Narrative:

I was working middletown radar sector; and it was combined at the time with xenia sector and urbana sector. Aircraft X was an arrival from the south and I was vectoring him northbound for a visual approach to day. As aircraft X was northbound about 8 miles east of day I turned him to a 270 heading to intercept the localizer. After my transmission; someone keyed up without using a callsign and just said 'hang on'. The read back sounded like multiple transmissions were made over top of each other so I repeated my instructions to aircraft X and he read back the instructions but also advised me that he saw traffic. He just said something to the effect of 'we have traffic out here about 1;000 feet.' I saw traffic after aircraft X turned to the localizer; it was a primary radar return with no transponder. I asked aircraft X to verify the traffic was 1;000 feet below him. Aircraft X said traffic was closer than 1;000 feet. I asked aircraft X to say the estimated altitude of the traffic. Aircraft X said the traffic was at about 2;500. At the area the traffic was at the time; he was under the edge of day's class C airspace shelf; which is a minimum altitude of 2;400 feet between 5 and 10 miles from the airport. Aircraft X was still descending at the time; and I saw his altitude at 3;200 when he reported the traffic. I cleared aircraft X for the approach and then switched him to day tower; and then just after I switched him I tried to catch him just to ask him if he had to do any evasive maneuvers for the traffic. Aircraft X had already switched; so I called day tower to have the pilot call us so we could ask him about the traffic. Day local controller said he would ask; and also have the pilot call us. A minute or two later day local controller called and told me that aircraft X reported that he did not have to make any maneuvers to miss the traffic. Aircraft X called later and assured the supervisor he did not wish to report any near midair collision. So since I didn't notice any maneuvers on the scope from aircraft X; the traffic was reported as at least 500 feet below aircraft X at the time; and he also advised day he had to make no maneuvers to miss traffic; I felt it was not a significantly unsafe situation.the next day I was made aware that day had filed a report describing the situation as a significant event; and according to the report that the pilot told day he did have to turn off his auto pilot and turn to miss the aircraft. That information was never passed to me from either the pilot or the day local controller. At some point the story seems to have changed. However; according to the data available and after listening to the recordings again; I saw nothing that would point to a near midair collision or maneuvers to miss traffic. The recordings between myself and the pilot; as well as myself and day tower; also seemed to indicate the VFR traffic was at least 500 feet below aircraft X; and at an altitude would even put the VFR aircraft below the class C shelf. The traffic appeared to have just departed the new carlisle; about 6 miles north of aircraft X located about 8 miles east of day. I was actually coordinating and vectoring a few other aircraft at the time; and I did not see the VFR target pop up.with all the information available; it seems as though everyone was legally where they should have been at the time. There is also a LOA (letter of agreement) for a flying club for that area that spells out altitudes and restrictions when flying in that area; although I do not know if the VFR is part of that flying club or not. I would say the only recommendation would be for me to have seen the traffic sooner and call the traffic to aircraft X. It seems like aircraft X was spooked by seeing traffic he wasn't expecting. Also if the traffic was climbing to an altitude that would be 500 feet below aircraft X; as aircraft X was descending; I can see how traffic could surprise the pilot and look as though it is going to continue climbing. There is also thepossibility the VFR pilot had violated class C airspace and was higher than aircraft X reported; and if that was the case then I would recommend education for the VFR pilot; although he was low altitude with no transponder and we lost radar on him as he flew further northeast. So we have no way of knowing who the VFR pilot was. Another recommendation would be possibly something published on VFR charts to advise pilots in the area that multiple airliners are expected in the area descending to 3;000 feet and to use caution; if something similar is not already published there.

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Original NASA ASRS Text

Title: An air carrier being vectored onto the final approach to DAY took evasive action to avoid a VFR aircraft not displaying a transponder or in communication with TRACON.

Narrative: I was working Middletown radar sector; and it was combined at the time with Xenia sector and Urbana sector. Aircraft X was an arrival from the south and I was vectoring him northbound for a visual approach to DAY. As Aircraft X was northbound about 8 miles east of DAY I turned him to a 270 heading to intercept the localizer. After my transmission; someone keyed up without using a callsign and just said 'Hang on'. The read back sounded like multiple transmissions were made over top of each other so I repeated my instructions to Aircraft X and he read back the instructions but also advised me that he saw traffic. He just said something to the effect of 'We have traffic out here about 1;000 feet.' I saw traffic after Aircraft X turned to the localizer; it was a primary radar return with no transponder. I asked Aircraft X to verify the traffic was 1;000 feet below him. Aircraft X said traffic was closer than 1;000 feet. I asked Aircraft X to say the estimated altitude of the traffic. Aircraft X said the traffic was at about 2;500. At the area the traffic was at the time; he was under the edge of DAY's class C airspace shelf; which is a minimum altitude of 2;400 feet between 5 and 10 miles from the airport. Aircraft X was still descending at the time; and I saw his altitude at 3;200 when he reported the traffic. I cleared Aircraft X for the approach and then switched him to DAY tower; and then just after I switched him I tried to catch him just to ask him if he had to do any evasive maneuvers for the traffic. Aircraft X had already switched; so I called DAY tower to have the pilot call us so we could ask him about the traffic. DAY local controller said he would ask; and also have the pilot call us. A minute or two later DAY local controller called and told me that Aircraft X reported that he did not have to make any maneuvers to miss the traffic. Aircraft X called later and assured the supervisor he did not wish to report any NMAC. So since I didn't notice any maneuvers on the scope from Aircraft X; the traffic was reported as at least 500 feet below Aircraft X at the time; and he also advised DAY he had to make no maneuvers to miss traffic; I felt it was not a significantly unsafe situation.The next day I was made aware that DAY had filed a report describing the situation as a Significant Event; and according to the report that the pilot told DAY he DID have to turn off his auto pilot and turn to miss the aircraft. That information was never passed to me from either the pilot or the DAY local controller. At some point the story seems to have changed. However; according to the data available and after listening to the recordings again; I saw nothing that would point to a NMAC or maneuvers to miss traffic. The recordings between myself and the pilot; as well as myself and DAY tower; also seemed to indicate the VFR traffic was at least 500 feet below Aircraft X; and at an altitude would even put the VFR aircraft below the Class C shelf. The traffic appeared to have just departed the New Carlisle; about 6 miles north of Aircraft X located about 8 miles east of DAY. I was actually coordinating and vectoring a few other aircraft at the time; and I did not see the VFR target pop up.With all the information available; it seems as though everyone was legally where they should have been at the time. There is also a LOA (Letter of Agreement) for a flying club for that area that spells out altitudes and restrictions when flying in that area; although I do not know if the VFR is part of that flying club or not. I would say the only recommendation would be for me to have seen the traffic sooner and call the traffic to Aircraft X. It seems like Aircraft X was spooked by seeing traffic he wasn't expecting. Also if the traffic was climbing to an altitude that would be 500 feet below Aircraft X; as Aircraft X was descending; I can see how traffic could surprise the pilot and look as though it is going to continue climbing. There is also thepossibility the VFR pilot had violated Class C airspace and was higher than Aircraft X reported; and if that was the case then I would recommend education for the VFR pilot; although he was low altitude with no transponder and we lost radar on him as he flew further northeast. So we have no way of knowing who the VFR pilot was. Another recommendation would be possibly something published on VFR charts to advise pilots in the area that multiple airliners are expected in the area descending to 3;000 feet and to use caution; if something similar is not already published there.

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.