The concept of “fly-by” and “flyover” waypoints is integral to RNAV and as such has been in existence for quite some time. As Performance Based Navigation is being increasingly used to reduce the distances between routes to a minimum, air traffic controllers have been surprised to see that aircraft do not follow consistent paths when turning from one track to another. This issue has been documented by Eurocontrol, ICAO and others. Such surprises should be prevented by changes in route structure and controller training.

More recent innovations such as the fixed radius transition for the en-route environment should allow for predictable flight paths and ensure separation where close spacing between routes or between a route and terrain or a danger area is desired.