Narrative:

I was working north radar position combined with north satellite. We were in a north/south configuration with another controller working south radar. I was vectoring crj for a visual approach to runway 10L. The south controller was vectoring a B752 for runway 10L from the right downwind and I had the crj southbound on a left base to follow the B752. The crj called the airport in sight approximately 20 northwest of the airport. When the crj called the field in sight; I told him he would be following the B752 that was turning north toward him at the same altitude 15 miles ahead. The crj asked which aircraft he was following and I did not understand the question as the only other aircraft was a B733 over the marker for runway 10R ahead of the B752. I told the crj that the aircraft he was to follow was the one pointed directly at him 15 miles ahead same altitude. The crj said he had that traffic in sight and I gave him a wake turbulence advisory on the B752; told him to follow him and cleared him for the visual approach to runway 10L. About 10 seconds after I cleared the crj; who was southeast bound when cleared approach; I saw him turn directly southbound. At first I thought he was widening out his base for wake turbulence avoidance and I asked if he still had the traffic in sight. He said he wasn't sure. I cancelled his approach clearance and turned him to join the 10L localizer as there was traffic coming up from the southeast in south radar's airspace and I needed him to continue toward the airport. The pilot then advised that there was another aircraft off their left. At that point I observed a primary target northwest bound about a mile northeast of the crj. The target had been obscured by the data block of the B757 aircraft. After some further comments from the pilot I told them that the target appeared to be no longer a factor and asked if they had the B752 in sight again. When they advised that they did; I re-cleared them for the visual approach to 10L and told them to contact the tower. Recommendation; I needed to have my scope set up at a smaller range to see the primary target and not have it obscured by the other aircraft's data block. I also needed to listen more critically to what the pilot is saying. Although they tried to describe the situation; my focus was on the tagged targets and I did not see the primary target. When the pilot first told me they were deviating around the target; I still didn't 'see' it until I understood exactly what they were describing. The target was probably visible the whole time while not obscured by the other data block; but I didn't expect that it would be a factor in my plan; so I didn't let it into my world view. I have made a point of teaching this to my trainees; but I obviously am subject to the same trap.

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Original NASA ASRS Text

Title: CMH controller experienced a confused sequencing event during a vector of an air carrier for a visual approach to Runway 10L; failing to observe a primary target; the air carrier was confused as to which aircraft to follow.

Narrative: I was working North RADAR position combined with North Satellite. We were in a north/south configuration with another Controller working South RADAR. I was vectoring CRJ for a visual approach to Runway 10L. The South Controller was vectoring a B752 for Runway 10L from the right downwind and I had the CRJ southbound on a left base to follow the B752. The CRJ called the airport in sight approximately 20 northwest of the airport. When the CRJ called the field in sight; I told him he would be following the B752 that was turning north toward him at the same altitude 15 miles ahead. The CRJ asked which aircraft he was following and I did not understand the question as the only other aircraft was a B733 over the marker for Runway 10R ahead of the B752. I told the CRJ that the aircraft he was to follow was the one pointed directly at him 15 miles ahead same altitude. The CRJ said he had that traffic in sight and I gave him a wake turbulence advisory on the B752; told him to follow him and cleared him for the visual approach to Runway 10L. About 10 seconds after I cleared the CRJ; who was southeast bound when cleared approach; I saw him turn directly southbound. At first I thought he was widening out his base for wake turbulence avoidance and I asked if he still had the traffic in sight. He said he wasn't sure. I cancelled his approach clearance and turned him to join the 10L localizer as there was traffic coming up from the southeast in South Radar's airspace and I needed him to continue toward the airport. The pilot then advised that there was another aircraft off their left. At that point I observed a primary target northwest bound about a mile northeast of the CRJ. The target had been obscured by the data block of the B757 aircraft. After some further comments from the pilot I told them that the target appeared to be no longer a factor and asked if they had the B752 in sight again. When they advised that they did; I re-cleared them for the visual approach to 10L and told them to contact the Tower. Recommendation; I needed to have my scope set up at a smaller range to see the primary target and not have it obscured by the other aircraft's data block. I also needed to listen more critically to what the pilot is saying. Although they tried to describe the situation; my focus was on the tagged targets and I did not see the primary target. When the pilot first told me they were deviating around the target; I still didn't 'see' it until I understood exactly what they were describing. The target was probably visible the whole time while not obscured by the other data block; but I didn't expect that it would be a factor in my plan; so I didn't let it into my world view. I have made a point of teaching this to my trainees; but I obviously am subject to the same trap.

Data retrieved from NASA's ASRS site as of April 2012 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.