Narrative:

A typical, busy approach into sna. I was flying as first officer with captain and FAA jumpseat rider monitoring. Flying wbound approaching kayoh intersection, we were vectored by final controller to a 310 degree heading, cleared to descend from 7000 ft to 4M, and told of traffic at 11 O'clock, 5 NM at 3500 or 4000'. We spotted him right away. We were also told to expect an east side turn-on. In my mind, I was thinking west side when he said it, so I thought we had plenty of time. Soon the captain said 'east side turn-on, we better get down'. With that, I increased descent rate. Then approach said, 'left turn to 220 degree, cleared for approach, maintain 4000 until on localizer'. I believe he also called the traffic again, but I was focused on the approach, and it didn't register what he said, although we were still aware of the traffic, now bout 2 NM. In the turn, passing about 240 degree, the captain asked if I still had the traffic, now about 1/2 NM. As I now focused on the traffic, it became apparent we would collide if I continued (we were passing 4300' in a shallow descent). He was heading about 180 degree at 4000'. I made a mild evasive maneuver by rolling out and pulling up slightly. I estimate this leveled us off at 4300-4400'. Several seconds later, he was spotted out the left. I rolled back into my turn, started a descent and completed the approach. I'm not sure if he was IFR or VFR, but he was at our cleared altitude. Something broke down somewhere. My impression was that he was under positive control, and couldn't possibly be vectored toward us. Don't get complacent! He never took any evasive action.

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Original NASA ASRS Text

Title: LGT DESCENDING FOR APCH TO SNA HAD NMAC WITH AN UNKNOWN SIZE ACFT.

Narrative: A TYPICAL, BUSY APCH INTO SNA. I WAS FLYING AS F/O WITH CAPT AND FAA JUMPSEAT RIDER MONITORING. FLYING WBOUND APCHING KAYOH INTXN, WE WERE VECTORED BY FINAL CTLR TO A 310 DEG HDG, CLRED TO DSND FROM 7000 FT TO 4M, AND TOLD OF TFC AT 11 O'CLOCK, 5 NM AT 3500 OR 4000'. WE SPOTTED HIM RIGHT AWAY. WE WERE ALSO TOLD TO EXPECT AN EAST SIDE TURN-ON. IN MY MIND, I WAS THINKING WEST SIDE WHEN HE SAID IT, SO I THOUGHT WE HAD PLENTY OF TIME. SOON THE CAPT SAID 'EAST SIDE TURN-ON, WE BETTER GET DOWN'. WITH THAT, I INCREASED DSCNT RATE. THEN APCH SAID, 'LEFT TURN TO 220 DEG, CLRED FOR APCH, MAINTAIN 4000 UNTIL ON LOC'. I BELIEVE HE ALSO CALLED THE TFC AGAIN, BUT I WAS FOCUSED ON THE APCH, AND IT DIDN'T REGISTER WHAT HE SAID, ALTHOUGH WE WERE STILL AWARE OF THE TFC, NOW BOUT 2 NM. IN THE TURN, PASSING ABOUT 240 DEG, THE CAPT ASKED IF I STILL HAD THE TFC, NOW ABOUT 1/2 NM. AS I NOW FOCUSED ON THE TFC, IT BECAME APPARENT WE WOULD COLLIDE IF I CONTINUED (WE WERE PASSING 4300' IN A SHALLOW DSCNT). HE WAS HDG ABOUT 180 DEG AT 4000'. I MADE A MILD EVASIVE MANEUVER BY ROLLING OUT AND PULLING UP SLIGHTLY. I ESTIMATE THIS LEVELED US OFF AT 4300-4400'. SEVERAL SECONDS LATER, HE WAS SPOTTED OUT THE LEFT. I ROLLED BACK INTO MY TURN, STARTED A DSCNT AND COMPLETED THE APCH. I'M NOT SURE IF HE WAS IFR OR VFR, BUT HE WAS AT OUR CLRED ALT. SOMETHING BROKE DOWN SOMEWHERE. MY IMPRESSION WAS THAT HE WAS UNDER POSITIVE CTL, AND COULDN'T POSSIBLY BE VECTORED TOWARD US. DON'T GET COMPLACENT! HE NEVER TOOK ANY EVASIVE ACTION.

Data retrieved from NASA's ASRS site as of August 2007 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.