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Reporter received anomalous reading on glide slope approaching fsd when compared to programmed descent path of RNAV equipment.
| Attributes | |
| ACN | 127527 |
| Time | |
| Date | 198911 |
| Day | Mon |
| Local Time Of Day | 0601 To 1200 |
| Place | |
| Locale Reference | atc facility : fsd |
| State Reference | SD |
| Altitude | msl bound lower : 3000 msl bound upper : 3000 |
| Environment | |
| Flight Conditions | VMC |
| Light | Daylight |
| Aircraft 1 | |
| Controlling Facilities | tracon : fsd |
| Operator | common carrier : air carrier |
| Make Model Name | Medium Large Transport, Low Wing, 2 Turbojet Eng |
| Navigation In Use | ils localizer & glide slope : fsd Other Other |
| Flight Phase | cruise other descent : approach |
| Flight Plan | IFR |
| Person 1 | |
| Affiliation | company : air carrier |
| Function | flight crew : captain oversight : pic |
| Qualification | pilot : commercial pilot : atp pilot : instrument |
| Experience | flight time type : 40 |
| ASRS Report | 127527 |
| Person 2 | |
| Affiliation | company : air carrier |
| Function | flight crew : first officer |
| Qualification | pilot : commercial pilot : instrument |
| Events | |
| Anomaly | aircraft equipment problem : less severe altitude deviation : overshoot altitude deviation : excursion from assigned altitude non adherence : published procedure other anomaly other |
| Independent Detector | other flight crewa |
| Resolutory Action | aircraft : equipment problem dissipated flight crew : overcame equipment problem |
| Consequence | Other |
| Supplementary | |
| Primary Problem | Navigational Facility |
| Air Traffic Incident | Pilot Deviation other |
Narrative:
Flying medium large transport with computerized cockpit. Cleared for visibility approach to runway 3 at sioux falls (fsd). Approaching from southeast, had ILS (109.0, 029 degrees) tuned in addition to RNAV descent path. Was following ILS GS, but noticed it was getting me too low (visibility and RNAV clues). I then ignored the GS until established on localizer, at which time it worked normally. I suspect that the false (low) GS was caused by being too far to the east of localizer, but we didn't seem to be that far east. Suggest you have this ILS checked for possible false GS's (low). If it meets the specifications, perhaps a note on the approach chart should advise pilots that on this particular ILS, you must be very close to localizer before you can trust the GS.
Original NASA ASRS Text
Title: REPORTER RECEIVED ANOMALOUS READING ON GLIDE SLOPE APCHING FSD WHEN COMPARED TO PROGRAMMED DESCENT PATH OF RNAV EQUIPMENT.
Narrative: FLYING MLG WITH COMPUTERIZED COCKPIT. CLRED FOR VIS APCH TO RWY 3 AT SIOUX FALLS (FSD). APCHING FROM SE, HAD ILS (109.0, 029 DEGS) TUNED IN ADDITION TO RNAV DSCNT PATH. WAS FOLLOWING ILS GS, BUT NOTICED IT WAS GETTING ME TOO LOW (VIS AND RNAV CLUES). I THEN IGNORED THE GS UNTIL ESTABLISHED ON LOC, AT WHICH TIME IT WORKED NORMALLY. I SUSPECT THAT THE FALSE (LOW) GS WAS CAUSED BY BEING TOO FAR TO THE E OF LOC, BUT WE DIDN'T SEEM TO BE THAT FAR E. SUGGEST YOU HAVE THIS ILS CHKED FOR POSSIBLE FALSE GS'S (LOW). IF IT MEETS THE SPECS, PERHAPS A NOTE ON THE APCH CHART SHOULD ADVISE PLTS THAT ON THIS PARTICULAR ILS, YOU MUST BE VERY CLOSE TO LOC BEFORE YOU CAN TRUST THE GS.
Data retrieved from NASA's ASRS site as of August 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.