Not sure if this was the right forum or not, there wasn't any specific 747-400X forum. (Edit: Just realised where the 747-400X posts were.)I am having a problem with the 747 holding altitude. With VNAV selected or ALT selected, it will constantly "hunt" for the altitude. What I mean is that it will change the vertical speed up to +/- 1600FPM in order to get to the altitude. When it busts it, it goes the other way. I then change the altitude setting (lower or higher by 2000ft) and this seems to solve the problem for only a few minutes before it starts up again. Some flights this doesn't happen much (about +- 2-300FPM for the whole flight), whilst others it is quite bad (+- 1600FPM). The current flight I am doing I took off at MTOW from VHHH to EGLL with an optimal level of FL297 and a set Alt of FL300. It continued to hunt for the altitude until i descended to FL280 which isn't good for such a long flight. I usually take the 747 for longer flights so I use the load manager and take off at MTOW. The FMC IS set correctly with the weights as given by the load manager. I do fly with FSPax but I disable the weight feature so that the PMDG one handles the weights. I have searched the forums and the only useful thing I saw was to use the PMDG load manager instead of the FSPax one which I have always done. Apart from that, nothing else useful. I have had both head and tail winds of varying speeds as well (3 hrs into flight) so it can't be a weather issue (hopefully). Am using ASE though if that helps.This has happened so often that I am getting a little tired of using the 747 and seems a huge waste of money considering I bought both the 747-400 and 747-8 at the same time. It is as bad as the LNAV not being able to keep path when using real-world weather. Any help would be greatly appreciated and I hope I have provided enough information.Alan Clarke.

I'd the same problem and i didn't solve it yet. When flying i disconeted the MCP and reduced throtle because the aircraft was clibing without control. After leveled , i'd adjust the rate of descend and it worked very well until reach the preseted flight level.

Hard to answer this since there are so many elements but I'll hopefully touch on the two most important causes. Step climbs and baro shifts. If you're too heavy even 25k' isn't going to be possible in certain conditions.Baro shifts. On occasions and probably at least once when on really long hauls I'll see it. It always seems to hit me after the majority of the trip and ruins a 10hr flight. Well, it did anyway. FSUIPC and ASE has smoothing options but sophisticated aircraft model things like "TAT", and that can be a problem. Say the temps shift dramatically, you'll fall like a rock and the only thing you can do about it catch it in time to change your thrust to TO thrust. I've flown several attempts from Sydney to Los Angelos to come back and see my queen taking a bath.If you (or others) experience the second one, make absolute sure your default FSX flight is set to clear weather! NEVER use anything else. When FSX loads it seems to grab bits and pieces it later doesn't want to let go of and for instance if you have thunderstorms set for your default flight then load FSX and change that flight to "Clear" before even getting in the sim, you will see lightning your entire trip. Now, that's just what you can see. You can't see the differences in temp and baro, so when FSX holds onto what it stupidly wants to and you have ASE or anything telling it otherwise, it does attempt to listen but can't, or won't let go of what it already has stored. Even FSUIPC's clear all weather hotkey won't help you there. So just an FYI, set it to clear if it's not already. Once loaded set it however you want. OR, as another option that Grzegorz mentioned here a year ago, was to launch a specific flight by clicking on the saved flight file directly. Unless you changed its properties it will auto launch FSX and bypass the gui altogether saving you time as well. In any case, we've all experienced your issues, but I haven't had them in a very long (knock on wood) time.Hope some of this helps.

I had this problem when I had my FSX on a 2ndary drive, not primary. I don't know why, but reinstalling on my :C fixed it. Also I recently discovered FSX may not be 64-bit compatible. Check out the following site:http://www.microsoft.com/Windows/compatibility/windows-7/en-us/Details.aspx?type=Software&p=Microsoft%20Flight%20Simulator%20X%20Deluxe&v=Microsoft&uid=10&l=en&pf=0π=5&c=PC%20Gaming&sc=Simulation%20%26%20Driving&os=32-bitYou can do a check for yourself.My altitude problem is now resolved, incidentally. But the FSX still crashes from time to time, with "fatal error" or whatever. Other times its flawless.

Sorry but honestly your results are just a placebo effect, I promise. Not that your other drive could issues or your bus, or many factors creating similar, or even worse. On my D:, runs great, with none of the above. I've been around this queen since she was merely a princess and I promise you that I correct on all counts. They aren't just theories, do some digging. Well, the FSX weather was actually my theory a year ago but has now become common knowledge.As for the 32/64 bit compatibility. Again not trying to argue, just educate. That has nothing to do with it. Many of us have even changed OS's to 32 bit XP last year since it was the only way to fix a texture disappearing issue that was later fixed with the high mem fix (thank god). Good luck with your stability though. Anything that works can't ever be a bad thing, that's for sure.