Narrative:

Aircraft Y was a northbound departure off ZZZ1. We routinely flash these aircraft to departure radar 2; but work them out to ZZZ center if neither departure radar is busy. I thought my trainee gave aircraft Y 17;000 ft and runway heading; which is the norm and these aircraft climb above the ZZZ2 traffic and go north. Either he gave him 7;000 ft or the pilot read back 7;000 ft and I missed it. We turned him north to go on course and he leveled right next to aircraft X off of ZZZ2. I believe we were discussing an earlier false start off ZZZ2; but I'm not sure. Recommendation; be more clear on altitude assignments and verify read backs. Don't turn north until positive we are above ZZZ2 traffic.

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Original NASA ASRS Text

Title: TRACON Controller providing OJT described a loss of separation event when the Developmental failed to hear an incorrect read back; listing a side conversation as a causal factor.

Narrative: Aircraft Y was a northbound departure off ZZZ1. We routinely flash these aircraft to Departure Radar 2; but work them out to ZZZ Center if neither Departure Radar is busy. I thought my trainee gave aircraft Y 17;000 FT and runway heading; which is the norm and these aircraft climb above the ZZZ2 traffic and go north. Either he gave him 7;000 FT or the pilot read back 7;000 FT and I missed it. We turned him north to go on course and he leveled right next to aircraft X off of ZZZ2. I believe we were discussing an earlier false start off ZZZ2; but I'm not sure. Recommendation; be more clear on altitude assignments and verify read backs. Don't turn north until positive we are above ZZZ2 traffic.

Data retrieved from NASA's ASRS site as of April 2012 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.