I also got this once. It was a while ago so I don't have the details anymore. I selected the arrival while in cruise, then got a VNAV DISCONNECT message. No T/D or E/D info on VNAV pages, and nothing shown on the MAP, and no speed/alt in LEGS.

I am also getting this on everyflight although i save quite a lot. I get VNAV disconnect everytime i change a star or even change the cruise altitude. There is no way to re-engage vnav and i've checked every page on the cdu, its really weird. Also when i then go and put in a new FL in the clb page it will say invalid entry to everything ie FL400 or 40000. Its like the CDU has given up and doesn't want to play anymore . Regards, Ceri

Happened to me tonight on a flight from KSFO to KPHX. Also, last night from KCLT to KDTW. Tonight, the VNAV didn't arm from takeoff. Last night, it just disconnected mid flight with no changes made to the MCP or the FMC. Strange indeed. I'm looking for any more insight to start my investigation. Is anyone else using FSCommander?

Hi there.Please need some help.Not with the VNAV.But Updating the CDU.I think there is some issue updating the CDU.It happen all the time.1) http://forum.avsim.net/topic/354147-cant-change-runway-in-flight/2) http://forum.avsim.net/topic/354557-cdu-pages-not-updating/

I don't think this is correctly modeled, but you might be able to fix it by "re-cruising" the FMC to your current altitude.So, you might get a runway change, execute it, and then get a VNAV disconnect. If that happens, I'd hit ALT HOLD, go to the FMC cruise, select your current altitude and execute it, and then try VNAV again. The "real" sims sometimes have issues with this as well, and we often need to re-cruise it, especially if we're doing multiple approaches and repositions.

I had a similar but not exact thing happen last night. I was flying LGA DCA on the Clipper1 arrival. I changed the BAL xcross to 10000 per the published STAR but the CDU failed to update the subsequent waypoints (and yes I hit exec), and I got the "unable next altitude" message even though I was well able to descend to the correct altitude. I was able to fly the arrival fine but only with vs and fl chng. This is disconcerting esp flying vatsim since alt constraints can vary and reminds me of the difficulties with the Wilco airbus. I wonder if the CDU logic needs to be looked at more closely.Marc Fourneau

BTW I didn't notice whether vnav had disengaged or not since I switched to vs mode.

I don't think this is correctly modeled, but you might be able to fix it by "re-cruising" the FMC to your current altitude.So, you might get a runway change, execute it, and then get a VNAV disconnect. If that happens, I'd hit ALT HOLD, go to the FMC cruise, select your current altitude and execute it, and then try VNAV again. The "real" sims sometimes have issues with this as well, and we often need to re-cruise it, especially if we're doing multiple approaches and repositions.

Hi there.This is also happening at my end.Also same with FORCAST page, not able to update it.PMDG any solution to this issue?I hope it will solved ASAPThanking YouSameer Mankame