Narrative:

I was PIC and the non-flying pilot sitting left seat on a flight to ont on a CE560. The flight was the second leg as a crew paired earlier together that day. The entire flight was under VMC conditions. Due to the short duration of the flight; most of the enroute and approach briefings were done prior to our departure including a review of the arriving airport; expected runways. We were filed for 10;000 ft enroute; but were given 7;000 ft as a final in our clearance. We accomplished the short segment checklist and did a final review of the airport diagram and approach. As we approached ont; we were given a decent to 5;000 ft and a heading; which put us on a right downwind for 26L. At 5000 ft; we saw the airport; and we were asked by socal if we wanted the full ILS procedure or take a visual. We both agreed to a visual approach and I stated that to socal. Socal asked if we had an air carrier in sight at the one o'clock position on final for 26R. We both had an air carrier in sight in that position and relayed that we had contact. Socal then cleared us number three for the visual for 26L; maintain contact with the air carrier that was cleared for 26R and cautioned us on wake turbulence. I acknowledge and my first officer started to descend and turn base for 26L. At about 4600 ft; socal issued a verbal traffic alert; canceled our approach clearance; and told us that we were to follow another air carrier that was on final which we just saw as this was all happening. At the same time we received a 'traffic; traffic' annunciation from our TCAS. My first officer immediately executed a climbing left turn (at the same time ATC was giving us climb back to 5000 ft and a heading away from the traffic). I acknowledged the instructions and we climbed back to 5000 ft on the easterly assigned heading given by socal approach. We were then vectored back towards the airport and at five miles out we got the airport insight and we were cleared for the visual 26L and told to contact the tower. Tower cleared us to land and the rest was uneventful. Neither approach nor tower said anything about the earlier conflict. No RA was issued by our TCAS during the event. In review of what happened; I should have noted that we were number three for the approach to my first officer; and that until we counted the two aircraft ahead of us we shouldn't have turned base or descended. Also if I had noted or asked for an altitude on the air carrier that we were following; that could have better helped our positioning in the traffic pattern. I was lured into a false sense of security that we saw an air carrier and figured incorrectly the proper air carrier to follow; not knowing that there were two air carriers on final. In the future I will be more vigilant in spotting and confirming traffic to follow in VFR conditions

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Original NASA ASRS Text

Title: A corporate jet on vectors for visual approach to ONT sequenced as number three following an air carrier; turned base to follow the first aircraft conflicting with second air carrier.

Narrative: I was PIC and the non-flying pilot sitting left seat on a flight to ONT on a CE560. The flight was the second leg as a crew paired earlier together that day. The entire flight was under VMC conditions. Due to the short duration of the flight; most of the enroute and approach briefings were done prior to our departure including a review of the arriving airport; expected runways. We were filed for 10;000 FT enroute; but were given 7;000 FT as a final in our clearance. We accomplished the short segment checklist and did a final review of the airport diagram and approach. As we approached ONT; we were given a decent to 5;000 FT and a heading; which put us on a right downwind for 26L. At 5000 FT; we saw the airport; and we were asked by SOCAL if we wanted the full ILS procedure or take a visual. We both agreed to a visual approach and I stated that to SOCAL. SOCAL asked if we had an air carrier in sight at the one o'clock position on final for 26R. We both had an air carrier in sight in that position and relayed that we had contact. SOCAL then cleared us number three for the visual for 26L; maintain contact with the air carrier that was cleared for 26R and cautioned us on wake turbulence. I acknowledge and my First Officer started to descend and turn base for 26L. At about 4600 FT; SOCAL issued a verbal traffic alert; canceled our approach clearance; and told us that we were to follow another air carrier that was on final which we just saw as this was all happening. At the same time we received a 'traffic; traffic' annunciation from our TCAS. My First Officer immediately executed a climbing left turn (at the same time ATC was giving us climb back to 5000 FT and a heading away from the traffic). I acknowledged the instructions and we climbed back to 5000 FT on the easterly assigned heading given by SOCAL approach. We were then vectored back towards the airport and at five miles out we got the airport insight and we were cleared for the visual 26L and told to contact the tower. Tower cleared us to land and the rest was uneventful. Neither approach nor tower said anything about the earlier conflict. No RA was issued by our TCAS during the event. In review of what happened; I should have noted that we were number three for the approach to my First Officer; and that until we counted the two aircraft ahead of us we shouldn't have turned base or descended. Also if I had noted or asked for an altitude on the air carrier that we were following; that could have better helped our positioning in the traffic pattern. I was lured into a false sense of security that we saw an air carrier and figured incorrectly the proper air carrier to follow; not knowing that there were two air carriers on final. In the future I will be more vigilant in spotting and confirming traffic to follow in VFR conditions

Data retrieved from NASA's ASRS site as of April 2012 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.