Tower Controller trainee and their instructor reported an aircraft on upwind in the pattern reported a NMAC with another aircraft.
Synopsis
Tower Controller trainee and their instructor reported an aircraft on upwind in the pattern reported a NMAC with another aircraft.
Narrative
I was training on LC (Local Control) and had 6 aircraft in the left traffic pattern for RWY XXL not including arriving/departing itinerants. Upwind and downwinds were being extended to accommodate all requests. Aircraft X reported going around at the approach end and was instructed to follow the aircraft ahead on upwind which was Aircraft Y. Aircraft X reported aircraft in sight. Aircraft Z was the next aircraft to the runway. Multiple aircraft called ready for departure and inbound to include a Skywagon from the south inbound to land. I gave the Skywagon a left traffic entry and to maintain at or above 6500 ft. in reference to my traffic pattern. Also at this time there were aircraft 'stepping' on each other as well as a convective SIGMET that needed to be read. At this point I believed I had all my traffic sequenced enough to read the SIGMET as my instructor advised me to. I did not realize I had not given Aircraft Z an upwind instruction though my intent was to have them follow Aircraft X ahead of the Skywagon. As I continued working my traffic Aircraft Z questioned if I still needed him straight out. I looked out the window as well as the RADAR to ensure i had enough space infront of the Skywagon. Spacing appeared good so I instructed Aircraft Z to turn crosswind. Aircraft Z then advised they could not turned crosswind. I then scanned again to understand why since they did not give a reason. I did not see one out the window due to distant and building weather to the south but as I looked back at the RADAR Aircraft X's target reappeared after having dropped off. At this time their target appeared abeam and passing Aircraft Z. I then again gave Aircraft Z a crosswind turn. Aircraft X position was unexpected due to the aircraft they were instructed to follow being significantly further downwind. I continued to work the session which remained busy for 15 plus minutes and was not fully aware of the severity of the issue. I was still on position when the Supervisor advised that an aircraft wanted to report a possible aircraft collision. I tried to not get distracted as the supervisor spoke with my trainer specifics about the incidents and what i should have done. Traffic load and frequency congestion was definitely a factor. Having specific VFR reporting/ pattern entries could help alleviate some of the conflicts with the traffic pattern and help standardize the flow. Also a local assist could help be an extra pair of eyes dedicated to specific congested spots in the pattern. Having a standard pattern limit may also be something to consider.
Second reporter narrative
Training on LC (Local Control); I was the OJTI (On-the-job Training Instructor). At the time we had a minimum of 5 to 6 aircraft in the left traffic pattern for RWY XXL. Aircraft were being extended upwind and downwind to work in arrivals and departures. Aircraft X said he was going around. He was instructed to follow the aircraft ahead on upwind which was Aircraft Y; Aircraft X said they had them in sight. Behind Aircraft X was Aircraft Z. After this touch and go Aircraft Z never got an upwind instruction. At this time multiple aircraft were calling ready for departure and also aircraft from outside the airspace were calling to be sequenced in for arrival. Also a Convective SIGMET was placed at the position and the Supervisor asked that I have my trainee read it over the frequency. At some point Aircraft Y turned downwind and Aircraft X continued on the upwind; and his VFR tag disappeared from Radar.After multiple departures Aircraft Z asked if we wanted him to continue straight out. The trainee looked at the Radar display and saw a SkyWagon inbound for left traffic restricted at an altitude of at or above 6500 ft; 500 ft. above the traffic pattern; and was about 3 miles SW of Aircraft Z. Any other conflicting aircraft appeared to be about a mile and a half to 2 miles behind Aircraft Z on the downwind. The trainee told Aircraft Z to turn crosswind; a moment later Aircraft Z said 'we can't turn downwind'; so the controller then said Aircraft Z fly straight out. Then I noticed a primary radar tag slightly ahead and to the left of Aircraft Z's RADAR tag. I looked out the window but the aircraft was so far extended (about 4-4 1/2 miles upwind); when I looked back at the RADAR display I then saw a VFR target reappear on the scope next to Aircraft Z. I told the trainee I believe there is an aircraft in the downwind that disappeared off radar next to Aircraft Z. The trainee then told Aircraft Z to follow the aircraft off 'his left wing'; he said he would follow. We continued to work the traffic. When Aircraft Z landed he informed the Ground Controller that he almost turned into an aircraft on the downwind when he was told to turn crosswind and that was when we realized what he meant when he said he couldn't turn crosswind. This was an extremely busy session. Normally most of the VFR traffic pattern will be put on (Local Control 2 but there was a new trainee on his first session working the local traffic and his trainer requested we take 'it easy on him' so we kept 6 aircraft in our pattern. This is not normal. There was multiple factors that contributed to this happening. Aircraft not following instructions. Aircraft X didn't follow Aircraft Y as instructed and extended upwind significantly before turning crosswind. Aircraft X then dropped off radar; Aircraft Z did not receive instructions on the upwind; the amount of traffic; aircraft stepping on each other and having to repeat instructions; the Supervisor who was working GC insisting we read a weather advisory at a time that the workload did not permit.
Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.