AD/AT/23 Amdt 1 - Aft Fuselage Structure Upper Longeron and Upper Diagonal Tube

This AD is structured around a small set of operational concepts, each stated in the instrument text and referenced to Snow Engineering service instructions: applicability by model and serial number; mandatory inspections for cracking; repeat inspection intervals; and a terminating modification action. The main concepts and their mechanistic interplay are set out below.

Applicability: The AD limits its mandatory scope to specific model and serial-number cohorts. The instruments lists Model AT-401, AT-401B, AT-402, AT-402A and AT-402B aircraft, serial numbers 0716 through 1144; and Model AT-501, AT-502, AT-502A, AT-502B and AT-503A aircraft, serial numbers 0037 through 0658. The Requirement clauses then address subsets of these models differently. This is a point-of-application concept: compliance duties attach only to aircraft within those serial-number bounds.

Inspection target and technique: The structural locality is precisely described: "the upper longeron and upper diagonal tube on the left hand side of the fuselage frame, just forward of the vertical fin front spar attachment" for some models, and only "the upper longeron on the left hand side of the fuselage frame, just forward of the vertical fin front spar attachment" for others. The AD does not itself contain the technical inspection procedure; it delegates the inspection technique and detailed instructions to specific Snow Engineering Service Letters (SL Nos 218A, 195, 195B). Practically, the AD makes the referenced SLs mandatory descriptive material for how to carry out the inspections and how to perform the terminating modification, where applicable.

Inspection cadence and terminating modification: The Compliance clauses prescribe initial inspection triggers in total hours time in service and then require inspections at intervals "not to exceed 100 hours time in service" until the terminating modification/replacement is completed in accordance with the identified SL. The AD expressly links the end of the repetitive inspection obligation to completion of the SL-specified replacement or modification (SL No. 218B and SL No. 195A revised are named as terminating action documents). The AD thus establishes a two-stage compliance pathway: short-term recurring inspections to detect cracks and a medium-term structural modification/replacement that terminates the inspection cycle.

Delegation and legal basis: The AD is issued by a CASA delegate under subregulation 39.1(1) of CASR 1998. The instrument revokes the previous AD/AT/23 and issues Amdt 1. It becomes effective on a specified date and is notified in the Gazette, which is the formal administrative mechanism for bringing it into legal effect and informing operators.

Rationale link: The Background supplies the safety rationale: FAA reports of three occurrences of cracks on Model AT-602 aircraft, causing loss of torsional rigidity and excessive empennage movement. Amendment 1 is tied to a new FAA AD that expanded applicability, altered compliance times, and incorporated new/revised service information with a terminating action. The AD records this as the operational justification for imposing inspections and modifications on the listed models.

Interdependence of documents: The AD does not stand alone; full compliance requires following the referenced Snow Engineering SLs. The AD specifies which SL number and date apply to which models, and where a later SL provides a terminating action. That makes the AD document a control instrument that refers to separate technical documents as normative material.

Primary regulated entities: The AD directly affects owners and operators of the specific Airtractor aircraft identified in the Applicability clause. The AD enumerates Model AT-401, AT-401B, AT-402, AT-402A, AT-402B (serials 0716-1144) and Model AT-501, AT-502, AT-502A, AT-502B, AT-503A (serials 0037-0658). The instrument text requires the prescribed actions "in relation to the aircraft or aeronautical product mentioned in the applicability section" and therefore creates obligations tied to aircraft with those serial numbers.

Entity that issues and enforces: The AD is issued by a CASA delegate under subregulation 39.1(1) of CASR 1998. The delegate whose signature appears is David Villiers and the AD is effective from 30 September 2004, with notification in the Commonwealth Gazette on 8 September 2004. The delegate decides the content of the AD and the operative timing; compliance is required as the AD instructs.

Maintenance and technical service providers: While not explicitly named in the AD, the practical performance of the required inspections and of the replacement/modification actions will involve maintenance personnel, licensed engineers and possibly the manufacturer or authorised service centres to perform the work in accordance with the Snow Engineering Service Letters. The AD itself delegates the technical instruction set to those SLs, which will determine the scope of work for technicians.

Passengers and third parties: The AD is safety-directed. Its immediate effect on passengers is indirect: it aims to prevent structural failure that could affect flight safety. The AD does not create direct customer-facing obligations for passengers, insurers, financiers or lessors, but these stakeholders may be affected indirectly through aircraft downtime, maintenance costs or airworthiness records.

Regulatory intermediaries: Organisations responsible for continuing airworthiness (for example operators with airworthiness management responsibilities) must ensure the AD's requirements are implemented. The text requires that "the action set out in the requirement section ... be taken ... in the circumstances mentioned in the requirement section; and ... in accordance with the instructions set out in the requirement section; and ... at the time mentioned in the compliance section." That language places procedural obligations on the person or entity charged with maintaining the aircraft's airworthiness.

Serial-number exclusions and fleet segmentation: The AD’s applicability is limited to particular serial-number ranges. Aircraft of the same model outside those serial-number ranges are not captured by this AD. This segmentation distributes cost and obligation across a subset of fleet owners rather than across all owners of a given model.

International regulatory link: The AD explicitly notes FAA activity, and refers to FAA AD 2004-15-15. Amendment 1 is described as being issued "in response to a new FAA AD," which indicates cross-jurisdictional regulatory coordination that affects operators who may operate internationally or who source maintenance data from the US-based manufacturer or Service Letters.

Duties prescribed by the AD

• Identify applicability: Operators must determine whether an aircraft is within the serial-number ranges listed under the Applicability clause. The AD applies only to the models and serials listed; compliance duties attach to those aircraft.

• Conduct inspections as required: For each model group the AD prescribes an inspection scope and references a precise Snow Engineering Service Letter for the inspection procedure:

  • For Models AT-401 and AT-401B (serials 0716-1144): inspect the upper longeron and upper diagonal tube on the left-hand side of the fuselage frame, just forward of the vertical fin front spar attachment, for cracks in accordance with Snow Engineering Co. Service Letter No. 218A (dated 10 November 2003), as specified in SL No. 195, re-issued 10 November 2003 (Requirement 1).
  • For Models AT-402, AT-402A, and AT-402B (serials 0716-1144): same inspection requirement and SL references as Requirement 2.
  • For Models AT-501, AT-502, AT-502B, and AT-503A (serials 0037-0658): inspect the upper longeron on the left-hand side for cracks in accordance with SL No. 195B (dated 10 November 2003), as specified in SL No. 195 (Requirement 3).
  • For Models AT-502A (serials 0037-0658): inspect the upper longeron as per SL No. 195B, as specified in SL No. 195 (Requirement 4).

• Meet inspection timing: The Compliance section sets model-specific initial inspection triggers and a repeat inspection interval not to exceed 100 hours time in service:

  • Requirements 1 and 2 (AT-401 and AT-402 groups): initial inspection upon accumulation of 1,250 total hours TIS or within the next 100 hours TIS after 30 September 2004, whichever occurs later (Requirement 1 Compliance; Requirement 2 Compliance notes initial inspection timing in relation to prior inspections). Inspections thereafter at intervals not to exceed 100 hours TIS until replacement/modification per SL No. 218B.
  • Requirements 3 (AT-501/502/502B/503A): initial inspection at 4,800 total hours TIS or within the next 100 hours TIS after 30 September 2004, whichever occurs later. Repeat inspections at intervals not to exceed 100 hours TIS until the upper longeron is replaced and modified per SL No. 195A revised.
  • Requirement 4 (AT-502A): initial inspect at 2,800 total hours TIS or within the next 100 hours TIS after 30 September 2004, and then every 100 hours until modification per SL No. 195A revised.

• Implement terminating modification if chosen: The AD links the repetitive inspection obligation to completion of the SL-prescribed replacement/modification (SL No. 218B for the AT-401/402 group; SL No. 195A revised for the AT-500 group). Completion of the specified replacement and modification is the terminating action for the repetitive inspection requirement.

Rights and limits implicit in the AD text

• No independent discretion to ignore: The AD revokes the prior AD and imposes mandatory actions. The AD’s language requires that the actions be taken "in accordance with the instructions set out in the requirement section" and "at the time mentioned in the compliance section." That phrasing leaves little room to depart from the specified SL procedures or timing without regulatory approval.

• Right to use SLs as normative guidance: The AD gives the referenced Snow Engineering Service Letters normative status for the inspection and terminating modification work. Operators must follow the referenced SLs to meet the AD’s requirements.

• Right to terminating action: The AD provides a clear path to terminate the repetitive inspections by performing the SL-specified replacement and modification. The AD gives operators a choice in compliance pathway timing: continue with 100-hour interval inspections indefinitely until the terminating modification is completed, at which point the repetitive inspection obligation ceases.

• Regulatory appeal or variation not described: The AD itself does not set out an internal process for seeking relief, deferral or an alternative method of compliance (AMOC). Those procedural mechanisms, if any, would be located in the broader regulatory framework under CASR 1998 or CASA administrative processes. The AD text does not include AMOC provisions.

Decision and responsibility chains

• The CASA delegate determined the AD and effective date. The primary operational responsibility to effect the inspections and modifications rests with the person or organisation that manages the aircraft's continuing airworthiness, which in practice is the aircraft owner or operator. The AD’s binding effect is on the aircraft identified in the Applicability clause; the AD instructs that the actions be taken "in relation to the aircraft ... in the circumstances ... and in accordance with the instructions ... at the time mentioned." This places a duty on the responsible airworthiness entity to ensure compliance, procure or perform the SL work, and schedule aircraft availability for inspections and the terminating modification.

Statutory basis and notification

• The AD is issued under subregulation 39.1(1) of CASR 1998 and was signed by the CASA delegate on 20 August 2004. It becomes effective on 30 September 2004 and was notified in the Commonwealth of Australia Gazette on 8 September 2004. The AD therefore has formal regulatory effect under the Civil Aviation Safety Regime.

Content of the AD regarding enforcement and penalties

• The AD text does not itself specify penalty amounts, enforcement procedures or sanctions for non-compliance. It requires the actions set out in the requirement section to be taken "in the circumstances mentioned in the requirement section; and in accordance with the instructions set out in the requirement section; and at the time mentioned in the compliance section." That mandatory formulation imposes a legal obligation on affected aircraft to comply, but particulars of enforcement, inspection by regulators, issuance of notices, suspension of operations or monetary penalties are not detailed in the AD text provided.

Practical enforcement implications derived from structure

• The AD creates an affirmative, time-bound duty to inspect and, where required, to undertake a structural replacement/modification per the referenced Snow Engineering SLs. Because the AD is issued under CASR 1998, failure to carry out the AD’s requirements may expose the operator or owner to regulatory enforcement under CASR-based enforcement mechanisms. The AD itself records the regulatory instrument and effective date, which is necessary for enforcement action by CASA or its delegate.

• The AD’s requirement to carry out inspections "until the upper and diagonal longerons are replaced and modified in accordance with SL No. 218B" or "until the upper longeron is replaced and modified in accordance with SL No. 195A, revised" creates a clear compliance end-point: an operator who has not completed the terminating modification remains subject to the repetitive inspection duty and could be assessed non-compliant if inspections are not performed at the prescribed intervals.

What the AD does not detail

• The AD does not provide information on authorised repair stations, required qualifications of persons performing the inspection or modification, documentation or record-keeping protocols, timelines for enforcement action following non-compliance, or any appeal or AMOC procedures. Those details are likely handled under CASR 1998, CASA operational guidance, or in the technical content of the Snow Engineering Service Letters to which the AD refers.

• The AD does not identify civil or criminal penalties in its text. To understand concrete enforcement and penalty exposure for non-compliance, an operator must consult CASR 1998 and CASA enforcement policy and practice, which are not reproduced in the AD text.

Primary regulatory context

• The AD is issued under subregulation 39.1(1) of CASR 1998. The AD itself references that statutory basis in its opening paragraph, stating that the CASA delegate "revokes Airworthiness Directive (AD) AD/AT/23 and issues the following AD under subregulation 39.1 (1) of CASR 1998." That locates the AD within the Civil Aviation Safety Regulations framework, which governs continuing airworthiness obligations and the issuance of airworthiness directives. The AD must be understood as a subordinate instrument operating within that regulatory architecture.

Interaction with manufacturer technical material

• The AD makes several Snow Engineering Company Service Letters normative for compliance: SL No. 218A (10 Nov 2003), SL No. 195 (re-issued 10 Nov 2003), SL No. 195B (10 Nov 2003), SL No. 218B (10 Nov 2003) and SL No. 195A (revised 10 Nov 2003). These SLs are incorporated by reference in the Requirement section, meaning the technical and procedural instructions in those documents become mandatory for the purpose of compliance with the AD. The AD therefore creates a legal force that imports manufacturer technical instructions into regulatory obligation.

Cross-jurisdictional regulatory linkage

• The AD explicitly references FAA activity. The Note states "FAA AD 2004-15-15 Amdt 39-13749 refers" and the Background says the AD "is issued in response to a new FAA AD, which adds certain AT-500 series aircraft to applicability, changes the compliance times, and incorporates new and revised manufacturer service information that contains a terminating action for the repetitive inspection requirement." This shows regulatory alignment with a foreign authority; operators that operate across jurisdictions must account for both CASA and FAA directives. Where both CASA and FAA ADs apply, the operator must comply with the applicable jurisdictional requirements.

Revocation and amendment interactions

• The AD revokes the prior AD/AT/23 and issues Amdt 1. The revocation indicates that earlier requirements contained in the original AD/AT/23 are replaced by the requirements of this Amendment. The AD text does not reproduce the original AD language; operators must ensure they are complying with the current AD/AT/23 Amdt 1 rather than prior iterations. The Compliance section refers to some inspections "after the last inspection required by the original issue of this Directive," revealing that the AD interacts with earlier inspection cycles established under the initial AD.

Technical standards and continuing airworthiness obligations

• By importing the Snow Engineering SLs as prescriptive guidance, the AD interacts with the operator’s continuing airworthiness obligations, typically enforced under CASR and through airworthiness management systems. The AD sets a specific defect mitigation path that becomes part of an aircraft’s continuing airworthiness requirements until a terminating modification is completed.

Limitations in the AD text on legal interactions

• The AD does not address insurance, finance, contractual rights between lessors and lessees, or how compliance affects certificate validity. It does not specify whether completion of the SL-specified modification requires CASA acceptance or certification beyond the AD’s language. Those interactions depend on adjacent regulatory provisions in CASR, maintenance and release-to-service practices, and contractual arrangements, none of which are specified in the AD document itself.

Documented change process in the AD text

• The AD is presented as "AD/AT/23 Amdt 1," which by its title indicates it is the first amendment to AD/AT/23. The opening text makes the procedural steps explicit: the CASA delegate "revokes Airworthiness Directive (AD) AD/AT/23 and issues the following AD under subregulation 39.1 (1) of CASR 1998." That statement both revokes the prior instrument and replaces it with the amended AD.

Dates and sequence

• Key dates documented in the AD:
  • Service Letter dates: Snow Engineering Co. Service Letter No. 218A and SL No. 218B dated 10 November 2003, SL No. 195 (re-issued) and SL No. 195A (revised) dated 10 November 2003, and SL No. 195B dated 10 November 2003. These SL dates fix the technical material the AD incorporates.
  • Delegate signature: David Villiers, Delegate of the Civil Aviation Safety Authority, dated 20 August 2004.
  • AD effective date: "This Amendment becomes effective on 30 September 2004."
  • Gazette notification: The AD is notified in the Commonwealth of Australia Gazette on 8 September 2004, which is the formal public notification step recorded in the AD.

Nature of amendment and stated reasons

• The Background explains what Amendment 1 changes relative to the earlier AD: it responds to a new FAA AD that (1) adds certain AT-500 series aircraft to the applicability, (2) changes the compliance times, and (3) incorporates new and revised manufacturer service information that contains a terminating action for the repetitive inspection requirement. The AD text thus records that the amendment adjusts scope, timing and provides a terminating modification route.

Evidence base for amendment

• The Background links the substantive reason for the AD to FAA reports of three occurrences of cracks on Model AT-602 aircraft, where the cracks were found in the left hand upper longeron and upper diagonal support tubes at their intersection just forward of the vertical fin front spar attachment point. The Background further describes the operational symptom that led to the discovery: pilots and/or ground crew noticed excessive movement of the empennage due to loss of torsional rigidity. Those FAA incident reports form the operational evidence base for extending inspection and modification requirements.

Termination of previous inspection cycles

• The Compliance section references the inspections required "until the upper and diagonal longerons are replaced and modified in accordance with SL No. 218B" or "until the upper longeron is replaced and modified in accordance with SL No. 195A, revised." Those SLs are identified in the amendment as containing the terminating actions for the repetitive inspections. The AD therefore converts previously open-ended inspection requirements into a schedule that terminates upon completion of the manufacturer's modification instructions.

Record of revocation

• The AD’s opening sentence expressly revokes AD/AT/23 and issues the amended AD. The AD does not reproduce the full text of the revoked AD, but operators are informed by the revocation and replacement wording that earlier obligations are superseded by the amended requirements.

Document content on litigation

• The AD text does not refer to any litigation, court decisions, administrative appeals, or formal challenges to the AD, its predecessor, or the underlying FAA actions. No cases, appeals or enforcement actions are recorded in the AD text provided.

Implication for practitioners

• Because the AD does not contain litigation history, anyone seeking case law interpreting the AD, seeking judicial review of the AD as a regulatory exercise, or challenging enforcement would need to consult external records and case reports beyond this AD text. The AD itself contains the administrative record relevant to the amendment (background incident reports, cross-reference to FAA AD, Snow Engineering SLs, delegate signature, effective date and Gazette notification), but no litigation is documented.

What is available in the AD for legal evidentiary use

• The AD records the factual basis relied on by the issuing authority for the safety action: FAA reports of cracked longeron/diagonal tube intersections on Model AT-602 and the empirical sign of reduced torsional rigidity and empennage movement. It also records the regulatory connection to the FAA AD and the specific manufacturer SLs that provide the technical mitigation. These items would form part of the administrative record in the event of judicial review or compliance litigation, but the AD text itself does not report outcomes of litigation or dispute.

Precise applicability boundaries

• The AD applies only to specified serial-number ranges. Failure to check the exact serial number may produce erroneous conclusions about applicability. The AD lists two distinct serial-number ranges: 0716 through 1144 for some AT-300/400 variants, and 0037 through 0658 for AT-500 variants. Operators who hold aircraft of the same model but outside those serial ranges are not captured by this AD and must take care not to conflate model identity with applicability.

Left-hand side specificity

• The inspection target is explicitly on the left hand side of the fuselage frame "just forward of the vertical fin front spar attachment." The AD does not require inspection of the right side. Practically, this requires maintainers to inspect the specified left-hand locality; an inspection checklist that generically checks "longerons" without side-specific instruction could miss compliance. The AD’s language is precise and side-specific.

Different inspection scopes across models

• Some models require inspection of both the upper longeron and the upper diagonal tube (AT-401 and AT-402 model groups), while other models require only the upper longeron (AT-501/502 families and AT-502A). Misreading the Requirements could lead to applying the wrong inspection scope to a given aircraft.

Varying initial inspection triggers

• The Compliance section sets different initial inspection triggers depending on model and, for one group, depending on whether the aircraft has already undergone prior inspections required by the original AD. For example, AT-401/401B and some AT-402 variants have an initial trigger at 1,250 total hours TIS or within 100 hours TIS after 30 September 2004, whichever later; some AT-500 series have initial thresholds of 4,800 or 2,800 total hours TIS. Those different numbers must be applied correctly to avoid premature or late inspections.

Repetitive inspections until terminating action

• The AD requires inspections "at intervals not to exceed 100 hours time in service, until the upper and diagonal longerons are replaced and modified in accordance with SL No. 218B" (and analogous language for other models). If a maintainer fails to effect the terminating modification, the repetitive inspection duty remains. There is no automatic cessation of inspections unless the SL-prescribed replacement/modification is completed.

Dependence on external Service Letters

• The AD does not contain the technical inspection procedure or the modification instructions. It requires compliance "in accordance with" the identified Snow Engineering SLs. Operators must obtain and follow those SLs to comply. If the SLs are not available, or if there are multiple revisions, operators must ensure they are following the exact SL version and date referenced in the AD. The AD references SL No. 195 re-issued 10 November 2003, SL No. 218A dated 10 November 2003, SL No. 195B dated 10 November 2003, SL No. 218B dated 10 November 2003 and SL No. 195A revised 10 November 2003. Using a different revision than the one referenced could invite regulatory scrutiny.

Relationship to FAA AD

• The Background refers to FAA reports on Model AT-602 cracks and says Amendment 1 is issued "in response to a new FAA AD." The AD also includes a Note indicating "FAA AD 2004-15-15 Amdt 39-13749 refers." Operators should be careful to read both CASA AD/AT/23 Amdt 1 and the FAA AD it references to understand any harmonised or diverging technical or compliance issues.

No stated administrative relief mechanism in the AD text

• The AD itself does not provide an alternative method of compliance (AMOC) process or a process for seeking deferral or variation. If an operator believes an alternative maintenance method or different timing is appropriate, the AD text does not set out how to obtain approval; operators must look to CASR 1998 and CASA processes for AMOC or exemptions.

Record-keeping and certification not described

• The AD does not explicitly state how compliance should be recorded in maintenance logs or whether publication of the completed SL modification requires CASA sign-off. Operators must ensure their usual continuing airworthiness records reflect compliance, but the AD itself does not provide procedural detail on records or releases to service.

Step-by-step mechanistic compliance path derived from the AD

1. Confirm applicability

   • Identify each aircraft by model and serial number. The AD applies to:
     • Model AT-401, AT-401B, AT-402, AT-402A, AT-402B: serial numbers 0716-1144.
     • Model AT-501, AT-502, AT-502A, AT-502B, AT-503A: serial numbers 0037-0658.
   • If the aircraft serial number falls within these ranges, the AD’s requirements apply.

2. Obtain the referenced technical documents

   • Obtain the Snow Engineering Co. Service Letters referenced in the AD for the relevant model:
     • SL No. 218A dated 10 November 2003 for AT-401/401B and AT-402 group inspections (as specified in SL No. 195, re-issued 10 November 2003).
     • SL No. 195B dated 10 November 2003 for AT-501/502/502B/503A and AT-502A inspections (as specified in SL No. 195, re-issued 10 November 2003).
     • SL No. 218B dated 10 November 2003 and SL No. 195A revised 10 November 2003 for terminating replacements and modifications.
   • Treat those SLs as the operative technical procedures for inspection and modification, because the AD explicitly makes them the inspection/modification instructions "in accordance with" which work must be done.

3. Schedule and perform the initial inspection per the Compliance timings

   • For AT-401/401B and AT-402 series (Requirements 1 and 2): initially inspect upon accumulation of 1,250 total hours TIS or within the next 100 hours TIS after 30 September 2004, whichever is later; for some AT-402 series aircraft the initial inspection timing references the last inspection required by the original issue of the Directive, so check prior inspection history.
   • For AT-502A aircraft (Requirement 4): initially inspect upon accumulation of 2,800 total hours TIS or within the next 100 hours TIS after 30 September 2004, whichever occurs later.
   • For AT-501/502/502B/503A (Requirement 3): initially inspect upon accumulation of 4,800 total hours TIS or within the next 100 hours TIS after 30 September 2004, whichever occurs later.
   • Perform the inspection exactly as set out in the applicable SL, inspecting the left hand upper longeron and, where the model requires it, the upper diagonal tube at the intersection just forward of the vertical fin front spar attachment for cracks.

4. Maintain the mandated repeat inspection cadence

   • After the initial inspection, perform inspections thereafter at intervals not to exceed 100 hours TIS until the terminating modification is completed in accordance with the applicable SL (SL No. 218B for AT-401/402 groups; SL No. 195A revised for AT-500 groups). The AD is explicit: inspections are required "until" the SL-specified replacement/modification is completed.

5. Implement the SL-specified terminating modification where chosen

   • If the operator elects to perform the replacement/modification described in SL No. 218B or SL No. 195A revised, completion of that work is the terminating action for the repetitive inspection requirement. Make sure the modification is performed in exact accordance with the SL referenced in the AD so that the repetitive inspection obligation is validly terminated.

6. Coordinate with authorised maintenance personnel

   • Ensure that the persons performing the inspection and any modification have the necessary technical capability and authority to perform the work in accordance with the applicable SLs and prevailing maintenance regulations. While the AD does not specify which licence or authorisation is required, the technical nature of the work requires appropriately qualified maintenance staff.

7. Keep contemporaneous maintenance records and evidence of compliance

   • While the AD does not set out a record-keeping format, best practice is to record inspection dates, TIS at inspection, findings, corrective actions, and details of any terminating modification in the aircraft maintenance records and to retain copies of the Snow Engineering SLs used. Those records will be necessary to demonstrate compliance to CASA or other authorised inspectors.

8. Monitor for further regulatory updates

   • The AD replaced a prior AD and was itself an amendment responding to FAA action and revised SLs. Operators should monitor CASA and manufacturer publications for further ADs, revisions of the SLs, or clarifications that may affect procedures, timings or terminating actions.

Practical notes tied to AD text

• Strictly follow SL versions and dates: The AD ties compliance to specific Service Letter numbers and dates. Use the exact SL version referenced in the AD text, unless and until the AD is revised to reference a different technical document.

• Apply side-specific inspection: The AD requires inspection of the left hand side location "just forward of the vertical fin front spar attachment." Do not generalise the location.

• Read the Background for operational context: The AD’s Background indicates the cracks were discovered because of excessive empennage movement and loss of torsional rigidity, which helps maintenance teams appreciate the defect mode they are inspecting for.

• Link inspection results to follow-up: The AD requires inspections for cracks. If cracks are detected, the Snow Engineering SLs will specify actions; those SLs become the operative technical instructions for repairs or replacements. Follow the SL’s guidance exactly as required by the AD.

• Interaction with other jurisdictions: If an aircraft is operated internationally or is on a foreign registry, consult the relevant national authority’s directives (for example the FAA AD referenced) for any additional or differing requirements. The AD explicitly cross-references FAA AD 2004-15-15.

• Effective date and compliance windows: The AD was effective 30 September 2004 and sets various "or within the next 100 hours time in service after 30 September 2004, whichever occurs later" triggers. If an operator did not meet the initial inspection window, they should treat the AD as immediately applicable and schedule the required inspection at the earliest practicable TIS consistent with the AD’s language.

• If an operator seeks a different compliance method, consult CASA procedures: The AD does not provide an alternative method of compliance pathway within its text; any alternate approach requires consultation with CASA under CASR provisions or other CASA processes.