Hello,I have recently (on two recent flight....744X) experiencing VNAV problems. With autopilot, FD, LNAV all engaged in mid-flight, the plane does not keep the programmed altitude. Neither will it even respond to ALT HOLD command. I'm currently on a flight to WMKK at a programmed initial flight level of FL330. However, about an hour into the flight, this wield thing started happening and has been going on for the next three hours. I have checked and cross checked everything and cannot pinpoint it to anything right now. I should mention that, I'm flying at normal rate (real-time), with FSUIPC 4.20 (REG), ASX/XG,XPAX and PFE. Again my other previous 50 flights were all uneventful. Any help will be appreciated. ThnxGus

I can now confirm that, whatever that is happening is NOT weather related (the notorious wind shift). I see that the entire vertical profile of the flight automations have "broken down". The aircraft keeps joggling up/down the vertical axis without control. It keeps going down to FL310 or as high as FL385 although it's to fly at the programmed level of FL330. It will not respond to changes like FLCH or the VERT SPD 9no problems with LNAV and A/P). I have not done any modificationS to this add-on and as I said previous flightS were all successful. This happens to all engine variants. Please help if you know the reason as even with weather cleared and off this happens. ThnxGus

You eliminated the common problem by clearing the wx... now a screen shot or two might help get a feel for the problem you're having.

>You eliminated the common problem by clearing the wx... now a>screen shot or two might help get a feel for the problem>you're having.Dan,I have never taken a screen shot before, so that might be a challenge. In any event, after several hours(5-HRS of flight time) of this see-saw affair, I decided to disengage the autopilot, manually climbed to the actual flight level (FL350....the aircraft at this point was descending to FL280 because it did not respond to the step climb command to FL350 from FL330), and then after reaching there, I leveled and flew it for awhile still manually. After few seconds, I re-engaged the autopilot and everything was fine for the remainder of the flight. I will see what will happen on my next flight and report. ThnxGus