The modern military industry is characterized by very complex technical systems. Therefore, the demands of technical support are becoming more and more demanding. This creates that the characteristics of avialability and reliability are becoming the major factors that determine the developmental and technical quality of those systems. The focus of the research presented in the thesis is the examination of the applicability of the Fault Tree Method in the analysis of the efficiency of highly reliable system for the ejection of pilot’s seat MkCH-11, training aircraft Pilatus, PC-9. The main goal of the project is to contribute to the possible improvements in existing systems that are already in use for the maintenance of complicated technical systems. The analysis of operational availability was performed by examining data collected over the period of 10 years for the set of samples for technical system MkCH-11. Suggestions were made in the thesis for possible interventions at “critical points”and “critical personnel” in the aircraft maintenance system. Provided positive changes in reorganization would have direct influence on the increase of operational availability of maintained technical systems within organisation of aircraft maintenance. In addition, the modifications would also contribute to the increased quality of the technical condition of the system. The analysis of the reliability of technical system MkCH-11 using the Fault Tree Method with use the «CAFTA» software package was completed. Obtained results and derived conclusions may be used as a theoretical basis for the improvement of the system for the maintenance of complex technical systems that are currently in use in Croatian Armed Forces.