Narrative:

After checking in with ont approach, air carrier X given descend clearance from 15000 ft down to 10000 ft. We were flying the kayoh 3 arrival into sna. We were proceeding direct to kayoh intersection as instructed by ont approach (134.00) our FMC profile showed us to be approximately 2100 ft high for the anticipated restr at kayoh intersection of 210 KTS and 8000 ft as normal issued by ont approach we were descending at approximately 3500 FPM descending through 12400 ft when ont approach amended our altitude to 12000 ft. The first officer disconnected the autoplt to try to stop our rate of descent as quickly as possible to level at 12000 ft. At about 12100 ft we received a TCASII advisory of 'traffic, traffic.' we observed an amber filled circle on our vsi-TCASII display climbing at our 1-2 O'clock position reading right to left. At approximately 11600 ft we received a descend, descend, descend RA from TCASII, by now the first officer is climbing back to 12000 ft. I had visual contact with the traffic now at our 12 O'clock position: (a B-737-300). I instructed my first officer to ignore the RA and maintain 12000 ft. Ont approach was slow in providing IFR separation with my flight, as well as the air carrier Y flight. We were never advised of the Y flight crossing below us.

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Original NASA ASRS Text

Title: LATE CLRNC CAUSED ALTDEV DSCNT THROUGH ASSIGNED ALT BY ACR X TCASII RA IGNORED WITH ACR Y.

Narrative: AFTER CHKING IN WITH ONT APCH, ACR X GIVEN DSND CLRNC FROM 15000 FT DOWN TO 10000 FT. WE WERE FLYING THE KAYOH 3 ARR INTO SNA. WE WERE PROCEEDING DIRECT TO KAYOH INTXN AS INSTRUCTED BY ONT APCH (134.00) OUR FMC PROFILE SHOWED US TO BE APPROX 2100 FT HIGH FOR THE ANTICIPATED RESTR AT KAYOH INTXN OF 210 KTS AND 8000 FT AS NORMAL ISSUED BY ONT APCH WE WERE DSNDING AT APPROX 3500 FPM DSNDING THROUGH 12400 FT WHEN ONT APCH AMENDED OUR ALT TO 12000 FT. THE FO DISCONNECTED THE AUTOPLT TO TRY TO STOP OUR RATE OF DSCNT AS QUICKLY AS POSSIBLE TO LEVEL AT 12000 FT. AT ABOUT 12100 FT WE RECEIVED A TCASII ADVISORY OF 'TFC, TFC.' WE OBSERVED AN AMBER FILLED CIRCLE ON OUR VSI-TCASII DISPLAY CLBING AT OUR 1-2 O'CLOCK POS READING R TO L. AT APPROX 11600 FT WE RECEIVED A DSND, DSND, DSND RA FROM TCASII, BY NOW THE FO IS CLBING BACK TO 12000 FT. I HAD VISUAL CONTACT WITH THE TFC NOW AT OUR 12 O'CLOCK POS: (A B-737-300). I INSTRUCTED MY FO TO IGNORE THE RA AND MAINTAIN 12000 FT. ONT APCH WAS SLOW IN PROVIDING IFR SEPARATION WITH MY FLT, AS WELL AS THE ACR Y FLT. WE WERE NEVER ADVISED OF THE Y FLT XING BELOW US.

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.