Plain English Meaning

When you fly a GPS route that isn't a charted airway, your navigation has to be accurate enough to keep the aircraft inside the strip of protected airspace that follows the route's centerline. You can't just be heading the right general direction — you have to actually stay inside that protected corridor.

Full Definition

A navigation performance standard used when flying a route defined by GPS that is not part of the published airway structure, requiring the aircraft's navigation system to keep the aircraft within the lateral boundaries of the controlled airspace surrounding the route centerline. In practice on a or , must use a navigation system capable of the aircraft within the protected airspace on either side of the centerline, typically four each side below FL450.