AD/AC-CLA/6 Amdt 1 - Wing Struts Carry-Through Tube

The directive’s central engineering control is a periodic physical inspection targeted at a single structural component: the wing strut carry-through tube where it runs through the hopper. The concept rests on three linked elements: location and access; inspection trigger/criteria; and remedial specification.

• Location and access. The AD requires removal of the hopper top to access the carry-through tube, and provides fixed reference coordinates for the tube relative to the hopper forward bulkhead (625 mm aft) and the hopper surface (150 mm below). This converts the inspection into a repeatable procedure that prescribes a consistent inspection point (Requirement).

• Inspection trigger and criteria. The initial inspection is a visual check of the fibreglass wrapping for cracks. If cracking is present, the AD requires removal of the wrapping to expose the tube and a corrosion inspection. The document sets quantitative condition thresholds: corrosion depth of more than 0.25 mm in one location, or corrosion amounting to more than 2 per cent of the tube cross-sectional area, triggers mandatory replacement. The AD supplies a nominal cross-sectional area figure (262.5 sq. mm), which allows calculation of the 2 per cent area threshold (5.25 sq. mm).

• Remedial specification. If corrosion is removed and thresholds are not exceeded, the AD prescribes finishing the tube with two coats of zinc chromate primer and rewrapping the exposed tube in a fibreglass laminate using a minimum of three layers of MIL-C-9084 glass cloth or an approved local equivalent, bonded with a chemical resistant resin such as Reichhold 33-402 (Requirement and Note 1). The AD expressly permits local equivalents for glass cloth and resin (Note 1), and references FAA AD 78-20-06 (Note 2).

The compliance schedule is periodic: inspections at intervals of three years after 12 December 1978 (Compliance). The amendment text also deletes a prior reference to a “major inspection”, stating that such a requirement is no longer required by legislation (Background). Two attribution points are explicit in the source: the AD’s origin (originally raised in 1979 after reports of severe corrosion and a fatal accident) and the issuing authority (a CASA delegate signed the amendment on 7 August 2008).

Mechanistically, the AD converts a safety concern identified through overseas incidents into a prescriptive maintenance procedure with fixed measurement thresholds and material standards. It blends qualitative steps (visual inspection for cracking) with quantitative failure criteria (0.25 mm depth; 2 per cent area), and it imposes an inspection periodicity with retrospective effect dating to 1978.

The AD applies to a specific and narrow aircraft population. The instrument’s Applicability clause states: "All models A-9, A-9A and A-9B with wing struts carry through tube running through hopper." That language focuses the obligation on owners, operators, maintenance organisations and licensed engineers who are responsible for the airworthiness of those CALL AIR A-9 series aeroplanes configured with the carry-through tube located in the hopper. It does not apply to those A-9 series aircraft if their carry-through tube is not routed through the hopper; the scope is conditional on the component arrangement described.

Immediate affected parties include:

• Aircraft owners and operators of CALL AIR A-9, A-9A and A-9B models that meet the applicability criterion. They must ensure the inspection and any necessary remedial work is completed at the intervals required by the AD (Compliance).

• Maintenance organisations and licensed aircraft engineers who carry out inspections, corrosion removal, structural replacements, primer application and fibreglass rewrapping. The AD prescribes materials and minimum layering requirements (Requirement), so maintenance operators will need access to the specified primers, fibreglass cloth or approved local equivalents and appropriate resins.

• Parts suppliers and replacement-tube manufacturers. Where corrosion exceeds the specified thresholds, the directive requires replacement of the main carry-through tube, creating demand for appropriately dimensioned replacement tubes and associated documented compliance for fitment.

• Regulatory staff charged with oversight, because the AD is issued by the Civil Aviation Safety Authority (as indicated by the signature block), and the directive sets standards that CASA delegates have certified by publication of the amendment (signed by David Villiers, Delegate).

Less directly affected are third parties whose obligations derive from the operator’s safety management system, including insurers and auditors, because compliance or non‑compliance with the AD will be material to maintenance records and airworthiness determinations. The document does not expressly allocate costs, compensation, or specify penalties, nor does it state record-keeping requirements. The AD does, however, set material and procedural standards that those responsible for maintaining the listed aeroplanes must deliver to meet the directive’s inspection and remedial requirements.

The AD converts a safety concern into prescriptive duties for the specified aeroplanes. The duties set out in the document are concrete and procedural:

• Duty to inspect at specified intervals. The Compliance clause requires that inspections be carried out "At intervals of three years after 12 December 1978." That creates a recurring duty on owners/operators to ensure the inspection schedule is observed.

• Duty to access and visually inspect. The Requirement mandates removal of the hopper top and a visual inspection of the fibreglass wrapping to detect cracks. The AD identifies where the tube is located in the hopper to provide a consistent access point (Requirement).

• Duty to remove wrapping and inspect corrosion when cracking is detected. If wrapping is cracked, the operator must remove it and inspect the tube itself for corrosion (Requirement).

• Duty to remediate or replace. If corrosion is present, the AD requires removal of corrosion. If corrosion exceeds either (i) depth of 0.25 mm at a single location, or (ii) an amount equal to 2 per cent of the tube cross-sectional area (nominal cross-sectional area stated as 262.5 sq. mm), then the main carry-through must be replaced (Requirement).

• Duty to finish and rewrap where replacement is not required. After corrosion removal, the tube must be finished with two coats of zinc chromate primer and rewrapped with a fibreglass laminate using a minimum of three layers of MIL-C-9084 glass cloth or equivalent, and a chemical resistant resin such as Reichhold 33-402 (Requirement and Note 1). Local equivalents may be substituted for glass cloth and resin (Note 1).

Rights and limits present in the document:

• Right to use local equivalents. The AD allows substitution of local equivalents for the specified glass cloth and resin (Note 1). That grants some flexibility to maintenance providers but leaves selection authority and acceptability to the implementing parties and, implicitly, the regulator.

• No express enforcement or appeal mechanism specified. The document does not set out procedural rights such as appeal against the AD, nor does it specify penalties, compliance enforcement mechanisms, or record-keeping obligations within the text provided. The AD does, however, include the issuing signature of a CASA delegate, which indicates that the AD was issued under CASA’s administrative authority; the AD itself does not describe further enforcement steps.

• Deletion of the prior "major inspection" requirement. The Background notes that the amendment removes reference to "major inspection" because it is no longer required by legislation. That alters the prior procedural duty set out in earlier versions of the AD and contracts the scope of inspections required by law as of this amendment.

Practically, the AD places the onus on operators and maintenance organisations to interpret and apply its procedural and material prescriptions. Where the AD allows equivalence, judgement falls to the operator and, ultimately, to regulator oversight for acceptability. The document provides measurement thresholds (0.25 mm depth; 2 per cent area) which function as bright-line criteria for replacement decisions.

The instrument as provided does not state penalties, enforcement mechanisms, or procedural remedies within its text. The AD is signed by a Delegate of the Civil Aviation Safety Authority (David Villiers, 7 August 2008) and is labelled as an amendment (Amdt 1) to AD/AC-CLA/6, with an effective date for this amendment of 25 September 2008 (Requirement; Compliance; signature block). However, the directive itself contains no express penalty provisions, no administrative sanctioning clause, and no description of monitoring, inspection, or audit processes by which compliance will be verified.

From the document alone, the following points can be stated:

• The AD imposes prescriptive maintenance obligations (inspection method, location, thresholds, materials) but does not set out sanctions for non-compliance within its text. It therefore creates duties but leaves the question of formal enforcement procedures and penalties unspecified in the instrument as presented.

• The AD is issued by a CASA delegate, which indicates it is an instrument published under the administrative framework of the Civil Aviation Safety Authority. The presence of the delegate’s signature denotes official issue, but the text does not expand on how CASA will enforce the AD, nor does it attach monetary fines, grounding orders or particulars concerning enforcement processes to the AD itself.

• The AD omits any procedural detail about record-keeping, notification of findings to the regulator, or certification requirements after remedial work. Those matters are commonly governed elsewhere in aviation regulation or organisational procedures; however, in this instrument no such obligations are articulated.

Analysts and practitioners seeking to understand enforcement consequences will need to look beyond this instrument to the broader regulatory framework administered by CASA and to applicable statutory provisions or regulatory enforcement policies that govern airworthiness directives, maintenance obligations and consequences for non-compliance. The AD as provided cannot by itself be cited as specifying penalties or enforcement steps.

The AD explicitly references external material and makes one express statement about prior legislative requirements. The source contains two interactions:

• Cross-reference to FAA AD. Note 2 states "FAA AD 78-20-06 refers." That shows the AD recognises or relies upon a corresponding FAA airworthiness directive as relevant background or technical reference. The inclusion suggests that the FAA AD contains related or antecedent requirements, and that the Australian AD sits in a technical dialogue with that FAA instrument. The AD does not prescribe how compliance with FAA AD 78-20-06 intersects with compliance of this AD beyond noting its relevance.

• Deletion tied to unspecified legislation. The Background says the AD "has been amended to remove reference to 'major inspection' which is no longer required by legislation." That statement indicates a change in the legal landscape that removes a previous legislative foundation for a "major inspection" requirement. The AD does not identify the legislation whose effect it follows, so the precise statutory interaction is not stated in the instrument. The practical effect, as recorded in the AD, is that the AD’s requirements are narrowed relative to earlier versions insofar as the "major inspection" is no longer mandated.

Beyond those two explicit references, the AD does not mention other Commonwealth Acts, regulations, or standards in its text. It does, however, prescribe technical materials (MIL-C-9084 glass cloth, Reichhold 33-402 resin) which tie maintenance practices to recognised material specifications. The AD’s authority derives from issuance by the Civil Aviation Safety Authority delegate, which implies its situational relationship to CASA’s broader airworthiness regulatory powers, but the instrument does not itself enumerate or cite the enabling statute, regulatory provisions, or the interaction rules for foreign directives and approvals.

Practitioners should therefore note that the AD sits in a regulatory network: it refers to a foreign authority’s AD for technical reference and acknowledges that prior references to a "major inspection" were withdrawn because of changes in legislation. For a complete legal mapping of interactions with legislation, enforcement powers, and compliance certification, the AD alone is not sufficient; one must consult CASA’s enabling statutes, accompanying regulations and CASA guidance on AD implementation and compliance record-keeping.

The document before you is AD/AC-CLA/6 Amdt 1, with visible metadata and a short amendment narrative. The AD includes the following chronology and amendment notes as stated in the text:

• Original AD raised in 1979. The Background states the AD was "originally raised in 1979 following reports of severe corrosion of the wing strut carry-through tube being found in a number of overseas aeroplanes, causing a fatal accident due failure of the wing strut carry-through tube." This records the initiating safety events driving the first AD.

• Compliance retrospective date of 12 December 1978. The Compliance clause requires inspections at three-year intervals after 12 December 1978, indicating the AD’s inspection periodicity was intended to have retrospective effect to late 1978.

• Amendment effective 25 September 2008. The document declares, "This Amendment becomes effective on 25 September 2008." The amendment is recorded as AD/AC-CLA/6 Amdt 1, with amendment identifier Amdt 1 and date marker "10/2008" displayed in the header.

• Date and signature. The AD as amended bears the signature block of David Villiers, Delegate of the Civil Aviation Safety Authority, dated 7 August 2008, which provides the administrative signature and date of issue preceding the stated effective date.

• Content change in the amendment. The Background explains the specific content change effected by the amendment: it "has been amended to remove reference to 'major inspection' which is no longer required by legislation. Reference to FAA AD 78-20-06 also included." That records a narrowing of the AD’s inspection language and the addition of an explicit reference to the FAA AD as part of the update.

• Recurrent metadata repetition. The document contains repeated headings and date markers (AD/AC-CLA/6 Amdt 1; Wing Struts Carry-Through Tube; 10/2008) which indicate the AD’s amendment identity and date. These repetitions are administrative formatting rather than substantive changes.

No further amendments, superseding directives or later revision dates are provided in the text offered. The instrument therefore documents a 1979 origin, a retrospective compliance anchor in 1978, and a formal amendment issued in 2008 that became effective 25 September 2008, with the amendment specifically removing an older "major inspection" reference and adding the FAA AD reference.

The instrument as presented contains no litigation history. There are no cases, tribunal decisions, prosecutions, enforcement actions, appeals, or judicial interpretations cited in the AD text. The Background narrates factual events (reports of severe corrosion in overseas aeroplanes and a fatal accident) that prompted the original AD but does not record any legal proceedings arising from those events or from the AD itself.

Therefore, based solely on the content of this document:

• No litigation is recorded or referenced in the AD.

• There are no judicial authorities, determinations or precedents cited that interpret the AD’s scope, thresholds, or implementation.

Practitioners who require information about any litigation or enforcement action relating to this AD will need to consult external legal records, CASA enforcement records or public court databases. The AD does not supply any litigative context, nor does it reference later adjudication concerning compliance or disputes about the AD’s technical or procedural requirements.

This AD contains several implementation details and explicit allowances that can generate practical traps if misread or incompletely applied. The following are concrete points drawn from the text that can affect compliance, cost and operational choices.

• Applicability is conditional on configuration. The AD applies only to A-9, A-9A and A-9B models "with wing struts carry through tube running through hopper." If the carry-through tube is routed elsewhere, this AD does not apply. Misidentifying aircraft configuration can lead to unnecessary work or missed obligations (Applicability).

• Access requires removal of the hopper top. The AD requires removal of the hopper top to inspect the tube, meaning the inspection is intrusive and will have labour and downtime implications. The AD gives precise placement of the tube (625 mm aft, 150 mm below the hopper surface), which presumes accurate measurement and access inside the hopper (Requirement).

• Visual inspection threshold triggers further invasive inspection. The initial visual step concerns the fibreglass wrapping only; corrosion is inspected only if wrapping is cracked. Operators relying on surface appearance might miss subsurface corrosion if the wrapping is intact, because the AD does not mandate removal of the wrapping absent cracking. The AD’s wording therefore creates different inspection paths depending on wrapping condition (Requirement).

• Quantitative corrosion thresholds require measurement and judgement. The AD sets two numeric thresholds that trigger replacement: 0.25 mm maximum corrosion depth at a single location, and 2 per cent of the tube cross-sectional area. The AD also supplies a nominal cross-sectional area (262.5 sq. mm) enabling calculation of the area threshold (2 per cent = 5.25 sq. mm). The AD does not prescribe the measurement technique or instrumentation to determine depth or area of corrosion; the evaluator must therefore select an accepted measurement method and be prepared to justify it.

• Replacement is mandatory if thresholds exceeded. The AD uses mandatory language ("must be replaced") when thresholds are exceeded. That produces discrete decision points: either remove corrosion and refinish/rewrap, or replace the tube entirely (Requirement).

• Material specifications and equivalence. The AD prescribes minimum three layers of MIL-C-9084 glass cloth and a resin example (Reichhold 33-402) but allows local equivalents (Note 1). The allowance for local equivalents introduces potential variation in repair quality and may require an equivalence assessment that the AD does not specify.

• Finish specification but limited procedural detail. The AD requires two coats of zinc chromate primer after corrosion removal but provides no detail on surface prep, primer specification beyond name, cure times, bonding tests or inspection acceptance criteria. Maintenance organisations will need to translate those finishing instructions into their standard procedures.

• Removal of "major inspection" reference. The amendment deletes a prior reference to "major inspection" because it is no longer required by legislation (Background). Practitioners must ensure they are following the current AD text rather than earlier versions that referenced a "major inspection."

• Reference to FAA AD without incorporation detail. The AD notes FAA AD 78-20-06 but does not incorporate any of its text or make it mandatory; reliance on the FAA AD’s procedures requires checking whether the FAA text contains different or additional instructions that an operator may wish to follow but which are not compulsory under this AD (Note 2).

• Effective dates and retrospective compliance cadence. The effective date of the amendment is 25 September 2008, but the Compliance clause anchors inspection intervals to 12 December 1978. There may be legacy compliance record complications in demonstrating three-yearly inspections dating back decades. The AD does not state how to treat lapses or missed historic inspections.

• No enforcement, record-keeping or notification steps specified. The AD does not set out how findings must be reported to the regulator, how compliance is to be recorded, or what documentary proof will satisfy an audit. Practitioners must therefore clarify those processes with CASA or through their maintenance and continuing airworthiness management procedures.

Each of these points is grounded in the AD’s text. They represent operational and compliance risks that should be addressed by aircraft operators and maintenance providers when implementing the inspection and remedial procedures the AD prescribes.

The AD states specific procedural steps; compliance requires following those steps and resolving several practical implementation choices that the AD leaves open. The following is a step-by-step practical compliance checklist, drawn explicitly from the AD text, followed by recommended practical actions where the AD is silent.

Mandatory steps as set out in the AD:

1. Confirm applicability. Verify the aircraft model is A-9, A-9A or A-9B and that the wing struts carry-through tube runs through the hopper (Applicability).

2. Schedule inspection at the required interval. Ensure the inspection is performed at intervals of three years, measured from 12 December 1978 or at three-yearly intervals thereafter (Compliance).

3. Access the tube. Remove the hopper top to access the main carry-through tube. Locate the tube at 625 mm aft of the hopper forward bulkhead and 150 mm below the hopper surface (Requirement).

4. Visual inspection of fibreglass wrapping. Inspect the fibreglass wrapping for cracks. This is the initial screening step (Requirement).

5. Remove wrapping if cracked. If any wrapping is cracked, remove the wrapping to expose the tube and inspect for corrosion (Requirement).

6. Assess corrosion. Remove corrosion found on the tube. Measure corrosion depth at the worst location and estimate the area of corrosion relative to the tube’s cross-sectional area. Use the nominal tube cross-sectional area of 262.5 sq. mm as supplied in the AD to calculate the 2 per cent threshold (Requirement).

7. Replacement trigger. If corrosion exceeds depth of 0.25 mm at any one location or exceeds 2 per cent of the tube cross-sectional area (2 per cent of 262.5 sq. mm = 5.25 sq. mm), replace the main carry-through tube (Requirement).

8. Finishing when not replaced. If corrosion is removed and the tube passes the thresholds, finish the tube with two coats of zinc chromate primer, then rewrap the exposed tube with a fibreglass laminate using a minimum of three layers of MIL-C-9084 glass cloth (or local equivalent) and a chemical resistant resin such as Reichhold 33-402 (Requirement; Note 1).

9. Allowable material substitutions. Where local equivalents are used for glass cloth or resin, document the trade name and specification relied upon (Note 1).

Recommended practical actions where the AD is silent (good-practice interpretive steps):

• Adopt and document an accepted measurement method for corrosion depth and area. The AD specifies numeric thresholds but not measurement technique. Use calibrated measurement tools, note measurement method and tolerances, and retain photographic evidence. Document method to substantiate decisions to remove corrosion or replace the tube.

• Ensure maintenance procedures address surface preparation, primer application, cure times and inspection acceptance criteria. The AD requires two coats of zinc chromate primer but does not provide procedural detail. Maintenance providers should apply their established, approved processes consistent with airworthiness standards to ensure adhesion and corrosion protection.

• Where local equivalents are used, keep equivalence evidence on file. Because the AD allows local substitution for glass cloth and resin, record the technical specifications of the substitute and the rationale for equivalence to MIL-C-9084 and Reichhold 33-402.

• Plan for downtime and parts availability. Removing the hopper top is an intrusive task. If replacement is required, ensure availability of appropriately dimensioned carry-through tubes and verify fitment parameters before starting disassembly.

• Record-keeping and notification. Although the AD does not mandate documentation or notification, maintain inspection records, measurement records, repair records, materials used and the identity of personnel performing the work. If regulatory practice or the operator’s continuing airworthiness management requires notification to CASA, follow those processes.

• Review FAA AD 78-20-06 for technical guidance. The AD references FAA AD 78-20-06; while that FAA AD is not incorporated verbatim, reviewing it may provide additional technical context or method recommendations that could inform compliant practice.

• Clarify regulatory expectations with CASA where uncertain. Because the AD does not specify enforcement, reporting or acceptable measurement methods, consult CASA or authorised continuing airworthiness management organisations where procedural or documentary expectations are unclear.

Documenting compliance steps, measurements and materials is prudent even though the AD does not itself mandate a particular form of record-keeping. The AD’s explicit numerical thresholds create bright-line decision points; to protect airworthiness and to justify maintenance decisions, operators and maintenance organisations should keep contemporaneous records that evidences compliance with the AD’s requirements.