This work is intended to investigate the Aircraft Technical Diagnostics Systems by focusing on Central Maintenance Systems and the Fault Detection and Isolation (FDI) process among the avionic components. A review about the Computer Control Systems and background about the Avionic Architecture is presented prior to introducing to most popular FDI method; model-based diagnosis. The discussions about the onboard FDI practices are followed by a maintenance hangar FDI perspective which was concluded as a result of the field research. The outcomes of the field research and pointing the “real” fault isolation are analyzed to point the practical needs of a hangar FDI tools. Subsequently, a proposal technique, which can improve fault isolation by preventing No-Fault-Found (NFF), is given by discussing the methods to implement it. Finally, the results of investigation and conclusions of analysis are presented. / Baigiamajame darbe lietuviškos anotacijos nepateikta.