AD/AS 355/98 Amdt 1 - Stabiliser Upper and Lower Fin Attachment Fitting - Modification

The Directive rests on four interlocking technical and regulatory concepts: targeted hardware modification (MOD 073330), interim repetitive inspections and torque checks tied to earlier modification status (MOD 073288), corrective actions triggered by a quantitative threshold (80% of minimum torque value), and restriction on spare parts usage. Each is specified by reference to Eurocopter Alert Service Bulletins which provide the procedural detail.

1. Hardware modification as terminating action: Requirement 3 mandates physical modification of the upper and lower fittings on the tail boom for helicopters with fins pre-MOD 073330. The modification consists of increasing the bolt-hole diameter and replacing original bolts and washers (22126BV060032L and 23112AG060LE) with special bolts 350A23-4016-20 and special washers 350A23-4017-22, according to EUROCOPTER ASB No. 55.00.12 Revision 1. The Directive states that compliance with Requirement 3 is "considered as acceptable compliance" with certain earlier replacement/inspection requirements (Requirements 1.a and 1.b) and is a "terminating action" for the specified repetitive checks (Requirements 1.c, 2.a and 2.b). Mechanistically, increasing bolt-hole diameter plus using different bolts/washers indicates a design or fitment change intended to change load distribution or clearance to arrest cracking mechanisms.

2. Interim repairs, screw replacement and torque checks: For helicopters with upper and lower fins pre-MOD 073288 the Directive prescribes replacement of upper and lower fin attachment screws within specified flight-hour windows (Requirement 1.a and 1.b). Where replacement is not the chosen course, the Directive sets an on-going inspection regime,check torque and reinforcement splice for cracks and loose rivets at intervals "not to exceed 110 flight hours" in accordance with paragraph 2.B.3 of ASB No. 55.00.11 Revision 2 (Requirements 1.c and 2.c). This creates a recurring maintenance obligation focused on detection and correction rather than an immediate redesign.

3. Quantitative threshold for immediate corrective action: The Directive specifies a numeric trigger: if tightening torque of one or both attachment screws is less than 80% of the minimum torque value, operators must apply corrective actions prescribed in ASB No. 55.00.11 Revision 2 before further flight (Requirements 1.d and 2.c). The presence of a defined threshold provides a clear, measurable criterion for groundings and repairs.

4. Parts control and spares management: Requirement 4 forbids installation after 31 March 2009 of upper and lower fins with the listed part numbers unless MOD 073330 has been incorporated. This restricts the fitment of legacy spare parts and creates an inventory management obligation for operators and spares suppliers; the Directive labels these spares as unacceptable for installation unless modified.

Additional concepts in the instrument:

• Applicability is narrowly defined by model and the presence or absence of MOD 073330, and by the specific part numbers listed (Applicability).
• The Directive cross-references Eurocopter ASBs as the operative technical documents: ASB No. 55.00.11 Revision 2 (MOD 073288) for screw replacement and inspection instructions and ASB No. 55.00.12 Revision 1 (MOD 073330) for the modification procedure (Requirements 1-3).
• Timing dependencies: the actions required depend on elapsed flight hours in relation to 31 August 2006 and the timing of prior checks (Requirements 1-2). There are separate instructions for helicopters pre-MOD 073288 and post-MOD 073288 and for those pre-MOD 073330.

The official safety rationale is explicit in the Background: EASA reports of cracking in the stabiliser upper fin and risk that crack growth could lead to fin loss. The Directive therefore prescribes either interventions to arrest the cracking mechanism (MOD 073330) or repetitive surveillance and screw replacements to detect and correct deterioration (Requirements 1-3; Background). The Directive also records its relationship to EASA actions: EASA AD 2008-0120 supersedes earlier EASA ADs and Amendment 1 aligns CASA action with new EASA applicability and periodic checks (Background).

The Directive identifies direct and indirect stakeholders in the operational chain. Directly affected are operators and owners of Eurocopter AS 355 series helicopters (models AS 355 E, F, F1, F2 and N) that are fitted with the specified upper and lower fin assembly part numbers and that have not had MOD 073330 incorporated (Applicability). The precise part numbers listed for upper fin assemblies are 355A14-0522-00XX, -01XX, -02XX, -03XX, -13XX, -14XX and -15XX; lower fin assembly part numbers are 355A14-0521-00XX, -01XX, -02XX and -03XX. The applicability language,"fitted with the following upper and lower fins to which Modification (MOD) 073330 has not been incorporated",means the class of aircraft is those with legacy fittings still in original configuration.

Maintenance organisations, approved maintenance engineers and shops that perform the work mandated by Eurocopter ASBs are affected because the Directive requires specific tasks "in accordance with the instructions specified" in ASB No. 55.00.11 Revision 2 and ASB No. 55.00.12 Revision 1 (Requirements 1-3). Those bodies will need to schedule inspections, order specified replacement screws, special bolts and washers, and follow repair instructions when torque readings or inspections reveal defects.

Suppliers of spare fins and spare parts are affected by the post-31 March 2009 ban on installing certain spare fin part numbers unless MOD 073330 has been incorporated. Operators holding such spare parts will need to decide whether to modify the spares to incorporate MOD 073330 or to write them off for service use (Requirement 4).

Regulatory and certification entities are implicated in the sense that the Directive is cross-referenced to EASA ADs; the Background notes that EASA AD 2008-0120 supersedes earlier EASA ADs and that Amendment 1 was issued in response to a new EASA AD adding part numbers to applicability (Background). Eurocopter (the manufacturer) is implicated as the origin of the Alert Service Bulletins supplying the technical instructions; the Directive expressly relies on Eurocopter ASBs (Requirements 1-3).

Operators of helicopters that have already incorporated MOD 073330 are less affected because the Directive’s principal recurring obligations are aimed at helicopters without that modification; the Directive states that MOD 073330 is terminating action for certain requirements (Requirement 3). Where aircraft are post-MOD 073288, the timing and nature of required checks differ (Requirement 2), so maintenance status mod history determines the precise actions an operator must take.

Finally, there are temporal groups within the operator population:

• Aircraft that had accumulated less than 110 flight hours after 31 August 2006 (subject to a 110 flight-hour window to replace screws per Requirement 1.a).
• Aircraft that had accumulated more than 110 flight hours after 31 August 2006 (subject to a 15 flight-hour window after 26 February 2009 per Requirement 1.b).
• Aircraft that had accumulated less than or more than 110 flight hours since the latest check under paragraph 2.B.3 of ASB No. 55.00.11 Revision 0 (Requirements 2.a and 2.b).

These timing groupings affect scheduling and likely affect which operators must take immediate action versus those who follow the routine 110-hour inspections.

The Directive imposes specific duties with defined timing, and creates one explicitly stated procedural right: to use later EASA-approved revisions of the referenced ASBs. The duties are technical maintenance and modification obligations and a restriction on installing listed spare parts.

Primary duties

• Comply with the replacement, inspection, modification and parts-control requirements "as specified in Requirement 1, Requirement 2, Requirement 3 and Requirement 4" (Compliance). The Directive text repeatedly instructs that actions must be carried out "in accordance with the instructions specified" in the referenced Eurocopter ASBs (Requirements 1-3). The operative duty is therefore to follow the ASB work-sheets, steps and corrective actions cited.
• For helicopters with fins pre-MOD 073288:
  • If they had less than 110 flight hours after 31 August 2006, operators must, within 110 flight hours after 31 August 2006, replace the upper and lower fin attachment screws per paragraph 2.B.2 of ASB No. 55.00.11 Revision 2 (Requirement 1.a).
  • If they had more than 110 flight hours after 31 August 2006, operators must, within 15 flight hours after 26 February 2009, replace the screws per same ASB paragraph (Requirement 1.b).
  • Repetitive torque checks and reinforcement splice inspections at intervals not to exceed 110 flight hours (Requirement 1.c).
  • If cracks, loose rivets or torque less than 80% of minimum value are found, apply corrective actions in ASB No. 55.00.11 Revision 2 paragraphs 2.B.3.a.1-3 before further flight (Requirement 1.d).
• For helicopters with fins post-MOD 073288:
  • If they had less than 110 flight hours since the latest check performed in accordance with paragraph 2.B.3 of ASB No. 55.00.11 Revision 0, then within 110 flight hours after that check, perform the torque check and reinforcement splice inspection per paragraph 2.B.3 of ASB No. 55.00.11 Revision 2, repeating at intervals not to exceed 110 flight hours (Requirement 2.a).
  • If they had more than 110 flight hours since that latest check, perform the torque check and reinforcement splice inspection within 15 flight hours after 26 February 2009 and thereafter at intervals not to exceed 110 flight hours (Requirement 2.b).
  • Similar corrective-action triggers apply (Requirement 2.c).
• For helicopters with fins pre-MOD 073330:
  • Remove the fins, modify fittings by increasing bolt-hole diameter, replace bolts and washers with the specified special parts and do so no later than 31 March 2009, per EUROCOPTER ASB No. 55.00.12 Revision 1 (Requirement 3). Requirement 3 is explicitly a terminating action for certain repetitive checks and replacements (Requirement 3).
• Spare parts duty:
  • After 31 March 2009, upper and lower fins with the listed part numbers held as spares must not be installed unless MOD 073330 has been incorporated (Requirement 4).

Rights and options

• Use of later approved revisions: Where the Directive references ASB No. 55.00.11 Revision 2 or ASB No. 55.00.12 Revision 1, the text allows compliance "or later EASA approved revision" in several places (e.g., Requirement 1.a references "or later EASA approved revision"). This gives operators and maintainers the right to use subsequent EASA-approved revisions of the Eurocopter ASBs as the operative technical guidance.
• Termination option: Incorporation of MOD 073330 serves as a terminating action for repetitive inspections and as acceptable compliance with earlier screw-replacement requirements. That gives operators an option to adopt a one-off modification (with its own cost and downtime) to remove the ongoing inspection burden enacted by Requirements 1.c and 2.a/2.b. The Directive explicitly states that "Compliance with Requirement 3 of this Directive is considered as acceptable compliance with Requirements 1.a. and 1.b, and terminating action for the repetitive checks of Requirements 1.c, 2.a. and 2.b of this Directive" (Requirement 3).

Procedural obligations

• The Directive mandates specific timing windows keyed to flight hours and calendar dates (31 August 2006, 26 February 2009, 31 March 2009) and to whether an aircraft is pre- or post-MOD 073288 or 073330. Operators must audit aircraft modification status and flight-hour logs to determine which prescribed actions apply.
• The Directive ties permitted actions to the specified ASB paragraphs (2.B.2, 2.B.3 and 2.B.3.a.1-3). The Duty is therefore not only to perform an inspection or modification but to perform it in the exact manner, and to apply the corrective manuals referenced.

Record-keeping and documentation

• Although the Directive text does not lay out record-keeping format, the specified timings and "before further flight" corrective action mandate will generally require operators and maintenance organisations to document inspections, torque readings, repairs and MOD 073330 incorporation to demonstrate compliance with the Directive's requirements.

Who decides and when

• The Directive itself imposes what must be done and by when. Operators (owners) and their contracted maintenance organisations must decide how to schedule and resource the work. The Directive grants no discretion to bypass the technical steps except where the operator elects to incorporate MOD 073330 as terminating action; otherwise the inspection and corrective obligations are mandatory.

The Directive is framed as a mandatory safety instrument with specified compliance dates and actions. The text contains explicit language that the actions are "Required as indicated" and that "This Amendment becomes effective on 26 February 2009" (Compliance). The instrument is signed by the "Delegate of the Civil Aviation Safety Authority" and dated 18 February 2009, which records the issuing authority and effective date.

What is explicit in the source

• The Directive declares required actions and effective dates. It establishes precise deadlines for replacement, inspections and modifications (Requirements 1-4; Compliance). The text states that compliance must be carried out "in accordance with the instructions specified" in particular Eurocopter ASBs or later EASA-approved revisions (Requirements 1-3). It also sets out that MOD 073330 is terminating action for certain requirements (Requirement 3).
• The Directive does not include within the text any enumerated monetary penalties, enforcement mechanisms, or administrative review pathways. The source itself offers no fine amounts, license consequences, or criminal sanctions text.

What readers should infer from the source and typical regulatory practice

• The Directive’s use of imperative language, its signature by a CASA delegate and its cross-reference to EASA ADs all indicate that the instrument is regulatory and prescriptive in nature. The text leaves no voluntary option except the trade-off provided: either conduct repetitive inspections and possible screw replacements, or incorporate MOD 073330 as terminating action (Requirement 3). The Directive does not specify operational exemptions or waivers in the text provided.
• The Directive references Eurocopter ASBs as the technical means of compliance; adherence to the ASBs is the method the Directive prescribes. The instrument allows later EASA-approved revisions of those ASBs to be used (Requirements 1-3).

Information the Directive does not supply

• The Directive does not set out enforcement procedures, notice-and-comment processes, or appeal rights. It contains no schedule of monetary penalties or explicit statement of sanctions for non-compliance. The instrument does not describe inspection or audit processes that CASA might use to verify compliance, nor does it record any administrative or judicial challenge history.

Operational implications for enforcement

• Because the Directive prescribes actions with specific timing and technical procedures, operators will need contemporaneous documentation to demonstrate compliance with those requirements. The absence of explicit penalty text in the Directive means readers should consult the broader CASA regulatory framework, Civil Aviation Regulations or Civil Aviation Safety Authority enforcement policies to understand civil or administrative consequences of non-compliance. The Directive itself, however, is explicit about required actions, effective dates, and technical references.

Reference to external regulatory instruments

• The Background notes that the EASA AD (EASA AD 2008-0120) supersedes earlier EASA ADs and that Amendment 1 responds to new EASA AD content. The Directive thus sits within a broader regulatory architecture of EASA ADs and Eurocopter ASBs. Operators that must demonstrate compliance may be required to show alignment with both CASA ADs and the referenced EASA ADs and ASBs.

In short, the Directive imposes mandatory technical duties with fixed deadlines and tolerances but the text provided does not itself list enforcement mechanisms or penalties. Users needing to understand sanctioning processes must consult CASA’s enforcement instruments and the applicable aviation safety regulations outside this Directive.

The Directive expressly situates itself within the international and manufacturer service-information framework: it cross-references EASA ADs and Eurocopter Alert Service Bulletins, and it records that certain EASA ADs supersede earlier EASA ADs. The interaction is procedural and technical; the Directive imports EASA-approved technical instructions and embodies them within CASA’s national airworthiness requirements.

Explicit cross-references in the source

• The Directive's Background states that "The EASA AD related to this Directive, AD 2008-0120, supersedes EASA ADs 2006-0096 (AD/AS 355/84 Amdt 1) and 2006-0097R1 (AD/AS 355/91 Amdt 1), and thereby constitutes terminating action to the requirements of these CASA ADs" (Background). This records a direct chain of regulatory succession and the manner in which EASA actions have been used to justify CASA amendments.
• The Directive further notes that Amendment 1 was issued in response to a new EASA AD which "adds new upper and lower fin assembly part numbers to applicability, and includes the repetitive checks of previous Directives; until accomplishment of MOD 073330" (Background). The instrument therefore adopts EASA's broader applicability and recurring inspection regime.
• The Requirements repeatedly instruct compliance "in accordance with the instructions specified" in EUROCOPTER Alert Service Bulletin No. 55.00.11 Revision 2 and Eurocopter ASB No. 55.00.12 Revision 1, with allowance for "later EASA approved revision" where indicated (Requirements 1-3). This imports manufacturer-prescribed technical methods into regulatory obligation.

Interface with manufacturer service documentation

• The Directive does not recreate ASB technical steps; it mandates reliance on the ASBs. That creates a dependence on the content and approval status of those ASBs. Operators must use the specified ASB paragraphs (2.B.2, 2.B.3 and 2.B.3.a.1-3) for the detailed procedures. The Directive’s effect is to make compliance with Eurocopter ASBs binding for Australian operators of the affected aircraft.

Parts and modification interaction

• The Directive links modification status (MOD 073288 and MOD 073330) to the specific obligations. It prescribes different procedures depending on whether a helicopter is pre- or post-MOD 073288, and it makes MOD 073330 the terminating action for certain requirements. That creates an interaction between the AD and an aircraft’s modification and maintenance history. Determining which law applies in practice therefore requires cross-referencing the AD with an aircraft’s approved modification records.

Spares management and installation restrictions

• The Directive’s Requirement 4 operates as a regulatory restriction on installing specified spare parts after a given date unless a modification has been incorporated. This interacts with contractual law, inventory management, and supply chains: parts held under commercial contracts will be subject to regulatory constraints on their permissible installation. The Directive does not state commercial remedies but imposes a compliance condition on parts use.

Territorial and international law context

• The Directive references EASA ADs and aligns CASA action with EASA determinations. The Background indicates that EASA AD 2008-0120 supersedes earlier EASA ADs and that Amendment 1 aligns with new EASA ADs and part-number applicability. While the text does not set out the full territorial or international legal relationships, it demonstrates that CASA is adopting EASA findings and manufacturer ASBs as the technical basis for its national directive. Operators operating in jurisdictions governed by EASA ADs will see similar obligations under EASA.

Matters not decided in the Directive

• The Directive does not articulate how it interfaces with air operator certificates, continuing airworthiness management arrangements, or commercial warranty terms. It does not itself modify the scope of any civil aviation law beyond the technical obligations. In practice, operators will have to integrate these requirements with their continuing airworthiness obligations, maintenance arrangements and any contractual warranties or obligations with the OEM or maintenance providers.

In summary, the Directive functions by importing and giving regulatory force to EASA AD findings and Eurocopter ASBs, by creating modification-linked obligations, and by imposing a post-deadline parts installation restriction. For a complete picture of legal interactions (enforcement, appeals, commercial consequences), operators should consider CASA’s broader regulatory framework and relevant contracts.

The document before you is titled AD/AS 355/98 Amdt 1 and is dated 18 February 2009, signed by the Delegate of the Civil Aviation Safety Authority. The Compliance section states "This Amendment becomes effective on 26 February 2009." The Background explains the impetus and relationship to earlier EASA ADs, thus providing the amendment context.

Sequence and drivers recorded in the source

• The Background records that the EASA received reports of cracking in the stabiliser upper fin of Model AS 355 N helicopters. Those reports led to EASA AD action (EASA AD 2008-0120). The source states that EASA AD 2008-0120 supersedes EASA ADs 2006-0096 and 2006-0097R1; in turn, the EASA action "constitutes terminating action to the requirements of these CASA ADs" (Background). That explains why CASA issued an amendment: to reflect new EASA findings and to incorporate expanded applicability and checks until MOD 073330 accomplishment.
• The text then notes that Amendment 1 is issued in response to a new EASA AD which "adds new upper and lower fin assembly part numbers to applicability, and includes the repetitive checks of previous Directives; until accomplishment of MOD 073330" (Background). This indicates that the Amendment broadened the scope of applicability to capture additional fin part numbers discovered to be affected.

Dates and effective periods

• The Directive gives several operative dates for compliance:
  • The general effective date of this Amendment is 26 February 2009 (Compliance).
  • For helicopters pre-MOD 073288 that had fewer than 110 flight hours after 31 August 2006, the Replacement action was required within 110 flight hours after 31 August 2006 (Requirement 1.a). For those that had more than 110 flight hours after 31 August 2006, replacement was required within 15 flight hours after 26 February 2009 (Requirement 1.b).
  • For pre-MOD 073330 helicopters, removal and modification were required no later than 31 March 2009 (Requirement 3). Requirement 4 implements a non-installation rule effective after 31 March 2009.
• These dates show a staged approach where earlier flight-hour thresholds anchored to 31 August 2006 are combined with dates in early 2009 to create short-term windows for operators who had already exceeded the earlier threshold.

Relationship to earlier ADs

• The Background footnotes that EASA AD 2008-0120 supersedes EASA AD 2006-0096 and 2006-0097R1, and that those earlier CASA ADs are thereby terminated in their requirements. The Amendment thus both updates CASA’s position to align with EASA and reintroduces certain repetitive checks until termination via MOD 073330.

Referenced service documents and revisions

• The Amendment explicitly references EUROCOPTER ASB No. 55.00.11 Revision 2 (MOD 073288), ASB No. 55.00.11 Revision 0 (for prior checks), and EUROCOPTER ASB No. 55.00.12 Revision 1 (MOD 073330). It permits compliance with “later EASA approved revision[s]” in several places, indicating that the Amendment mechanism anticipates future ASB revisions.

Practical reading of amendment history

• The Amendment is the instrument that updates AD/AS 355/98 to reflect EASA findings and new part-number applicability. The document available does not include a running list of prior CASA AD amendment dates other than referring to the earlier EASA ADs and the two CASA ADs that EASA superseded; it also does not append a full historical table. The signature and effective date provide the immediate reference for when the amended obligations became nationally operative.

What the source does not include

• The source does not provide a prior version of AD/AS 355/98 within the text presented, nor does it provide a catalogue of previous CASA AD publication dates. It does not list subsequent amendments beyond Amdt 1 or whether further CASA follow-ups occurred after 2009. Users seeking a full administrative history should consult CASA’s AD database and EASA AD records for earlier and later entries.

In sum, Amendment 1 (AD/AS 355/98 Amdt 1) was issued in early 2009 to align CASA’s obligations with EASA findings about fin cracking, to add newly identified affected part numbers, and to reconcile temporary repetitive checks with a definitive modification (MOD 073330) that the Directive recognises as terminating action.

The Directive as provided contains no record of litigation, court decisions, administrative appeals, or legal challenges. The source lists only the technical and compliance requirements, effective dates, the EASA AD references, and the signature of the CASA delegate; it does not narrate any dispute history or provide citations to judicial or administrative proceedings.

What the source states

• The Background section indicates regulatory succession (EASA AD 2008-0120 superseding earlier EASA ADs) and technical responding (AD/AS 355/98 Amdt 1 issued in response). It does not record any recourse by affected parties or any litigation in relation to the Directive or any referenced EASA ADs.

What is not in the source and practical consequences

• Because the document provides no litigation history, researchers and practitioners should treat the absence of litigation references as silence, not as evidence that no challenges exist. The Directive invites compliance with manufacturer service documentation and EASA ADs; disputes could in theory arise over cost allocation, the scope of applicability, or interpretation of maintenance records. None of those matters are addressed in the text.

Recommended follow-up for legal research

• To establish whether any legal proceedings, administrative reviews, or enforcement actions occurred in relation to this Directive, a practitioner should check:
  • CASA enforcement and administrative records around 2009 and later.
  • Federal court and tribunal databases for any judicial review or appeal challenging CASA ADs.
  • Industry or trade publications, operator bulletins and manufacturer communications for reports on contested implementation or disputes over parts inventory or modification costs.
• The Directive itself names specific documents (EASA AD 2008-0120, EASA AD 2009-0029 reference, EUROCOPTER ASB No. 55.00.11 Revision 2, EUROCOPTER ASB No. 55.00.12 Revision 1). Any litigation that touched on technical interpretation would likely reference those documents; searches should include those instruments.

Limitations of the source

• The Directive is an administrative safety instrument and not a legal opinion or adjudicative record. Its absence of litigation references limits what can be asserted about legal contestation. Legal outcomes and enforcement practices are not discussed in the text.

Bottom line

• The instrument provided has no litigation history recorded. If litigation history or precedent is required for compliance risk assessment, users must consult external legal databases and CASA records for cases or enforcement events that post-date or relate to this Directive.

This Directive contains multiple procedural and technical points where operators and maintainers commonly trip up. Below are concrete pitfalls drawn directly from the text.

1. Applicability is part-number specific and modification-status dependent

• The Directive applies to AS 355 E, F, F1, F2 and N helicopters "fitted with the following upper and lower fins to which Modification (MOD) 073330 has not been incorporated" and then lists specific part numbers (Applicability). A helicopter that differs only by a part-number subtype may fall in or out of applicability; operators must verify fin part numbers and MOD 073330 incorporation status in the aircraft records. Failure to do so can result in misclassifying an aircraft as exempt when it is in scope.

2. Two overlapping MODs set different obligations (073288 versus 073330)

• The Directive distinguishes helicopters that are pre- or post-MOD 073288 for different timing of screw replacement and repetitive checks (Requirements 1-2). The meaning of "pre" and "post" MOD 073288 matters for which paragraph applies. Misreading "pre" versus "post" can lead to incorrect timing (e.g., mistakenly using the longer 110 flight-hour window when the shorter 15 flight-hour window applies).

3. Flight-hour counting triggers

• Several actions depend on whether the helicopter had accumulated "less than 110 flight hours after 31 August 2006" or "more than 110 flight hours after 31 August 2006" (Requirements 1.a and 1.b), or whether it had accumulated "less than 110 flight hours since the latest check performed in accordance with paragraph 2.B.3 of ASB No. 55.00.11 Revision 0" (Requirement 2.a). Operators must be precise in reading flight logs and linking the relevant reference dates. Counting errors could compress or extend compliance windows inappropriately.

4. Tight torque threshold is quantitative and can ground aircraft

• The Directive specifies that if tightening torque of one or both attachment screws is less than 80% of the minimum torque value, corrective actions described in the ASB must be applied "before further flight" (Requirements 1.d and 2.c). Operators must know the "minimum torque value" specified in the ASB and measure torque accurately. A misinterpretation of the baseline torque or using improper measuring tools can produce false positives or false negatives.

5. Repetitive checks at intervals not to exceed 110 flight hours

• The inspection interval is specified as "not to exceed 110 flight hours" (Requirements 1.c and 2.a/2.b). Operators must incorporate these checks into continuing airworthiness programs and not rely on calendar intervals unless they map to flight hours. Failing to track hours correctly risks non-compliance.

6. ASB versioning and EASA-approved revisions

• Several instructions permit compliance using "later EASA approved revision[s]" of the cited ASBs (Requirements 1-3). The gotcha is ensuring any later revision used is in fact EASA-approved. Using an unapproved manufacturer revision or an internal procedures document instead of an EASA-approved ASB revision would not meet the literal terms of the Directive.

7. MOD 073330 is both a compliance option and a parts-control trigger

• Incorporation of MOD 073330 is terminating action for several requirements, but the Directive also mandates that after 31 March 2009, listed fin part numbers held as spares must not be installed unless MOD 073330 has been incorporated (Requirement 4). Operators holding older spares must decide whether to modify the spares, dispose of them, or restrict their use. Failure to enforce the spares ban may result in installation of non-conforming parts after the date specified.

8. Part numbers and special fasteners are specific

• Requirement 3 prescribes replacement of bolts part number 22126BV060032L and washers part number 23112AG060LE with special bolts part number 350A23-4016-20 and special washers part number 350A23-4017-22. Using incorrect substitutes or fasteners that differ in material or treatment could nullify the intent of the modification and would not be compliant with the Directive.

9. Compliance deadlines are mixed and short

• For some groups, the Directive provided short windows (e.g., within 15 flight hours after 26 February 2009 for certain helicopters), creating immediate scheduling pressure. Operators who did not audit their fleets promptly could have missed tight windows. Retrospective compliance assessment must be careful to document when inspections or replacements were performed relative to the specified windows.

10. Reliance on ASB paragraphs for corrective actions

• The Directive directs specific corrective actions to ASB No. 55.00.11 Revision 2 paragraphs 2.B.3.a.1, 2.B.3.a.2 and 2.B.3.a.3. Those paragraphs likely contain a range of options (repair, replace, reinforce). Misapplying the wrong corrective step or misunderstanding repair limitations could lead to inadequate remediation.

11. EASA AD relationships and supersession

• The Background states EASA AD 2008-0120 superseded earlier EASA ADs and that the CASA Amendment was issued in response to a new EASA AD. Operators should not assume earlier EASA/CASA ADs remain authoritative for the same subject without checking supersession: misplaced reliance on obsolete AD text is a compliance risk.

12. Documentation and audit trail

• The Directive imposes specific timing and procedural steps but does not set out the form of evidence required to demonstrate compliance. The operator must therefore prepare a clear audit trail: logs of flight hours, ASB revision used, records of torque measurements (including the minimum torque baseline), photos/inspection reports for rivet or crack detection, and records of MOD 073330 incorporation using the specified fasteners.

In short, the combination of part-number specificity, modification-status dependence, short compliance windows, quantitative torque thresholds, and a spares-installation ban presents multiple practical pitfalls. Operators must reconcile aircraft configuration records with ASB procedures and build thorough documentation.

This section sets out a practical checklist and procedural steps, referencing the exact requirements in the Directive. The Directive requires following EUROCOPTER ASB No. 55.00.11 Revision 2 (and earlier Revision 0 where specified) and EUROCOPTER ASB No. 55.00.12 Revision 1 for the modification. The Directive also allows later EASA-approved revisions in several places.

Step 1 , Audit affected fleet and parts inventory

• Verify model: confirm aircraft are Model AS 355 E, F, F1, F2 or N (Applicability).
• Confirm fin part numbers: check whether the aircraft are fitted with listed upper fin assembly part numbers 355A14-0522-00XX, -01XX, -02XX, -03XX, -13XX, -14XX and -15XX or lower fin assembly part numbers 355A14-0521-00XX, -01XX, -02XX and -03XX (Applicability).
• Determine whether MOD 073330 has already been incorporated for each affected aircraft. The Directive applies only to aircraft "to which MOD 073330 has not been incorporated" (Applicability).
• Inventory spares: list all held spare upper and lower fins with the listed part numbers; Requirement 4 forbids installing these spares after 31 March 2009 unless MOD 073330 is incorporated.

Step 2 , Determine which Requirement applies to each aircraft

• If aircraft are pre-MOD 073288:
  • Check whether the aircraft accumulated less than or more than 110 flight hours after 31 August 2006.
  • If less than 110 flight hours after 31 August 2006: you must replace the upper and lower fin attachment screws within 110 flight hours after 31 August 2006 per paragraph 2.B.2 of ASB No. 55.00.11 Revision 2 (Requirement 1.a).
  • If more than 110 flight hours after 31 August 2006: you must replace the screws within 15 flight hours after 26 February 2009 per paragraph 2.B.2 of ASB No. 55.00.11 Revision 2 (Requirement 1.b).
  • Thereafter, check tightening torque and reinforcement splice at intervals not to exceed 110 flight hours (Requirement 1.c).
• If aircraft are post-MOD 073288:
  • Identify whether they have accumulated less than or more than 110 flight hours since the latest check done per paragraph 2.B.3 of ASB No.55.00.11 Revision 0.
  • If less than 110 flight hours since that check: perform torque and splice check within 110 flight hours after that check and then at intervals not exceeding 110 flight hours (Requirement 2.a).
  • If more than 110 flight hours since that check: perform the torque and splice check within 15 flight hours after 26 February 2009 and then repeat at intervals not to exceed 110 flight hours (Requirement 2.b).

Step 3 , Implement inspections, replacements and torque checks per the ASBs

• Obtain the exact text and procedures of EUROCOPTER ASB No. 55.00.11 Revision 2 and ASB No. 55.00.12 Revision 1, or a later EASA-approved revision if available and approved (Requirements 1-3).
• Perform replacement of upper and lower fin attachment screws or torque checks as required. Use the ASB-specified tools, torque values and procedures. Record torque measurements and results.
• If the tightening torque of one or both attachment screws is found to be less than 80% of the minimum torque value, apply the corrective actions in ASB No. 55.00.11 Revision 2 paragraphs 2.B.3.a.1, 2.B.3.a.2 or 2.B.3.a.3 before further flight (Requirements 1.d and 2.c). Do not return the aircraft to service before applying the ASB-prescribed corrective action.

Step 4 , For pre-MOD 073330 helicopters, plan and perform MOD 073330

• For helicopters with upper and lower fins pre-MOD 073330, remove the fins and perform modification of the upper and lower fittings on the tail boom by increasing the diameter of the bolt holes and replace bolts part number 22126BV060032L and washers part number 23112AG060LE with special bolts part number 350A23-4016-20 and special washers part number 350A23-4017-22, in accordance with EUROCOPTER ASB No. 55.00.12 Revision 1 (Requirement 3).
• Ensure the modification is carried out to the ASB standard, using the specified special parts. After incorporation, document MOD 073330 completion in the aircraft maintenance records.

Step 5 , Use MOD 073330 as terminating action where appropriate

• Recognise that completing MOD 073330 is "considered as acceptable compliance" with initial screw replacement requirements (1.a and 1.b) and is "terminating action" for the repetitive checks required by 1.c, 2.a and 2.b (Requirement 3). Decide whether to incur immediate modification cost in exchange for eliminating recurring inspection obligations. Record the modification to demonstrate terminating action has been accomplished.

Step 6 , Manage spare parts and inventory

• On and after 31 March 2009, do not install upper and lower fins with listed part numbers unless MOD 073330 has been incorporated (Requirement 4). Update parts-control procedures and procurement specifications to prevent inadvertent installation of non-modified spares.
• If existing spare fins with affected part numbers are in inventory, plan to either modify them (incorporate MOD 073330) or segregate them as non-installable.

Step 7 , Documentation and record-keeping

• Keep documented evidence of:
  • The ASB revision used to perform the work.
  • Flight-hour logs showing flight hours at the relevant dates.
  • Torque measurements and inspection reports (including photos if appropriate) showing results of reinforcement splice inspection and rivet condition.
  • Records of corrective actions applied when torque or cracks/loosened rivets were found.
  • Records of MOD 073330 incorporation including part numbers of special bolts and washers installed.
• Because the Directive mandates actions tied to specific dates and flight hours, audit-quality records are the primary way to demonstrate compliance.

Step 8 , Procedural integration and ongoing compliance

• Add the "not to exceed 110 flight hours" inspection to the continuing airworthiness maintenance schedule for any aircraft remaining pre-MOD 073330 until the modification is carried out.
• If electing to delay or stagger MOD 073330 across a fleet, schedule inspections to ensure no gap in compliance occurs between checks.

Step 9 , Consult EASA-approved ASB revisions

• Where the Directive permits "later EASA approved revision" of a cited ASB, ensure that the revision in use is EASA-approved. If a later revision exists that changes procedures or thresholds, adopt it where appropriate and record authority for the revision.

Step 10 , Monitor associated regulatory updates

• The Background notes a link to EASA AD 2008-0120 and that "EASA AD 2009-0029 refers." Continue to monitor EASA and CASA AD bulletins for any subsequent clarifications, revocations, or superseding directives.

In sum, compliance consists of: auditing configuration and parts inventory, mapping each aircraft to the correct Requirement, executing the ASB-prescribed repairs, inspections or MOD 073330, documenting the work and updating maintenance schedules and spares controls. The Directive gives operators a terminating-option pathway (MOD 073330) that removes repetitive inspection burdens, but that choice requires a one-off modification using specified special parts and must be fully recorded.