AD/ECUREUIL/117 - Main Servo-Controls

This AD rests on several core concepts that determine its scope and required actions.

Applicability concept: The AD applies only to Eurocopter AS 350 models B, BA, BB, B1, B2, B3 and D with main servo-controls of any part number, provided two conditions are met: (1) the servo-controls are not modified per MOD 073343; and (2) the tightening torque of the nut that secures the upper ball-end has been increased following either embodiment of MOD 073191 or compliance with MET Work Card 67.30.00.402 since MET Revision 04-06. The AD therefore targets a defined subset of the fleet, linked to modification/maintenance history as well as parts installed (Applicability).

Inspection-and-response concept: The AD requires an initial visual/structural inspection of the tapered housing of each main servo-control for cracks (Requirement, paragraph 1). The AD delegates the specific inspection methods and subsequent actions to specified paragraphs of Eurocopter ASB No. 05.00.51, namely 2.B.2., 2.B.3., 2.B.4., and 2.A., which the AD makes mandatory. For example, if no crack is evident the operator must still "comply once with paragraph 2.B.3." of the ASB, then may resume flights. If a vertical crack less than 20 mm is found, the AD requires a one‑off compliance with 2.B.3., marking the end of the crack with indelible ink and resumption of flights, plus compliance with 2.B.4. If certain crack thresholds or types are present (vertical crack ≥ 20 mm, growth >5 mm, oblique or horizontal cracks, or multiple cracks), replacement of the servo-control in accordance with 2.A. is mandated.

Interim management concept: The AD sets an interim inspection schedule where replacement cannot be done immediately. It requires checks "during the check after the last flight of the day, without exceeding 10 flight hours between two inspections," pending replacement, and sets an upper bound on the temporary operating window: replacement must occur "no later than within 150 flight hours without exceeding 3 months." These dual limits create both a flight-hour and a calendar ceiling.

Spare-part concept: For servo-controls held as spares, the AD requires inspection (paragraph 3), citing paragraph 2.B.2.b. of the ASB. If no crack is evident, comply once with paragraph 2.B.3. before installation; if a crack is evident, return the servo-control for repair. The AD explicitly requires inspection of spares before they are installed.

Reference and delegation concept: The AD delegates technical detail to an operator technical document issued by the manufacturer (ASB No. 05.00.51). The AD does not reproduce the ASB procedures but makes compliance with specified ASB paragraphs mandatory. It also notes EASA AD 2006-0055-E as a related document. The AD is issued under CASA authority, signed by the Delegate (signature block).

Risk-linkage concept: The AD makes explicit the safety risk that motivates the measures: undetected cracking in the tapered housing of a main servo-control could lead to loss of attachment to the swashplate and consequent loss of control (Background). The inspection and replacement regime follows directly from that causal safety concern.

Together, these concepts determine who must act, how to inspect, how to mark, when to replace, what to do with spares, and the timeframes in which those actions must occur, with the procedural methods mandated by named ASB paragraphs.

The AD identifies a specific and limited set of actors and equipment. Primary affected parties are:

• Operators and owners of Eurocopter AS 350 models B, BA, BB, B1, B2, B3 and D aircraft that have main servo-controls installed which meet the AD's applicability conditions (Applicability). Those conditions are: the main servo-controls are of any part number; they have not been modified per MOD 073343; and they are on helicopters where the tightening torque of the nut securing the upper ball-end was increased either through embodiment of MOD 073191 or compliance with MET Work Card 67.30.00.402 since MET Revision 04-06. Operators must confirm both airframe model and the presence or absence of particular modifications and maintenance actions before treating an aircraft as in or out of scope.

• Maintenance organisations and licensed engineers who perform inspections, marking, repairs and replacements of main servo-controls. The AD mandates actions that must be executed in accordance with named ASB paragraphs (Requirement). Maintenance personnel will therefore be directly responsible for following the ASB procedural steps and for recording compliance.

• Holders of spare main servo-controls. The AD explicitly covers servo-controls held as spares (Requirement, paragraph 3). Spares must be inspected and, if cracked, returned for repair before installation.

• The Civil Aviation Safety Authority (CASA) as the enforcing authority. The AD was issued by the CASA Delegate and became effective on 6 March 2006. CASA's delegate is the named issuer and therefore the administrative source of the mandatory requirement (signature line and effective date).

Not in scope: Helicopters or servo-controls that have been modified per MOD 073343 are excluded by the Applicability wording. Also excluded are helicopters where the tightening torque increase described in the Applicability has not been carried out; that is, the AD targets only aircraft where that specific tightening-torque action occurred. This makes applicability dependent on historical modification and maintenance records, so records custodians, maintenance planners and parts controllers within the operator must be involved in determining coverage.

Costs and responsibilities fall mainly on operators: they must schedule, perform and document inspections; mark and monitor any cracks found; plan for and carry out replacement or arrange repair of spares; and comply with the time limits. Maintenance providers will incur labour and possibly parts costs. The AD does not refer to any regulatory exemptions or cost-sharing; the instrument imposes mandatory actions on those whose aircraft meet the Applicability criteria.

Finally, the AD’s safety rationale implicates pilots and passengers only indirectly: the actions are intended to reduce the risk of loss of control, a safety outcome. The AD does not institute operational limitations such as flight bans, but the inspection frequency and replacement timeline constrain how long equipment with certain conditions may remain installed.

The AD imposes specific duties on operators and maintenance personnel and gives no express rights beyond compliance pathways. Key duties are:

Determine applicability: Operators must identify whether their aircraft and installed or spare servo-controls meet the Applicability condition , models AS 350 B, BA, BB, B1, B2, B3, and D, equipped with main servo-controls of any part number, that are not modified per MOD 073343 and where the tightening torque increase has been carried out following embodiment of MOD 073191 or MET Work Card compliance since MET Revision 04-06. The AD ties legal obligation to that factual determination.

Conduct inspections per the ASB: For main servo-controls installed on helicopters, the AD requires that the tapered housings be checked for cracks "in accordance with paragraph 2.B.2. of Eurocopter AS 350 Alert Service Bulletin (ASB) No. 05.00.51" (Requirement 1). The AD then prescribes differing follow-up steps depending on the inspection result: no crack, vertical crack <20 mm, vertical crack ≥20 mm, crack growth >5 mm, oblique/horizontal crack, and multiple cracks. Each outcome maps to a required action: compliance with ASB paragraph 2.B.3., marking the crack end with indelible ink, compliance with 2.B.4., or replacement in accordance with 2.A.

Mark and monitor: If a vertical crack less than 20 mm is found, the AD requires identifying the end of the crack "using an indelible ink marker" and resuming flights after compliance with the relevant ASB paragraph. That creates an obligation to both mark and monitor the indicated crack.

Follow interim inspection cadence and replacement windows: Where a replacement is pending, operators must inspect at the end of each day’s flying such that no interval exceeds 10 flight hours between inspections; replacement must be completed "no later than within 150 flight hours without exceeding 3 months" (Compliance 1.b.(ii)). These are concrete monitoring and repair scheduling duties.

Inspect spares before installation: For servo-controls held as spares, the AD requires accomplishing paragraph 2.B.2.b. of ASB No. 05.00.51 and, if no crack is evident, to comply once with paragraph 2.B.3. before installing; if cracked, return the spare for repair (Requirement 3).

Compliance timing duties: The AD sets initial compliance windows. For installed servo-controls, initial inspection must be done "within 10 flight hours or 10 days after 6 March 2006, whichever occurs first." For spares, inspection must be done "within 10 days after 6 March 2006, or before installing" (Compliance). If a crack is found that triggers immediate action, the AD stipulates replacement "before further flight" in some cases (Compliance 2).

Documentation and traceability duties: While the AD does not explicitly prescribe the precise form of records, compliance will require operators to document inspections, markings, actions taken under ASB paragraphs, and timing to demonstrate adherence to the AD’s time limits. The AD’s effective enforcement depends on such records.

Rights and procedural provisions: The AD does not state express rights such as appeals, deferral mechanisms, or alternative methods of compliance within its text. It does, however, rely on the ASB for technical method. Any deviation from the mandated actions would therefore require an alternate method of compliance acceptable to the regulator, but the AD text provided does not describe an approval pathway. The issuing authority is shown as the CASA Delegate (signature), and the AD is effective as of 6 March 2006; duty-holders must conform to the AD from that effective date.

In short, the AD's duties require operators and maintainers to identify applicability, perform the specified inspections, apply prescribed marking and monitoring procedures, complete replacements under the set flight-hour and calendar limits, and inspect spares before use. The AD references ASB No. 05.00.51 for the procedural details that make up these duties.

The text supplied is an Airworthiness Directive issued by the Civil Aviation Safety Authority (CASA) and signed by the Delegate, effective 6 March 2006. The AD itself sets mandatory technical directions for affected equipment. The AD text does not state criminal, civil or administrative penalties, nor does it reproduce the statutory enforcement provisions that give CASA powers to require compliance or to sanction non-compliance. Therefore the AD should be read as a mandatory regulatory instrument whose enforceability rests on the regulator’s statutory powers, which are not reproduced in the AD text provided.

What the AD does supply relevant to enforcement is:

• The AD is issued by the CASA Delegate (signature block). That identifies the administrative source and indicates that the requirement is a formal regulatory instrument, not merely guidance (effective date and signature).

• Time limits for compliance are explicit. Enforcement can reasonably be expected to focus on whether inspections, markings, replacements and spares-handling occurred within the stated windows: initial inspection within 10 flight hours or 10 days after 6 March 2006; interim inspection cadence not to exceed 10 flight hours between inspections pending replacement; replacement within 150 flight hours or 3 months; spares inspection within 10 days or before installation.

Because the AD text does not set out penalties, readers must not infer specific sanctions from the AD alone. The practical enforcement mechanisms that CASA typically uses (not stated here) may include audit, directives to ground an aircraft for non-compliance, mandatory repair notices, or administrative penalties under the enabling aviation safety legislation. The AD itself creates an obligation to perform the specified actions; failure to do so would leave the aircraft non-compliant with the AD and thus non-compliant with the regulator’s airworthiness requirements, as the AD is the instrument specifying required actions.

From an operator's perspective, the risk of enforcement is that the aircraft would be operated contrary to a mandatory safety requirement; enforcement consequences will depend on CASA’s regulatory framework and discretionary decisions, which are not contained in the AD text. The AD’s clear timeframes and prescriptive linkage to the ASB mean that evidence of compliance (inspection records, markings, replacement records) is the practical way to demonstrate adherence in any enforcement or audit process.

Finally, the AD refers to EASA AD 2006-0055-E without reproducing any enforcement or penalty provisions from that document; it is a cross-reference that may inform international regulatory alignment but does not itself alter the enforcement text in this AD.

The AD explicitly refers to and incorporates by reference certain technical documents and modification records; however, it does not recite other statutory provisions. The interactions evident in the AD text are procedural and technical rather than legislative cross-references. The following interactions can be drawn from the document as written:

• Incorporation of manufacturer's procedures: The AD mandates compliance with specific paragraphs of Eurocopter AS 350 Alert Service Bulletin No. 05.00.51 (Requirement). By doing so it binds operators to follow the ASB paragraphs cited (2.B.2., 2.B.3., 2.B.4., and 2.A.) as the method for inspection, marking, repair and replacement. The ASB is therefore the technical instrument through which the AD is implemented.

• Dependence on maintenance modification records: Applicability is explicitly defined in relation to certain modifications and maintenance actions: units "not modified per MOD 073343" are included, and the AD applies only to helicopters "on which the tightening torque of the nut that secures the upper ball-end has been increased following embodiment of MOD 073191; or compliance with MET Work Card 67.30.00.402 since MET Revision 04-06." That creates an interaction between the AD and the operator’s maintenance records, modification logs and compliance with manufacturer MET work cards. These records are part of an aircraft’s technical file and relevant maintenance law and procedures. The AD therefore leverages the maintenance recordkeeping regime to determine legal scope.

• Cross-reference to foreign authority: The AD notes "EASA AD 2006-0055-E refers" (Note). This indicates that the European Aviation Safety Agency has a related AD. The AD therefore interacts with international regulatory activity, signalling alignment of airworthiness requirements across jurisdictions. The AD does not, however, adopt EASA’s enforcement mechanisms; it merely references the EASA AD as related material.

• Procedural relationship with installation of spares: The AD requires spares to be inspected in accordance with the ASB before installation, and if cracked to be returned for repair. That requirement interacts with parts-handling and airworthiness directives controlling component conformity, traceability and repair processes in the maintenance regime.

• Non-coverage by specific modifications: Aircraft modified according to MOD 073343 are excluded. Thus, compliance with or evidence of certain modifications will remove an aircraft from the AD’s scope. That creates an interaction between the AD and any regulatory or contractual processes that address modification approvals and implementation.

The AD text does not reference other specific statutes, civil aviation acts, administrative law procedures, or penalty provisions. Therefore, any legal consequences of non-compliance, or procedural mechanisms for seeking alternative methods of compliance or appeals, are not stated in the AD and must be sought in the governing aviation statutes, regulations and CASA procedural rules outside the AD document.

In summary, the AD interacts with other legal and regulatory elements through mandatory incorporation of manufacturer service bulletin procedures, reliance on maintenance and modification records to determine applicability, cross-reference to an EASA AD, and requirements affecting spare parts handling. The specific legal mechanisms for enforcement, appeals or alternative compliance are not set out in the AD text provided.

The AD text supplied contains a single version with an effective date and signature; it does not list prior amendments, revisions, or supersessions. The concrete items in the text relevant to amendment history are:

• Effective date: "This Airworthiness Directive becomes effective on 6 March 2006." That establishes the operative start date for the measures laid out.

• Issuer and date signed: The AD is signed by David Punshon, Delegate of the Civil Aviation Safety Authority, with the date "3 March 2006." That indicates the administrative action was taken prior to the effective date.

• Cross-reference to EASA AD 2006-0055-E and ASB No. 05.00.51: The AD contains a Note that "EASA AD 2006-0055-E refers," which suggests concurrent or related regulatory action elsewhere, but the AD does not incorporate any amendment history arising from EASA or from subsequent CASA action.

• Internal references to modifications and MET work card revisions: The Applicability references modifications (MOD 073343 and MOD 073191) and "MET Work Card 67.30.00.402 since MET Revision 04-06." Those references implicitly indicate a chronology of modification embodiments and maintenance-revision events that are relevant for determining applicability. However, the AD itself does not provide a historical timeline beyond those mentions.

Because no subsequent amendments or revocations are present in the supplied text, an operator reading this AD must treat the version provided as the only operative version under the supplied material. Any later CASA amendments, superseding ADs, or withdrawn directives would not be visible from this document alone; the AD does not include an amendment log or history beyond signature and effective date.

If users require the official amendment history,such as any later revisions, supersessions, or relationship to subsequent EASA/CASA directives,that information is not contained in the AD text here and must be obtained from the regulator's AD database or official aeronautical publications. The AD as presented is self-contained and shows the initial action date (signed 3 March 2006, effective 6 March 2006) with no further amendments recorded in the text supplied.

The AD text contains no mention of litigation, appeals, legal challenges, or case law arising from this directive. It refers only to the technical issue, the required remedial action, and its issuance by the CASA Delegate. There are no cases or legal proceedings cited in the document.

Consequently, within the boundaries of the supplied source, there is no recorded litigation history. Any litigation or administrative appeals that may have occurred after the AD’s issuance, or any compliance disputes, are not reported here. Readers who need to know whether the AD was subsequently challenged, interpreted by courts or tribunals, or involved in enforcement proceedings will need to consult external legal records, court databases or CASA's enforcement records because none of that material appears in the AD text provided.

For practical purposes, the absence of litigation references in the AD means that the AD should be treated as a technical regulatory instrument with no documented adversarial history in this source. However, the procedural and evidentiary aspects of demonstrating compliance (inspection logs, markings, replacement records) will be relevant in any enforcement or legal scrutiny, even though specific litigation events are not noted.

The AD contains several specific details that carry practical implementation risks or traps for operators. These are matters that may cause misapplication or non-compliance if not carefully managed:

Narrow applicability based on modifications and work-card history: The AD does not apply to all AS 350 helicopters categorically. Applicability is limited to aircraft whose main servo-controls are not modified per MOD 073343 and where the tightening torque increase has been carried out following embodiment of MOD 073191 or compliance with MET Work Card 67.30.00.402 since MET Revision 04-06. This creates a narrow population in which the AD applies; operators must check maintenance and modification records diligently. Failure to verify MOD and MET histories could lead to unnecessary work for unaffected aircraft or missed obligations for affected ones.

Reference to but non-reproduction of ASB procedures: The AD mandates compliance with specific paragraphs of Eurocopter ASB No. 05.00.51 (2.B.2., 2.B.3., 2.B.4., 2.A.). The AD itself does not reproduce the detailed inspection or repair procedures. Operators must obtain and follow the ASB paragraphs identified. Relying on a paraphrase of the ASB or on informal practices risks non-compliance.

Marking requirement is specific: If a vertical crack less than 20 mm is found, the AD requires identifying the end of the crack "using an indelible ink marker" before resuming flights (Requirement 1.b.(i)). The choice of ink, marking permanence, and placement are specified at a high level; failure to mark with indelible ink or to document the marking may be argued as non-compliance.

Dual limit for temporary continued operation: Where replacement is pending, the AD requires checks "during the check after the last flight of the day, without exceeding 10 flight hours between two inspections," and replacement must occur "no later than within 150 flight hours without exceeding 3 months" (Compliance 1.b.(ii)). Operators must manage both flight-hour and calendar limits simultaneously. A plan that meets flight-hours but exceeds the 3-month calendar limit, or vice versa, would not satisfy the AD. Scheduling must therefore track both metrics.

Immediate grounding conditions may exist: For some findings the AD requires replacement in accordance with paragraph 2.A. of the ASB and, in the Compliance section, states "Before further flight" for certain cases. Operators must be prepared to carry out immediate removals/replacements or otherwise ensure the aircraft is not returned to flight until the requisite action is taken.

Spare parts inspected before installation: The AD requires inspection of spares within 10 days after 6 March 2006 or before installing a spare (Compliance), and to return cracked spares for repair. Stock-control systems must ensure that any spare servo-control installed after the effective date has been inspected and cleared in accordance with the ASB paragraphs.

Record-keeping and evidentiary burden: The AD implies but does not specify documentation form. Demonstrating compliance will require inspection records, marking evidence, repair/replacement records, and traceability of parts and MOD/MET histories. Inadequate records could lead to enforcement exposure even if inspections were done.

Parts interchangeability and part numbers: The AD covers all part numbers of main servo-controls but excludes those modified by MOD 073343. Operators must ensure that part numbers and modification status are accurately tracked. Misidentifying a part as unmodified or modified could lead to incorrect application of the AD.

Dependency on ASB availability: Since the AD requires specific ASB paragraphs, lack of immediate access to ASB No. 05.00.51 could delay compliant action. Operators should obtain the ASB promptly.

International cross-references: The Note referencing EASA AD 2006-0055-E may lead some organisations to assume equivalence in wording or effect; however, the AD here is the binding CASA instrument, and any differences between EASA and CASA instruments must be reconciled by reference to each authority's text.

These practical "gotchas" are mechanical and procedural; they do not alter the AD’s safety rationale but are points where implementation can fail if attention is not paid to record verification, ASB compliance, marking, timing, spares control and coordination between flight schedules and maintenance windows.

The AD prescribes a clear set of mandatory steps; the following is a concrete, source-grounded checklist operators and maintainers should follow to comply with the AD as written. Each action references the AD text (Applicability, Requirement, Compliance) and the specific ASB paragraphs cited.

1. Determine applicability immediately:

   • Identify aircraft that are AS 350 models B, BA, BB, B1, B2, B3 or D.
   • For each such helicopter, confirm whether the installed main servo-controls have been modified per MOD 073343. If they have been modified per MOD 073343, the AD does not apply to those units.
   • Confirm whether the tightening torque of the nut securing the upper ball-end was increased following embodiment of MOD 073191 or compliance with MET Work Card 67.30.00.402 since MET Revision 04-06. The AD applies only where that tightening torque increase has been carried out. Source: Applicability.

2. Obtain the referenced ASB:

   • Acquire Eurocopter AS 350 Alert Service Bulletin No. 05.00.51 and locate paragraphs 2.B.2., 2.B.3., 2.B.4. and 2.A. The AD makes compliance with those paragraphs mandatory (Requirement).

3. Schedule initial inspections within the AD’s compliance windows:

   • For installed servo-controls, perform the required inspection "within 10 flight hours or 10 days after 6 March 2006, whichever occurs first" (Compliance). Given the AD’s effective date, treat this as an immediate priority.
   • For spares, accomplish the inspection "within 10 days after 6 March 2006, or before installing a main servo-control held as spares" (Compliance). Do not install a spare without completing the mandated ASB paragraph steps.

4. Perform the inspection per paragraph 2.B.2. of the ASB:

   • Follow the ASB’s specified inspection method (the AD mandates adherence to paragraph 2.B.2. for tapered housing inspection). Document the inspection outcome.

5. Take action based on inspection result:

   • If no crack is evident: comply once with paragraph 2.B.3. of the ASB and resume flights (Requirement 1.a).
   • If a vertical crack less than 20 mm is found: comply once with paragraph 2.B.3. of the ASB, identify the end of the crack using an indelible ink marker, and resume flights; additionally, comply with paragraph 2.B.4. of the ASB (Requirement 1.b.(i) and (ii)).
   • If a vertical crack of 20 mm or longer is found, or the crack has grown by more than 5 mm, or an oblique or horizontal crack is present, or there are several cracks: replace the servo-control in accordance with paragraph 2.A. of the ASB (Requirement 2).
   • For spares, accomplish paragraph 2.B.2.b. of the ASB; if no crack is evident, comply with paragraph 2.B.3. before installation; if cracked, return the unit for repair (Requirement 3).

6. Manage interim operation where replacement is pending:

   • If replacement is delayed, perform the check after the last flight of the day, ensuring that no interval between inspections exceeds 10 flight hours (Compliance 1.b.(ii)).
   • Ensure replacement is completed no later than within 150 flight hours and does not exceed 3 months from the point at which the interim regime began (Compliance 1.b.(ii)).
   • If the condition found triggers "Before further flight" action, do not return the helicopter to service until the mandated replacement or repair per paragraph 2.A. of the ASB has been completed (Compliance 2).

7. Marking and recording:

   • Use an indelible ink marker to identify the end of any crack as specified when applicable (Requirement 1.b.(i)). Take photographic and written records of the marking and the inspection result.
   • Log the inspection date, flight hours at inspection, findings, marked locations, subsequent inspections and replacements, and any spare inspections. Maintain these records in the aircraft maintenance log and in the component history as evidence of compliance.

8. Spare parts control:

   • Inspect all spare main servo-controls held in stock in accordance with paragraph 2.B.2.b. of the ASB within the AD’s timing window (Compliance). Log the inspection and clear the spare for installation only if it passes the ASB paragraph 2.B.3. check; otherwise return for repair.

9. Arrange repair/replacement logistics:

   • Identify suppliers or repair facilities capable of carrying out servo-control replacement or the repairs required by the ASB. Plan for potential lead-times so that replacement can occur within 150 flight hours or 3 months where interim monitoring is required.
   • If replacement parts are not immediately available, ensure daily end-of-day inspections occur and document management steps taken to obtain replacements.

10. Ensure maintenance personnel are briefed and authorised:

    • Provide maintenance personnel with the AD text and the specified ASB paragraphs. Ensure that those individuals are authorised and competent to perform the inspections and replacements per the ASB procedures.

11. Confirm regulatory compliance evidence:

    • Prepare a compliance pack including the AD, the ASB paragraphs used, inspection reports, photographs, marking evidence, replacement or repair invoices and component-change documentation to present to an auditor or inspector if required.

12. Note cross-reference materials:

    • Be aware that EASA AD 2006-0055-E is referenced in the AD as related material; operators engaged in international operations or with European oversight may wish to consult the EASA AD for further context, but compliance with this CASA AD is mandatory for the aircraft of applicability in Australia (Note).

Following these steps will align operational practice with the AD’s mandatory requirements as stated in the supplied text. Because the AD delegates detailed methods to ASB paragraphs, operators must ensure they have the correct and current ASB and implement those paragraphs in full. The AD’s time limits are explicit and must be tracked both by flight hours and calendar time.