ACR X HAD LTSS FROM SMT Y LNDG ON INTERSECTING RWY. SYS ERROR.

Narrative

ACR X (A B757) WAS OVER THE THRESHOLD OF RWY 33 AND SMA Y WAS ON A 1 - 1 1/4 MI FINAL TO RWY 21 WHICH INTERSECTS WITH RWY 33. WHEN X HAD LANDED ON RWY 33 I ASKED HIM IF HE COULD TURN ON BRAVO; WHICH IS A TXWY THAT IS PARALLEL TO RWY 21 AND WOULD NOT REQUIRE THE B757 TO CROSS RWY 21. X RESPONDED TO THAT QUESTION WITH A 'STANDBY.' AT THIS POINT THE C303 WAS ON A 1/4 MI FINAL TO RWY 21. I WENT BACK TO X AND TOLD HIM TO TURN R ON BRAVO. X REPLIED HE WAS GOING TO ROLL PAST BRAVO AND HE ASKED IF I WOULD LIKE HIM TO CONTINUE THROUGH -- WHEN AT THIS POINT I LOOKED AT THE C303 AND REALIZED HE HAD ALREADY CROSSED THE RWY 21 THRESHOLD. IT APPEARED AS IF HE WAS STILL IN THE AIR; SO I TOLD THE C303 TO GAR. HOWEVER; I CALLED THE C303 THE WRONG CALL SIGN AT FIRST; THEN WHEN I REALIZED THIS; I WENT BACK AND CORRECTED MYSELF. THE C303 THEN INFORMED ME THAT HE WAS ON THE GND AND THAT HE WOULD HOLD SHORT OF RWY 33. I INFORMED X OF THE C303 INTENTIONS AND THEN CONTINUED TO TAXI BOTH OF THEM TO THEIR RESPECTIVE RAMPS. I BELIEVE THE MAJOR REASON WHY THE SIT OCCURRED IS THIS: I WAS RUNNING BOTH ACFT VERY TIGHT ON THE SEQUENCE BECAUSE OF 1) PAST PERFORMANCE OF THE B757 (ALL PRIOR TIMES DURING THE SAME CONDITIONS THE B757 HAD TURNED ON BRAVO) AND 2) I DIDN'T WANT TO DELAY THE C303. I SHOULD HAVE NEVER ASSUMED ANYTHING AS TO THE B757; AND SHOULD HAVE APPLIED IN AMPLE TIME ALTERNATE CTL INSTRUCTIONS TO THE C303 WHEN I REALIZED THE B757 MIGHT NOT MAKE THE TXWY. SUPPLEMENTAL INFO FROM ACN 278746: NORMAL DSCNT APCH AND TOUCHDOWN ON RWY 33 AT FSD. ON ROLLOUT TWR CTLR ASKED IF WE COULD MAKE AN EXIT AT TXWY B. WE DIDN'T REPLY IMMEDIATELY BECAUSE WE WERE UNCERTAIN AS TO WHETHER WE COULD COMPLY. AS WE WERE ABOUT TO STATE THAT WE WERE UNABLE; THE TWR CTLR TOLD US TO TAKE TXWY B TO WHICH WE REPLIED 'UNABLE WE JUST PASSED IT.' AT THAT TIME SHE ADVISED SMA Y TO GAR. THIS OTHER ACFT WAS A CESSNA 303 LNDG ON THE INTERSECTING RWY 21. WE IMMEDIATELY SAW THE CESSNA 303 ON LNDG ROLLOUT AND APPLIED FULL BRAKING TO HOLD SHORT OF HIS RWY 21. WE STOPPED SHORT OF THE RWY 21 INTXN. THE CESSNA 303 ALSO STOPPED ABOUT 1000 FT SHORT OF THE INTXN. I BELIEVE THE CESSNA 303 WAS ALSO ON HIS LNDG ROLLOUT WHEN THE TWR ADVISED HIM TO GAR. IF THE CESSNA HAD GONE AROUND AND WE DIDN'T HOLD SHORT OF RWY 21; I BELIEVE WE MAY HAVE COLLIDED. THE CREW VIGILANCE ON OUR PART AND THE PART OF THE CESSNA PLT AVOIDED AN ACCIDENT.