1. A collision avoidance system, comprising: sensors configured during flight to receive navigational data regarding intruding aerial vehicle and an own aircraft; non-transitory storage configured to store a plurality of offline calculated predefined presimulated escape trajectories for the own aircraft, a processor configured during flight to presimulate the predefined presimulated escape trajectories, associate each predefined presimulated escape trajectory to a set of navigational data related to the own aircraft and to an escape manoeuvre direction, and compare at least a subset of the predefined presimulated escape trajectories with a presumed trajectory of the intruding aerial vehicle, and to select one of the predefined presimulated escape trajectories based on said comparison, such that the processor does not calculate the predefined presimulated escape trajectories, and an escape manoeuvre execution unit configured to permit the own aircraft to execute the selected one of the predefined presimulated escape trajectories.