Narrative:

Aircraft X called in bound from the south (reported circling over 680/24 interchange); I didn't catch his call sign so I told him to enter and report a 2 mile left base for runway 32L; and say again his numbers. On his read back he gave his call sign again; but cut out before the assigned runway so I had him verify a left base for 32L and he verified left base for 32L. Upon review of the tapes I realized that while he verified a left base for 32L he did not verify the 2 mile report. At this time I also had 2 aircraft in right closed traffic for 32R; another departing 32R north bound and a aircraft entering the 45 for 32R to join the pattern (this aircraft also being traffic for the departing aircraft). I had a aircraft in left closed traffic for 32L as well. Aircraft X reported that he had a near midair collision with aircraft Y that he overflew he reported at 30 ft. I asked him to say position and altitude he reported altitude of 800 feet about to turn left base for 32L. I then saw that he was not 'about to turn base' rather he was already on a short approach to overfly the tower on a left base for 32L; I told him that I had not heard his 2 mile base report and told him to go around and continue in left closed traffic. Aircraft Y never reported a near midair collision or anything else. Aircraft X went around and landed with no further incident. The weather at the time was hazy; I was spotting aircraft out the window about 3-4nm out. When asked one of the pattern aircraft reported in flight visibility at 6-7nm.I had a lot happening on 32R and my attention was focused on giving traffic to my departing aircraft and incoming aircraft as well as sequencing the other aircraft in their pattern sequence. I never got a position report on aircraft X until it was too late; neither did I see him on the radar; but I should have paid more attention to the other runway. I only had the one aircraft in the pattern for 32L; but I knew aircraft X was inbound; I should have been thinking that it had been awhile since he called inbound where is he? I should also have made sure he read back the need for a 2 mile base report.

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Original NASA ASRS Text

Title: CCR Tower Controller reports of a reported NMAC by an aircraft that did not report a 2 mile left base.

Narrative: Aircraft X called in bound from the south (reported circling over 680/24 interchange); I didn't catch his call sign so I told him to enter and report a 2 mile left base for runway 32L; and say again his numbers. On his read back he gave his call sign again; but cut out before the assigned runway so I had him verify a left base for 32L and he verified left base for 32L. Upon review of the tapes I realized that while he verified a left base for 32L he did not verify the 2 mile report. At this time I also had 2 aircraft in right closed traffic for 32R; another departing 32R North bound and a aircraft entering the 45 for 32R to join the pattern (this aircraft also being traffic for the departing aircraft). I had a aircraft in left closed traffic for 32L as well. Aircraft X reported that he had a NMAC with Aircraft Y that he overflew he reported at 30 ft. I asked him to say position and altitude he reported altitude of 800 feet about to turn left base for 32L. I then saw that he was not 'about to turn base' rather he was already on a short approach to overfly the tower on a left base for 32L; I told him that I had not heard his 2 mile base report and told him to go around and continue in left closed traffic. Aircraft Y never reported a NMAC or anything else. Aircraft X went around and landed with no further incident. The weather at the time was hazy; I was spotting aircraft out the window about 3-4nm out. When asked one of the pattern aircraft reported in flight visibility at 6-7nm.I had a lot happening on 32R and my attention was focused on giving traffic to my departing aircraft and incoming aircraft as well as sequencing the other aircraft in their pattern sequence. I never got a position report on Aircraft X until it was too late; neither did I see him on the radar; but I should have paid more attention to the other runway. I only had the one aircraft in the pattern for 32L; but I knew Aircraft X was inbound; I should have been thinking that it had been awhile since he called inbound where is he? I should also have made sure he read back the need for a 2 mile base report.

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.