Medium Large Transport; Low Wing; 2 Turbojet Eng
Air Traffic Control Fully Certified
Situational Awareness
ATC Issue All Types; Conflict Ground Conflict; Critical; Deviation / Discrepancy - Procedural Clearance; Ground Incursion Runway
Air Traffic Control Issued Advisory / Alert; Air Traffic Control Issued New Clearance; Air Traffic Control Separated Traffic; Flight Crew Executed Go Around / Missed Approach; General Flight Cancelled / Delayed
Procedure; Human Factors
I was the Local Controller for the following event. Aircraft X had been cleared to land. As he approached the runway; Aircraft Y called up ready for takeoff. I responded by saying 'Aircraft Y; Lexington tower; roger.' After a minute or so later as I was scanning the runway I noticed that Aircraft Y had begun taxiing on to the runway in front of Aircraft X who was now very short final. I immediately issued go around instructions to Aircraft X to avoid a collision. At the point of go around Aircraft X was less than 100 ft AGL and within 1/8 of a mile of the landing threshold.
Tower Controller sent an aircraft on short final around when they observed another aircraft taxi onto the runway without a clearance.