Military flights are separated from civilian flights by the use of flexible airspace structures that restrict access to civilian users. This approach is becoming less and less rigid and increasingly cooperative. There is a clear need to adapt existing airspace and air traffic flow management models to increase cost-effectiveness and reduce the negative impact of military flights on commercial air traffic. A prerequisite for this is to research the specifics of the functioning of military airspace users and their impact on civilian air traffic. It is necessary to research the specifics of military flying requirements and determine the limits of the range of optimization according to the unacceptable level of impact on the ability to perform military tasks. The existing methodology for planning and management of the training operations of high-performance military aircraft in flexible airspace structures is based on a temporary allocation of structures to either military or civilian users. The allocation is performed according to previous reservations in a way that corresponds as much as possible to real-time military aircraft operations. The aim of the research conducted within the doctoral dissertation is to develop a new procedure for proactive planning and management of high-performance military aircraft pilot training operations in flexible airspace structures. The hypothesis set out in the paper is: "Proactive planning and management of high-performance military aircraft pilot training operations can manage their impact on civil air traffic and improve the joint use of flexible airspace structures." Expected doctoral thesis original scientific contributions are: 1. A new process for proactive planning and management of high-performance military aircraft pilot training operations in flexible airspace structures; 2. Defining parameters for the evaluation of proactive planning and management of high-performance military aircraft pilot training operations in flexible airspace structures; 3. Defining indicators of the effectiveness of proactive planning and management of high-performance military aircraft pilot training operations in flexible airspace structures. The paper is structured in six parts. The introductory chapter of the paper describes the problem and the motivation for its research and presents an overview of previous research. The goal of the research as well as the basic hypothesis of the doctoral thesis and the scientific contribution is presented. In the second chapter, the Legislative Framework of Airspace Management, an overview of the international legal framework of ATM, the European legislative framework of airspace management and the legislative framework of airspace management in the Republic of Croatia is given from the aspect of civil-military airspace management. High-performance military aircraft training operations in flexible airspace structures designed to achieve the assigned mission within a given time frame are pre-determined by the limitations and interactions of the flight training syllabus, availability of pilots and aircraft and peculiarities of airspace structures used. In the third chapter, the process of planning and implementation of high-performance military aircraft flying in pilot training is elaborated through its components and organization of flying. The flight training program, the availability of pilots and aircraft, and the specifics of airspace structures in the Republic of Croatia used for the purpose of military pilots training on high-performance aircraft are described. The structure of the daily process of planning and management of high-performance military aircraft pilot training is elaborated. The notions of start time and exit at start time that shape daily flight planning are given. The process of creating a daily flight plan for a squadron is shown. In the fourth chapter, the impact of the use of flexible airspace structures on civil air traffic, the time of day exit as an organizational form of high-performance military aircraft flying in pilot training is elaborated. The results of the research performed on flexible airspace structures used for high - performance military aircraft pilot training are presented. The analysis of traffic demand in these airspace structures represents the foundation for further research into the impact of high-performance military aircraft flying on pilot training in flexible airspace structures. The existing performance indicators of civil-military air traffic management are explained and new parameters for evaluation and indicators of efficiency of planning and management of high-performance military aircraft pilot training operations in flexible airspace structures are introduced. The paper proposes a proactive model for planning and managing the training operations of high - performance military aircraft that takes into account the specifics of civil aircraft traffic demand in flexible airspace structures. In order to reduce the impact of military aircraft operations on civil air traffic, the planning of the use of flexible airspace structures is carried out on the basis of data on the local daily minimum number of civil aircraft flights affected by the use of flexible airspace structures. The fifth chapter presents the results of the simulation of the impact of the use of flexible airspace structures on the operations of civilian airspace users. The data obtained using the computer program NEST (Network Strategic Tool) are the basis for creating a database of exits with daily minimums of civil air traffic in flexible airspace structures. The similarity of the distribution of the values of the number of actual and simulated flights of civil aircraft was confirmed for the entire research period. The algorithm for the planning and management of high-performance military aircraft operations in pilot training is explained. The Esquire program developed to enable experimentation with the proposed proactive model of planning and managing high-performance military aircraft operations in pilot training in flexible airspace structures is presented. Simulation scenarios are developed for the single-track (existing), the multi-track, the two-track and the segregated model, and the proactive planning simulation of all the above scenarios are presented. The analysis of the results of all conducted simulation scenarios was performed using the proposed evaluation parameters and performance indicators for planning and managing high-performance military aircraft pilot training operations in flexible airspace structures. By comparing the planning model, the set scientific hypothesis is confirmed and the scientific contribution of the paper is verified. The conclusion explains the relevance of the research, emphasizes the contribution to the development of the new model and points to the area of further research based on the acquired knowledge on the impact of planning and managing operations of high-performance military aircraft in pilot training in flexible airspace structures on civil air traffic. The results of proactive planning and management of high-performance military aircraft training operations in flexible airspace structures indicate the ability to manage their impact on civil air traffic and to improve the joint use of flexible airspace structures. The effect of proactive planning is reflected in the improvement of efficiency indicators through the reduction of fuel consumption and pollutant emissions and through the reduction of air traffic control losses.