Encounter Analysis to Support Detect, Sense, and Avoid (DSA) Elevation Field of Regard (FOR) Requirements

Abstract

Widespread integration of Unmanned Aircraft Systems (UAS) in the National Airspace System (NAS) continues to be hindered by the inability to meet “see and avoid” requirements stated in Title 14 of the Code of Federal Regulations (CFR). Ongoing efforts by standard development organizations are attempting to establish performance standards that will ultimately lead to development of Federal Aviation Administration (FAA) certifiable Detect, Sense, and Avoid (DSA) systems. Previous efforts have also attempted to define UAS collision avoidance system performance requirements necessary for operating in the NAS at a level of safety equivalent to that of a manned aircraft. Although several of these efforts actually proposed values for sense and avoid performance parameters, most of these values were based solely upon the CFR regulations for manned aircraft or the specifications for existing traffic advisory systems such as TCAS. One of the performance parameters defined in recent studies is sensor Field of Regard (FOR) - the volume of airspace that must be surveyed in order to detect other aircraft that may pose a collision threat. The values proposed in these studies go beyond references to the regulations and are based on a study conducted by NASA specifically for high-altitude, long-endurance UAS. That study assumed a head-on encounter between two aircraft in level flight and recommended a volume of +/-15 degree elevation and +/-110 degree azimuth. Although these FOR values may be valid for the assumed conditions, they do not account for maneuvering aircraft or aircraft on a similar course. Additional in-depth analysis of encounters is necessary to establish quantitative values required for field of regard standards that provide a sufficient basis for system certification. The primary measure of effectiveness for this analysis was the percentage of conflicting traffic within the UAS sensor’s elevation FOR. Given representative flight parameter ranges for the UAS and conflicting traffic, the methodology uses statistical distributions to randomly generate multiple collision encounters and determine the conflicting aircraft’s relative azimuth and elevation. This methodology can, therefore, provide a realistic assessment of FOR coverage capability necessary for determination of DSA system requirements. The results from this study indicate that a +/-15 degree elevation requirement may not be sufficient for all potential collision geometries and flight conditions. This study has resulted in the development of a methodology that can play an important role in determining collision avoidance system’s performance necessary to achieve the required level of safety while avoiding over-stating requirements which could delay DSA system development.