{"id":"F2006B02130","name":"AD/AC/70 - Engine Oil Breather Line - Modification","slug":"ad-ac-70-engine-oil-breather-line-modification","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"repealed","isInForce":false,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":41360,"registerId":"commonwealth-F2006B02130-current","compilationNumber":null,"startDate":"2026-04-01","status":"Repealed","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/AC/70 - Engine Oil Breather Line - Modification","content":"---\nmeta-content-style-type: text/css\nmeta-content-type: application/xhtml+xml; charset=utf-8\nmeta-description: CASA Airworthiness Directive\nmeta-generator: Aspose.Words for .NET 22.10.0\nmeta-keywords: Issue 8/1979,Aircraft below 5700 kg,Twin Commander (Gulfstream/Rockwell/ Aerocommander 500, 600 and 700) Series Aeroplanes,Engine Oil Breather Line - Modification,70\ntitle: Airworthiness Directive - AD/AC/70 - Engine Oil Breather Line - Modification\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)  Twin Commander (Gulfstream/Rockwell/ Aerocommander 500, 600 and 700) Series Aeroplanes\n\n \n\nAD/AC/70 Engine Oil Breather Line - Modification 8/79\n\nApplicability: Models 680F, 680F(P), 680FL and 680FL(P) modified per STCs SA2691WE or SA2891WE (Lycoming IO-720 conversion).\n\n \n\nDocument: Mr. R.P.M. Inc. SB No. 004.\n\n \n\nCompliance: Within 100 hours’ time in service after 31 August 1979.\n\n \n\nBackground:  The manufacturer has found it necessary to provide an alternative oil breather line outlet in the event that the primary vent becomes blocked by ice in flight.\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":{"_metrics":{"model":"kimi-k2.5","source":"moonshot-batch","completionTokens":1360},"content_quality":"ok","complexity_score":2,"scope_assessment":{"changed":false,"description":"This airworthiness directive maintains its original narrow scope targeting specific aircraft models for a specific safety-critical engine modification. There is no evidence of scope creep beyond the original technical safety issue addressed."},"complexity_factors":["Extremely short document (approximately 150 words of substantive content)","Single, unambiguous technical requirement referencing only one external service bulletin","Limited applicability restricted to four specific aircraft models with identified engine modifications","Clear compliance deadline with no nested conditions or exceptions"],"plain_english_summary":"**What this rule does:** Requires owners of specific Twin Commander aircraft to modify the engine oil breather line to prevent engine failure.\n\n**Who it affects:** Owners of Twin Commander Models 680F, 680F(P), 680FL, and 680FL(P) that have been fitted with Lycoming IO-720 engines under special modification certificates (called STCs) numbered SA2691WE or SA2891WE.\n\n**What must be done:** Install an alternative oil breather line outlet according to the technical instructions in Mr. R.P.M. Inc. Service Bulletin No. 004.\n\n**Why it matters:** If the primary oil vent (a pipe that releases pressure from the engine) becomes blocked by ice during flight, pressure can build up inside the engine. This can cause serious engine damage or complete engine failure. The modification creates a backup vent path to prevent this dangerous situation.\n\n**When it must be done:** Within 100 hours of flying time after 31 August 1979."}},"importantCases":[],"_links":{"self":"/api/acts/ad-ac-70-engine-oil-breather-line-modification","history":"/api/acts/ad-ac-70-engine-oil-breather-line-modification/history","analysis":"/api/acts/ad-ac-70-engine-oil-breather-line-modification/analysis","conflicts":"/api/acts/ad-ac-70-engine-oil-breather-line-modification/conflicts","importantCases":"/api/acts/ad-ac-70-engine-oil-breather-line-modification/important-cases","documents":"/api/acts/ad-ac-70-engine-oil-breather-line-modification/documents"}}