This thesis, developed in collaboration with MAVTech s.r.l., presents a modular architecture for collision avoidance in UAVs designed for outdoor applications. The system is implemented in ROS2 and integrated with the PX4 Autopilot for flight operations. The primary objective is to enhance safety while maintaining operational continuity: avoidance maneuvers are triggered only when necessary, ensuring no alteration of system nominal conduct. The approach combines an A* local planner operating on a dynamic costmap—fed by on-board sensors—with a Bug-like reactive behavior as a fallback strategy when local scheduling does not locate safe steps. A context-aware mode management system determines which algorithm to activate and when to apply its output to vehicle control.