Narrative:

I was PIC on a non passenger flight rom dfw to bna. My copilot was the PF in the left seat and I was the PNF in the right seat. We were cleared to depart runway 17R from dfw on the TRISS2 RNAV departure. Both of us verified the programming of our honeywell nz-2000 FMS. We had runway 17R as the departure runway and the TRISS2 departure in the box. Before switching to tower; ground control asked us to verify our FMS departure runway and the first waypoint. We verified runway 17R and that our first waypoint was navye. Ground said that was correct and told us to contact tower. The PF said that she would select navigation on the mode selector and the flight director was in the FMS or LNAV mode. At about 1100 ft MSL that command bars commanded a right turn and the PF followed the command bars. After only going into about a 5 degree bank the command bars turned left to follow the 153 degree course on the departure. 30 minutes later while en route; center gave us a phone number for the dfw tower east and told us to call. On arrival at bna; I called and talked to a controller and she explained that the computer showed our short right turn after departure. She also stated that they had had other similar deviations recently from other aircraft on the same runway and SID. In conclusion; I know we had our FMS programmed correctly and I know that the flight director briefly commanded the right turn. On RNAV arrs and departures a pilot relies on the FMS and the flight director. I think there is possibly a software problem with the departure and transition. At no time was any aircraft separation compromised.callback conversation with reporter revealed the following information: both rptrs confirmed the aircraft was light and did reach the required altitude while still over the runway proper. They described the flight director commands as first indicating a right turn and about the time they initiated the response; the command was reversed to a left turn. Both felt this was likely the result of the FMS pursuing the 'course' inbound to triss which was to the right of the aircraft when they satisfied the conditional fix altitude requirement of at or above 1080 ft MSL.

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Original NASA ASRS Text

Title: C560 FLT CREW TAKING OFF ON RWY 17R ON TRISS RNAV SID FROM DFW MAKES INITIAL TURN TO THE RIGHT VICE LEFT TO INTERCEPT THE 153 DEG COURSE IN NAVYE.

Narrative: I WAS PIC ON A NON PAX FLT ROM DFW TO BNA. MY COPLT WAS THE PF IN THE L SEAT AND I WAS THE PNF IN THE RIGHT SEAT. WE WERE CLRED TO DEPART RWY 17R FROM DFW ON THE TRISS2 RNAV DEP. BOTH OF US VERIFIED THE PROGRAMMING OF OUR HONEYWELL NZ-2000 FMS. WE HAD RWY 17R AS THE DEP RWY AND THE TRISS2 DEP IN THE BOX. BEFORE SWITCHING TO TWR; GND CTL ASKED US TO VERIFY OUR FMS DEP RWY AND THE FIRST WAYPOINT. WE VERIFIED RWY 17R AND THAT OUR FIRST WAYPOINT WAS NAVYE. GND SAID THAT WAS CORRECT AND TOLD US TO CONTACT TWR. THE PF SAID THAT SHE WOULD SELECT NAV ON THE MODE SELECTOR AND THE FLT DIRECTOR WAS IN THE FMS OR LNAV MODE. AT ABOUT 1100 FT MSL THAT COMMAND BARS COMMANDED A RIGHT TURN AND THE PF FOLLOWED THE COMMAND BARS. AFTER ONLY GOING INTO ABOUT A 5 DEG BANK THE COMMAND BARS TURNED LEFT TO FOLLOW THE 153 DEG COURSE ON THE DEP. 30 MINUTES LATER WHILE ENRTE; CTR GAVE US A PHONE NUMBER FOR THE DFW TWR EAST AND TOLD US TO CALL. ON ARR AT BNA; I CALLED AND TALKED TO A CTLR AND SHE EXPLAINED THAT THE COMPUTER SHOWED OUR SHORT RIGHT TURN AFTER DEP. SHE ALSO STATED THAT THEY HAD HAD OTHER SIMILAR DEVS RECENTLY FROM OTHER ACFT ON THE SAME RWY AND SID. IN CONCLUSION; I KNOW WE HAD OUR FMS PROGRAMMED CORRECTLY AND I KNOW THAT THE FLT DIRECTOR BRIEFLY COMMANDED THE RIGHT TURN. ON RNAV ARRS AND DEPS A PLT RELIES ON THE FMS AND THE FLT DIRECTOR. I THINK THERE IS POSSIBLY A SOFTWARE PROBLEM WITH THE DEP AND TRANSITION. AT NO TIME WAS ANY ACFT SEPARATION COMPROMISED.CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: BOTH RPTRS CONFIRMED THE ACFT WAS LIGHT AND DID REACH THE REQUIRED ALT WHILE STILL OVER THE RWY PROPER. THEY DESCRIBED THE FLT DIRECTOR COMMANDS AS FIRST INDICATING A RIGHT TURN AND ABOUT THE TIME THEY INITIATED THE RESPONSE; THE COMMAND WAS REVERSED TO A LEFT TURN. BOTH FELT THIS WAS LIKELY THE RESULT OF THE FMS PURSUING THE 'COURSE' INBOUND TO TRISS WHICH WAS TO THE RIGHT OF THE ACFT WHEN THEY SATISFIED THE CONDITIONAL FIX ALT REQUIREMENT OF AT OR ABOVE 1080 FT MSL.

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.