Narrative:

While descending to 5000 ft MSL on downwind for 17L, with PF and autoplt off, controller gave us a turn on a modified base leg for vectors to 18R. This meant that we had to cross to the other side of the field. Copilot was looking up new localizer frequency, controller called out crossing traffic. He was crossing over to 17L. Also at this time TCASII was signalling traffic. We were in tight and endeavoring to slow the aircraft to 170 KTS (this made landing gear warning come on) as requested when given the turn. While all this was going on at the same time the altitude alert went off indicating 300 ft below our assigned altitude. I began to level off when controller reclred us to 4000 ft and called the crossing widebody transport traffic out to us at 3000 ft. We continued our descent, spotting the widebody transport passing near at 3000 ft. We were then cleared to fly the visual to 18R after he passed. On reflection I realize I became overloaded with clearance changes and distrs. I would have been better off with autoplt on. Also, I do not think it is a good idea to change runways so late in the approach and crossing aircraft to different sides of the airfield, unless there is a good reason. This is done quite a bit at dfw, and I feel it reduces the margin of safety.

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Original NASA ASRS Text

Title: FLC OF MLG ON APCH TO DFW HAD RWY CHANGE -- ACFT XING TO OTHER SIDE OF ARPT FOR APCH BECAME TFC FOR EACH OTHER -- RPTR HAD ALTDEV.

Narrative: WHILE DSNDING TO 5000 FT MSL ON DOWNWIND FOR 17L, WITH PF AND AUTOPLT OFF, CTLR GAVE US A TURN ON A MODIFIED BASE LEG FOR VECTORS TO 18R. THIS MEANT THAT WE HAD TO CROSS TO THE OTHER SIDE OF THE FIELD. COPLT WAS LOOKING UP NEW LOC FREQ, CTLR CALLED OUT XING TFC. HE WAS XING OVER TO 17L. ALSO AT THIS TIME TCASII WAS SIGNALLING TFC. WE WERE IN TIGHT AND ENDEAVORING TO SLOW THE ACFT TO 170 KTS (THIS MADE LNDG GEAR WARNING COME ON) AS REQUESTED WHEN GIVEN THE TURN. WHILE ALL THIS WAS GOING ON AT THE SAME TIME THE ALT ALERT WENT OFF INDICATING 300 FT BELOW OUR ASSIGNED ALT. I BEGAN TO LEVEL OFF WHEN CTLR RECLRED US TO 4000 FT AND CALLED THE XING WDB TFC OUT TO US AT 3000 FT. WE CONTINUED OUR DSCNT, SPOTTING THE WDB PASSING NEAR AT 3000 FT. WE WERE THEN CLRED TO FLY THE VISUAL TO 18R AFTER HE PASSED. ON REFLECTION I REALIZE I BECAME OVERLOADED WITH CLRNC CHANGES AND DISTRS. I WOULD HAVE BEEN BETTER OFF WITH AUTOPLT ON. ALSO, I DO NOT THINK IT IS A GOOD IDEA TO CHANGE RWYS SO LATE IN THE APCH AND XING ACFT TO DIFFERENT SIDES OF THE AIRFIELD, UNLESS THERE IS A GOOD REASON. THIS IS DONE QUITE A BIT AT DFW, AND I FEEL IT REDUCES THE MARGIN OF SAFETY.

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.