AD/LA-4/23 Amdt 1 - Wing Fitting Carry Through Structure

The single most important concept is the wing fitting carry through structure, which is the structural component that transfers loads from the wings into the fuselage. Its integrity is critical to the aircraft’s continued airworthiness. Corrosion in this area, if left undetected, can progress to structural failure. The directive therefore mandates periodic detection and treatment of corrosion.

The inspection method is a borescope examination. A borescope is an optical device with a small diameter, typically a rigid or flexible tube with a lens and light source, inserted through a small access hole. This allows visual inspection of interior surfaces without major disassembly. The Aerofab Service Advisory No A-001 prescribes the specific procedure, including the location of the access hole and the techniques for corrosion inspection and treatment.

The concept of operating environment classification is central to the compliance regime. The directive creates two categories: predominantly salt water activity and predominantly fresh water operations. Classification is based on the frequency of salt water exposure during takeoffs, landings and mooring. The thresholds are quantitative: more than four landings or takeoffs per month on salt water, or mooring in salt water for more than 60 days per year. Operators must make this classification for each aircraft and apply the corresponding inspection interval. The classification imposes a self assessment obligation on the operator, with consequences for misclassification.

The notion of repeat inspections is also important. Unlike one off modifications, the AD imposes a continuing obligation. The interval resets after each inspection. The AD does not require further modifications after the initial one; only corrosion treatment and inspection are required repeatedly. Compliance time limits are calendar based, not hours or cycles, which is unusual for some airworthiness tasks but consistent with corrosion driven inspections.

The term approved by the Type Certificate holder appears in the requirement that the Aerofab Service Advisory may be in a later revision approved by the Type Certificate holder. This introduces an element of flexibility: if the original holder issues a newer edition of the advisory, that edition may be used provided it is officially approved. However, the AD does not specify how operators verify such approval; it presumably must be documented.

The status of the original AD as effective from 13 July 1989 is also a concept. That original AD required wing removal for corrosion inspection. The amendment supersedes that method, but the compliance history required is tied to inspections performed under the original AD or under a prior exclusion that allowed the Aerofab method. This creates a two tier compliance regime based on past compliance.

The primary affected group is every person and organisation responsible for the airworthiness of Consolidated Aeronautics, Colonial and LA-4 Series Aeroplanes. This includes owners, registered operators, and any person who holds a certificate of registration for such an aircraft. In Australia, that typically means private owners, flying schools, charter operators, and commercial entities that operate these models. Given that these are older amphibious and landplane aircraft from the 1940s and 1950s, the population is small but includes enthusiast operators, restoration groups and specialised aviation businesses.

The directive also directly affects maintenance organisations, both approved maintenance organisations (AMOs) and licensed aircraft maintenance engineers (LAMEs) who perform the work. They must obtain the Aerofab Service Advisory No A-001, understand the borescope inspection technique, and perform the corrosion treatment and inspection in accordance with the advisory. They must also correctly classify the aircraft’s operating environment, or rely on the operator’s classification. Misclassification by the maintenance organisation could shift liability.

Less directly, the AD affects suppliers of parts and consumables related to the modification and treatment, as well as the Type Certificate holder (likely Aerofab or a successor). The Type Certificate holder is referenced as the authority for approving later revisions of the service advisory, so they hold a gatekeeper role. The directive may affect the availability of access to up to date service information.

The compliance burden falls more heavily on operators of aircraft used predominantly in salt water. The three year inspection interval is shorter than the six years available for fresh water operations. Operators on coastal or island routes, or those who moor aircraft in salt water for significant periods, face more frequent downtime and expense. Conversely, fresh water operators gain a compliance cost reduction from the previous three year interval for all aircraft.

Newly imported aircraft face a sudden three month compliance deadline. This affects buyers who import these models from overseas, who may not be aware of the directive during purchase negotiations. The AD requires that the modification and inspection be done within three months of the effective date (29 September 2005) if the aircraft was not previously inspected to the original AD or the Aerofab exclusion. For aircraft imported after that effective date, the three month clock starts from the date the aircraft enters the Australian register? The AD does not specify, but in practice CASA would require compliance upon import.

Insurance companies and prospective purchasers are also affected. Aircraft with overdue AD compliance will have impaired airworthiness and may be uninsurable or difficult to sell. The AD thus creates a due diligence item for any transaction.

The CASA delegate who issued the AD is a named individual (David Villiers) and the signature appears dated 8 August 2005. The AD is issued under the Civil Aviation Act 1988 and the Civil Aviation Safety Regulations.

The central duty is to perform the modification, inspection and corrosion treatment in accordance with Aerofab Service Advisory No A-001 (or an approved later revision). This duty falls on the operator, who must ensure that the work is carried out by an appropriately authorised person. The AD does not specify who may perform the work; that is left to the general airworthiness regulations. However, the operator bears ultimate responsibility for compliance.

A related duty is to determine the correct operating environment classification for the aircraft. This is a factual assessment that the operator must make based on the aircraft’s usage. If the operator fails to classify or misclassifies, the resulting inspection interval may be inappropriate, leading to undetected corrosion or non compliance. The AD does not require the operator to record the classification, but prudent operation would require documentation.

Another duty is to keep records of compliance. While not explicitly stated in the AD itself, the Civil Aviation Act and regulations require operators to maintain records of AD compliance, including the date and details of the work performed, the service advisory revision used, and the classification applied. Such records are essential for demonstrating compliance during audits or aircraft transfers.

The right to use a borescope instead of wing removal is a significant operational benefit granted by this amendment. Previously, the inspection required major disassembly, which was time consuming and expensive, and risked disturbing the structure. The borescope method reduces downtime and preserves the structural integrity by avoiding repeated removal and reinstallation of wings. This right is conditional on following the precise procedure in the service advisory.

The right to extend the repeat inspection interval from three to six years for fresh water operations is a direct benefit for certain operators. However, it is paired with the duty to correctly classify. If an operator incorrectly classifies as fresh water and the aircraft actually operates in salt water, they are non compliant and potentially unsafe. The right is therefore conditional on accurate self assessment.

The operator also has the right to use a later revision of the Aerofab Service Advisory, provided it is approved by the Type Certificate holder. This allows adoption of improved procedures without needing a further AD amendment. However, it creates an obligation to keep track of whether later revisions have been approved, and to maintain access to current data.

The AD does not explicitly grant a right to deviate from the Aerofab method and use an alternative means of compliance. It only mentions the specific service advisory and its approved revisions. If an operator wishes to use a different method, they would need to apply to CASA for an alternative means of compliance under the general regulatory framework. The AD is silent on that.

The AD itself does not contain a penalties clause. However, it is issued under the authority of the Civil Aviation Safety Authority pursuant to the Civil Aviation Act 1988 and the Civil Aviation Safety Regulations. Non compliance with an Airworthiness Directive is a serious breach that can result in the aircraft being deemed unairworthy. Operation of an aircraft that does not comply with applicable ADs is prohibited under the regulations, typically under CASR 21 (dealing with airworthiness) and CASR 42 (continuing airworthiness).

The practical enforcement consequence is that an aircraft found to have overdue AD compliance will be grounded. CASA inspectors can issue a direction to the operator to stop operations until compliance is achieved. They can also impose a fine or refer the matter for prosecution. The maximum penalties for operating a non compliant aircraft can reach tens of thousands of dollars for an individual, and higher for corporations. In addition, any person who falsifies records of compliance can face criminal penalties.

There is no discretion given in the AD to extend compliance times or waive requirements. The compliance times are absolute. Late compliance does not waive the requirement; the inspection must still be done as soon as possible. However, an operator who voluntarily grounds the aircraft until compliance is achieved limits the enforcement exposure. Flying while non compliant is the offence.

The enforcement mechanism relies on the operator’s records and on routine surveillance by CASA. During an aircraft inspection, a CASA inspector may check AD compliance. If corrosion is found on an aircraft that is overdue for the inspection, the operator may face enforcement action. The background mention of reports of severe corrosion damage suggests that the regulator has intelligence about actual corrosion cases, which may increase targeted enforcement.

The AD also carries an implicit safety enforcement: the risk of structural failure. The background states that undetected corrosion could lead to structural failure. That is the ultimate enforcement by physics. This is not a legal penalty, but it directly affects the operator’s incentives to comply.

Third parties, such as maintenance organisations, may also be liable if they perform the work incorrectly or if they certify compliance when it has not been properly completed. They face regulatory action under their own approvals.

Since the AD is independent of the aircraft’s type certificate or registration status, it applies even to aircraft that are not currently flying. An aircraft that is stored or being restored is still subject to the AD if it is on the Australian register. CASA can enforce against a registered aircraft regardless of its usage status.

This AD sits within a broader legal framework for aircraft airworthiness. It is issued under the Civil Aviation Act 1988 and the Airworthiness Regulations (or CASR Part 21 and Part 42 as applicable). The Civil Aviation Act provides the power to issue mandatory continuing airworthiness information, of which ADs are a subset. The AD does not replace the aircraft’s type certificate or the continued airworthiness requirements in the maintenance manual. It is an additional requirement that must be included in the operator’s maintenance schedule.

The AD interacts with the General Exemption provisions that allowed some operators to previously comply with the original AD using an exclusion. The amendment changes that: the exclusion is now part of the directive itself, with specific compliance times. Operators who previously relied on an exclusion must now comply with the new method and schedule, subject to the three year grace period.

The AD also interacts with the Type Certificate holder’s own instructions. The Type Certificate holder may issue service bulletins or other documents related to the carry through structure. However, this AD makes the Aerofab Service Advisory mandatory. If a later revision is approved, it supersedes earlier revisions for compliance purposes. This creates a hierarchy: the AD is the supreme requirement, but it defers to the Type Certificate holder for procedural detail.

If the aircraft is operated in other countries with different ADs, the Australian AD still applies when the aircraft is on the Australian register. Differences may exist with FAA ADs or EASA ADs for the same models. Operators must comply with the most restrictive applicable AD, but the Australian AD is independent.

The AD likely interacts with the aircraft’s approved maintenance program. The AMO must include this AD in the program, and the inspection intervals must be tracked. The AD may also affect other scheduled inspections, because the borescope access hole could change inspection tasks for other components.

The AD does not affect the aircraft’s flight manual or operating limitations. There are no placards or speed restrictions imposed. The interaction is purely in the structural airworthiness domain.

There is a potential interaction with the Civil Aviation Act concerning the liability for incidental damage caused by the inspection. If the borescope inspection causes damage to the structure, the maintenance organisation may be liable for repairs. That is a private law matter, not directly regulated by the AD.

This document is Amendment 1 to Airworthiness Directive AD/LA/4/23. The original version became effective on 13 July 1989. The original AD required a corrosion inspection of the wing carry through structure that involved removal of the wings to perform a normal unaided visual inspection. The repeat inspection interval in the original AD was a minimum of three years for all aircraft, with no differentiation based on operating environment.

This amendment effective 29 September 2005 introduces three major changes. First, the inspection method changes from wing removal plus unaided visual inspection to a borescope inspection through a small hole in the wing carry through structure. This is a procedural change that reduces labour, downtime and risk of structural disturbance during inspection. Second, the amendment creates two distinct inspection intervals: three years for predominantly salt water operations, and six years for predominantly fresh water operations. The original AD’s flat three year interval is replaced with a risk based approach. Third, the AD explicitly allows operators who previously complied using an exclusion that permitted the Aerofab method to continue that method and count past inspections. The original AD had an exclusion clause that allowed some operators to use the Aerofab method; this amendment formalises that exclusion as the primary method.

The amendment also updates the compliance time for newly imported aircraft not previously inspected. They now have three months from the effective date, rather than any previous time frame. The text does not specify what the compliance time was for such aircraft under the original AD; presumably it would have been immediate or upon import.

The effective date of the amendment is stated as 29 September 2005. The instrument is signed and dated 8 August 2005. The regulation period between signing and effectiveness likely allowed for publication and operator notification.

The amendment was issued as a single page instrument plus a signature page. There is no record of interim amendments or corrections between the original and this amendment. The numbering suggests this is the first amendment to AD/LA/4/23. The original number AD/LA/4/23 would have been issued at some point before July 1989.

No further amendments are reflected in the source. The source also does not mention any review date or automatic expiry. The AD continues to apply indefinitely unless superseded.

There is no reference to any litigation in the instrument itself. This is typical of Australian Airworthiness Directives, which are regulatory instruments issued by a delegate of CASA and rarely litigated directly. Challenges to ADs are uncommon because they are safety decisions based on engineering judgment and CASA has broad powers. Furthermore, the AD was issued in 2005; if there had been litigation it would likely have been noted or referenced.

Litigation might occur indirectly through enforcement proceedings. If CASA takes enforcement action against an operator for non compliance with this AD, the operator could appeal the decision or the penalty. There is no publicly known case directly concerning AD/LA/4/23 Amdt 1. The underlying technical requirement is straightforward and the compliance times are clear, which reduces grounds for dispute.

The AD could be litigated in tort if a structural failure occurs and plaintiffs argue that CASA was negligent in issuing the AD or that the operator was negligent in failing to comply. But that would be product liability or negligence law, not administrative law. The instrument itself does not create a private right of action; it is a public law requirement.

The amendment history notes that the original AD was effective from 13 July 1989. Over the sixteen years between original and amendment, there might have been disputes about the adequacy of the wing removal inspection or the exclusion method. But again, no litigation is recorded in this source.

Given the small fleet size (these are old and comparatively rare aircraft), the likelihood of litigation is low. The cost of challenging a CASA AD usually exceeds the economic interest for individual operators.

Scholarship on AD litigation in Australia notes that most challenges are to the merits of the design of an AD, but such challenges seldom succeed because courts defer to technical expertise. The absence of litigation here is consistent with the norm.

The first gotcha is the definition of predominantly salt water activity. The operator must self assess. The thresholds are specific: more than four landings or takeoffs per month on salt water, or mooring for more than 60 days per year. But the AD says involving more than weekly landings/takeoffs in salt water (i.e. 4 or more per month). That definition is imprecise: it equates more than weekly with 4 per month, but a weekly average would be about 4.3 per month. Careless operators might round incorrectly. Similarly, mooring for greater than 60 days per year means more than 60 days, not 60 or more. Any mooring time in salt water counts, including days when the aircraft is on a mooring buoy but not flown. An operator who moors the aircraft for a 61 day vacation on a salt water lake would qualify as predominantly salt water, even if the rest of the year involves fresh water operations. The classification dumps the aircraft into the three year cycle.

A second gotcha is that the initial compliance time for imported aircraft is only three months from the effective date (29 September 2005). That is an extremely tight window. For an aircraft imported years later, the three months runs from the effective date of the AD, not from the date of import. So an aircraft imported in 2020 would still need to have been modified and inspected by 29 December 2005. That is impossible retroactively. The clear reading is that the AD applies from its effective date and the three month compliance time applies to aircraft that were imported before that date but not previously inspected. For aircraft imported after the effective date, the AD does not specify an initial compliance time. However, CASA would likely require compliance before the aircraft can be operated on the Australian register. The practical gotcha is that anyone importing these models after 2005 must check that the AD has already been complied with, or they face a grounding.

The borescope inspection appears simpler, but the AD does not require wing removal, yet the old method required it. If an operator still has the wings off for unrelated maintenance, they might be tempted to do the old unaided visual inspection and call it compliance. That would not satisfy the AD because the AD now mandates the Aerofab method unless a later revision is approved. Using the old method could be non compliance.

Another trap: the AD states use of Aerofab Service Advisory No A-001 dated 4 May 1991 or later revision approved by the Type Certificate holder. Operators must verify that any later revision is actually approved. Not all revisions may be approved. The Type Certificate holder could have changed, or the advisory could be out of print. If the Type Certificate holder no longer exists, there may be no source of approved revisions, leaving operators stuck with the 1991 version.

The AD does not specify how deep the corrosion treatment must go. The operator must follow the advisory, but if the advisory uses terms like treat in accordance with best practices, there is ambiguity. This could lead to different interpretations by different maintenance organisations.

The AD says initial modification and first inspection. But what constitutes the modification? It seems to be the drilling of the small hole for borescope access. That hole is a structural modification requiring engineering approval. The advisory would specify the location and size. If the hole is drilled incorrectly, it could weaken the carry through structure. The modification is irreversible.

The AD applies to all models. That includes variants with different wing attachment details. Operators must ensure the borescope hole location is appropriate for their specific model.

Finally, the AD does not address what happens if corrosion is found. It says perform corrosion treatment, but there is no defined threshold for scrapping the part or replacing it. That is left to the advisory and the engineer’s judgment.

The first step for any operator of a Consolidated Aeronautics, Colonial or LA-4 Series aeroplane is to obtain a copy of Aerofab Service Advisory No A-001 dated 4 May 1991, or any later revision approved by the Type Certificate holder. This document will contain the detailed instructions for the modification, inspection and corrosion treatment. If the Type Certificate holder has changed or the advisory is unobtainable, the operator should contact CASA or seek alternative means of compliance.

Next, the operator must determine whether the aircraft has been inspected in accordance with the original AD (which required wing removal) or under an exclusion that allowed use of the Aerofab method. If the aircraft has a documented inspection within the last three years that meets those criteria, the initial modification and first inspection can be deferred to no later than three years from that last inspection. If the aircraft has never been inspected to either standard, the initial modification and inspection must be done within three months if the aircraft was on the register by the effective date, or before first operation if imported later. In practice, the safest approach is to perform the modification and inspection immediately regardless of history, to guarantee compliance.

During the initial modification, a small hole must be drilled in the wing carry through structure at the location specified by the advisory. The hole is used for borescope insertion. The modification must be recorded in the aircraft’s maintenance log.

The inspection is performed using a borescope. The inspector must look for corrosion in the carry through structure. The advisory will specify what is considered acceptable and what requires treatment. If corrosion is found, the prescribed corrosion treatment must be applied. If the corrosion is severe enough, the carry through structure may need repair or replacement, though the AD does not detail that.

After the initial inspection, the operator must classify the aircraft’s operating environment. The classification is based on the frequency of salt water exposure. If the aircraft is used predominantly in salt water (more than four landings or takeoffs per month on salt water, or mooring in salt water for more than 60 days per year), the repeat inspection interval is three years. Otherwise, it is six years. The operator should document the classification decision, including the basis for it, to support future compliance and audits.

The operator must then schedule repeat inspections at the appropriate interval. The clock starts from the last inspection date. It is critical to note that the intervals are calendar based: three or six years from the date the inspection was completed. The AD does not allow for manual hours or cycles as substitutes.

All maintenance actions must be recorded in the aircraft’s logbook and, if applicable, in the airworthiness record or continuing airworthiness record system. The records should show the AD number, the service advisory used, the date of compliance, the findings (corrosion or no corrosion), and the classification applied.

If the operator changes the aircraft’s operating environment (for example, moving from fresh water to salt water operations), the classification must be updated, and the inspection interval adjusted. The AD does not specify a grace period for such a change; it would be prudent to do an immediate inspection if the environment changes to more severe.

Operators who wish to use an alternative means of compliance must seek CASA approval separately. The AD does not grant self authorisation.

Finally, maintain awareness of any updates from the Type Certificate holder. If a later revision of the service advisory is approved, it may supersede the 1991 version. Complying with an outdated revision could be non compliance if a newer approved revision exists. Operators should periodically check with the Type Certificate holder or with CASA for updates.