Hi again,How do you get the work VNAV button,i make a flight plan then take off but when i click on VNAV does not work FMC says VNAV Disconnect, am i missing something? LNAV works fine it will engage.

Hi, sorry this isnt much of an answer, but re-check your flight plan, especially your cruising altitude + N1 & takeoff pages, Ive had the same problem in the 737NG quite a few times but never in the 747. Im sure its a discontinuity between the set altitude in the FMC and the AP MCP ALT, maybe it cant reach the correct alt of the first way point in time?Ill have a look in the manual see if i can figure it out!Paul

Hi,I have made dozens of flights without having this problem - until last weekend. Flight from EGPF - EGHI I had the same problem couldn't get VNAV to engage. When I checked the FMC, it had not calculated any altitudes or flight levels even though I had selected FL300 for the cruise. No TOD was marked and no fuel predications either if I remember rightly. I just assumed it was a computer error or maybe a simulated FMC failure (is this modelled ?) and ignored it and flew the thing manually so far as heights go.Hasn't happened since so maybe just one of those things !!