Collision avoidance method and device for an aircraft formation relative to an intrusive aircraft. The device manages a collision avoidance for an aircraft formation, relative to an aircraft external to the aircraft formation, the aircraft formation comprising a lead aircraft and at least one following aircraft, the device comprising a formation flight management unit with which all the aircraft of the aircraft formation are equipped and configured to manage the formation flight thereof, and management and control assemblies for determining and applying a coordinated avoidance maneuver intended for all the aircraft of the aircraft formation, this coordinated avoidance maneuver being determined so as to make it possible to avoid the collision with the intrusive aircraft while maintaining the formation flight.