Narrative:

I was working our entire airspace combined on 4 frequencys. Traffic had been light, but built to moderate just prior to this occurrence. Frequency congestion at the time of the occurrence was high due to several aircraft calling in at once on separate frequencys. The IFR small aircraft X was inbound from the south for an ILS runway 27 practice approach. The VFR small aircraft Y was a lost student pilot who I was guiding to the airport with vectors. When the small aircraft's got close to the final approach course I had to vector for sequence since there was also an mdt inbound from the northwest at the same time. I had decided to make the mdt #1 in the sequence so I turned the IFR small aircraft X northeast to give the mdt room for his base leg. At this point the student small aircraft Y was approximately 12 northeast of the airport so I turned him south since I intended to make him last in sequence. Once he turned south his ground speed increased dramatically (a factor I failed to take into account). During this time I was distracted identifying VFR aircraft which all seemed to call at approximately the same time requesting traffic advisories. Communication was a major problem. There were poor radios, amateurish transmissions, as well as several unreadable transmissions. I went back to the IFR small aircraft X and turned him back northwest to intercept the localizer. I still did not recognize the potential conflict at this point. When the IFR small aircraft X requested a lower altitude I finally recognized the now imminent situation. I told the student small aircraft Y to look for the traffic and turn right heading 270. I told the other small aircraft X about the small aircraft Y and to descend immediately. They reported each other in sight simultaneously (they were on separate frequencys). It is not known how close they actually passed. The student pilot did not turn west as instructed and reported that the other small aircraft X passed beneath him.

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Original NASA ASRS Text

Title: POTENTIAL NMAC.

Narrative: I WAS WORKING OUR ENTIRE AIRSPACE COMBINED ON 4 FREQS. TFC HAD BEEN LIGHT, BUT BUILT TO MODERATE JUST PRIOR TO THIS OCCURRENCE. FREQ CONGESTION AT THE TIME OF THE OCCURRENCE WAS HIGH DUE TO SEVERAL ACFT CALLING IN AT ONCE ON SEPARATE FREQS. THE IFR SMA X WAS INBND FROM THE SOUTH FOR AN ILS RWY 27 PRACTICE APCH. THE VFR SMA Y WAS A LOST STUDENT PLT WHO I WAS GUIDING TO THE ARPT WITH VECTORS. WHEN THE SMA'S GOT CLOSE TO THE FINAL APCH COURSE I HAD TO VECTOR FOR SEQUENCE SINCE THERE WAS ALSO AN MDT INBND FROM THE NW AT THE SAME TIME. I HAD DECIDED TO MAKE THE MDT #1 IN THE SEQUENCE SO I TURNED THE IFR SMA X NE TO GIVE THE MDT ROOM FOR HIS BASE LEG. AT THIS POINT THE STUDENT SMA Y WAS APPROX 12 NE OF THE ARPT SO I TURNED HIM SOUTH SINCE I INTENDED TO MAKE HIM LAST IN SEQUENCE. ONCE HE TURNED SOUTH HIS GND SPEED INCREASED DRAMATICALLY (A FACTOR I FAILED TO TAKE INTO ACCOUNT). DURING THIS TIME I WAS DISTRACTED IDENTIFYING VFR ACFT WHICH ALL SEEMED TO CALL AT APPROX THE SAME TIME REQUESTING TFC ADVISORIES. COM WAS A MAJOR PROBLEM. THERE WERE POOR RADIOS, AMATEURISH TRANSMISSIONS, AS WELL AS SEVERAL UNREADABLE TRANSMISSIONS. I WENT BACK TO THE IFR SMA X AND TURNED HIM BACK NW TO INTERCEPT THE LOC. I STILL DID NOT RECOGNIZE THE POTENTIAL CONFLICT AT THIS POINT. WHEN THE IFR SMA X REQUESTED A LOWER ALT I FINALLY RECOGNIZED THE NOW IMMINENT SITUATION. I TOLD THE STUDENT SMA Y TO LOOK FOR THE TFC AND TURN RIGHT HDG 270. I TOLD THE OTHER SMA X ABOUT THE SMA Y AND TO DSND IMMEDIATELY. THEY REPORTED EACH OTHER IN SIGHT SIMULTANEOUSLY (THEY WERE ON SEPARATE FREQS). IT IS NOT KNOWN HOW CLOSE THEY ACTUALLY PASSED. THE STUDENT PLT DID NOT TURN WEST AS INSTRUCTED AND REPORTED THAT THE OTHER SMA X PASSED BENEATH HIM.

Data retrieved from NASA's ASRS site as of August 2007 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.