Design principles and algorithm development for two types of NextGen airborne conflict detection and collision avoidance

Abstract

As the aviation community moves toward the Next Generation Air Transportation System (NextGen), the current Traffic Alert and Collision Avoidance System (TCAS II) may become inadequate. This paper describes two types of algorithms that use Automatic Dependent Surveillance-Broadcast (ADS-B) as the surveillance source for future airborne collision avoidance systems (CASs). The first type, denoted by NextCAS I, estimates the range, range rate, altitude and altitude rate from the ADS-B state vector information but maintains much of the detection and all of the resolution logic structure of the current TCAS. The second type, denoted by NextCAS II, provides a novel approach to detection and resolution of air traffic conflicts in the 3-dimensional (3-D) airspace between two aircraft. The inputs to the detection algorithm are the current 3-D position and speed vector of both aircraft and a cylindrical minimum safety protection zone (PZ) around the conflicting aircraft. For a CAS, the size of the configurable PZ can be assigned values that the Federal Aviation Administration (FAA) considers as a near mid-air collision (NMAC <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sup> ) incident. When available, additional inputs, such as measurement uncertainties and intruder type (e.g., manned/unmanned), can be used to alter the default protection zone. The conflict detection takes into account the 3-D encounter (e.g., closure rate, miss distance, relative converging maneuver). The resolution algorithm initially computes a set of six resolution advisories (RAs) and associated resolution alert times that ensure no violation of the protection zone. The six resolutions consist of three sets of two maneuvers related to: ground track (left, right), forward speed (speed up, slow down), and vertical speed (climb, descend). The initial solutions take into account ownship capability (i.e., max climb/descent rate, max turn rate, max speed/stall speed) and ownship pilot response delay (e.g., autonomous vs. manual RA execution). These six solutions are subsequently down-selected in two steps: first, based on the encounter geometry, a single implicitly coordinated, independent solution is selected for each of the three dimensions; then, based on ownship preferences and operational considerations, a final RA solution is selected.