A novel four-dimensional guidance for continuous descent approaches

This paper proposes an innovative guidance for descending aircraft, the so-called CDA-MP 4D Guidance, where CDA-MP stands for Continuous Descent Approaches for Maximum Predictability. The vertical guidance consists of a novel combination of elevator and throttle actuations that enable accurate continuous 4D navigation while minimizing fuel consumption, throttle activity, gas emissions, and noise production during descent. The method uses elevator actuations to control groundspeed and efficiently match a prescribed groundspeed law. By conservation of energy, uncertainties such as wind translate into potential energy (vertical) errors if the along-track position of the aircraft is to match the guidance reference at all times. Along-track predictability makes spacing between aircraft or estimated arrival times to metering fixes more predictable, and due to its continuous nature provides an enhanced level of integrity for the entire system. All these factors represent enormous advantages for the future Air Transportation System. Previous vertical guidance developments have included ground speed control by elevator actuation, but this method includes an additional logic for throttle activity to control the mechanical energy of the aircraft, which is the actual contribution of this method. The engine is actuated with a given law that uses near-idle thrust values in order to confine vertical deviations within predefined thresholds from the guidance reference with minimal engine interventions. Simulated descents for Boeing aircraft under the proposed guidance are presented, and the potential strengths and benefits of this guidance with respect to existing methods are discussed.