Date: 201909
Local time of day: 0601-1200
Location: ZZZ.Airport, US
Flight conditions: VMC
Light: Daylight
Aircraft: PA-28 Cherokee/Archer/Dakota/Pillan/Warrior
Operator: Personal
Operating under: Part 91
Flight plan: VFR
Mission: Personal
Flight phase: Initial Approach
Airspace: Class D ZZZ
ATC / advisory: Tower ZZZ
Second aircraft: B737 Undifferentiated or Other Model
Reporter organization: Government
Reporter function: Local; Flight Data / Clearance Delivery; Ground
Reporter qualification: Air Traffic Control Fully Certified
Human factors: Situational Awareness; Distraction
Anomaly: ATC Issue All Types; Conflict NMAC; Deviation / Discrepancy - Procedural Clearance
Detector: Person Flight Crew
When detected: In-flight
Result: Air Traffic Control Issued New Clearance; Air Traffic Control Issued Advisory / Alert; Flight Crew Took Evasive Action; Flight Crew Executed Go Around / Missed Approach
Contributing factors: Human Factors; Procedure
Primary problem: Human Factors

Narrative: I was working all positions combined in the tower and it was a sunny clear day. Aircraft Y was on Runway XX Approach. Aircraft X was inbound from the northwest on the VFR arrival route and negative transponder. Aircraft Y was on 9 mile final when Aircraft X was just north of the airport. I instructed Aircraft X to continue left traffic for runway XX (west-bound runway heading) and follow Aircraft Y on 9 mile final. Aircraft X acknowledged and continued on left traffic Runway XX. I cleared Aircraft Z for departure on Runway XX when Aircraft Y was on 6 mile final. I next told Aircraft X to follow the 737 caution wake turbulence Runway XX cleared to land number two. Aircraft X read back roger cleared to land after the 737. The morning sun and the hills in the background made it difficult to see but it looked like Aircraft X was cutting it in close on base to final behind Aircraft Y. I next told Aircraft X that the jet needs to be clear of runway and s turns are approved if he needs it. Next Aircraft Y says he was going around. I issue the go around and Aircraft Y elects to come back around on the Visual Approach. Then Aircraft X elects to go around as well and issue the go around and a wake turbulence cautionary and a resequence. Both aircraft flew a lap in the pattern and landed without incident. I told the pilot of Aircraft X to call the tower as he was taxing to parking. While on the downwind the pilot of Aircraft Y said that he went around because the cherokee was too close at about 300 ft and he would call it a near midair. After talking to the pilot of Aircraft X on the phone he said that the sun was in his eyes and lost sight of Aircraft Y and he thought number two behind the departing B737 and apologized for the mix up resulting in Aircraft Y going around.It would have helped in Aircraft X had a transponder as I could have had a better idea of his position on our [radar] display. Also the pilot of Aircraft X could be educated on sequencing/following traffic. He got mixed up and lost sight of the other jet and thought he was number two behind the departing B737.




Synopsis: Tower Controller reported a VFR aircraft that was supposed to follow a B737 on short final turned into the B737 instead resulting in a NMAC.