AD/CONVAIR/22 - Wing Lower Skin Inboard of Station 8

The AD rests on a few core technical and administrative concepts that determine obligations and choices for operators and maintenance organisations.

• Applicability scope: The directive applies to Convair Model 340 and 440 aeroplanes and to those models converted to turbopropeller power (Applicability). That defines the population of aircraft to which the inspection and repair regime applies.

• Designated inspection zone and method: The inspection area is tightly defined , the inside surface of the wing lower skin inboard of Station 8, in the vicinity of the second rivet from the outboard end of the short stringer, aligned with the wing access door in the wheel well (Requirement 1). The required inspection is a "detailed visual inspection" after cleaning the inside surface. The AD therefore prescribes both a spatial locus and a non-destructive inspection technique (visual) rather than mandating non‑visual techniques such as eddy current or ultrasound.

• Service-hour stratification of obligations: The AD differentiates obligations by accumulated hours time in service: (a) 15,000 hours or less; (b) more than 15,000 and less than 20,000; (c) 20,000 hours or more (Requirement 1, opening paragraph). Different initial timing and repetitive intervals apply in those bands (Compliance).

• Graduated corrective path by crack length: The AD sets discrete actions depending on measured crack length:

  • less than 2 inches: stop-drill each end with a 0.50-inch diameter drill, then repetitive inspections at prescribed intervals (Requirement 4.a);
  • between 2 and 3 inches: stop-drill then impose reduced airspeed limitations (Vne 243 kt, Vno 217 kt) and install a cockpit placard; continue internal visual inspections (Requirement 4.b);
  • between 3 and 6 inches: repair by installing internal reinforcement plates inboard of Station 8 per Convair Service Engineering Report No. 6820-340-47B/440-47B dated 15 January 1963; again impose reduced airspeed limits and placard (Requirement 4.c);
  • greater than 6 inches: repair in accordance with the Convair Service Engineering Report (Requirement 6).

• Temporary vs permanent repair paths and placarding: Temporary measures include stop-drilling and temporary plate repairs with continued inspections and speed restrictions. Permanent repair is described as installing internal reinforcement plates both inboard and outboard of Station 8 per the specified Convair report , this text appears in the AD but is not cleanly labelled as a numbered requirement in the supplied copy.

• Modification option that reduces inspection burden: The AD offers an option: remove a 3/16-inch rivet above where cracks originate, enlarge the hole to 1/4-inch, inspect the skin around the hole, and, if clear, install a close tolerance -8 rivet or 1/4-inch bolt. If that modification is performed and no cracks exist, inspection intervals may increase to 1,000 hours (Requirement 1, middle paragraph). That creates a trade-off between a one-off modification and ongoing inspection costs.

• Cross-reference to manufacturer's/airframe reports and an FAA AD: The AD requires repairs "in accordance with Convair Service Engineering Report No. 6820-340-47B/440-47B" and references Convair Service Engineering Report No. 15-4-340-18/440-22 dated 9 May 1958 as a basis for exemption from the AD. It additionally contains a Note referencing FAA AD 63-10-03 Amdt 562 Part 507 (Requirement 7 Note). Therefore compliance will require access to and adherence to those historic service engineering reports.

• Effective date and administrative provenance: The AD becomes effective on 8 June 2006 and is signed by David Villiers, delegate of CASA (closing paragraph). The AD is described as responding to an FAA requirement to detect and correct wing lower skin fatigue cracking (Background).

These concepts create a regulatory framework that is procedural (inspection plus escalation), document-dependent (Convair reports), and hour-based, with an explicit pathway to remove repetitive obligations if a permanent repair or earlier conforming modification is in place (Requirement 7).

The AD places duties and options on several identifiable actors explicitly and implicitly.

• Aircraft owners and operators of Convair Model 340 and 440 aeroplanes, including those converted to turbopropeller power (Applicability). The directive’s inspection, repair and placarding requirements are operational obligations for the person or entity that operates the aircraft and maintains its airworthiness records.

• Maintenance organisations and licensed aircraft maintenance engineers (AMEs) responsible for conducting the prescribed inspections and repairs. The AD specifies actions that must be "accomplished" and references specific engineering reports for repair works (Convair Service Engineering Report No. 6820-340-47B/440-47B and No. 15-4-340-18/440-22). Those documents set the technical method; the AME or maintenance organisation will need access to them and to implement the procedures they contain.

• Pilots/flight crew to the extent they must comply with and enforce placard requirements and revised operating limitations. The AD requires installation of a cockpit placard stating the reduced speeds when certain repairs are made (Requirement 4.b and 4.c). That places a duty on the operator and pilot to ensure the aircraft is flown within those limits until a permanent repair removes the placard.

• Regulators and CASA: The AD is issued by CASA (delegate), thereby procedurally obliging operators in the CASA jurisdiction to comply. The AD itself does not list enforcement measures or penalties, but the issuing authority and effective date imply regulatory oversight and a duty to comply.

• Suppliers and parts providers: The AD specifies rivet sizes (3/16-inch removal, enlarge to 1/4-inch, install close tolerance -8 rivet or 1/4-inch bolt) and internal reinforcement plates per Convair reports. That creates demand for specific parts and possibly for historical or reproduced engineering documentation. Operators will be dependent on suppliers for rivets/bolts, reinforcement plates (or engineered equivalents approved under the referenced Convair report), and any required fasteners.

• Insurance underwriters and lessors: Although not mentioned in the AD, the obligations to inspect and repair, and any imposed operating limitations, will affect aircraft availability, utilisation and risk profiles; that is relevant to insurers and lessors who will be informed by operators’ compliance with the AD. This inference is derived from the operational effects the AD prescribes.

Who pays: the AD places the expense of compliance , labour for inspections, parts, any reinforcement plates, possible downtime and potentially temporary reduced operational capability (due to placarded speed limits) , on the aircraft owner/operator and their maintenance providers. The AD’s text does not provide funding or government reimbursement; costs are therefore private.

Who decides: the AD fixes the mandatory actions and references mandatory repair procedures. In practice, decisions about whether to perform the optional rivet modification (to increase inspection intervals), whether to conduct temporary stop-drilling or proceed to permanent reinforcement, and scheduling of work are operational choices for the owner/operator and the maintenance organisation, within the constraints and deadlines set by the AD (Requirements 1-7 and Compliance). If ambiguity arises (for example in the supplied text’s numbering), operators may need to seek clarification from CASA.

Duties (expressly set out in the AD):

• Inspect the specified area: Clean the inside surface of the wing lower skin inboard of Station 8 in the vicinity of the second rivet from the outboard end of the short stringer in line with the wing access door in the wheel well, and conduct a detailed visual inspection for any indication of wing skin cracks (Requirement 1, repeated in the three service-hour bands). This is the principal recurring duty.

• Follow the graduated crack-management pathway: If cracks are found, apply the steps prescribed for the measured crack length:

  • <2 inches: stop-drill each crack end with a 0.50-inch diameter drill before further flight, then continue repetitive inspections (Requirement 4.a).
  • 2-3 inches: stop-drill each end with 0.50-inch diameter drill before further flight; revise airspeed limitations (Vne to 243 kt, Vno to 217 kt) and install a cockpit placard; conduct internal visual repetitive inspections (Requirement 4.b).
  • 3-6 inches: repair by installing internal reinforcement plates inboard of Station 8 according to Convair Service Engineering Report No. 6820-340-47B/440-47B dated 15 January 1963; revise airspeed limits as above and placard; conduct internal visual repetitive inspections (Requirement 4.c).

  • 6 inches: repair in accordance with Convair Service Engineering Report No. 6820-340-47B/440-47B (Requirement 6).

• Apply inspection intervals as required: The Compliance section gives precise initial and repetitive time windows and intervals depending on hours in service and whether initial inspections have recently been performed (Compliance).

• Carry out the rivet modification option if chosen: Operators may remove the 3/16-inch rivet above where cracks originate, enlarge hole to 1/4 inch, inspect the surrounding skin, and if clear, install a close tolerance -8 rivet or 1/4-inch bolt; if performed and no skin cracks are detected, inspection intervals may be increased to 1,000 hours (Requirement 1).

• Install cockpit placards where required: When speed limitations are imposed under Requirements 4.b and 4.c, the placard must be installed “in full view of the pilot stating the reduced speeds” (Requirement 4.b and 4.c).

Rights or options (express in the AD):

• Option to adopt the rivet modification that permits increased inspection intervals, contingent on inspection results (Requirement 1 middle paragraph).

• Option to use permanent repair to discontinue repetitive inspections and remove placards and operating limitations: the AD provides that “the repetitive inspections required by Requirements 1, 2, 3, and 4 may be discontinued, and the operating limitations and placard specified in Requirements 4.b. and 4.c. may be removed from the aircraft when it is repaired in the manner specified in Requirement 5 or 6” (Requirement 7). That is a right to pursue a permanent repair path to restore normal operations.

• Exemption for pre-existing compliant repairs or modifications: The AD does not apply to aircraft already repaired in accordance with Requirement 5 or 6 before the effective date, or aircraft modified before any cracking in accordance with Convair Service Engineering Report No. 15-4-340-18/440-22 dated 9 May 1958 (Requirement 7). This is a carve-out for prior conforming work.

Prescribed references and constraints:

• Repairs must be carried out “in accordance with” specified Convair Service Engineering Reports (e.g., No. 6820-340-47B/440-47B dated 15 January 1963) , these reports set technical standards that the repair work must satisfy (Requirement 4.c, Requirement 6, Requirement 7).

Procedural constraints and timing:

• The Compliance section fixes time windows for when actions must be accomplished (e.g., “Before the accumulation of 15,100 hours time in service, and thereafter at intervals not to exceed 1,000 hours … after the accumulation of 20,000 hours time in service, and before the accumulation of 20,500 hours … accomplish Requirement 1 at intervals not to exceed 500 hours time in service.”) Operators must follow these timing rules exactly.

Notes on textual ambiguity:

• The supplied AD text contains references to “Requirement 5” and a Compliance line that says “As specified in Requirement 5” without a clear, separately numbered Requirement 5 text block in this copy. There is text that reads like a permanent repair option (install internal reinforcement plates inboard and outboard of Station 8) which appears to be the operative permanent repair provision but is not clearly labelled 5. This creates a practical duty: operators must ensure they interpret the AD correctly and, if necessary, request formal clarification from CASA before undertaking or certifying works labelled under Requirement 5.

The AD document supplied does not specify penalties, sanctions, or the precise enforcement mechanisms within its text. The instrument states the effective date (8 June 2006) and is signed by a CASA delegate, and prescribes mandatory actions and timing for affected aircraft. Absent a penalty clause in the AD itself, the enforcement regime , whether administrative penalties, grounding, suspension of an aircraft’s certificate, or other compliance measures , is not set out in this document as provided.

What the AD does provide that is relevant to enforcement:

• Mandatory actions and compliance timetables: The AD sets out precise actions and deadlines (see Compliance). Non‑performance against those deadlines will leave aircraft in a state non‑conforming to the requirements of this directive.

• Clear technical performance standards: Repairs are required to be done “in accordance with” specified Convair Service Engineering Reports. That provides an objective standard against which compliance could be assessed.

Absent explicit penalties in the AD, the practical enforcement implications must be inferred from the AD’s nature as an airworthiness instrument: if an operator or maintainer does not accomplish the required inspections or repairs within the specified time windows, the aircraft will not have complied with the directive’s mandatory requirements. The supplied text itself does not identify the consequences an operator might face for non-compliance, or the process for CASA to enforce compliance, issue directions, or penalise infractions. The AD therefore leaves open the following implementation and enforcement risks unless CASA’s broader regulatory framework (not included in this document) is referenced or invoked:

• Uncertainty for operators about the immediate regulatory consequence of non-compliance as expressed in this copied instrument.

• Potential operational decisions (e.g., whether to operate the aircraft while non-conforming) that will need to be resolved with reference to CASA’s broader regulatory practice and enforcement policies, which are not contained in the AD text provided.

In short, the document sets mandatory technical and timing obligations, but the specific legal penalties and enforcement steps are not described in the provided text. Operators and maintenance organisations should treat the AD as a binding operational requirement and, if uncertain about enforcement consequences, seek clarification from CASA or their nominated continuing airworthiness authority.

The AD text itself is self-contained with technical requirements but explicitly cross-references other aviation artefacts which determine how compliance must be achieved and when the AD does not apply.

• Convair Service Engineering Reports as prescriptive technical standards: The AD requires repairs to be done “in accordance with Convair Service Engineering Report No. 6820-340-47B/440-47B, dated 15 January 1963” for 3-6 inch repairs and for repairs over six inches (Requirement 4.c and Requirement 6). It also references Convair Service Engineering Report No. 15-4-340-18/440-22 dated 9 May 1958 as the basis for exempting aircraft which had been modified in accordance with that report prior to any wing-skin cracking (Requirement 7). Practically, these documents determine the technical acceptability of repairs and modifications; compliance with the AD therefore requires access to and adoption of those reports’ methods.

• Reference to FAA AD: The AD includes a Note stating “FAA AD 63-10-03 Amdt 562 Part 507 refers.” That indicates that the FAA has taken related regulatory action and that CASA’s AD is aligned to or informed by that FAA action. The extent to which FAA AD content modifies interpretation of this CASA AD is not elaborated in the supplied text, but the cross-reference shows that operators and maintainers with cross-jurisdictional fleets might need to reconcile both directives. The AD does not indicate any direct legal primacy between the FAA AD and the CASA AD; it is a reference.

• Interaction with aircraft-specific modifications and prior repairs: The AD explicitly removes its requirements where aircraft were repaired in accordance with Requirement 5 or 6 before the AD’s effective date, or if before any wing skin cracking the aircraft had been modified between stringers 6 and 10 in accordance with Convair Service Engineering Report No. 15-4-340-18/440-22 (Requirement 7). That introduces an interaction with an aircraft’s maintenance and modification history: compliance obligations depend on what was already performed and recorded on the aircraft.

• Operating limitations and placarding as operational law: The AD mandates reduced speed limitations (Vne to 243 kt, Vno to 217 kt) when certain temporary repairs are in place and requires a placard in full view of the pilot stating the reduced speeds (Requirement 4.b and 4.c). Those placarded limitations interact with operational rules and the pilot’s obligations to adhere to flight limits. The AD does not itself cite the regulatory instrument that empowers placarding, but it obliges installation of the placard as a compliance action.

• Silent on administrative enforcement: The AD does not spell out administrative or criminal penalties or reference specific enforcement provisions from other statutory instruments. Therefore any procedural interaction with other laws (for example, where CASA might issue directions under broader aviation safety legislation) is not documented in this instrument and must be sought from CASA’s wider regulatory framework or other legal provisions (not included here).

• Document-dependence risk: By requiring adherence to historical Convair service engineering reports and referring to an FAA AD, the AD implicitly ties compliance to other non‑statutory or foreign regulatory materials. Operators must ensure access to those materials and confirm their applicability. That creates an interactional dependency: compliance with this CASA AD requires execution of measures specified outside the AD’s text, and operators must ensure those documents are used as authoritative technical standards.

In sum, the AD interacts with other technical and regulatory instruments by mandating compliance with particular Convair engineering reports and by acknowledging related FAA action. The AD does not, in the provided copy, spell out procedural enforcement mechanisms or how it sits within the entirety of CASA’s regulatory enforcement regime.

The supplied document shows a single airworthiness directive entry labelled AD/CONVAIR/22 and a date code “6/2006” and states, twice, that it becomes effective on 8 June 2006. The final lines bear the signature of David Villiers, Delegate of the Civil Aviation Safety Authority, and the date 11 April 2006. No subsequent amendments, revocations, supersessions, or re-issues are included in the supplied text.

Items of note from the document relevant to amendment history:

• The AD repeatedly shows the code AD/CONVAIR/22 and the identifier “6/2006”, indicating the issuance month and year. There is no trace, in this copy, of later amendments, errata, or referenda amending the content.

• The AD contains a Note referencing FAA AD 63-10-03 Amdt 562 Part 507, which may be antecedent regulatory material that informed the CASA AD. The supplied text does not indicate whether subsequent FAA amendments affected this CASA AD after 8 June 2006.

• The AD’s text as supplied shows internal formatting and numbering irregularities (for example, references to Requirement 5 without a clearly labelled Requirement 5 in the copied layout). If those irregularities reflect the original published AD, they may have been addressed by later amendment or clarification; none is included here. This is important: where the AD’s internal numbering is ambiguous, practitioners should check the official CASA register or contact CASA for any corrigenda or amendment notices that clarify the intended requirement numbering and scope.

• The document’s “Background” line states that the FAA requires certain inspections and modifications to detect and correct wing lower skin fatigue cracking. That background suggests that CASA’s AD may be an implementing or harmonising action rather than a standalone research-based innovation. The supplied text does not provide a trail of prior or later CASA ADs amending this AD.

Therefore, based on the provided instrument alone, the amendment history is limited to initial issuance in mid‑2006 with no recorded amendments in the supplied copy. For certainty on subsequent revisions or superseding actions, the operator should consult the CASA AD register, official gazette, or CASA contact channels.

The supplied AD contains no litigation history, court decisions, or references to judicial or tribunal proceedings. It does not name any cases, nor does it report any litigation challenging the AD, its scope, or its enforcement. The only external instrument referenced is an FAA AD and Convair Service Engineering Reports; neither of those is accompanied in the text by any litigation record.

Where the AD itself contains ambiguous numbering or text (references to Requirement 5 without a clearly labelled block), the absence of included litigation or judicial clarification in this document means that any legal disputes over interpretation are not recorded here. Practitioners working from this copy should treat the absence of litigation history as simply that: the document does not record any adjudicated disputes; it does not mean disputes cannot arise or have not arisen elsewhere. For information on whether any legal challenges, enforcement actions, or litigation followed issuance of this AD, one must consult court records, regulatory enforcement notices or CASA’s subsequent documentation; none of that material is present within the supplied AD text.

The AD contains several practical pitfalls, ambiguities and implementation risks that operators, maintainers and compliance teams should confront directly.

1. Textual and numbering ambiguity: The supplied copy repeatedly refers to “Requirement 5” while the visible numbered requirements include 1, 2, 3, 4 (with subparts), 6 and 7. There is a paragraph describing a permanent repair by installing internal reinforcement plates inboard and outboard of Station 8 that appears to be the logical content of Requirement 5, but it is not clearly labelled as such in this copy. This ambiguity creates a material risk: parties that rely on the AD for compliance must ensure they have the officially numbered and formatted version or seek CASA clarification before certifying compliance.

2. Reliance on historical Convair documents: The AD requires repairs and modifications “in accordance with Convair Service Engineering Report No. 6820-340-47B/440-47B” dated 15 January 1963 and makes reference to Convair Service Engineering Report No. 15-4-340-18/440-22 dated 9 May 1958. Those documents are nearly half a century old and may be difficult to source. Operators must ensure they obtain authentic copies and that the specified procedures therein can be complied with in a contemporary maintenance environment, potentially requiring approved equivalents or engineering authority sign-off.

3. Precision of the inspection locus: The AD specifies the precise rivet location to inspect , “the second rivet from the outboard end of the short stringer in line with the wing access door in the wheel well.” That level of precision demands that maintenance personnel identify station 8 and the particular short stringer locations precisely; misidentification would expose the aircraft to undetected cracking risk and may be treated as non-compliance.

4. Tight service-hour windows around 20,000 hours: The Compliance section creates a tight band between 20,000 and 20,500 hours time in service where inspection intervals may change to 500 hours for certain requirements. Operators must track accumulated airframe hours accurately to avoid missing a narrowed inspection interval, which has operational planning impacts and creates a scheduling obligation that may be overlooked in routine maintenance scheduling.

5. Options create strategic choices with cost and downtime trade-offs: The AD allows an optional rivet modification that can extend inspection intervals to 1,000 hours if no cracks are present after modification, and it allows permanent reinforcement to remove repetitive inspection and placard obligations. Operators must weigh one-off modification and reinforcement costs (parts, engineering, downtime) against continuing inspection labour and lost availability, factoring in the probability of future cracking. The AD itself does not provide economic analysis; operators must perform their own cost-benefit analysis.

6. Placard and reduced speed obligations can affect operations: When intermediate repairs are used (2-3 inch stop-drill, 3-6 inch internal plates), the AD mandates reduction of Vne and Vno to 243 and 217 knots respectively and requires cockpit placarding. This may materially limit permitted operations (e.g., cruise speeds, dispatch to certain routes) and could interfere with commercial schedules or operational performance expectations unless a permanent repair is accomplished.

7. No enforcement detail in the AD text: The AD is silent on penalties and enforcement steps. That silence leaves operators uncertain regarding immediate regulatory consequences of non-compliance or enforcement priorities. Operators should not construe this as permissive; instead they should confirm compliance expectations and enforcement approach with CASA.

8. Potential need to coordinate with foreign regulators or operators: The AD references an FAA AD. Operators that operate across jurisdictions need to ensure their compliance aligns with both CASA and any applicable foreign authority directives. The AD does not specify harmonisation, so coordination may be required.

9. Parts and materials specification choices: The rivet change calls for a “close tolerance -8 rivet or 1/4-inch bolt.” The AD does not specify material types, heat-treatment, or procurement standards for any replacement fastener or reinforcement plate. Maintenance organisations should ensure that parts meet airworthiness standards and that any deviations are approved by relevant engineering authority.

10. Record-keeping and proof of pre-existing repairs or modifications: The AD exempts aircraft repaired in accordance with Requirement 5 or 6 before the effective date, or modified per Convair Service Engineering Report No. 15-4-340-18/440-22 before any cracking, from the requirements. Operators must be able to demonstrate such prior repairs or modifications with maintenance records to rely on these carve-outs.

These “gotchas” point to practical steps: obtain the official AD document from CASA to resolve formatting ambiguities, secure the referenced Convair reports, verify part specifications and supply availability, and integrate the inspection and repair schedule into maintenance planning systems with attention to the service-hour bands.

This section provides a practical, stepwise approach to complying with the AD, as expressed in the supplied text, including required actions, timing and documentation considerations. It assumes operators will obtain the official, correctly formatted CASA AD and the Convair Service Engineering Reports referenced.

1. Verify applicability: Confirm the aircraft is a Convair Model 340 or 440, or such model converted to turbopropeller power (Applicability). If the aircraft has been modified previously in accordance with Convair Service Engineering Report No. 15-4-340-18/440-22 dated 9 May 1958, or repaired per Requirement 5 or 6 prior to the AD effective date, document that work thoroughly because the AD states it does not apply in those circumstances (Requirement 7).

2. Obtain referenced documents: Secure copies of Convair Service Engineering Report No. 6820-340-47B/440-47B dated 15 January 1963 and Convair Service Engineering Report No. 15-4-340-18/440-22 dated 9 May 1958, and the official CASA AD (to resolve the numbering ambiguity noted in this copy). Confirm that the maintenance organisation has the authorised right to use those engineering reports as the basis for repairs.

3. Schedule initial inspections according to time-in-service band and the Compliance table:

   • For aircraft with 15,000 hours or less time in service: accomplish Requirement 1 before the accumulation of 15,100 hours time in service, and thereafter at intervals not to exceed 1,000 hours until 20,000 hours accumulated (Compliance item 1).
   • For aircraft with more than 15,000 and less than 20,000 hours: follow the same inspection requirement in the relevant clause of Requirement 1; check Compliance item 1 for timing consistency.
   • For aircraft with 20,000 hours time in service or more: before accumulation of 20,500 hours time in service, accomplish Requirement 1 at intervals not to exceed 500 hours (Compliance item 1).
   • For Requirements 2 and 3 (which are referenced and have their own initial timing rules), note the initial windows “within 100 hours time in service after 8 June 2006, unless accomplished within the last 900/400 hours” and the repetitive intervals thereafter (Compliance items 2 and 3). Interpret these with the official AD to map to the aircraft’s recent inspection history.

4. Perform the inspection as specified:

   • Clean the inside surface of the wing lower skin inboard of Station 8 in the vicinity specified (second rivet from outboard end of the short stringer in line with the wing access door in wheel well).
   • Conduct a detailed visual inspection for any wing skin cracks in that area (Requirement 1).
   • Record the results precisely (location, length of any crack, measurements, photos if possible) in the aircraft maintenance records.

5. If no cracks are detected, consider the rivet modification option:

   • Optionally remove the 3/16-inch rivet located above where cracks originate, enlarge the hole to 1/4-inch, inspect the wing lower skin around the hole, and if no wing skin crack is detected, install a close tolerance -8 rivet or 1/4-inch bolt (Requirement 1).
   • If the modification is accomplished and the area is crack-free, inspection intervals may be increased to 1,000 hours time in service (Requirement 1). Document the modification in maintenance records, including the rivet/bolt specification and inspection results.

6. If cracks are detected, follow the graduated remedies precisely:

   • Less than 2 inches: before further flight, stop-drill each end of the crack with a 0.50-inch diameter drill; thereafter perform repetitive inspections per the relevant Requirement (Requirement 4.a). If the crack later progresses beyond a stop-drill but remains under 2 inches, stop-drilling may be repeated; when crack reaches 2 inches, follow Requirement 4.b.
   • Between 2 and 3 inches: before further flight, stop-drill each end with 0.50-inch diameter drill; reduce never-exceed speed (Vne) to 243 kt and normal operating speed (Vno) to 217 kt and install a cockpit placard in full view stating those reduced speeds; continue internal visual repetitive inspection per Requirements 1, 2, or 3 as applicable (Requirement 4.b). If crack progresses beyond a stop-drill but remains <3 inches, continue the stop-drill & 100-hour inspections until 3-inch threshold met.
   • Between 3 and 6 inches: before further flight, repair the wing lower skin by installing internal reinforcement plates inboard of Station 8 in accordance with Convair Service Engineering Report No. 6820-340-47B/440-47B dated 15 January 1963; reduce Vne to 243 kt and Vno to 217 kt and placard in cockpit; perform internal visual repetitive inspections per Requirements 1, 2, or 3; if further cracking is detected within 1,000 hours from the temporary repair, repair in accordance with Requirement 6 (Requirement 4.c).
   • Less than 2-inch cracks may, unless already repaired under Requirement 6, be permanently repaired by installing internal reinforcement plates inboard and outboard of Station 8 in accordance with the same Convair report (this text appears in the AD and should be reviewed in the official numbering context).
   • Greater than 6 inches: repair in accordance with Convair Service Engineering Report No. 6820-340-47B/440-47B (Requirement 6). Before further flight after detection, ensure repairs conform to the Convair report instructions.

7. Placarding and operational limits: When repairs trigger reduced speeds (2-6 inch cracks and temporary plate repairs), install a placard in full view of the pilot stating the reduced speeds (Requirement 4.b and 4.c). Ensure flight crew are briefed and dispatch control enforces the reduced operational limits until the placard is removed as permitted.

8. Record-keeping: Log all inspections, findings, rivet modifications, stop-drilling actions, temporary repairs, permanent repairs (including the specific Convair Service Engineering Report references and work performed under those instructions), and placard installation/removal in the aircraft maintenance records. If relying on pre‑existing modifications or repairs to claim exemption under Requirement 7, ensure documentary proof of the prior work is available.

9. Re-evaluate inspection intervals after repairs or modifications: If the permanent repair per Requirement 5 or 6 is completed, the AD allows discontinuation of the repetitive inspections and removal of the operating limitations and placards (Requirement 7). If the rivet modification was performed, follow the guidance on inspection interval increases (Requirement 1). Keep maintenance programmes updated to match the changed inspection periodicity.

10. Clarify ambiguities with CASA: Given the formatting ambiguities in this supplied copy (e.g., missing explicit Requirement 5), contact CASA or consult the official AD register to obtain the authoritative version and any applicable service letters, interpretation guidance, or AMOC (alternative method of compliance) procedures. If an alternative repair method is proposed that diverges from the specified Convair reports, seek approval from the applicable engineering authority before implementation.

Implementing these steps will align maintenance practice with the AD as provided. Because the AD ties compliance to historical engineering reports and to precise inspection loci and hours thresholds, compliance planning should incorporate parts procurement, staff training for the specific inspection area, and scheduling to avoid the narrow inspection windows around service-hour thresholds.