Date: 201703
Local time of day: 0001-0600
Location: PRC.Airport, AZ
Light: Daylight
Aircraft: Small Aircraft; High Wing; 1 Eng; Fixed Gear
Operating under: Part 91
Flight phase: Final Approach
Airspace: Class D PRC
ATC / advisory: Tower PRC
Second aircraft: Helicopter
Reporter organization: Government
Reporter function: Local
Reporter qualification: Air Traffic Control Fully Certified
Human factors: Workload; Situational Awareness; Distraction; Confusion; Human-Machine Interface
Second reporter function: Supervisor / CIC
Anomaly: ATC Issue All Types; Conflict Airborne Conflict; Deviation - Track / Heading All Types; Deviation / Discrepancy - Procedural Clearance
Detector: Person Flight Crew
When detected: In-flight
Result: Flight Crew Took Evasive Action
Contributing factors: Staffing; Procedure; Human Factors
Primary problem: Procedure

Narrative: During a period of heavy VFR traffic pattern volume on Local 2; Aircraft Y checked on my frequency for closed traffic upwind RWY 3R. I was working RWY 3L on LC2. Aircraft X was upwind RWY 3L off a touch n go in left closed traffic on my frequency. Aircraft X was much lower than Aircraft Y who had departed from RWY 3R (offset runways). Aircraft Y also appeared to me to be well behind; and above; Aircraft X on the upwind. I issued traffic on left downwind for Aircraft Y to follow; Aircraft Y reported the traffic in sight and turned crosswind over the upwind of RWY 3L to follow. Aircraft Y did not turn crosswind when I had expected them to (as their traffic to follow was passing them on the downwind). Aircraft X later reported Aircraft Y in sight crossing in front of them on the upwind. When this report was made Aircraft Y was on the left downwind at 5700 following the traffic previously reported; and Aircraft X was still on the upwind below approximately 5500. Aircraft X reported the need to maneuver in order to avoid a conflict with Aircraft Y on the crosswind. Due to the volume of traffic; staffing the Local Assist 1/LA2 position could have helped both local controllers with an extra pair of eyes. We typically do not staff the local assist position during periods of heavy volume. In this instance; I had just relieved a controller from the LC2 position; it could have been beneficial for the controller being relieved to remain plugged in after the overlap on LA2 to assist me.Visibility from the tower on upwind RWY 3L is very poor due to the distance from and height of the tower. Radar coverage is typically non-existent until aircraft reach pattern altitude of 6000. Controllers typically have the need to work with binoculars in their hands constantly in order to better see the exact position of aircraft in the pattern which inhibits the ability to fluidly scan all of the traffic during high volume times.


Second narrative: I was on CIC at the time monitoring Local 2 as traffic was busy and quite complex. Aircraft Y was upwind of Runway 3R sequenced to follow aircraft X who was on left downwind for Runway 3L. Aircraft Y had that traffic in sight. After aircraft Y turned left crosswind; aircraft X transmitted that they had to make maneuvers to avoid hitting aircraft Y. Aircraft X was upwind of Runway 3L at the time. Aircraft Y did not report a NMAC.


Synopsis: PRC Tower Controller reported an unsafe operation when an aircraft had to maneuver out of the way of another aircraft.