Impact of GPS and ADS-B Reported Accuracy on Conflict Detection Performance in Dense Traffic

In this paper, we present preliminary results on the impact of GPS and ADS-B reported position on the performance of a novel conict/collision alerting algorithm primarially intended for General Aviation (GA). For this purpose, we analyze the dynamics of GA trac using 6 months of trac in the San Francisco bay terminal area and several representative airport trac areas. The observed standard proximity of GA aircraft to each other and their maneuvring dynamics indicate that existing collision avoidance systems such as TCAS would have unacceptably high nuiscence alarm rates for low altitude GA operations. We then present a novel collision alerting algorithm, based on ADS-B. This algorithm uses a buer zone, the Collision Airspace Zone (CAZ), around the target/intruder aircraft and alerts the pilot of the ownship aircraft of the predicted penetration of the CAZ by the ownship. The size of the CAZ is determined by the reported ownship GPS and target ADS-B position accuracies. Our analysis suggests that the CAZ should be a cylinder of radius 528 ft and semi-height 200 ft. This is very close to the traditional near mid-air collision cylinder dimensions (500 ft radius, 200 ft sem-height) . Simulations are presented which analyze the performance of the algorithm, in terms of detection time, as a function of the CAZ dimension.