{"id":"F2006B09879","name":"AD/F50/51 - Auto Feather Control Unit","slug":"ad-f50-51-auto-feather-control-unit","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":55004,"registerId":"commonwealth-F2006B09879-current","compilationNumber":null,"startDate":"2026-04-02","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/F50/51 - Auto Feather Control Unit","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 F50 (F27 Mk 50) Series Aeroplanes\n\n \n\nAD/F50/51 Auto Feather Control Unit 2/92\n\nApplicability: All F50 aircraft.\n\n \n\nRequirement: Action in accordance with the technical requirements of Netherlands AD BLA 91-134 dated 22 November 1991.\n\n \n\nNote: Fokker SB F50-61-011 and Pratt and Whitney Canada SB No 21046 refers.\n\n \n\nCompliance: By 30 September 1992.\n\n \n\nBackground: A number of inadvertent auto feather incidents have been reported.\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\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 addressing a specific technical defect in a specific aircraft type. It has not expanded beyond its original purpose of mandating a fix for inadvertent auto feather incidents."},"complexity_factors":["Very short document (approximately 150 words of substantive content)","No defined terms section — uses standard aviation terminology only","Single, unambiguous compliance requirement (follow Netherlands AD)","No conditional logic or nested exceptions","Clear applicability statement ('All F50 aircraft')","Single compliance date with no alternative methods or phased implementation","Minimal cross-referencing (only two service bulletins mentioned in a note)"],"plain_english_summary":"This is an **Airworthiness Directive (AD)** issued by Australia's Civil Aviation Safety Authority (CASA) for **Fokker F50 aircraft**.\n\n**What it does:**\nOrders all operators of Fokker F50 aeroplanes to fix a safety problem with the **Auto Feather Control Unit** — a system that automatically adjusts propeller blades to reduce drag if an engine fails.\n\n**The problem:**\nThere had been reports of this system activating **when it shouldn't** (\"inadvertent auto feather incidents\"). This is dangerous because it could cause an engine to shut down or lose power unexpectedly during flight.\n\n**What must be done:**\nAircraft owners/operators must follow the technical instructions in a **Netherlands aviation safety directive** (BLA 91-134) from November 1991. This essentially means adopting the fix that Dutch regulators already required.\n\n**Who it affects:**\n- All Fokker F50 aircraft registered in Australia\n- Airlines and operators flying these planes\n- Maintenance organisations servicing them\n\n**Why it matters:**\nUncommanded engine feathering could lead to loss of control or forced landings. This directive ensures a known safety defect is corrected before it causes an accident.\n\n**Deadline:**\nCompliance was required by **30 September 1992**.\n\n**References:**\n- Fokker Service Bulletin F50-61-011\n- Pratt & Whitney Canada Service Bulletin No 21046"},"flash_summary":{"complexity_score":3,"scope_assessment":{"changed":false,"description":"The text sets out a single-scope directive applying to all F50 aircraft and requires compliance with a specified foreign AD and service bulletins by a fixed date (Applicability; Requirement; Note; Compliance). The instrument does not indicate any expansion or narrowing of scope from an earlier or different intent within this text."},"complexity_factors":["Single, clear mandatory action: follow Netherlands AD BLA 91-134 (Requirement) — lowers internal complexity.","Applicability to an entire aircraft type (all F50 aircraft) simplifies scope but increases aggregate operational impact (Applicability).","Dependence on external documents (Netherlands AD and two service bulletins) requires operators to obtain and interpret additional technical materials (Requirement; Note), adding procedural complexity.","Fixed compliance deadline creates scheduling pressure and potential logistical complexity for operators (Compliance).","The AD itself contains no detailed technical steps, concentrating technical complexity in the referenced documents (Requirement; Note)."],"plain_english_summary":"CASA requires all operators/owners of Fokker F50 (F27 Mk 50) aeroplanes to carry out the corrective actions on the Auto Feather Control Unit set out in Netherlands AD BLA 91-134 (and referenced Fokker/Pratt & Whitney service bulletins), with compliance by 30 September 1992. \n\nThe measure, prompted by reported inadvertent auto-feather incidents, creates a binding maintenance obligation and associated costs and downtime for operators to reduce that safety risk."}},"importantCases":[],"_links":{"self":"/api/acts/ad-f50-51-auto-feather-control-unit","history":"/api/acts/ad-f50-51-auto-feather-control-unit/history","analysis":"/api/acts/ad-f50-51-auto-feather-control-unit/analysis","conflicts":"/api/acts/ad-f50-51-auto-feather-control-unit/conflicts","importantCases":"/api/acts/ad-f50-51-auto-feather-control-unit/important-cases","documents":"/api/acts/ad-f50-51-auto-feather-control-unit/documents"}}