A method to maintain trajectory synchronization performed by an aircraft system comprising: comparing an active trajectory with a synchronized trajectory, wherein the comparison is triggered by at least one disturbance, periodic trigger, communication event between different trajectory systems, or downlink/ uplink event; if the comparing indicates a difference between the active trajectory and the synchronized trajectory, then performing the actions of: updating the synchronized trajectory with the active trajectory; and transferring the synchronized trajectory or sending a command to modify a flight plan to an external system; if a downlinked synchronized trajectory is received, then performing the action of: comparing the downlinked synchronized trajectory with a ground predicted trajectory for the aircraft; if the comparison indicates a difference between the synchronized trajectory and the ground predicted trajectory, then initiating a synchronization process; else a local synchronized trajectory is updated with the downlinked synchronized trajectory; wherein the disturbance is at least one of a change detected by an aircraft, change data from an external source, or a periodic trigger, and further wherein the change detected by an aircraft is at least one of atmospheric condition change, pilot input change, airline input change, a change to a predicted trajectory, or other state measurement, and furthermore wherein ground route or lateral route comprises at least one of an en route segment, and departure segment or arrival segment which relate to a set of airport, runway, and terminal procedure names. comparing an active trajectory with a synchronized trajectory, wherein the comparison is triggered by at least one disturbance, periodic trigger, communication event between different trajectory systems, or downlink/ uplink event; if the comparing indicates a difference between the active trajectory and the synchronized trajectory, then performing the actions of: updating the synchronized trajectory with the active trajectory; and transferring the synchronized trajectory or sending a command to modify a flight plan to an external system; if a downlinked synchronized trajectory is received, then performing the action of: updating the synchronized trajectory with the active trajectory; and transferring the synchronized trajectory or sending a command to modify a flight plan to an external system; if a downlinked synchronized trajectory is received, then performing the action of: comparing the downlinked synchronized trajectory with a ground predicted trajectory for the aircraft; if the comparison indicates a difference between the synchronized trajectory and the ground predicted trajectory, then initiating a synchronization process; else a local synchronized trajectory is updated with the downlinked synchronized trajectory; wherein the disturbance is at least one of a change detected by an aircraft, change data from an external source, or a periodic trigger, and further wherein the change detected by an aircraft is at least one of atmospheric condition change, pilot input change, airline input change, a change to a predicted trajectory, or other state measurement, and furthermore wherein ground route or lateral route comprises at least one of an en route segment, and departure segment or arrival segment which relate to a set of airport, runway, and terminal procedure names.