The use and understanding of the proximate status indication in traffic displays

Traffic Collision Avoidance System (TCAS) traffic displays use symbol fill to distinguish "proximate" from "non-proximate" targets, where proximate targets are within a specified range and altitude of ownship, and non-proximate targets are outside these parameters. While this is satisfactory for TCAS displays, Cockpit Displays of Traffic Information (CDTI) can present much more information than TCAS displays, and an alternative use of symbol fill may be preferred. Since a symbol for traffic has a limited number of visual features for encoding information, CDTI symbology should only encode information that can be used effectively by pilots. This study evaluated the utility of the proximate status indication in an effort to understand whether it is useful enough to show on CDTIs. One hundred and one corporate and airline pilots were recruited for the web-based study via advertisements in on-line pilot newsletters. Pilots viewed videos of traffic scenarios depicted on a traffic display. Half the pilots were shown displays with a proximate status indication, and half the subjects were shown displays without a proximate status indication. Results showed that the proximate status indication did not improve consistency of pilot ratings relative to objective measures of threat and visibility. Furthermore, pilots who had the proximate status indication were 9% less accurate on average in selecting the highest threat traffic, whether the most threatening traffic was proximate or not. Pilots also answered questions about the proximate indication status in TCAS. Most pilots reported they found it useful, usually for prioritizing their attention. Most pilots recognized that a proximate symbol must be within a specific range and altitude, but nearly equal proportions of pilots also believed proximate traffic must always be a higher threat than non-proximate traffic, which is not the case. The combined results suggest that when assessing traffic threat, pilots place greater weight on the closeness of traffic than other key characteristics such as relative closing speed.