Trajectory Specification for High-Capacity Air Traffic Control

The doubling or tripling of airspace capacity that will be needed over the next couple of decades is likely to require four-dimensional trajectory assignment (three-dimensional position as a function of time) for appropriately equipped aircraft in high-density airspace. This paper proposes a standard trajectory specification language based on XML, the Extensible Markup Language. Trajectories are specified as a series of parametric segments. The horizontal path consists of a series of straight (greatcircle) segments connected by turns of specified radius. Altitude is specified as a low-order polynomial function of alongtrack position, and along-track position is specified as low-order polynomial function of time. Flight technical error tolerances in the along-track, cross-track, and vertical axes determine a bounding space, at each point in time, in which the aircraft is required to be contained. Periodic updates in the along-track axis can adjust for errors in the predicted along-track winds. Developing a consensus for an international standard is a major challenge, but a common trajectory language can greatly simplify the logistics of high-capacity air traffic control.