737 VNAV inaccuracy
Ok, when you set up the fmc for a VNAV descent, with reasonable descent fcst winds and LNAV descent restrictions, why is it that very often after a 'direct to' VNAV gets into a pickle? It often says you are 2000ft or so high or low, when using simple arithmetic you know you are on pofile?
I don't mean when you have put some very restrictive hard altitude that has been lost with the direct to, or unrealistic predicted winds, just when an update to the LNAV track causes VNAV to lose the plot. Any comments?
PP