{"id":"F2006B02641","name":"AD/B727/12 - Addition of Access Doors to Horizontal Stabilizer","slug":"ad-b727-12-addition-of-access-doors-to-horizontal-stabilizer","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":41957,"registerId":"commonwealth-F2006B02641-current","compilationNumber":null,"startDate":"2026-04-01","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/B727/12 - Addition of Access Doors to Horizontal Stabilizer","content":"---\nmeta-content-style-type: text/css\nmeta-content-type: application/xhtml+xml; charset=utf-8\nmeta-generator: Aspose.Words for .NET 22.10.0\n---\n\n?xml version=\"1.0\" encoding=\"utf-8\" standalone=\"no\"?>\n\nCOMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 105 CIVIL AVIATION SAFETY AUTHORITY\n\nSCHEDULE OF AIRWORTHINESS DIRECTIVES\n\n \n\n![](image.001.png)  Boeing 727 Series Aeroplanes\n\n \n\nAD/B727/12 Addition of Access Doors to Horizontal Stabilizer 11/65\n\nApplicability: All models.\n\n \n\nDocument: Boeing SB No. 55-12 (R)-1. Compliance:  Before 12,000 hours total time in service.\n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n","sortOrder":0}],"analysis":{"flash_summary":{"complexity_score":2,"scope_assessment":{"changed":false,"description":"The supplied text states a single, specific requirement (add access doors per Boeing SB No. 55-12 (R)-1) applicable to all Boeing 727 models with a fixed compliance threshold (before 12,000 hours TIS). The document contains no information indicating that the scope differs from the original intent; therefore there is no evidence in the source that the scope has changed."},"complexity_factors":["Short, narrowly focused directive: text contains a single clear modification requirement (addition of access doors).","Universal applicability across all Boeing 727 models increases administrative reach despite simple text (\"Applicability: All models.\").","Fixed compliance trigger measured in flight hours (\"Before 12,000 hours total time in service.\") creates a clear deadline but requires accurate time-in-service tracking.","Dependency on an external technical document (Boeing SB No. 55-12 (R)-1) for specific procedures shifts technical complexity to the service bulletin.","Practical implementation requires certified maintenance personnel and aircraft downtime (logistic complexity, though not legal complexity).","AD text provides no alternatives or waiver process in the supplied excerpt, reducing regulatory flexibility."],"plain_english_summary":"What this instrument changes mechanically:\n\n- AD/B727/12 (Addition of Access Doors to Horizontal Stabilizer) requires Boeing 727 series aeroplanes to have access doors added to the horizontal stabilizer. The AD directs compliance with Boeing Service Bulletin No. 55-12 (R)-1. (See: \"AD/B727/12...\", \"Document: Boeing SB No. 55-12 (R)-1.\")\n- The requirement applies to all Boeing 727 models (\"Applicability: All models.\").\n- Work must be completed before the aeroplane reaches 12,000 hours total time in service (\"Compliance: Before 12,000 hours total time in service.\").\n\nWho does what, who pays, and how behaviour changes:\n\n- Who decides: The Civil Aviation Safety Authority (CASA) issued the airworthiness directive; the AD mandates the modification and points to the Boeing service bulletin as the required procedural reference. (See: AD title and Document citation above.)\n- Who pays: Aircraft owners/operators are the parties required to carry out the modification and therefore will incur costs for parts, labour, certification and any associated downtime. The AD text identifies the operator/owner as the obligated party by setting the compliance requirement and applicability.\n- Behaviour changes: Operators must plan and schedule the structural modification before 12,000 hours TIS, engage maintenance providers able to install per the Boeing SB, and update aircraft maintenance records to reflect the modification.\n\nStated or implied purpose and how that matters for costs and incentives:\n\n- The AD text itself does not state an explicit rationale other than the title \"Addition of Access Doors to Horizontal Stabilizer.\" That title implies the mechanical change is to add access points to the horizontal stabilizer (for example, to facilitate inspection or maintenance), but no explicit safety finding or explanatory memorandum is included in the supplied text.\n- If the implied purpose is to improve inspection or maintenance access, the immediate effects are procedural: increased upfront cost and downtime for modification in exchange for easier future inspections/maintenance. Operators face a trade-off between spending resources now to modify airframes and potential savings or operational changes later (for example, lower labour time per inspection). The AD fixes the timing (before 12,000 hours), so private choice about timing is constrained.\n\nCompliance burden, discretion, and implementation risks:\n\n- Compliance burden: The AD imposes a clear compliance obligation (install per Boeing SB) and a firm deadline (12,000 hours). Burdens include procurement of parts, specialist labour, aircraft out-of-service time, and administrative record updates.\n- Discretion: The AD points to a service bulletin for the method of compliance, so technical discretion rests with the maintenance provider and certifying personnel executing the service bulletin. The AD text does not provide alternative means of compliance or outline any CASA waiver process in the supplied excerpt.\n- Implementation risks and trade-offs: Technical installation risk (incorrect installation can affect airworthiness), scheduling conflicts for operators, and short-term operational disruption are concrete risks. There is also a potential for different operators to experience different cost impacts depending on maintenance capability and access to parts and certified technicians.\n\nPractical effects on markets and operators (mechanical, not evaluative):\n\n- Private firms providing maintenance and parts will receive demand for the modification work; costs may vary by provider and location.\n- Aircraft owners must allocate capital and maintenance slots to meet the mandated deadline; this can affect aircraft availability and operating schedules until the modification is complete.\n\nSource citations within the instrument: AD identifier and title (AD/B727/12 Addition of Access Doors to Horizontal Stabilizer), Document: Boeing SB No. 55-12 (R)-1, Applicability: All models, Compliance: Before 12,000 hours total time in service."},"kimi_summary":{"content_quality":"ok","complexity_score":2,"scope_assessment":{"changed":false,"description":"This is a discrete, single-purpose safety directive issued in 1965 (as indicated by '11/65'). It has not expanded beyond its original intent: mandating a specific structural modification to a specific aircraft type within a specific timeframe. The scope remains precisely what it was when issued."},"complexity_factors":["Extremely short document — approximately 100 words of substantive content","Only one defined term implicitly referenced (the Boeing Service Bulletin)","No cross-references to other legislation or regulations beyond the enabling authority (Civil Aviation Regulations 1998, Part 39)","Single, unambiguous compliance requirement (install doors before 12,000 hours)","No conditional logic, exceptions, or nested provisions","Straightforward applicability clause ('All models') with no exclusions"],"plain_english_summary":"This is an **Airworthiness Directive (AD)** — essentially a mandatory safety order issued by Australia's Civil Aviation Safety Authority (CASA) for aircraft.\n\n**What it does:**\nRequires owners and operators of **Boeing 727 series aircraft** to install additional access doors on the horizontal stabilizer (the small wing at the tail of the plane that helps control pitch). This modification is specified in Boeing Service Bulletin No. 55-12 (R)-1.\n\n**Who it affects:**\nAnyone who owns or operates any model of Boeing 727 aircraft in Australia.\n\n**Why it matters:**\nAccess doors allow maintenance crews to properly inspect and maintain the internal structure of the horizontal stabilizer. Without adequate access, critical structural components could deteriorate undetected, potentially leading to catastrophic failure. The directive sets a hard deadline: the work must be completed **before the aircraft reaches 12,000 total flight hours**.\n\n**Key point:** This is not optional. Airworthiness Directives are legally binding safety requirements. Non-compliance means the aircraft cannot legally fly."}},"importantCases":[],"_links":{"self":"/api/acts/ad-b727-12-addition-of-access-doors-to-horizontal-stabilizer","history":"/api/acts/ad-b727-12-addition-of-access-doors-to-horizontal-stabilizer/history","analysis":"/api/acts/ad-b727-12-addition-of-access-doors-to-horizontal-stabilizer/analysis","conflicts":"/api/acts/ad-b727-12-addition-of-access-doors-to-horizontal-stabilizer/conflicts","importantCases":"/api/acts/ad-b727-12-addition-of-access-doors-to-horizontal-stabilizer/important-cases","documents":"/api/acts/ad-b727-12-addition-of-access-doors-to-horizontal-stabilizer/documents"}}