Ecological interface design for terrain awareness

Advanced terrain warning systems, such as the enhanced ground proximity warning system, and safety-enhancing displays, like the synthetic vision system, have proven to play an important role in reducing the number of controlled flight into terrain accidents. Research indicated, however, that terrain collisions may still occur for aircraft equipped with these systems. Synthetic vision allows for perception of the environment, but lacks properties to support understanding and extrapolation of the perceived data. A terrain warning system provides elementary meaning to the environment, but is not well integrated into synthetic vision displays. To further increase terrain awareness and, ultimately, eliminate terrain collisions, synthetic vision should be integrated with a terrain awareness functionality that allows the pilot to be continuously informed about how the external constraints (imposed by the terrain) relate to the internal aircraft constraints (e.g., climb performances). Based on that information, pilots canjudge for themselves what an obstacle actually means to them in terms of possibilities to fly over it, and if not, what the alternatives for action are. In this article, the paradigm of ecological interface design is used to analyze the aircraft manual control task in the vertical plane and to develop a more meaningful interface for (vertical) terrain awareness. An abstraction hierarchy is presented, developed for the task of guiding an aircraft through a terrain-challenged environment. The design and experimental evaluation of a vertical situation display are discussed, enhanced with ecological overlays to increase terrain awareness.