ERJ FLT CREW DEVIATES FROM DFW RNAV SID TRACK DUE TO FMS COMPUTATION OF TURN POINT AND TURN RATE.

Narrative

THIS WAS THE FIRST LEG OF IOE FOR MY TRAINEE. UPON RECEIVING CLRNC FROM ATC; WE WERE GIVEN AN RNAV SID; WHICH WAS THE FIRST FOR ME. AS IT WAS ENTERED INTO THE FMS; WE DISCUSSED THE PROC AND REVIEWED THE CHART FOR THE SID. DURING THIS BRIEFING; MY TRAINEE BROUGHT TO MY ATTN THAT THESE SIDS HAVE BEEN A PROB FOR OTHER CREWS AND HAD ALSO BEEN INSTRUCTED THAT TO COMPLY WITH THE SID THE FIXES ALONG THE PROC SHOULD BE SET UP TO FLY OVER THE POINT TO AVOID MAKING EARLY TURNS PRIOR TO THE FIX. SO WE MADE THE FLYOVER CHANGES TO THE FMS AND REVIEWED THE PROC AGAIN WITH THE CHART ALONG WITH THE FMS ENTRIES. ONCE TAXIING OUT; WE WERE INSTRUCTED TO CONTACT 'Q' CTLR TO VERIFY DEP RWY; SID; AND FIRST FIX. I THEN ASKED THE CTLR TO VERIFY THAT WE WERE TO OVERFLY EACH OF THE FIXES ON THE SID RATHER THAN SOFT TURNS PRIOR TO THE FIX AND WAS TOLD THAT WAS CORRECT. SO AGAIN WE BRIEFED THE SID PER THE CHART AND MADE SURE IT CORRESPONDED WITH THE FMS. AFTER TKOF; CALLOUTS AND CONFIGNS WERE A BIT SLOW; DUE TO THIS BEING THE FIRST LEG FLYING FOR MY IOE TRAINEE. HOWEVER; WE FOLLOWED THE SID AS DEPICTED AND ON PROFILE WITH AUTOPLT COUPLED TO FMS; AUTOTHROTTLE ON; FLT LEVEL CHANGE ENGAGED; SPD SET AT 210 KTS. AS THE TURN STARTED OVER THE FIRST FIX; I NOTICED THE TRACK DEPICTED ON THE FMS MAP SHOWED THAT OUR TURN WOULD NOT TAKE US OVER THE NEXT FIX WITHOUT MAKING AN EXTREME MANEUVER WITH AN EXCESSIVE BANK ANGLE TO GET ON COURSE. I THEN BROUGHT IT TO THE PF'S ATTN AND THEN NOTIFIED ATC. ATC THEN PROMPTLY GAVE US A HDG; FOLLOWED BY A DIRECT TO A FIX ON OUR FILED RTE. ATC THEN ASKED US WHY WE COULD NOT STAY ON THE SID AND I TOLD THEM THAT THE FMS/AUTOMATION COULD NOT MAKE THAT TIGHT OF A TURN. ATC MADE NO MENTION OF A DEV; AIRSPACE VIOLATION; NOR WERE THERE ANY TA/RA CONFLICTS DURING THIS. ONCE ENRTE; WE WENT BACK OVER THE SID AND DFW SID PROCS AND DISCUSSED WHAT HAPPENED AND WHAT MAY HAVE CAUSED IT; BUT DECIDED SINCE THERE WAS NOT A CLR MISTAKE; WE DECIDED THAT WE WOULD NOT ACCEPT ANOTHER RNAV SID WHEN WE CAME BACK THROUGH LATER THAT DAY. IN SUMMARY; THIS PROC WAS BRIEFED THOROUGHLY 3 TIMES PRIOR TO TKOF; AND ALSO WE ASKED ATC FOR CLARIFICATION ON PROPER EXECUTION OF THE PROC. ALSO; ONCE WE KNEW THAT WE COULD NOT FOLLOW THE SID; I PROMPTLY NOTIFIED ATC WITHOUT THEM HAVING TO BRING IT TO OUR ATTN FIRST.