A C172 CONDUCTING AN APCH TO LSE RECEIVED A FALSE LOCALIZER SIGNAL.

Narrative

TRACKING THE 14 DME ARC TO LSE WITH A STUDENT IN IFR TRAINING WE RECEIVED WHAT WE BELIEVED TO BE A LOCALIZER SIGNAL; AND TURNED INBND AS THE INSTRUMENTS INDICATED. BEING IN VMC CONDITIONS; WE QUICKLY REALIZED THAT THERE WAS SOMETHING WRONG. ALL FREQS WERE CORRECT; TUNED IN 2ND VOR NAV IN THE AIRPLANE AND RECEIVED THE SAME INDICATION AGAIN. WE BELIEVE AT THIS TIME WE WERE RECEIVING A FALSE LOCALIZER INDICATION DUE TO THE REACTION OF THE CDI ON BOTH VOR NAVS. WE CONTINUED TO FLY THE ARC VISUALLY NOW BUT BY THIS TIME WE WERE WELL INSIDE THE 14 DME ARC BY 5 MILES (9.2 FROM NAVAID). ALT CLEARANCES WERE MAINTAINED; BUT APCH COURSE WASN'T TRACKED CORRECTLY DUE TO FALSE INDICATIONS FROM THE LOCALIZER SIGNAL. WE DID OBTAIN A NEW CORRECT SIGNAL FARTHER INTO THE APCH AND WERE ABLE TO COMPLETE THE APCH SUCCESSFULLY. WX CONDITIONS WERE VMC THROUGHOUT THIS TIME FRAME. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR STATED THAT SHE AND THE OTHER PLT ARE FAMILIAR WITH THE ARPT AREA AND CONSEQUENTLY KNEW THE LOCALIZER SIGNAL WAS INCORRECT. THEY ESTIMATED THAT THE SIGNAL WAS OFF BY AS MUCH AS 20 DEGS. THEY HAD APCHED FROM THE WEST; DSCNDED AND THEN CLBED BACK TO 4000 FT FOR TFC. A 2449 FT ANTENNA OBSTACLE EXISTS IN THAT QUADRANT. THEY SAW THE ANTENNA BECAUSE THEY WERE VFR; KNEW WHERE THE ANTENNA WAS LOCATED; AND THEREFORE IT WAS NOT A PROB. IN FULL IMC CONDITIONS AT A LOWER ALT; SHE FELT THIS COULD HAVE BEEN A DIFFERENT STORY. ATC HAD NO COMMENTS TO THEM ABOUT THEIR APCH TRACK.