Narrative:

On final vector to the ILS runway 35R approach to centennial (apa) I was cleared to 9000 ft MSL until established on the localizer. I hit approach mode and hit altitude select and was coupled to the autoplt as I intercepted the localizer and descended to 8000 ft MSL which is the altitude within 10 mi I needed to intercept the localizer. After reaching 8000 ft MSL everything seemed normal until I received a low altitude alert from the apa tower. I immediately checked my altitude and altimeter setting and everything seemed to be normal. As I approached the OM (casse) on the approach I noticed the GS was acting erratic showing varied up and down movement with no GS flag. I progressed through the approach with various other GS variations and low altitude alerts from the apa tower. After crossing (casse) within a quarter mi I was able to get a visual on the runway and airport. Altitude both on the VASI and GS seemed to be the same and altitudes seemed to be on. It should be noted that throughout the approach GS variations were noted. Callback conversation with reporter revealed the following information: reporter states that the problem was with the GS receiver on her aircraft which was replaced. Aircraft was allowed to descend prior to reaching OM which triggered MSAW in the tower.

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Original NASA ASRS Text

Title: BE90 PLT RPTS ERRATIC GS INDICATIONS ON APCH TO RWY 35R AT APA.

Narrative: ON FINAL VECTOR TO THE ILS RWY 35R APCH TO CENTENNIAL (APA) I WAS CLRED TO 9000 FT MSL UNTIL ESTABLISHED ON THE LOC. I HIT APCH MODE AND HIT ALT SELECT AND WAS COUPLED TO THE AUTOPLT AS I INTERCEPTED THE LOC AND DSNDED TO 8000 FT MSL WHICH IS THE ALT WITHIN 10 MI I NEEDED TO INTERCEPT THE LOC. AFTER REACHING 8000 FT MSL EVERYTHING SEEMED NORMAL UNTIL I RECEIVED A LOW ALT ALERT FROM THE APA TWR. I IMMEDIATELY CHKED MY ALT AND ALTIMETER SETTING AND EVERYTHING SEEMED TO BE NORMAL. AS I APCHED THE OM (CASSE) ON THE APCH I NOTICED THE GS WAS ACTING ERRATIC SHOWING VARIED UP AND DOWN MOVEMENT WITH NO GS FLAG. I PROGRESSED THROUGH THE APCH WITH VARIOUS OTHER GS VARIATIONS AND LOW ALT ALERTS FROM THE APA TWR. AFTER XING (CASSE) WITHIN A QUARTER MI I WAS ABLE TO GET A VISUAL ON THE RWY AND ARPT. ALT BOTH ON THE VASI AND GS SEEMED TO BE THE SAME AND ALTS SEEMED TO BE ON. IT SHOULD BE NOTED THAT THROUGHOUT THE APCH GS VARIATIONS WERE NOTED. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR STATES THAT THE PROB WAS WITH THE GS RECEIVER ON HER ACFT WHICH WAS REPLACED. ACFT WAS ALLOWED TO DSND PRIOR TO REACHING OM WHICH TRIGGERED MSAW IN THE TWR.

Data retrieved from NASA's ASRS site as of January 2009 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.