OK, I think that PMDG 747 is great, but I have a problem. I know how to work with Flight Management Computers, and I haven't had this problem with any other aircraft, but I can't engage VNAV on the 747. I program everything, and when I press VNAV, I get an "unable crz alt" messege. What is wrong?

Did you program an altitude that is obtainable, given the weight of the aircraft? I.e. did you assign a cruise level of FL410 when your aircraft weighs 800,000 lbs?You may need to enter an obtainable altitude and perform step climbs along the route.

Here's something quick to check. Look at Vnav's cruise page. At the bottom of the page are the "OPT" and "MAX" cruise altitudes the FMC has calculated. Is your cruise altitude < or = "MAX?"

yes guys, i did set the cruise alt to FL330, when I weighed only 500,000 lbs. My opt that time was FL380, so I switched to FL380 on the MCP and the FMC, but it still displayed the same messege. I can get the VNAV to work on the LDS767 and the PMDG737NG/8/900 but I can't get it to work on the PMDG747. I don't know what I'm doing wrong.I program all the pages, from the performance page, then the takeoff, route, VNAV, etc.

>yes guys, i did set the cruise alt to FL330, when I weighed>only 500,000 lbs. My opt that time was FL380, so I switched to>FL380 on the MCP and the FMC, but it still displayed the same>messege. I can get the VNAV to work on the LDS767 and the>PMDG737NG/8/900 but I can't get it to work on the PMDG747. I>don't know what I'm doing wrong.I program all the pages, from>the performance page, then the takeoff, route, VNAV, etc. Is it a particularly short route? I.e. is it long enough to even get to FL330?I'm just trying to put together scenerios where you can't get to the requested FL. It's entirely possible for teh FMC to say the optimum alt is FL380, but you won't have enough time to get to that level before the descent is commanded.

Well, the flight was around 500nm.

Check the second page on VNAV, where the destination is listed, and see if there are any anomalies. I use FSPassengers, for example, and although I load fuel through the PMDG loader, I have to load cargo and pax through FSP, and in that case, for climb at least, VNAV is partially unusable, and under the destination ETA and fuel on the 2nd VNAV page it shows something crazy like -222222. I have to use FLCH to get up to the ALT, and then engage VNAV for the rest of the flight. A little quirk of getting the two progs to work together.

Yes, I also use FsPassengers. And it did show something crazy like -2000000. But after that flight, I loaded the plane again, without FsP, and it wouldn't work. I'll have to try it again without FsP. I think I have gotten the VNAV to work before in the 747. Anyways, if all else fails, I'll just reinstall the Quenn.