Narrative:

On approach to runway 12L at stl, we were given an altitude of 4500 ft for leveloff. During a turn from base to final, we were also given an expect lda DME runway 12L. This was not what we were expecting. We planned a visual with ILS backup, and had those plates out. Both the copilot and I had to get the new plates, and while doing that, controller was giving us traffic and runway information. I saw the runway but couldn't find traffic. Controller kept giving traffic information and said 'I can't do anything until you have the traffic.' so I was looking while the first officer was flying. While this was all going on, we went below our 4500 ft. Altitude warning went off at 4200 ft and we recovered. Other than the obvious fact that we missed a leveloff, I will say we were helped by numerous other events. First, we were put in holding on the arrival due to an emergency at the field. This put fuel on my mind. We were then told to expect a 15-20 mi final and we were descending accordingly. We were then turned at 10-11 mi and switched to lda-DME runway 12. This put us behind. While trying to catch up, we were told of this traffic, so I was spending most of my time looking out for it. The combination of all those factors resulted in us going below 4500 ft assigned altitude. Performance wise, it was the last leg of the day and we had a short layover with an XA00 departure the next day, however, I do not feel that was really a factor. We just simply got overloaded and missed an altitude.

Related reports:

Google
 

Original NASA ASRS Text

Title: FO OF A DC9-50 DSNDED BELOW ASSIGNED ALT FOR TRANSITION FOR APCH DUE TO MANY DISTRS AND A LAST MIN CHANGE IN TYPE OF APCH. THE CTLR INTERVENED AND DIRECTED RPTRS BACK ON ASSIGNED ALT.

Narrative: ON APCH TO RWY 12L AT STL, WE WERE GIVEN AN ALT OF 4500 FT FOR LEVELOFF. DURING A TURN FROM BASE TO FINAL, WE WERE ALSO GIVEN AN EXPECT LDA DME RWY 12L. THIS WAS NOT WHAT WE WERE EXPECTING. WE PLANNED A VISUAL WITH ILS BACKUP, AND HAD THOSE PLATES OUT. BOTH THE COPLT AND I HAD TO GET THE NEW PLATES, AND WHILE DOING THAT, CTLR WAS GIVING US TFC AND RWY INFO. I SAW THE RWY BUT COULDN'T FIND TFC. CTLR KEPT GIVING TFC INFO AND SAID 'I CAN'T DO ANYTHING UNTIL YOU HAVE THE TFC.' SO I WAS LOOKING WHILE THE FO WAS FLYING. WHILE THIS WAS ALL GOING ON, WE WENT BELOW OUR 4500 FT. ALT WARNING WENT OFF AT 4200 FT AND WE RECOVERED. OTHER THAN THE OBVIOUS FACT THAT WE MISSED A LEVELOFF, I WILL SAY WE WERE HELPED BY NUMEROUS OTHER EVENTS. FIRST, WE WERE PUT IN HOLDING ON THE ARR DUE TO AN EMER AT THE FIELD. THIS PUT FUEL ON MY MIND. WE WERE THEN TOLD TO EXPECT A 15-20 MI FINAL AND WE WERE DSNDING ACCORDINGLY. WE WERE THEN TURNED AT 10-11 MI AND SWITCHED TO LDA-DME RWY 12. THIS PUT US BEHIND. WHILE TRYING TO CATCH UP, WE WERE TOLD OF THIS TFC, SO I WAS SPENDING MOST OF MY TIME LOOKING OUT FOR IT. THE COMBINATION OF ALL THOSE FACTORS RESULTED IN US GOING BELOW 4500 FT ASSIGNED ALT. PERFORMANCE WISE, IT WAS THE LAST LEG OF THE DAY AND WE HAD A SHORT LAYOVER WITH AN XA00 DEP THE NEXT DAY, HOWEVER, I DO NOT FEEL THAT WAS REALLY A FACTOR. WE JUST SIMPLY GOT OVERLOADED AND MISSED AN ALT.

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.