Narrative:

While descending into ont on the ziggy 3 arrival/hec transition, we were cleared to 11000 ft by ZLA then turned over to ont approach. Approach cleared us to 8000 ft and asked us to report the field for a visual to runway 26R. Through 9000 ft we called the field in sight and were cleared to 4000 ft, turn left 190 degrees account of traffic. Through 8500 ft we got a TCASII TA, and noted traffic on the screen 12 O'clock approximately 5 mi indicating level at 8000 ft. I slowed the rate of descent and saw a medium size twin at 12 O'clock and closing. TCASII commanded climb and I climbed right while traffic dove right. Approach called turn wbound after we had already begun. Estimate closest point approximately 200-300 ft. Then cleared for a normal approach and landing. Contacted ont TRACON by phone.

Related reports:

Google
 

Original NASA ASRS Text

Title: ACR X DSCNT THROUGH OCCUPIED ALT TCASII TA RA HAD NMAC LTSS FROM ACFT Y. SYS ERROR. EVASIVE ACTION TAKEN.

Narrative: WHILE DSNDING INTO ONT ON THE ZIGGY 3 ARR/HEC TRANSITION, WE WERE CLRED TO 11000 FT BY ZLA THEN TURNED OVER TO ONT APCH. APCH CLRED US TO 8000 FT AND ASKED US TO RPT THE FIELD FOR A VISUAL TO RWY 26R. THROUGH 9000 FT WE CALLED THE FIELD IN SIGHT AND WERE CLRED TO 4000 FT, TURN L 190 DEGS ACCOUNT OF TFC. THROUGH 8500 FT WE GOT A TCASII TA, AND NOTED TFC ON THE SCREEN 12 O'CLOCK APPROX 5 MI INDICATING LEVEL AT 8000 FT. I SLOWED THE RATE OF DSCNT AND SAW A MEDIUM SIZE TWIN AT 12 O'CLOCK AND CLOSING. TCASII COMMANDED CLB AND I CLBED R WHILE TFC DOVE R. APCH CALLED TURN WBOUND AFTER WE HAD ALREADY BEGUN. ESTIMATE CLOSEST POINT APPROX 200-300 FT. THEN CLRED FOR A NORMAL APCH AND LNDG. CONTACTED ONT TRACON BY PHONE.

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.