Patent ID: 8788189

Claim:
A method for providing reliability for both a four dimensional trajectory of an aircraft along a path to a waypoint and a required time of arrival (RTA) at the waypoint, the aircraft including a flight management system processor including a trajectory predictor and an RTA solver, the method comprising: enabling, by the flight management system processor, a temporary speed correction that compensates for unpredicted environmental errors in addition to a long term speed profile, the enabling step including: computing, by the trajectory predictor, a time error as a difference between an estimated time of arrival (ETA) and the RTA without use of a guidance margin, wherein the guidance margin is a target speed modification that would delay or prevent re-computation of the long term speed profile along the trajectory; setting, by the flight management system processor, a guidance speed as the target speed required to reach the waypoint at the RTA plus an updated guidance margin; computing, by the RTA solver, the guidance margin to delay or prevent a long term speed profile computation and reach the waypoint at the RTA if the time error exceeds an interval determined by a first positive time threshold and a first negative time threshold, which change in magnitude as the distance to the waypoint decreases; setting, by the RTA solver, a guidance margin to zero and setting the guidance speed to equal the target speed plus the guidance margin if a time error reduces under a second positive time threshold and a second negative time threshold; repeating from the computing of the time error.