Air Traffic Control Fully Certified
Air Traffic Control Time Certified In Pos 1 (yrs) 0.5
Situational Awareness
Conflict Airborne Conflict; Deviation - Track / Heading All Types; Deviation / Discrepancy - Procedural Clearance
Air Traffic Control Issued New Clearance; Flight Crew Became Reoriented; Flight Crew Requested ATC Assistance / Clarification; Flight Crew Took Evasive Action
Aircraft; Environment - Non Weather Related; Human Factors; Procedure
I was working Local 1. Aircraft X went around for runway 31L. I instructed him to follow the second [Aircraft] on downwind (Aircraft Y) and make left closed traffic. Several minutes later I had to extend Aircraft Y in the downwind. I told Aircraft X to continue following the Aircraft Y and extend downwind. Aircraft X read back 'extend downwind.' Several minutes later I missed Aircraft X state on frequency 'turning base.' He turned base on his own and managed to cut off the Aircraft Y he had been following. Aircraft Y had to make an evasive left turn to avoid Aircraft X; who cut him off on final. I was able to resequencing everyone; and they landed without incident.I was busy and I missed Aircraft X turning base on his own. In the future I will continue to exercise vigilance to ensure that the aircraft are following my instructions.
A Tower Local Controller did not notice that an aircraft that was supposed to follow another aircraft turned in front of the aircraft it was supposed to follow.