{"id":"F2006B02930","name":"AD/B737/234 - Pylon Sealing","slug":"ad-b737-234-pylon-sealing","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":42272,"registerId":"commonwealth-F2006B02930-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/B737/234 Pylon Sealing 1/2005","sectionType":"part","heading":"AD/B737/234 Pylon Sealing 1/2005","content":"# AD/B737/234 Pylon Sealing 1/2005\n\nApplicability: Model 737-600, \\-700, \\-700C, \\-800, and \\-900 series aeroplanes, line numbers 1\n\nthrough 946 inclusive.\n\nRequirement: 1. Perform a general visual inspection for sealant at the interface of the diagonal brace fitting and the aft bulkhead and at the four bolts common to the interface, in accordance with the Accomplishment Instructions of Boeing Special Attention Service Bulletin 737-54-1039, Revision 1, dated 10 October 2002.\n\n    (a) If the findings of the general visual inspection are as described in paragraphs (1)(a)(i) and (1)(a)(ii) of this Directive, then no further action is required by this Directive.\n\n    (i) The seal is continuous or there is evidence of fay seal squeeze out present.\n\n    (ii) The bolts have evidence of sealant squeeze out or a cap seal exists.","sortOrder":1},{"sectionNumber":"Application of Fillet Seal","sectionType":"part","heading":"Application of Fillet Seal","content":"## Application of Fillet Seal\n\n    (b) The seal is not continuous and there is no evidence of fay seal squeeze out present, fillet seal around the interface of the diagonal brace fitting and the aft bulkhead, in accordance with the Accomplishment Instructions of Boeing Special Attention Service Bulletin 737-54-1039 Revision 1.","sortOrder":2},{"sectionNumber":"Application of Cap Seal","sectionType":"part","heading":"Application of Cap Seal","content":"## Application of Cap Seal\n\n    (c) If the bolts do not have evidence of sealant squeeze out and no cap seal exists, cap seal the four bolts common to the interface, in accordance with the Accomplishment Instructions of Boeing Special Attention Service Bulletin 737-54- 1039, Revision 1.\n\nNote: FAA AD 2004-22-27 Amdt 39-13855 refers.\n\nCompliance: For Requirement 1: Unless previously accomplished, within 18 months or 3,500 flight cycles after the effective date of this Directive, whichever occurs first:\n\nFor Requirement 1(b) and 1(c): Before further flight.","sortOrder":3},{"sectionNumber":"Boeing 737 Series Aeroplanes","sectionType":"part","heading":"Boeing 737 Series Aeroplanes","content":"## Boeing 737 Series Aeroplanes\n\nAD/B737/234 (continued)\n\nThis Airworthiness Directive becomes effective on 20 January 2005.\n\nBackground: This Directive requires a general visual inspection for sealant at the interface between the diagonal brace fitting and the aft bulkhead and at the four bolts common to the interface. It also requires applying sealant if none is present or if it is not continuous. This action is necessary to prevent flammable fluid in the upper or rear pylon areas from leaking past unsealed areas and onto a hot engine nozzle, which could result in ignition of the fluid, causing an undetected and uncontrollable fire to spread into the engine struts. This action is intended to address the identified unsafe condition.\n\n![Signature of James Coyne, Delegate of the Civil Aviation Safety Authority.](image.002.png)  \n\nJames Coyne\n\nDelegate of the Civil Aviation Safety Authority 1 December 2004\n\n![](image.001.png)  \n\nThe above AD is notified in the Commonwealth of Australia Gazette on 22 December 2004.","sortOrder":4}],"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"},"flash_summary":{"complexity_score":2,"scope_assessment":{"changed":false,"description":"The AD's scope matches the stated safety problem in the Background: it requires inspection and sealing at a specific structural interface to prevent flammable fluid migration and ignition. There is no text in the instrument expanding or narrowing that safety focus beyond the listed models/line numbers and the remedial actions set out (Applicability; Requirement; Background)."},"complexity_factors":["Narrow applicability to specific Boeing 737 variants and line numbers reduces operational scope (Applicability).","Single, non-destructive action: a general visual inspection and application of fillet or cap seal where absent (Requirement).","Clear compliance timetable with both a long-stop deadline (18 months or 3,500 flight cycles) and an immediate ‘before further flight’ remediation for missing sealant (Compliance).","Dependency on external technical instructions (Boeing Special Attention Service Bulletin 737-54-1039 Rev 1) and reference to FAA AD 2004-22-27, introducing implementation reliance on a service bulletin (Requirement / Note).","Safety-critical consequence raises prioritisation and potential scheduling pressure for operators and maintenance providers (Background).","Modest material and labour cost per aircraft (sealant application), but aggregate cost scales with fleet size and scheduling constraints."],"plain_english_summary":"This AD requires operators of Boeing 737-600/700/700C/800/900 (line numbers 1–946) to visually inspect the sealant at the diagonal-brace-fitting / aft-bulkhead interface and at the four common bolts, and to apply fillet or cap seal where sealant is missing. Compliance must follow Boeing Special Attention Service Bulletin 737-54-1039 Rev 1, within 18 months or 3,500 flight cycles, but any missing sealant found on an in-service aeroplane must be corrected before further flight. The stated aim is to prevent flammable fluid reaching a hot engine nozzle and causing fire."},"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 condition (potential fire risk from unsealed pylon joints) on specific Boeing 737 variants. The requirements remain tightly focused on the inspection and sealing task without expansion into unrelated maintenance areas."},"complexity_factors":["Single, clearly defined applicability (5 specific Boeing 737 models, line numbers 1–946)","Straightforward conditional logic: inspection → if/then branching to three outcomes (no action, fillet seal, or cap seal)","References to external technical document (Boeing Service Bulletin 737-54-1039 Rev 1) without reproducing its contents","Simple compliance timeline with two alternative triggers (time or flight cycles)","No nested definitions, no interpretation section, no cross-references to other legislation beyond a note about the corresponding FAA directive","Total length: approximately 1 page of substantive requirements"],"plain_english_summary":"This CASA safety order requires operators of Boeing 737-600/700/700C/800/900 aircraft (line numbers 1–946) to inspect and, if needed, reseal the joint in the engine pylon where diagonal brace fittings meet the aft bulkhead. It aims to stop fuel/oil leaking onto hot engine parts and prevent undetected strut fires, with inspections and corrective sealing mandated within a set compliance window."}},"importantCases":[],"_links":{"self":"/api/acts/ad-b737-234-pylon-sealing","history":"/api/acts/ad-b737-234-pylon-sealing/history","analysis":"/api/acts/ad-b737-234-pylon-sealing/analysis","conflicts":"/api/acts/ad-b737-234-pylon-sealing/conflicts","importantCases":"/api/acts/ad-b737-234-pylon-sealing/important-cases","documents":"/api/acts/ad-b737-234-pylon-sealing/documents"}}