It is delayed by at most 1 second plus the update rate of the GPS (about 0.1 seconds), and gives current heading and speed. WAAS receivers are accurate to a fe

It is delayed by at most 1 second plus the update rate of the GPS (about 0.1 seconds), and gives current heading and speed. WAAS receivers are accurate to a few meters. For a plane following an instrument approach to intercept the ILS, it would be trivial to predict their real-time position given the information available.