Narrative:

Light transport Y landed on runway 27R and made a 120 degree right turn to exit the runway. This action I watched with binoculars. When the light transport X was clear of the runway, I cleared large transport X for takeoff on runway 27R. After large transport X had rolled about 1500' down the runway I saw some bright white lights come on in front of the large transport X about 2000' in front of him wbound. I cancelled large transport X takeoff clearance and the large transport X was able to come to a stop before coming into contact with the light transport Y. At the time I did not know that it was the light transport Y. Ground control determined that it was the light transport Y after talking with the pilot, who later called the tower to apologize for his mistake. He informed that he was the copilot and that had and the captain had not flown that much together and there had been some missed communication in the cockpit after clearing the runway. The captain ordered the aircraft back onto the runway. They did all of this while hearing the large transport X readback his takeoff clearance. Apparently after the light transport Y initially cleared the runway, the crew had chosen to turn off the headlights in order to see the taxiway lights. After re-entering the runway the crew hearing the large transport X beginning his takeoff roll switched the headlights back on. This is what alerted me to the fact that they had re-entered the runway environment and presented a potential problem for the large transport X.

Related reports:

Google
 

Original NASA ASRS Text

Title: LTT LANDED RWY 27R CLEARED THE RWY AND THEN TAXIED BACK ON WHILE LGT IN THE TKOF ROLL. TWR HAD LGT ABORT TKOF.

Narrative: LTT Y LANDED ON RWY 27R AND MADE A 120 DEG RIGHT TURN TO EXIT THE RWY. THIS ACTION I WATCHED WITH BINOCULARS. WHEN THE LTT X WAS CLR OF THE RWY, I CLRED LGT X FOR TKOF ON RWY 27R. AFTER LGT X HAD ROLLED ABOUT 1500' DOWN THE RWY I SAW SOME BRIGHT WHITE LIGHTS COME ON IN FRONT OF THE LGT X ABOUT 2000' IN FRONT OF HIM WBOUND. I CANCELLED LGT X TKOF CLRNC AND THE LGT X WAS ABLE TO COME TO A STOP BEFORE COMING INTO CONTACT WITH THE LTT Y. AT THE TIME I DID NOT KNOW THAT IT WAS THE LTT Y. GND CTL DETERMINED THAT IT WAS THE LTT Y AFTER TALKING WITH THE PLT, WHO LATER CALLED THE TWR TO APOLOGIZE FOR HIS MISTAKE. HE INFORMED THAT HE WAS THE COPLT AND THAT HAD AND THE CAPT HAD NOT FLOWN THAT MUCH TOGETHER AND THERE HAD BEEN SOME MISSED COM IN THE COCKPIT AFTER CLRING THE RWY. THE CAPT ORDERED THE ACFT BACK ONTO THE RWY. THEY DID ALL OF THIS WHILE HEARING THE LGT X READBACK HIS TKOF CLRNC. APPARENTLY AFTER THE LTT Y INITIALLY CLRED THE RWY, THE CREW HAD CHOSEN TO TURN OFF THE HEADLIGHTS IN ORDER TO SEE THE TXWY LIGHTS. AFTER RE-ENTERING THE RWY THE CREW HEARING THE LGT X BEGINNING HIS TKOF ROLL SWITCHED THE HEADLIGHTS BACK ON. THIS IS WHAT ALERTED ME TO THE FACT THAT THEY HAD RE-ENTERED THE RWY ENVIRONMENT AND PRESENTED A POTENTIAL PROB FOR THE LGT X.

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.