Narrative:

We just passed cardi intersection on the cardi 2 arrival into san diego and were cleared from 15000 ft to 7000 ft direct the mzb VOR. I had just finished writing down the san ATIS and computing some landing performance data when I decided to look for traffic. The second I looked out, I saw a light twin engine directly in front of us, moving left to right (heading approximately 220 degrees). The first officer saw the plane at the same time I did and immediately he grabbed the yoke and rolled the plane into a 20 degree left bank, disengaging the autoplt. The light twin passed by us less than 100 ft horizontally and less than 10 ft vertically, at our 1 O'clock position. We were heading 140 degrees, descending at 2000 FPM and 260 KIAS. We immediately notified the approach controller, who did not have the aircraft on radar. Upon landing at san the captain contacted the approach control supervisor and filed a report. At the time of the incident a rare eclipse of the sun was occurring, and we were told afterward there were many, many targets on the radar. We theorize that the light twin was a sightseer (of the eclipse) and in all probability never saw us. Also, we were not TCASII equipped, so even if the plane had an operating transponder, we wouldn't have been able to detect his presence sooner by seeing him on the TCASII display.

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Original NASA ASRS Text

Title: ACR BEGINNING DSCNT HAS NMAC WITH LIGHT TWIN.

Narrative: WE JUST PASSED CARDI INTXN ON THE CARDI 2 ARR INTO SAN DIEGO AND WERE CLRED FROM 15000 FT TO 7000 FT DIRECT THE MZB VOR. I HAD JUST FINISHED WRITING DOWN THE SAN ATIS AND COMPUTING SOME LNDG PERFORMANCE DATA WHEN I DECIDED TO LOOK FOR TFC. THE SECOND I LOOKED OUT, I SAW A LIGHT TWIN ENG DIRECTLY IN FRONT OF US, MOVING L TO R (HDG APPROX 220 DEGS). THE FO SAW THE PLANE AT THE SAME TIME I DID AND IMMEDIATELY HE GRABBED THE YOKE AND ROLLED THE PLANE INTO A 20 DEG L BANK, DISENGAGING THE AUTOPLT. THE LIGHT TWIN PASSED BY US LESS THAN 100 FT HORIZLY AND LESS THAN 10 FT VERTICALLY, AT OUR 1 O'CLOCK POS. WE WERE HDG 140 DEGS, DSNDING AT 2000 FPM AND 260 KIAS. WE IMMEDIATELY NOTIFIED THE APCH CTLR, WHO DID NOT HAVE THE ACFT ON RADAR. UPON LNDG AT SAN THE CAPT CONTACTED THE APCH CTL SUPVR AND FILED A RPT. AT THE TIME OF THE INCIDENT A RARE ECLIPSE OF THE SUN WAS OCCURRING, AND WE WERE TOLD AFTERWARD THERE WERE MANY, MANY TARGETS ON THE RADAR. WE THEORIZE THAT THE LIGHT TWIN WAS A SIGHTSEER (OF THE ECLIPSE) AND IN ALL PROBABILITY NEVER SAW US. ALSO, WE WERE NOT TCASII EQUIPPED, SO EVEN IF THE PLANE HAD AN OPERATING TRANSPONDER, WE WOULDN'T HAVE BEEN ABLE TO DETECT HIS PRESENCE SOONER BY SEEING HIM ON THE TCASII DISPLAY.

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