A collision avoidance method and system for a trailer aircraft of an aircraft formation relative to an intruder aircraft. The collision avoidance system is embedded in a trailer aircraft of an aircraft formation and it is intended to avoid a collision relative to at least one aircraft external to the aircraft formation, called intruder aircraft, the aircraft formation including a lead aircraft and the at least one trailer aircraft, the collision avoidance system being configured to bring the trailer aircraft to a safety point dependent on a safety zone, prior to the implementation of an avoidance maneuver, the safety zone corresponding to a zone located to the rear of the lead aircraft and with no wake turbulence generated by the lead aircraft.