Narrative:

Cleared for reedr 2 arrival after hec while flying in an large transport. Subsequently cleared by next controller, 'after hec, direct civet, direct lax.' approaching civet, cleared by center controller to fly civet 2 profile descent. Just outside arnes sent over to approach control and reported level 10000, with ATIS 'X'. Given clearance to turn right 10 degree, maintain 10000 to intercept 24R localizer frequency 108.5 and ATIS 'Y' now current. Told captain I'd be off frequency for a min to get new ATIS. While listening to new ATIS, noticed aircraft descending out of 10000 and asked if we had been cleared out of 10000. Captain had misunderstood clearance and thought that we were still cleared for the profile descent. Reversed descent at 9500 ft. Subsequently cleared to 8000 while climbing back to 10000. Frequency congestion would not allow us to question our clearance. Electric jets are too hard to deprogram once VNAV is in control. A momentary distraction with VNAV programmed allows aircraft to descend before you are ready. Even disengaging autoplt once aircraft has initiated descent makes it very difficult to remain within 300 ft of assigned altitude. I had to report to national guard duty at a remote station for 4 days after my airline trip. I mailed this report as soon as possible.

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Original NASA ASRS Text

Title: ACFT EXCURSION FROM ASSIGNED ALT ON LAX CIVET PROFILE.

Narrative: CLRED FOR REEDR 2 ARR AFTER HEC WHILE FLYING IN AN LGT. SUBSEQUENTLY CLRED BY NEXT CTLR, 'AFTER HEC, DIRECT CIVET, DIRECT LAX.' APCHING CIVET, CLRED BY CENTER CTLR TO FLY CIVET 2 PROFILE DSCNT. JUST OUTSIDE ARNES SENT OVER TO APCH CTL AND RPTED LEVEL 10000, WITH ATIS 'X'. GIVEN CLRNC TO TURN R 10 DEG, MAINTAIN 10000 TO INTERCEPT 24R LOC FREQ 108.5 AND ATIS 'Y' NOW CURRENT. TOLD CAPT I'D BE OFF FREQ FOR A MIN TO GET NEW ATIS. WHILE LISTENING TO NEW ATIS, NOTICED ACFT DSNDING OUT OF 10000 AND ASKED IF WE HAD BEEN CLRED OUT OF 10000. CAPT HAD MISUNDERSTOOD CLRNC AND THOUGHT THAT WE WERE STILL CLRED FOR THE PROFILE DSCNT. REVERSED DSCNT AT 9500 FT. SUBSEQUENTLY CLRED TO 8000 WHILE CLBING BACK TO 10000. FREQ CONGESTION WOULD NOT ALLOW US TO QUESTION OUR CLRNC. ELECTRIC JETS ARE TOO HARD TO DEPROGRAM ONCE VNAV IS IN CTL. A MOMENTARY DISTR WITH VNAV PROGRAMMED ALLOWS ACFT TO DSND BEFORE YOU ARE READY. EVEN DISENGAGING AUTOPLT ONCE ACFT HAS INITIATED DSCNT MAKES IT VERY DIFFICULT TO REMAIN WITHIN 300 FT OF ASSIGNED ALT. I HAD TO RPT TO NATIONAL GUARD DUTY AT A REMOTE STATION FOR 4 DAYS AFTER MY AIRLINE TRIP. I MAILED THIS RPT AS SOON AS POSSIBLE.

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.