{"id":"F2006B09835","name":"AD/F50/10 - Outboard Nacelle Ventilation Air Inlets","slug":"ad-f50-10-outboard-nacelle-ventilation-air-inlets","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":54867,"registerId":"commonwealth-F2006B09835-current","compilationNumber":null,"startDate":"2026-04-02","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/F50/10 - Outboard Nacelle Ventilation Air Inlets","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/F50/10 Outboard Nacelle Ventilation Air Inlets 3/89\n\nDM\n\n \n\nApplicability: F27-050 S/Nos 20103 to 20108 and 20110 to 20128. Requirement:  Action in accordance with Fokker SB F50-54-003.\n\nNote: RLD AD 88-94 refers.\n\n \n\nCompliance: Prior to 31 March 1989.\n\n \n\nBackground:  There have been several reports of ice build-up on cable systems. These occurred at high altitude and high humidity conditions with low OAT.\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 targeting a specific technical issue on a specific aircraft type. It has not expanded beyond its original narrow scope of addressing ice accumulation in nacelle ventilation systems."},"complexity_factors":["Very short document (approximately 150 words)","Only 2 defined applicability criteria (aircraft serial number ranges)","Single compliance requirement referencing external technical document (Fokker SB)","No nested conditional logic or exceptions","No cross-references to other legislation beyond a single note referencing Dutch authority directive","Straightforward command structure: applicability → requirement → compliance deadline"],"plain_english_summary":"This is an **Airworthiness Directive (AD)** — essentially a mandatory safety order issued by Australia's Civil Aviation Safety Authority (CASA).\n\n**What it does:**\nIt requires specific Fokker F50 aircraft to undergo a safety modification concerning the **outboard nacelle ventilation air inlets** (the air intake openings on the outer engine housings).\n\n**Who it affects:**\nOwners and operators of Fokker F50 aircraft with serial numbers 20103 to 20108 and 20110 to 20128 — a limited batch of 25 aircraft.\n\n**Why it matters:**\nIce was building up on cable systems inside these aircraft during high-altitude, high-humidity, cold conditions. This ice formation could potentially interfere with flight controls or other critical systems. The directive mandates compliance with a specific Fokker Service Bulletin (SB F50-54-003) to fix this problem before 31 March 1989.\n\n**Key points:**\n- **Mandatory action:** Operators cannot legally fly these aircraft without completing this modification\n- **Deadline:** Strict compliance deadline of 31 March 1989\n- **Source:** Based on a manufacturer service bulletin and references a Dutch aviation authority directive (RLD AD 88-94)"},"flash_summary":{"complexity_score":3,"scope_assessment":{"changed":false,"description":"The directive confines its scope to a defined set of F27-050 serial numbers and mandates the manufacturer’s corrective action to address reported ice build-up on cable systems. The text provided does not indicate any change from that original, stated intent; it remains narrowly focused on specified aircraft and on implementing Fokker SB F50-54-003 by the stated compliance date. (Applicability; Requirement; Background; Compliance)"},"complexity_factors":["Narrow applicability limited to specific aircraft serial numbers (Applicability)","Dependence on an external document (Fokker SB F50-54-003) for the technical remedy rather than specifying details in the AD (Requirement)","Mandatory compliance with a fixed deadline (Compliance)","Technical subject matter (icing on cable systems) requires specialist maintenance actions and parts, creating practical implementation complexity not described in the AD (Background; Requirement)","Cross-reference to a related airworthiness directive (RLD AD 88-94) increases cross-document navigation"],"plain_english_summary":"What this directive does (mechanical change)\n\n- It requires operators of certain Fokker F50 (F27 Mk 50) aeroplanes — specifically serial numbers F27-050 S/Nos 20103 to 20108 and 20110 to 20128 — to take the actions set out in Fokker Service Bulletin F50-54-003. (Applicability; Requirement)\n- The work called for by that service bulletin must be completed before 31 March 1989. (Compliance)\n- The directive cross-references related material in RLD AD 88-94. (Note)\n\nWhy the directive was issued (official rationale)\n\n- The directive cites several reports of ice forming on cable systems, occurring at high altitude, high humidity and low outside air temperature. The stated purpose is to address those ice-build-up reports by mandating the manufacturer’s corrective action. (Background; Requirement)\n\nWho is affected and who pays\n\n- Affected parties are the owners/operators of the listed F27-050 serial-numbered aircraft. (Applicability)\n- The directive requires those operators to implement the manufacturer’s service bulletin; therefore the operators will incur the direct costs of implementing the measures the bulletin specifies (labour, parts and aircraft downtime). (Requirement; Compliance)\n\nHow it changes decision-making and incentives\n\n- The directive prescribes a manufacturer-defined technical fix by referencing the Fokker service bulletin, so the regulator directs operators to follow the manufacturer’s specified method rather than leaving operators to choose alternative mitigations. (Requirement)\n- Because compliance is mandatory by a fixed date, operators have an incentive to schedule and complete the work promptly to remain airworthy; delaying attracts regulatory non-compliance risk. (Compliance)\n\nCompliance burden, implementation risk and trade-offs\n\n- The directive imposes a compliance burden of performing the actions described in the service bulletin by the deadline; the bulletin’s content is not reproduced in this instrument, so the precise scope of work, parts needed and man-hours are specified in the manufacturer document rather than here. (Requirement)\n- Implementation risk includes any operational downtime while the work is done and any supply or technical constraints tied to the service bulletin’s parts or procedures. (Requirement; Compliance)\n- The directive centralises the technical solution in the manufacturer’s service bulletin, which reduces discretion for operators but concentrates the technical remedy with the manufacturer and the regulator. (Requirement)\n\nTrade-offs and opportunity costs\n\n- The directive implicitly trades operator time, labour and possible parts expense (short-run costs) against the regulatory objective of preventing ice-related cable system problems at the stated flight conditions. The directive does not quantify costs, so operators must absorb the opportunity cost of scheduling the mandated work. (Background; Requirement; Compliance)\n\nImplementation and enforcement notes\n\n- Compliance is measured against completing the service bulletin actions by the stated date; the AD itself does not detail inspection records or ongoing monitoring requirements in the text presented. (Requirement; Compliance)\n\nConcise summary\n\n- Mandatory action: follow Fokker SB F50-54-003 for the listed F50 serial numbers.\n- Deadline: complete the actions before 31 March 1989.\n- Reason given: reports of ice build-up on cable systems in specific atmospheric conditions.\n\n(Section references: Applicability; Requirement; Compliance; Background; Note.)"}},"importantCases":[],"_links":{"self":"/api/acts/ad-f50-10-outboard-nacelle-ventilation-air-inlets","history":"/api/acts/ad-f50-10-outboard-nacelle-ventilation-air-inlets/history","analysis":"/api/acts/ad-f50-10-outboard-nacelle-ventilation-air-inlets/analysis","conflicts":"/api/acts/ad-f50-10-outboard-nacelle-ventilation-air-inlets/conflicts","importantCases":"/api/acts/ad-f50-10-outboard-nacelle-ventilation-air-inlets/important-cases","documents":"/api/acts/ad-f50-10-outboard-nacelle-ventilation-air-inlets/documents"}}