Narrative:

Aircraft X was inbound to fai from the south on the LIBER2 arrival. I issued him a descent to 085; the MVA in the area. I saw a primary target at aircraft X's 1 o'clock and I issued him the traffic. The traffic was not transponder equipped or did not have it on so no altitude readout was available -- I explained this to the pilot when he questioned not having the traffic on TCAS. As aircraft X got closer to the traffic I issued the traffic again and advised him that their radar targets appeared likely to merge and told him if he would like a vector I would suggest 20 degrees left. The pilot advised that they were in VFR conditions above the clouds and opted to continue on their present route of flight. I advised when the traffic was no factor and issued aircraft X a descent to 045 then subsequently cleared him for the visual approach to runway 2L after he reported the field in sight. When aircraft X was on approximately a 10 mile final he radioed to advise that the traffic I had issued him had been pretty close. I asked him if he could describe the aircraft and proximity and the pilot advised that it appeared to have been a white and blue [aircraft] that passed approximately 300' below him. Going back and looking at the falcon; it appears that aircraft X may have climbed 200' in an evasive response to seeing the aircraft at the last minute but did not state over the frequency whether or not evasive actions were taken. Because the other aircraft did not have a transponder; aircraft X never got any TCAS ras. Aircraft X would have been at the aircraft Y's 5 o'clock and it was unlikely from that vantage point that aircraft Y would have seen the aircraft X. With his direction of flight north east; I assumed the other aircraft would at least be at an appropriate (odd) VFR altitude. I called my supervisor right away to begin filling out the report.I tried to encourage pilots to call the approach controller whenever operating in the airspace for traffic advisories or to request flight following with the center. The pending requirement for all aircraft to have transponders is in the best interest of safety and would have given both aircraft a better idea of where the traffic was. The VFR aircraft also appears to have not been adhering to appropriate VFR altitudes for direction of flight. This may have prevented the incident as well. The best thing we can do is educate VFR pilots like this on the surrounding airspace and typical IFR arrival routes and encourage them to call approach control/center for traffic advisories; use appropriate altitudes for direction of flight and suggest the use of a transponder at all times.

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Original NASA ASRS Text

Title: FAI controller reported B737 rejected a vector to avoid non transponder equipped traffic; but then climbed unannounced and aircraft passed 300 feet below.

Narrative: Aircraft X was inbound to FAI from the south on the LIBER2 arrival. I issued him a descent to 085; the MVA in the area. I saw a primary target at Aircraft X's 1 o'clock and I issued him the traffic. The traffic was not transponder equipped or did not have it on so no altitude readout was available -- I explained this to the pilot when he questioned not having the traffic on TCAS. As Aircraft X got closer to the traffic I issued the traffic again and advised him that their radar targets appeared likely to merge and told him if he would like a vector I would suggest 20 degrees left. The pilot advised that they were in VFR conditions above the clouds and opted to continue on their present route of flight. I advised when the traffic was no factor and issued Aircraft X a descent to 045 then subsequently cleared him for the visual approach to runway 2L after he reported the field in sight. When Aircraft X was on approximately a 10 mile final he radioed to advise that the traffic I had issued him had been pretty close. I asked him if he could describe the aircraft and proximity and the pilot advised that it appeared to have been a white and blue [Aircraft] that passed approximately 300' below him. Going back and looking at the FALCON; it appears that Aircraft X may have climbed 200' in an evasive response to seeing the aircraft at the last minute but did not state over the frequency whether or not evasive actions were taken. Because the other aircraft did not have a transponder; Aircraft X never got any TCAS RAs. Aircraft X would have been at the Aircraft Y's 5 o'clock and it was unlikely from that vantage point that Aircraft Y would have seen the Aircraft X. With his direction of flight North East; I assumed the other aircraft would at least be at an appropriate (odd) VFR altitude. I called my supervisor right away to begin filling out the report.I tried to encourage pilots to call the approach controller whenever operating in the airspace for traffic advisories or to request flight following with the center. The pending requirement for all aircraft to have transponders is in the best interest of safety and would have given both aircraft a better idea of where the traffic was. The VFR aircraft also appears to have not been adhering to appropriate VFR altitudes for direction of flight. This may have prevented the incident as well. The best thing we can do is educate VFR pilots like this on the surrounding airspace and typical IFR arrival routes and encourage them to call approach control/center for traffic advisories; use appropriate altitudes for direction of flight and suggest the use of a transponder at all times.

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.