured components must have no effect on continued operational safety and airworthiness. The deactivation must not require additional instructions for continued airworthiness. That means the deactivation cannot create new periodic inspections, life limits, or maintenance tasks. The operator must design the deactivation so that the aircraft can be maintained solely using the existing OEM maintenance programme and the STC procedures (which are now rendered inapplicable except for the deactivated components).

The primary class of affected entities is operators of Bombardier CL-600-2B19 aeroplanes (the Regional Jet Series 100 and 440) that have been fitted with auxiliary fuel tanks under STC ST00365NY or ST00365NY-D, unless those tanks were installed as part of Configuration 5. This is a narrow fleet: it covers only those specific aircraft that underwent the aftermarket PATS modification. Many RJ100 and RJ440 aircraft in Australia and potentially other regions operated by Australian carriers or under CASA’s regulatory remit will be affected. The AD is binding on the registered operator of the aircraft, not on the owner or lessor per se, though in practice the operator bears compliance responsibility.

The AD also affects maintenance organisations that perform the deactivation work. They must familiarise themselves with the criteria in Appendix A and assist operators in drafting the CASA-approved procedure. Because the deactivation procedure requires approval in advance, maintenance organisations cannot simply perform the work and then submit a report; they must wait for approval. This may cause scheduling delays if CASA’s review timeline is uncertain.

CASA itself is affected as the approving authority. The Manager, Systems and New Technologies, Airworthiness Engineering Group must receive the initial reports and review and approve deactivation procedures. The AD expects submissions “as soon as possible to ensure timely review and approval”. This imposes an administrative burden on CASA, and if CASA is slow in processing approvals, operators may be unable to meet the 16 December 2009 compliance deadline through no fault of their own. The AD does not create an automatic extension mechanism for operators who submit procedures promptly but face regulatory delay.

Engineers, flight operations personnel, and flight crews are indirectly affected. The deactivation requires amendment of the Aeroplane Flight Manual to remove auxiliary tank operating procedures and limitations. Flight crews must be trained on the placard and the fact that the auxiliary tank is inoperative. Weight and balance documentation must be revised to reflect the mass of the deactivated tank system. Maintenance personnel must remove auxiliary tank maintenance procedures from the maintenance manual to prevent confusion.

Third parties such as lessors, financiers, and insurers may also be affected. An aircraft that loses auxiliary fuel capacity may have reduced utility and residual value. If the deactivation is not properly documented, it could complicate future lease transitions or sales. Insurers may require proof of compliance as a condition of coverage for fuel-system related risks. The AD does not address these commercial consequences; it treats them as private matters.

The exemption for Configuration 5 means that operators who already have that modification do not need to comply. However, an operator must verify whether its STC installation corresponds to Configuration 5. If the paperwork is missing or ambiguous, the operator may face uncertainty about whether the exemption applies. The AD does not define Configuration 5. An operator would need to consult with PATS or CASA to confirm. That verification itself consumes time and resources.

The AD imposes two sequential duties: a reporting duty and a deactivation duty. The reporting duty must be satisfied within 45 days after the AD’s effective date of 15 January 2009, which falls in late February 2009. The report must include the aeroplane registration, the auxiliary tank STC number, total flights per year, and flights per year using the auxiliary tank. The AD does not specify the format for the report, nor does it require a particular form. The operator must ensure the report reaches the named officer by fax. The AD provides a fax number but does not state that fax is the only method; it might be prudent to confirm receipt another way.

The second duty requires deactivation before 16 December 2009, using a procedure approved by CASA. The operator must submit the proposed deactivation procedure to the Manager, Systems and New Technologies for approval. The AD suggests submitting the procedure “as soon as possible” to allow time for review. The deactivation must meet the criteria in Appendix A, though the AD says those criteria “should” be included, not “must”. That gives some leeway, but the approving officer is likely to treat the criteria as mandatory unless a variation is justified. The operator must demonstrate that the deactivation eliminates the unsafe condition without introducing new risks.

The deactivation procedure must ensure that any component of the auxiliary tank that remains on the aeroplane is secured and has no effect on continued operational safety and airworthiness. That means the operator cannot simply leave loose wiring or uncapped lines. The deactivation must not result in the need for additional instructions for continued airworthiness. This is a crucial limitation: the operator cannot create a new maintenance requirement (e.g., periodic inspections of the deactivated tank) as part of the deactivation. The existing maintenance programme should suffice.

If the deactivation is not completed by 16 December 2009, the aircraft may be grounded or subject to enforcement action. The AD does not provide for extensions. Operators who face delays in CASA’s approval process should document their timely submission to show due diligence if enforcement arises.

Operators have the right to propose a deactivation procedure that goes beyond the criteria in Appendix A. The AD explicitly allows the inclusion of any relevant information or additional steps deemed necessary by the operator. This gives flexibility to address unique configurations or operational practices. However, proposing additional steps may slow approval if CASA questions their necessity.

After deactivation, the operator must verify that the aeroplane’s fuel quantity indication system (FQIS) and fuel distribution systems have not been adversely affected. This requires leak checks and pressure checks. The operator has the duty to ensure the aircraft is airworthy before returning to service.

The AD does not explicitly create a right to appeal CASA’s rejection of a proposed deactivation procedure, but general administrative law principles would apply. An operator could seek internal review or pursue judicial review if CASA’s decision were unreasonable. The AD does not address costs; the operator bears all costs.

Finally, the AD refers to FAA AD 2008-22-01. Operators who are subject to both jurisdictions must comply with both. Compliance with the FAA directive does not automatically satisfy the CASA directive unless they are equivalent. The operator should coordinate with both authorities if operating cross-border.

The AD itself does not set out specific penalties for non-compliance, but as a mandatory Airworthiness Directive issued under the Civil Aviation Safety Regulations, failure to comply is a breach of those regulations. Under the Civil Aviation Act 1988 and associated regulations, the maximum penalties for non-compliance with an AD can be substantial. For individuals, fines may reach thousands of penalty units, and for body corporates, the fines can be multiplied. Additionally, CASA can suspend or cancel the aircraft’s certificate of airworthiness, effectively grounding the aircraft until compliance is demonstrated.

Enforcement is typically handled by CASA’s enforcement branch. Inspectors may audit compliance during routine surveillance, or specifically check AD compliance during ramp checks. Because this AD has a strict compliance date (16 December 2009 for deactivation), any aircraft found to have an active auxiliary tank system after that date without a CASA-approved deactivation would be non-compliant. The operator would face enforcement action, possibly including a direction to ground the aircraft, a fine, or both.

The AD does not include a provision for alternative means of compliance (AMOC) other than the procedure approval process. Some ADs allow operators to propose equivalent methods; here, the approval of the deactivation procedure serves that function. If an operator proposes a procedure that CASA deems inadequate, CASA can reject it, and the operator must revise and resubmit. If no approved procedure exists by the compliance date, the operator is non-compliant even if a submission is pending. This creates a risk of technical non-compliance due to regulatory processing delays.

The “note” that the proposed deactivation procedures should be submitted “as soon as possible to ensure timely review and approval” is a warning: do not wait until the last minute. Operators who submit a procedure in late November 2009 may not receive approval before 16 December 2009. The operator then has no defence: the AD puts the onus on the operator to initiate the approval process early.

CASA may also take enforcement action against maintenance organisations that perform deactivation without an approved procedure, or against engineering staff who sign off on non-compliant work. Individual engineers could face their own regulatory sanctions.

There is no private right of action under the AD. It is a public safety regulation. However, non-compliance could be used in civil litigation if an accident occurs, as evidence of a breach of duty of care.

The AD does not provide for monetary penalties as a specific remedy; rather, it operates within the general enforcement framework of the Civil Aviation Act. The practical enforcement is likely to be case-by-case. Given that the AD is clearly safety-driven, CASA may be strict.

This AD operates within the broader regulatory framework of the Civil Aviation Act 1988 and the Civil Aviation Safety Regulations. ADs are part of the continued airworthiness system, which requires that aircraft be maintained in accordance with the approved maintenance programme and all applicable ADs. Compliance with this AD is a condition of maintaining a certificate of airworthiness for the affected aircraft.

The AD explicitly references FAA AD 2008-22-01. That US directive is identical in substance. For aircraft that are operated in both US and Australian airspace, compliance with the FAA directive may be necessary for FAA type certification, but the CASA directive imposes an independent legal requirement for aircraft under Australian registration. The operator cannot rely solely on FAA compliance to satisfy CASA. The two directives may be harmonised in effect, but the approval process is separate. An operator could potentially use the FAA-approved procedure as a basis for the CASA submission, but CASA would still need to approve it under Australian law. The AD does not say that CASA will automatically accept an FAA-approved procedure.

The AD interacts with the STC approval system. The STC ST00365NY is itself a product of the type certification process. The AD effectively revokes the approval for continued operation of that STC’s fuel system, though the STC itself is not rescinded. The deactivation does not remove the STC from the aircraft’s modification list; it merely renders the modification inoperative. That could create confusion if the aircraft is later sold and a buyer wants to reactivate the tanks. The AD does not address reactivation; presumably that would require a new STC revision or a new AD to reinstate.

The AD interacts with the maintenance regulations. Part 145 of CASR (Maintenance Organisations) will govern who can perform the deactivation work. The work likely constitutes a major modification or repair, requiring a licensed aircraft maintenance engineer or an approved maintenance organisation. The operator must ensure that the person performing the deactivation has the appropriate approvals.

The AD also interacts with the regulations on weight and balance and flight manual amendments. Revisions to the AFM must be approved by CASA, but the AD allows insertion of a copy of the AD into the AFM as a means of documenting the deactivation. That simplifies the AFM revision process, but the operator must also remove auxiliary tank operating procedures. Failure to do so could lead to confusion in the cockpit.

The deactivation criteria reference AC 25-8 (Advisory Circular on Auxiliary Fuel System Installations) for an approved method of capping fuel plumbing. That AC is not a regulation but provides guidance. The operator must use a method approved by CASA; AC 25-8 is one acceptable means, but not the only one.

There is potential interaction with environmental regulations if draining and vapour clearing involve handling aviation fuel and fuel vapours. The operator must comply with environmental protection laws regarding disposal of fuel and management of vapours. The AD does not address this; it is a separate compliance domain.

Finally, the AD may interact with international agreements on aircraft safety. Australia is a signatory to the Chicago Convention, and CASA’s ADs are part of Australia’s system of airworthiness regulation. Other states may recognise this AD for imported or exported aircraft.

This AD is a standalone directive with no amendment history provided in the source. It was issued on 27 November 2008 and becomes effective on 15 January 2009. The document includes only one version. There are no subsequent amendments listed. The AD number is AD/CL-600/106, and the serial number is 1/2009, indicating it is the first AD on this subject for this aircraft type in 2009.

The lack of amendment history suggests the AD was issued as a final rule without a prior proposal period. Emergency or urgent ADs are often issued without notice-and-comment because of the immediate safety risk. The background states that the manufacturer has not provided corrective actions, implying that the regulator moved quickly. Future amendments could occur if the manufacturer releases a fix or if the FAA modifies its AD, but no amendments are documented in the source.

The AD may be superseded by a later directive if conditions change. For example, if PATS eventually developed a corrective modification, CASA might issue a new AD to require installation of that modification instead of deactivation. But as of the source text, no such modification exists. The operator should monitor CASA ADs for CL-600 series aircraft to see if a replacement AD appears.

Given that the AD only requires a one-time deactivation, once completed and documented, the AD is complied with permanently for that aircraft. There is no recurring requirement. The AD does not require periodic inspection of the deactivated system. That is consistent with the requirement that deactivation not create additional instructions for continued airworthiness.

The AD does not provide for a sunset or review date. It remains in effect indefinitely unless withdrawn or superseded. Operators who acquire an aircraft that has been deactivated under this AD should verify that the deactivation was done in accordance with an approved procedure and that all records are updated. If not, the new operator may need to request approval retroactively. That could be difficult if the original operator is no longer in business.

The AD’s Appendix A criteria may evolve over time as CASA gains experience with deactivation proposals. The criteria stated are labelled as “should” rather than “must”, suggesting they are guidance. Future amendments to the AD could make them mandatory or add criteria. The operator should check for any updated versions before beginning the deactivation design.

In summary, the amendment history is nil. The AD is a one-off directive with a single issue date. Its simplicity reduces compliance ambiguity but also means less procedural flexibility for operators.

The source document contains no reference to any litigation related to this AD. No court cases, tribunal decisions, or enforcement actions are mentioned. That is not surprising: airworthiness directives are rarely the subject of direct judicial challenge. They are safety regulations with a strong presumption of validity. Operators typically comply rather than sue, because non-compliance carries immediate grounding risk and potential liability in case of an accident.

If an operator did challenge an AD, the grounds would likely be procedural (e.g., failure to consult, lack of evidence of unsafe condition) or substantive (e.g., the AD is disproportionate or technically unjustified). However, courts typically defer to the technical expertise of aviation safety regulators. The High Court of Australia has upheld CASA’s powers to issue ADs without prior hearing in urgent cases, provided natural justice is met later.

In the United States, FAA ADs have been challenged with mixed success. The US Court of Appeals for the District of Columbia Circuit has occasionally overturned ADs where the FAA relied on flawed data or acted arbitrarily. But the FAA usually wins. Given that FAA AD 2008-22-01 is the basis for this CASA AD, an Australian court might look to US precedent but would apply Australian administrative law.

No Australian litigants are known to have challenged this particular AD. If litigation arose, it would likely involve an operator who missed the compliance date and faced enforcement action. The operator could argue that CASA caused the delay by slow approval of the deactivation procedure. That might be a defence against a penalty, but not against the AD’s legal validity.

Another litigation scenario: if an aircraft with a deactivated tank suffered a fuel-related incident, the operator might sue the manufacturer or the STC holder, arguing that the tank design was defective and that the AD’s deactivation criteria were inadequate. Or the operator might sue CASA for negligence in approving an insufficient procedure. However, CASA enjoys statutory immunity for regulatory decisions made in good faith.

The absence of litigation history does not mean the AD is unchallengeable; it means no challenge has been successful or publicly reported. The operator should not assume the AD is immune from legal scrutiny, but for practical compliance, it is enforceable.

Several aspects of this AD could catch operators off guard. The first is the distinction between deactivation and removal. Operators who assume they can simply remove the auxiliary fuel tank and its associated plumbing may find they need additional CASA approval for that removal, because removal would alter the aircraft’s structure and empty weight more significantly than deactivation. The AD requires only deactivation. If an operator wants total removal, they would need to submit a different engineering procedure for CASA approval, possibly under a separate modification process. The AD does not forbid removal, but the operator cannot rely on the AD’s approval process for that.

The second gotcha is the reporting requirement: it must be done within 45 days of the effective date, not within 45 days of the operator’s receipt of the AD. An operator who acquires an affected aircraft after the effective date but before the compliance date may already be in breach if the prior operator did not report. The new operator should check AD compliance status at purchase.

Third, the exemption for Configuration 5 is not defined. An operator whose STC paperwork says “ST00365NY-D” might assume it is the same as Configuration 5, but the AD says “unless installed with Configuration 5”. The operator must confirm with PATS or CASA that their specific installation qualifies. If uncertain, the operator should treat the AD as applicable and comply, rather than risk non-compliance.

Fourth, the deactivation procedure must be approved by CASA before execution. The AD does not allow the operator to deactivate first and then submit the procedure for retroactive approval. Doing so would constitute non-compliance even if the deactivation is technically correct. The operator must have an approved procedure in hand before starting work.

Fifth, the criteria in Appendix A require the operator to “Permanently drain auxiliary fuel tanks, and clear them of fuel vapours to eliminate the possibility of out-gassing of fuel vapours from the emptied auxiliary tank.” That means simply draining the fuel is not enough; vapours must be cleared. This may involve purging with inert gas or other methods. The cost and complexity of vapour clearing can be significant, especially for tanks located in confined spaces within the fuselage.

Sixth, after deactivation, the operator must verify that the aeroplane’s FQIS and fuel distribution systems have not been adversely affected. If the auxiliary tank’s FQIS was integrated with the OEM system, disconnecting it could cause false readings or system failure. The operator may need to reconfigure the OEM FQIS. The AD does not prescribe how; it leaves that to the operator’s procedure and CASA approval.

Seventh, the requirement to revise the AFM Limitations Section to indicate that the AFM Supplement for the STC is not in effect could be overlooked. An operator might insert a copy of the AD into the AFM but forget to remove the STC supplement. That could mislead a flight crew into thinking the auxiliary tank is available.

Eighth, the AD requires the operator to pull and collar all circuit breakers used to operate the auxiliary tank. If those circuit breakers also serve other systems (possible if the STC used shared breakers), collaring them could disable other functions. The operator must identify dedicated breakers or face design challenges. The AD does not address this conflict; the operator should propose a solution in the deactivation procedure, such as removing the breakers or reconfiguring the electrical bus.

Ninth, the deactivation must not create additional instructions for continued airworthiness. That means the operator cannot impose a recurring check on the deactivated system. If the deactivation itself creates a condition that requires periodic inspection (e.g., loosening clamps in a vibration environment), the operator must design it out. That may be difficult if the secured components are subject to fatigue.

Tenth, the AD is effective immediately upon its effective date; there is no grace period after the effective date for reporting. Operators with affected aircraft in remote locations or undergoing maintenance may struggle to gather the usage data within 45 days.

Compliance involves a structured process that begins immediately upon the AD’s effective date. The following step-by-step approach uses the AD’s requirements, Appendix A criteria, and common maintenance practices.

Step 1: Identify affected aircraft. Review the fleet to find all CL-600-2B19 aeroplanes that have auxiliary fuel tanks installed under STC ST00365NY or ST00365NY-D, excluding those already modified to Configuration 5. If uncertain, contact the STC holder (PATS Aircraft, LLC) or CASA for confirmation. Document the findings.

Step 2: Within 45 days of 15 January 2009, submit the required report to the Manager, Systems and New Technologies, Airworthiness Engineering Group, CASA, by fax to (02) 6217 1914. The report must include for each aircraft: registration mark, STC number, total number of flights per year (based on records or reasonable estimate), and number of flights per year using the auxiliary tank. Keep a record of the fax transmission and any acknowledgment. If the operator has multiple affected aircraft, a single report covering all of them is acceptable if it lists each individually.

Step 3: Initiate development of a deactivation procedure that meets the criteria in Appendix A. Engage an engineering organisation familiar with the aircraft type and STC. Key tasks: define the method for permanently draining and vapour clearing the tanks; plan the disconnection of all electrical connections (FQIS, pumps, float switches, etc.) and stow them at the auxiliary tank interface; disconnect and cap pneumatic connections; disconnect fuel feed and vent lines and cap at the aeroplane tank side using an approved method (such as AC 25-8); leave open and secure the auxiliary fuel tank vent lines to prevent structural deformation during decompression; pull and collar all circuit breakers dedicated to the auxiliary tank. If circuit breakers serve other systems, propose alternative isolation (e.g., removal of breakers).

Step 4: Develop documentation revisions: weight and balance revision reflecting the mass of the deactivated tank system; AFM amendment to remove auxiliary tank supplement and operating procedures, insert a limitation that the STC supplement is not in effect, and include a placard requirement; maintenance manual amendment to remove auxiliary tank maintenance procedures; revision of instructions for continued airworthiness (ICA) to remove any references to the auxiliary tank.

Step 5: Submit the proposed deactivation procedure to the Manager, Systems and New Technologies for approval. Include all engineering drawings, schematics, and justifications. Mark the submission as “AD/CL-600/106 Deactivation Procedure”. Do this as early as possible, ideally within the first 90 days after effective date, to allow CASA time for review and possible requests for revision.

Step 6: Upon receiving CASA approval, schedule the deactivation work. Ensure the work is performed by an approved maintenance organisation under the appropriate regulations. Perform the physical tasks per the approved procedure. After work completion, conduct leak checks and pressure checks to verify the OEM fuel system is unaffected. Verify FQIS and fuel distribution system function normally.

Step 7: Update all documentation: revise weight and balance and obtain CASA approval if required; revise AFM by inserting a copy of the AD as allowed; place a placard in the flight deck stating the auxiliary tank is deactivated; remove auxiliary tank operating procedures from AFM; amend maintenance manual and ICA; keep records of all approvals and sign-offs.

Step 8: Verify compliance before the 16 December 2009 deadline. If delays occur, document all submissions and communications with CASA to demonstrate due diligence.

Step 9: If the aircraft is sold or leased after deactivation, include all deactivation records in the technical records package, so the new operator knows compliance status. The deactivation is permanent; no further action is required unless a future AD supersedes this one.

Step 10: Monitor CASA and FAA for any superseding ADs or new corrective actions from the manufacturer that could allow reactivation or provide a less burdensome solution. If such an AD is issued, the operator may need to comply with it instead.

By following these steps carefully, the operator can meet both the letter and spirit of the AD while minimising the risk of enforcement action. The costs are unavoidable, but careful planning reduces the risk of rework or missed deadlines.