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VOR reliability questioned at mfe after flying the VOR runway 31 approach using both VOR and FMS instruments. VOR produced erratic cockpit indications.
| Attributes | |
| ACN | 496910 |
| Time | |
| Date | 200001 |
| Day | Tue |
| Local Time Of Day | 0601 To 1200 |
| Place | |
| Locale Reference | airport : mfe.airport |
| State Reference | TX |
| Altitude | msl bound lower : 660 msl bound upper : 3000 |
| Environment | |
| Flight Conditions | IMC |
| Light | Daylight |
| Aircraft 1 | |
| Controlling Facilities | tower : mfe.tower |
| Operator | common carrier : air carrier |
| Make Model Name | Fokker 100 |
| Operating Under FAR Part | Part 121 |
| Navigation In Use | other other vortac |
| Flight Phase | descent : approach landing : missed approach |
| Route In Use | approach : instrument non precision |
| Flight Plan | IFR |
| Person 1 | |
| Affiliation | company : air carrier |
| Function | flight crew : captain oversight : pic |
| Qualification | pilot : atp |
| ASRS Report | 496910 |
| Person 2 | |
| Affiliation | company : air carrier |
| Function | flight crew : first officer |
| Qualification | pilot : commercial pilot : instrument pilot : multi engine |
| Events | |
| Anomaly | other anomaly other |
| Independent Detector | aircraft equipment other aircraft equipment : vor/fms other flight crewa |
| Resolutory Action | flight crew : executed missed approach flight crew : diverted to alternate |
| Consequence | other |
| Supplementary | |
| Problem Areas | Navigational Facility |
| Primary Problem | Navigational Facility |
Narrative:
Aircraft shot VOR31 approach to min, using navigation, VOR backup. VOR fluctuating. At mins saw ground, no airport, at map saw airport, went miss. Next approach used VOR, navigation as back up. VOR a little erratic outside of FAF. Inside a little more. At 660 ft full scale deflection. Recommended that VOR mfe is unreliable for runway 31 approachs. Recommend FAA check of VOR facility. Divert to sat. Callback conversation with reporter revealed the following information: callback revealed that the normal operation on a VOR or other non precision approach is to fly the approach as an FMS LNAV approach while monitoring the VOR indication for accuracy of the FMS track recognizing that the VOR is the deciding and authorized indication to define track. In this case the VOR gave less than reliable information, hence the missed approach. The reporter said that aircraft VOR indications using other ground stations during the course of a multi leg trip were normal.
Original NASA ASRS Text
Title: VOR RELIABILITY QUESTIONED AT MFE AFTER FLYING THE VOR RWY 31 APCH USING BOTH VOR AND FMS INSTRUMENTS. VOR PRODUCED ERRATIC COCKPIT INDICATIONS.
Narrative: ACFT SHOT VOR31 APCH TO MIN, USING NAV, VOR BACKUP. VOR FLUCTUATING. AT MINS SAW GND, NO ARPT, AT MAP SAW ARPT, WENT MISS. NEXT APCH USED VOR, NAV AS BACK UP. VOR A LITTLE ERRATIC OUTSIDE OF FAF. INSIDE A LITTLE MORE. AT 660 FT FULL SCALE DEFLECTION. RECOMMENDED THAT VOR MFE IS UNRELIABLE FOR RWY 31 APCHS. RECOMMEND FAA CHK OF VOR FAC. DIVERT TO SAT. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: CALLBACK REVEALED THAT THE NORMAL OP ON A VOR OR OTHER NON PRECISION APCH IS TO FLY THE APCH AS AN FMS LNAV APCH WHILE MONITORING THE VOR INDICATION FOR ACCURACY OF THE FMS TRACK RECOGNIZING THAT THE VOR IS THE DECIDING AND AUTHORIZED INDICATION TO DEFINE TRACK. IN THIS CASE THE VOR GAVE LESS THAN RELIABLE INFO, HENCE THE MISSED APCH. THE RPTR SAID THAT ACFT VOR INDICATIONS USING OTHER GND STATIONS DURING THE COURSE OF A MULTI LEG TRIP WERE NORMAL.
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.