Narrative:

We were descending into lax on the seavu one arrival in a B-300 series aircraft. The captain was the PF and I was the pm. The WX in lax was 5500 ft overcast and 10 mi visibility. Prior to the top of descent; the captain briefed the arrival and approach for runway 24R. After being switched to socal approach we were given a clearance to descend via the seavu one arrival for runway 25L. As the pm; I programmed the FMC for runway 25L from runway 24R and proceed to check the waypoints on the FMC to ensure they match the chart. While level at 12000 ft waiting to pass dixxn intersection; I was on legs page 2. The captain thought we had passed the waypoint and began a descent to 10000 ft for krain. I acknowledged the descent and finished checking the waypoints and went to legs page one where we both saw that we had started our descent over seavu instead of dixxn (3 mi prior to dixxn). We reached approximately 11300 ft and climbed back to 12000 ft. There were no traffic conflicts and we corrected the error without any ATC conflicts. When flying the arrs for lax; it is easy to assume that 'we will get 24R' because it happens 95% of the time. When switching to approach from center on the seavu arrival; the runway 25L profile happens prior to the runway 24R profile. A good technique may be to brief a backup plan to runway 25L and have in mind the first descent point krain at or above 10000 ft; especially in a B-300/500 where resources are more limiting (1 FMC; no map). There are many advantages to being in a B-700 series aircraft. With the ever changing arrs and departures; RNAV procedures; descent via clrncs; ATC congestion; and changes to normal operations (ie; runway changes that affect the descent profile) the B-700 offers a visual map of the route as well as an additional FMC for the pm's use. I feel if we would have had these additional tools for our use; this situation would have not happened.

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Original NASA ASRS Text

Title: B737-300 BUSTS CROSSING RESTRICTION ON SEAVU STAR TO LAX WHILE PROGRAMMING A LATE RWY CHANGE.

Narrative: WE WERE DSNDING INTO LAX ON THE SEAVU ONE ARR IN A B-300 SERIES ACFT. THE CAPT WAS THE PF AND I WAS THE PM. THE WX IN LAX WAS 5500 FT OVCST AND 10 MI VISIBILITY. PRIOR TO THE TOP OF DSCNT; THE CAPT BRIEFED THE ARR AND APCH FOR RWY 24R. AFTER BEING SWITCHED TO SOCAL APCH WE WERE GIVEN A CLRNC TO DSND VIA THE SEAVU ONE ARR FOR RWY 25L. AS THE PM; I PROGRAMMED THE FMC FOR RWY 25L FROM RWY 24R AND PROCEED TO CHK THE WAYPOINTS ON THE FMC TO ENSURE THEY MATCH THE CHART. WHILE LEVEL AT 12000 FT WAITING TO PASS DIXXN INTXN; I WAS ON LEGS PAGE 2. THE CAPT THOUGHT WE HAD PASSED THE WAYPOINT AND BEGAN A DSCNT TO 10000 FT FOR KRAIN. I ACKNOWLEDGED THE DSCNT AND FINISHED CHKING THE WAYPOINTS AND WENT TO LEGS PAGE ONE WHERE WE BOTH SAW THAT WE HAD STARTED OUR DSCNT OVER SEAVU INSTEAD OF DIXXN (3 MI PRIOR TO DIXXN). WE REACHED APPROX 11300 FT AND CLBED BACK TO 12000 FT. THERE WERE NO TFC CONFLICTS AND WE CORRECTED THE ERROR WITHOUT ANY ATC CONFLICTS. WHEN FLYING THE ARRS FOR LAX; IT IS EASY TO ASSUME THAT 'WE WILL GET 24R' BECAUSE IT HAPPENS 95% OF THE TIME. WHEN SWITCHING TO APCH FROM CTR ON THE SEAVU ARR; THE RWY 25L PROFILE HAPPENS PRIOR TO THE RWY 24R PROFILE. A GOOD TECHNIQUE MAY BE TO BRIEF A BACKUP PLAN TO RWY 25L AND HAVE IN MIND THE FIRST DSCNT POINT KRAIN AT OR ABOVE 10000 FT; ESPECIALLY IN A B-300/500 WHERE RESOURCES ARE MORE LIMITING (1 FMC; NO MAP). THERE ARE MANY ADVANTAGES TO BEING IN A B-700 SERIES ACFT. WITH THE EVER CHANGING ARRS AND DEPS; RNAV PROCS; DSCNT VIA CLRNCS; ATC CONGESTION; AND CHANGES TO NORMAL OPS (IE; RWY CHANGES THAT AFFECT THE DSCNT PROFILE) THE B-700 OFFERS A VISUAL MAP OF THE RTE AS WELL AS AN ADDITIONAL FMC FOR THE PM'S USE. I FEEL IF WE WOULD HAVE HAD THESE ADDITIONAL TOOLS FOR OUR USE; THIS SITUATION WOULD HAVE NOT HAPPENED.

Data retrieved from NASA's ASRS site as of January 2009 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.