AD/B737/139 - Wire Bundle Chafing - Electric Motor Driven Hydraulic Pump

This Airworthiness Directive, AD/B737/139, issued under the Civil Aviation Regulations 1998, Part 39 and published as 3/2000, mandates a one-time detailed visual inspection of specific wire bundles and associated hydraulic hoses for the electric motor driven pump, EMDP, of hydraulic system "B" on certain Boeing 737 series aeroplanes. The AD distinguishes two groups of aircraft. For Model 737-300, -400 and -500 series the subject wire bundle is identified as W0334 and the relevant Boeing Alert Service Bulletin is 737-29A1076 (Requirements 1 to 3). For Model 737-600, -700 and -800 series the subject wire bundle is identified as W5230 and the ASB is 737-29A1077 (Requirements 4 to 6).

Mechanically, the AD requires operators to perform a one-time detailed visual inspection in accordance with either Part 1 or Part 2 of the Accomplishment Instructions in the relevant Boeing ASB, depending on whether an earlier ASB has already been accomplished for that aeroplane (see Requirements 1.a and 1.b; 4.a and 4.b). If any "discrepancy" is found during the inspection the operator must perform corrective actions in accordance with the corresponding Part of the ASB (Requirements 2, 3, 5 and 6). The AD sets compliance windows: the required inspections must be completed within 90 days of the AD effective date; where corrective action is necessary the AD requires those corrective actions to be completed prior to further flight (Compliance section).

The AD also contains a defined scope for the inspection. Note 1 provides a definition of "detailed visual inspection" that specifies the intensity of examination, lighting, and use of aids, and permits surface cleaning and access procedures where necessary. The AD becomes effective on 23 March 2000 and explicitly references Boeing ASB revision dates and the FAA AD 99-26-21 Amdt 39-11480 (Notes and Background). The Background describes the manufacturer's report of chafing of the wire bundle to Hydraulic System B EMDP and states the AD's intended preventative outcome as the prevention of electrical arcing and consequent fire risk caused by such chafing.

The AD revolves around a small set of operationally concrete concepts: the identification of specific aircraft models and wire bundle part numbers, a one-time inspection obligation, conditional corrective actions tied to the Boeing ASB Accomplishment Instructions, and defined compliance timing. The central risk identified in the source material is physical chafing of the electrical wire bundle adjacent to the hydraulic case drain and pressure hoses for the EMDP of hydraulic system B. The AD describes the hazard as causing electrical arcing with a subsequent risk of fire (Background). The AD treats discovery of any "discrepancy" as requiring action; the examples given in the AD for a discrepancy include damage, chafing, and incorrect separation between the wire bundle and the hydraulic hoses (Requirements 1 and 4).

The ASB-based structure: the AD does not itself provide technical corrective steps. Instead it mandates adherence to Boeing Alert Service Bulletins as the source of inspection and corrective procedures. The AD instructs operators to follow Part 1 of the ASB if the earlier ASB was not previously accomplished, or Part 2 if it was (Requirements 1.a/b and 4.a/b). The AD specifically cites Boeing ASB 737-29A1076 Revision 1 dated 21 October 1999 for the -300/-400/-500 group and Boeing ASB 737-29A1077 Revision 1 dated 21 October 1999 for the -600/-700/-800 group. The AD also notes (Note 2) the corresponding FAA AD for cross-reference.

Inspection scope and standard: Note 1 defines a "detailed visual inspection" as an intensive examination targeting a specific area, supplemented lighting, and the use of inspection aids such as mirrors and magnifying lenses. It allows surface cleaning and "elaborate access procedures" where necessary. This definition shapes both the expected time and technical means required for compliance because it permits actions beyond a cursory visual check and signals that inspections may require removal of panels, cleaning, or use of inspection tools.

Temporal constraints and operational effect: The compliance terms split tasks into two time buckets. The primary inspections must be completed within 90 days of the AD effective date (Compliance). Any corrective action identified by those inspections must be completed "prior to further flight" (Requirements 2, 3, 5, 6; Compliance). That structure means that while the inspection itself can be scheduled within the 90-day window, any aircraft where a discrepancy is found cannot depart on a subsequent flight until the corrective actions specified by Boeing's ASB are carried out. The AD therefore imposes a conditional, immediate operational constraint in the event of detected defects.

The AD explicitly applies to specific Boeing 737 model series as enumerated in the Applicability clause and referenced Boeing ASBs. That list covers Model 737-300, -400 and -500 series aeroplanes as listed in Boeing ASB 737-29A1076, Revision 1 dated 21 October 1999, and Model 737-600, -700 and -800 series aeroplanes as listed in Boeing ASB 737-29A1077, Revision 1 dated 21 October 1999 (Applicability). The AD language ties applicability to the aircraft "as listed in" the relevant Boeing ASB, so the cohort affected is those individual aircraft specified in those ASB lists.

Primary responsibility sits with the operator of each applicable aeroplane. The operator must ensure the one-time detailed visual inspection is performed for that aeroplane in accordance with the correct Part of the Boeing ASB, within the 90-day compliance window, and must ensure any corrective action required is completed prior to further flight (Requirements 1 to 6; Compliance). Maintenance organisations that conduct the inspection and corrective work will be operationally affected. The AD requires adherence to the Accomplishment Instructions in the ASBs, so technicians and maintenance supervisors must consult those documents to perform the tasks and corrective procedures in the manner Boeing prescribes (Requirements and Parts reference).

Regulatory decision-makers: The Civil Aviation Safety Authority is the issuing authority as shown by the heading identifying the AD as part of the Schedule of Airworthiness Directives under the Civil Aviation Regulations 1998, Part 39. The AD also references Boeing as the source of the ASBs. Aircraft owners, operators and maintenance organisations therefore face a dual interface: the regulatory imposition of the AD by CASA and the technical methods provided by Boeing's ASBs.

Timing stakeholders: Since corrective action, if required, must be completed prior to further flight, flight operations and scheduling are affected if a discrepancy is found. An aircraft that fails the inspection cannot be dispatched until the corrective measures in the ASB are implemented. The AD establishes a precise operational consequence that ties technical maintenance decisions to flight dispatch.

Other affected parties: The AD references the FAA AD 99-26-21 but does not make that AD a compliance tool; rather it is listed as a reference (Note 2). The presence of that FAA AD suggests alignment with foreign regulator action, but the AD itself binds only those aircraft specified and the operators responsible for them under Australian regulatory requirements.

Duties

• Perform a one-time detailed visual inspection: For each applicable aeroplane, the operator must perform a one-time detailed visual inspection of the specified wire bundle and the hydraulic case drain and pressure hoses for the EMDP of hydraulic system B. The content and method of that inspection are set out in the relevant Boeing ASB Accomplishment Instructions, Part 1 or Part 2 depending on prior accomplishment status (Requirements 1.a, 1.b, 4.a, 4.b).

• Select the correct ASB Part based on prior accomplishment: The AD requires different Parts of the ASB depending on whether an earlier edition of the ASB (Boeing ASB dated 2 April 1998 for 737-29A1076 or Boeing ASB dated 4 March 1999 for 737-29A1077) has been previously accomplished. If the earlier ASB has not been accomplished the operator follows Part 1; if it has been accomplished the operator follows Part 2 (Requirements 1.a/b and 4.a/b).

• Carry out corrective actions where discrepancies are found: If the inspection reveals any discrepancy, the operator must perform corrective actions in accordance with the corresponding Part of the ASB (Requirements 2, 3, 5, 6). The AD defers to Boeing's Accomplishment Instructions for the content of the corrective actions.

• Meet timing obligations: The inspections are required to be completed within 90 days of the AD effective date. Any corrective action identified must be completed prior to further flight (Compliance).

Rights and procedural features

• Prescribed inspection definition: The AD provides a specific definition of what constitutes a "detailed visual inspection" (Note 1). That definition gives the inspecting technician a standard to follow (an "intensive" examination, with supplemental lighting and inspection aids, allowing surface cleaning and elaborate access procedures). The definition shapes how an inspector demonstrates that they have complied with the inspection obligation.

• Reliance on Boeing ASB for technical steps: The AD delegates the technical detail of both the inspection process and the corrective actions to the Boeing ASBs. Operators therefore have the right to follow the ASB instruction set as the compliance mechanism specified by the AD. In practice the ASB forms the technical prescription the AD enforces.

• Conditional routing based on prior work: Operators who have previously accomplished the older ASB are directed to a different Part of the current ASB. The AD thereby recognises prior compliance steps and provides a procedural pathway for them, rather than mandating full repetition of earlier steps.

The AD text itself does not specify criminal or civil penalties, fines, or administrative sanctions for non-compliance. It does, however, set mandatory compliance actions and deadlines: inspections within 90 days of the AD effective date and corrective action "prior to further flight" where discrepancies are found (Compliance; Requirements 2, 3, 5, 6). The AD is published under the heading COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39, Schedule of Airworthiness Directives, indicating it is an instrument within the regulatory framework of the Civil Aviation Regulations 1998, Part 39.

Enforcement mechanism implicit in the document

• Regulatory instrument status: Because the AD is issued under Civil Aviation Regulations 1998 Part 39, compliance obligations arise from that regulatory regime. The AD sets binding inspection and corrective obligations but does not include an adjudicative or sanctions clause in the text provided. Enforcement of an AD generally operates through the relevant aviation regulator's powers under the enabling regulations; the AD document itself does not recite those enforcement powers.

• Operational enforcement: The AD’s requirement that corrective actions be completed prior to further flight creates an operational enforcement mechanism. If a maintenance organisation or operator permits an aircraft to fly with an unresolved discrepancy identified under this AD, the aircraft will be non-compliant with the AD’s explicit "prior to further flight" requirement and consequently with the regulatory instrument. The text does not list penalties but sets an unambiguous affirmative duty whose breach would be a regulatory non-compliance under Part 39.

• Documentation and oversight: The AD binds operators to follow Boeing ASB Accomplishment Instructions. While the AD does not state record-keeping requirements, compliance with ADs is commonly demonstrated through maintenance records and flight release documentation. The AD does not itself detail the documentary proof required; it only prescribes the actions and timelines.

Reference to other regulators: Note 2 refers to FAA AD 99-26-21 Amdt 39-11480. That cross-reference indicates parallel regulatory action elsewhere but does not change the enforcement or penalty text in this AD.

In summary, the AD creates mandatory duties and tight operational deadlines but does not list penalties in its text. Enforcement will therefore depend on the regulatory framework and powers established by the Civil Aviation Regulations 1998 and on operational controls that prevent flight with unresolved discrepancies, as the AD requires.

The AD is presented within the regulatory framework of the Civil Aviation Regulations 1998, Part 39 and the document heading identifies it as part of the Schedule of Airworthiness Directives issued by the Civil Aviation Safety Authority. Thus the AD is a regulatory instrument that operates in that statutory/regulatory environment. The AD explicitly references and binds operators to Boeing Alert Service Bulletins, making the ASBs the technical method of compliance under the regulatory instrument.

Interaction with manufacturer documentation: The AD does not create new technical procedures; it deems compliance achieved by following the Accomplishment Instructions in the cited Boeing ASBs (737-29A1076 Revision 1 and 737-29A1077 Revision 1 dated 21 October 1999). This means that the AD functions as a legal requirement referencing an external technical document. Operators must therefore reconcile regulatory obligations and the ASB's content: the AD prescribes the legal duty, the ASB supplies the technical steps to meet that duty.

Interaction with foreign regulator instruments: Note 2 specifically refers to FAA AD 99-26-21 Amdt 39-11480. The AD thereby signals a cross-reference to a corresponding FAA action. The AD itself, however, remains an instrument issued under the Commonwealth regulations and binds Australian operators as set out in this AD. The AD does not purport to enforce the FAA AD or to be enforced by FAA processes; it simply references the FAA action.

Complementarity with maintenance and airworthiness obligations: The AD’s inspection and corrective action requirements operate alongside other airworthiness and maintenance responsibilities that operators have under the Civil Aviation Regulations and applicable continuing airworthiness rules. The AD imposes a one-time inspection and potential corrective action with definitive timing (90 days and prior to further flight). The AD does not specify how it interacts or is prioritised with routine scheduled maintenance tasks; the text provided does not include transitional provisions or explicit instructions on coordination with maintenance schedules. Operators must therefore place the AD's time-limited requirements into their existing maintenance planning to ensure compliance within the AD’s windows.

Delegation and technical compliance: The AD delegates technical detail to Boeing’s ASB, creating a legal-technical interplay: the regulator prescribes the obligation and the manufacturer prescribes how to discharge it. The AD does not modify or extend the ASB beyond making the ASB’s Parts the required method to address the identified risk for the specified aircraft.

The AD itself is dated 3/2000 and states that it "becomes effective on 23 March 2000." The AD references specific Boeing Alert Service Bulletins and dates which form part of its instruction set:

• Boeing ASB 737-29A1076: The AD refers to Boeing ASB 737-29A1076 dated 2 April 1998 and to Boeing ASB 737-29A1076, Revision 1, dated 21 October 1999. The AD directs operators that where the earlier 2 April 1998 ASB has been accomplished they should follow Part 2 of Revision 1; where it has not been accomplished they should follow Part 1 of Revision 1 (Requirements 1.a and 1.b; Requirement 2 and 3 reference Part 1 and Part 2 corrective actions respectively).

• Boeing ASB 737-29A1077: For the -600/-700/-800 series, the AD refers to Boeing ASB 737-29A1077 dated 4 March 1999 and to Boeing ASB 737-29A1077, Revision 1, dated 21 October 1999. The AD sets the same structure: if the earlier ASB dated 4 March 1999 has not been accomplished the operator follows Part 1 of Revision 1; if it has been accomplished the operator follows Part 2 (Requirements 4.a and 4.b; Requirements 5 and 6 reference Part 1 and Part 2 corrective actions respectively).

• FAA cross-reference: Note 2 cites FAA AD 99-26-21 Amdt 39-11480 as a related or corresponding action.

The AD document does not itself record prior amendments to the AD (for example, it does not show earlier versions of this AD). It is presented as AD/B737/139, issued as 3/2000 with the stated effective date. The AD’s internal routing between ASB Part 1 and Part 2 depending on prior accomplishment effectively recognises and accommodates earlier Boeing service guidance. The AD does not, in the text provided, include later amendments, superseding directives, revocation, or other changes to AD/B737/139 itself beyond those references. Any later amendments or supersessions are not contained within this document.

The AD’s reliance on specific ASB revision dates is central to its operative content. Operators need to follow the cited Revision 1 of the ASBs dated 21 October 1999 and to check their aircraft records for whether earlier ASB editions (2 April 1998 for 737-29A1076 and 4 March 1999 for 737-29A1077) were accomplished. The AD provides distinct compliance paths based on that prior history.

The AD text supplied does not reference any litigation, appeals, or judicial determinations relating to this directive. It does not name any court decisions or legal challenges, nor does it cite administrative appeals under the Civil Aviation Regulations. The document contains only the regulatory requirement, the ASB references, compliance times, notes (including the definition of a detailed visual inspection), and the Background statement identifying the manufacturer’s report of chafing and the AD’s intended prevention of electrical arcing and fire risk.

Because the document does not provide any litigation record, neither specific cases nor outcomes can be cited from the AD itself. If an operator disputes an AD or seeks review, the AD does not outline appeal routes or judicial remedies in its text; the AD simply imposes the inspection and corrective duties and supplies the dates and technical references. Any litigation arising from compliance disputes, enforcement actions, or interpretation of the AD would not be reflected in the AD document unless expressly noted; there are no such notes in the source provided.

• Model and wire-bundle specificity: The AD applies only to aeroplanes "as listed" in the cited Boeing ASBs. The wire bundle identifiers differ by model group: W0334 for 737-300/-400/-500 and W5230 for 737-600/-700/-800 (Applicability; Requirements). Operators must confirm that a specific airframe appears on the ASB list. Assuming applicability on model series alone risks misapplication if an aircraft is not listed in the ASB.

• Dependence on prior ASB accomplishment status: The AD creates two different inspection procedures depending on whether an earlier ASB was previously accomplished. Operators must determine, from maintenance records, whether Boeing ASB 737-29A1076 dated 2 April 1998 (for -300/-400/-500) or Boeing ASB 737-29A1077 dated 4 March 1999 (for -600/-700/-800) was previously accomplished. If records are unclear, the AD instructs following the appropriate Part of Revision 1; misclassification can lead to following the wrong Part and potential non-compliance.

• One-time inspection with immediate grounding if defects found: The AD prescribes a one-time detailed visual inspection within 90 days, but any corrective action identified must be completed prior to further flight. That requirement means that discovery of a discrepancy creates an immediate operational constraint: the aircraft must be grounded until the ASB-prescribed corrective action is completed. Operators who schedule the inspection near the end of the 90-day window may face increased operational disruption if defects are found.

• Definition of "detailed visual inspection" allows significant scope: Note 1 permits supplemental lighting, mirrors, magnifying lenses, surface cleaning and "elaborate access procedures". In practice that could require removal of panels, cleaning of routed harnesses, or use of inspection aids. Operators who plan only a superficial inspection risk non-compliance; inspection planning should account for potentially extensive access work.

• Reliance on Boeing ASBs for corrective content: The AD requires corrective actions in accordance with the ASB Parts. The AD does not summarise those corrective actions. Compliance therefore requires access to and strict adherence to the relevant Boeing ASB Revision 1 Accomplishment Instructions. Failure to follow the ASB's exact corrective steps or to document that the ASB steps were performed could create compliance gaps.

• Timing and record ambiguities: The AD requires actions within 90 days and corrective work prior to further flight but does not set out record-keeping or reporting detail in the text provided. Operators must rely on their regulatory duties under the Civil Aviation Regulations and on standard maintenance documentation practices to demonstrate compliance. The AD’s text does not itself specify what documentary evidence the regulator will accept.

Stepwise, from the AD text:

1. Determine applicability: Confirm whether each aeroplane is listed in the relevant Boeing ASB for its model series. The AD’s Applicability ties affected aeroplanes to the lists in Boeing ASB 737-29A1076 Revision 1 (for 737-300/-400/-500) and Boeing ASB 737-29A1077 Revision 1 (for 737-600/-700/-800) (Applicability).

2. Check prior ASB accomplishment status: For each applicable aeroplane, check maintenance records to determine whether the earlier ASB (737-29A1076 dated 2 April 1998 for the -300/-400/-500 group, or 737-29A1077 dated 4 March 1999 for the -600/-700/-800 group) has already been accomplished. This determination dictates whether you must follow Part 1 or Part 2 of the Revision 1 ASB (Requirements 1.a/b and 4.a/b).

3. Schedule the inspection within the regulatory window: Arrange for the one-time detailed visual inspection to be performed within 90 days of the AD effective date (Compliance). Because the inspection may require supplemental lighting, inspection aids, surface cleaning and elaborate access (Note 1), plan for adequate labour, tooling and access time.

4. Perform the inspection per the ASB Accomplishment Instructions: Conduct the inspection in strict accordance with the relevant Part (Part 1 or Part 2) of the Accomplishment Instructions in Boeing ASB 737-29A1076 Revision 1 (for W0334) or Boeing ASB 737-29A1077 Revision 1 (for W5230). Use the "detailed visual inspection" standard set out in Note 1 as the operative definition of the inspection technique and scope.

5. Assess and document any discrepancy: The AD identifies typical discrepancies as damage, chafing, or incorrect separation between the wire bundle and hydraulic hoses (Requirements 1 and 4). If a discrepancy is found, follow the ASB to determine the precise corrective action. Document the discrepancy, the ASB procedures followed, and the corrective steps taken.

6. Complete corrective action before further flight: If the inspection uncovers a discrepancy, perform corrective actions in accordance with the corresponding ASB Part and ensure that those corrective actions are completed prior to the next flight of the aeroplane (Requirements 2, 3, 5, 6; Compliance). Ensure that maintenance release procedures reflect that the corrective actions are complete and that the aircraft is airworthy to return to service.

7. Maintain maintenance records as evidence of compliance: The AD does not specify record-keeping requirements in its text. Nonetheless, operators should contemporaneously record the inspection, findings, ASB part followed, any corrective actions performed, and the personnel who performed the work. That documentation will demonstrate compliance with the AD’s requirements and with normal regulatory maintenance record obligations.