Date: 201707
Local time of day: 1201-1800
Location: MYR.Airport, SC
Aircraft: Small Transport; Low Wing; 2 Recip Eng
Flight plan: IFR
Flight phase: Final Approach
Airspace: Class C MYR
ATC / advisory: Tower MYR
Second aircraft: Small Aircraft; High Wing; 1 Eng; Fixed Gear
Reporter organization: Government
Reporter function: Local
Reporter qualification: Air Traffic Control Fully Certified
Human factors: Distraction; Situational Awareness
Anomaly: ATC Issue All Types; Conflict Ground Conflict; Less Severe; Deviation / Discrepancy - Procedural Clearance; Ground Incursion Runway
Detector: Person Air Traffic Control
When detected: Taxi; In-flight
Result: Air Traffic Control Issued New Clearance; Air Traffic Control Separated Traffic; Flight Crew Executed Go Around / Missed Approach
Contributing factors: Human Factors; Procedure
Primary problem: Procedure

Narrative: I started my time on position by working Ground/Tower CIC for 0+28 minutes. I was then relieved on Ground so that training may be accomplished on Ground. After the 2 minute overlap; I moved over to Local and remained on Tower CIC for the next 01+09. We were landing Runway 36. Time on position was pretty busy and complex. Numerous arrivals and departures mixed with sightseeing helicopters. There was a lot of frequency congestion during my time on position due to the sightseeing helicopters requesting the routes and an aircraft requesting to cross the approach end of Runway 36 on many occasions.Approximately 40 minutes into my time on Local; Aircraft X checked in 10 miles northwest of the airport on the visual approach Runway 36. At the time; Aircraft Y was taxiing to Runway 36 on the ground frequency. A few minutes later; Aircraft Y called me ready for takeoff. I cleared Aircraft Y for takeoff Runway 36 and to fly runway heading. A minute later; I heard the ground trainee mention that this was not going to work. I looked up and realized that Aircraft X was approximately 1 mile final at 400 feet. Aircraft Y was past the hold short line turning the corner onto the runway. I then told Aircraft X to go around and Aircraft Y to hold his position for a minute. Once they were no longer a factor for each other; I instructed Aircraft X to enter the downwind and re-cleared Aircraft Y for takeoff. Aircraft X was climbing on the go around prior to reaching the runway threshold.At the time of the event; training was in progress on Ground Control. The Instructor and CPC-IT were engaged in a conversation that was work/personal related; but not training related. It did create some distraction.I have suggested many times that during busy summer traffic; sightseeing helicopters should have their own frequency and a separate Local Controller. Not sure if this is a good solution to fix the problem of confusion that can be created by frequency congestion; but the recommendation is not very welcome when brought up. I have not heard anybody else make any recommendations on how to make the situation better.At the time of this go around; there were a few helicopters making their runs. They all operate at or below 1;200. When there is a lot of congestion; the D-BRITE is very cluttered around MYR which makes it hard to see when aircraft are flying through this area. Aircraft X entered the downwind from the northwest and his tag was lost in all the clutter. That is the only reasoning I can come up with in forgetting that he was there. This is not something I normally do.




Synopsis: MYR Tower Controller reported an unsafe situation when noticing an aircraft on final after clearing an aircraft for takeoff.