AN AIRBUS PLT DESCRIBES AN FMGC ANOMALY CAUSING A TRACK DEV ON THE LAX VTU 5 SHORTLY AFTER TKOF.

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DEPARTING RWY 24L; VENTURA 5 DEP; NAV MODE. AFTER LIFTOFF; NAV ARMED IMMEDIATELY. ABOUT THE TIME WE CROSSED THE 154 DEG RADIAL FROM SMO; THE ACFT FLT DIRECTOR BARS BEGAN TO COMMAND A R TURN. UNFORTUNATELY; I FOLLOWED THE COMMAND INITIALLY. ON THE NAV DISPLAY I NOTICED AN ARC GOING OFF SCALE. NOT SURE WHAT WAS GOING ON; I SHALLOWED THE BANK. SHORTLY THEREAFTER; THE NAV DISPLAY RE-INDEXED AND DREW A STRAIGHT LINE OFF SCALE THAT APPEARED TO BE FROM SMO TO VTU. AT THAT TIME WE WERE ON ABOUT A 280 DEG HDG. ATC ASKED OUR HDG AS I WAS TURNING BACK TO THE L. WE SAID HDG TOWARDS 255 DEGS; THE CTLR SAID MAINTAIN HDG 250 DEGS; WHICH WE SELECTED AND FLOWN. ONCE ESTABLISHED ON THE HDG; AUTOPLT WAS SELECTED. AT THIS TIME I'D ESTIMATE WE WERE ABOUT 1200 FT; AND AROUND 1 MI LATERALLY N OF RWY TRACK. IT WAS AS IF THE FMGC WANTED US TO GO DIRECT SMO; THEN AFTER WE CROSSED THE 154 DEG RADIAL THE FMGC ASSUMED WE HAD PASSED THE FIX AND SEQUENCED THE RTE. I DID REVIEW THE FLT PLAN BEFORE THE DEP BRIEF AND DURING THE BRIEF. I CAN'T RECALL 100%; BUT I DON'T REMEMBER SEEING A BAD RTE IN THE FLT PLAN. I DO REMEMBER SEEING THE DISCONTINUITY AS EXPECTED; BUT I DON'T RECALL SEEING THE INITIAL HDG. THE NAV DISPLAY LOOKED ACCURATE DURING THE BRIEF. AFTER LNDG; THE ACFT PRINTED A RPT INDICATING AN FMGC #1 MALFUNCTION; BUT THE TIME STAMP WAS DURING LNDG; NOT DEP. WE BOTH WONDERED IF THE FMGC #1 MALFUNCTIONED AND RESET INCORRECTLY BEFORE RESYNCING WITH FMGC #2. WITHOUT QUESTIONS; I DON'T KNOW HOW BETTER TO DESCRIBE THE INCIDENT. THE WHOLE OCCURRENCE LASTED ABOUT 45 SECONDS TO 1 MIN IN MY ESTIMATION. I SHOULD HAVE BEEN QUICKER IN MY RECOGNITION OF THE FMGC MALFUNCTION AND SELECTED HDG.