Narrative:

I was providing OJT to a developmental. This is his last function in the facility. ZZZ was north flow and the ceilings were just about 2;700 ft. There was a developmental controller working the ds position and a low time cpc working the de position. There was a large volume of jet traffic inbound to ZZZ at the time and several low performance prop aircraft as well. My developmental had been able to get the prop aircraft below the clouds for visual approaches to runway xxr and allow the jet traffic to stay fast on ILS approaches to runway xxl. He had had to break out a slow prop earlier in the session when the prop wasn't able to get the visual. Aircraft X; a DA42; was inbound on the runway xxr localizer about 15 miles from the field. The developmental had descended aircraft X to 3;000 but the aircraft was descending very slowly. Aircraft Y a H25B; was inbound from the northeast at 4;000 and the developmental turned aircraft Y from a heading going behind aircraft X to a westbound heading in front of aircraft X. I asked what the plan was and apparently the developmental thought that aircraft X was already at 3;000. I prompted the developmental again for a plan and he hesitated a bit too long; and then when realizing that aircraft X was just leaving 3;300; turned aircraft Y south to heading 180. I told him to break aircraft X out to the west heading 260 and he did but it was too late. This event happened because I was wanting my developmental to see what was happening and take charge of the situation and fix it. I should have overridden him to break aircraft X out to the east behind aircraft Y but waited to see if my developmental would make the right call. My developmental is at a point in training where he needs to do these things on his own. It was my responsibility and I waited too long. Recommendation; developmental's can't be allowed to go too far. I need to break in sooner.

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Original NASA ASRS Text

Title: TRACON Controller providing OJT described a loss of separation event when the developmental failed to take timely action and instructor intervention was too late.

Narrative: I was providing OJT to a developmental. This is his last function in the facility. ZZZ was north flow and the ceilings were just about 2;700 FT. There was a developmental controller working the DS position and a low time CPC working the DE position. There was a large volume of jet traffic inbound to ZZZ at the time and several low performance prop aircraft as well. My developmental had been able to get the prop aircraft below the clouds for Visual Approaches to Runway XXR and allow the jet traffic to stay fast on ILS approaches to Runway XXL. He had had to break out a slow prop earlier in the session when the prop wasn't able to get the visual. Aircraft X; a DA42; was inbound on the Runway XXR localizer about 15 miles from the field. The developmental had descended Aircraft X to 3;000 but the aircraft was descending very slowly. Aircraft Y a H25B; was inbound from the northeast at 4;000 and the developmental turned Aircraft Y from a heading going behind Aircraft X to a westbound heading in front of Aircraft X. I asked what the plan was and apparently the developmental thought that Aircraft X was already at 3;000. I prompted the developmental again for a plan and he hesitated a bit too long; and then when realizing that Aircraft X was just leaving 3;300; turned Aircraft Y South to heading 180. I told him to break Aircraft X out to the West heading 260 and he did but it was too late. This event happened because I was wanting my developmental to see what was happening and take charge of the situation and fix it. I should have overridden him to break Aircraft X out to the East behind Aircraft Y but waited to see if my developmental would make the right call. My developmental is at a point in training where he needs to do these things on his own. It was my responsibility and I waited too long. Recommendation; Developmental's can't be allowed to go too far. I need to break in sooner.

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.