Narrative:

ATC facility: gdl approach control. Location: gdl/070 degree radial/10 NM. While being radar vectored to the ILS runway 28, gdl, the F100 afs captured a false localizer and GS. Aircraft heading was 190 degrees at 9500 ft MSL with the autoplt engaged and land armed, we were cleared to intercept the localizer and cleared the ILS runway 28 approach. The autoplt captured a false localizer and GS approximately 5 NM north of the actual ILS course. Both localizer and GS capture annunciated on the pfd and the aircraft began a right turn. Xchk of raw data (localizer and VOR) and the nd map (had built the ILS manually since it is not in the database) confirmed aircraft north of the localizer centerline. Disconnected the autoplt and initiated a turn back to heading 190 degrees. Gdl approach control confirmed our position, gave us heading 180 degrees and 7500 ft MSL and reconfirmed approach clearance. Completed the approach manually in VMC. (After rearming land, normal localizer and GS capture occurred.) callback conversation with reporter revealed the following information: reporter had used other means of navigation to fly into gdl besides the ILS. The WX was clear. The flight crew tuned in the ILS, but used a VOR radial as reference, and also manually built an approach into the FMC. As the aircraft was on a 190 degree heading, it turned to an ILS heading for the localizer intercept. The ILS command showed localizer capture. Flight crew recognized early that the aircraft had turned to an ILS heading and capture, but the localizer was 30 degrees off from the airport. Flight crew turned off all autoplt functions and flight instrument commands and reset the flight instruments after taking up a westerly heading. Then, everything worked perfectly. Reporter feels it was just an anomaly that can happen. This is the only time it has happened to him and has not heard of any other incidents of this type.

Google
 

Original NASA ASRS Text

Title: AN F100 ACFT FLYING INTO GDL, FO, SETS UP THE INSTS FOR AN APCH WITH THE ILS. THE ILS CAPTURES AND INTERCEPTS A FALSE LOC. ARPT IS 30 DEGS OFF TO THE SIDE.

Narrative: ATC FACILITY: GDL APCH CTL. LOCATION: GDL/070 DEG RADIAL/10 NM. WHILE BEING RADAR VECTORED TO THE ILS RWY 28, GDL, THE F100 AFS CAPTURED A FALSE LOC AND GS. ACFT HDG WAS 190 DEGS AT 9500 FT MSL WITH THE AUTOPLT ENGAGED AND LAND ARMED, WE WERE CLRED TO INTERCEPT THE LOC AND CLRED THE ILS RWY 28 APCH. THE AUTOPLT CAPTURED A FALSE LOC AND GS APPROX 5 NM N OF THE ACTUAL ILS COURSE. BOTH LOC AND GS CAPTURE ANNUNCIATED ON THE PFD AND THE ACFT BEGAN A R TURN. XCHK OF RAW DATA (LOC AND VOR) AND THE ND MAP (HAD BUILT THE ILS MANUALLY SINCE IT IS NOT IN THE DATABASE) CONFIRMED ACFT N OF THE LOC CTRLINE. DISCONNECTED THE AUTOPLT AND INITIATED A TURN BACK TO HDG 190 DEGS. GDL APCH CTL CONFIRMED OUR POS, GAVE US HDG 180 DEGS AND 7500 FT MSL AND RECONFIRMED APCH CLRNC. COMPLETED THE APCH MANUALLY IN VMC. (AFTER REARMING LAND, NORMAL LOC AND GS CAPTURE OCCURRED.) CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR HAD USED OTHER MEANS OF NAV TO FLY INTO GDL BESIDES THE ILS. THE WX WAS CLR. THE FLC TUNED IN THE ILS, BUT USED A VOR RADIAL AS REF, AND ALSO MANUALLY BUILT AN APCH INTO THE FMC. AS THE ACFT WAS ON A 190 DEG HDG, IT TURNED TO AN ILS HEADING FOR THE LOC INTERCEPT. THE ILS COMMAND SHOWED LOC CAPTURE. FLC RECOGNIZED EARLY THAT THE ACFT HAD TURNED TO AN ILS HEADING AND CAPTURE, BUT THE LOC WAS 30 DEGS OFF FROM THE ARPT. FLC TURNED OFF ALL AUTOPLT FUNCTIONS AND FLT INST COMMANDS AND RESET THE FLT INSTS AFTER TAKING UP A WESTERLY HEADING. THEN, EVERYTHING WORKED PERFECTLY. RPTR FEELS IT WAS JUST AN ANOMALY THAT CAN HAPPEN. THIS IS THE ONLY TIME IT HAS HAPPENED TO HIM AND HAS NOT HEARD OF ANY OTHER INCIDENTS OF THIS TYPE.

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.