This paper describes a concept for a coplanar airborne self-separation display, which is designed to aid pilots in their separation task, by visualizing the possibilities for conflict resolution that the airspace provides. This study is a part of an ongoing research toward the design of a constraint-based 3-D separation assistance interface that can present all the relevant properties of the spatiotemporal separation problem. A display concept is proposed that presents speed, heading, and altitude action possibilities in two planar projections of the maneuver action space. The interface also visualizes how these projections interact with each other.