Ok, so I'm flying the 744 from KJFK to KMCO at FL384 and everythings fine. All of a sudden warnings go of all over the place, the AP cancells itself, an FMC message says "max alt FL324" and the plane goes into a vertical nose dive which was unrecoverable.I was flying at M0.876 with plenty of fuel, LNAV & VNAV working fine, along the J121 bewetween SAWED & MILIE (min alt FL180).I got out of it by cheating (slewing) and leveling the aircraft out before I hit the sea at over M1.0. From that point onward I could not reach FL384 again no matter how hard I tried, the AC would just stall at ~FL350 even at 99.8% thrust, flaps 0 degrees, no spoilers and a very horrible grating noise prior to stalling.I managed to land at KMCO by flying at FL300 and making last minute change of runway.Any ideas?Thanks, Paul

Try using the "Opt" altitude on Vnav's cruise page. The airplane gets real touchy up at the "max" altitude. There have been several reports of a very slow decelleration at max alt/cruise power that might really be more MSFS related. The airplane should be able to maintain max altitude/cruise airspeed and cruise power . . . but sometimes, it can't and you'll get just about what your are describing. (That horrible noise is the stall warning stick shaker.) So, it you have FSUIPC (registered) set wind smoothing 'on.' Also set your EICAS thrust limit to 'Climb' (or even 'CON'). That'll give you a little more power if you need it. Your best bet, though, is stay at the FMC's calculated 'opt(imum)' altitude. MD-11 performance tables say cruise power will maintain the FMC's calculated cruise mach at 'max' altitude. I expect the 747-400's FMC would provide the same function. But after all, every airplane has its own personality and this video version is no different. Maybe a patch might fix this or maybe PMDG's model is just too 'real' for it's platform, FS9. That's a good thing. FS10 is coming.

The real airplane is very touchy about max altitude! Make sure that you have the right weights entered in the FMC as to your zero fuel weight here, the plane makes it's alt calculations based on what you tell it. If it is heavier than you say, trouble may ensue. 2000' above optimum is a good practical max, not to be exceeded for most normal conditions. The plane is not at it's best too ar above or below optimum.Tom

Ill try the flight again and pay ore attention to the loading of information into the FMC. Ill let you know how it goes, thanks.Paul