Modesto2 From United States of America, joined Jul 2000, 2730 posts, RR: 6 Reply 4, posted (12 years 11 months 6 days 19 hours ago) and read 1785 times:
It's probably because you reached the runway threshold. If you've noticed, the same thing happens when the NAV function is executed on the autopilot. When crossing above a VOR, the plane will rock left and right. I guess it's a little confused? Not quite as smooth as a human...that's why YOU have to fly it...not the computer!