Hello, I have the most recent patched version of the 747 for FS9, I'm running Windows Vista, and my issue is that when I am in cruise, I have my autopilot on and set to LNAV and VNAV, and every once in a while, my nose will start pitching up and down wildly until I reset the autopilot. If I let it go without intervention, the autopilot switches off VNAV mode and goes to Speed Hold mode. Then the aircraft slows and eventually starts to stall. This wouldn't be so bad, except that I also leave my computer for hours on end sometimes while the aircraft flies and I can't always be there to correct the autopilot. How can I fix this problem so that the aircraft will just fly on its own like I'd like it to?

What is your weather selection? I use a registered version of FSUIPC to smooth winds and pressure, which was required to allieviate wind swings. MSFS WX engine is responsible for almost all disturbances in flight.

I've got ActiveSky 6, however the weather was fairly light on this flight and on flights with every other addon I have, even in more turbulent weather, I have not had this problem, their autopilots fly very smoothly.

The Queen's autopilot is very smooth too, believe me. There's something upsetting her tho and it's usually wx related. Airspeed changes are cause by wind shifts, altitude changes are cause by pressure changes. If these are not happening maybe a screenshot during an incident would help.