Narrative:

We were proceeding to the civet intersection and anticipating the civet arrival to lax. The arrival was selected from the database and inserted into the flight plan, the crossing restrs were reviewed and the approach for runway 25L reviewed. Prior to civet we were cleared direct to snrkl intersection with a clearance to descend on the mitts one arrival, the first officer inserted the new arrival into the FMGC and cleared up the remainder of the flight plan. We reviewed the crossing altitudes and briefed the approach to runway 24R. When the approach was selected from the database it was inserted using the 'via' function from the STAR, which is normal for that approach to lax. The end of the STAR and the IAF for runway 24R are the denay intersection at an altitude of 8000 ft (at or above). We were given a frequency change at about the same time we arrived at denay descending to 8000 ft. As the first officer was checking in on the next frequency, I was looking at the approach plate and the display on my navigation data screen which had the altitude constraints displayed for the STAR and the approach. Because the A320 is hard to 'slow down and go down' I was a little concerned with making the next altitude of 4000 ft in about 8 mi. There was no discontinuity between the STAR and the approach and I mistakenly set 4000 ft in the FCU and started a descent. The first officer and the controller both questioned our altitude at the same time but because of our relatively high rate of descent, we were already 500-700 ft low. Too great a reliance on the navigation display, coupled with a busy approach environment and a failure on my part to confirm the altitudes with the other pilot led to this altitude deviation which fortunately caused no conflicts with other aircraft. Supplemental information from acn 453578: on descent into lax we were given a last min change to descend via the mitts arrival. We had previously anticipated the civet arrival. The descent was accomplished using selected airspds and selected altitudes flown using the autoplt. The captain was the PF. Our clearance limit was denay intersection at or above 8000 ft, the last fix on the arrival. ATC did not turn us over to the approach controller until we were at denay. Denay is also depicted on the ILS approach runway 24R. The captain mentioned he was continuing the descent to 4000 ft (the aircraft was in continuos descent and was obviously going to be slightly above 8000 ft at denay). The captain probably saw 4000 ft was the altitude shown at the next intersection on the approach plate and was also depicted on the navigation display. As I was dialing the new frequency I mentioned to the captain that we are not cleared for the approach. I tried to get my call into ATC quickly so we may continue the descent and receive clearance to join the approach. As I called the controller I noticed we were at 7700 ft and descending. At the same time the captain disconnected the autoplt and attempted to stop the descent. The controller queried my call and reminded us the arrival ended at denay at 8000 ft then immediately cleared us for the approach. It was our responsibility to follow the assigned clearance although ATC had not give us clearance beyond denay until we were at denay, but that is not unusual in a busy area such as this. Flying aircraft is our primary task, ATC and other duties are secondary. As the PNF I could have been more proactive towards ensuring the PF remains focused to the task of flying the aircraft and adhering to the clearance. A thorough briefing prior to the descent phase is good technique, but ATC sometimes operates in a dynamic environment that last min changes are necessary. During a busy phase of flight such as in a descent, these changes can lead to increased workload and potential for errors.

Related reports:

Google
 

Original NASA ASRS Text

Title: A320 CREW DSNDS EARLY ON ARR INTO LAX.

Narrative: WE WERE PROCEEDING TO THE CIVET INTXN AND ANTICIPATING THE CIVET ARR TO LAX. THE ARR WAS SELECTED FROM THE DATABASE AND INSERTED INTO THE FLT PLAN, THE XING RESTRS WERE REVIEWED AND THE APCH FOR RWY 25L REVIEWED. PRIOR TO CIVET WE WERE CLRED DIRECT TO SNRKL INTXN WITH A CLRNC TO DSND ON THE MITTS ONE ARR, THE FO INSERTED THE NEW ARR INTO THE FMGC AND CLRED UP THE REMAINDER OF THE FLT PLAN. WE REVIEWED THE XING ALTS AND BRIEFED THE APCH TO RWY 24R. WHEN THE APCH WAS SELECTED FROM THE DATABASE IT WAS INSERTED USING THE 'VIA' FUNCTION FROM THE STAR, WHICH IS NORMAL FOR THAT APCH TO LAX. THE END OF THE STAR AND THE IAF FOR RWY 24R ARE THE DENAY INTXN AT AN ALT OF 8000 FT (AT OR ABOVE). WE WERE GIVEN A FREQ CHANGE AT ABOUT THE SAME TIME WE ARRIVED AT DENAY DSNDING TO 8000 FT. AS THE FO WAS CHKING IN ON THE NEXT FREQ, I WAS LOOKING AT THE APCH PLATE AND THE DISPLAY ON MY NAV DATA SCREEN WHICH HAD THE ALT CONSTRAINTS DISPLAYED FOR THE STAR AND THE APCH. BECAUSE THE A320 IS HARD TO 'SLOW DOWN AND GO DOWN' I WAS A LITTLE CONCERNED WITH MAKING THE NEXT ALT OF 4000 FT IN ABOUT 8 MI. THERE WAS NO DISCONTINUITY BTWN THE STAR AND THE APCH AND I MISTAKENLY SET 4000 FT IN THE FCU AND STARTED A DSCNT. THE FO AND THE CTLR BOTH QUESTIONED OUR ALT AT THE SAME TIME BUT BECAUSE OF OUR RELATIVELY HIGH RATE OF DSCNT, WE WERE ALREADY 500-700 FT LOW. TOO GREAT A RELIANCE ON THE NAV DISPLAY, COUPLED WITH A BUSY APCH ENVIRONMENT AND A FAILURE ON MY PART TO CONFIRM THE ALTS WITH THE OTHER PLT LED TO THIS ALTDEV WHICH FORTUNATELY CAUSED NO CONFLICTS WITH OTHER ACFT. SUPPLEMENTAL INFO FROM ACN 453578: ON DSCNT INTO LAX WE WERE GIVEN A LAST MIN CHANGE TO DSND VIA THE MITTS ARR. WE HAD PREVIOUSLY ANTICIPATED THE CIVET ARR. THE DSCNT WAS ACCOMPLISHED USING SELECTED AIRSPDS AND SELECTED ALTS FLOWN USING THE AUTOPLT. THE CAPT WAS THE PF. OUR CLRNC LIMIT WAS DENAY INTXN AT OR ABOVE 8000 FT, THE LAST FIX ON THE ARR. ATC DID NOT TURN US OVER TO THE APCH CTLR UNTIL WE WERE AT DENAY. DENAY IS ALSO DEPICTED ON THE ILS APCH RWY 24R. THE CAPT MENTIONED HE WAS CONTINUING THE DSCNT TO 4000 FT (THE ACFT WAS IN CONTINUOS DSCNT AND WAS OBVIOUSLY GOING TO BE SLIGHTLY ABOVE 8000 FT AT DENAY). THE CAPT PROBABLY SAW 4000 FT WAS THE ALT SHOWN AT THE NEXT INTXN ON THE APCH PLATE AND WAS ALSO DEPICTED ON THE NAV DISPLAY. AS I WAS DIALING THE NEW FREQ I MENTIONED TO THE CAPT THAT WE ARE NOT CLRED FOR THE APCH. I TRIED TO GET MY CALL INTO ATC QUICKLY SO WE MAY CONTINUE THE DSCNT AND RECEIVE CLRNC TO JOIN THE APCH. AS I CALLED THE CTLR I NOTICED WE WERE AT 7700 FT AND DSNDING. AT THE SAME TIME THE CAPT DISCONNECTED THE AUTOPLT AND ATTEMPTED TO STOP THE DSCNT. THE CTLR QUERIED MY CALL AND REMINDED US THE ARR ENDED AT DENAY AT 8000 FT THEN IMMEDIATELY CLRED US FOR THE APCH. IT WAS OUR RESPONSIBILITY TO FOLLOW THE ASSIGNED CLRNC ALTHOUGH ATC HAD NOT GIVE US CLRNC BEYOND DENAY UNTIL WE WERE AT DENAY, BUT THAT IS NOT UNUSUAL IN A BUSY AREA SUCH AS THIS. FLYING ACFT IS OUR PRIMARY TASK, ATC AND OTHER DUTIES ARE SECONDARY. AS THE PNF I COULD HAVE BEEN MORE PROACTIVE TOWARDS ENSURING THE PF REMAINS FOCUSED TO THE TASK OF FLYING THE ACFT AND ADHERING TO THE CLRNC. A THOROUGH BRIEFING PRIOR TO THE DSCNT PHASE IS GOOD TECHNIQUE, BUT ATC SOMETIMES OPERATES IN A DYNAMIC ENVIRONMENT THAT LAST MIN CHANGES ARE NECESSARY. DURING A BUSY PHASE OF FLT SUCH AS IN A DSCNT, THESE CHANGES CAN LEAD TO INCREASED WORKLOAD AND POTENTIAL FOR ERRORS.

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.