Hi All,Just now I was flying from Suriname to Brazil in the 600. Weather was calm, no external engine. The plane was flying on AP in LNAV-VNAV mode and perfectly on course.When I approached my first waypoint the plane started to make small corrections from left to right to left and so on. There was no obvious reason for this behaviour, fuel tanks were balanced, engines were running normal. When getting closer to the waypoint the s-turns became slowly more steep and the course deviations were increasing as well. At a certain point I disengaged the AP and I passed the waypoint hand flown.Then, enroute to the next waypoint I engaged the AP again in LNAV-VNAV and everything went smooth from there on.Has anybody any idea what has been going on?Best regards,Herman.

Hi All,Just now I was flying from Suriname to Brazil in the 600. Weather was calm, no external engine. The plane was flying on AP in LNAV-VNAV mode and perfectly on course.When I approached my first waypoint the plane started to make small corrections from left to right to left and so on. There was no obvious reason for this behaviour, fuel tanks were balanced, engines were running normal. When getting closer to the waypoint the s-turns became slowly more steep and the course deviations were increasing as well. At a certain point I disengaged the AP and I passed the waypoint hand flown.Then, enroute to the next waypoint I engaged the AP again in LNAV-VNAV and everything went smooth from there on.Has anybody any idea what has been going on?Best regards,Herman.

FSUIPC installed ?

Yes, why? This was a first time in many flights. Only software change in the past weeks was installing TrackIR last Saturday.

Those are called s-turns. There is plenty of info on this forum. Search for turbulence and fsuipc.http://forum.avsim.net/topic/361731-autopilot-will-not-track-lnav-or-hdg/page__view__findpost__p__2254580

Lots of possible reasons in that thread. I'll check them one by one. Thank you!

Disabling gust and turbulence in FSUIPC did the trick for me. Succes.