{"id":"F2005L03570","name":"AD/B737/264 - Horizontal Stabiliser Centre Section Front Spar","slug":"ad-b737-264-horizontal-stabiliser-centre-section-front-spar","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":39134,"registerId":"commonwealth-F2005L03570-current","compilationNumber":null,"startDate":"2026-04-01","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/B737/264 | Horizontal Stabiliser Centre Section Front Spar | 13/2005 |\n| ----------- | ----------------------------------------------- | ------- |\n\n| Applicability: | Model 737-100, -200, and -200C series aircraft; line numbers 1 through 315, 323, and 324.                                                                                                                                                                                                                                                                                                  |\n| -------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ |\n| Requirement:   | Action in accordance with the technical requirements of FAA AD 2000-15-12Amdt 39-11844.Note: Boeing Alert Service Bulletin 737-55A1071 original issue, or later FAA approved revision, refers.                                                                                                                                                                                             |\n| Compliance:    | As specified in the Requirement document, with a revised effective date of22 December 2005.                                                                                                                                                                                                                                                                                                |\n|                | This Airworthiness Directive becomes effective on 22 December 2005.                                                                                                                                                                                                                                                                                                                        |\n| Background:    | The FAA received reports indicating that, during regular maintenance, operators found stress corrosion cracks in the front spar of the centre section of the horizontal stabiliser on two Model 737-100 and -200 series aircraft. Cracks in the front spar will decrease the structural strength of the centre section of the horizontal stabiliser, and could lead to structural failure. |\n\n![](image.001.png)  \nDavid Villiers  \nDelegate of the Civil Aviation Safety Authority\n\n10 November 2005","sortOrder":0},{"sectionNumber":"AD/B737/264","sectionType":"part","heading":"AD/B737/264","content":"## AD/B737/264","sortOrder":1},{"sectionNumber":"Horizontal Stabiliser Centre Section Fro","sectionType":"part","heading":"Horizontal Stabiliser Centre Section Front Spar","content":"## Horizontal Stabiliser Centre Section Front Spar","sortOrder":2},{"sectionNumber":"13/2005","sectionType":"part","heading":"13/2005","content":"## 13/2005","sortOrder":3}],"analysis":{"flash_summary":{"complexity_score":3,"scope_assessment":{"changed":false,"description":"The instrument enforces an existing FAA airworthiness directive and Boeing service bulletin for a narrowly defined set of older 737 airframes. It does not broaden the subject matter beyond its original safety purpose (detecting and correcting stress‑corrosion cracking in the horizontal stabiliser front spar). The AD’s scope remains focused on the identified models and line numbers and on mandating compliance with the referenced FAA/Boeing technical requirements."},"complexity_factors":["Short single‑issue AD focused on one structural component (front spar of horizontal stabiliser)","Narrow applicability by model and specific line numbers (limited population)","Primary content consists of incorporation by reference to external documents (FAA AD 2000-15-12 amendment and Boeing Alert Service Bulletin) rather than detailed procedures in the AD itself","Revised effective date noted (administrative detail)","Limited number of conditional exceptions or nested rules in the text"],"plain_english_summary":"**What this directive does (mechanically)**\n\n- It requires operators of certain older Boeing 737 aeroplanes to carry out inspections and any required corrective work on the front spar of the horizontal stabiliser centre section, following the detailed technical instructions set out in the referenced FAA Airworthiness Directive and Boeing Alert Service Bulletin. (See “Requirement”.)\n- The AD makes those external technical instructions mandatory in Australia for the specified aircraft. (See “Compliance”.)\n\n**Which aircraft are affected**\n\n- Model 737-100, -200 and -200C aircraft with line numbers 1 through 315, and line numbers 323 and 324. (See “Applicability”.)\n\n**Why it matters (safety risk and mechanics)**\n\n- During maintenance, operators found stress-corrosion cracks in the front spar of the horizontal stabiliser centre section on some 737-100/200 aircraft. Cracking in that spar reduces the structural strength of the stabiliser centre section and could lead to structural failure. The AD forces inspections and any repairs to remove that safety risk. (See “Background”.)\n\n**Who pays and who decides**\n\n- The aircraft operators (owners/operators) pay for the inspection, repair, parts and labour required by the AD. Maintenance organisations carrying out the work decide the exact sequencing and procedures subject to the FAA/Boeing instructions and national maintenance regulations.\n\n**What behaviour changes are required of operators**\n\n- Operators must locate affected aircraft by model and line number and then perform the inspections and corrective actions exactly as specified in FAA AD 2000-15-12Amdt 39-11844 and the Boeing Alert Service Bulletin (or later FAA‑approved revision). Records of compliance must be maintained under usual maintenance documentation rules. (See “Requirement”.)\n\n**How the AD works legally and practically**\n\n- The AD does not itself set out step‑by‑step inspection technique; instead it incorporates by reference the FAA AD and Boeing service bulletin. That makes compliance dependent on those external documents being followed exactly or any later FAA‑approved revisions. (See “Requirement”.)\n- The Australian regulator enforces compliance from the AD effective date (revised effective date 22 December 2005). Non‑compliance can lead to grounding or enforcement action under aviation safety law. (See “Compliance”.)\n\n**Costs, incentives and trade‑offs**\n\n- Direct costs: inspection labour, replacement parts or repair costs, possible temporary removal from service (downtime), and any additional inspections or modifications required by the FAA/Boeing documents.\n- Concentrated beneficiaries: passengers and the public benefit from reduced risk of structural failure; operators bear concentrated costs (maintenance expense and downtime) for a relatively small, identifiable subset of aircraft.\n- Market effects: limited — the AD targets older 737 variants (early line numbers), so effects fall mainly on operators of vintage fleets, lessor portfolios containing those line numbers, and maintenance providers. There is limited scope for substitution (operators can’t operate without complying or obtain an FAA‑approved alternative method of compliance). \n- Implementation risks: reliance on external documents means Australian compliance tracks FAA/Boeing technical choices. If the FAA/Boeing instructions change, operators must follow the FAA‑approved revision to remain compliant in Australia.\n\n**Administrative and compliance burden**\n\n- The AD imposes a clear regulatory duty (inspect and fix to the FAA/Boeing standard). That produces record‑keeping, inspection scheduling and parts‑procurement burdens. Maintenance organisations must certify the work per standard aviation maintenance rules.\n\n**Summary statement**\n\n- This is a safety‑directed, targeted airworthiness directive that makes adherence to an FAA airworthiness directive and Boeing service bulletin mandatory for specific early Boeing 737 airframes to detect and correct stress‑corrosion cracking in the horizontal stabiliser centre‑section front spar. It shifts the direct costs of inspection and repair to aircraft operators while reducing the risk of structural failure for the affected fleet. (See “Applicability”, “Requirement”, “Background”, “Compliance”.)"},"kimi_summary":{"content_quality":"ok","complexity_score":3,"scope_assessment":{"changed":false,"description":"This AD maintains its original narrow scope. It targets a specific structural defect in a limited population of early-model Boeing 737 aircraft (line numbers 1-315, 323, 324). The document does not expand beyond its original safety purpose of addressing stress corrosion cracks in the horizontal stabiliser centre section front spar."},"complexity_factors":["Very short document (under 300 words)","Only 3 defined applicability criteria (aircraft models and line numbers)","Single technical requirement referencing external documents rather than spelling out procedures","No nested exceptions or conditional logic — compliance is mandatory for all affected aircraft","Simple effective date structure with one deadline","Heavy reliance on incorporated external standards (FAA AD and Boeing Service Bulletin) which contain the actual technical complexity"],"plain_english_summary":"This CASA Airworthiness Directive mandates inspections and repairs for stress‑corrosion cracks in the horizontal stabiliser front spar on early Boeing 737s (series -100, -200, -200C) with line numbers 1–315, 323–324. It adopts FAA AD 2000‑15‑12 and Boeing Alert SB 737‑55A1071 to prevent structural failure and loss of control; compliance is required by 22 December 2005."},"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"}},"importantCases":[],"_links":{"self":"/api/acts/ad-b737-264-horizontal-stabiliser-centre-section-front-spar","history":"/api/acts/ad-b737-264-horizontal-stabiliser-centre-section-front-spar/history","analysis":"/api/acts/ad-b737-264-horizontal-stabiliser-centre-section-front-spar/analysis","conflicts":"/api/acts/ad-b737-264-horizontal-stabiliser-centre-section-front-spar/conflicts","importantCases":"/api/acts/ad-b737-264-horizontal-stabiliser-centre-section-front-spar/important-cases","documents":"/api/acts/ad-b737-264-horizontal-stabiliser-centre-section-front-spar/documents"}}