FAILURE TO NOTICE ROUTE DISCONNECT SUBSEQUENT TO PROGRAMMING AN ARR RWY CHANGE RESULTS IN A TRACK DEV ON ARR TO LAX.

Narrative

DSCNT INTO LAX ON RIIVR ARR RWY 24R PROGRAMMED INTO BOX HAD A DSCNT VIA CLRNC. I RECALL SOMEWHERE AFTER GRAMM INTXN BEING ASSIGNED RWY 25L AFTER CONSIDERABLE VECTORING AND SLOWING ON THE APCH. PM WAS LOADING THE BOX WHILE ACFT WAS ON AUTOPLT; A PRACTICE I HAD MEANT TO DISCOURAGE. UNFORTUNATELY; THIS IS A BIT OF A NEGATIVE TRANSFER FROM THE CLASSIC FLEET AS IT IS COMMON FOR THE FO TO MAKE BOX CHANGES EVEN WHEN NOT THE PF DUE TO SINGLE BOX INSTALLATION. I VERIFIED WHAT HE DID ON THE BOX BUT FAILED TO SEE THE DISCONNECT WHICH WAS PRESENT AFTER RUSTT INTXN AND THE PLANE MISSED THE TURN TO HABSO. I NOTICED THIS PRETTY QUICKLY AND CORRECTED TO THE LNAV TRACK BETWEEN HABSO AND RIIVR. SOCAL SIMULTANEOUSLY LET US KNOW WE HAD GONE THROUGH THE ARR AND WE INFORMED CORRECTING. NO OTHER COMMUNICATION REGARDING THE DEVIATION TRANSPIRED. I MOSTLY ELECTED TO RPT TO SHARE THE STORY AND THE UNDERLYING IMPORTANCE OF VERIFYING EACH AND EVERY FMC/CDU INPUT/MODIFICATION. AFTER LOTS OF LEGS IN A CLASSIC ACFT IT IS EASY TO ALLOW THIS PRACTICE TO CREEP INTO THE NEXT GENERATION AIRPLANES (LETTING FO MAKE BOX INPUTS WHEN NOT THE PF) AND THE AIRPLANE IS ON AUTOPLT BECAUSE IT IS EASIER. I LEARNED MY LESSON AND WILL MODIFY FUTURE BEHAVIOR.