This thesis addresses technological support to decision-making in time-critical environments. In particular, I develop and apply an information-theoretic approach to situation management in aviation security. This thesis investigates the factors affecting situation management and addresses the challenges of establishing timely situation awareness to support the 'course of action' selection. In order to efficiently manage an aviation security incident, a situation management approach can provide the required technological capability in this dynamic and complex environment. Situation management research is still in its infancy and more research concerning underlying methodologies and techniques is required. This work therefore models situation management as a collaborative information problem and explores the factors from a macro-perspective modelling the problem as a multi-agent system. The goal of the research is to explore and develop an information-theoretic framework for decision support systems in situation management contexts. This thesis presents the approach to design and develop a situation management framework within the aviation security context. The modelling work and experiments were implemented with an agent-based simulation software tool (Repast version 2.0). The framework and its implementation has been validated based on use case studies. The performance of the proposed agent model in comparison to two recent European live trial scenarios has been tested to emulate real-time constraints and requirements. The results obtained indicate that automation support for time-critical decision-making in aviation security supports the early identification of incidents and increases the situational awareness during the management of an incident. This allows decision-makers to select from a wider range of options, as the time-window for the deployment of responses increases. Next to the validation of the concept and framework developed, an initial situation management capability for aviation security in SESAR is defined. The work reported in this thesis demonstrates that the situation management concept and framework is applicable for multi-agency coordination and collaboration in aviation security incident management.