Narrative:

Small aircraft X was cleared to land runway 26L and instructed to exit the runway at C4 intersection. After small aircraft X crossed landing threshold, I instructed air carrier Y to taxi into position and hold. On landing roll I again instructed small aircraft X to exit the runway at C4 intersection, and the pilot acknowledged. At this time, I performed other colateral duties necessary to the position. I then observed small aircraft X approximately 100' short of C4 intersection and instructed the pilot to taxi west/O delay. At this time, I cleared air carrier Y for takeoff anticipating small aircraft X would be clear of runway when air carrier Y started takeoff roll. Between 5 and 15 seconds later I observed small aircraft X well past C4 intersection and nearly down to C3 intersection. At this time air carrier Y had rolled approximately 800'. I cancelled takeoff clearance, but the pilot never acknowledged and departed.there was approximately 3800' between small aircraft X and air carrier Y when small aircraft X left the runway. The pilot of small aircraft X later advised he did not see C4 intersection until he had passed it, and felt he should go to the next intersection rather than make a 180 degree on the runway and exit at C4 intersection. I believe this operational error occurred for 1 of 2 reasons: 1) I allowed myself to become distracted by providing aural instructions to a student, and 2) most of the airport taxiway lighting is the standard blue lighting; C4 intersection, however, is equipped with green centerline lighting. I feel this error would not have occurred had C4 intersection been equipped with the standard blue lighting or during daylight hours.

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Original NASA ASRS Text

Title: ACR WAS CLEARED FOR TKOF ON AN OCCUPIED RWY.

Narrative: SMA X WAS CLRED TO LAND RWY 26L AND INSTRUCTED TO EXIT THE RWY AT C4 INTXN. AFTER SMA X CROSSED LNDG THRESHOLD, I INSTRUCTED ACR Y TO TAXI INTO POS AND HOLD. ON LNDG ROLL I AGAIN INSTRUCTED SMA X TO EXIT THE RWY AT C4 INTXN, AND THE PLT ACKNOWLEDGED. AT THIS TIME, I PERFORMED OTHER COLATERAL DUTIES NECESSARY TO THE POS. I THEN OBSERVED SMA X APPROX 100' SHORT OF C4 INTXN AND INSTRUCTED THE PLT TO TAXI W/O DELAY. AT THIS TIME, I CLRED ACR Y FOR TKOF ANTICIPATING SMA X WOULD BE CLR OF RWY WHEN ACR Y STARTED TKOF ROLL. BTWN 5 AND 15 SECS LATER I OBSERVED SMA X WELL PAST C4 INTXN AND NEARLY DOWN TO C3 INTXN. AT THIS TIME ACR Y HAD ROLLED APPROX 800'. I CANCELLED TKOF CLRNC, BUT THE PLT NEVER ACKNOWLEDGED AND DEPARTED.THERE WAS APPROX 3800' BTWN SMA X AND ACR Y WHEN SMA X LEFT THE RWY. THE PLT OF SMA X LATER ADVISED HE DID NOT SEE C4 INTXN UNTIL HE HAD PASSED IT, AND FELT HE SHOULD GO TO THE NEXT INTXN RATHER THAN MAKE A 180 DEG ON THE RWY AND EXIT AT C4 INTXN. I BELIEVE THIS OPERROR OCCURRED FOR 1 OF 2 REASONS: 1) I ALLOWED MYSELF TO BECOME DISTRACTED BY PROVIDING AURAL INSTRUCTIONS TO A STUDENT, AND 2) MOST OF THE ARPT TXWY LIGHTING IS THE STANDARD BLUE LIGHTING; C4 INTXN, HOWEVER, IS EQUIPPED WITH GREEN CENTERLINE LIGHTING. I FEEL THIS ERROR WOULD NOT HAVE OCCURRED HAD C4 INTXN BEEN EQUIPPED WITH THE STANDARD BLUE LIGHTING OR DURING DAYLIGHT HRS.

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.