With the rise of new and innovative Urban Air Mobility solutions, there also arises a need to integrate these into the existing airspace. Current airspace users include conventional civil, commercial and general aviation, military air users, police and emergency services as well as a plethora of avian life. Planned additions to the airspace are electric vertical take-off and landing vehicles such as logistics drones and air taxis. The airspace for conventional users is stringently controlled. Urban Air Mobility operations are expected to mainly take place in individual corridors to be added to the currently uncontrolled low-level airspace. This airspace is also intended for various types of drone operations, out of which, small-scale drones can be non-co-operative. In addition, the operational altitudes of Urban Air Mobility aircraft will strongly expose them to birds. Due to abundance of these non-cooperating airspace users (like hobby-drones and birds), conflicts with Urban Air Mobility aircraft are expected to be inevitable. The aim of this paper is to develop a concept of Urban Air Mobility Collision Avoidance System to reduce the likelihood of collision between air taxis and non-cooperating airspace users. As such, this work proposes the introduction of an additional safety layer to prevent collisions during operations of strong exposure. The concept consists of a conflict detection and resolution method tailored for Urban Air Mobility operations. A three-dimensional safety envelope is designed using the geometric and performance values of the aircraft configurations currently available. Procedures to avoid conflicts prior to as well as during the flights are presented. Finally, the concept is visualized for the common use case of a shuttle service between an airport and a railway station. The results demonstrate the importance of incorporating individual aircraft configuration into conflict avoidance approach and report its effect to avoid collision.@en