ATC HANDLING IN APCH CTLR TECHNIQUE COM ATC CREATES A FLC WORKLOAD PROB IN A LAST MIN RWY ASSIGNMENT. TCASII TA STOPS ACFT FROM DSCNT NEAR BUT NOT IN CONFLICT WITH OTHER APCH TFC.

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ON DOWNWIND LEG S OF THE FIELD; WE WERE CLRED FROM 7000 FT TO 3500 FT. WE WERE ON A 270 DEG HDG AND TOLD TO EXPECT 9R. WE WERE EXPEDITING OUR DSCNT FOR A SHORT APCH. WE WERE GIVEN A 360 DEG HDG FOR A BASE LEG AND SIMULTANEOUSLY TOLD TO NOW EXPECT RWY 8L. THIS REQUIRED US TO CROSS FINAL FOR 9R WHICH HAD AN ACFT ESTABLISHED ON FINAL AT 3500 FT. TIME WAS VERY COMPRESSED AT THIS POINT AND CHANGES WERE NUMEROUS. WE WERE AWARE OF THE FINAL APCH TFC DUE TO OUR ONBOARD TCASII. THE TCASII AIDED US IN ACQUIRING THE TFC AND SUBSEQUENTLY GAVE US A TA. WITH US EXPEDITING OUR DSCNT FOR A SHORT APCH AND PASSING 4500 FT FOR 3500 FT OUR ALT CLRNC WAS CHANGED FROM 3500 FT TO 4500 FT. A LEVEL OFF WAS INITIATED IMMEDIATELY. OUR MOMENTUM IN THE DSCNT CAUSED US TO DSND A COUPLE HUNDRED FT BELOW 4500 FT PRIOR TO LEVEL OFF AND WE QUICKLY RETURNED TO 4500 FT. AS STATED EARLIER; WE DID RECEIVE A TCASII TA BUT NEVER RECEIVED AN RA. SUBSEQUENT APCH AND LNDG WERE UNEVENTFUL. CONTRIBUTING FACTORS: WX IN REGION REQUIRING INBOUND AND OUTBOUND TFC TO DEVIATE -- POSSIBLY CAUSING A LAST MIN RWY CHANGE. LAST MIN RWY CHANGE COUPLED WITH NUMEROUS INSTRUCTIONS. TIME COMPRESSION MINIMIZING COM. TCASII WAS INSTRUMENTAL IN BREAKING THE CHAIN. IT AIDED US IN ACQUIRING A VISUAL ON THE TFC. SUPPLEMENTAL INFO FROM ACN 244854: APCH ASKED IF WE WERE PASSING 4500 FT. WE SAID THAT WE WERE CLRED TO 3500 FT. HE SAID WE WERE CLRED TO 4500 FT. SUPPLEMENTAL INFO FROM ACN 244985: NEITHER THE COPLT OR I HEARD ANY NEW ALT CHANGE AND NEVER SET IN A NEW ALT ON THE ALERTER. AS WE CROSSED THE CTRLINE FOR 9R; WE SAW AN LTT ON FINAL FOR 9R AT 3500 FT. WE GOT AN ALERT ON THE TCASII AS WE WERE DSNDING OUT OF 4200 FT. WE STOPPED OUR DSCNT AND THE CTLR CALLED AND SAID TO MAINTAIN 4500 FT.