Downstream Effects of Separation Assurance on Encounters Between Unmanned and Manned Aircraft

Abstract

This paper documents a crucial piece of the ongoing effort to develop minimum operational performance standards for unmanned aircraft detect-and-avoid systems: the estimation of the rate of encounters between unmanned aircraft and manned aircraft operating under visual flight rules. In fast-time simulations that included both simulated future unmanned aircraft and actual present-day manned aircraft operating under visual flight rules, unmanned aircraft encountered manned aircraft operating under visual flight rules once every 5.3 unmanned aircraft flight hours. Modeled air traffic controller mitigations for conflicts between unmanned aircraft and manned aircraft operating under instrument flight rules only reduced the rate of encounters between unmanned aircraft and manned aircraft operating under visual flight rules by 0.2%, with no statistically significant or practical effect on encounter geometry characteristics. Analysis of the simulations without modeled air traffic controller mitigations showed that the highest rates of encounter and loss of well clear occurred at altitudes below 5000 feet. In addition, a surveillance range of 14.3 n mile was needed to detect all encounters between unmanned aircraft and manned aircraft operating under visual flight rules. A surveillance range of 3.6 n mile was necessary to detect all losses of well clear. These results primarily inform the safety case and the surveillance requirements for unmanned aircraft detect-and-avoid systems.