Narrative:

On radar vectors at 4500 ft, told to expect lda DME runway 30L, to intercept localizer. Then cleared for ILS runway 30L, maintain 4500 ft until fonti. I changed #2 navigation to ILS runway 30L and verbally stated so. I thought #1 navigation was tuned to stl VOR. I announced DME 22.4 stl, at fonti, descending to 3500 ft. #1 DME was actually tuned to lda DME runway 30L. At 4000 ft, captain announced I still have #1 tuned to lda DME runway 30L, you are not to fonti yet. I leveled off at 4000 ft then intercepted GS and shot approach. I think some contributing factors are: approach control being very busy, changing approach at last min, flight deck crew being in busy part of flight. The captain not stating when changing #1 navigation/DME, myself not verifying #1 navigation/DME selection. Had I chosen to descend when intercepting the GS at 4500 ft, the problem could have been avoided. It was our first day flying together, I feel if our communication level was better, the problem could have been avoided. I have also seen in many cases, a lot of last min changes in clrncs causing confusion mainly due to time constraints and communication errors. There were no aircraft below us, VFR conditions existed, the altitude deviation did not cause an aircraft conflict.

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Original NASA ASRS Text

Title: LGT FLC DSNDS BELOW ASSIGNED PRIOR TO REACHING INTXN. WRONG VOR TUNED.

Narrative: ON RADAR VECTORS AT 4500 FT, TOLD TO EXPECT LDA DME RWY 30L, TO INTERCEPT LOC. THEN CLRED FOR ILS RWY 30L, MAINTAIN 4500 FT UNTIL FONTI. I CHANGED #2 NAV TO ILS RWY 30L AND VERBALLY STATED SO. I THOUGHT #1 NAV WAS TUNED TO STL VOR. I ANNOUNCED DME 22.4 STL, AT FONTI, DSNDING TO 3500 FT. #1 DME WAS ACTUALLY TUNED TO LDA DME RWY 30L. AT 4000 FT, CAPT ANNOUNCED I STILL HAVE #1 TUNED TO LDA DME RWY 30L, YOU ARE NOT TO FONTI YET. I LEVELED OFF AT 4000 FT THEN INTERCEPTED GS AND SHOT APCH. I THINK SOME CONTRIBUTING FACTORS ARE: APCH CTL BEING VERY BUSY, CHANGING APCH AT LAST MIN, FLT DECK CREW BEING IN BUSY PART OF FLT. THE CAPT NOT STATING WHEN CHANGING #1 NAV/DME, MYSELF NOT VERIFYING #1 NAV/DME SELECTION. HAD I CHOSEN TO DSND WHEN INTERCEPTING THE GS AT 4500 FT, THE PROB COULD HAVE BEEN AVOIDED. IT WAS OUR FIRST DAY FLYING TOGETHER, I FEEL IF OUR COM LEVEL WAS BETTER, THE PROB COULD HAVE BEEN AVOIDED. I HAVE ALSO SEEN IN MANY CASES, A LOT OF LAST MIN CHANGES IN CLRNCS CAUSING CONFUSION MAINLY DUE TO TIME CONSTRAINTS AND COM ERRORS. THERE WERE NO ACFT BELOW US, VFR CONDITIONS EXISTED, THE ALTDEV DID NOT CAUSE AN ACFT CONFLICT.

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.