Narrative:

An small aircraft Y on IFR training was cleared for NDB-B at fat approximately two mi after procedure turn inbound the small aircraft Y veered an estimated 40 degree left of final approach course. I turned the small aircraft Y back to the final approach course and reclred him, stating altitude again. At the same time an small aircraft Z was flying the outbnd leg of the approach requesting IFR. Two mi from fat I realized small aircraft Y would not intercept the final approach in a timely manner, I cancelled approach clearance and turned him back to parallel the final approach course at 2000'. The small aircraft Z was non inbound on the final approach course at 2000', at the same place as small aircraft Y. The small aircraft Z turned an estimated 40 degree left of the final approach course, directly toward small aircraft Y (opp direction, same altitude). I immediately turned small aircraft Z right approximately 70 degree and climbed him 500', then I descended small aircraft Y 500' immediately. The small aircraft Z complied in the climb, while slow turning; the small aircraft Y was advised of immediate 'request' to descend. Neither saw the other. At approximately 1 mi lateral the aircraft passed, I advised traffic no longer a factor. The small aircraft Z went on to execute the NDB-B. The small aircraft Y was issued 2000'. He then radioed 'climbing from 1800' to 2000''. I advised him that immediate instructions mean 'now'. No acknowledgement.

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Original NASA ASRS Text

Title: TRACON APCH CTLR FAILED TO ISSUE POSITIVE CTL INSTRUCTION TO TWO SMA ACFT CONDUCTING PRACTICE IFR APCHS WHICH RESULTED IN LTSS.

Narrative: AN SMA Y ON IFR TRNING WAS CLRED FOR NDB-B AT FAT APPROX TWO MI AFTER PROC TURN INBND THE SMA Y VEERED AN ESTIMATED 40 DEG L OF FINAL APCH COURSE. I TURNED THE SMA Y BACK TO THE FINAL APCH COURSE AND RECLRED HIM, STATING ALT AGAIN. AT THE SAME TIME AN SMA Z WAS FLYING THE OUTBND LEG OF THE APCH REQUESTING IFR. TWO MI FROM FAT I REALIZED SMA Y WOULD NOT INTERCEPT THE FINAL APCH IN A TIMELY MANNER, I CANCELLED APCH CLRNC AND TURNED HIM BACK TO PARALLEL THE FINAL APCH COURSE AT 2000'. THE SMA Z WAS NON INBND ON THE FINAL APCH COURSE AT 2000', AT THE SAME PLACE AS SMA Y. THE SMA Z TURNED AN ESTIMATED 40 DEG L OF THE FINAL APCH COURSE, DIRECTLY TOWARD SMA Y (OPP DIRECTION, SAME ALT). I IMMEDIATELY TURNED SMA Z R APPROX 70 DEG AND CLBED HIM 500', THEN I DSNDED SMA Y 500' IMMEDIATELY. THE SMA Z COMPLIED IN THE CLB, WHILE SLOW TURNING; THE SMA Y WAS ADVISED OF IMMEDIATE 'REQUEST' TO DSND. NEITHER SAW THE OTHER. AT APPROX 1 MI LATERAL THE ACFT PASSED, I ADVISED TFC NO LONGER A FACTOR. THE SMA Z WENT ON TO EXECUTE THE NDB-B. THE SMA Y WAS ISSUED 2000'. HE THEN RADIOED 'CLBING FROM 1800' TO 2000''. I ADVISED HIM THAT IMMEDIATE INSTRUCTIONS MEAN 'NOW'. NO ACKNOWLEDGEMENT.

Data retrieved from NASA's ASRS site as of July 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.