European airspace is currently facing significant challenges due to increasing traffic demand and limited sector capacity. This situation leads to an overload of demand, so Air Traffic Controllers (hereinafter ATCOs) are often forced to implement regulations that cause delays. Moreover, an ATCO cannot be endorsed in an unlimited number of sectors, as doing so would compromise the maintenance of operational proficiency and specific sector skills. Consequently, the limited cross-sector flexibility of controllers has become a key constraint in optimizing airspace management. Additionally, the strategic definition of sector groups has a direct impact on which sector configurations can be activated. An inadequate sector grouping strategy may hinder operations by restricting access to more efficient sector configurations. While in some cases, controllers may be endorsed for multiple sectors (up to ten), this flexibility remains insufficient to mitigate capacity and efficiency challenges fully. IFAV3 (Increased Flexibility of ATCO Validation En-Route) project has been developed within the Single European Sky ATM Research (hereinafter SESAR) framework, aiming to maximize flexibility in ATCO rostering. Its main expected benefits include an improvement in cost efficiency in Air Traffic Control (hereinafter ATC) through reduced training costs and optimized rostering by a better utilization of existing capacity. The research presented in this paper has been conducted in the frame of the European IFAV3 project. The IFAV3 project has received funding from the SESAR 3 Joint Undertaking under grant agreement No 101114683 under European Union’s Horizon Europe research and innovation programme.