A method for aircraft traffic spacing and timing control with flight path variation of an aircraft, comprising: receiving, at a communication interface of a computing device, information of aircraft traffic for an area comprising aircraft traffic location and speed; determining, by the computing device, an aircraft spacing plan for the aircraft traffic for the area based on spacing requirements due to one or more separation standards or flow management constraints for the aircraft traffic, said spacing plan comprising relative longitudinal spacing between aircraft of the aircraft traffic; determining that a modification to a flight path of an aircraft is required to meet said longitudinal spacing requirement between the aircraft and one or more additional aircraft of the aircraft traffic based on the aircraft spacing plan, wherein the aircraft is flying a required navigation performance instrument flight procedure that indicates a fixed-route accuracy and containment boundaries (136, 138) required during flight for the aircraft to fly a path between two points along the flight path, and wherein the containment boundaries are defined by a flight path centerline with limits determined by associated margins (144, 146); determining, by the computing device, said flight path modification to the flight path for the aircraft that causes the aircraft to remain within the associated margins of the RNP instrument flight procedure and alters the longitudinal spacing between the aircraft and the one or more additional aircraft of the aircraft traffic, wherein determining the flight path modification comprises determining a flight path stretch within limitations of the RNP instrument flight procedure, wherein determining the flight path stretch is defined by a sinusoidal flight path for the aircraft that lengthens the flight path and increases the longitudinal spacing between the aircraft and the one or more additional aircraft of the aircraft traffic while maintaining the aircraft within the associated margins, wherein the flight path modification to the flight path for the aircraft comprises determining symmetric path variations about the flight path centerline to apply in a sinusoidal manner; and assigning the flight path modification to the aircraft via a data communication link. receiving, at a communication interface of a computing device, information of aircraft traffic for an area comprising aircraft traffic location and speed; determining, by the computing device, an aircraft spacing plan for the aircraft traffic for the area based on spacing requirements due to one or more separation standards or flow management constraints for the aircraft traffic, said spacing plan comprising relative longitudinal spacing between aircraft of the aircraft traffic; determining that a modification to a flight path of an aircraft is required to meet said longitudinal spacing requirement between the aircraft and one or more additional aircraft of the aircraft traffic based on the aircraft spacing plan, wherein the aircraft is flying a required navigation performance instrument flight procedure that indicates a fixed-route accuracy and containment boundaries (136, 138) required during flight for the aircraft to fly a path between two points along the flight path, and wherein the containment boundaries are defined by a flight path centerline with limits determined by associated margins (144, 146); determining, by the computing device, said flight path modification to the flight path for the aircraft that causes the aircraft to remain within the associated margins of the RNP instrument flight procedure and alters the longitudinal spacing between the aircraft and the one or more additional aircraft of the aircraft traffic, wherein determining the flight path modification comprises determining a flight path stretch within limitations of the RNP instrument flight procedure, wherein determining the flight path stretch is defined by a sinusoidal flight path for the aircraft that lengthens the flight path and increases the longitudinal spacing between the aircraft and the one or more additional aircraft of the aircraft traffic while maintaining the aircraft within the associated margins, wherein the flight path modification to the flight path for the aircraft comprises determining symmetric path variations about the flight path centerline to apply in a sinusoidal manner; and assigning the flight path modification to the aircraft via a data communication link.