Narrative:

I was working local control at the time of the incident. I was giving training to one of our deviation's. Runway 27R (the runway normally used for lndgs) was closed at the time. So, we were landing and departing off one runway. Commuter Z had just landed. Large transport air carrier Y was on final approach approximately 5 mi out. I instructed medium large transport air carrier X to, 'taxi into position and hold, be prepared for an immediate' departure. When aircraft Z had cleared the runway I issued takeoff clearance to X. At this point air carrier Y was about 2 mi out, and X was on the runway but not lined up and he was still moving. I assumed he would execute a rolling takeoff, and neglected to issue an 'immediate' takeoff clearance. I then looked away from the runway to locate another aircraft inbound for the secondary runway. When I looked back, air carrier Y was over the landing threshold and air carrier X was about halfway down the runway but was not airborne.

Google
 

Original NASA ASRS Text

Title: OPERATIONAL ERROR. LNDG AND DEPARING ACR ACFT WERE ON RWY AT SAME TIME.

Narrative: I WAS WORKING LCL CTL AT THE TIME OF THE INCIDENT. I WAS GIVING TRNING TO ONE OF OUR DEV'S. RWY 27R (THE RWY NORMALLY USED FOR LNDGS) WAS CLOSED AT THE TIME. SO, WE WERE LNDG AND DEPARTING OFF ONE RWY. COMMUTER Z HAD JUST LANDED. LGT ACR Y WAS ON FINAL APCH APPROX 5 MI OUT. I INSTRUCTED MLG ACR X TO, 'TAXI INTO POS AND HOLD, BE PREPARED FOR AN IMMEDIATE' DEP. WHEN ACFT Z HAD CLRED THE RWY I ISSUED TKOF CLRNC TO X. AT THIS POINT ACR Y WAS ABOUT 2 MI OUT, AND X WAS ON THE RWY BUT NOT LINED UP AND HE WAS STILL MOVING. I ASSUMED HE WOULD EXECUTE A ROLLING TKOF, AND NEGLECTED TO ISSUE AN 'IMMEDIATE' TKOF CLRNC. I THEN LOOKED AWAY FROM THE RWY TO LOCATE ANOTHER ACFT INBND FOR THE SECONDARY RWY. WHEN I LOOKED BACK, ACR Y WAS OVER THE LNDG THRESHOLD AND ACR X WAS ABOUT HALFWAY DOWN THE RWY BUT WAS NOT AIRBORNE.

Data retrieved from NASA's ASRS site as of August 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.