Uncorrelated Encounter Model of the National Airspace System Version 2.0

Airspace encounter models, which provide realistic close encounter situations representative of the airspace, are a critical component in the safety assessment of sense and avoid (SAA) systems. Of particular relevance to Unmanned Aircraft Systems (UAS) is the potential for encountering general aviation aircraft that are flying under Visual Flight Rules (VFR) and which may not be in contact with air traffic control. In response to the need to develop a model of these types of encounters, Lincoln Laboratory undertook an extensive radar data collection and modeling effort involving over 200 radars across the United States. This report describes the structure, content, and usage of that encounter model. The model is based on the use of Bayesian networks to represent relationships between dynamic variables and to construct random aircraft trajectories that are statistically similar to those observed in the radar data. The result is a framework from which representative intruder trajectories can be generated and used in fast-time Monte Carlo simulations to provide accurate estimates of collision risk. The model described in this report covers only uncorrelated encounters. An encounter with an intruder that does not have a transponder, or between two aircraft using a Mode A beacon code of 1200 (VFR), is uncorrelated in the sense that it is unlikely that there would be prior intervention by air traffic control. The uncorrelated model described in this report is based on data from transponderequipped aircraft using a 1200 (VFR) Mode A code observed by radars nationwide. As determined from a previous comparison against primary-only tracks, in addition to representing cooperative VFR-on-VFR encounters, this model is representative of encounters between a cooperative aircraft and conventional noncooperative aircraft similar to those using a 1200 transponder code. The uncorrelated model described in this report is one of several developed by Lincoln Laboratory; the other Lincoln Laboratory encounter models are described in separate reports. For example, a second uncorrelated model was developed for unconventional aircraft that have different flight characteristics than 1200-code aircraft. A correlated encounter model was developed to represent situations in which it is likely that there would be air traffic control intervention prior to a close encounter; the correlated model applies to intruders using a discrete, non-1200 code. Also, a model covering international airspace was developed. Separate electronic files are available from Lincoln Laboratory that contain the statistical data required to generate and validate uncorrelated encounter trajectories. Details on how to interpret the data file and an example of how to randomly construct trajectories are provided in Appendix A and Appendix B, respectively. A Matlab software package is also available to generate random encounter trajectories based on the data tables.