AN A319 FMS TURNS THE ACFT TOWARDS AN ON COURSE RADIAL PRIOR TO REACHING THE TURNING FIX. ATC QUESTIONS THIS AND REASSIGNS THE FLT A NEW HDG.

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DEP FROM SJC LOUPE 9 DYBLO LINDEN TRANSITION. I WAS FLYING THE DEP FOLLOWING THE FLT DIRECTOR COMMAND BARS; AS COMMANDED BY THE FMGS ON THE A319. THE DEP CALLS FOR TRACKING THE SJC 339 DEG RADIAL TO DYBLO THEN TRACK THE LIN 234 DEG RADIAL TO LINDEN. THE FMGS COMMANDED A TURN TO JOIN THE LINDEN 234 DEG RADIAL PRIOR TO REACHING DYBLO INTXN -- THIS IS NORMAL. DEP ASKED IF WE HAD BEGUN A TURN TO LINDEN; WE SAID YES; AND THEY GAVE US A TURN 15 DEGS TO THE L; A HDG OF 355 DEGS AND TOLD US TO CONTACT ZOA. DEP ALSO TOLD US WE WOULD MISS DYBLO INTXN; WHICH WE KNEW BECAUSE OF THE DEPICTION ON THE NAV DISPLAY. THIS IS A NORMAL OP FOR THE FMGS IN THE A319/320. WHAT CAUSED THE PROB? EITHER IGNORANCE ON THE PART OF THE CTLR ABOUT THE WAY GLASS AIRPLANES WITH FMS/FMGS FLY OR FMS/FMGS BEING CERTIFIED TO FLY INCORRECTLY. IF IT IS OK FOR FMS/FMGS TO COMMAND TURNS TO JOIN COURSES PRIOR TO REACHING FIXES; THEN WE NEED TO EDUCATE THE CTLRS THAT THIS WILL HAPPEN. IF IT IS REQUIRED TO FLY TO A FIX OR INTXN PRIOR TO INITIATING A TURN; THEN THE SOFTWARE FOR THE FMS/FMGS MUST BE REPROGRAMMED. SUPPLEMENTAL INFO FROM ACN 448124: THIS GUIDANCE STARTED A TURN TO THE R PRIOR TO DYBLO SO AS TO INTERCEPT AND ROLL OUT ON THE LINDEN 234 DEG RADIAL (THIS IS A TURN OF 75 DEGS).