E135 ON RNAV SID FROM DFW TURNS EARLY AND SLOWLY AND EXCEEDS TRACK PARAMETERS. RPTR SUGGESTS THE PERFORMANCE IS ENDEMIC TO THE FLEET.

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WHILE DEPARTING DFW USING AN FMS SID THE FMS INITIATED AN EARLY TURN THAT MAY HAVE RESULTED IN AN AIRSPACE DEV. THE PRE-TKOF PROCS WENT NORMALLY. THE CLRNC WAS RECEIVED AND INCLUDED AN FMS SID; THE CLARE 2 WITH A DEP FROM RWY 17R. THE SID WAS RECALLED FROM THE FMS DATABASE AND CROSS CHKED WITH THE PAPER CHART. THE DEP PROC WAS BRIEFED AND ALL COMPANY FMS SID PROCS WERE FOLLOWED. THE TKOF AND INITIAL CLB WERE UNEVENTFUL. WHEN APCHING THE FIRST FIX (WHICH IS DUE S OF THE ARPT; THE NEXT FIX IS 90 DEGS TO THE E FROM THE FIRST FIX) THE FMS INITIATED ITS TURN APPROX 8 MI FROM THE FIX. THIS SEEMED UNUSUAL; BUT WE UNDERSTOOD IT TO BE PART OF THE FMS SID. THE TURN WAS GENTLE AND INTERCEPTED THE OUTBOUND FROM THE FIRST FIX WITHOUT DIFFICULTY. HOWEVER; THIS SLOW TURN (COMMANDED BY THE FMS) WAS MOST LIKELY OUTSIDE PROTECTED AIRSPACE ON THE DEP. NOTHING WAS MENTIONED BY ATC AT THE TIME. I FEEL THE FMS IN THE EMB135/145 SERIES ACFT SHOULD BE EVALUATED FOR ITS ABILITY TO MAKE 90 DEG TURNS IN THE TERMINAL ENVIRONMENT. I HAVE WITNESSED THE FMS MAKE PAINFULLY WIDE 90 DEG TURNS IN CRUISE; AND I FEEL THIS TENDENCY SHOULD BE CORRECTED PRIOR TO TERMINAL OPS USING THE FMS.