{"id":"F2006B04975","name":"AD/CESSNA 170/47 Amdt 1 - Crankcase Breather Tube and Oil Seal","slug":"ad-cessna-170-47-amdt-1-crankcase-breather-tube-and-oil-seal","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":44864,"registerId":"commonwealth-F2006B04975-current","compilationNumber":null,"startDate":"2026-04-02","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/CESSNA 170/47 Amdt 1 - Crankcase Breather Tube and Oil Seal","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)  \nCessna 170, 172, F172, FR172 and 175 Series Aeroplanes\n\nAD/CESSNA 170/47\n\nAmdt 1\n\n  \nCrankcase Breather Tube and Oil Seal 4/86\n\nApplicability: All models 170A, 170B, 172, 172A to 172P, 175, 175A, 175B, 175C, R172D and R172E fitted with Lycoming 0-320 series or 0-360 series engines.\n\nRequirement: To reduce the possibility of rapid loss of engine oil caused by ice obstruction of the engine crankcase breather, accomplish the following:\n\n    Visually examine the engine crankcase breather to determine if an alternate air outlet is drilled or cut in the tube as shown in Figure 1. If any of these provisions exist, make an appropriate entry in the aircraft maintenance records. No further action is necessary.\n\n    2. If the hole or cutout shown in Figure 1 is not in the engine crankcase breather tube:\n\n    (a) Inspect the crankcase to crankshaft seal and ensure that the seal is secure. (This seal is located behind the starter ring gear in the forwardmost part of the crankcase). Reinstall or replace this seal if it is not flush with the forward face of the crankcase.\n\n    (b) Drill the engine crankcase breather tube line to include an alternate air outlet as shown in Figure 1.\n\nCompliance: Unless already accomplished, within 100 hours time in service after 30 June 1982.\n\nBackground: This AD has been amended to clarify the situation where the breather is still in close proximity to the exhaust outlet. Although this may currently prevent the breather from freezing, the exhaust system has been redesigned and the outlet moved to the opposite side. The original exhaust system is no longer available, and if a new exhaust is fitted the breather will then be unprotected. Therefore all breathers should be modified regardless of position.\n\nCOMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 \\- 105 CIVIL AVIATION SAFETY AUTHORITY\n\nSCHEDULE OF AIRWORTHINESS DIRECTIVES\n\n![](image.002.png)","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"},"flash_summary":{"complexity_score":3,"scope_assessment":{"changed":true,"description":"Yes. The amendment broadened the directive's practical scope. The Background explains that some breathers had previously been protected by the original exhaust outlet position, but because the exhaust design and outlet location were changed, the AD now requires modification of all breathers regardless of their current proximity to the exhaust (Background). Operators must therefore inspect/modify breathers that earlier might have been excluded; compliance remains within 100 hours TIS after 30 June 1982 (Compliance)."},"complexity_factors":["Clear, narrow applicability to specific Cessna models and Lycoming 0-320/0-360 engines (Applicability).","Simple inspection task with a binary outcome: alternate outlet present or not (Requirement ¶1).","Low-complexity corrective actions: check/secure or replace a forward crankcase-to-crankshaft seal and drill an alternate outlet in the breather tube (Requirement ¶2a–2b).","Mandatory maintenance logging of findings and actions, creating a record-keeping burden (Requirement ¶1 and ¶2, maintenance records entry).","Fixed compliance window: completion within 100 hours TIS after 30 June 1982 (Compliance) imposes scheduling constraints on operators.","Technical access requirement: the seal is located behind the starter ring gear in the forward crankcase, which may require partial engine access or qualified maintenance personnel (Requirement ¶2a).","Background clarification increases universality of the mandate by removing reliance on previous exhaust placement as protection (Background), which affects aircraft that were previously considered 'protected'."],"plain_english_summary":"This airworthiness directive requires owners/operators of the listed Cessna 170/172/175 series aeroplanes with Lycoming 0-320 or 0-360 engines to inspect the engine crankcase breather and its forward crankcase seal, and to drill an alternate air outlet in the breather tube if one is not present. The work must be recorded in the aircraft maintenance log and completed within 100 hours time-in-service to reduce the risk of rapid engine oil loss from breather icing."},"kimi_summary":{"content_quality":"ok","complexity_score":2,"scope_assessment":{"changed":false,"description":"This AD remains tightly focused on its original purpose: preventing ice obstruction of crankcase breather tubes on specific Cessna models. Amendment 1 slightly expanded the mandatory scope to include breathers near exhaust outlets (previously considered protected), but this is a technical refinement within the same safety objective, not mission creep. The amendment responds to changed circumstances (exhaust system redesigns) rather than expanding to unrelated aircraft systems."},"complexity_factors":["Single, clearly defined applicability section listing specific aircraft models and engine types","Straightforward two-step compliance path with simple conditional logic (if hole exists → record; if no hole → modify)","Only one defined term implied ('time in service' — standard aviation term)","No cross-references to other legislation or regulations beyond the enabling authority (Civil Aviation Regulations 1998, Part 39)","Single background paragraph explaining rationale in plain language","Visual reference to Figure 1 (diagram) for technical specification, but no complex tabular data or formulae","Total length: approximately 250 words"],"plain_english_summary":"This CASA Airworthiness Directive mandates modifying the crankcase breather tube on specified Cessna 170/172/175 models with Lycoming O‑320/O‑360 engines to add an alternate air outlet (or verify it exists) and secure/replace the oil seal if needed. It affects aircraft owners, operators and maintenance engineers — required to prevent ice blocking the breather, which can cause oil seal failure and catastrophic engine loss. The AD was amended because exhaust changes no longer assured breather protection."}},"importantCases":[],"_links":{"self":"/api/acts/ad-cessna-170-47-amdt-1-crankcase-breather-tube-and-oil-seal","history":"/api/acts/ad-cessna-170-47-amdt-1-crankcase-breather-tube-and-oil-seal/history","analysis":"/api/acts/ad-cessna-170-47-amdt-1-crankcase-breather-tube-and-oil-seal/analysis","conflicts":"/api/acts/ad-cessna-170-47-amdt-1-crankcase-breather-tube-and-oil-seal/conflicts","importantCases":"/api/acts/ad-cessna-170-47-amdt-1-crankcase-breather-tube-and-oil-seal/important-cases","documents":"/api/acts/ad-cessna-170-47-amdt-1-crankcase-breather-tube-and-oil-seal/documents"}}