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.