Patent ID: 8630756

Claim:
A method for monitoring positional accuracy of an airplane approaching a runway, comprising the following steps performed by a computer system during the approach: (a) determining a first ground distance between a location of the airplane and a location along an extended runway centerline that is closest to the airplane location based on respective coordinates of the locations; (b) determining a second ground distance between the airplane location and a location of a ground-based antenna based on respective coordinates of the airplane and ground-based antenna locations; (c) determining a first lateral angular deviation of the airplane from the runway centerline based on the first and second ground distances; (d) receiving a second lateral angular deviation of the airplane from the runway centerline based on measurements of a difference in the depth of modulation of first and second modulated signals transmitted from the ground-based antenna and received by an antenna onboard the airplane; (e) comparing the first and second lateral angular deviations; and (f) generating an alert signal if the first and second lateral angular deviations differ by an amount greater than a threshold value.