{"id":"F2006B09843","name":"AD/F50/18 - Door Mechanism Gearbox Cover","slug":"ad-f50-18-door-mechanism-gearbox-cover","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":54889,"registerId":"commonwealth-F2006B09843-current","compilationNumber":null,"startDate":"2026-04-02","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/F50/18 - Door Mechanism Gearbox Cover","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/F50/18 Door Mechanism Gearbox Cover 5/89\n\nApplicability: Model F27 Mark 050 with serial numbers 20103 through 20108 and 20110 through 20145.\n\n \n\nRequirement: Action in accordance with Fokker 50 SB No F50-52-005.\n\n \n\nNote: RLD AD BLA 88-96 refers.\n\n \n\nCompliance: Prior to 31 August 1989.\n\n \n\nBackground:  The manufacturer has determined that the operating mechanism gearbox of the passenger, cargo, and service/emergency doors, can collect water as a result of condensation; which may freeze at low temperatures and prevent the mechanism from operating correctly.\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":2,"scope_assessment":{"changed":false,"description":"The directive is limited to a defined set of F27 Mk 50 serial numbers and mandates a specific manufacturer action (Fokker 50 SB No F50-52-005) to address a described mechanical issue (condensation leading to freezing in door gearbox). The text shows no change in scope from those stated elements: Applicability, Requirement, Compliance, and Background are tightly aligned and self-contained."},"complexity_factors":["Narrow applicability limited to specific serial numbers (Applicability).","Single mandated action (follow Fokker 50 SB No F50-52-005) rather than multiple alternative procedures (Requirement).","Fixed, short compliance deadline (Compliance: prior to 31 August 1989).","Dependence on an external document (manufacturer service bulletin) for technical detail and costs (Requirement).","Cross-reference to another AD (RLD AD BLA 88-96) that may add related obligations (Note)."],"plain_english_summary":"### What this directive does\n\nThis is an airworthiness directive (AD) that requires specific Fokker F50 (F27 Mk 50) aeroplanes to be modified or inspected in line with the manufacturer’s service bulletin. The AD instructs operators to carry out the action described in Fokker 50 Service Bulletin No F50-52-005 to address a water-collection issue in the door operating-mechanism gearbox. (See: \"Requirement\" and \"Background\".)\n\n### Who it affects\n\n- Owners and operators of Fokker F27 Mark 050 aeroplanes with serial numbers 20103–20108 and 20110–20145. (See: \"Applicability\".)\n\n### What must be done and by when\n\n- Operators must perform the action specified in Fokker 50 SB No F50-52-005.\n- The work must be completed on the listed aeroplanes prior to 31 August 1989. (See: \"Requirement\" and \"Compliance\".)\n\n### Why this requirement exists (mechanics, not motives)\n\n- The manufacturer found that the gearbox that drives passenger, cargo and service/emergency door mechanisms can collect water from condensation, which can freeze at low temperatures and stop the mechanism from working. The SB is the manufacturer’s remedy to prevent or mitigate that water collection and freezing. (See: \"Background\".)\n\n### Who pays and who decides\n\n- The obligation to comply falls on the aircraft owners/operators of the listed serial-numbered aeroplanes; they are responsible for arranging and funding the work required by the service bulletin. (Implied by the AD’s mandatory wording: \"Requirement: Action in accordance with Fokker 50 SB No F50-52-005\" and the listed Applicability.)\n- The AD is issued under the Commonwealth civil aviation safety framework and sets the deadline for compliance; operators have limited discretion beyond following the SB. (See: header and \"Requirement\".)\n\n### Compliance burden and implementation notes\n\n- Compliance requires implementing the manufacturer’s instructions in the referenced service bulletin. That typically means maintenance labour time, parts or materials specified by the SB, and aircraft downtime while work is carried out (opportunity cost to operators). (See: \"Requirement\" and \"Compliance\".)\n- The AD cross-references RLD AD BLA 88-96, which operators may need to consult for related obligations or context. (See: \"Note\".)\n\n### Trade-offs and operational effects to consider\n\n- The action reduces the risk of door mechanism failure from frozen condensation by following a manufacturer-specified correction, while imposing direct costs on the affected operators (maintenance cost, scheduling, and short-term loss of aircraft availability). (See: \"Background\", \"Requirement\", \"Compliance\".)\n- The AD ties compliance to an external manufacturer document (the service bulletin). The practical effect and cost depend on the SB’s technical content and required parts/ labour. (See: \"Requirement\".)"},"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 specific aircraft. It has not expanded beyond its original purpose of mandating a door mechanism fix for the identified Fokker F50 serial numbers."},"complexity_factors":["Very short document (under 200 words)","Only 4 substantive sections: Applicability, Requirement, Compliance, and Background","Single cross-reference to a manufacturer service bulletin (F50-52-005) and one foreign directive (RLD AD BLA 88-96)","No defined terms section or interpretation provisions","Simple conditional logic: if you operate this specific aircraft model with these serial numbers, you must do this action by this date","No nested exceptions or subordinate legislation references"],"plain_english_summary":"This is an **Airworthiness Directive** — 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 F50 aeroplanes** (specific serial numbers 20103–20108 and 20110–20145) to carry out a safety fix on the door mechanism gearbox covers.\n\n**The problem:**\nThe manufacturer found that water could collect inside the operating mechanism gearboxes for passenger, cargo, and emergency doors due to condensation. In cold temperatures, this water could freeze and jam the door mechanism — potentially trapping people inside or preventing emergency exits from working.\n\n**What must be done:**\nOperators must follow the instructions in **Fokker Service Bulletin F50-52-005** (a technical repair notice from the manufacturer) to fix this issue.\n\n**Who it affects:**\n- Owners and operators of specific Fokker F50 aircraft (those built between serial numbers 20103–20145, excluding 20109)\n- Maintenance engineers servicing these aircraft\n\n**Why it matters:**\nFrozen door mechanisms could prevent passengers and crew from evacuating during an emergency. This directive makes the repair **legally mandatory** — not optional — and sets a hard deadline of **31 August 1989** for compliance.\n\n**Note:** This references a Dutch aviation safety directive (RLD AD BLA 88-96), showing Australia was harmonising its safety requirements with international standards."}},"importantCases":[],"_links":{"self":"/api/acts/ad-f50-18-door-mechanism-gearbox-cover","history":"/api/acts/ad-f50-18-door-mechanism-gearbox-cover/history","analysis":"/api/acts/ad-f50-18-door-mechanism-gearbox-cover/analysis","conflicts":"/api/acts/ad-f50-18-door-mechanism-gearbox-cover/conflicts","importantCases":"/api/acts/ad-f50-18-door-mechanism-gearbox-cover/important-cases","documents":"/api/acts/ad-f50-18-door-mechanism-gearbox-cover/documents"}}