I wonder if somebody could help. I've been using FS for years but only just purchased PMDG B747-400 and getting to grips with programming the FMC. I've read the tutorials and manage to create a plan, the LNAV engages and works fine but VNAV hit and miss and more often that not I end going to ALT Hold to get FL I want. Then the most annoying thing is that on flying from EGLL to BIKF today the Autopilot whilst in VNAV/LNAV or even in ALT/HGD Hold mosts kept disconnecting itself repeatedly it would sometimes go minutes before it did it and later in the flight about every 10 seconds until it drove me crazy.Anybody any idea what I could be doing wrong or is there a patch I don't know of. Any ideas most welcomed.Thanks in advance.

This problem is already discribed and has mostly to do with your joystick.Go to your PMDG-menu and look for the AFDS / AP-Controls-override-options- menu.Make sure these two options are NOT selected!If so a minimal movement of your joystick (even unwanted like spikes) will disconnect the AP.Hope this helps...PS : sign your posts with your real name (as per forum rules!) and there will be more and better solutions from others...

William, that's actually not what controls override does. The AP will disconnect with yoke movement regardless of whether that's on or off. I'm honestly not sure what it does for the yoke, but for the throttles it makes it so your physical joystick throttle will move the throttles in A/T hold mode, which is how it works on the real plane. It becomes an issue only because our joysticks and yokes don't have mechanical servos to ensure that the commanded thrust and the throttle position are always the same.You definitely want to calibrate your joystick and throttle and if that fails try disabling them completely right after you engage the AP. If you're still getting disconnects then something else is wrong with how the FMC/MCP is getting set up. Come to think of it, I don't think you can actually knock the plane out of its AFDS *modes* with yoke motion - you can kick it out of actually having the AP attached in CMD mode, but you should still see VNAV and LNAV on the PFD. I assume you mean it's just disconnecting CMD?

Ryan,I fully agree with you about the throttle.Same with the joystick, but when you accidentally touch your joystick nothing will happen (no AP disconnect) but if you really want to disconnect to interact (with an emergency for example) you have to move the stick with full motion and only then the AP will disconnect.That is how i see the control override option works.