CRJ FLT CONTINUED THROUGH INTXN ON A STAR RATHER THAN MAKING THE DEPICTED TURN.

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THE FLT WAS ON THE BYP.BYP5 ARR AT 210 KTS AND 11000 FT. WE ARE NOT AUTHORIZED TO ALLOW THE FMS TO FLY TO STONZ INTXN EVEN THOUGH IT WILL DO IT. THE PROC IS TO SELECT HDG MODE AND TURN THE ACFT IN HDG MODE TO 175 DEGS FOR LNDG N RWYS. THIS WAS BRIEFED TO THE FO WHO WAS FLYING. THE RWY ASSIGNMENT WAS GIVEN JUST BEFORE LEMYN AND IT WAS BRIEFED FOR RWY 35R. WE WERE EXPECTING RWY 35C WHICH WAS PREVIOUSLY BRIEFED. WHEN THE NEW RWY WAS SELECTED IN THE FMS; FOR WHATEVER REASON WHEN THE FO EXECUTED THE NEW RWY IT CAUSED A DISCONTINUITY IN THE FLT PLAN AFTER STONZ. I; THE CAPT; WAS ON THE RADIO WITH ATC AND DID NOT NOTICE WHAT HAD HAPPENED. WE HAD A RADIO FREQUENCY CHANGE AT THIS TIME AND THE FO DID NOT SELECT HDG MODE AND 175 DEG AS WE GOT TO STONZ INTXN. WHEN I FINISHED CHKING IN I NOTICED THE ACFT HAD NOT TURNED YET; THE FMS WAS IN DISCONTINUITY AND IN ROLL MODE. I INSTRUCTED THE FO TO GO TO HDG MODE AND TURN TO 175 DEGS L TURN. ON HIS FIRST ATTEMPT THE MODE SELECTION DID NOT CHANGE FROM ROLL TO HDG. HE FINALLY REPEATED THIS SELECT AND THE ACFT TURNED; HOWEVER ATC ASKED IF WE WERE TURNING AND I REPLIED YES WE ARE. THE ACFT WAS TURNED ABOUT 1.5 MILES LATE. THERE WERE NO OTHER ISSUES. PROPER PROCS WERE NOT FOLLOWED AND I THE CAPT GOT DISTRACTED. ALSO; THE FMS DID NOT EXECUTE PROPERLY; HOWEVER I DO NOT KNOW IF THIS WAS OPERATOR ERROR OR NOT; BECAUSE IT WAS NOT VERIFIED.CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR STATED THAT THE ARR HAD BEEN SUFFICIENTLY BRIEFED; BUT HE DIVERTED HIS ATTENTION FOR A FREQ CHANGE AS THE FLT APCHED 'STONZ.' THE FO FAILED TO PROPERLY SELECT THE HDG MODE FOR THE L TURN TO 175 DEGS AFTER THE INTXN; SO THE FLT CONTINUED UNTIL THE HDG MODE WAS AGAIN SELECTED AND CONFIRMED. THE RPTR FELT THAT THE FO'S INEXPERIENCE WAS INSTRUMENTAL IN THE DEV. NO TFC CONFLICT RESULTED FROM THE DEV.