Date: 201907
Local time of day: 1201-1800
Location: ZZZ.Airport, US
Flight conditions: VMC
Light: Daylight
Aircraft: Light Transport; Low Wing; 2 Turboprop Eng
Operator: Corporate
Operating under: Part 91
Flight plan: IFR
Mission: Passenger
Flight phase: Final Approach
Airspace: Class D ZZZ
ATC / advisory: Tower ZZZ
Second aircraft: Helicopter
Reporter organization: Government
Reporter function: Trainee; Local
Reporter qualification: Air Traffic Control Developmental
Human factors: Training / Qualification; Situational Awareness; Distraction; Communication Breakdown; Workload
Second reporter function: Instructor
Anomaly: ATC Issue All Types; Conflict NMAC
Detector: Person Flight Crew
When detected: In-flight
Result: Flight Crew Took Evasive Action; Flight Crew Requested ATC Assistance / Clarification; Flight Crew Executed Go Around / Missed Approach
Contributing factors: Environment - Non Weather Related; Human Factors; Procedure
Primary problem: Human Factors

Narrative: I was receiving training on Local Control. A helicopter came in from the north and was cleared to land Runway XX. Upon landing; the helicopter requested to perform hover work on Runway XX and I approved it; with no other traffic inbound. I then placed the helicopter memory aid on the radar display. Aircraft X reported on with me; approximately 6 miles east of the airfield. His data tag [showed] he was on a visual approach to Runway XX. I issued traffic to Aircraft X; for a C182 approximately 3 miles west of Aircraft X. Aircraft Z reported Aircraft X in sight to be no factor. I then issued traffic for Aircraft A who was 2 miles west of the extended final. Aircraft A reported Aircraft X in sight; and he was approved for visual separation.I then scanned Runway XX and cleared Aircraft X to land. I did not see the helicopter on the runway. I do not know if it was assumption bias; or the helicopter was behind a window beam from my perspective; or because the helicopter was black and seemed to blend in- I just didn't see him and I didn't scan the TDW (Tower Display Workstation) to see the helicopter memory aid.Aircraft X was approximately half-mile final; and asked if there was a dark piece of asphalt on the runway; or if it was a helicopter. I immediately remembered the helicopter and told Aircraft X that his landing clearance was cancelled and to make a go-around on the right side of the runway. Aircraft X came back stating that I was cut off; and asked about the dark mark on the runway. At this point; [the] helicopter was picking up from the runway; to a taxiway on the right side. So I told Aircraft X to go-around again; without the 'right side' instruction. Aircraft X stated that there must be something wrong with our radios and he was going around. I then instructed Aircraft X to enter right closed traffic and coordinated this with Approach Control. [The] helicopter asked to taxi back to the ramp; so I issued him taxi instructions across the intersecting runway; then to Ground Control frequency. I was then relieved from the position and the relieving Controller cleared Aircraft X to land with no further incidents.


Second narrative: I was conducting a student training flight. Tower cleared us to land. We landed and I asked to do hover work over the runway if they had no traffic. The Tower advised she did not have any inbounds and we were approved as requested. During hover work over the touchdown markers I heard Aircraft X ask if there was somebody or something on their runway. The Tower replied to him to cancel his landing clearance and go-around. He asked again. It appeared he did not hear the Tower tell him to go around. I took the controls from the student and moved quickly to the grass area adjacent to the runway just as Aircraft X passed over the runway centerline at approximately 100 feet. during his go around. I then advised the Tower we were moving over to the taxiway and that we wanted to return to our hangar. After we shutdown; I spoke with the Aircraft X pilot and he said that he saw us when he was on base leg; but never heard the Tower cancel his landing clearance or tell him to go-around.


Synopsis: A Tower Local Control Trainee; their instructor and a helicopter pilot reported the Trainee cleared an aircraft to land with a helicopter hovering over the runway.