Downlinking TCAS Resolution Advisories - EUROCONTROL Study Results

Abstract

The widely used Traffic-alert and Collision Avoidance System (TCAS) gives pilots vertical maneuver advice to avoid mid-air collisions. Pilots should follow this advice and report any deviation from clearance to Air Traffic Control (ATC); however, pilot reports of TCAS Resolution Advisories (RAs) are often inadequate and contradictions between ATC instructions and RAs have contributed to accidents. Therefore safety recommendations have been made to automatically downlink RA information to controllers. A EUROCONTROL feasibility study concluded that RA downlink can potentially reduce contradictions between ATC and TCAS. Implementation is technically feasible in areas covered by a Mode S ground radar and should be feasible for areas covered by ADS-B receiver networks. Most of the time, both options deliver data faster than pilots and quickly enough to be relevant. Moreover, real-time simulations in enroute airspace provided quantified results that were favorable to RA downlink. Controllers participating in the simulations generally supported the concept. Finally, a safety assessment noted several safety requirements for RA downlink and qualitative reasoning indicated their implementation would allow a net safety benefit from RA downlink. A risk assessment model has been independently developed and data are now being gathered to estimate the net safety effect.