VNAV Crazy Descend

[Guest abrahamchan]

Dear All, Recently when I fly the PMDG744, i discovered the VNAV will descend rapidly at T/D at an V/S of 5000-6000ftpm. The descend path was also unstable. I once installed the PMDG737 wrongly after the PMDG744, and now my computer only have PMDG744 & 744F. Would anyone help me if it's my FMC setting's problem or it's the plane's problem? Would it be the FS passengers add-on that afftect the aircraft? Thank you.

[Tabs 2,790]

Hi, (please sign your name next time)Really need more info here - what altitude, what VNAV constraints were loaded, weight etc... If you were at high altitude it's not unusual to see high rates of descent, but 5 or 6k does sound kind of excessive. The plane was not following the path deviation indicator on the right side of the ND screen?

[Guest abrahamchan]

Hi,The altitude veried as this happened a few times. I used VNAV PTH and aircraft was at light load. Aircraft was following the path deviation indicator. I tried to lower down the cost index and it seemed a bit better..about 2.6k-2.7k ftpm. Another question I would like to ask is that in the past i installed the 737NG wrongly after 744 installed. I uninstalled everything, and now i only use 744+744F. Still, I always have some problems on the 744(like engine sound very low, VNAV SPD engage failure at low altitudes etc..). Would it be the side-effects of the installation crash of 737NG and 747? What can I do to solve this problem? Thank you. Abraham Chan

[Tabs 2,790]

Abraham,1. As long as it's following the PDI the calculation is being done correctly... 2.6-2.7 is perfectly normal, I've seen much higher in the 4-5k range from high up (FL370 and higher). As long as you aren't over or under speeding, the descent (or climb) rate doesn't really matter all that much - if you've got a constant vertical speed rate with no acceleration, the passengers will be none the wiser as to how fast they're actually descending or climbing.2. The 747 shouldn't work at all if you had the NG's PMDGOptions.dll installed. That's the only real shared thing between them that needs to have the newer version there to work with the 747.