CHALLENGES IN DEVELOPING SENSE & AVOID CAPABILITY FOR UNMANNED AIRCRAFT SYSTEMS

Umnanned Aircraft Systems will require a Sense & Avoid function to protect against collisions with other aircraft as well as various other hazards. Architectural alternatives in the distributions of functionality between aircraft and a ground control station make the development of requirements and standards more complex. A broad variety of candidate sensor technologies has potential to fulfill the surveillance portion of the system. The paper explores the capabilities and limitations of these technologies, and suggests deploying combinations of technologies to capitalize upon their respective strengths. A discussion of algorithmic requirements draws upon the experience of the Traffic Alert and Collision Avoidance System (TCAS) in the airspace. Differences and challenges in implementing an algorithm for a UAS are discussed. The broad range of UAS aerodynamic characteristics complicate the process of standardizing an algorithm for Sense & Avoid. In order to build a safety case supporting the certification of a UAS, its performance must be thoroughly evaluated. In the case of Sense & Avoid, flight testing cannot be sufficiently thorough, and instead, the simulation of the system for large numbers of aircraft encounters is recommended. The paper discusses the considerations in performing such simulations, and in modeling various components of the system and of the potential encounter geometries. Unlike TCAS, an encounter model cannot be constructed solely from observed data, as UAS are not yet performing the desired uses. The Sense & Avoid work within the RTCA SC-203 standards committee is described.