Narrative:

Air carrier X B737 on approach for runway 18R following a B737 by 4 mi was asked to reduce to final approach speed for a saab departure prior to arrival. After crossing threshold, I instructed air carrier Y to taxi into position and hold runway 18R, traffic on 3 mi final, be ready for immediate. The previous B737 was requested to advise if he had the high speed. He said he would have the next one. He turned on the 90 degree turn at wm. This caused a small delay. The prevailing wind was 10 degrees at 6 KTS when I cleared air carrier Y for takeoff, air carrier X was on a 2 mi final. Under normal conditions, this was more than enough room to get a departure out but the saab was slow to roll and air carrier X was fast on final due to tailwinds. At the time air carrier X crossed the threshold air carrier Y was approximately 4000 ft and airborne. Under normal circumstances, I would've initiated a go around to air carrier X but because of his speed 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 system. One indicated south and one indicated north. The saab was slow to roll. Air carrier X did not reduce or inform me that he couldn't.

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Original NASA ASRS Text

Title: 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.

Narrative: 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.

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.