Date: 202103
Local time of day: 1201-1800
Location: ZZZ.Tower, US
Aircraft: Small Aircraft
Operating under: Part 91
Flight plan: VFR
Mission: Training
Flight phase: Landing
Airspace: Class C ZZZ
ATC / advisory: Tower ZZZ
Second aircraft: Small Aircraft
Reporter organization: Government
Reporter function: Local
Reporter qualification: Air Traffic Control Fully Certified
Human factors: Confusion; Situational Awareness; Training / Qualification; Workload; Fatigue
Anomaly: ATC Issue All Types; Conflict Ground Conflict; Less Severe; Deviation / Discrepancy - Procedural Published Material / Policy; Ground Incursion Runway
Detector: Person Air Traffic Control
When detected: Taxi
Result: Air Traffic Control Issued New Clearance; Air Traffic Control Provided Assistance; Flight Crew Requested ATC Assistance / Clarification
Contributing factors: Human Factors; Environment - Non Weather Related; Procedure
Primary problem: Human Factors

Narrative: When I was assigned a Tower position I inquired as to working a different position as it was my 6th day working and my last round of the day. I was told no. When I got to the tower it appeared to me that Local Control and Ground Control had been on position for the same amount of time. I went to relieve Ground Control and the Supervisor told me 'no your not going to ground' when I inquired about the the time on position he told me that Local Control had been on position over 2 hours. I again asked if I could work Ground Control. The Supervisor did not answer and ordered me to go to Local Control.Another controller in the tower said the Local Controller had requested to go from a previous position to Local when he was relieved without a break. When I first assumed the position the Supervisor asked me if I wanted him to write some of the call signs on the strips. I declined since it did was not busy at the time. This session turned into a heavy arrival push with some departures and multiple crossings. There were numerous data tags constantly overlapping as well as approximately one half separation between several arrivals making it difficult not only to write down the aircraft call signs on the half strips used for this position but also to ensure the preceding arrival was off the runway prior to the succeeding aircraft crossing the landing threshold.The Supervisor stood at the Cab Coordinator position (which was not staffed) actively listening the entire time I was on position. The only coordination performed by the Supervisor was to tell me I could issue a 110 heading out of 1;500 feet which at the time was completely unnecessary as well as a distraction. Aircraft X had been cleared to land and hold short of taxiway whiskey for crossing traffic. I had an Aircraft Z that was going to do a missed approach with a 030 heading behind Aircraft X. Aircraft Y had previously called ready for departure I cleared Aircraft Y for departure then realizing it was not going to work when I did my 3 part scan I complete prior to every departure. I immediately went back to Aircraft Y and cancelled takeoff clearance and instructed them to hold short. The aircraft did not acknowledge; and even if a readback was accomplished and complied with; crossing the hold short line was inevitable. I chose to transmit to Aircraft X to get off the runway to prevent a possible departure creating a more dangerous situation. I have not had the opportunity to listen to the tape but I am almost positive Aircraft X exited the runway at an intersection. Aircraft Y was still northbound entering the runway when Aircraft X exited the runway. Aircraft Y was on the runway on an easterly heading and asked to verify if cleared for departure. I advised negative and instructed to hold in position to alleviate any further confusion on Aircraft Y part. After a short time went by I then cleared Aircraft Y for departure. At that point the Supervisor asked me if there was anything he needed to be looking into.I advised since he wasn't aware of what happened 'I didn't know' and then told him what is written above. I think it would be a good idea if a new Supervisor who may not be fully aware of the ins and outs of the facility during extreme pushes to have a Cab Coordinator opened. Also for whatever the reason; the Supervisor is unable to keep abreast of what is happening while actively listening with a headset standing 3 feet from the busiest position; then opening a Cab Coordinator would have been a good call. Perhaps a Cab Coordinator would have caught the situation not going to work prior to my clearing the aircraft for departure to begin with and would have definitely helped with the numerous crossings.




Synopsis: A Local Controller reported they allowed an aircraft to taxi onto the runway for departure with insufficient spacing from a previous arriving aircraft.