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Flight crew of B757 experienced false localizer capture at mmun. False capture initiated FMS update which caused map shift. Subsequent capture of actual localizer produced another update and map shift back to correct display. Approach and landing made visually.
| Attributes | |
| ACN | 586233 |
| Time | |
| Date | 200306 |
| Day | Mon |
| Local Time Of Day | 1201 To 1800 |
| Place | |
| State Reference | FO |
| Altitude | msl bound lower : 2000 msl bound upper : 3000 |
| Aircraft 1 | |
| Controlling Facilities | tracon : mmun.tracon tower : iah.tower |
| Operator | common carrier : air carrier |
| Make Model Name | B757 Undifferentiated or Other Model |
| Operating Under FAR Part | Part 121 |
| Navigation In Use | ils localizer & glide slope : 12 |
| Flight Phase | descent : approach |
| Route In Use | approach : instrument precision |
| Flight Plan | IFR |
| Person 1 | |
| Affiliation | company : air carrier |
| Function | flight crew : captain oversight : pic |
| Qualification | pilot : atp |
| ASRS Report | 586233 |
| Person 2 | |
| Affiliation | company : air carrier |
| Function | flight crew : first officer |
| Events | |
| Anomaly | aircraft equipment problem : critical other spatial deviation |
| Independent Detector | other flight crewa |
| Resolutory Action | aircraft : equipment problem dissipated flight crew : overcame equipment problem flight crew : returned to intended or assigned course |
| Supplementary | |
| Problem Areas | Flight Crew Human Performance Navigational Facility Aircraft |
| Primary Problem | Navigational Facility |
Narrative:
Flight director captured a false localizer signal for runway 12. This caused a map shift when the FMS tried to update the relative position to the airport. We were about 2 NM north of desired course. Raw data localizer signal also centered then went immediately to expanded scale on his. Then showed full right. Then map shifted to the south and onto the correct position. Flew visually to the airport.
Original NASA ASRS Text
Title: FLT CREW OF B757 EXPERIENCED FALSE LOC CAPTURE AT MMUN. FALSE CAPTURE INITIATED FMS UPDATE WHICH CAUSED MAP SHIFT. SUBSEQUENT CAPTURE OF ACTUAL LOC PRODUCED ANOTHER UPDATE AND MAP SHIFT BACK TO CORRECT DISPLAY. APCH AND LNDG MADE VISUALLY.
Narrative: FLT DIRECTOR CAPTURED A FALSE LOC SIGNAL FOR RWY 12. THIS CAUSED A MAP SHIFT WHEN THE FMS TRIED TO UPDATE THE RELATIVE POS TO THE ARPT. WE WERE ABOUT 2 NM N OF DESIRED COURSE. RAW DATA LOC SIGNAL ALSO CTRED THEN WENT IMMEDIATELY TO EXPANDED SCALE ON HIS. THEN SHOWED FULL R. THEN MAP SHIFTED TO THE S AND ONTO THE CORRECT POS. FLEW VISUALLY TO THE ARPT.
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.