Narrative:

We were on the civet arrival into lax; planning on runway 24R. ATC changed runway to runway 25R. PNF reprogrammed the FMC for the new runway. The FMC dumped all points; without any indication. ATC asked if there was a problem and we noticed the aircraft wasn't complying with arrival. ATC cleared us to civet; which was no longer in the box. We informed ATC of LNAV problems and they gave a vector to intercept localizer and cleared us for approach. Non eventful approach and landing on runway 25R. Should have had all approach plates out prior to arrival. Devoted too much time trying to analyze the problem instead of just transitioning to the VOR or asking for a vector.

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Original NASA ASRS Text

Title: FLT CREW OF B737-300 LOSES FMC RTE GUIDANCE WHEN PROGRAMMING RWY CHANGE ON CIVET START TO LAX.

Narrative: WE WERE ON THE CIVET ARR INTO LAX; PLANNING ON RWY 24R. ATC CHANGED RWY TO RWY 25R. PNF REPROGRAMMED THE FMC FOR THE NEW RWY. THE FMC DUMPED ALL POINTS; WITHOUT ANY INDICATION. ATC ASKED IF THERE WAS A PROB AND WE NOTICED THE ACFT WASN'T COMPLYING WITH ARR. ATC CLRED US TO CIVET; WHICH WAS NO LONGER IN THE BOX. WE INFORMED ATC OF LNAV PROBS AND THEY GAVE A VECTOR TO INTERCEPT LOC AND CLRED US FOR APCH. NON EVENTFUL APCH AND LNDG ON RWY 25R. SHOULD HAVE HAD ALL APCH PLATES OUT PRIOR TO ARR. DEVOTED TOO MUCH TIME TRYING TO ANALYZE THE PROB INSTEAD OF JUST TRANSITIONING TO THE VOR OR ASKING FOR A VECTOR.

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.