With SESAR and NextGen readying towards implementing novel operational concepts and technical enablers in ATM/CNS, the question of how to manage security in a dynamic environment across a highly distributed and networked system gains higher attention. The Global ATM Security Management project (GAMMA) addresses the development of such a security situation management capability. Following the September 11 attacks and major large-scale outages of critical infrastructures, the security of air navigation has emerged as a critical capability gap. On-going transformation programs like SESAR and NextGen are moving into the deployment phase with limited to none tangible security solutions. GAMMA addresses this gap by investigating a security situation management capability. The framework of this capability is devised as a distributed network of aviation stakeholders that jointly collaborate in identifying and localizing security incidents while considering the constraints given by the different participants, national responsibilities, and collaboration-related requirements. This paper addresses the preparatory work for the validation of an initial security situation management capability. For that purpose, project partners setup a joint configuration and trial network for the security functions and systems developed in the frame of a real-time human-in-the-loop simulation. The simulation results have been measured against the mapping of the operational concept and validation requirements, in particular in terms of situational awareness on the operator side and networked incident management response. These results will inform the further validation activities of the project.