{"id":"F2009L01843","name":"AD/B737/235 Amdt 1 - Fuselage Skin Area at the Dorsal Fin Assembly","slug":"ad-b737-235-amdt-1-fuselage-skin-area-at-the-dorsal-fin-assembly","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":78851,"registerId":"commonwealth-F2009L01843-current","compilationNumber":null,"startDate":"2026-04-02","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"Boeing 737 Series Aeroplanes","sectionType":"division","heading":"Boeing 737 Series Aeroplanes","content":"### Boeing 737 Series Aeroplanes\n\n| AD/B737/235 Amdt 1 | Fuselage Skin Area at the Dorsal Fin Assembly | 6/2009 |\n| ------------------ | --------------------------------------------- | ------ |\n\n| Applicability: | All Model 737-300, -400, and -500 series aircraft.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         |\n| -------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ |\n| Requirement:   | Action in accordance with the technical requirements of FAA AD 2009-07-11 Amdt 39-15870.Note: Boeing Alert Service Bulletin 737-53A1266 original issue, or later FAA approved revision, and Boeing Message Number 1-QX035, dated 13 October 2004, refer.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   |\n| Compliance:    | As specified in the Requirement document, with a revised effective date of4 June 2009.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     |\n|                | This Amendment becomes effective on 4 June 2009.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           |\n| Background:    | The FAA received a report of an 18-inch crack found in the fuselage skin area under the blade seals of the nose cap of the dorsal fin due to previous wear damage. Such damage could result in fatigue cracking due to cabin pressurisation, and consequent rapid in-flight decompression of the aircraft fuselage.Amendment 1 is issued in response to a new FAA AD, which introduces an inspection for any chafing or cracking in the fuselage skin and abrasion resistant coating at the dorsal fin landing, an inspection for damage to the dorsal fin seals, attach clip, and seal retainer, and other specified and corrective actions as necessary. The new requirements will end the need for the existing repetitive inspections. |\n\n![](image.001.png)  \nDavid Villiers  \nDelegate of the Civil Aviation Safety Authority\n\n17 April 2009","sortOrder":0},{"sectionNumber":"AD/B737/235 Amdt 1","sectionType":"part","heading":"AD/B737/235 Amdt 1","content":"## AD/B737/235 Amdt 1","sortOrder":1},{"sectionNumber":"Fuselage Skin Area at the Dorsal Fin Ass","sectionType":"part","heading":"Fuselage Skin Area at the Dorsal Fin Assembly","content":"## Fuselage Skin Area at the Dorsal Fin Assembly","sortOrder":2},{"sectionNumber":"6/2009","sectionType":"part","heading":"6/2009","content":"## 6/2009","sortOrder":3}],"analysis":{"flash_summary":{"complexity_score":5,"scope_assessment":{"changed":true,"description":"Amendment 1 modifies the prior directive by introducing new inspections for chafing, cracking and seal/clip/retainer damage and by prescribing corrective actions as needed, and it ends the previously required repetitive inspections (Background; Requirement). The amendment thus narrows applicability to specific dorsal‑fin assembly issues while replacing an existing inspection cadence with a different inspection/repair regime; compliance remains mandatory from 4 June 2009 (Compliance)."},"complexity_factors":["Reliance on external documents: mandatory compliance references FAA AD 2009-07-11 and Boeing Alert Service Bulletin / Boeing Message (Requirement).","Technical inspection and repair work: requires inspection for chafing/cracking, abrasion‑resistant coating condition, and seal/clip/retainer damage, plus corrective actions as necessary (Background; Requirement).","Change-management: Amendment 1 replaces prior repetitive inspections with the new inspection regime, requiring operators to update maintenance and tracking procedures (Background).","Applicability narrowly targeted: applies only to Model 737-300, -400 and -500 series aircraft, concentrating compliance burden on operators of those fleets (Applicability).","Compliance timing: an explicit effective date creates a firm implementation deadline (Compliance).","Operational impact uncertainty: corrective actions may include structural repairs or part replacement, introducing variable cost and downtime depending on findings (Requirement; Background)."],"plain_english_summary":"This airworthiness directive requires operators of Boeing 737-300, -400 and -500 series aeroplanes to perform inspections and corrective actions on the fuselage skin and dorsal‑fin assembly in accordance with FAA AD 2009-07-11 and referenced Boeing service information.\n\nIt responds to a reported 18‑inch crack under the dorsal‑fin nose cap blade seals and aims to detect chafing, cracking or seal damage to prevent fatigue cracking and possible rapid in‑flight decompression; compliance is mandatory from 4 June 2009."},"flash_summary_failed":{"failed":true,"reason":"Unauthenticated. Configure AI_GATEWAY_API_KEY or use a provider module. Learn more: https://ai-sdk.dev/unauthenticated-ai-gateway","source":"analysis-cron"},"kimi_summary":{"content_quality":"ok","complexity_score":2,"scope_assessment":{"changed":false,"description":"This is a standard amendment to an existing Airworthiness Directive. Amendment 1 updates the requirements based on new FAA guidance, replacing repetitive inspections with a more comprehensive inspection and repair regime. The scope remains tightly focused on the specific fuselage skin area at the dorsal fin assembly of the specified aircraft models — it has not expanded beyond this original safety purpose."},"complexity_factors":["Very short document (approximately 250 words of substantive content)","Only 3 defined applicability criteria (specific aircraft models)","Single primary requirement referencing external technical document (FAA AD 2009-07-11)","No nested conditional logic or exceptions within the instrument itself","Cross-reference to Boeing Service Bulletin and FAA directive rather than detailed technical specifications embedded in text","Simple compliance structure: single effective date with reference to external compliance schedule"],"plain_english_summary":"This CASA Airworthiness Directive requires operators of Australian-registered Boeing 737-300/-400/-500s to follow FAA AD 2009-07-11 (Amendment 1) to inspect and repair the fuselage skin near the dorsal fin where chafing and cracking have been found. It aims to stop cracks that can enlarge with pressurisation cycles and potentially cause rapid decompression."}},"importantCases":[],"_links":{"self":"/api/acts/ad-b737-235-amdt-1-fuselage-skin-area-at-the-dorsal-fin-assembly","history":"/api/acts/ad-b737-235-amdt-1-fuselage-skin-area-at-the-dorsal-fin-assembly/history","analysis":"/api/acts/ad-b737-235-amdt-1-fuselage-skin-area-at-the-dorsal-fin-assembly/analysis","conflicts":"/api/acts/ad-b737-235-amdt-1-fuselage-skin-area-at-the-dorsal-fin-assembly/conflicts","importantCases":"/api/acts/ad-b737-235-amdt-1-fuselage-skin-area-at-the-dorsal-fin-assembly/important-cases","documents":"/api/acts/ad-b737-235-amdt-1-fuselage-skin-area-at-the-dorsal-fin-assembly/documents"}}