{"id":"F2006B02260","name":"AD/AL 250/49 - N2 Overspeed Control System - Disarming","slug":"ad-al-250-49-n2-overspeed-control-system-disarming","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":41490,"registerId":"commonwealth-F2006B02260-current","compilationNumber":null,"startDate":"2026-04-01","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/AL 250/49 - N2 Overspeed Control System - Disarming","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 - 106 CIVIL AVIATION SAFETY AUTHORITY\n\nSCHEDULE OF AIRWORTHINESS DIRECTIVES\n\n \n\n![](image.001.png)  Allison Turbine Engines - 250 Series\n\n \n\nAD/AL 250/49 N2 Overspeed Control System - Disarming 4/82\n\nApplicability: Allison 250-C28B.\n\n \n\nDocument: 1. Detroit Diesel Allison Commercial Engine Bulletin 250-C28B CEB-A-73-2020; or\n\n \n\n2. FAA AD 82-03-02 Detroit Diesel Allison Amendment 39-4305. Compliance: Before further flight after 2 March 1982.\n\nBackground: Overseas, there have been 5 reported spooling downs of Allison 250-C28B engines in flight which were attributed to intermittent and spurious activation of the N2 (Electronic) Overspeed Control System. This Directive is issued in order to preclude further such intermittent or spurious power reductions or shut-downs.\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":{"kimi_summary":{"content_quality":"ok","complexity_score":2,"scope_assessment":{"changed":false,"description":"This is a discrete, time-bound safety directive with a single specific purpose. It has not expanded beyond its original intent of addressing the N2 Overspeed Control System fault in the specified engine model."},"complexity_factors":["Very short document (approximately 150 words of substantive content)","Only one defined term implicitly referenced (N2 - engine speed/rotational speed)","Single, unambiguous compliance requirement with clear deadline","No nested exceptions or conditional logic","Simple binary applicability (applies to Allison 250-C28B engines only)","References external technical documents rather than incorporating complex internal provisions"],"plain_english_summary":"**What this is:** This is an Airworthiness Directive (AD) — essentially a mandatory safety order issued by Australia's Civil Aviation Safety Authority (CASA) for aircraft engines.\n\n**What it does:** It requires owners and operators of **Allison 250-C28B turbine engines** to disable (\"disarm\") the N2 Overspeed Control System before flying again after 2 March 1982.\n\n**Why:** The N2 Overspeed Control System was causing problems — specifically, it was triggering false alarms that made engines suddenly lose power or shut down mid-flight. There had been **5 reported incidents overseas** where engines \"spooled down\" (rapidly lost speed/power) due to these faulty electronic signals. This directive prevents that dangerous situation by turning the system off.\n\n**Who must comply:** Anyone operating an aircraft with an Allison 250-C28B engine. \"Before further flight\" means you cannot fly until you've done this fix.\n\n**How to comply:** Follow the instructions in either:\n- Detroit Diesel Allison Commercial Engine Bulletin 250-C28B CEB-A-73-2020, **or**\n- FAA AD 82-03-02 (the equivalent American safety order)\n\n**Why it matters:** Uncommanded engine shutdowns or power loss in flight can be catastrophic. This directive is a straightforward safety fix to prevent engines from cutting out due to electronic glitches."},"flash_summary":{"complexity_score":3,"scope_assessment":{"changed":false,"description":"The directive's scope is consistent with its stated purpose in the background: it applies to all Allison 250-C28B engines (Applicability) and mandates disarming the N2 Overspeed Control System as described in the referenced documents to prevent reported spooling downs (Background; Document; Compliance). There is no textual indication in the instrument that the scope was broadened or narrowed from that stated purpose."},"complexity_factors":["Narrow technical scope: applies only to Allison 250-C28B engines (Applicability).","Clear, fixed compliance deadline: \"before further flight after 2 March 1982\" (Compliance).","Dependence on external technical documents for the exact procedure (Document).","Safety-critical nature requires maintenance work and grounding until completed (Compliance).","Limited regulatory discretion within the instrument itself — technical choices are deferred to the referenced documents (Document)."],"plain_english_summary":"This airworthiness directive requires disarming the N2 electronic Overspeed Control on Allison 250‑C28B engines, performed in accordance with one of two referenced technical documents, and completed before any flight after 2 March 1982. It applies to owners/operators and maintenance organisations for affected engines and aims to prevent intermittent or spurious N2 overspeed activations that caused in‑flight spooling downs; operators must arrange and fund the required work and accept the resulting downtime."}},"importantCases":[],"_links":{"self":"/api/acts/ad-al-250-49-n2-overspeed-control-system-disarming","history":"/api/acts/ad-al-250-49-n2-overspeed-control-system-disarming/history","analysis":"/api/acts/ad-al-250-49-n2-overspeed-control-system-disarming/analysis","conflicts":"/api/acts/ad-al-250-49-n2-overspeed-control-system-disarming/conflicts","importantCases":"/api/acts/ad-al-250-49-n2-overspeed-control-system-disarming/important-cases","documents":"/api/acts/ad-al-250-49-n2-overspeed-control-system-disarming/documents"}}