The focus of the research is the analysis and assessment of Air Traffic Control (ATC) maintenance and technical service processes. Deriving from the general ATC process model, which is the part of the Air Transport System, the related ATC Services including a Key Performance Indicator System were developed. A theoretical analysis was performed to develop a special correlation matrix between the Air Transport System to ATC service and ATC technical services, which reflect the top-down approach of process modelling proceeding. A particular research of different international ATC service organization, selected by defined parameter was performed for analysis. The analysis was implemented with different scientific research methods. Basing on this international research, a detailed SWOT analysis and conclusions of each ATC organization itself and additionally a parameter-oriented comparison between the different organizations and their specifics were performed. The results of this research were described in a SWOT analysis, rating assessment of utilization of the theoretical methods and qualified evaluation of implemented KPI System. For final maintenance process evaluation an ATC-Maintenance Process Maturity method based on ISO /IEC Standard 15504 was developed. The results and developments of the research will be the essential prerequisite for the further research of dissertation and development of a harmonized ATC Meta Frame Maintenance Process Model as a part of the Air Transport System on macro model level and deriving to the ATC specific Maintenance Service Model on micro level for the specific ATC organization basing on service and business modelling methods.