Carl Westin

200 Solution Space Diagram ! (a) Triangle SSD with entire maneuver envelope (b) Heading band SSD that only shows current speed F IGURE B-6: Simplification of the SSD for en-route ATC. aircraft’s entire maneuver envelope, and (b) the simplified heading band SSD, which only depicts heading options for the current speed. This representation was believed to better fit en-route CD&R. Heading commands are often preferred at high (flight) levels (as opposed to speed, and unless vertical options are available), because air- craft often operate close to their maximum performance envelope and therefore have a narrow control space for speed. To support controllers’ understanding of time, no- go areas were color coded to better reflect the proximity of other aircraft and time available before conflict (fourth comment). Red areas were defined to reflect that separation loss would occur in less than one minute. Yellow areas (sometimes per- ceived as orange) reflected that separation loss would occur between one and four minutes ahead in time.