Narrative:

After handoff to socal approach, given descent on kayoh 4 arrival. In vicinity of dawna, given heading off of arrival, one additional heading, then direct kayoh 4, 4000 ft. First officer flying, captain radio. Read back clearance and complied. During descent, below 7000 ft, we got a traffic alert, showing 300 ft below and within 2 mi at 1:30 O'clock position. ATC then said traffic alert, climb immediately. We had seen a B737 above us and several mi out at 1-2 O'clock position, but looking for the alert aircraft. TCASII then gave an alert for the B737 and a descend command. ATC cleared the B737 behind us and cleared us up to 8000 ft. Upon landing, we were asked to call. Was told there might be a pilot deviation. I spoke with the manager and he gave me a number to call back. Said we were only cleared to 8000 ft, I had read back 4000 ft and the controller missed it. First officer and I firmly believe we were given 4000 ft as read back. Manager later called and left a message the separation had not been lost and therefore no action would be pursued. His words...no harm, no foul. We were VFR and being vectored off the arrival, the 4000 ft clearance would have been suspect IFR, but not VFR and on vectors. I do not know what traffic the controller was directing us away from. We never saw another plane. His vector did direct us up to the B737's altitude as he was turning to us. Supplemental information from acn 537094: we were on the prado 5 departure out of ont established at 7000 ft MSL. Socal departure advised us of airbus traffic 10 O'clock position, 6 mi maintaining 8000 ft MSL. On our TCASII, we monitored the traffic descending through 8000 ft MSL, when socal instructed us to climb immediately to 8600 ft MSL and an immediate turn to 060 degrees. We complied. Socal did an excellent job. Socal requested us to call on the ground at our destination. The phone call revealed the airbus busted altitude.

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Original NASA ASRS Text

Title: A320 CREW AND B737 ARE VECTORED AWAY FROM EACH OTHER BY SCT WHEN AN INCORRECT CLRNC IS NOT CORRECTED.

Narrative: AFTER HDOF TO SOCAL APCH, GIVEN DSCNT ON KAYOH 4 ARR. IN VICINITY OF DAWNA, GIVEN HEADING OFF OF ARR, ONE ADDITIONAL HEADING, THEN DIRECT KAYOH 4, 4000 FT. FO FLYING, CAPT RADIO. READ BACK CLRNC AND COMPLIED. DURING DSCNT, BELOW 7000 FT, WE GOT A TFC ALERT, SHOWING 300 FT BELOW AND WITHIN 2 MI AT 1:30 O'CLOCK POS. ATC THEN SAID TFC ALERT, CLB IMMEDIATELY. WE HAD SEEN A B737 ABOVE US AND SEVERAL MI OUT AT 1-2 O'CLOCK POS, BUT LOOKING FOR THE ALERT ACFT. TCASII THEN GAVE AN ALERT FOR THE B737 AND A DSND COMMAND. ATC CLRED THE B737 BEHIND US AND CLRED US UP TO 8000 FT. UPON LNDG, WE WERE ASKED TO CALL. WAS TOLD THERE MIGHT BE A PLTDEV. I SPOKE WITH THE MGR AND HE GAVE ME A NUMBER TO CALL BACK. SAID WE WERE ONLY CLRED TO 8000 FT, I HAD READ BACK 4000 FT AND THE CTLR MISSED IT. FO AND I FIRMLY BELIEVE WE WERE GIVEN 4000 FT AS READ BACK. MGR LATER CALLED AND LEFT A MESSAGE THE SEPARATION HAD NOT BEEN LOST AND THEREFORE NO ACTION WOULD BE PURSUED. HIS WORDS...NO HARM, NO FOUL. WE WERE VFR AND BEING VECTORED OFF THE ARR, THE 4000 FT CLRNC WOULD HAVE BEEN SUSPECT IFR, BUT NOT VFR AND ON VECTORS. I DO NOT KNOW WHAT TFC THE CTLR WAS DIRECTING US AWAY FROM. WE NEVER SAW ANOTHER PLANE. HIS VECTOR DID DIRECT US UP TO THE B737'S ALT AS HE WAS TURNING TO US. SUPPLEMENTAL INFO FROM ACN 537094: WE WERE ON THE PRADO 5 DEP OUT OF ONT ESTABLISHED AT 7000 FT MSL. SOCAL DEP ADVISED US OF AIRBUS TFC 10 O'CLOCK POS, 6 MI MAINTAINING 8000 FT MSL. ON OUR TCASII, WE MONITORED THE TFC DSNDING THROUGH 8000 FT MSL, WHEN SOCAL INSTRUCTED US TO CLB IMMEDIATELY TO 8600 FT MSL AND AN IMMEDIATE TURN TO 060 DEGS. WE COMPLIED. SOCAL DID AN EXCELLENT JOB. SOCAL REQUESTED US TO CALL ON THE GND AT OUR DEST. THE PHONE CALL REVEALED THE AIRBUS BUSTED ALT.

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.