Narrative:

Flight from las to lax we were cleared by las clearance delivery to lax via oasis 7 gifs direct hec J64 lax. Between gfs and hec we were given a vector for the 25 localizer at lax. About 110 mi from lax, we were given an amended heading. About 80- 85 mi out. I thought we were instructed to descend to 14000 ft, intercept the 25 localizer, cleared civet 1 arrival to lax. I intercepted the localizer and arrived at 14000 ft about 54 mi out or about 2 mi before civet intersection. At civet intersection, I verbally stated 'there's civet, down to 12000 ft' and reset the MCP altitude display to 12000 ft and began further descent. Descending through about 12400 ft and about 45 mi out, the center controller said 'descend and maintain 12000 ft. You should be at 14000 ft. You were not cleared for the arrival.' the captain responded by saying 'we thought we were cleared for the profile. What do you want us to do -- climb back to 14000 ft.' the center controller said 'no, you were not cleared for the arrival -- just maintain 17000 ft and contact lax approach on 124.9.' we were not aware of any traffic conflict caused by this misunderstanding. Lesson to be learned: 1) sometimes maybe we think we have heard what we expect to hear; 2) listen more carefully; 3) verify arrival with other crewmember; 4) verify 'next' altitude with other crewmember before resetting MCP altitude display.

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Original NASA ASRS Text

Title: ALTDEV.

Narrative: FLT FROM LAS TO LAX WE WERE CLRED BY LAS CLRNC DELIVERY TO LAX VIA OASIS 7 GIFS DIRECT HEC J64 LAX. BTWN GFS AND HEC WE WERE GIVEN A VECTOR FOR THE 25 LOC AT LAX. ABOUT 110 MI FROM LAX, WE WERE GIVEN AN AMENDED HDG. ABOUT 80- 85 MI OUT. I THOUGHT WE WERE INSTRUCTED TO DSND TO 14000 FT, INTERCEPT THE 25 LOC, CLRED CIVET 1 ARR TO LAX. I INTERCEPTED THE LOC AND ARRIVED AT 14000 FT ABOUT 54 MI OUT OR ABOUT 2 MI BEFORE CIVET INTXN. AT CIVET INTXN, I VERBALLY STATED 'THERE'S CIVET, DOWN TO 12000 FT' AND RESET THE MCP ALT DISPLAY TO 12000 FT AND BEGAN FURTHER DSCNT. DSNDING THROUGH ABOUT 12400 FT AND ABOUT 45 MI OUT, THE CTR CTLR SAID 'DSND AND MAINTAIN 12000 FT. YOU SHOULD BE AT 14000 FT. YOU WERE NOT CLRED FOR THE ARR.' THE CAPT RESPONDED BY SAYING 'WE THOUGHT WE WERE CLRED FOR THE PROFILE. WHAT DO YOU WANT US TO DO -- CLB BACK TO 14000 FT.' THE CTR CTLR SAID 'NO, YOU WERE NOT CLRED FOR THE ARR -- JUST MAINTAIN 17000 FT AND CONTACT LAX APCH ON 124.9.' WE WERE NOT AWARE OF ANY TFC CONFLICT CAUSED BY THIS MISUNDERSTANDING. LESSON TO BE LEARNED: 1) SOMETIMES MAYBE WE THINK WE HAVE HEARD WHAT WE EXPECT TO HEAR; 2) LISTEN MORE CAREFULLY; 3) VERIFY ARR WITH OTHER CREWMEMBER; 4) VERIFY 'NEXT' ALT WITH OTHER CREWMEMBER BEFORE RESETTING MCP ALT DISPLAY.

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.