Narrative:

While departing dfw using an FMS SID the FMS initiated an early turn that may have resulted in an airspace deviation. The pre-takeoff procedures went normally. The clearance was received and included an FMS SID; the clare 2 with a departure from runway 17R. The SID was recalled from the FMS database and cross checked with the paper chart. The departure procedure was briefed and all company FMS SID procedures were followed. The takeoff and initial climb were uneventful. When approaching the first fix (which is due south of the airport; the next fix is 90 degrees to the east from the first fix) the FMS initiated its turn approximately 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 departure. Nothing was mentioned by ATC at the time. I feel the FMS in the EMB135/145 series aircraft should be evaluated for its ability to make 90 degree turns in the terminal environment. I have witnessed the FMS make painfully wide 90 degree turns in cruise; and I feel this tendency should be corrected prior to terminal operations using the FMS.

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Original NASA ASRS Text

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

Narrative: 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.

Data retrieved from NASA's ASRS site as of January 2009 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.