{"id":"F2006B09907","name":"AD/F50/77 - Stabilizer De-Icing Monitoring System","slug":"ad-f50-77-stabilizer-de-icing-monitoring-system","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":55097,"registerId":"commonwealth-F2006B09907-current","compilationNumber":null,"startDate":"2026-04-02","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/F50/77 - 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 F50 (F27 Mk 50) Series Aeroplanes\n\nAD/F50/77 Stabilizer De-Icing Monitoring System 6/98\n\nApplicability: Model F.27 Mk.050 (Fokker 50) aeroplanes with serial numbers 20103 through 20245 inclusive, 20248, 20250 through 20255 inclusive, 20257 through 20269\n\ninclusive, 20272 through 20275 inclusive, 20278, 20280 through 20283 inclusive,\n\n20285, 20287 through 20302 inclusive, 20304, 20305 and 20307 through 20311 inclusive.\n\nRequirement: Install a horizontal and vertical stabilizer de-icing monitoring system in accordance with Fokker Service Bulletin SBF50-30-025 dated 31 October 1997.\n\nNote: RLD AD 1997-113 (A) refers.\n\nCompliance: For aeroplanes without any tail de-icing distributor valve heating system installed \\- Within the next 10 calendar months after the effective date of this directive.\n\nFor aeroplanes that have a tail de-icing distributor valve heating system installed, either in accordance with Fokker Service Bulletin SBF50-30-024 dated 26 March 1997 or Fokker Engineering Report TT95.55175 - Within the next 16 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 operators have 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. Fokker has developed an optional service bulletin (SBF50.30.024), which introduces heater muffs on the affected distributor valves, to decrease the likelihood of the valves freezing. However, on early models, the operation of the de-icing system is not monitored.\n\nThis directive introduces a system to monitor the operation status of the horizontal and vertical stabilizer de-icing, and provide a warning in the cockpit when operation is interrupted.","sortOrder":0}],"analysis":{"flash_summary_failed":{"failed":true,"reason":"A positive credit balance is required for all requests, including BYOK, so fallback providers remain available. Add credits at https://vercel.com/d?to=%2F%5Bteam%5D%2F%7E%2Fai%3Fmodal%3Dtop-up to continue.","source":"analysis-cron"},"kimi_summary":{"content_quality":"ok","complexity_score":3,"scope_assessment":{"changed":false,"description":"This is a standard airworthiness directive with a focused, single-purpose scope: mandating a specific safety modification to address a known icing system failure mode. The scope remains tightly constrained to the de-icing monitoring requirement without expansion into broader operational or maintenance areas."},"complexity_factors":["Single technical requirement with two conditional compliance deadlines based on existing aircraft configuration","Specific serial number applicability list with multiple ranges and gaps (17 separate number ranges)","References to external technical documents (Fokker Service Bulletin and Engineering Report) without reproducing their content","Cross-reference to Dutch aviation authority directive (RLD AD 1997-113)","No defined terms section or interpretation provisions"],"plain_english_summary":"This safety order requires owners/operators of specified Fokker 50 aircraft (serials 20103–20311, with some gaps) to install a cockpit warning/monitoring system for the horizontal and vertical stabilizer de-icing system per Fokker Service Bulletin SBF50-30-025. Compliance is mandated to prevent undetected de-ice failures in extreme cold—10 months if valves lack heating, 16 months if heating is fitted."},"flash_summary":{"complexity_score":3,"scope_assessment":{"changed":true,"description":"This AD moves beyond reporting and the manufacturer's optional heater-muff fix by mandating a monitoring system for stabilizer de-icing on specified serial-numbered F50s (Requirement: SBF50-30-025; Background). It imposes operator-paid installation and compliance timing (Compliance: 10 or 16 calendar months), thereby changing scope from optional mitigations to compulsory monitoring and warning capability."},"complexity_factors":["Granular applicability by specific serial numbers increases administrative tracking (Applicability).","Single technical requirement but mandatory conformity to a manufacturer's service bulletin constrains method of compliance (Requirement: SBF50-30-025).","Two-tier compliance timeline based on prior installation of distributor valve heating creates conditional deadlines (Compliance: 10 vs 16 calendar months).","Cross-reference to an optional earlier fix (heater muffs via SBF50-30-024) requires verification of modification status (Background; Compliance).","Safety-critical equipment installation implies maintenance shop time, parts lead-time and certification/recording obligations (Requirement; Compliance).","Regulatory enforceability of an Airworthiness Directive leaves little operator discretion on compliance approach (Directive effective date and Requirement)."],"plain_english_summary":"This directive requires installation of a horizontal and vertical stabilizer de-icing monitoring system on specified Fokker F50 (F.27 Mk.050) aeroplanes per Fokker Service Bulletin SBF50-30-025. It is intended to give cockpit warning when tail de-icing boots fail to inflate after prolonged very-low-temperature operation. Operators must comply within 10 months if valve heaters are not fitted, or 16 months where heater muffs (SBF50-30-024) are already installed."}},"importantCases":[],"_links":{"self":"/api/acts/ad-f50-77-stabilizer-de-icing-monitoring-system","history":"/api/acts/ad-f50-77-stabilizer-de-icing-monitoring-system/history","analysis":"/api/acts/ad-f50-77-stabilizer-de-icing-monitoring-system/analysis","conflicts":"/api/acts/ad-f50-77-stabilizer-de-icing-monitoring-system/conflicts","importantCases":"/api/acts/ad-f50-77-stabilizer-de-icing-monitoring-system/important-cases","documents":"/api/acts/ad-f50-77-stabilizer-de-icing-monitoring-system/documents"}}