Resolution Advisory Detection Algorithm

A TCAS-II Resolution Advisory Detection Algorithm

César Muñoz

⇤ Anthony Narkawicz

James Chamberlain

NASA, Langley Research Center, Hampton, VA, 23681, USA

The Tra�c Alert and Collision Avoidance System (TCAS) is a family of airborne systems

designed to reduce the risk of mid-air collisions between aircraft. TCAS II, the current

generation of TCAS devices, provides resolution advisories that direct pilots to maintain

or increase vertical separation when aircraft distance and time parameters are beyond

designed system thresholds. This paper presents a mathematical model of the TCAS II

Resolution Advisory (RA) logic that assumes accurate aircraft state information. Based on

this model, an algorithm for RA detection is also presented. This algorithm is analogous

to a conflict detection algorithm, but instead of predicting loss of separation, it predicts

resolution advisories. It has been formally verified that for a kinematic model of aircraft

trajectories, this algorithm completely and correctly characterizes all encounter geometries

between two aircraft that lead to a resolution advisory within a given lookahead time

interval. The RA detection algorithm proposed in this paper is a fundamental component

of a NASA sense and avoid concept for the integration of Unmanned Aircraft Systems in

civil airspace.