{"id":"F2006B09713","name":"AD/F27/146 - Stabilizer De-Icing Monitoring System","slug":"ad-f27-146-stabilizer-de-icing-monitoring-system","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":115887,"registerId":"commonwealth-F2006B09713-current","compilationNumber":null,"startDate":"2026-04-03","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/F27/146 - Stabilizer De-Icing Monitoring System","content":"COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 \\- 105 CIVIL AVIATION SAFETY AUTHORITY\n\nSCHEDULE OF AIRWORTHINESS DIRECTIVES\n\n![](image.001.png)  \nFokker F27 Series Aeroplanes\n\n| AD/F27/146     | Stabilizer De-Icing Monitoring System                                                                                          | 6/98 |\n| -------------- | ------------------------------------------------------------------------------------------------------------------------------ | ---- |\n| Applicability: | Model F.27 Mk.200, Mk.400M, Mk.500, Mk.500F, Mk.500RF and Mk.600aeroplanes, with serial numbers 10603 through 10692 inclusive. |      |\n\nRequirement: Install a horizontal and vertical stabilizer de-icing monitoring system in accordance with Fokker Service Bulletin F27/30-44 dated 20 February 1998.\n\nNote: RLD AD 1998-019 (A) refers.\n\nCompliance: Within the next 18 calendar months after the effective date of this directive.\n\nThis airworthiness directive becomes effective on 21 May 1998.\n\nBackground: The Netherlands airworthiness authority has advised that a number of F.27 Mk.050 (Fokker 50) operators have reportedly experienced problems with the tail de-icing system. After prolonged operation at very low outside air temperatures, one or more sections of the de-icing ‘boots’ do not inflate when the system is selected ON. Investigation shows that interrupted ‘boot’ operation may be caused by freezing of one or more distributor valves.\n\nEarly model F.27 ‘Friendship’ aeroplanes are equipped with a tailplane de-icing system which enables the flight crew to monitor the correct functioning of each individual ‘boot’ segment. However, later model F27 aeroplanes have a similar tail de-icing system as that fitted to Fokker 50 aeroplanes, where the operation of the de- icing system is not monitored. Consequently, information on the system’s operational status is not available to the flight crew and any failure would not be detected.\n\nThis directive introduces a system to monitor the operational status of the horizontal and vertical stabilizer de-icing, which will provide a warning in the cockpit when failure to correctly inflate any ‘boot’ occurs.","sortOrder":0}],"analysis":{"flash_summary_failed":{"failed":true,"reason":"Unauthenticated. Configure AI_GATEWAY_API_KEY or use a provider module. Learn more: https://ai-sdk.dev/unauthenticated-ai-gateway","source":"analysis-cron"},"kimi_summary":{"content_quality":"ok","complexity_score":2,"scope_assessment":{"changed":false,"description":"This is a standard airworthiness directive with a narrow, specific safety purpose. The scope remains tightly focused on the identified safety issue with the stabilizer de-icing system on specific Fokker F27 variants."},"complexity_factors":["Single, specific technical requirement with no conditional logic or exceptions","Only one defined applicability criterion (aircraft model and serial number range)","No cross-references to other legislation sections (only a reference to a Fokker Service Bulletin and a Dutch airworthiness directive for context)","Straightforward compliance deadline (18 months from effective date)","Short document (approximately 250 words) with clear structure"],"plain_english_summary":"Owners and operators of certain Fokker F27 (Mk.200/400M/500/500F/500RF/600) aeroplanes (serials 10603–10692) must install a cockpit monitoring system for the tail de‑icing boots. Valves can freeze closed so boots may not inflate and pilots would have no warning, risking tail ice and loss of control. Install per Fokker Service Bulletin F27/30‑44 within 18 months of 21 May 1998."},"flash_summary":{"complexity_score":3,"scope_assessment":{"changed":false,"description":"The directive targets later-model F.27 aeroplanes lacking tailplane boot monitoring by imposing installation on the specified serial-number range. This aligns the regulatory scope with the reported failure mode (frozen distributor valves) and does not expand beyond the identified affected aircraft."},"complexity_factors":["Technical installation required to conform with Fokker Service Bulletin F27/30-44 (makes compliance dependent on a manufacturer procedure).","Applicability limited to specific models and serial numbers (serials 10603–10692), requiring operators to check aircraft-specific applicability.","Safety-critical monitoring of de-icing ‘boots’ — involves avionics/airframe integration and testing to validate cockpit warnings.","Fixed compliance window (18 months) creates scheduling and downtime pressure for operators.","Cross-reference to a foreign authority action (Netherlands) and RLD AD 1998-019(A) increases regulatory provenance but does not change technical requirements."],"plain_english_summary":"Install a horizontal and vertical stabilizer de‑icing monitoring system on specified Fokker F27 aeroplanes (serials 10603–10692) per Fokker Service Bulletin F27/30‑44, within 18 months of 21 May 1998. The system provides a cockpit warning if any de‑icing \"boot\" fails to inflate.\n\nOperators of the affected aircraft must pay for and schedule the installation. The directive responds to reported frozen distributor valves at very low temperatures and shifts failure detection to onboard monitoring."}},"importantCases":[],"_links":{"self":"/api/acts/ad-f27-146-stabilizer-de-icing-monitoring-system","history":"/api/acts/ad-f27-146-stabilizer-de-icing-monitoring-system/history","analysis":"/api/acts/ad-f27-146-stabilizer-de-icing-monitoring-system/analysis","conflicts":"/api/acts/ad-f27-146-stabilizer-de-icing-monitoring-system/conflicts","importantCases":"/api/acts/ad-f27-146-stabilizer-de-icing-monitoring-system/important-cases","documents":"/api/acts/ad-f27-146-stabilizer-de-icing-monitoring-system/documents"}}