Project E2 designs safe human-to-machine handover techniques in mixed-initiative control and addresses the recent trend to human oversight in autonomous vehicles and aviation. If a critical situation arises, operators need to be supported by an efficient interface for regaining and maintaining situational awareness during a handover. The research goals are 1) to extend the simulation environment to a physical lab representing a control centre for human oversight of multiple drones, 2) in the case of a critical situation, to explain not just the current system state, but also relevant information from the past and the foreseeable future, and 3) to develop suitable multimodal output techniques to explain the situation to the operator, also considering multiple drones.