Carl Westin

70 Source bias effects Participants interacted with aircraft by pointing on an aircraft symbol and click- ing the left mouse button. This opened up the SSD for the aircraft. Vectors were implemented by dragging a selected aircraft’s velocity trend vector to a desired area, and executing the command by pressing the ENTER keyboard key. Speed was controlled by scrolling the mouse scroll wheel up for an increase, and down for a decrease. Vector and speed commands could also be combined into one com- mand. Participants were supported by a CD&R decision aid that identified potential conflicts and provided resolution advisories. When this occurred, the SSD for the affected aircraft automatically opened up with the advisory plotted within the SSD. Participants could either accept or reject the advisory. 4-3-4 Measurement scenario and designed conflict The simulation consisted of an en-route environment with a single squared sector, 80 x 80 nmi in size, with eight entry/exit waypoints evenly distributed around the sector. The airspace represented a free route airspace. Figure 4-2 shows the mea- surement scenario used, consisting of two parallel traffic flows with one crossing flow. The scenarios lasted two minutes. In total 27 aircraft were included, with between 19 and 22 aircraft always present in the sector. The high traffic load was used to create a more complex scenario than participants were accustomed with. The measurement scenario contained a carefully designed conflict consisting of two aircraft (QS1338 and OM3185) approaching at perpendicular tracks. The conflict can be seen in the middle of the sector, with QS on a western heading (270 degrees at 260 knots, with a speed envelope between 200 and 320 knots) and OM flying a northern heading (360 degrees at 260 knots, with an identical speed envelope as QS). With 0 nmi defined as the closest point of approach (CPA), both aircraft will collide at the exact center of the sector 120 seconds after scenario start. Context aircraft were used to increase task difficulty, prevent early conflict de- tection, and make scenarios more realistic. They were placed and configured so that their presence would not interfere with the designed conflict or restrict conflict solv- ing. The use of context aircraft is commonly used in ATC research for purposes of making scenarios more complex. 35, 184 Certain simplifying assumptions were made for purpose of experimental control. The simulation was restricted to the horizontal plane, leaving only heading and speed commands available for solving conflicts. Therefore, all traffic was restricted to flight level 270. Moreover, there were no meteorological factors, such as wind or adverse weather, affecting traffic.