Narrative:

As developmental controller; I was training on the dallas south/south high/ar-6/ar-7 position combined on a north flow. An SF34 was descended to 3000 ft in anticipation of a visual approach clearance to dfw runway 31R. When aircraft X was on 8 mi final; established on runway 31R localizer; I ascertained that the pilot had the airport in sight and cleared him for the visual approach to runway 31R; but issued an incorrect frequency change to dal tower and did not notice that the pilot did not read back the approach clearance. I last observed aircraft X's mode C readout of 2900 ft and assumed he had started the visual approach. Approximately 2 mins later; the pilot stated he was executing a missed approach. The instructor assumed the frequency and turned/descended aircraft X to avoid traffic (a CL60) departing dal. Simultaneously; separation was lost between aircraft X and aircraft Z (E15) departing dfw runway 35R. Contributory was my not insuring the approach clearance readback by aircraft X.

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Original NASA ASRS Text

Title: D10 DEVELOPMENTAL CTLR EXPERIENCED OPERROR AT 3000 FT WHEN FAILING TO ENSURE FLT CREW RECEIVED VISUAL APCH CLRNC AND EXECUTED GAR.

Narrative: AS DEVELOPMENTAL CTLR; I WAS TRAINING ON THE DALLAS S/S HIGH/AR-6/AR-7 POS COMBINED ON A N FLOW. AN SF34 WAS DSNDED TO 3000 FT IN ANTICIPATION OF A VISUAL APCH CLRNC TO DFW RWY 31R. WHEN ACFT X WAS ON 8 MI FINAL; ESTABLISHED ON RWY 31R LOC; I ASCERTAINED THAT THE PLT HAD THE ARPT IN SIGHT AND CLRED HIM FOR THE VISUAL APCH TO RWY 31R; BUT ISSUED AN INCORRECT FREQ CHANGE TO DAL TWR AND DID NOT NOTICE THAT THE PLT DID NOT READ BACK THE APCH CLRNC. I LAST OBSERVED ACFT X'S MODE C READOUT OF 2900 FT AND ASSUMED HE HAD STARTED THE VISUAL APCH. APPROX 2 MINS LATER; THE PLT STATED HE WAS EXECUTING A MISSED APCH. THE INSTRUCTOR ASSUMED THE FREQ AND TURNED/DSNDED ACFT X TO AVOID TFC (A CL60) DEPARTING DAL. SIMULTANEOUSLY; SEPARATION WAS LOST BTWN ACFT X AND ACFT Z (E15) DEPARTING DFW RWY 35R. CONTRIBUTORY WAS MY NOT INSURING THE APCH CLRNC READBACK BY ACFT X.

Data retrieved from NASA's ASRS site as of January 2009 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.