Michael Zuschlag

Impact of traffic symbol directional cues on pilot performance during TCAS events

Implementation of Automatic Dependent Surveillance — Broadcast (ADS-B) technology enables aircraft to broadcast, receive and display a number of aircraft parameters that were not previously available to pilots. While significant research has been conducted regarding Cockpit Display of Traffic Information (CDTI) display format, there is little research to assess the impact this additional information would have on pilot response to Traffic Alert and Collision Avoidance System II (TCAS II) Traffic Advisory (TA)/Resolution Advisory (RA) events. The purpose of this study is to determine the impact of providing directionality information for traffic symbols on a TCAS traffic display during a TA/RA event. This issue is particularly relevant for shared TCAS/CDTI displays. The study supported the development of CDTI performance standards through RTCA, Inc. Twenty-three current and qualified Boeing 737 (B737) pilots flew two 35-minute flight segments in a full motion B737 Next Generation (NG) flight simulator, one flight segment with modified symbology that included traffic directionality information and one with standard TCAS symbology that does not directly provide directionality information. During each flight segment, pilots experienced six separate TA/RA encounters that were counter-balanced to vary encounter geometry, phase of flight and visual conditions. Of the 276 planned RA encounters, 251 RAs actually occurred. In some cases, no RA was received due to either pilot maneuvering (22 cases) or simulator issues (three cases). Dependent measures included pilot responses to TCAS TA/RA encounters and pilot use of TCAS displays as measured by eye tracking data. The results indicate that inclusion of traffic directional information on a traffic display during TCAS TA/RA encounters does not negatively affect pilot response to RAs as measured by timing and magnitude of the RA response. Directional information also yielded no observed effect on pilot scans (allocation of gaze). Although effect of symbology was not observed, horizontal and/or vertical maneuvering beyond that commanded by the RA was observed in 90 of 273 possible TCAS TA/RA encounters, independent of symbology. Such maneuvering may be appropriate, depending on the information and context. However, eye tracking and subjective data suggest the maneuvering decisions may be based on the traffic display and not based on visual acquisition or other information. While the overall RA compliance rate was high, the degree of vertical and horizontal maneuvering during the TA/RA event should be better understood since TCAS traffic displays are not intended to support maneuvering. Further research is required to better understand the circumstances in which maneuvering occurs and the resulting impact on the air traffic system.

Symbols for Cockpit Displays of Traffic Information

A web-based study assessed pilots ability to learn and remember traffic symbols that may be shown on Cockpit Displays of Traffic Information (CDTI). These displays convey data obtained from Automatic Dependent Surveillance-Broadcast (ADS-B) and related Aircraft Surveillance Applications System (ASAS) technologies, as well as other surveillance data sources. We evaluated three aspects of using the traffic symbols when presented in isolation on a static display: intuitiveness, ease of learning, and ease of remembering the symbols. Four symbol sets were tested, each with approximately 22 symbols. Each participant saw only one of the four symbol sets. The sets used different visual features of the traffic symbol to represent the Directionality, Data Quality, Air/Ground Status, Alert Level, Selection Status, and Pairing Status of nearby aircraft. A total of 623 pilots with a broad range of experience participated in the main portion of the study. Results showed that while some conventions are well understood, such as the use of red and yellow for warnings and cautions (respectively), other conventions may be confusing and should be avoided. Two examples of confusing conventions are (a) using more than one visual feature (e.g., two different shapes) to represent the same traffic information, and (b) using similar visual features (e.g., two different outlines) to represent different traffic information. Results of the study were considered by a Federal Advisory Committee that develops standards for these traffic displays (RTCA Special Committee (SC) 186).

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 U.S. Government work not protected by U.S. copyright the closeness of traffic than other key characteristics such as relative closing speed.