The article presents a proposal of the established in the Institute of Aviation program and tools that are to enable General Aviation Operators in our country to perform on-condition maintenance of piston engines. Program apart from the existing (strictly supervised) Engine Manual tasks, introduces new mandatory maintenance activities such as: monitoring of engine parameters during cruise and climb, with determination of their diagnostic tolerance limits (never been performed in the maintenance practice), oil spectrographic analysis, also with determination of tolerances and oil particle size monitoring. The article shows results of half year long monitored exploitations of Continental IO -240-B engines installed on Diamond DA20-C1 „Katana” aircraft.