Narrative:

Air carrier X was being vectored from the west to a 25L approach at lax. Coast approach control assigned an altitude clearance of 'descend to and maintain 6000 ft.' altitude clearance of 6000 was read back to approach control and 6000 was set in altitude select window. Shortly after 6000 ft clearance was received and acknowledged coast approach directed us to contact los angeles approach. First officer checked in with los angeles approach as aircraft was passing through 6500 ft and repeated altitude assignment of 6000 ft. At that time los angeles approach replied 'we need you at 7000 ft, climb at this time to 7000.' a climb to 7000 was immediately initiated and level off at 7000 ft occurred approximately 15 seconds later. No known traffic conflicts. Supplemental information from acn 195598: air carrier X clearance to descend to 6000 ft MSL understood and read back to coast approach control. Changed frequency to lax approach control, on initial contact first officer reported out of 7000 for 6000 ft with no remark from approach control than 'roger, depart sli 330 degree vectors for runway 25L visual approach.' approach control called and said 'your altitude should be 7000 ft, climb to 7000 now for traffic.' we complied but still believe we were initially cleared to 6000 ft. Our descent from 12000 ft (initial crossing restriction) was interrupted at 8000 for traffic. We were given numerous aircraft to visually acquire, which with help of TCASII, we accomplished.

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Original NASA ASRS Text

Title: SNA APCH CTLR UNAUTHORIZED DSCNT TO OCCUPIED ALT WITH ACR X. OPDEV.

Narrative: ACR X WAS BEING VECTORED FROM THE W TO A 25L APCH AT LAX. COAST APCH CTL ASSIGNED AN ALT CLRNC OF 'DSND TO AND MAINTAIN 6000 FT.' ALT CLRNC OF 6000 WAS READ BACK TO APCH CTL AND 6000 WAS SET IN ALT SELECT WINDOW. SHORTLY AFTER 6000 FT CLRNC WAS RECEIVED AND ACKNOWLEDGED COAST APCH DIRECTED US TO CONTACT LOS ANGELES APCH. FO CHKED IN WITH LOS ANGELES APCH AS ACFT WAS PASSING THROUGH 6500 FT AND REPEATED ALT ASSIGNMENT OF 6000 FT. AT THAT TIME LOS ANGELES APCH REPLIED 'WE NEED YOU AT 7000 FT, CLB AT THIS TIME TO 7000.' A CLB TO 7000 WAS IMMEDIATELY INITIATED AND LEVEL OFF AT 7000 FT OCCURRED APPROX 15 SECONDS LATER. NO KNOWN TFC CONFLICTS. SUPPLEMENTAL INFO FROM ACN 195598: ACR X CLRNC TO DSND TO 6000 FT MSL UNDERSTOOD AND READ BACK TO COAST APCH CTL. CHANGED FREQ TO LAX APCH CTL, ON INITIAL CONTACT FO RPTED OUT OF 7000 FOR 6000 FT WITH NO REMARK FROM APCH CTL THAN 'ROGER, DEPART SLI 330 DEG VECTORS FOR RWY 25L VISUAL APCH.' APCH CTL CALLED AND SAID 'YOUR ALT SHOULD BE 7000 FT, CLB TO 7000 NOW FOR TFC.' WE COMPLIED BUT STILL BELIEVE WE WERE INITIALLY CLRED TO 6000 FT. OUR DSCNT FROM 12000 FT (INITIAL XING RESTRICTION) WAS INTERRUPTED AT 8000 FOR TFC. WE WERE GIVEN NUMEROUS ACFT TO VISUALLY ACQUIRE, WHICH WITH HELP OF TCASII, WE ACCOMPLISHED.

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.