In this work, a Fuzzy Inference System (FIS) is proposed to develop a sense and avoid technique for conflict-free Unmanned Aerial Vehicle (UAV) flight operations in the national airspace. The proposed method is implemented alongside the flight control software guiding the UAV towards a predefined goal. The fuzzy system makes decisions for sense and avoid with respect to the state of other intruder aircraft in the airspace. The fuzzy rules are selected under consideration of the heading and position data of the intruder aircraft obtained using ADS-B sensor relative to the controlled UAV. The avoidance controller is implemented alongside a traditional PID-based flight controller to test the effectiveness of the sense-and-avoid technique. The PID controller drives the controlled UAV towards the goal and the fuzzy controller is for conflict avoidance based on an event trigger logic if the controlled UAV is in the intrusion zone of another aircraft. The integration of the dynamic model of the controlled UAV and fuzzy inference system is described. The numerical simulations are shown to evaluate the performance of the proposed method in the presence of moving as well as stationary intruder aircraft.