Cross Track Error (XTE)

The shortest lateral distance from a vessel’s position to its active intended track line.

Usually abbreviated XTE or XTD, it is calculated by a navigation system relative to the selected route leg and may be given a port or starboard sign. It is a distance, not a rate of drift, and depends on how the system defines the leg, geodesic and waypoint transition.

An alarm can warn that a set limit has been exceeded, but steering directly back towards the line may be unsafe if hazards, traffic or route geometry intervene. The navigator must confirm the active leg and charted surroundings before using XTE to alter course.