Monitoring of TCAS Resolution Advisories in Core European Airspace

Abstract

Downlink and display of Resolution Advisories (RAs) – which are issued by the airborne Traffic alert and Collision Avoidance System (TCAS) – has been proposed as a means of informing the air traffic controller that an RA has been posted onboard the aircraft. Previous research has pointed to a number of operational benefits of RA downlink display, such as an improved controller situational awareness and a smaller likelihood of contradictory clearances to aircraft involved in an RA event. However, these benefits of RA downlink display only pertain to RAs that, if complied with, cause a deviation from the Air Traffic Control (ATC) clearance. In order to investigate the frequency and type of RAs in core European airspace, EUROCONTROL initiated the PASS monitoring study. Within this study, RA downlink data from six Mode-S radars covering a large part of the core European airspace were collected from September 2007 to March 2008. The results of the monitoring indicate that approximately a fourth of the RAs issued are likely to cause a deviation from the ATC clearance. However, because of the low overall number of RA encounters (i.e. 1 RA encounter per 2160 flight hours), the display of all RAs – including those that do not yield a deviation from the ATC clearance – is not likely to cause problems related to screen clutter or controller desensitization. On the basis of the results of the RA monitoring, some concerns are identified and refinements to the operational concept for RA downlink display are proposed.