Aircraft control system and method for reaching a waypoint at a required time of arrival

A method for providing reliability for both an aircraft 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:

• computing, by the flight management system processor, a first estimated speed to reach the waypoint at the required time of arrival;
• computing, by the trajectory predictor, a time difference between an estimated time of arrival at the first estimated speed and the required time of arrival;
• setting and maintaining, by the flight management system processor, a target speed equal to the first estimated speed required to reach the waypoint at the required time of arrival plus a guidance margin if the time difference between the estimated time of arrival and the required time of arrival exceeds a first time threshold, the first time threshold defined by an estimated time of arrival tolerance and an estimated time to the waypoint, the first time threshold decreasing in magnitude as a distance to the waypoint decreases and as long as it is larger than a third time threshold, wherein the third time threshold is less than the first time threshold, wherein the guidance margin is a speed delta applied to the first estimated speed;
• updating, by the RTA solver, the target speed to equal a second estimated speed required to reach the waypoint at the required time of arrival plus the guidance margin if the difference between the estimated time of arrival and the required time of arrival exceeds a second time threshold, the second time threshold decreasing in magnitude as the distance to the waypoint decreases, and maintaining the guidance margin to compensate for accumulated time and position error in comparison to initial predicted trajectory;
• and
• setting, by the RTA solver, the guidance margin to zero and setting a guidance target speed to equal an estimated speed required to reach the waypoint at the RTA if the time difference goes below the third time threshold.

A system for providing reliability for both a four dimensional trajectory of an aircraft along a path to a waypoint and a required time of arrival at the waypoint, the system comprising:

• a flight management system processor enabling a temporary speed correction that compensates for unpredicted environmental errors in addition to a long term speed profile, the enabling step including:
• a required time of arrival solver configured to calculate a first estimated speed to reach the waypoint at the required time of arrival;
• a trajectory predictor configured to compute in real time a time difference between an estimated time of arrival at the first estimated speed and the required time of arrival;
• a speed profile generator configured to set and maintain a target speed equal to the first estimated speed required to reach the waypoint at the required time of arrival plus a guidance margin if the time difference between the estimated time of arrival and the required time of arrival exceeds a first time threshold, the first time threshold defined by an estimated time of arrival tolerance and the time to the waypoint and which decreases in magnitude as the distance to the waypoint decreases and as long as it is larger than a third time threshold, wherein the guidance margin is a speed delta applied to the first estimated speed;
• wherein the required time of arrival solver is further configured to compute a second estimated speed required to reach the waypoint at the required time of arrival if a time error exceeds a second time threshold;
• wherein the speed profile generator is further configured to update the target speed to equal the second estimated speed required to reach the waypoint at the required time of arrival plus the guidance margin if the time error exceeds a second time threshold and maintaining the guidance margin to compensate an accumulated time error, wherein the second time threshold is larger than the first time threshold;
• and
• wherein the speed profile generator is configured to set the guidance margin to zero and setting a guidance target speed to equal the second estimated speed required to reach the waypoint at the required time of arrival if the time difference goes below a third time threshold.