Real-Time Simulation (RTS) is used to validate new operational concepts with the contribution of ATCOs proficient in the measured airspace. In order to create realistic and high fidelity scenarios CRDS offers the clients the opportunity to use the HMI of their “home” ATM system reproduced by the Simulation Developers. The RTS platform encompasses 34 controller and 27 pilot working positions with advanced ATM tools and applications, System Coordination and Data-Link environment. The validation methodology is in line with the European Operational Concept Validation Methodology (E-OCVM). The results of the validation exercises are analysed by the Human Factors Analyst at CRDS. Human-in-the-loop parameters such as objective data (e.g. the number of coordination events, ATM tool usage, short term conflict alerts) and subjective feedback through generic and simulation-specific questionnaires are gathered during the simulation. This way, ATM experts and decision makers will be able to foresee potential changes in human performance and to prevent safety issues related to workload and situational awareness.