{"id":"F2006B09688","name":"AD/F27/121 - Flight Controls - Elevator Trim System","slug":"ad-f27-121-flight-controls-elevator-trim-system","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":115839,"registerId":"commonwealth-F2006B09688-current","compilationNumber":null,"startDate":"2026-04-03","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/F27/121 - Flight Controls - Elevator Trim System","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)  Fokker F27 Series Aeroplanes\n\n \n\nAD/F27/121 Flight Controls - Elevator Trim System 2/91\n\nApplicability: F27 aircraft with S/No’s 10102 to 10684 inclusive, 10686, 10687 and 10689 to 10692 inclusive.\n\n \n\nRequirement: Action in accordance with the technical requirements of Netherlands AD BLA 90-106.\n\n \n\nNote: Fokker SB F27/27-130 refers.\n\n \n\nCompliance: As specified in the Requirement document with effective date 5 October 1990.\n\n \n\nBackground: Country of origin AD. To modify the elevator and trim tab systems so that they are considerably more resistant to flutter and easier to maintain.\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":4,"scope_assessment":{"changed":false,"description":"The AD does not indicate a change in scope from its original intent. It applies to the listed Fokker F27 serial numbers and mandates modification of the elevator and trim tab systems by requiring action in accordance with Netherlands AD BLA 90-106, with compliance as specified and effective 5 October 1990 (Applicability, Requirement, Compliance, Background)."},"complexity_factors":["Mandatory modification references an external foreign airworthiness directive (Netherlands AD BLA 90-106) rather than containing technical steps itself (Requirement)","Applicability limited to specific serial number ranges, requiring precise aircraft identification (Applicability)","Technical nature of work (flight controls—elevator and trim tab systems) requires specialised maintenance and parts","Compliance timing and procedures are determined by the referenced document (effective date 5 October 1990), adding a cross-document compliance step (Compliance)","Reference to a manufacturer service bulletin (Fokker SB F27/27-130) means operators must reconcile multiple documents (Note)"],"plain_english_summary":"What this directive does (mechanics)\n\n- Requires specified Fokker F27 aeroplanes to be modified in their elevator and trim tab systems. The AD does not reproduce the technical steps; it mandates compliance with the Netherlands airworthiness directive BLA 90-106 (the Requirement) (Requirement).\n- Compliance must be carried out as set out in that Netherlands AD, with the effective date of compliance set as 5 October 1990 (Compliance).\n- The AD cross-references Fokker Service Bulletin F27/27-130 for related work (Note).\n\nWho is affected\n\n- Owners/operators of Fokker F27 aircraft with serial numbers 10102 to 10684 inclusive, plus 10686, 10687 and 10689 to 10692 inclusive (Applicability). These operators must ensure the specified modifications are done to remain in compliance.\n\nWhy this is required (official rationale)\n\n- The stated reason is to modify the elevator and trim tab systems so they are considerably more resistant to flutter and easier to maintain (Background). The AD is issued as a country-of-origin (Netherlands) airworthiness directive adopted for Australian-registered aircraft (Background, Requirement).\n\nWho pays, who decides, and how behaviour changes\n\n- Who pays: The aircraft owners/operators bear the cost of implementing the modifications and any associated maintenance, parts and downtime. The AD itself delegates the technical specification to the Netherlands AD BLA 90-106, so the work to be performed will be those tasks and parts identified in that foreign AD and the referenced Fokker service bulletin (Requirement, Note).\n- Who decides: The Civil Aviation Safety Authority issues the AD and makes compliance mandatory for the listed serial numbers. The technical content and procedures are set by the referenced Netherlands AD (Requirement). There is no allowance or alternative specified in this text; operators must follow the referenced documentation (Applicability, Requirement).\n- Behaviour changes: Operators must schedule and complete the modifications specified in the Netherlands AD and Fokker SB. That may require booking maintenance facilities, acquiring parts or kits, and may remove aircraft from service for the duration of the work (Requirement, Compliance).\n\nCompliance burden, implementation risk and discretionary points\n\n- Compliance burden: The AD requires a physical modification to flight control components, which typically involves qualified maintenance personnel, possible parts procurement and aircraft downtime. The AD text requires adherence to an external technical document (Netherlands AD BLA 90-106), which operators must obtain and follow (Requirement, Note, Compliance).\n- Implementation risk: The AD relies on a foreign-origin technical document; operators must correctly interpret and apply that document. The AD text does not itself specify testing, inspection acceptance criteria, or timelines beyond referring to the foreign AD, so those operational details depend on the referenced documents (Requirement, Compliance).\n- Discretion: The AD text does not state any discretionary exemptions or alternative means of compliance; the directive requires action “in accordance with” the Netherlands AD for the listed serial numbers (Applicability, Requirement).\n\nTrade-offs and opportunity costs (mechanical terms)\n\n- Resources used to implement the mandated modification (labour, parts, maintenance line time) are diverted from other activities; aircraft may be temporarily unavailable while work is carried out (Compliance). The directive’s mechanism is a mandatory retrofit for identified serial numbers rather than an optional inspection regime (Applicability, Requirement).\n\nRelated documents to consult\n\n- Netherlands AD BLA 90-106 (technical requirement referenced by this AD) (Requirement).\n- Fokker Service Bulletin F27/27-130 (referenced) (Note).\n\nSource references in the AD: Applicability; Requirement; Compliance; Note; Background."},"kimi_summary":{"content_quality":"ok","complexity_score":2,"scope_assessment":{"changed":false,"description":"This is a discrete, targeted safety directive addressing a specific technical issue (elevator trim flutter) in a specific aircraft type. It has not expanded beyond its original purpose."},"complexity_factors":["Very short document (approximately 150 words)","Only 4 substantive paragraphs (Applicability, Requirement, Note, Compliance, Background)","No defined terms section — uses plain language and references external technical documents","Single cross-reference to Netherlands AD BLA 90-106 and Fokker Service Bulletin F27/27-130","No conditional logic, exceptions, or nested provisions","Clear, unambiguous applicability criteria (specific serial number ranges)"],"plain_english_summary":"This is an **Airworthiness Directive (AD)** — essentially a mandatory safety order issued by Australia's Civil Aviation Safety Authority (CASA) for specific aircraft.\n\n**What it does:**\nOrders owners and operators of certain **Fokker F27 aircraft** to modify the **elevator trim system** (the part of the tail that helps control the plane's pitch and stability). The modification makes the system more resistant to **flutter** (dangerous, rapid vibrations that can damage or destroy aircraft control surfaces) and easier to maintain.\n\n**Who it affects:**\n- Owners and operators of Fokker F27 aircraft with specific serial numbers: 10102 through 10684, plus 10686, 10687, and 10689 through 10692.\n- These are mostly older regional turboprop aircraft.\n\n**Why it matters:**\nFlutter in flight control systems can cause catastrophic structural failure. This directive prevents that risk by requiring a specific technical fix developed by the Dutch aviation authority (the country where Fokker aircraft are originally from).\n\n**What must be done:**\nOperators must follow the technical instructions in **Netherlands AD BLA 90-106** (the original Dutch safety order) and comply by **5 October 1990**. They can also refer to **Fokker Service Bulletin F27/27-130** for guidance on how to make the changes."}},"importantCases":[],"_links":{"self":"/api/acts/ad-f27-121-flight-controls-elevator-trim-system","history":"/api/acts/ad-f27-121-flight-controls-elevator-trim-system/history","analysis":"/api/acts/ad-f27-121-flight-controls-elevator-trim-system/analysis","conflicts":"/api/acts/ad-f27-121-flight-controls-elevator-trim-system/conflicts","importantCases":"/api/acts/ad-f27-121-flight-controls-elevator-trim-system/important-cases","documents":"/api/acts/ad-f27-121-flight-controls-elevator-trim-system/documents"}}