Narrative:

I was on LC1 with multiple aircraft in the south patter when aircraft X checked in from the west requesting left traffic for runway 28L. LC2 was working runway 28R and the north pattern. I sequenced the pilot to follow aircraft a on base turning final and also told the pilot about aircraft Y on final for the parallel runway. Aircraft X reported the cessna to follow in sight; so I cleared him to land. Aircraft X turned too early and I informed him that spacing between him and the cessna was not going to work out. The pilot then says he's going to make a 360 and took action without realizing there is other traffic in his vicinity. I quickly informed him of traffic and he responded that he had traffic in sight. He made a right turn directly towards aircraft Y who was on final for the parallel runway. Aircraft Y had to take evasive action to avoid aircraft X. I told aircraft X to go around and offset right of the runway and told him about traffic in the north pattern. He reported a cessna in sight and began a turn to the right downwind quickly overtaking the cessna on downwind. I instructed aircraft X to extend downwind to follow traffic on final. He reported the cessna to follow in sight (aircraft B). Again; he turned base too early and I had to send the cessna around to get aircraft X to land.the pilot of aircraft X may have misjudged the spacing required to follow aircraft that are much slower than a BE20. The pilot took action on his own without being aware of his surroundings. He should have verified with ATC before making any turns.

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Original NASA ASRS Text

Title: Air Traffic Controller and BE200 Captain reported confusing instructions which created an airborne conflict resulted in pilot reporting a NMAC.

Narrative: I was on LC1 with multiple aircraft in the south patter when Aircraft X checked in from the west requesting left traffic for runway 28L. LC2 was working runway 28R and the north pattern. I sequenced the pilot to follow Aircraft A on base turning final and also told the pilot about Aircraft Y on final for the parallel runway. Aircraft X reported the Cessna to follow in sight; so I cleared him to land. Aircraft X turned too early and I informed him that spacing between him and the Cessna was not going to work out. The pilot then says he's going to make a 360 and took action without realizing there is other traffic in his vicinity. I quickly informed him of traffic and he responded that he had traffic in sight. He made a right turn directly towards Aircraft Y who was on final for the parallel runway. Aircraft Y had to take evasive action to avoid Aircraft X. I told Aircraft X to go around and offset right of the runway and told him about traffic in the north pattern. He reported a Cessna in sight and began a turn to the right downwind quickly overtaking the Cessna on downwind. I instructed Aircraft X to extend downwind to follow traffic on final. He reported the Cessna to follow in sight (Aircraft B). Again; he turned base too early and I had to send the Cessna around to get Aircraft X to land.The pilot of Aircraft X may have misjudged the spacing required to follow aircraft that are much slower than a BE20. The pilot took action on his own without being aware of his surroundings. He should have verified with ATC before making any turns.

Data retrieved from NASA's ASRS site and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.