Narrative:

I was providing radar advisory services for VFR aircraft X; a RV12/G enroute eastbound at 9;500 ft. A fast-moving mode-C intruder target was level at 11;500 northwest of aircraft X. I noted that the mode-C intruder had descended to 10;500 ft and appeared to have leveled there for quite some time. Due to the fast rate of speed of that target; I made a traffic call to aircraft X; noting traffic was at 7 to 8 o'clock and 5 miles at 10;500 ft; altitude unverified and type unknown; overtaking; and passing north to south. Aircraft X reported the traffic in sight. At some point; I commenced giving a position relief briefing. During the briefing; the mode-C intruder started descending into aircraft X. Around the same time; there was a large number of track jumps; and the mode-C intruder was in close proximity with aircraft X. I immediately issued a traffic alert to aircraft X giving an approximate position due to the track jumps; apparent mode-C swaps; and aircraft X's vector line spinning quickly clockwise; either due to radar anomaly; or pilot action. There was no response to the traffic alert. Roughly 15 seconds later; the pilot noted that he had taken evasive action; and that the traffic was really close. I asked if the pilot of aircraft X had seen the aircraft type of the other aircraft; and he responded that it was a large 4 engine prop; possibly an [P3] orion. Following the incident; the mode-C intruder continued to descend and turn westbound toward the big bear (L35) airport. I immediately reported the event to management; the only aircraft that landed within that time period was a cheyenne. The pilot of the cheyenne was apparently questioned and noted that he did not see any traffic during the descent.

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Original NASA ASRS Text

Title: ZLA Controller described a conflict event involving an apparent military aircraft and a VFR transiting aircraft at 9;500 FT; the identity of the second aircraft was never determined.

Narrative: I was providing RADAR advisory services for VFR Aircraft X; a RV12/G enroute eastbound at 9;500 FT. A fast-moving Mode-C Intruder target was level at 11;500 NW of Aircraft X. I noted that the Mode-C intruder had descended to 10;500 FT and appeared to have leveled there for quite some time. Due to the fast rate of speed of that target; I made a traffic call to Aircraft X; noting traffic was at 7 to 8 o'clock and 5 miles at 10;500 FT; altitude unverified and type unknown; overtaking; and passing north to south. Aircraft X reported the traffic in sight. At some point; I commenced giving a position relief briefing. During the briefing; the Mode-C Intruder started descending into Aircraft X. Around the same time; there was a large number of track jumps; and the Mode-C Intruder was in close proximity with Aircraft X. I immediately issued a traffic alert to Aircraft X giving an approximate position due to the track jumps; apparent Mode-C swaps; and Aircraft X's vector line spinning quickly clockwise; either due to RADAR anomaly; or pilot action. There was no response to the traffic alert. Roughly 15 seconds later; the pilot noted that he had taken evasive action; and that the traffic was really close. I asked if the pilot of Aircraft X had seen the aircraft type of the other aircraft; and he responded that it was a large 4 engine prop; possibly an [P3] Orion. Following the incident; the Mode-C intruder continued to descend and turn westbound toward the Big Bear (L35) Airport. I immediately reported the event to Management; the only aircraft that landed within that time period was a Cheyenne. The pilot of the Cheyenne was apparently questioned and noted that he did not see any traffic during the descent.

Data retrieved from NASA's ASRS site as of July 2013 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.