Narrative:

I was working as local controller at the time; runways xx right/left were in use. Aircraft X was cleared for takeoff on runway xx right and told to make right closed traffic; per pilot's request. In the upwind; aircraft X was told to make left closed traffic pattern for inbound traffic aircraft Y; which he did.I asked aircraft X if he preferred runway xx right; and he indicated that he did. I advised for traffic aircraft Y that he was cleared for the option on runway xx left (emphasizing the word 'left') and on the go to make right closed traffic. The pilot of aircraft X read back 'xx left for this one and then switch to xx right; aircraft X.'I called traffic to aircraft X 'traffic turning opposite base for the parallel; cessna.' I then called traffic to aircraft X using the same phraseology. Neither aircraft called the other in sight. After giving instructions to another aircraft calling inbound from the northeast; aircraft Y keyed up and said 'that plane shot over to runway xx right.' I looked and observed aircraft X and aircraft Y side by side on approximately a quarter mile final. I keyed up and asked aircraft X 'verify landing runway xx left?' aircraft X replied he was landing runway xx right. I observed aircraft Y taking evasive action and turning right; away from aircraft X. It appeared to me that the aircraft were side by side and estimated them to be 30 to 50 feet apart. I instructed aircraft X to go around. Aircraft X keyed up and said 'that's my bad;' but did not go around. I again I instructed him to go around and instructed him to make left closed traffic for runway xx left and gave the pilot a brasher warning. The controller in charge then relieved me on local so I could review tapes. I observed aircraft Y land on runway xx right without further problems; aircraft X remained in the pattern.I was looking north towards where the inbound aircraft was calling but believe that; with two aircraft of final; I should have been watching the planes and perhaps I would have caught the error sooner. Even after aircraft Y advised the other aircraft was lined up for the wrong runway; from my perspective I couldn't tell which runway he was lined up for. I believe that; though my scan could have been more timely; the main problem fell with the pilot proceeding as instructed; even with a correct readback.

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Original NASA ASRS Text

Title: ATC assigned parallel runways to VFR arrivals. The aircraft assigned the Left runway mistakenly lined up to land on the Right runway. There was another aircraft on final approach to the right runway which took evasive action.

Narrative: I was working as Local controller at the time; runways XX R/L were in use. Aircraft X was cleared for takeoff on Runway XX Right and told to make right closed traffic; per pilot's request. In the upwind; Aircraft X was told to make left closed traffic pattern for inbound traffic Aircraft Y; which he did.I asked Aircraft X if he preferred Runway XX Right; and he indicated that he did. I advised for traffic Aircraft Y that he was cleared for the option on Runway XX Left (emphasizing the word 'LEFT') and on the go to make right closed traffic. The pilot of Aircraft X read back 'XX left for this one and then switch to XX right; Aircraft X.'I called traffic to Aircraft X 'traffic turning opposite base for the parallel; Cessna.' I then called traffic to Aircraft X using the same phraseology. Neither aircraft called the other in sight. After giving instructions to another aircraft calling inbound from the northeast; Aircraft Y keyed up and said 'That plane shot over to runway XX right.' I looked and observed Aircraft X and Aircraft Y side by side on approximately a quarter mile final. I keyed up and asked Aircraft X 'verify landing runway XX left?' Aircraft X replied he was landing Runway XX Right. I observed Aircraft Y taking evasive action and turning right; away from Aircraft X. It appeared to me that the aircraft were side by side and estimated them to be 30 to 50 feet apart. I instructed Aircraft X to go around. Aircraft X keyed up and said 'that's my bad;' but did not go around. I again I instructed him to go around and instructed him to make left closed traffic for Runway XX Left and gave the pilot a brasher warning. The CIC then relieved me on Local so I could review tapes. I observed Aircraft Y land on Runway XX Right without further problems; Aircraft X remained in the pattern.I was looking North towards where the inbound aircraft was calling but believe that; with two aircraft of final; I should have been watching the planes and perhaps I would have caught the error sooner. Even after Aircraft Y advised the other aircraft was lined up for the wrong runway; from my perspective I couldn't tell which runway he was lined up for. I believe that; though my scan could have been more timely; the main problem fell with the pilot proceeding as instructed; even with a correct readback.

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.