This paper describes the development of the first known successful three-micron absolute main oil filter for an aircraft gas turbine lubrication system, replacing the 40-micron nominal filter on the Avco Lycoming T53 engines. The new disposable elements, running approximately 300 hours without clogging, provide a much cleaner lubrication system and have eliminated requirements for 25 hour filter inspections and 100 hour oil drains. Despite past filter experience, the clean pressure drop through the new filter is close to that of the 40-micron unit. Two benefits of the new elements are described. The first is prevention of the wear caused by the abrasive action of oil containing fine one to five-micron particles. Once these particles are removed, the system stays clean for hundreds of hours. This period is not shortened unless lube system component failures, engine teardowns and rebuilds, or frequent oil changes occur. The second benefit is the marked absence of oil degradation with clean oil over long drain intervals. The paper describes the design of the filter assembly and indicator system, bench testing, and the 6000 hours of engine testing of the filter prior to its proposed incorporation into the production engines.

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