The 4D trajectory data link (4DTRAD) service - Closing the loop for air traffic control

One of the key services envisioned in support of the NextGen and SESAR concepts is the 4D Trajectory Data Link (4DTRAD) Service, which is being defined by RTCA SC-214 and EUROCAE WG78. One key principle of these concepts is the use of a closed loop clearance from takeoff to landing. The aim of 4DTRAD is to provide a data communication service for ATC clearances and a trajectory downlink application for trajectory data from the aircraft to the ground system to support enhanced trajectory modeling, coordination and constraint conformance monitoring. This data link service will enable the users to leverage advanced airborne avionics that can accurately and efficiently manage the flight of aircraft in 4 dimensions to meet ATC imposed trajectory constraints. 4DTRAD will allow optimized flight profiles while supporting dynamic demand, capacity balancing and queue management during the execution phase of the flight in the strategic conflict management layer, and for non time critical communication. Benefits include reductions in flight delay, fuel consumption, emissions, environmental noise, pilot and controller workload, and frequency congestion. The 4DTRAD service described in this paper is focused on the mid-term (approximately 2015 - 2020) which is anticipated to be a transition environment where mixed equipage is expected to be predominant. This paper presents technologies that are planned to be used and improved as part of NextGen and SESAR that will improve the predictability of the aircraft trajectories and facilitate use of optimized profile descent procedures in high density terminal areas. This paper also raises concerns about challenges in implementing this integrated solution.