A method and apparatus includes long term and short term strategies for improving 4D trajectory reliability and required time of arrival reliability. The long term strategy changes speeds along the trajectory to remove the time error in predictions. The short term strategy compensates for wind and position error, for example, by temporarily changing an aircraft guidance speed by applying a guidance margin that would either delay or prevent recomputation of the speed targets along the flight path. The predictions would use the original speed target without the guidance margin application. The guidance speed target will stay applied until the predicted time error crosses a threshold.
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