{"id":"F2006B02732","name":"AD/B727/31 Amdt 2 - Stabilizer Upper Rear Spar Chord - Inspection and Modification","slug":"ad-b727-31-amdt-2-stabilizer-upper-rear-spar-chord-inspection-and-modification","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":42074,"registerId":"commonwealth-F2006B02732-current","compilationNumber":null,"startDate":"2026-04-01","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/B727/31 Amdt 2 - Stabilizer Upper Rear Spar Chord - Inspection and Modification","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/B727/31\n\nAmdt 2\n\n\nStabilizer Upper Rear Spar Chord - Inspection and Modification\n\n\n4/67\n\n \n\nApplicability: All models.\n\n \n\nDocument: Boeing SB No. 55-17, Rev. 2.\n\n \n\nCompliance: As detailed in inspection schedules Section II of SB No. 55-17, Rev. 2.\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":5,"scope_assessment":{"changed":false,"description":"The AD text provided (AD/B727/31 Amdt 2) sets applicability as \"All models\" and directs compliance to Boeing SB No. 55-17, Rev. 2 Section II. The instrument, as published here, does not indicate any change in the scope of applicability from that statement. The AD delegates technical detail to the referenced Service Bulletin, but the stated scope (all Boeing 727 models) remains explicit in this text."},"complexity_factors":["References an external technical document (Boeing SB No. 55-17, Rev. 2) for all procedural detail rather than containing procedures in the AD itself, requiring users to obtain and interpret that document.","Applies to all Boeing 727 models, creating potentially large and varied compliance populations with differing maintenance histories.","Implementation requires technical inspection and possible modification work, which involves specialist maintenance skills, parts availability and scheduling of aircraft downtime.","Regulatory enforcement is under Part 39, so operators must integrate AD compliance into airworthiness records and regulatory oversight processes.","The AD text does not enumerate inspection intervals, criteria, or corrective actions in-line, increasing reliance on cross-referencing and procedural interpretation."],"plain_english_summary":"### What this instrument does\n\nThis Airworthiness Directive (AD/B727/31 Amdt 2) requires inspections and any necessary modifications of the stabilizer upper rear spar chord on Boeing 727 series aeroplanes. The AD makes compliance mandatory by referring operators to the inspection schedules in Section II of Boeing Service Bulletin No. 55-17, Revision 2. (See: \"Applicability: All models\"; \"Document: Boeing SB No. 55-17, Rev. 2\"; \"Compliance: As detailed in inspection schedules Section II of SB No. 55-17, Rev. 2.\")\n\n### Who it affects\n\n- Aircraft operators and owners of any Boeing 727 series aeroplane (the AD states applicability: \"All models\").\n- Maintenance organisations and engineers who carry out inspections and modifications.\n- The Civil Aviation Safety Authority (CASA) as the enforcing regulator under Part 39 (Airworthiness Directives). (Header: \"COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - CIVIL AVIATION SAFETY AUTHORITY\".)\n\n### How it works mechanically\n\n- The AD does not set out the inspection intervals or procedures itself. Instead it makes compliance conditional on following the inspection schedules and modification instructions contained in Section II of Boeing Service Bulletin No. 55-17, Revision 2. Operators must follow the steps and timing set out in that external document.\n- Compliance is mandatory: the AD is the legal instrument that imposes the obligation; the Service Bulletin supplies the technical detail.\n\n### Who pays and what changes in behaviour\n\n- Operators and owners bear the direct costs: arranging, performing and documenting the inspections and any modifications required by the referenced Service Bulletin (in staff time, parts, and aircraft downtime). (Inferred from the AD’s instruction that operators comply with the SB schedules.)\n- Maintenance organisations carry out the work to the technical standard in the SB and record compliance for regulatory oversight.\n- The regulator enforces the AD; operators must demonstrate compliance as required by airworthiness rules.\n\n### Implementation, incentives and trade-offs\n\n- Incentives and burdens: The AD converts technical guidance (the Boeing SB) into a mandatory requirement. That shifts the incentive onto operators to schedule and fund the inspections/modifications to keep aircraft legally airworthy. (See: \"Compliance: As detailed in inspection schedules Section II of SB No. 55-17, Rev. 2.\")\n- Opportunity costs: Aircraft will be unavailable while inspected or modified; operators must trade aircraft time and maintenance capacity against meeting the AD schedule.\n- Discretion and delegation: The AD delegates technical specification to an external manufacturer document (Boeing SB No. 55-17, Rev. 2). The AD itself does not specify intervals or techniques; those are set in the referenced Service Bulletin. This concentrates technical decision-making in the SB while the regulator retains legal authority to require compliance under Part 39.\n\n### Risks, concentrated benefits and diffuse costs (mechanisms, not judgments)\n\n- Concentrated compliance burden: Every Boeing 727 operator is obliged to act (the AD lists applicability as \"All models\"). Costs of inspections and modifications are borne by those operators.\n- Concentrated technical control: The Service Bulletin (Boeing SB No. 55-17, Rev. 2) defines the detailed inspection and modification steps; parties relying on or supplying parts and procedures in that SB will play a central role in implementation.\n- Diffuse enforcement cost: The regulator uses Part 39 authority to require and verify compliance; resources are needed to oversee and, if necessary, enforce the AD.\n\n### Where to find the technical requirements\n\n- The AD points operators to Section II of Boeing Service Bulletin No. 55-17, Revision 2 for the precise inspection schedules and modification instructions that must be followed. (See: \"Document: Boeing SB No. 55-17, Rev. 2\"; \"Compliance: As detailed in inspection schedules Section II of SB No. 55-17, Rev. 2.\")"},"kimi_summary":{"content_quality":"ok","complexity_score":2,"scope_assessment":{"changed":false,"description":"This is Amendment 2 of a long-standing airworthiness directive originally issued in 1967 (reference '4/67'). The scope remains tightly focused on the specific structural inspection and modification requirement for the Boeing 727 stabilizer. As an amendment, it likely incorporates updated technical guidance from the revised Boeing Service Bulletin without expanding beyond the original safety purpose."},"complexity_factors":["Very short document (approximately 150 words)","No defined terms section — relies entirely on external Boeing Service Bulletin for technical details","No conditional logic or nested exceptions within the directive itself","Single, clear applicability clause ('All models')","Single external reference (Boeing SB No. 55-17, Rev. 2)","Straightforward compliance requirement referencing external schedule"],"plain_english_summary":"This is an **Airworthiness Directive (AD)** — a mandatory safety order issued by Australia's Civil Aviation Safety Authority (CASA) that requires specific maintenance actions on certain aircraft.\n\n**What it does:**\n- Requires owners and operators of **Boeing 727 series aeroplanes** to inspect and potentially modify the **stabilizer upper rear spar chord** — a critical structural component at the back of the aircraft that helps control pitch (up and down movement).\n\n**Who it affects:**\n- All owners, operators, and maintenance organisations responsible for Boeing 727 aircraft registered in Australia.\n\n**Why it matters:**\n- This directive addresses potential structural fatigue or damage that could compromise flight safety. The stabilizer is essential for controlling the aircraft's attitude. If the rear spar chord fails, it could lead to loss of control.\n- Compliance is **mandatory** — operators must follow the inspection schedules and modification procedures detailed in Boeing Service Bulletin No. 55-17, Revision 2.\n\n**Key requirement:**\n- Operators must complete inspections and any required modifications according to the timelines specified in Section II of the referenced Boeing document."}},"importantCases":[],"_links":{"self":"/api/acts/ad-b727-31-amdt-2-stabilizer-upper-rear-spar-chord-inspection-and-modification","history":"/api/acts/ad-b727-31-amdt-2-stabilizer-upper-rear-spar-chord-inspection-and-modification/history","analysis":"/api/acts/ad-b727-31-amdt-2-stabilizer-upper-rear-spar-chord-inspection-and-modification/analysis","conflicts":"/api/acts/ad-b727-31-amdt-2-stabilizer-upper-rear-spar-chord-inspection-and-modification/conflicts","importantCases":"/api/acts/ad-b727-31-amdt-2-stabilizer-upper-rear-spar-chord-inspection-and-modification/important-cases","documents":"/api/acts/ad-b727-31-amdt-2-stabilizer-upper-rear-spar-chord-inspection-and-modification/documents"}}