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 included the FMS clare 2 departure; 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 (a 90 degree turn to the east for our transition); the FMS began a turn approximately 8 miles prior to the fix. It performed a gentle turn to intercept the outbound course for that fix. That turn (while commanded by the FMS; on an FMS departure); was most likely outside the oncourse airspace. Nothing was mentioned by ATC at the time of the deviation. I feel the FMS in the 135/145 series aircraft should be evaluated for 90 degree turns in FMS departure procedures. I have witnessed what I consider to be slow turns to course; and that is unacceptable in the terminal environment. Supplemental information from acn 681514: we didn't think much of it because the RNAV departures must be flown by the autoplt; and that's how the honeywell always operates; so we thought it was normal because of past experience with the honeywell FMS. I think the FMS needs to be re-softwared or fixed to turn correctly. Everybody knows it tries to turn early for any significant turn; and it can barely command a full standard rate turn in normal flight.

Related reports:

Google
 

Original NASA ASRS Text

Title: E135 DEVIATES FROM DFW RNAV SID TRACK. CREW CITES AUTOFLT SYSTEM COMPUTATION OF TURN POINT AND RATE OF TURN AS THE CAUSE.

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 INCLUDED THE FMS CLARE 2 DEP; 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 (A 90 DEG TURN TO THE E FOR OUR TRANSITION); THE FMS BEGAN A TURN APPROX 8 MILES PRIOR TO THE FIX. IT PERFORMED A GENTLE TURN TO INTERCEPT THE OUTBOUND COURSE FOR THAT FIX. THAT TURN (WHILE COMMANDED BY THE FMS; ON AN FMS DEP); WAS MOST LIKELY OUTSIDE THE ONCOURSE AIRSPACE. NOTHING WAS MENTIONED BY ATC AT THE TIME OF THE DEV. I FEEL THE FMS IN THE 135/145 SERIES ACFT SHOULD BE EVALUATED FOR 90 DEG TURNS IN FMS DEP PROCS. I HAVE WITNESSED WHAT I CONSIDER TO BE SLOW TURNS TO COURSE; AND THAT IS UNACCEPTABLE IN THE TERMINAL ENVIRONMENT. SUPPLEMENTAL INFO FROM ACN 681514: WE DIDN'T THINK MUCH OF IT BECAUSE THE RNAV DEPS MUST BE FLOWN BY THE AUTOPLT; AND THAT'S HOW THE HONEYWELL ALWAYS OPERATES; SO WE THOUGHT IT WAS NORMAL BECAUSE OF PAST EXPERIENCE WITH THE HONEYWELL FMS. I THINK THE FMS NEEDS TO BE RE-SOFTWARED OR FIXED TO TURN CORRECTLY. EVERYBODY KNOWS IT TRIES TO TURN EARLY FOR ANY SIGNIFICANT TURN; AND IT CAN BARELY COMMAND A FULL STANDARD RATE TURN IN NORMAL FLT.

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.