Real-time 4-D trajectory planning for RNP flight operations

Optimizing a flight path in-flight to take into account real-time unforeseen events, such as wind conditions, moving storm cells, or pop-up tactical threats, can enable aircraft to fly a safer and more fuel efficient route than the flight path created before takeoff. It is critical that the replanned trajectory still complies with various requirements for flight operations to ensure the safety of the aircraft. In this paper, we present a real-time 4-D flight planner, named ldquoAirborne E*,rdquo that can efficiently modify the active flight plan in-flight to take into account real-time unforeseen events and vehicle performance limits. To ensure the safety of the aircraft, the replanned 4-D flight path generated by Airborne E* complies with Required Navigation Performance (RNP) requirements. In addition, both lateral and vertical RNP containments centered on this new flight path are assured to be free of any terrain obstacles. After the new flight path is constructed, it will be presented to pilots (and air traffic controllers if required) for approval. Upon approval, Airborne E* will automatically load the modified flight plan into FMS as the active flight plan. We will discuss the application of this innovative real-time flight planner to low altitude flights for both civil and military aviation. Simulation and flight test results are also discussed in the paper.