The local control center (LCC) controller in the Cincinnati/Northern Kentucky International Airport (CVG) air traffic control tower (ATCT) cleared Trans State Airlines (LOF) Flight 8069, call-sign Water-Ski, an E-145 to land on runway 18C. Delta Air Lines (DAL) Flight 2809, a B738, had been instructed to line up and wait (LUAW) on runway 18C. The LCC withheld the takeoff clearance for the B738 until a helicopter had crossed the departure path at low level, four miles south of the airport. The LCC momentarily lost sight of the helicopter and could not locate the helicopter on the tower radar presentation. After re-acquiring the helicopter and determining that no conflict existed for the departing B738, the LCC issued the B738 a takeoff clearance. Contrary to FAA orders, the takeoff clearance did not include traffic information that another aircraft, the E-145, was on approach to the same runway. On short final for runway 18C, the E-145 queried the local controller if they should go around, as they were inside of 1/2 nautical mile final to runway 18C and the B738 was in position on the approach end of runway 18C. At approximately the same time, the tower Airport Movement Area Safety System (AMASS) alerted to the developing conflict between the B738 and the E-145. Prior to the E-145 crossing the landing threshold, the LCC instructed the E-145 to go around; fly runway heading and climb and maintain 4,000 feet. The E-145 passed to the right side of the runway 18C landing threshold and did not overfly the B737. The FAA identified this event as a significant operational error; "SIGNIFICANT OPERATIONAL ERROR/1125E/OPERATIONAL ERROR REPORTED WHEN TRANS WORLD EXPRESS 8069, EMBRAER E145, WAS CLEARED TO LAND RWY 18C WITH DELTA 2809, B738, CLEARED TO DEPART SAME RUNWAY. TRANS WORLD EXPRESS 8069 WAS THEN ISSUED GO AROUND AND OVERFLEW DELTA 2809 DURING TAKEOFF ROLL. CLOSEST PROXIMITY 300 FEET VERTICAL." An on-site investigation and analysis of ATC data by NTSB and FAA investigators revealed that an operational error did not occur. The E-145 offset its flight path during the go-around and passed to the right side of the landing threshold and the departing B738. While it was determined that the local controllers performance was not in compliance with local operating procedures or FAA Order 7110.65 and the missed approach instructions could have been more definitive, a loss of separation did not occur and assured separation was established prior to the E-145 crossing the landing threshold.