Small Aircraft
Air Traffic Control Fully Certified
Air Traffic Control Time Certified In Pos 1 (yrs) 5
Communication Breakdown; Confusion; Situational Awareness
ATC Issue All Types; Conflict Ground Conflict; Less Severe; Deviation / Discrepancy - Procedural Clearance
Air Traffic Control Separated Traffic; Flight Crew Executed Go Around / Missed Approach
Procedure; Human Factors
Aircraft X was instructed to taxi up to the hold line runway 30R and say direction of flight.  Aircraft X fumbled his words and I was able to catch his direction of flight. Aircraft X was then observed in position with aircraft Y on short final.  I sent aircraft Y around and departed aircraft X.I believed he understood the instructions and did not check on the words he fumbled. Listening to the tape it was clear he read back in position.  Will work on listening closer to poor read backs.
A BJC Local Controller reports on asking an aircraft direction of flight. The pilot reports direction and also says something unintelligible to the Controller. Local observes aircraft in position with another aircraft on final. The Controller sends final traffic around and realizes he did not listen correctly to the read back or receive clarification.