AD/CESSNA 336/11 Amdt 3 - Wing Front and Rear Spars - Inspection

The instrument operates through a small set of tightly specified technical requirements and cross-references. The core concepts are:

• Applicability by serial number. The AD applies only to Cessna 336 aeroplanes with serial numbers 336-0001 through 336-0195. The applicability is expressed as an explicit serial-number range in the document.

• Reference-based inspection procedure. The substantive inspection work is to be done "in accordance with Cessna SL ME78-2 Supplement No. 1." The AD does not reproduce the full inspection steps or the inspection periodicity; instead it delegates precise procedural and timing detail to that service letter and its "Action Required" section.

• Eddy current testing with specified sensitivity. For the front spar inspection, the AD prescribes how to establish eddy current test sensitivity: the test must be set so that a 10 per cent full scale meter deflection is produced by a specific machined slot in a 3/16" diameter hole in an aluminium alloy test block. The slot dimensions are stated to tolerances: .030" + .003" deep, .060" + .003" long, .010" maximum width. This is an objective calibration target for equipment set-up.

• Test block identification. The AD identifies a "suitable test block" as Nortec Part No. TB-12. The AD also notes that Amendment 2 clarified the test block specifications, and this Amendment (No. 3) defines the serial-number scope.

• Caution on bolt-hole scoring. The AD warns that scoring of bolt holes can produce spurious eddy current indications and might cause future fatigue crack initiation, therefore advising great care when removing bolts. The warning is both diagnostic (false positives) and structural (risk of inducing fatigue).

• Timing and an STC exception. Compliance timing is referenced to the rear spar inspection schedule in the Cessna supplement's "Action Required" section. Aircraft modified under Robertson Aircraft Corporation STC 1627 WE are subject to earlier and more frequent inspections: a reduction in the inspection threshold by 1,000 hours and in intervals by 100 hours, but that exception is conditional on the absence of fatigue-substantiating data; the Authority may change it if such data are supplied.

• Cross-reference to FAA AD. The AD states that "FAA AD 78-09-05 also refers," indicating a cross-jurisdictional reference to an earlier Federal Aviation Administration directive, but it does not reproduce that AD or its requirements.

These concepts together frame a compliance regime combining a prescriptive measurement/calibration requirement (eddy current sensitivity and test block), procedural dependence on a manufacturer supplement for interval timing and actions, and a specific adjustment for a particular STC conversion.

The AD directly affects owners, operators and maintenance organisations responsible for Cessna 336 aircraft with serial numbers within the specified range, 336-0001 through 336-0195. Because the AD imposes inspection obligations that refer to a Cessna service letter, it also implicates any maintenance provider or maintenance-release authority that is charged with carrying out or certifying compliance with that service letter.

Specifically identified affected parties and roles in the AD text are:

• The registered owner/operator of the listed aeroplanes, who must ensure that inspections are carried out in accordance with the AD and Cessna SL ME78-2 Supplement No. 1. The AD's requirement to inspect makes the owner/operator responsible for arranging and funding the inspections and any subsequent work triggered by inspection findings.

• Maintenance organisations and licensed personnel performing eddy current inspections, who must establish test equipment sensitivity to the specified calibration target and take care when removing bolts to avoid scoring bolt holes. The AD's technical prescription (10 per cent full scale deflection on the specified slot) imposes an equipment-setup obligation on the inspector.

• Holders or installers of Robertson Aircraft Corporation Modification to United States STC 1627 WE. The AD creates a specific adjustment for those aeroplanes: a reduction of 1,000 hours in the inspection threshold and 100 hours in the inspection intervals. That group therefore faces earlier and more frequent inspections.

• Suppliers of test blocks (and those responsible for procuring test artefacts). The AD notes that Nortec Part No. TB-12 is a suitable test block, so operators and maintainers procuring equipment for compliance may prefer or acquire that part. While the AD does not mandate a single part number as exclusive, it does expressly identify a suitable test block.

• Civil Aviation Safety Authority (CASA) as regulator, represented by the Delegate who issued the AD (David Villiers). The AD is an instrument issued by CASA and sets the compliance standard; the document does not, however, enumerate enforcement mechanisms or penalties.

• Operators or technical support entities referencing FAA AD 78-09-05. The AD's cross-reference indicates that there is relevant FAA material that "also refers"; those engaged in compliance may need to consult that FAA AD for context or historical practice, though the AD does not require following the FAA AD beyond noting it.

Indirectly, the AD affects insurers, lessors, and purchasers who need to know airworthiness status: an aircraft subject to this AD must have the required inspections to be considered airworthy. Lenders, underwriters or purchasers acting after 29 September 2005 will need to confirm compliance because the AD creates a defined inspection obligation tied to specific serial numbers.

The AD's text does not address exemptions, alternate methods of compliance, or delegated acceptance procedures within the document itself; it does note that the Robertson-conversion exception is subject to revision on receipt of fatigue data. The AD also does not list penalty or enforcement clauses in the supplied text.

Duties imposed by the AD are technical and procedural, anchored to the Cessna service supplement. The principal duties are:

• Inspect both the front and rear spars. The AD requires inspection of both front and rear spars "in accordance with the times specified for the rear spar in 'Action Required' Section of Cessna SL ME78-2 Supplement No. 1." The duty therefore ties the inspection timeframes to the manufacturer supplement rather than enumerating them in the AD.

• Establish eddy current test sensitivity for the front spar inspection. The AD expressly requires that, "in connection with the front spar inspection the eddy current test sensitivity shall be established so that a 10% full scale meter deflection is obtained from a slot .030" + .003" deep, .060" + .003" long and .010" maximum width, machined in the wall of a 3/16" diameter hole in an aluminium alloy test block." This is a calibration obligation on the inspector and the inspection equipment.

• Use an appropriate test block. The AD identifies Nortec Part No. TB-12 as "a suitable test block" (Note 2). The identification of a suitable part is directional; the AD requires that eddy current sensitivity be established to the specified standard, and the Nortec block is provided as a suitable means to achieve that calibration.

• Exercise caution when removing bolts. The AD contains a diagnostic and preventative instruction: "Scoring of bolt holes can cause spurious eddy current indications of cracking and may be the cause of future fatigue crack initiations. Great care must therefore be taken when removing the subject bolts." That creates a duty of care during disassembly to avoid inducing surface damage that may both compromise diagnosis and promote fatigue.

• Apply the Robertson STC adjustment where relevant. The AD imposes an altered inspection schedule for aircraft incorporating Robertson Aircraft Corporation Modification under US STC 1627 WE: a reduction of 1,000 hours in the inspection threshold and 100 hours in inspection intervals. Operators of such modified aeroplanes are obliged to follow these shortened timeframes unless and until the Authority amends the exception.

• Monitor for potential changes to the exception. The AD states the Robertson-related exception "is subject to change should fatigue substantiating data on the Robertson conversion be supplied to the Authority." That language gives the Authority the possibility of changing inspection timing for affected aeroplanes upon receipt of further data, and therefore creates an ongoing compliance monitoring duty for affected operators.

Rights or procedural options are not explicitly detailed in the AD text provided. The AD does not itself set out an alternative method of compliance (AMOC) process, does not specify an appeal or review route, and does not authorise departures from the specified calibration requirement. Because the AD refers work to Cessna SL ME78-2 Supplement No. 1, rights that might exist to seek alternative compliance would be found either in CASA administrative practice, in provisions external to this text, or in the referenced service letter, none of which are included in the AD text provided. The AD also does not list penalties or enforcement processes in the supplied text, and does not specify record-keeping requirements; those matters, if present, must be sought in other regulatory material.

In short, the AD imposes concrete technical duties: perform both spars inspections per the Cessna supplement at the times specified for the rear spar; set eddy current sensitivity to a precise calibration; use a suitable test block (Nortec TB-12 given as an example); take care with bolt removal; and apply modified intervals for Robertson-converted aeroplanes, recognising the Authority may change that exception on receipt of fatigue data.

The text of AD/CESSNA 336/11 Amendment 3, as supplied, does not include an express penalties or enforcement section. It is an Airworthiness Directive issued by the Civil Aviation Safety Authority and signed by the Authority's Delegate, but the AD text itself limits its content to applicability, inspection requirements, compliance timing references, technical calibration specifications, notes, and background explaining the reason for the amendment. It does not set out sanctions, infringement penalties, certificate suspension mechanisms, or enforcement procedures.

Because the AD does not state enforcement mechanisms in the provided text, the document does not specify the administrative or civil remedies that would follow non-compliance, nor does it identify a formal process for reporting non-compliance in this instrument. The AD does, however, create mandatory technical obligations (inspection requirements tied to the Cessna supplement and a specified calibration procedure), and practitioners should treat the AD as an operative airworthiness requirement from CASA as the issuer. The AD also contains a clear effective date, 29 September 2005, which fixes when the obligations become operative.

Given that the AD text itself is silent on penalties and enforcement, readers who need to understand sanctioning, remedial, or AMOC procedures must consult the wider CASA regulatory framework, instrument registers, or guidance documents beyond the AD itself. The AD does not prescribe who is authorised to accept alternative methods, how to petition for an amendment to compliance timing, or whether the Authority will accept equivalent test-block hardware other than the Nortec TB-12 example. The only procedural conditionality stated in the AD relates to the Robertson-conversion exception being subject to change upon receipt of fatigue substantiating data by the Authority.

In summary, the supplied instrument imposes technical and timing obligations and fixes an effective date, but it does not set out penalties, notification procedures, or enforcement mechanisms in the text provided.

The AD explicitly interacts with at least three external instruments or authorities by reference. The nature of those interactions is limited to the references contained in the AD text; the AD does not import the full content of those external instruments. The referenced instruments and effects are:

• Cessna SL ME78-2 Supplement No. 1. The AD makes the Cessna supplement the primary procedural and timing source. Inspections are to be performed "in accordance with Cessna SL ME78-2 Supplement No. 1" and the timing for both front and rear spar inspections is tied to "the times specified for the rear spar in 'Action Required' Section" of that supplement. The AD therefore creates a dependent relationship: the AD sets a regulatory obligation but delegates specific intervals and procedural actions to the manufacturer service letter. Compliance with the AD requires compliance with the referenced service letter.

• FAA AD 78-09-05. The AD notes that "FAA AD 78-09-05 also refers." This indicates cross-reference to an earlier Federal Aviation Administration directive concerning similar structures or inspections. The AD does not state that FAA AD 78-09-05 must be complied with as part of this CASA AD; it merely indicates the FAA AD is relevant or has been referred to. Practically, operators and maintenance organisations may need to consult that FAA AD for additional context or historical rationale, but the CASA AD does not reproduce or directly require the FAA AD’s content.

• Robertson Aircraft Corporation Modification under United States STC 1627 WE. The AD establishes a specific modification to inspection thresholds and intervals where that STC has been incorporated. That creates an operational intersection between a Supplemental Type Certificate modifying the aircraft and this CASA AD. The AD reduces the inspection threshold by 1,000 hours and the inspection interval by 100 hours for aircraft with that STC, and makes that exception conditional on the absence of fatigue substantiating data to the Authority. Thus, the AD modifies compliance timing for aircraft altered under a particular STC.

The AD does not reference other Australian legislation, civil penalty provisions, or administrative processes within the AD text itself. It does not provide cross-references to Parts of the Civil Aviation Safety Regulations or to any enforcement instruments. Therefore this AD should be read alongside the broader CASA regulatory framework to understand how the AD’s requirements are enforced or how alternative compliance pathways are administered. The AD’s reliance on an external manufacturer supplement for action and timing means that its effective operational content is a combination of the AD text and the content of Cessna SL ME78-2 Supplement No. 1: the two must be read together to determine inspection frequency, threshold, and specific remedial actions where cracks are found.

Finally, the AD’s identification of a test block (Nortec TB-12) and the cross-reference to FAA AD 78-09-05 suggest interaction with international technical practice and supplier parts. The AD therefore anchors domestic compliance to both manufacturer guidance and internationally recognised inspection techniques without reproducing the external material in full.

The document is titled AD/CESSNA 336/11 Amendment 3 and includes a brief amendment history in its background notes. Two concrete amendment-related points are in the supplied text:

• Amendment number. The instrument is Amendment 3 to AD/CESSNA 336/11. The document includes the header "AD/CESSNA 336/11 Amdt 3" repeated in several places in the supplied text, indicating its status as the third amendment to the Airworthiness Directive.

• Relation to Amendment 2. The background states that "Amendment 2 was issued to clarify the eddy current test block specifications." That explains why the current amendment further addresses that technical element: Amendment 3's stated purpose is to "clearly define which serial numbered aircraft are affected by this AD." In other words, Amendment 2 dealt with test block specification clarity and Amendment 3 deals with applicability clarity by serial number.

The AD also records administrative metadata relevant to amendment timing:

• Date of signature. The AD is signed by David Villiers, Delegate of the Civil Aviation Safety Authority, and dated 8 August 2005. This shows the delegate’s approval date.

• Effective date. The amendment becomes effective on 29 September 2005. This provides the interval between signature and operational effect, during which affected parties could prepare for compliance.

The supplied text does not include the text of the earlier Amendments 1 and 2, other than the one-line background note about Amendment 2's subject matter. The AD does not include a redline or a history of textual changes between the earlier versions and Amendment 3. It does not reproduce the original AD text or earlier amendments. It also does not include any later amendments beyond Amendment 3.

Because the AD ties actions to Cessna SL ME78-2 Supplement No. 1 and states that earlier Amendment 2 clarified test block specifications, users should assume that the operative inspection protocol is the result of successive changes culminating in the current text. The AD itself, however, provides only the present requirement and the two-line background statement and therefore any detailed tracking of what changed between the original AD, Amendment 1, Amendment 2, and Amendment 3 would require inspection of the prior amendment texts which are not included in the supplied document.

Finally, the AD notes that the Robertson-conversion exception "is subject to change should fatigue substantiating data on the Robertson conversion be supplied to the Authority." That language creates an open-ended amendment mechanism tied to the production of technical data rather than a defined amendment timetable; it indicates that further amendment is possible if evidence is supplied, but does not prescribe a process or timeframe for any subsequent amendment.

The supplied AD/CESSNA 336/11 Amendment 3 text contains no litigation history, judicial decisions, or references to administrative appeals. The document is a technical regulatory instrument and its text is limited to applicability, inspection requirements, calibration specifics, notes and a short background statement. There are no cases cited in the AD, no record of disputes or challenges in the text, nor any indication of enforcement actions or appeals recorded within the instrument.

Given the absence of litigation material in the AD itself, an analyst cannot infer from this document whether the AD has been the subject of judicial review, administrative challenge, or compliance disputes. To identify litigation that may have arisen from this AD would require searching external sources , court or tribunal records, CASA enforcement logs, or industry reports , none of which are part of this instrument. The AD does reference FAA AD 78-09-05, but it does not characterise or reproduce any associated litigation or administrative history related to the FAA directive.

For practitioners needing to know if the AD has been the subject of legal challenge, the AD itself provides no record. The absence of litigation references in the AD means the document does not supply precedent, case law, or contested interpretations that would inform legal positions about the AD’s validity, scope or enforceability. Any such litigation history must be obtained from other sources, including CASA records, public court databases, or regulatory publications. The AD’s silence on litigation does not indicate whether disputes have occurred, only that the AD text does not include that material.

The AD contains several technical and procedural details that can trip up operators, maintainers, and compliance officers if they are not read carefully. The most consequential "gotchas" in the instrument are:

• Applicability limited by serial numbers. The AD applies only to Cessna 336 aeroplanes with serial numbers 336-0001 through 336-0195. Operators who rely on model identification alone may incorrectly assume applicability; compliance must be determined by serial number. That scope limitation matters for owners, lessors and lessees during airworthiness checks and sale/purchase transactions.

• Calibration requirement is exacting. The eddy current test sensitivity requirement for the front spar is specific and technical: equipment must be set to produce a 10 per cent full scale meter deflection from a slot with tightly specified dimensions (.030" + .003" deep, .060" + .003" long and .010" maximum width) machined in the wall of a 3/16" diameter hole in an aluminium alloy test block. Failure to set sensitivity to that calibration may produce false negatives or positives. The AD prescribes a precise measurable target rather than a qualitative check.

• Test block example vs exclusive mandate. The AD identifies Nortec Part No. TB-12 as a "suitable test block." This is phrased as an example of a suitable test block, not as the sole permitted artefact. However, organisations that do not use TB-12 must ensure their test block yields the same calibration result; otherwise the eddy current sensitivity requirement will not be met. Do not assume TB-12 is mandatory where the text calls it "suitable."

• Bolt-hole scoring risk. The AD warns that scoring of bolt holes can cause spurious eddy current indications and may itself cause future fatigue crack initiations. That warning creates two risks: (a) false-positive eddy current readings if bolt holes are scored, potentially triggering unnecessary part removals or repairs; and (b) actual structural damage caused during maintenance if bolts are removed carelessly. Maintenance processes must explicitly address bolt removal technique, tooling, and inspection of hole condition both before and after bolt removal.

• Timing dependency on external document. The AD ties inspection times to the Cessna SL ME78-2 Supplement No. 1 "Action Required" section. The AD itself does not include the intervals. Operators need to obtain that supplement to know thresholds and intervals; any failure to obtain the supplement will leave an operator unable to determine when inspections are due.

• Robertson-conversion scheduling change is conditional. For aeroplanes with the Robertson STC 1627 WE conversion, the AD specifies a reduction of 1,000 hours in threshold and 100 hours in interval. This is unconditional in the AD text but the AD adds that the exception is "subject to change should fatigue substantiating data on the Robertson conversion be supplied to the Authority." That leaves open the possibility of retroactive changes if new data emerge; operators should track any subsequent communications from the Authority.

• Cross-reference to FAA AD without content. The AD notes that FAA AD 78-09-05 "also refers," but it does not reproduce that AD. Relying on the FAA AD for full compliance without ensuring alignment with this CASA AD may result in incomplete compliance; the CASA AD controls for Australian registered aeroplanes to the extent of its text.

• No enforcement or AMOC language in AD text. The supplied instrument does not state penalties, enforcement processes, or a process to obtain an alternative method of compliance. Maintenance organisations should not assume that informal departures or undocumented calibrations are acceptable. Where operators seek an alternative method or relief, they must consult CASA practices and other regulatory materials outside the AD to understand the process.

• Effective date lag. The AD is signed on 8 August 2005 and becomes effective 29 September 2005. That period must be considered when looking at records and the date from which compliance obligations are examined; work done before the effective date may be insufficient if it did not meet the AD’s calibration and procedural standards.

Each of these points is drawn from the AD text. Failure to attend to the AD’s calibration prescription, reliance on incomplete documentation, or sloppy bolt removal techniques are concrete operational risks with diagnostic and structural consequences.

To achieve compliance with AD/CESSNA 336/11 Amdt 3, follow a concise, source-grounded checklist based on the AD text. The AD itself ties to Cessna SL ME78-2 Supplement No. 1 for procedural detail and timing; the checklist below identifies the mandatory items stated in the AD plus immediate practical steps to align work with the AD.

1. Confirm applicability by serial number.

   • Verify the aircraft serial number. The AD applies to models 336 with serial numbers 336-0001 through 336-0195. If the serial number falls outside this range, the AD does not apply to that airframe as drafted.

2. Obtain and review Cessna SL ME78-2 Supplement No. 1.

   • The AD requires inspections "in accordance with Cessna SL ME78-2 Supplement No. 1" and ties inspection timing to the supplement's "Action Required" section. Secure the latest revision of that supplement and identify the rear spar inspection times and action steps specified there. The AD does not reproduce those intervals.

3. Plan inspections for both front and rear spars.

   • The AD requires inspection of both spars "in accordance with the times specified for the rear spar" in the supplement. Schedule inspections accordingly. For aircraft with Robertson STC 1627 WE, adjust the schedule by reducing the inspection threshold by 1,000 hours and the inspection intervals by 100 hours as required by the AD.

4. Prepare eddy current inspection equipment and calibration block.

   • For the front spar inspection, set eddy current test sensitivity so that a 10 per cent full scale meter deflection is achieved from a slot with the following dimensions: .030" + .003" deep, .060" + .003" long, and .010" maximum width, machined in the wall of a 3/16" diameter hole in an aluminium alloy test block. Nortec Part No. TB-12 is identified as a suitable test block; if using a different block, ensure it produces the same calibration result.

5. Train and brief personnel on bolt removal technique.

   • The AD warns that scoring of bolt holes can cause spurious eddy current indications and may initiate fatigue cracking. Ensure maintenance staff use appropriate tools, techniques and protective measures when removing bolts in the inspection area to avoid scoring. Document the procedure and post-removal inspection of hole condition.

6. Execute inspections and document results.

   • Perform the eddy current inspections per the Cessna supplement and the AD’s calibration requirement. Record calibration settings, the test block used (including part number if applicable), serial numbers, dates, inspection hours, and any findings. Maintain traceable records in the aircraft maintenance log as appropriate for airworthiness documentation.

7. Take corrective action for any findings in accordance with the Cessna supplement.

   • If cracking or suspect indications are found, follow the "Action Required" guidance in Cessna SL ME78-2 Supplement No. 1 for repair or further inspection. The AD itself does not list remedial steps, so the supplement is the operative source for corrective action.

8. Apply Robertson-conversion schedule adjustment where relevant.

   • For aeroplanes incorporating Robertson Aircraft Corporation Modification to US STC 1627 WE, apply a reduction of 1,000 hours to the inspection threshold and 100 hours to inspection intervals. Record that the aeroplane is so modified and the adjusted inspection schedule.

9. Monitor for Authority changes.

   • The AD states that the exception for Robertson conversions is "subject to change should fatigue substantiating data on the Robertson conversion be supplied to the Authority." Keep an internal compliance watch for further ADs, amendments, or communications from CASA that might alter the schedule.

10. Cross-check FAA AD 78-09-05 where helpful.

• Although the AD notes that FAA AD 78-09-05 "also refers," it does not impose the FAA AD. Consult the FAA AD for technical context if necessary, but ensure compliance strictly with the CASA AD and the Cessna supplement for Australian-registered aircraft within the serial-number scope.

11. Retain evidence for airworthiness review and audits.

• Although the AD text does not specify enforcement or penalty procedures, maintain complete records of inspections, calibrations (including the specific test block and the calibration reading of 10 per cent full scale), and any corrective actions. These records will be necessary for demonstrating compliance to regulators, auditors, or potential buyers.

12. Consider procurement and calibration logistics.

• If you do not have a suitable test block (e.g. Nortec TB-12), plan procurement lead times. Validate any alternative test block by producing the required calibration response before conducting in-service inspections.

This compliance approach follows directly from the AD’s text: confirm serial-number applicability, perform both spars inspections per the Cessna supplement, meet the eddy current sensitivity calibration target using a specified test block or equivalent, take care during bolt removal to avoid scoring, and apply the Robertson STC scheduling adjustment where relevant. The AD’s effective date is 29 September 2005; inspections scheduled after that date should reflect the AD’s requirements.