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.