Patent ID: 6414632
Filing Date: 2002-07-02
Classification: B64D,G01S,G08G

Abstract:
A method for monitoring a localizer course facility in an instrument landing system, comprising:modulating a course signal at a first signal frequency and at a second signal frequency; modulating a clearance signal at the first signal frequency and at the second signal frequency; transmitting the modulated course and clearance signals; detecting by sensors the modulated course and clearance signals; demodulating the molded course and clearance signals; monitoring variables obtained from the demodulated course and clearance signals to ensure that said variables are within limit values; subjecting the demodulated course and clearance signals to Fourier transformation; determining a first phase difference for a first modulation frequency between the course and clearance signals, detected by the sensors and a second phase difference for a second modulation frequency in the course and clearance signals, between the course and clearance signals detected by the sensors; comparing the phase differences which have been determined for the first and second modulation frequencies with the limit values provided for each of these differences; and producing a warning signal if the limit values are infringed.