Narrative:

From left downwind to 30L I was cleared to land 30L and was advised of another aircraft landing on 30R. Reported aircraft in sight. Turning base; the wing blocked the two landing runways and sight of the landing aircraft was lost. Upon leveling off on base; the runway seen at my 10:00 o'clock was mistakenly thought to be 30L when it was actually 30R. Runway 30L was probably at my 9:00 o'clock and by virtue of that fact and the fact that its threshold is about 1500 feet further northwest than the threshold of 30R; I did not observe runway 30L in my field of view. I proceeded to make a gradual turn to final for what I thought was 30L but was actually 30R. When my turn to final was approximately half-way complete; i.e. My aircraft was at approximately a 45-degree angle to the runway; I suddenly glimpsed the other aircraft; in close proximity in front of my wing at my same altitude and with my aircraft heading directly toward the aircraft. My instant reaction was to turn my aircraft in a steep turn to the left and was thus able to avoid a collision. I then saw 30L and was able to land on the correct runway. My situational awareness was high up until I turned base. I was very mindful that I was landing 30L and there was another aircraft landing 30R and at virtually the same relative position in the pattern; i.e. He was turning base as I was turning base. All that made me very wary. However; situational awareness was lost as I rolled level and my vision became fixed on the wrong runway. I was also focused on trying to sight the landing aircraft. Both of these kept my vision focused out the front of the aircraft. Had I scanned to the left; I would have seen the correct runway. Obviously; the hazard was multiplied by having two aircraft in roughly the same relative positions in the pattern. Given the same situation in the future; the easy way to eliminate the hazard multiplier would be to request a downwind extension. Even a 30-second extension would bring about at least several thousand feet of horizontal separation. Towers could do the same as a standard procedure. A contributing factor is the displacement of the threshold of 30L to the threshold of 30R.

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Original NASA ASRS Text

Title: C206 pilot reported an NMAC in the pattern at BJC when he lined up for the wrong runway.

Narrative: From left downwind to 30L I was cleared to land 30L and was advised of another aircraft landing on 30R. Reported aircraft in sight. Turning base; the wing blocked the two landing runways and sight of the landing aircraft was lost. Upon leveling off on base; the runway seen at my 10:00 o'clock was mistakenly thought to be 30L when it was actually 30R. Runway 30L was probably at my 9:00 o'clock and by virtue of that fact and the fact that its threshold is about 1500 feet further northwest than the threshold of 30R; I did not observe runway 30L in my field of view. I proceeded to make a gradual turn to final for what I thought was 30L but was actually 30R. When my turn to final was approximately half-way complete; i.e. my aircraft was at approximately a 45-degree angle to the runway; I suddenly glimpsed the other aircraft; in close proximity in front of my wing at my same altitude and with my aircraft heading directly toward the aircraft. My instant reaction was to turn my aircraft in a steep turn to the left and was thus able to avoid a collision. I then saw 30L and was able to land on the correct runway. My situational awareness was high up until I turned base. I was very mindful that I was landing 30L and there was another aircraft landing 30R and at virtually the same relative position in the pattern; i.e. he was turning base as I was turning base. All that made me very wary. However; situational awareness was lost as I rolled level and my vision became fixed on the wrong runway. I was also focused on trying to sight the landing aircraft. Both of these kept my vision focused out the front of the aircraft. Had I scanned to the left; I would have seen the correct runway. Obviously; the hazard was multiplied by having two aircraft in roughly the same relative positions in the pattern. Given the same situation in the future; the easy way to eliminate the hazard multiplier would be to request a downwind extension. Even a 30-second extension would bring about at least several thousand feet of horizontal separation. Towers could do the same as a standard procedure. A contributing factor is the displacement of the threshold of 30L to the threshold of 30R.

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.