A computer-implemented method for optimizing a stream of at least two aircraft (200a, 200b) forming at least one aircraft pair, wherein each aircraft (200a, 200b) enters a predefined environment, in particular an airspace, via an individual or common entry waypoint and wherein the aircraft (200a, 200b) approach a common predefined merging waypoint, the method comprising: - receiving an estimated entry time for each aircraft (200a, 200b) at the at least one entry waypoint, - receiving a target time for each aircraft (200a, 200b) to arrive at the merging waypoint, wherein said target time comprises a delay to be absorbed before reaching said merging waypoint, - receiving routing information for each aircraft (200a, 200b) comprising waypoints for routing said aircraft (200a, 200b) from the entry waypoint to the merging waypoint, wherein the waypoints comprise at least one dedicated waypoint, - defining a desired minimum time based separation (Ŝ k) for each pair of aircraft, and - determining optimized target arrival times (T k), in particular target overflight times (T k), at the one or more dedicated waypoints for the at least two aircraft (200a, b) utilizing an optimization model considering the estimated entry time, the target time for each aircraft to arrive at the merging waypoint and the desired minimum time based separation (Ŝ k), wherein the optimized target arrival times (T k) are determined such that the delay to be absorbed for each aircraft (200a, 200b) is shared between route segments defined by said dedicated waypoints, characterized in that the optimization model utilizes the desired minimum time based separation (Ŝ k) as a soft constraint, wherein the optimization model considers maximizing a time based separation (s k) between each aircraft pair at the one or more dedicated waypoints considering the desired minimum time based separation (Ŝ k) as a first optimization goal, and wherein the time based separation (s k) is maximized only up to the predefined desired separation (Ŝ k). - receiving an estimated entry time for each aircraft (200a, 200b) at the at least one entry waypoint, - receiving a target time for each aircraft (200a, 200b) to arrive at the merging waypoint, wherein said target time comprises a delay to be absorbed before reaching said merging waypoint, - receiving routing information for each aircraft (200a, 200b) comprising waypoints for routing said aircraft (200a, 200b) from the entry waypoint to the merging waypoint, wherein the waypoints comprise at least one dedicated waypoint, - defining a desired minimum time based separation (Ŝ k) for each pair of aircraft, and - determining optimized target arrival times (T k), in particular target overflight times (T k), at the one or more dedicated waypoints for the at least two aircraft (200a, b) utilizing an optimization model considering the estimated entry time, the target time for each aircraft to arrive at the merging waypoint and the desired minimum time based separation (Ŝ k), wherein the optimized target arrival times (T k) are determined such that the delay to be absorbed for each aircraft (200a, 200b) is shared between route segments defined by said dedicated waypoints, characterized in that the optimization model utilizes the desired minimum time based separation (Ŝ k) as a soft constraint, wherein the optimization model considers maximizing a time based separation (s k) between each aircraft pair at the one or more dedicated waypoints considering the desired minimum time based separation (Ŝ k) as a first optimization goal, and wherein the time based separation (s k) is maximized only up to the predefined desired separation (Ŝ k).