On Friday, June 26, 2009, a runway incursion occurred at Cleveland /Hopkins International Airport (CLE), Cleveland, Ohio involving Continental Express (BTA) flight 2426, call sign BTA2426, an Embraer 145 and Commutair (UCA) flight 8717, a De Havilland Canada Dash 8-200 (DH8). The incident occurred during daylight visual conditions. At the time of the incident there was a developmental controller being monitored by a certified controller at the local control position. Continental Express (BTA) flight 2426, call sign BTA2426, an Embraer 145, aircraft number N24103 was on a scheduled part 121 flight from CLE to Kansas City International Airport (MCI), Kansas City, Missouri. BTA2426 had a crew of 3, which included the pilot, first officer, a flight attendant, and 40 passengers plus 1 lap child on board. Commutair (UCA) flight 8717, a De Havilland Canada Dash 8-200 (DH8), aircraft number N375PH was on a scheduled part 121 flight from CLE to Port Columbus International Airport (CMH) Columbus, Ohio. UCA8717 had a crew of 3 which included the pilot, first officer, a flight attendant and 19 passengers on board. At 0856, the developmental controller directed UCA8717 to taxi into position and hold on the approach end of runway 24L at CLE. BTA2426, taxied from spot 5 to runway 24R via taxiways J and S and was directed to hold short of runway 24L by the ground controller before being directed to monitor the tower local controller on frequency 120.9. Nineteen seconds after directing UCA8717 to taxi into position and hold, the developmental trainee directed BTA2426 to cross runway 24L and advised BTA2426 that UCA8717 was in position for departure. Twenty seconds after directing BTA2426 to cross runway 24L, the local control developmental trainee directed UCA8717 to fly runway heading and issued a takeoff clearance. BTA2426 had not yet crossed runway 24L. UCA8717 acknowledged the takeoff clearance followed by the controller directing another aircraft to taxi into position and hold runway 24L. BTA2426 immediately called the tower with “BTA2426 we’re holding short of 24L you gave a clearance to cross though”. The local control developmental trainee did not respond. There were no other transmissions on the local control frequency until BTA2426 transmitted 10 seconds later “you copy for BTA2426”. The local control developmental trainee responded with “BTA2426 just hold there please”. According to the pilots of UCA8717, the tower controller instructed them to taxi into position and hold on runway 24L. As the pilot was positioning his aircraft, he noticed that a Jetlink (BTA2426) aircraft was approaching the intersection of taxiway S and runway 24L when the pilot heard the tower direct BTA2426 to cross runway 24L. Shortly thereafter, the tower issued UCA8717 a takeoff clearance. Noticing that BTA2426 had not crossed the runway but was still able to do so, the pilot of UCA8717 planned to ask the local controller about BTA2426 when BTA2426 asked the tower, “I thought I was cleared to cross”. After a few seconds of silence, the pilot of UCA8717 heard BTA2426 state that he would hold short of the runway. After observing BTA2426 hold his position, the pilot of UCA8717 commenced his takeoff roll, after which BTA2426 crossed runway 24L at taxiway S. Eighteen seconds later, BTA2426 was directed to taxi across runway 24L and advised that traffic was holding in position. BTA2426 crossed runway 24L without incident. CLE was on a south flow configuration landing 24L departing runway 24L/R. Reported weather at CLE at 0851 EDT/1251 UTC was wind 270 degrees at 8 knots, visibility 10 statute miles, scattered clouds at 1,200 feet. The temperature was 24 degrees Celsius, dew point 21 degrees Celsius. The altimeter was 2980. ATCT staffing included 4 air traffic control specialist (ATCS); a controller-in-charge (CIC) combined at the flight data/clearance delivery position (FD/CD), 1 ground controller (GC), and a local controller (LC) combined on local control 1 and 2 positions as an on the job training instructor (OJTI) monitoring a LC developmental trainee.