Narrative:

Vectored off otumba arrival at mex by ATC heading 200 degrees to intercept the runway 23L localizer. Tuned and idented the localizer and armed the FGS to intercept. The aircraft intercepted the localizer final almost immediately which was in error. ATC informed us we were 10 NM north of the localizer course. We then checked the cabin for electronic device use, but none was reported. The localizer continued to show on course throughout the approach which we completed visually since we did not trust the localizer. We reported the problem to ATC, but they did not seem concerned. The WX was VMC with good visibility so I was never uncomfortable with our situation from a safety standpoint. Had the WX been bad and the controller less attentive the situation could have deteriorated rapidly.

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Original NASA ASRS Text

Title: APPARENT FAULTY LOC SIGNAL AT MEXICO CITY ARPT. NOT THE FIRST TIME AN ERRONEOUS LOC SIGNAL AND THE ATC FACILITY IS AWARE OF IT, BUT DOESN'T APPEAR TO BE CONCERNED IF THE WX IS GOOD.

Narrative: VECTORED OFF OTUMBA ARR AT MEX BY ATC HDG 200 DEGS TO INTERCEPT THE RWY 23L LOC. TUNED AND IDENTED THE LOC AND ARMED THE FGS TO INTERCEPT. THE ACFT INTERCEPTED THE LOC FINAL ALMOST IMMEDIATELY WHICH WAS IN ERROR. ATC INFORMED US WE WERE 10 NM N OF THE LOC COURSE. WE THEN CHKED THE CABIN FOR ELECTRONIC DEVICE USE, BUT NONE WAS RPTED. THE LOC CONTINUED TO SHOW ON COURSE THROUGHOUT THE APCH WHICH WE COMPLETED VISUALLY SINCE WE DID NOT TRUST THE LOC. WE RPTED THE PROB TO ATC, BUT THEY DID NOT SEEM CONCERNED. THE WX WAS VMC WITH GOOD VISIBILITY SO I WAS NEVER UNCOMFORTABLE WITH OUR SIT FROM A SAFETY STANDPOINT. HAD THE WX BEEN BAD AND THE CTLR LESS ATTENTIVE THE SIT COULD HAVE DETERIORATED RAPIDLY.

Data retrieved from NASA's ASRS site as of July 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.