A present novel and non-trivial system and method for generating trajectory data for an aircraft in flight is disclosed. Data representative of an aircraft's current trajectory, aircraft parameter(s), and navigation service data are received. As embodied herein, the aircraft parameter(s) may be received from more than one aircraft. An optimized flight trajectory for the aircraft is determined from a trajectory optimizing function and based upon the aircraft's current trajectory data, the aircraft parameter(s) data, and the navigation service data. Then, dispatch center trajectory data representative of the optimized flight trajectory is generated and sent to at least one user such as an aircraft system of the aircraft and/or an air navigation service provider. As embodied herein, the trajectory optimization function could be based upon cost minimization, time minimization, an operator's internal prioritization, or any combination of these.