{"id":"F2006B01908","name":"AD/A320/18 - Trimmable Horizontal Surface Relay","slug":"ad-a320-18-trimmable-horizontal-surface-relay","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":41130,"registerId":"commonwealth-F2006B01908-current","compilationNumber":null,"startDate":"2026-04-01","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/A320/18 - Trimmable Horizontal Surface Relay","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)  \nAirbus Industrie A319, A320 and A321 Series Aeroplanes\n\nAD/A320/18 Trimmable Horizontal Surface Relay 9/91\n\nApplicability: All Airbus Industrie A320 aircraft without Airbus Industrie Modification 21659 or Airbus Industrie Service Bulletin A320-27-1012 embodied.\n\nRequirement: Action in accordance with the Technical Requirements of DGAC AD 91-119-017(B) R1.\n\nNote: Airbus Industrie Service Bulletin A320-27-1012 also refers.\n\nCompliance: 1. For aircraft which have performed more than 1400 flights or more since retrofit of SEC P/N B372ABM0606/B372BAM0404 - at the earliest opportunity, but before exceeding 1600 flights since retrofit of the SEC P/No referenced above.\n\n2. For aircraft which have performed less than 1400 flights or more since retrofit of SEC P/N B372ABM0606/B372BAM0404 - at the earliest opportunity, but within 800, but not exceeding 1600 flights following retrofit of the above referenced SEC.\n\nBackground: Relay 36 CE 3, which is energised by SEC 2 whenever it is active in pitch mode, has been found, in one case, to be stuck in the energised position. This affects the ability of the SEC 2 monitoring channel to neutralise any erratic movement of the THS initiated by the SEC 2 control channel.","sortOrder":0}],"analysis":{"flash_summary":{"complexity_score":4,"scope_assessment":{"changed":false,"description":"The instrument applies to all A319/A320/A321 aircraft lacking the specified modification or service bulletin and mandates actions per the referenced DGAC AD, with flight-count compliance windows. No textual change of scope from the stated applicability and requirements is evident in the provided text."},"complexity_factors":["Cross-reference to foreign airworthiness directive and manufacturer service bulletin (Requirement; Note): DGAC AD 91-119-017(B) R1 and A320-27-1012 adds external dependency","Applicability conditional on absence of specific modification or SB embodiment (Applicability): requires checks of modification status","Two-tier, flight-count-based compliance windows (Compliance paras 1 & 2): timing depends on number of flights since retrofit","Technical specificity tied to SEC/relay behaviour and single reported failure (Background): requires technical understanding of SEC channels and THS control","Vague timing phrase 'at the earliest opportunity' (Compliance): introduces implementation discretion for operators/maintenance planners"],"plain_english_summary":"Requires operators of Airbus A319/A320/A321 aircraft that have not embodied Airbus Modification 21659 or Service Bulletin A320-27-1012 to carry out corrective action specified in DGAC AD 91-119-017(B) R1. The directive targets Relay 36 CE 3, which has been found stuck energised in one case and can stop the SEC 2 monitoring channel from neutralising erratic trimmable horizontal surface (THS) movement. Compliance is set by flight-count windows after retrofit; operators must inspect/retrofit within those limits."},"kimi_summary":{"content_quality":"ok","complexity_score":4,"scope_assessment":{"changed":false,"description":"This is a standard single-issue Airworthiness Directive addressing a specific identified safety defect in a specific aircraft system. It maintains the typical narrow scope of ADs — one problem, one set of affected aircraft, prescribed remedy."},"complexity_factors":["Multiple conditional compliance deadlines based on flight counts since specific part retrofit (nested thresholds: 1400 flights, 1600 flights, 800 flights)","Technical aviation jargon requiring specialist knowledge (SEC P/N, THS, pitch mode, monitoring channel vs control channel)","Cross-reference to external foreign regulation (DGAC AD 91-119-017(B) R1) without reproducing its content","Reference to specific manufacturer service bulletins and modification numbers (A320-27-1012, Mod 21659)","Part number specificity (B372ABM0606/B372BAM0404) requiring precise technical identification"],"plain_english_summary":"This AD requires owners/operators of certain Airbus A319/A320/A321 aircraft (without Mod 21659 or SB A320-27-1012) to inspect or replace the flight‑control relay \"36 CE 3\" that controls the Trimmable Horizontal Stabiliser because a stuck relay can disable protections and allow uncontrolled tail movement. \n\nCompliance deadlines vary by flights since the SEC retrofit (high‑use: immediate/within 1,600 flights; lower‑use: within 800 flights, but before 1,600); follow DGAC AD 91‑119‑017(B) R1 instructions."}},"importantCases":[],"_links":{"self":"/api/acts/ad-a320-18-trimmable-horizontal-surface-relay","history":"/api/acts/ad-a320-18-trimmable-horizontal-surface-relay/history","analysis":"/api/acts/ad-a320-18-trimmable-horizontal-surface-relay/analysis","conflicts":"/api/acts/ad-a320-18-trimmable-horizontal-surface-relay/conflicts","importantCases":"/api/acts/ad-a320-18-trimmable-horizontal-surface-relay/important-cases","documents":"/api/acts/ad-a320-18-trimmable-horizontal-surface-relay/documents"}}