Due to the airliners and aircraft operators pressure on reducing the operating costs, the diagnostic systems are included in aircraft, so that the wearness of single functional elements of other functional systems can be monitored. This monitoring can save money, that are usually spent on maintenance and especially, it leads to an increase of the overall safety of aircraft operations. The task of this work is to design a diagnostic system for small transport aircraft. For the right and proper design, is the correct understanding of the functions of each part on aircraft systems needed. The part of this work is attended to the selection procedure of appropriate diagnostic parameters, next section deals with the suitable options of their scanning. I do mention the summary of the chosen diagnostic parameters for the scanning and the recomended ways of their measuring.