{"id":"F2006B06280","name":"AD/PMC/21 - Three Blade Propeller Hub - Modification or Replacement","slug":"ad-pmc-21-three-blade-propeller-hub-modification-or-replacement","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":47332,"registerId":"commonwealth-F2006B06280-current","compilationNumber":null,"startDate":"2026-04-02","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/PMC/21 - Three Blade Propeller Hub - Modification or Replacement","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 - 107 CIVIL AVIATION SAFETY AUTHORITY\n\nSCHEDULE OF AIRWORTHINESS DIRECTIVES\n\n \n\n![](image.001.png)  Propellers - Variable Pitch - McCauley\n\n \n\nAD/PMC/21 Three Blade Propeller Hub - Modification\n\nor Replacement\n\n\n7/71\n\n \n\nApplicability: Models D3A32C77, C79, C88 and C90 models with no model number change letter or letter “A” to “J” fitted to Cessna 206 series aircraft with normally aspirated Continental IO-520 engine not modified in accordance with McCauley SB No. 88 (AD/PMC/20 refers).\n\n \n\nDocument: 1. Cessna SL SE71-15; or\n\n \n\n2. McCauley SB No. 89.\n\n \n\nCompliance: 1. For propellers which have completed 600 hours or more total time in service - within 25 hours time in service after 30 July 1971.\n\n \n\n2. For propellers which have completed 500 hours total time in service - before achieving 600 hours total time in service.\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 Airworthiness Directive remains tightly scoped to its original purpose: addressing a specific mechanical defect in McCauley three-blade propeller hubs fitted to particular Cessna 206 aircraft. There is no evidence of scope creep; it targets a discrete safety issue with precise model applicability and clear compliance thresholds."},"complexity_factors":["Single, narrow applicability clause targeting specific aircraft models and engine configurations","Only two compliance conditions based on flight hours (time in service)","No defined terms section — all technical terms are standard aviation nomenclature","Minimal cross-referencing (only references one prior AD and two manufacturer service bulletins)","No nested exceptions or conditional logic beyond the basic applicability exclusion","Extremely short document (approximately 150 words of substantive content)"],"plain_english_summary":"This is an **Airworthiness Directive (AD)** — a mandatory safety order issued by Australia's Civil Aviation Safety Authority (CASA). It requires owners or operators of specific Cessna aircraft to inspect or modify their propeller hubs to prevent mechanical failure.\n\n**Who it affects:**\n- Owners of Cessna 206 series aircraft with normally aspirated Continental IO-520 engines\n- Specifically, those fitted with McCauley three-blade propeller hubs (models D3A32C77, C79, C88, and C90 — including variants marked A through J)\n- Only applies if the propeller hasn't already been modified under a previous directive (AD/PMC/20)\n\n**What it requires:**\n- **High-time propellers** (600+ hours of flight time): Must be fixed within 25 flight hours after 30 July 1971\n- **Medium-time propellers** (500–600 hours): Must be fixed before hitting 600 total hours\n\n**Why it matters:**\nAirworthiness Directives are legally binding. Ignoring this could result in the propeller hub failing in flight — with potentially catastrophic consequences. The directive references technical bulletins from Cessna and McCauley that detail the required modification or replacement procedure.\n\n**Key point:** This is old legislation (dated 1971) affecting vintage aircraft still in service. Compliance deadlines were tied to flight hours and a fixed calendar date over 50 years ago."},"flash_summary":{"complexity_score":3,"scope_assessment":{"changed":false,"description":"The directive's scope is limited to the specified propeller hub models on Cessna 206s with the stated engine and excludes hubs already modified under McCauley SB No. 88. The instrument prescribes the method (service documents) and deadlines; no broader scope change is evident from the text supplied."},"complexity_factors":["Narrow applicability to listed propeller hub models and specific Cessna 206 installations — requires accurate identification of parts and aircraft.","Dependence on external service documents for the required work (Cessna SL SE71‑15 or McCauley SB No. 89) — compliance requires obtaining and following those materials.","Time‑in‑service deadlines drive scheduling and record checks (>=600 hours: within 25 hours after 30 July 1971; 500 hours: before reaching 600 hours) — administrative and operational impact.","Exclusion for propellers already modified per McCauley SB No. 88 — operators must verify modification history.","Cross‑reference to a prior directive (AD/PMC/20) increases administrative linkage and potential sequencing of actions.","Direct cost and downtime borne by aircraft owner/operator for parts, labour and grounding while modification or replacement is carried out."],"plain_english_summary":"This airworthiness directive requires owners/operators to modify or replace specific McCauley three‑blade propeller hubs (models D3A32C77, C79, C88, C90) fitted to certain Cessna 206 aircraft with normally aspirated Continental IO‑520 engines, unless already modified under McCauley SB No. 88. Compliance must follow Cessna SL SE71‑15 or McCauley SB No. 89 and meet the time‑in‑service deadlines. It matters to operators because it mandates hardware work within set TIS limits, creating parts, labour, grounding and record‑keeping costs to maintain legal airworthiness."}},"importantCases":[],"_links":{"self":"/api/acts/ad-pmc-21-three-blade-propeller-hub-modification-or-replacement","history":"/api/acts/ad-pmc-21-three-blade-propeller-hub-modification-or-replacement/history","analysis":"/api/acts/ad-pmc-21-three-blade-propeller-hub-modification-or-replacement/analysis","conflicts":"/api/acts/ad-pmc-21-three-blade-propeller-hub-modification-or-replacement/conflicts","importantCases":"/api/acts/ad-pmc-21-three-blade-propeller-hub-modification-or-replacement/important-cases","documents":"/api/acts/ad-pmc-21-three-blade-propeller-hub-modification-or-replacement/documents"}}