Narrative:

While on vectors heading 080 degrees at 5000' we were searching for traffic at 12:30-1 O'clock that we would be following. While looking we spotted the conflicting aircraft, an small aircraft, at 1 O'clock climbing, turning heading nwesterly. At this time the aircraft was about 3 or 4 mi away. We watched him for about 45 seconds, but we were unable to detect how serious the conflict would be, possible because of the aircraft's heading changes and climb variation. No mention of this traffic was made by ATC. Seconds before possible impact it became clear we had a problem. I pushed the nose down, but only lost about 75' when I could see the plane would climb above us. The other aircraft made no detectable evasive maneuvers. We mentioned the traffic to ATC. The controller said he did not see him. A min later the controller reported having the aircraft on radar and would track him. I felt like we spotted the aircraft about as soon as it was physically possible under the existing conditions. For some reason even the training we've had in detecting aircraft on a collision course we were unable to make the determination until it was almost too late. I feel confident we would have missed even if we hadn't seen him and took evasive action. It's clear to me that difficulties in seeing the aircraft, detecting the danger and then reacting put see and avoid on shaky ground. The best prevention here is clearly to stop unauthorized entries into this type of heavily used airspace or the mathematical odds will soon catch up with us again.

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Original NASA ASRS Text

Title: CLOSE PROX ACR-SMT GA-SMA AT THE BASE OF LAX TCA.

Narrative: WHILE ON VECTORS HDG 080 DEGS AT 5000' WE WERE SEARCHING FOR TFC AT 12:30-1 O'CLOCK THAT WE WOULD BE FOLLOWING. WHILE LOOKING WE SPOTTED THE CONFLICTING ACFT, AN SMA, AT 1 O'CLOCK CLBING, TURNING HDG NWESTERLY. AT THIS TIME THE ACFT WAS ABOUT 3 OR 4 MI AWAY. WE WATCHED HIM FOR ABOUT 45 SECS, BUT WE WERE UNABLE TO DETECT HOW SERIOUS THE CONFLICT WOULD BE, POSSIBLE BECAUSE OF THE ACFT'S HDG CHANGES AND CLB VARIATION. NO MENTION OF THIS TFC WAS MADE BY ATC. SECS BEFORE POSSIBLE IMPACT IT BECAME CLEAR WE HAD A PROB. I PUSHED THE NOSE DOWN, BUT ONLY LOST ABOUT 75' WHEN I COULD SEE THE PLANE WOULD CLB ABOVE US. THE OTHER ACFT MADE NO DETECTABLE EVASIVE MANEUVERS. WE MENTIONED THE TFC TO ATC. THE CTLR SAID HE DID NOT SEE HIM. A MIN LATER THE CTLR RPTED HAVING THE ACFT ON RADAR AND WOULD TRACK HIM. I FELT LIKE WE SPOTTED THE ACFT ABOUT AS SOON AS IT WAS PHYSICALLY POSSIBLE UNDER THE EXISTING CONDITIONS. FOR SOME REASON EVEN THE TRNING WE'VE HAD IN DETECTING ACFT ON A COLLISION COURSE WE WERE UNABLE TO MAKE THE DETERMINATION UNTIL IT WAS ALMOST TOO LATE. I FEEL CONFIDENT WE WOULD HAVE MISSED EVEN IF WE HADN'T SEEN HIM AND TOOK EVASIVE ACTION. IT'S CLEAR TO ME THAT DIFFICULTIES IN SEEING THE ACFT, DETECTING THE DANGER AND THEN REACTING PUT SEE AND AVOID ON SHAKY GND. THE BEST PREVENTION HERE IS CLEARLY TO STOP UNAUTH ENTRIES INTO THIS TYPE OF HEAVILY USED AIRSPACE OR THE MATHEMATICAL ODDS WILL SOON CATCH UP WITH US AGAIN.

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.