RTA-compliant optimized profile descents with 4-D FMS

Optimized Profile Descents (OPDs) or Continuous Descent Approaches use idle or near-idle thrust during descents to reduce fuel consumption, engine noise and carbon emissions. With Optimized Profile Descents, aircraft can descend continuously from cruise altitude to the bottom of descent or to an initial approach fix without level path segments. However, to utilize OPDs without reducing the traffic throughput around an airport, a Required Time of Arrival is usually imposed at a metering waypoint to safely merge incoming traffic. The drawback to OPDs is that, if only idle thrust is used during descent, the descent profile is a function of not only aircraft speed, aircraft weight, wind and temperature, but also aircraft platforms and engine types. Therefore, the idle descent profile can vary from one aircraft to another and from one flight to another flight at a different date. One way to eliminate the path unpredictability, while retaining most of OPD benefits, is to only use path segments with constant flight path angles during descent. Thus, the vertical descent profile is clearly defined. This paper presents an enhanced design of Optimal E* (pronounced as E-Star) that, when integrated with a Flight Management System (FMS), can construct predictable RTA-compliant OPD trajectories and provide guidance commands to the automatic flight control system to enable aircraft to arrive at the metering waypoint on time, while reducing fuel consumption. Simulation results are also presented in this paper.