In this article we propose a concept of cognitive pilot assistance for on-board mission (re-)planning. Current research activities address the delegation of complex multi-vehicle planning tasks to automation, as well as the related monitoring tasks. However, opacity and loss of situation awareness may arise as a consequence of delegation. To counteract these shortcomings, we suggest a mixed-initiative planner approach. Adequate assistance shall be ensured by a planning strategy model, which represents the pilots' mental process during the planning. A pilot observer determines the pilot's current activities. In a next step, these activities are analyzed to identify the pilot's planning progress. The planning progress and other factors, for example situational changes, are used to shape the intervention policy. An overview of the current implementation status and the future work is given. The proposed concept is investigated in our military manned unmanned teaming application.