Narrative:

Taking off on TRISS2 RNAV departure runway 17R out of dfw; the aircraft started to bank to the right instead of staying on the RNAV course. This happened about 500 ft as soon as we engaged the autoplt coupled to the FMS navigation. We corrected back on course as soon as it started to bank to the right. We followed our RNAV departure procedures according to the company manual. We don't know what caused the aircraft to deviation from the RNAV departure. ATC inquired about the deviation and we told him we were correcting back on course.

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Original NASA ASRS Text

Title: E170 FLT CREW RPTS AUTOFLT SYSTEM TURNED EARLY AND IN THE WRONG DIRECTION ON TRISS2 RNAV SID FROM RWY 17R AT DFW.

Narrative: TAKING OFF ON TRISS2 RNAV DEP RWY 17R OUT OF DFW; THE ACFT STARTED TO BANK TO THE R INSTEAD OF STAYING ON THE RNAV COURSE. THIS HAPPENED ABOUT 500 FT AS SOON AS WE ENGAGED THE AUTOPLT COUPLED TO THE FMS NAV. WE CORRECTED BACK ON COURSE AS SOON AS IT STARTED TO BANK TO THE R. WE FOLLOWED OUR RNAV DEP PROCS ACCORDING TO THE COMPANY MANUAL. WE DON'T KNOW WHAT CAUSED THE ACFT TO DEV FROM THE RNAV DEP. ATC INQUIRED ABOUT THE DEV AND WE TOLD HIM WE WERE CORRECTING BACK ON COURSE.

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.