TWR CTLR CLRED A COMMUTER ACFT FOR TKOF WITH A LNDG ACFT ON SHORT FINAL. THE LNDG WAS MADE WHILE THE COMMUTER ACFT WAS STILL ROLLING ON THE RWY.

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ACR X B737 ON APCH FOR RWY 18R FOLLOWING A B737 BY 4 MI WAS ASKED TO REDUCE TO FINAL APCH SPD FOR A SAAB DEP PRIOR TO ARR. AFTER XING THRESHOLD; I INSTRUCTED ACR Y TO TAXI INTO POS AND HOLD RWY 18R; TFC ON 3 MI FINAL; BE READY FOR IMMEDIATE. THE PREVIOUS B737 WAS REQUESTED TO ADVISE IF HE HAD THE HIGH SPD. HE SAID HE WOULD HAVE THE NEXT ONE. HE TURNED ON THE 90 DEG TURN AT WM. THIS CAUSED A SMALL DELAY. THE PREVAILING WIND WAS 10 DEGS AT 6 KTS WHEN I CLRED ACR Y FOR TKOF; ACR X WAS ON A 2 MI FINAL. UNDER NORMAL CONDITIONS; THIS WAS MORE THAN ENOUGH ROOM TO GET A DEP OUT BUT THE SAAB WAS SLOW TO ROLL AND ACR X WAS FAST ON FINAL DUE TO TAILWINDS. AT THE TIME ACR X CROSSED THE THRESHOLD ACR Y WAS APPROX 4000 FT AND AIRBORNE. UNDER NORMAL CIRCUMSTANCES; I WOULD'VE INITIATED A GAR TO ACR X BUT BECAUSE OF HIS SPD AND TAILWIND I FELT THE SAFEST THING TO DO WAS LET HIM LAND. CONTRIBUTING FACTORS: TAILWIND; WE WERE DISPLAYING 2 WINDS; LLWAS INDICATOR AND TDWR WIND SYS. ONE INDICATED S AND ONE INDICATED N. THE SAAB WAS SLOW TO ROLL. ACR X DID NOT REDUCE OR INFORM ME THAT HE COULDN'T.