{"id":"F2006B09509","name":"AD/EMB-120/21 - Elevator Pitch Trim System","slug":"ad-emb-120-21-elevator-pitch-trim-system","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":54070,"registerId":"commonwealth-F2006B09509-current","compilationNumber":null,"startDate":"2026-04-02","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/EMB-120/21 - Elevator Pitch Trim System","content":"COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 \\- 105 CIVIL AVIATION SAFETY AUTHORITY\n\nSCHEDULE OF AIRWORTHINESS DIRECTIVES\n\n![](image.001.png)  \nEmbraer EMB-120 (Brasilia) Series Aeroplanes\n\nAD/EMB-120/21 Elevator Pitch Trim System 1/98\n\nApplicability: All models EMB-120 aircraft.\n\nRequirement: Action in accordance with Embraer Alert Service Bulletin 120-27-A081 change 1:\n\nPart I: A check to verify the proper installation of the movable backstop into the spiral groove on the pitch trim right control wheel, and the correct travel of the pitch trim tab surface.\n\nPart II: Installation of a support/guide to maintain the moveable backstop inside the spiral groove, on the control pedestal structure.\n\nNote: CTA AD 97-09-08R1 Amdt 39-811 refers.\n\nCompliance: For Part I: Unless already accomplished in accordance with the initial issue of the Requirement document, within 20 hours time in service after 1 January 1998.\n\nFor Part II: Unless already accomplished, within 75 hours time in service after 1 January 1998.\n\nThis airworthiness directive becomes effective on 1 January 1998.\n\nBackground: Reports were received of occurrences of a sudden reversion of the elevator pitch trim tab, during the descent phase, with the automatic pilot engaged in descent mode. The reports indicated that, when the trim control wheel reached the pitch down stop, the auto pilot disengaged and the aircraft suddenly reverted to a pitch up attitude, requiring prompt pilot action to control the aircraft.","sortOrder":0}],"analysis":{"kimi_summary":{"content_quality":"ok","complexity_score":2,"scope_assessment":{"changed":false,"description":"This is a discrete, targeted safety directive addressing a specific mechanical defect in a specific aircraft type. It has not expanded beyond its original purpose of mandating corrective action for the elevator pitch trim system issue."},"complexity_factors":["Single, specific aircraft type (Embraer EMB-120 series)","Only two distinct compliance actions required","Clear, fixed compliance deadlines (20 and 75 flight hours)","Minimal defined terms (only standard aviation terminology like 'time in service')","No nested exceptions or conditional logic","Short document (approximately 200 words)","Single cross-reference to related foreign directive (CTA AD 97-09-08R1) provided for context only"],"plain_english_summary":"This CASA airworthiness directive mandates inspections and corrective work on the elevator pitch‑trim system of Embraer EMB‑120 (Brasilia) aircraft to prevent the trim control wheel from hitting its pitch‑down stop and suddenly disconnecting the autopilot. It applies to all owners, operators and maintainers of EMB‑120s in Australia and addresses a hazard that can cause an unexpected pitch‑up and potential loss of control."},"flash_summary":{"complexity_score":3,"scope_assessment":{"changed":false,"description":"The directive sticks to the original corrective aim: it applies to all EMB‑120 models and mandates inspection and a retaining support installation to remedy reported pitch‑trim reversion events. It does not broaden applicability or add unrelated requirements."},"complexity_factors":["Narrow technical scope: targets a single flight‑control component (elevator pitch trim) on one aircraft type.","Two-step response: mandatory inspection plus a follow-up modification (support/guide installation).","Reliance on manufacturer service bulletin for procedural detail (Emb‑120-27-A081 change 1) rather than full procedures in the AD text.","Short compliance windows (inspection very soon after effective date; modification within a longer but still limited hours‑in‑service), raising scheduling pressure for operators.","Safety‑critical nature increases operational urgency and possible need for immediate grounding or maintenance slots, affecting operator costs and dispatch.","Cross‑reference to other authority (CTA AD 97-09-08R1) adds traceability but requires checking related documents for full context."],"plain_english_summary":"This directive requires EMB‑120 operators to check that the movable backstop on the pitch‑trim control wheel sits properly in its spiral groove and that the trim tab travels correctly, and to fit a support/guide to retain the backstop — actions to be done per Embraer Alert Service Bulletin 120‑27‑A081 change 1.\n\nOperators must do the inspection soon after the effective date and the modification within a slightly longer window; they bear the cost and operational downtime, while the rule aims to prevent autopilot disengagement and sudden pitch‑up events reported during descent."},"flash_summary_failed":{"failed":true,"reason":"Unauthenticated. Configure AI_GATEWAY_API_KEY or use a provider module. Learn more: https://ai-sdk.dev/unauthenticated-ai-gateway","source":"analysis-cron"}},"importantCases":[],"_links":{"self":"/api/acts/ad-emb-120-21-elevator-pitch-trim-system","history":"/api/acts/ad-emb-120-21-elevator-pitch-trim-system/history","analysis":"/api/acts/ad-emb-120-21-elevator-pitch-trim-system/analysis","conflicts":"/api/acts/ad-emb-120-21-elevator-pitch-trim-system/conflicts","importantCases":"/api/acts/ad-emb-120-21-elevator-pitch-trim-system/important-cases","documents":"/api/acts/ad-emb-120-21-elevator-pitch-trim-system/documents"}}