It's happened more than once now.In the 747, Vnav and Lnav engaged at FL350 in the middle of a 4h flight, with no weather to speak of, I was woken by the stall warning to see that I had lost 60kias of speed from the programmed 287.The Efis also displays 'Spd' in green but without a surrounding box, and no Lnav indicator at all: 'Cmd' is shown.Shame on me but it's been a while since Ive flown the 747 and I can't remember what it should display, but I do remember that I shouldn't lose speed in level flight.Any ideas please?

Are you using active sky. If you do a search thru this forum you will find quite a few references that are similar to what you describe.CheersSteve

No AS.I searched but I'll have another try.Thanks.