AD/BAe 146/127 - Hydraulic Power - Accumulator Cylinders

This AD mobilises a small set of technical and procedural concepts; their operational meaning in practice depends on referenced documents that the AD makes mandatory by reference.

• Identification: The AD requires identification of the installed hydraulic accumulator per paragraph 2C of BAe Systems ISB 29-047 (dated 3 October 2006). The AD does not reproduce paragraph 2C; it makes compliance with that paragraph a precondition. Practically, operators must obtain ISB 29-047 and follow its identification procedure to determine whether an accumulator is from the suspect supplier or batch. The AD expressly allows "later NAA approved revisions" of the referenced documents to be used.
• Removal from service: If an accumulator is identified as affected, the AD mandates removal "in accordance with paragraph 2D of BAe Systems ISB 29-047". Removal procedures, safe handling, and any associated paperwork are therefore driven by that ISB paragraph.
• Magnetic particle inspection: The AD requires magnetic particle inspection "in accordance with APPH SB AIR91666-29-03". That inspection method is a non-destructive test commonly specified for detecting surface and near-surface discontinuities in ferromagnetic materials. The AD makes that specific inspection method obligatory for identified cylinders.
• Replacement with serviceable unit: The AD requires immediate replacement "when any defects are found" and specifies replacement with a "serviceable unit" before further flight. The AD does not define "serviceable unit" within its text; it relies on the maintenance standards and the referenced service documents for the definition and acceptance criteria.
• Installation prohibition unless inspected: The AD forbids installing an accumulator identified by APPH SB AIR91666-29-03 unless that accumulator has been inspected per APPH SB AIR91666-29-02 or AIR91666-29-03. The AD points readers to a second Note in paragraph 1D(1) of ISB 29-047 for further explanation of that prohibition.
• Temporal compliance windows: The AD imposes multiple, task-specific compliance deadlines: identification within six weeks of the AD effective date; the inspection completion by 31 October 2009 for the step corresponding to the second requirement; replacement before further flight if defects are found; and a general "after the effective date" instruction for the prohibition on installation. The AD therefore stages obligations over time rather than imposing a single deadline for all actions.
• Cross-references to external documents and authorities: The AD makes compliance conditional on documents produced by the aircraft manufacturer (BAe Systems ISB) and component manufacturer (APPH Ltd SBs). It also references EASA AD 2007-0076 and CASA telex AD/BAe146/119. The AD expressly permits use of later NAA approved revisions of the referenced service bulletins.

These concepts are procedural and technical: the AD does not create new maintenance techniques, it prescribes which existing inspection and removal procedures must be used, and it ties operators to specific approved revisions of SBs and the ISB.

The AD’s stated applicability is explicit: "BAe 146 and AVRO 146-RJ aeroplanes - All models." That means every aircraft operator, lessor, owner and maintenance organisation responsible for airworthiness of those airframes is within the AD’s scope. The parties affected and the roles they will need to play, as shown in the AD text, include:

• Aircraft operators and owners: They must ensure all affected aircraft in their fleet are identified, inspected, and any defective accumulators are replaced within the timeframes set by the AD (see Requirement 1-4; Compliance 1-4). Operators will be the parties who plan maintenance schedules around the required actions and bear the direct costs of removal, inspection and replacement. The AD’s replacement-before-flight mandate (Requirement 3; Compliance 3) creates an immediate operational constraint if inspections reveal defects.
• Maintenance organisations and licensed engineers: The AD requires technical work to be performed "in accordance with" specified paragraphs of ISB 29-047 and APPH SB AIR91666-29-03 (Requirements 1-4). These maintenance actors must obtain and apply the referenced procedures, perform magnetic particle inspections, and certify serviceability or replacement. Because the AD ties compliance to external service documents, maintenance organisations must ensure they have access to the specific SB revisions and any later NAA-approved revisions.
• Component supplier and manufacturer (APPH Ltd): The AD arises from APPH’s SBs and the manufacturer's conclusions that cylinders from a particular supplier may not have been correctly inspected at manufacture. Although the AD does not impose direct obligations on APPH within its text, the AD’s corrective pathway uses APPH SB AIR91666-29-03 as the prescribed inspection method, making APPH’s documentation central to compliance. APPH is implicated as the origin of the inspection technique and as the supplier whose inspection regime is under scrutiny.
• Civil Aviation Safety Authority (CASA) and its delegate: CASA is the issuing authority; the document is signed by a CASA delegate (Charles Lenarcic) and becomes effective on 10 May 2007. CASA’s role, as evidenced by the AD, is to mandate the identification/inspection programme and to reference earlier communications such as CASA telex AD/BAe146/119. The AD imposes obligations upon regulated parties but does not itself set out enforcement mechanisms in the text supplied.
• National Aviation Authorities (NAAs): The AD explicitly permits the use of "later NAA approved revisions" of the referenced ISB and SBs. This creates an administrative dependency: operators may rely on updated NAA approvals of those service documents when carrying out the AD-mandated work.

Who pays: the AD allocates operational cost burden implicitly to operators and maintainers. Every required action,identification, removal, magnetic particle inspection, and replacement where necessary,will be performed under the operator’s maintenance programme, thus creating direct labour and parts costs for operators and possibly indirect costs from aircraft downtime. The AD does not allocate costs to CASA or APPH within the text; it establishes technical obligations for operators and maintenance organisations.

The AD sets out several express duties and a limited set of rights tied to the use of later approved revisions. Below are the duties and the textual basis for them.

Express duties (as stated in the AD text)

• Duty to identify installed hydraulic accumulators: Operators must "Identify the installed hydraulic accumulator in accordance with paragraph 2C of BAe Systems Inspection Service Bulletin (ISB) 29-047 dated 3 October 2006, which makes reference to APPH Ltd. Service Bulletin (SB) AIR91666-29-03, dated July 2006, or later NAA approved revisions of these documents." The AD therefore imposes an obligation to follow the ISB’s identification procedure (Requirement 1). The compliance window is "within 6 weeks after the effective date of this AD" (Compliance 1).
• Duty to remove affected accumulators from service and inspect: If an accumulator is identified as affected, it must be "removed from service in accordance with paragraph 2D of BAe Systems ISB 29-047 and magnetic particle inspect the cylinder in accordance with APPH SB AIR91666-29-03" (Requirement 2). The compliance deadline assigned to this step is "No later than 31 October 2009" (Compliance 2).
• Duty to replace any defective accumulators: "When any defects are found, replace the accumulator with a serviceable unit." The AD ties this duty to an operational constraint by requiring replacement "before further flight, after the effective date of this AD" (Requirement 3; Compliance 3). That is, a defective accumulator discovered during inspection must be replaced prior to returning the aircraft to service.
• Duty to refrain from installing uninspected accumulators: The AD states, "Do not install an accumulator identified by APPH Ltd. SB AIR91666-29-03 on an aircraft, unless it has been inspected in accordance with APPH Ltd. SB AIR91666-29-02 or AIR91666-29-03" (Requirement 4). The compliance timing for that prohibition is "After the effective date of this AD" (Compliance 4). The AD also directs readers to the second Note in paragraph 1D(1) of ISB 29-047 for further explanation.

Rights and permitted flexibilities (as stated in the AD text)

• Use of later NAA approved revisions: The AD expressly permits operators to rely on "later NAA approved revisions" of both BAe Systems ISB 29-047 and APPH SB AIR91666-29-03. That grants regulated parties a defined flexibility to follow updated, NAA-approved versions of the referenced documents rather than being locked to the particular revision of the SBs mentioned in the AD. This is the principal "right" or permitted variation the AD includes.
• Reference note: The AD points users to the second Note in paragraph 1D(1) of ISB 29-047 for further explanation concerning installation prohibitions. That referral gives operators a procedural channel (the ISB note) to obtain the AD’s rationale or further instruction, which may affect how the installation prohibition is applied.

Observations about duties and rights

• The AD binds operators and maintenance organisations to specific third-party service documents rather than prescribing technical steps inside the AD itself. Compliance therefore depends on access to those documents and, where relevant, to the NAA approval status of any later revisions.
• The AD creates an operational constraint of "no further flight" in two contexts: replacement of defective accumulators must occur before further flight after defects are found, and installation of certain accumulators is prohibited unless inspected per specific SBs. The AD does not define "serviceable unit" within its text; that definition will ordinarily be supplied by maintenance practice, the ISB/SBs, or the operator's maintenance control documentation.
• The AD’s duties are staged with differing deadlines; operators must interpret which actions must be completed immediately and which may be accomplished within a longer window (for example, the second requirement’s deadline of 31 October 2009).

The AD text supplied does not include an express statement of civil or criminal penalties, nor does it set out the administrative enforcement machinery associated with non-compliance. The document records the issuing authority and dates: it became effective on 10 May 2007 and is signed by a CASA delegate (Charles Lenarcic, 29 March 2007). Beyond those administrative facts, the AD itself is silent in the supplied text about penalties, sanctioning powers, or the mechanisms by which compliance will be enforced.

Consequences and enforcement-relevant features derivable from the AD text

• Mandatory compliance windows: The AD contains mandatory, task-specific deadlines (e.g. "within 6 weeks after the effective date", "no later than 31 October 2009", "before further flight"). These deadlines establish clear expectations of timely action for operators and maintenance organisations. The presence of a "before further flight" requirement is operationally enforceable by aircraft operators and maintenance organisations because it conditions airworthiness on compliance with the AD. The AD text itself, however, does not state what actions CASA will take if the AD is not complied with.
• Authority and provenance: The document is an Airworthiness Directive issued under CASA’s authority and signed by a CASA delegate. The AD therefore has the formal characteristics of an airworthiness mandate from the regulator; the AD text supplies no additional enforcement details.
• Interaction with other CASA communications: The AD refers to an earlier CASA telex (AD/BAe146/119). That telex may have been an earlier advisory or mandatory communication; however, the AD text supplied does not describe enforcement consequences that flowed from the telex.

What the AD does not state

• The AD does not set out fines, license suspensions, or criminal penalties for non-compliance in the supplied text. It does not describe a process for CASA to audit or verify compliance in the text provided. The AD does not specify how records of compliance should be retained or produced, beyond the procedural references to the ISB and SB requirements.
• The AD does not include a provision for alternative means of compliance (AMOC) within the text provided. The AD permits later NAA approved revisions of the ISB/SBs; however, it does not state whether other alternative inspection techniques or procedures may be used absent NAA approval.

Because the supplied AD document omits explicit penalty or enforcement provisions, regulated parties should treat the AD as a mandatory technical obligation and confirm the enforcement expectations, record-keeping requirements and any civil enforcement or sanctioning procedures with CASA or in the applicable regulatory framework outside this AD text.

The AD text explicitly cross-references other regulatory or safety instruments and relies on approvals from National Aviation Authorities. Those interactions, as stated in the AD, are as follows:

• Reference to EASA AD 2007-0076: The AD contains a note that "EASA AD 2007-0076 dated 21 March 2007 refers." That shows a cross-jurisdictional linkage: the CASA AD acknowledges a European Aviation Safety Agency AD addressing the same technical issue. The AD does not describe the content of EASA AD 2007-0076 in the supplied text; it simply records the reference. This establishes that the issue was considered in a related regulatory environment and that CASA aligned its directive with that other AD.
• Reference to CASA telex AD/BAe146/119: The Background states that the event (an in-flight burst failure) "resulted in the issue of CASA telex AD/BAe146/119 requiring the identification and check of cylinders from known suspect batches." The AD therefore sits in a sequence of regulatory communications from CASA concerning the same failure mode. The provided text implies that the telex was an earlier step in CASA’s response and that AD/BAe 146/127 supersedes or formalises further requirements. The AD text does not reproduce the telex’s terms.
• Dependence on NAA-approved revisions: The AD allows for use of "later NAA approved revisions" of the BAe Systems ISB 29-047 and APPH SB AIR91666-29-03. This creates an administrative interaction: compliance may be met by following later revisions of the service documents where those revisions have NAA approval. The AD therefore delegates part of the technical standard-setting to the relevant NAA approval process for service bulletin revisions.
• Reliance on manufacturer and supplier documentation: The AD makes mandatory the application of ISB 29-047 and APPH SB AIR91666-29-03 (and possibly AIR91666-29-02), which are manufacturer or supplier documents rather than statutory instruments. The AD thus incorporates those documents by reference, moving some of the normative technical detail out of the AD and into private technical documentation. The AD does not itself modify or replace the legal effect of the ISB or SBs; it makes compliance with their specified paragraphs a condition of airworthiness as determined by CASA.

What the AD text does not specify about interactions

• The AD does not set out how conflicts between the ISB/SBs and other laws or regulations should be resolved. It neither references a specific regulatory clause authorising the AD nor cites a statutory provision. The AD text supplied is an operational directive; any legal conflicts or supersession questions would need to be determined by reference to CASA’s broader regulatory framework, which is not present in the supplied text.
• The AD does not describe how an operator should treat parts or accumulated stock that pre-date the AD but are not currently installed. The AD does prohibit installation of identified accumulators unless inspected per APPH SB AIR91666-29-02 or -29-03. The interplay between that prohibition and other supply-chain or contractual obligations is not addressed in the AD text.

In short, the AD interacts with other regulatory instruments and manufacturer documents by reference; it relies on NAA approvals to permit updated procedures; and it records an antecedent CASA telex and an EASA AD as related instruments. The AD does not supply a comprehensive map of legal interactions or enforcement pathways in the supplied text.

The AD text supplied contains the following chronological and revision-relevant information:

• Date of issuer signature: 29 March 2007, signed by Charles Lenarcic, Delegate of the Civil Aviation Safety Authority.
• Effective date: "This Airworthiness Directive becomes effective on 10 May 2007." The AD therefore sets an effective date approximately six weeks after the signature date.
• References to prior CASA communications: The Background records that an in-flight burst prompted "the issue of CASA telex AD/BAe146/119" as an earlier CASA communication. The AD appears to be a subsequent formalisation of corrective measures.
• Reference to related foreign AD: The AD states that "EASA AD 2007-0076 dated 21 March 2007 refers." This indicates that a European AD addressing the same issue existed and is relevant to this CASA AD.
• References to service document dates: The AD prescribes BAe Systems ISB 29-047 dated 3 October 2006 and APPH SB AIR91666-29-03 dated July 2006 as the baseline documents for compliance, but explicitly permits "later NAA approved revisions of these documents."

What the supplied text does not show about amendments

• The document as provided does not record any subsequent amendments to AD/BAe 146/127 itself. There is no amendment log, reissue, withdrawal, or supersession notice in the supplied text. The AD’s allowance for later NAA-approved revisions of the ISB/SBs constitutes an avenue for technical updates without amending the AD itself, but the AD text contains no record of specific later revisions having been approved.
• The AD does not set out a formal procedure for amendment of the AD text itself within the supplied content; it simply records the effective date and the permissive rule for later NAA-approved service bulletin revisions.

Implications for traceability and compliance

• Operators should note that the AD ties compliance to specific service document revisions (ISB 29-047 dated 3 October 2006; APPH SB AIR91666-29-03 dated July 2006) but also allows later NAA-approved revisions. In practice, any amendment history affecting the inspection method, identification criteria, or acceptance standards will be reflected in those later NAA-approved revisions rather than in an amendment to the AD text itself, according to the wording of this AD.
• Because the supplied AD does not record later amendments to the AD text, parties should confirm whether subsequent CASA communications modified, superseded or clarified the AD, or whether later NAA-approved revisions of the ISB/SBs have been issued and approved.

The supplied AD contains no information about litigation, disputes, appeals, judicial review, or administrative challenges. The document is an administrative airworthiness directive with signature and dates, and the text does not report any legal proceedings arising from this AD or from the event described in the Background.

What the AD text shows about dispute avenues or appeals

• The AD does not include a section on appeals or a procedure for seeking alternative means of compliance (AMOC). It does not identify a tribunal or process for review of CASA’s decision within the supplied text.
• Because the AD refers to external documents and NAA approvals, any dispute over technical interpretation would likely be decided through the usual operational channels (for example, consultation with the component manufacturer, BAe Systems, or the NAA) rather than inside the AD text itself. The AD points readers to paragraph 1D(1) of ISB 29-047 for further explanation, which can be a focal point for resolving interpretive questions about installation prohibitions.

If litigation or appeals were pursued in relation to this AD, those matters do not appear in the provided text. The document supplies no case names, court references, or administrative adjudication outcomes. Parties relying on the AD should therefore treat the litigation history as not recorded in the AD document provided and seek external confirmation of any proceedings from CASA or other public records.

The AD’s brevity and reliance on external service bulletins create several practical pitfalls for operators and maintainers. These "gotchas" are drawn strictly from the text as provided.

1. Multiple and staggered compliance dates require interpretation: The AD assigns different compliance windows to different numbered requirements. Requirement 1 (identification per ISB 29-047 paragraph 2C) must be completed "within 6 weeks after the effective date." Requirement 2 (removal and magnetic particle inspection) has a terminal deadline "no later than 31 October 2009." Requirement 3 (replace defectives) must be satisfied "before further flight" after the effective date, and Requirement 4 (do not install unless inspected) applies "after the effective date." Operators must map those dates to maintenance schedules carefully; the AD does not offer a single master deadline. Misreading which deadline applies to which action is a likely operational error.
2. The AD mandates work "in accordance with" paragraphs of ISB 29-047 and APPH SBs that are not reproduced: The AD requires actions per paragraph 2C and 2D of ISB 29-047 and per APPH SB AIR91666-29-03, but it does not include the text of those paragraphs or the SBs. Compliance therefore requires obtaining and applying those external documents. Failure to retrieve and use the precise referenced revisions, or to confirm whether a later NAA-approved revision applies, will produce non-conformities.
3. The AD allows "later NAA approved revisions" but gives no process detail: The AD permits operators to use later NAA approved revisions of ISB 29-047 and APPH SB AIR91666-29-03. It does not state where or how to confirm whether a later revision has NAA approval. Operators must ensure they consult their NAA or the approval documentation for any revised SB used for compliance. Using an unapproved revision cannot be justified by the AD’s wording.
4. The identity of "a particular supplier" is not specified in the AD text: The Background states that "all cylinders from a particular supplier may not have been correctly inspected at manufacture." The AD, however, does not name that supplier in the text supplied. Identification of affected parts therefore depends on the ISB/SB procedures for batch or supplier traceability; if those procedures are ambiguous, operators may face difficulty determining whether a given accumulator is in scope.
5. "Serviceable unit" is not defined in the AD: The AD requires replacement with a "serviceable unit" when defects are found. The AD does not define that term. Operators must rely on their maintenance control documentation, the ISB/SBs, or accepted industry definitions to determine what constitutes a serviceable replacement.
6. Installation prohibition references multiple SBs and an ISB note for explanation: The AD’s "do not install" prohibition applies to accumulators identified by APPH SB AIR91666-29-03 unless inspected per APPH SB AIR91666-29-02 or AIR91666-29-03, and it points to the second Note in paragraph 1D(1) of ISB 29-047 for further explanation. The AD therefore layers cross-references that may be circular unless the referenced documents are read together. Operators who attempt to comply without reading the ISB note risk misunderstanding the conditions under which installation is permitted.
7. The AD’s effective date is later than the signature date: The AD was signed on 29 March 2007 but becomes effective on 10 May 2007. Operators must ensure they apply the "effective date" for calculating deadlines. Confusion between the signature date and effective date could cause missed compliance windows.
8. Recordkeeping expectations are not stated: The AD does not specify required records or retention periods for the identification, inspection and replacement steps. Operators must therefore ensure that documentation practices meet their own regulatory obligations beyond what this AD explicitly states. Lack of clear recordkeeping requirements in the AD does not relieve operators of the need to demonstrate compliance in the event of an audit.
9. The AD does not state alternative means of compliance: If an operator considers a different inspection method or repair technique, the AD contains no procedure within its text for approving such alternatives. The only permitted flexibility noted is to use later NAA-approved revisions of the referenced documents. Operators should therefore proceed on the basis that alternative techniques require formal NAA approval.

Each of these points follows from the AD’s text or its cross-references. Operators and maintainers should treat the AD as a directive that substitutes prescriptive reference documents for in-line technical detail; the operational risk is therefore concentrated in obtaining and correctly applying those referenced documents and meeting the disparate deadlines.

The AD supplies a practical, document-driven compliance pathway. The following step-by-step approach derives directly from the AD text and organises the required actions and timelines. Operators should follow the referenced ISB and SBs in detail; this checklist is a procedural rendering of the AD’s requirements and compliance dates.

1. Confirm applicability: Verify the aircraft is within scope. The AD’s Applicability states: "BAe 146 and AVRO 146-RJ aeroplanes - All models." If an aeroplane is in that class, proceed with the steps below.
2. Obtain the referenced documents: Secure copies of:
   • BAe Systems Inspection Service Bulletin (ISB) 29-047 dated 3 October 2006, and in particular paragraph 2C (identification) and paragraph 2D (removal).
   • APPH Ltd Service Bulletin (SB) AIR91666-29-03 dated July 2006 for the magnetic particle inspection procedure, and APPH SB AIR91666-29-02 where relevant for installation inspection requirements.
   • Any later NAA-approved revisions to those documents if available, as the AD permits the use of later NAA approved revisions. Confirm NAA approval status for any revision you intend to use.
3. Identification (Requirement 1; Compliance 1): Within six weeks after the AD effective date (calculate from 10 May 2007), identify installed hydraulic accumulators in accordance with paragraph 2C of ISB 29-047. That identification procedure will determine whether each accumulator is from the suspect supplier or batch described via the ISB/SB linkage. Ensure the identification process is documented in maintenance records.
4. If an accumulator is identified as affected, removal and inspection (Requirement 2; Compliance 2): For each accumulator identified as affected, remove it from service using the removal procedure in paragraph 2D of ISB 29-047 and perform a magnetic particle inspection of the cylinder per APPH SB AIR91666-29-03. The AD gives a final date of "no later than 31 October 2009" for this inspection step; however, operators should schedule removal and inspection promptly to avoid operational disruption and to ensure adherence to the AD’s staged requirements. Record inspection results and any defects found.
5. Replace defectives before flight (Requirement 3; Compliance 3): If any defects are detected during the magnetic particle inspection, replace the accumulator with a serviceable unit before further flight after the effective date of the AD. Ensure the replacement conformsto relevant maintenance release requirements and any acceptance standards in the ISB/SBs. Document the replacement and the serviceability determination.
6. Prohibition on installing uninspected accumulators (Requirement 4; Compliance 4): Do not install any accumulator identified by APPH SB AIR91666-29-03 on an aircraft unless it has been inspected in accordance with APPH SB AIR91666-29-02 or AIR91666-29-03. That prohibition begins "after the effective date of this AD." Consult the second Note in paragraph 1D(1) of ISB 29-047 for further explanation where required. Ensure supply-chain controls prevent inadvertent installation of uninspected parts.
7. Use of later NAA-approved revisions: Where later revisions of ISB 29-047 or the APPH SBs have been issued and have received NAA approval, those later revisions are permitted by the AD to be used for compliance. Confirm the NAA approval before using a later revision as the compliance basis.
8. Documentation and records: Although the AD does not prescribe specific recordkeeping intervals, retain inspection reports, removal and replacement records, parts traceability information (to show whether an accumulator was from the suspect supplier), and any NAA approval documentation for later SB revisions. Records will be the primary evidence of compliance if inspected or audited.
9. Liaise with suppliers and maintainers: Because the AD originates from a manufacturing inspection issue, liaise with the accumulator supplier(s), APPH if necessary, and BAe Systems for clarifications contained in the ISB/SBs. Where the supplier identity or batch traceability is ambiguous, coordinate with the parties listed in the ISB/SB to avoid mistaken acceptance or rejection of parts.
10. Operational planning: Because replacements for defective accumulators must occur before further flight, factor potential fleet downtime and parts lead times into operational planning. The AD provides differentiated deadlines; prioritise inspections on aircraft scheduled for imminent operations.
11. Seek clarification where necessary: The AD refers to the "second Note in paragraph 1D(1) of ISB 29-047 for further explanation" of the installation prohibition. If that note or any part of the referenced documents is unclear, seek clarification from BAe Systems, APPH, or the relevant NAA to ensure the intended scope and procedures are followed.

The AD’s structure makes compliance primarily about following specified paragraphs in the ISB and APPH SBs and observing the AD’s deadlines. The AD does not provide alternative means of compliance within the text supplied; therefore, any deviation from the specified procedures should be pursued only with formal NAA approval or other documented authorisation that the AD permits.