Narrative:

Our clearance was direct brave intersection, direct ugn. We were on a north course to brave intersection and upon crossing brave intersection we would turn left and track southwest to ugn. In a descent at over 400 KT ground speed, the FMS began a left turn about 6 mi south of brave intersection to intercept the course and proceed direct to ugn. We did not realize that it had turned that soon until the controller said 'we were 6 mi south of brave intersection and to turn right to 360 degrees to avoid traffic.' I acknowledged that we showed proceeding from brave intersection to ugn. On a flight that afternoon, we were cleared on the same route. About 6 mi south of brave intersection, the FMS began to turn the aircraft to the southwest. I went from 'navigation' to 'heading' on the autoplt and continued north a few more mi before turning to the southwest. As soon as the FMS showed us 6 mi south of brave intersection, it went from 'to' brave intersection to 'from' brave intersection. I made several attempts to go 'direct' to brave intersection when less than 6 mi and it repeatedly showed 'from.' the only way to get closer to the fix was to select 'heading' instead of 'navigation.' I believe due to the aircraft's high ground speed and the course change from north to southwest, the FMS began a turn in advance of the fix in order to intercept the southwest course. If the FMS had gone directly to the fix before making the turn, we would probably have been 6 mi on the north side of the course. I believe the major contributing factor was the large course change from north to southwest.

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Original NASA ASRS Text

Title: FMS TURNED ACFT 6 MI BEFORE FIX ON RTE WITH GREATER THAN 90 DEG TURN. ARTCC DIDN'T LIKE EARLY TURN AND RECLRED OVER THE FIX.

Narrative: OUR CLRNC WAS DIRECT BRAVE INTXN, DIRECT UGN. WE WERE ON A N COURSE TO BRAVE INTXN AND UPON XING BRAVE INTXN WE WOULD TURN L AND TRACK SW TO UGN. IN A DSCNT AT OVER 400 KT GND SPD, THE FMS BEGAN A L TURN ABOUT 6 MI S OF BRAVE INTXN TO INTERCEPT THE COURSE AND PROCEED DIRECT TO UGN. WE DID NOT REALIZE THAT IT HAD TURNED THAT SOON UNTIL THE CTLR SAID 'WE WERE 6 MI S OF BRAVE INTXN AND TO TURN R TO 360 DEGS TO AVOID TFC.' I ACKNOWLEDGED THAT WE SHOWED PROCEEDING FROM BRAVE INTXN TO UGN. ON A FLT THAT AFTERNOON, WE WERE CLRED ON THE SAME RTE. ABOUT 6 MI S OF BRAVE INTXN, THE FMS BEGAN TO TURN THE ACFT TO THE SW. I WENT FROM 'NAV' TO 'HDG' ON THE AUTOPLT AND CONTINUED N A FEW MORE MI BEFORE TURNING TO THE SW. AS SOON AS THE FMS SHOWED US 6 MI S OF BRAVE INTXN, IT WENT FROM 'TO' BRAVE INTXN TO 'FROM' BRAVE INTXN. I MADE SEVERAL ATTEMPTS TO GO 'DIRECT' TO BRAVE INTXN WHEN LESS THAN 6 MI AND IT REPEATEDLY SHOWED 'FROM.' THE ONLY WAY TO GET CLOSER TO THE FIX WAS TO SELECT 'HDG' INSTEAD OF 'NAV.' I BELIEVE DUE TO THE ACFT'S HIGH GND SPD AND THE COURSE CHANGE FROM N TO SW, THE FMS BEGAN A TURN IN ADVANCE OF THE FIX IN ORDER TO INTERCEPT THE SW COURSE. IF THE FMS HAD GONE DIRECTLY TO THE FIX BEFORE MAKING THE TURN, WE WOULD PROBABLY HAVE BEEN 6 MI ON THE N SIDE OF THE COURSE. I BELIEVE THE MAJOR CONTRIBUTING FACTOR WAS THE LARGE COURSE CHANGE FROM N TO SW.

Data retrieved from NASA's ASRS site as of July 2007 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.