Carl Westin

94 Automation transparency effects Protected zone Intruder aircraft B Controlled aircraft A V 2 V 1 (a) Conflict geometry A B Conflict zone - V 2 V 2 V 1 V relative (b) Conflict zone A B Current speed No-go zone V min V max (c) Triangle (TRI) SSD A B Current speed No-go zone (d) Heading band (HB) SSD F IGURE 5-1: Right angle conflict between aircraft A and B, with SSD shown for aircraft A. indicate time to separation loss, with the red color representing less time than the or- ange color. Time to separation loss is computed by processing the relative velocity and relative distance between aircraft. To avoid separation loss, the velocity vector of aircraft A must be positioned outside the triangle-shaped no-go zone. Figure 5-1(d) shows a simplified SSD representation in which the no-go zones are restricted to a narrow band representing the current speed of the controlled air- craft. This heading band (HB) SSD was developed for purposes of integrating the SSD directly with the radar display. 101 The HB SSD was considered appropriate for the particular ATC en-route environment considered, in which speed commands are infrequent, partly due to narrow speed performance envelopes of aircraft.