I need some help with the Vnav. I very new to this so I'll try to explain what was going on during my flight. My flight was from CYYZ to KSEA I loaded the flight plan the altitude was fl280 I set the fmc up and prepared for take off. I armed the Lnav and Vnav set my v2 speed and set an altitude of 5000 in the MCP.I increase throttle to 70 and then engaged the to/ga, after 1000 agl I engaged the autopilot.This is where I ran into problems, the aircraft just kept climbing,speeds were all over the place. I just let it be for awhile it would try to climb then it would kind of stall, then it would speed up again, the max airspeed I got was 200 KIAS ,it was constantly switching between Vnav and FLCH. It eventually reached FL280 but it still was climbing,so I disengaged the Vnav and selected FL280 Hold in the MCP but it still was climbing. I have been studying the manuals I checked and double checked the FMC. Did I miss a step somewhere. I realize that it may be hard to help with the info that I gave but if anyone See's something or has any suggestions at all I would greatly appreciate it. Thanks,Ian

Ian,In PMDG options, make sure you have the two Override boxes unchecked - sounds like your physical throttle may have been blocking the autothrottle...

Ian,Yes, uncheck BOTH override boxes, Throttle AND controls in the 747's PMDG Options, AFDS section. This problem was causing me no end of grief in trying to use the autopilot. You would get partial disconnects of both the A/P (primarily pitch control) and A/T (one or two engines not following A/T commands) and NOT getting a warning alarm of any sort other than this erratic behavior.What's funny, this problem doesn't occur when these boxes are checked for the PMDG 737NG series.Kim

Great thanks so much guys that was the problem. Ian

Just a suggestion to PMDG. You may want to put this problem and workaround on PMDG OPS, unless I missed it there. It seems to have cropped up recently and was really frustrating to figure out what was causing the problem. Trying to figure out whether it was caused by pilot error, Windows, FS9, FSUIPC, some other add on or even the PMDG 747 itself took a lot of work, and dumb luck.Also, you may want to send Zane767 an email (I think he corresponded with you) so he can get his PMDG 747 working again. He sounded exasperated last time he posted.Kim