{"id":"F2006B02923","name":"AD/B737/227 - Electrical Bonding","slug":"ad-b737-227-electrical-bonding","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":42265,"registerId":"commonwealth-F2006B02923-current","compilationNumber":null,"startDate":"2026-04-01","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"AIRWORTHINESS DIRECTIVE","sectionType":"part","heading":"AIRWORTHINESS DIRECTIVE","content":"# ![](image.001.png)  \nAIRWORTHINESS DIRECTIVE\n\nFor the reasons set out in the background section, the CASA delegate whose signature appears below issues the following Airworthiness Directive (AD) under subregulation 39.1 (1) of CASR 1998. The AD requires that the action set out in the requirement section (being action that the delegate considers necessary to correct the unsafe condition) be taken in relation to the aircraft or aeronautical product mentioned in the applicability section: (a) in the circumstances mentioned in the requirement section; and (b) in accordance with the instructions set out in the requirement section; and (c) at the time mentioned in the compliance section.\n\n![](image.001.png)  \n\nBoeing 737 Series Aeroplanes","sortOrder":0},{"sectionNumber":"AD/B737/227 Electrical Bonding 8/2004","sectionType":"part","heading":"AD/B737/227 Electrical Bonding 8/2004","content":"# AD/B737/227 Electrical Bonding 8/2004\n\nApplicability: Model 737-100, -200, -200C, -300, -400 and -500 series aeroplanes as listed in Boeing Alert Service Bulletin (ASB) 737-29A1096 Revision 1 dated 31 July 2003.\n\nRequirement: 1. Prepare the electrical bonding faying surfaces for the tubing penetrations of the hydraulic heat exchanger on the forward and aft surfaces of the rear spars of the fuel tanks of the left and right wings, together with carrying out a one-time measurement of the electrical bonding resistances between the penetration fittings of the hydraulic heat exchanger and the rear spars; and between the heat exchanger tube and the lower wing stringer surfaces, per the Accomplishment Instructions of ASB 737-29A1096 Revision 1.\n\n    2. If the bonding resistance is incorrect, repeat the preparation of the electrical bonding faying surface for the tubing penetrations of the hydraulic heat exchanger on the forward and aft surfaces of the rear spar of the fuel tanks of the left and right wings as necessary to achieve a bonding resistance below the threshold specified in the Accomplishment Instructions of ASB 737-29A1096 Revision 1.\n\n    3. Apply fillet sealant and protective finishes around the penetration fittings of the hydraulic heat exchanger in accordance with the Accomplishment Instructions of ASB 737-29A1096 Revision 1 (Figure 8 refers).\n\n    4. Service and pressurize the hydraulic systems and examine for signs of hydraulic fluid leakage. Service the fuel tank and examine for signs of fuel leakage. All these actions are to be accomplished in accordance with ASB 737-29A1096 Revision 1.\n\n    5. Repair any leaks found, during the Requirement 4 examination, in accordance with ASB 737-29A1096 Revision 1.\n\nActions accomplished before the effective date of this Directive in accordance with Boeing ASB 737-29A1096, dated 7 June 2001, are considered acceptable for compliance with the corresponding action specified in this Directive.\n\nNote: FAA AD 2004-10-06 Amdt 39-13636 refers.\n\nCompliance: For Requirement 1 \\- Within 60 months after the effective date of this Directive.","sortOrder":1}],"analysis":{"flash_summary_failed":{"failed":true,"reason":"A positive credit balance is required for all requests, including BYOK, so fallback providers remain available. Add credits at https://vercel.com/d?to=%2F%5Bteam%5D%2F%7E%2Fai%3Fmodal%3Dtop-up to continue.","source":"analysis-cron"},"kimi_summary":{"content_quality":"ok","complexity_score":3,"scope_assessment":{"changed":false,"description":"This Airworthiness Directive maintains its original narrow scope — addressing a specific unsafe electrical bonding condition in Boeing 737 hydraulic heat exchanger installations. It has not expanded beyond this technical safety issue."},"complexity_factors":["Single technical subject matter (electrical bonding of specific component)","Only 5 numbered requirements with clear sequential logic","Heavy reliance on external technical document (Boeing ASB 737-29A1096 Revision 1) for detailed instructions — the directive itself does not contain the full procedural details","One cross-reference to FAA AD 2004-10-06","Limited defined terms (only standard aviation terminology like 'faying surfaces' which is explained through context)","Simple conditional structure (Requirement 2 only triggers 'if' bonding resistance is incorrect)","Single compliance timeframe (60 months)"],"plain_english_summary":"This CASA safety order requires operators of older Boeing 737 series (-100 through -500) to inspect and restore electrical bonding for hydraulic heat‑exchanger tubes that pass through wing fuel‑tank areas, then seal and protect the fittings and confirm no hydraulic or fuel leaks.  \n\nIt must be completed within 60 months to eliminate spark/fire/explosion risk from poor bonding in the fuel tank area."},"flash_summary":{"complexity_score":4,"scope_assessment":{"changed":false,"description":"This AD largely implements and enforces the procedures and thresholds contained in Boeing ASB 737-29A1096 Revision 1; it does not expand the technical scope beyond the ASB. The AD accepts prior compliance performed in accordance with the earlier Boeing ASB dated 7 June 2001, so it does not broaden obligations relative to the manufacturer’s corrective actions — it formalises and mandates those actions for Australian operators without adding substantial new requirements beyond what the ASB prescribes."},"complexity_factors":["Single aircraft family (Boeing 737 −100 to −500) — limited applicability","Direct reference to an external technical document (Boeing ASB 737-29A1096 Revision 1) that contains key thresholds and procedures","A small number of conditional steps (measure resistance, repeat preparatory work if above threshold)","One compliance deadline explicitly stated (60 months for Requirement 1)","Acceptance clause for actions done under an earlier ASB (Boeing ASB dated 7 June 2001) — creates a backward-compatibility exception","Operational complexity due to fuel-tank access, hydraulic system pressurisation and leak testing (safety/procedural complexity lies outside the AD text in the ASB)"],"plain_english_summary":"**What this directive does (mechanics)\n\n- Applies to: Boeing 737 series −100, −200, −200C, −300, −400 and −500 aeroplanes listed in Boeing Alert Service Bulletin (ASB) 737-29A1096 Revision 1 (see \"Applicability\").\n\n- Requires maintenance work on the hydraulic heat exchanger penetrations that pass through the rear spars of the left and right wing fuel tanks. The key steps (Requirement 1–5) are:\n  - Prepare the electrical bonding faying surfaces around the tubing penetrations of the hydraulic heat exchanger on the forward and aft surfaces of the rear spars, and make a one-time measurement of the electrical-bonding resistances between specific fittings and structure (Requirement 1).\n  - If the measured bonding resistance is above the allowed threshold in the Boeing ASB, repeat the preparation work until the bonding resistance is below the threshold (Requirement 2).\n  - Apply fillet sealant and protective finishes around the penetration fittings as shown in the ASB (Requirement 3).\n  - Service and pressurize the hydraulic systems and inspect for hydraulic leaks; service the fuel tank and inspect for fuel leaks (Requirement 4).\n  - Repair any leaks found during the inspections in accordance with the ASB (Requirement 5).\n\n- Compliance timing: The primary measurement and preparation in Requirement 1 must be done within 60 months of the effective date of the Directive. The AD accepts equivalent actions already completed in line with the earlier Boeing ASB dated 7 June 2001.\n\n- The AD is issued to require operators to carry out the work specified in Boeing ASB 737-29A1096 Revision 1 (the AD refers operators to the ASB for detailed procedures).\n\n\nWhy CASA (the issuing authority) says this matters\n\n- The directive is issued to correct an identified unsafe condition related to electrical bonding and penetration fittings near fuel tanks and hydraulic heat exchangers. The AD itself points operators to the Boeing ASB for the technical justification (the AD references FAA AD 2004-10-06 as related material).\n\n\nPlain-language notes and practical consequences\n\n- \"Electrical bonding\" here means ensuring a good electrical connection between metal parts so they sit at the same electrical potential (reduces the chance of arcing or ignition sources from potential differences).\n- \"Faying surfaces\" are the mating surfaces where two parts meet; preparing them typically means cleaning, removing coatings or corrosion, and creating an uncoated, conductive surface for bonding.\n- Who pays: aircraft owners/operators pay for the inspections, measurements, any rework, sealant application, leak repairs, and associated labour and out-of-service time (Requirement 1–5).\n- Who decides how to do the work: maintenance providers must follow the procedures and thresholds set out in Boeing ASB 737-29A1096 Revision 1; an approved maintenance organisation (or other appropriately approved person) will carry out the tasks.\n- Operational effect: the work requires access to the rear spar/fuel tank area, electrical resistance measurement equipment and qualified personnel. It can require fuel-tank access and hydraulic system pressurisation, with attendant safety procedures and potential aircraft downtime.\n\n\nAssessment of incentives, costs, trade-offs and implementation issues (analyst’s lens)\n\n- Costs and incentives: the direct costs are labour, materials (sealants, finishes), measurement equipment and possible repairs. These are borne by the aircraft operator. The benefit is risk reduction (electrical bonding below the specified threshold and reduced risk of electrical sources near fuel) as defined by Boeing/CASA.\n- Compliance burden: following the ASB is prescriptive; operators must obtain and follow the ASB instructions, and demonstrate measurements meet the ASB thresholds. Measurement thresholds and detailed procedures are in the ASB, not repeated in the AD; that creates a dependency on the external Boeing document.\n- Implementation risk and opportunity cost: work requires qualified maintenance personnel and may require tank entry procedures and system pressurisation steps that increase complexity and grounding time. If bonding preparation is repeated to achieve resistance thresholds, that can increase labour and potentially remove protective coatings, which may require additional corrosion protection steps.\n- Effects on private enterprise and competition: independent approved maintenance organisations (AMOs) can perform the work if they are approved to follow the ASB procedures. The AD does not on its face restrict who may perform the work, but compliance requires access to the ASB procedures and test equipment. The requirement may increase maintenance costs for operators of affected 737 variants but does not alter ownership, operating certificates, or market structure.\n- Concentrated benefits vs diffuse costs: benefits of improved bonding (safety) accrue to operators, passengers and regulators; costs are concentrated on operators and maintenance providers.\n- Bureaucratic discretion: the AD is prescriptive and references Boeing's ASB for specific methods and thresholds; regulatory discretion primarily lies in acceptance of alternative methods if individually approved (standard AD practice), but the AD itself requires following the ASB instructions.\n\n\nWhere to look in the directive\n\n- Applicability: which aeroplanes are covered.\n- Requirement 1–5: the sequence of preparation, measurement, rework, sealing, system pressurisation/inspection, and repair.\n- Compliance: 60 months for Requirement 1; earlier compliance in line with Boeing's 2001 ASB is accepted.\n\n\nBottom line (concise): The AD mandates that operators of specified older Boeing 737 variants prepare and test electrical bonding at hydraulic-heat-exchanger penetrations through the rear spars of wing fuel tanks, fix any bonding failures, seal and finish the penetrations, and check and repair any hydraulic or fuel leaks — all in accordance with Boeing ASB 737-29A1096 Revision 1. The operator bears the cost and must use qualified maintenance procedures and equipment; the AD prescribes outcomes (bonding below a threshold and no leaks) rather than offering a wide range of alternative methods except by following the ASB or obtaining specific approval."}},"importantCases":[],"_links":{"self":"/api/acts/ad-b737-227-electrical-bonding","history":"/api/acts/ad-b737-227-electrical-bonding/history","analysis":"/api/acts/ad-b737-227-electrical-bonding/analysis","conflicts":"/api/acts/ad-b737-227-electrical-bonding/conflicts","importantCases":"/api/acts/ad-b737-227-electrical-bonding/important-cases","documents":"/api/acts/ad-b737-227-electrical-bonding/documents"}}