An unmanned aircraft, unmanned aviation system and method for collision avoidance during the flight operation of an unmanned aircraft are provided. The unmanned aircraft includes a lift and propulsion system and a flight control system having a flight control unit, a navigation system and an actuator system. The flight control unit has an autopilot unit. The flight control unit calculates control commands using data from the navigation system and/or the autopilot unit, which can be conveyed to the actuator system for actuating the lift and propulsion system. A collision warning system is connected with the flight control system, the collision warning system detects a collision situation and makes collision avoidance data available. A connection between the collision warning system and the autopilot unit is provided, in order to initiate an obstacle avoidance maneuver by the autopilot unit with the help of the collision avoidance data.