Narrative:

I'm working downey sector which handles lax arrivals runway 25L. I also work arrivals into hhr. I had aircraft X on a 070 heading south of the runway 25 localizer for hhr. Aircraft X was level at 3;000 and I descended him down to 1;600 when he entered my airspace. Lgb tower called and asked me for a release for aircraft Y to hhr. I released the aircraft with the intent to sequence aircraft Y behind aircraft X. Lgb tower says over the shout line; 'I'm trying to get aircraft Y to tag up on his beacon code;' and then hangs up the shout line. Seconds later; aircraft Y tags up on the scope; in my airspace; exactly 3.00NM and 500' ft from aircraft X on a converging course. The very next sweep the separation was 2.94NM and 300' ft; and I was still not talking to aircraft Y. I immediately turn aircraft X on a 270 heading. I key up the shout line and tell lgb tower to switch me aircraft Y because he is in my airspace and I need to turn him to avoid collision with aircraft X. When aircraft Y checks in I climb him to 3;000 and turn him right to 070. I cleared aircraft X for his localizer RWY25 approach to hhr from his 270 heading. I boxed aircraft Y around and cleared him for the visual approach into hhr.the only thing that I could have done is protect myself from the possibility that an IFR aircraft was going to be in my airspace without a transponder; and not in communication with me. I fully intended to turn aircraft Y behind aircraft X for sequencing to hhr.

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Original NASA ASRS Text

Title: SCT Controller describes a loss of separation between a HHR arrival and a LGB departure.

Narrative: I'm working Downey sector which handles LAX arrivals RWY 25L. I also work arrivals into HHR. I had Aircraft X on a 070 heading south of the RWY 25 localizer for HHR. Aircraft X was level at 3;000 and I descended him down to 1;600 when he entered my airspace. LGB Tower called and asked me for a release for Aircraft Y to HHR. I released the aircraft with the intent to sequence Aircraft Y behind Aircraft X. LGB Tower says over the shout line; 'I'm trying to get Aircraft Y to tag up on his beacon code;' and then hangs up the shout line. Seconds later; Aircraft Y tags up on the scope; in my airspace; exactly 3.00NM and 500' FT from Aircraft X on a converging course. The very next sweep the separation was 2.94NM and 300' FT; and I was still not talking to Aircraft Y. I immediately turn Aircraft X on a 270 heading. I key up the shout line and tell LGB Tower to switch me Aircraft Y because he is in my airspace and I need to turn him to avoid collision with Aircraft X. When Aircraft Y checks in I climb him to 3;000 and turn him right to 070. I cleared Aircraft X for his localizer RWY25 approach to HHR from his 270 heading. I boxed Aircraft Y around and cleared him for the visual approach into HHR.The only thing that I could have done is protect myself from the possibility that an IFR aircraft was going to be in my airspace without a transponder; and not in communication with me. I fully intended to turn Aircraft Y behind Aircraft X for sequencing to HHR.

Data retrieved from NASA's ASRS site 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.