Narrative:

Air carrier X was inbound to santa ana, ca over kayoh intersection, on the kayoh 1 arrival at 8000 MSL and 210 KTS. Flight was turned over to coast approach frequency 121.3. Air carrier X was cleared to 5000 MSL and assigned a heading for vectors to the 19R ILS. Was cleared to 4000 MSL on a heading of 220 degree. ATC assigned a heading 285 degree. At this time we saw an air carrier at 10 O'clock position on a northeast bound heading. It was very hazy and hard to distinguish the type of aircraft. ATC reported an air carrier Y medium large transport at 1 O'clock, reported we had an aircraft at 11 O'clock. ATC assigned a 310 degree heading. The heading change kept the air carrier at 12 O'clock position. ATC cleared our flight to 3500 MSL and a heading change to 020 degree. As we started to descend from 4000 to 3500 MSL, we heard ATC level the air carrier in front of us at 3500 MSL. This 12 O'clock position and leveling at the altitude we were cleared to, was a potential collision. At 3650 MSL we started a pull-up to 4000 MSL and told ATC we were climbing back to 4000. ATC gave us a turn to 360 degree heading. After the air carrier passed by the right side, we descended to 3500 MSL and ATC assigned a heading of 120 degree to intercept the localizer and cleared for approach 19R. I called coast approach on the telephone and talked to a supervisor. He said he was told that non controled pop-up traffic turned toward air carrier Y at 3000 MSL. That was why they stopped air carrier Y at 3500 and told us to turn to 360 degree heading. The controller said we were no closer than 3 mi.

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Original NASA ASRS Text

Title: FLT CREW STOPPED DESCENT BEFORE ASSIGNED ALT. PLT DEVIATION.

Narrative: ACR X WAS INBND TO SANTA ANA, CA OVER KAYOH INTXN, ON THE KAYOH 1 ARR AT 8000 MSL AND 210 KTS. FLT WAS TURNED OVER TO COAST APCH FREQ 121.3. ACR X WAS CLRED TO 5000 MSL AND ASSIGNED A HDG FOR VECTORS TO THE 19R ILS. WAS CLRED TO 4000 MSL ON A HDG OF 220 DEG. ATC ASSIGNED A HDG 285 DEG. AT THIS TIME WE SAW AN AIR CARRIER AT 10 O'CLOCK POSITION ON A NE BOUND HDG. IT WAS VERY HAZY AND HARD TO DISTINGUISH THE TYPE OF ACFT. ATC REPORTED AN ACR Y MLG AT 1 O'CLOCK, REPORTED WE HAD AN ACFT AT 11 O'CLOCK. ATC ASSIGNED A 310 DEG HDG. THE HDG CHANGE KEPT THE AIR CARRIER AT 12 O'CLOCK POSITION. ATC CLRED OUR FLT TO 3500 MSL AND A HDG CHANGE TO 020 DEG. AS WE STARTED TO DSND FROM 4000 TO 3500 MSL, WE HEARD ATC LEVEL THE AIR CARRIER IN FRONT OF US AT 3500 MSL. THIS 12 O'CLOCK POSITION AND LEVELING AT THE ALT WE WERE CLRED TO, WAS A POTENTIAL COLLISION. AT 3650 MSL WE STARTED A PULL-UP TO 4000 MSL AND TOLD ATC WE WERE CLIMBING BACK TO 4000. ATC GAVE US A TURN TO 360 DEG HDG. AFTER THE AIR CARRIER PASSED BY THE RIGHT SIDE, WE DESCENDED TO 3500 MSL AND ATC ASSIGNED A HDG OF 120 DEG TO INTERCEPT THE LOC AND CLRED FOR APCH 19R. I CALLED COAST APCH ON THE TELEPHONE AND TALKED TO A SUPVR. HE SAID HE WAS TOLD THAT NON CTLED POP-UP TFC TURNED TOWARD ACR Y AT 3000 MSL. THAT WAS WHY THEY STOPPED ACR Y AT 3500 AND TOLD US TO TURN TO 360 DEG HDG. THE CTLR SAID WE WERE NO CLOSER THAN 3 MI.

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.