A method and apparatus includes strategies for improving required time of arrival reliability by an aircraft comprising determining a speed correction for one of AT speed constraints or an AT or ABOVE speed constraints, wherein the determining is selected from one or more of the mechanisms from the group consisting of continuous RTA speed management between constraints, padding of the AT speed constraints and the AT or ABOVE speed constraints; decelerating proactively; and using a variable guidance margin, wherein the guidance margin is a speed change not reflected in a flight plan prediction.