Can any of the more technically astute, give a figure as to the point at which a VNAV PATH becomes invalid, when descending NOT on the magenta line.
More specifically, at what displacement is the FMC unable to calculate an
accurate profile reference
Personally, I get out of VNAV as soon as I leave the magenta, but observe quite often, very experienced pilots hanging on to VNAV at considerable displacements. The manuals I have read are mute on this issue.
Only interested in the Boeing case BTW.
Thanks
Maui