Narrative:

I was informed by quality control that an aircraft; aircraft X had filed a near midair collision. The other aircraft in question was aircraft Y; a parachute jumping aircraft that operates at ZZZ airport regularly. I did not remember the aircraft in question due to the event happening [12 days earlier]. I reviewed the falcon and tapes to see what had happened. I was providing flight following to aircraft X transitioning near ZZZ. When aircraft Y aircraft checks on frequency; we radar identify them and issue traffic advisories. They give us a 5 minute warning before jumpers away. At this point aircraft X was still about 40-50 miles away from ZZZ. The issue with aircraft Y is that they sometimes do not tell you when they are leaving frequency and they switch over to ZZZ tower. Aircraft Y descended and then went into coast track. Since I was not aware of any radar outages in that area; I assumed aircraft Y was lower than aircraft X or even on deck. Aircraft X was at 9500; and I did not remind them of parachute operations. Aircraft X transitioned near ZZZ and then I eventually handed the aircraft off to center. Aircraft X never told me that he/she came within close proximity to aircraft Y.in the future I would recommend that no aircraft be allowed to transition within 5 miles of the jump zone until ZZZ tower calls with all jumpers on the ground. Especially if our radar does not allow us to see what altitude the parachute jumping aircraft is at.

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Original NASA ASRS Text

Title: ZLA Center Controller reported that a pilot reported a NMAC between them and a skydiving aircraft.

Narrative: I was informed by Quality Control that an aircraft; Aircraft X had filed a NMAC. The other aircraft in question was Aircraft Y; a parachute jumping aircraft that operates at ZZZ airport regularly. I did not remember the aircraft in question due to the event happening [12 days earlier]. I reviewed the Falcon and tapes to see what had happened. I was providing flight following to Aircraft X transitioning near ZZZ. When Aircraft Y aircraft checks on frequency; we radar identify them and issue traffic advisories. They give us a 5 minute warning before jumpers away. At this point Aircraft X was still about 40-50 miles away from ZZZ. The issue with Aircraft Y is that they sometimes do not tell you when they are leaving frequency and they switch over to ZZZ tower. Aircraft Y descended and then went into Coast Track. Since I was not aware of any radar outages in that area; I assumed Aircraft Y was lower than Aircraft X or even on deck. Aircraft X was at 9500; and I did not remind them of parachute operations. Aircraft X transitioned near ZZZ and then I eventually handed the aircraft off to Center. Aircraft X never told me that he/she came within close proximity to Aircraft Y.In the future I would recommend that no aircraft be allowed to transition within 5 miles of the jump zone until ZZZ tower calls with all jumpers on the ground. Especially if our radar does not allow us to see what altitude the parachute jumping aircraft is at.

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.