{"id":"F2006B02269","name":"AD/AL 250/58 Amdt 2 - Gearbox Assembly - PTO Helical Gearshaft Assembly - Replacement","slug":"ad-al-250-58-amdt-2-gearbox-assembly-pto-helical-gearshaft-assembly-replacement","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":41499,"registerId":"commonwealth-F2006B02269-current","compilationNumber":null,"startDate":"2026-04-01","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/AL 250/58 Amdt 2 - Gearbox Assembly - PTO Helical Gearshaft Assembly - Replacement","content":"COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 \\- 106 CIVIL AVIATION SAFETY AUTHORITY\n\nSCHEDULE OF AIRWORTHINESS DIRECTIVES\n\n![](image.001.png)  \nAllison Turbine Engines \\- 250 Series\n\nAD/AL 250/58\n\nAmdt 2\n\n  \n\nGearbox Assembly - PTO Helical Gearshaft Assembly \\- Replacement\n\n  \n9/84\n\nApplicability: All Model 250-C18, C20, C20B, C20F, B15G, B17, B17B, and B17C, engines with exceptions as listed in the requirement document.\n\nRequirement: Allison 250-C18, C18A, C18B, C18C\n\nAllison 250-C20, C20B, C20F\n\nAllison 250-B15G\n\nAllison 250-B17, B17B, B17C\n\n  \n: CEB-203\n\n: CEB-1150\n\n: TP CEB-71\n\n: TP CEB-1126\n\n  \nRev. 7\n\nRev. 7\n\nRev. 7\n\nRev. 7\n\nCompliance: In accordance with the Requirement Document Para E.\n\nBackground: This Directive is amended to reflect the manufacturers Rev. 7 changes to the Requirement Documents Para 1.E Compliance Statement; sub-para 3 which requires the immediate replacement of superseded part numbered PTO shaft in the event of future shockload or sudden stoppage as defined in Para 3.1 and 3.2.","sortOrder":0}],"analysis":{"flash_summary":{"complexity_score":5,"scope_assessment":{"changed":true,"description":"The Directive was amended to adopt the manufacturer's Revision 7 changes to the Requirement Documents. Specifically, sub‑paragraph 3 of the Requirement Document Para 1.E (as updated in Rev.7) now requires immediate replacement of superseded part‑numbered PTO shafts if those shafts experience a future \"shockload\" or \"sudden stoppage\" (Background). Mechanically, this amendment changes the scope of mandatory action from whatever the prior compliance statement required to an event‑triggered immediate replacement obligation; the AD text directs compliance with the updated Requirement Document (Compliance)."},"complexity_factors":["Dependence on external technical documents (CEB‑203, CEB‑1150, TP CEB‑71, TP CEB‑1126 Rev.7) for definitions and procedures (Requirement).","Triggering condition is event‑based (\"shockload\" or \"sudden stoppage\") and those terms are defined only in the Requirement Document (Background: Para 3.1/3.2), creating interpretive burden.","Applicability includes exceptions that are listed only in the Requirement Document, requiring cross‑reference (Applicability).","Immediate replacement requirement creates operational timing pressure and potential unplanned downtime, increasing compliance complexity (Background; Compliance).","The AD references a specific compliance paragraph (Para E) rather than prescribing steps in the AD text, requiring users to consult the manufacturer’s procedures (Compliance)."],"plain_english_summary":"This AD adopts the manufacturer's Rev.7 requirements for specified Allison 250-series engines, requiring immediate replacement of a superseded PTO helical gearshaft if it experiences a defined \"shockload\" or \"sudden stoppage.\" It applies to listed engine models and directs compliance per the manufacturer's Requirement Documents (para 3.1/3.2 and Para E). Operators bear the cost, must follow the external documents for definitions and procedures, and may change inspections or operations to avoid unplanned replacements."},"kimi_summary":{"content_quality":"ok","complexity_score":3,"scope_assessment":{"changed":false,"description":"This amendment remains tightly focused on its original purpose — ensuring safe operation of PTO helical gearshaft assemblies in specific Allison 250 engines. The amendment simply updates compliance requirements to reflect manufacturer document revisions (Rev. 7), adding the immediate replacement requirement after shockload events. This is a refinement of existing safety controls, not an expansion of scope."},"complexity_factors":["Short, single-purpose directive focused on one mechanical component","Limited applicability to specific Allison 250 engine models (8 variants listed)","References external manufacturer documents (CEB-203, CEB-1150, TP CEB-71, TP CEB-1126) rather than detailing requirements in full","Simple conditional trigger: replacement required only upon shockload or sudden stoppage events","No nested exceptions or complex conditional logic within the directive text itself","Minimal defined terms (only 'shockload' and 'sudden stoppage' referenced by paragraph number)"],"plain_english_summary":"This is an **Airworthiness Directive** — a mandatory safety order issued by Australia's Civil Aviation Safety Authority (CASA) that requires aircraft owners and operators to take specific action to fix a known safety problem.\n\n**What it does:**\nThis directive orders the **replacement of a specific helicopter engine part** — the PTO (Power Take-Off) Helical Gearshaft Assembly in certain Allison 250 series turbine engines. These engines are commonly used in helicopters.\n\n**Who it affects:**\n- Owners and operators of aircraft using **Allison 250-C18, C20, C20B, C20F, B15G, B17, B17B, and B17C** model engines\n- Maintenance organisations servicing these engines\n\n**The key safety issue:**\nThe directive has been updated (Amendment 2) to require **immediate replacement** of certain outdated PTO shaft part numbers if the engine experiences a \"shockload\" (sudden impact force) or \"sudden stoppage\" (engine stops abruptly). This prevents potential catastrophic failure of the gearshaft assembly.\n\n**Why it matters:**\nHelicopter engine failures can be fatal. This directive closes a safety gap by ensuring that older, superseded gearshaft designs are removed from service immediately after stressful events that could damage them, rather than waiting for routine maintenance."}},"importantCases":[],"_links":{"self":"/api/acts/ad-al-250-58-amdt-2-gearbox-assembly-pto-helical-gearshaft-assembly-replacement","history":"/api/acts/ad-al-250-58-amdt-2-gearbox-assembly-pto-helical-gearshaft-assembly-replacement/history","analysis":"/api/acts/ad-al-250-58-amdt-2-gearbox-assembly-pto-helical-gearshaft-assembly-replacement/analysis","conflicts":"/api/acts/ad-al-250-58-amdt-2-gearbox-assembly-pto-helical-gearshaft-assembly-replacement/conflicts","importantCases":"/api/acts/ad-al-250-58-amdt-2-gearbox-assembly-pto-helical-gearshaft-assembly-replacement/important-cases","documents":"/api/acts/ad-al-250-58-amdt-2-gearbox-assembly-pto-helical-gearshaft-assembly-replacement/documents"}}