Urban Air Mobility is a new concept of regional aviation that has been growing in popularity as a solution to the issue of ever-increasing ground traffic. Electric vehicles with vertical take-off and landing capabilities are being developed by numerous market companies as a result of the push toward environmentally sustainable aviation. The next stage in this development process would be to define the concept of operation of these conceptual aircraft and then to integrate them with the existing airspace once they are airborne. In addition to coordinating with conventional air traffic and other Urban Air Mobility vehicles, collision avoidance with uncooperative airspace users has to be addressed. Birds and drones of all sizes pose a serious risk to these low-flying aircraft. Innovative collision detection and avoidance techniques need to be employed due to the uncooperative nature of these airspace users and different performance characteristics of Urban Air Mobility vehicles compared to classical fixed-wing aircraft. The aim of this study is to validate the concept of one such system by means of fast-time simulations. This system builds, similarly to the Airborne Collision Avoidance System, on safety envelopes and rule-based collision-avoidance to prevent collisions with non-cooperative airspace members. The system is designed to work with all aircraft configurations used for Urban Air Mobility operations. To assess its influence on safety and capacity, different scenarios are modelled by varying parameters such as intruder type, location, flight path. The parameters assessed are differences in flight time and closest point of approach with and without the collision avoidance system in place. Moreover, the influence of different configurations of Urban Air Mobility aircraft on these parameters is analysed. The results show that the separation between the ownship and intruder is increased substantially which leads to safe operations at bearable delay costs.