4Dtrajectory

4Dtrajectory is a concept in flight operations and air traffic management referring to a trajectory defined in four dimensions: three spatial dimensions and time. In aviation, a 4D trajectory includes an intended path through space (latitude, longitude, altitude) and timing information, such as estimated times of arrival at waypoints or metering points, to meet constraints and optimize routing, sequencing, and spacing.

A 4D trajectory is typically specified as part of performance-based navigation and can be dynamic, allowing updates during flight. It enables time-based management of air traffic by linking the flight plan to scheduling and sequencing decisions, which can improve predictability and reduce fuel burn and delays.

In practice, 4D trajectories are developed during planning and can be shared between pilots, operators, and air traffic services via data communications and surveillance systems. They rely on accurate weather information, surveillance, and navigation capability, including ADS-B, CPDLC, and flight management systems. Implementation has progressed as part of modernization programs such as NextGen in the United States and SESAR in Europe, with pilots and controllers operating within a time-based flow management framework.

Benefits include better airspace utilization, reduced congestion, fuel efficiency, and enhanced reliability. Challenges involve handling weather uncertainty and variability, ensuring system interoperability, and maintaining safety under dynamic conditions. See also four-dimensional navigation, time-based metering, next generation air transportation programs.