The aircraft was assigned the airport's Runway 22 for the takeoff, but used Runway 26 instead. Analysis of the cockpit voice recorder (CVR) indicated the aircraft was cleared to take off from Runway 22, a runway used by most airline traffic at Lexington. Instead, after confirming the takeoff clearance for runway 22, Captain Clay taxied onto Runway 26, a much smaller and unlit runway that is not authorized for commercial use, and turned the controls over to First Officer Polehinke for takeoff. The air traffic controller was not required to maintain visual contact with the aircraft; after clearing the aircraft for takeoff, he turned to perform administrative duties and did not see the aircraft taxi to the runway.