{"id":"F2006B09899","name":"AD/F50/7 - Dorsal Fin Gutter","slug":"ad-f50-7-dorsal-fin-gutter","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":55072,"registerId":"commonwealth-F2006B09899-current","compilationNumber":null,"startDate":"2026-04-02","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/F50/7 - Dorsal Fin Gutter","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/F50/7 Dorsal Fin Gutter 3/89 DM\n\n \n\nApplicability: F27-050 S/Nos 20103 to 20108 and 20110 to 20144. Requirement:  Action in accordance with Fokker SB F50-53-003.\n\nNote: RLD AD 88-85 refers.\n\n \n\nCompliance: Prior to 31 March 1989.\n\n \n\nBackground: Freezing of cable systems has occurred at high altitude. Rain, high humidity and low OAT were factors. Installation of a gutter is to prevent ingress of rainwater.\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":1,"scope_assessment":{"changed":false,"description":"This is a discrete, targeted safety directive addressing a specific technical defect in specific aircraft. It has not expanded beyond its original purpose of mandating a gutter installation to prevent freezing issues."},"complexity_factors":["Single, specific applicability (limited serial number range)","One clear requirement referencing an external technical document","No defined terms section","No conditional logic or exceptions","No cross-references to other legislation beyond a note about a related Dutch directive","Extremely short (under 150 words of substantive content)"],"plain_english_summary":"This is a **safety order** (called an \"Airworthiness Directive\") issued by Australia's Civil Aviation Safety Authority. It applies to specific **Fokker F50 aircraft** (serial numbers 20103-20108 and 20110-20144).\n\n**What it requires:**\n- Aircraft owners/operators must install a **gutter** on the dorsal fin (the vertical fin on top of the fuselage) following Fokker's Service Bulletin F50-53-003.\n\n**Why it matters:**\n- Rainwater was getting into the aircraft and freezing at high altitude, causing **cable systems to freeze up**. This is dangerous because control cables run the aircraft's flight surfaces.\n- The gutter prevents rainwater from entering areas where it can freeze and jam critical controls.\n\n**Deadline:**\n- The fix had to be done **before 31 March 1989**.\n\n**Who needs to know:**\n- Airlines or operators flying these specific Fokker F50 aircraft.\n- Aircraft maintenance engineers."},"flash_summary":{"complexity_score":2,"scope_assessment":{"changed":false,"description":"The AD's scope aligns with its stated intent: it targets a defined set of Fokker F50 aircraft serial numbers and mandates installation of a gutter per the referenced service bulletin to prevent rainwater ingress that contributed to cable freezing. The directive establishes the same technical remedy and applicability as described in the instrument and does not expand or narrow that scope in the text provided."},"complexity_factors":["Narrow technical scope: applies only to specified serial numbers (F27-050 S/Nos 20103–20108 and 20110–20144).","Reference to external technical document: requirement is to follow Fokker Service Bulletin F50-53-003 rather than specifying modification details in the AD.","Single, fixed compliance deadline (prior to 31 March 1989) creates a clear timeframe but may raise scheduling constraints for operators.","Safety rationale relies on a specific environmental interaction (rain + high humidity + low outside air temperature) that is technical but succinctly described.","Minimal regulatory discretion: directive prescribes mandatory action rather than optional measures, limiting interpretive complexity."],"plain_english_summary":"This AD mandates installation of a dorsal‑fin gutter on specified Fokker F50 (F27‑050) serial numbers to stop rainwater ingress that has led to cable freezing at altitude. It affects owners, operators and maintenance organisations responsible for those aircraft.\n\nOperators must fund and schedule the one‑off modification per Fokker Service Bulletin F50‑53‑003 by the compliance date, or face continued safety and regulatory risk."}},"importantCases":[],"_links":{"self":"/api/acts/ad-f50-7-dorsal-fin-gutter","history":"/api/acts/ad-f50-7-dorsal-fin-gutter/history","analysis":"/api/acts/ad-f50-7-dorsal-fin-gutter/analysis","conflicts":"/api/acts/ad-f50-7-dorsal-fin-gutter/conflicts","importantCases":"/api/acts/ad-f50-7-dorsal-fin-gutter/important-cases","documents":"/api/acts/ad-f50-7-dorsal-fin-gutter/documents"}}