When I activate VNAV nothing happens and the light doesn't illuminate. Any thoughts/support?Thanks.Chris Cole

Did you program the FMC properly? Activated A/T and A/P (although, I think AP doesn't have to be on for VNAV to work).

Hello Chris,Not much info to go on from you so far but as a starting point:To have VNAV available you must have set up the FMC correctly. This is a bit of a process but once you have it organised in your head it is easy.To provide VNAV guidance the FMC needs a minimum of your ZFW, current or expected cruise altitude and a hard SPEED/ALTITUDE waypoint to aim at. To refine it's guidance you add DES WINDS/PRESSURE, ANTI-ICE use etc.What VNAV PATH DES provides is a Flight Idle (Glide) DES from CRZ to a predetermined ENERGY value = a SPEED (Kinetic Enegry) and a HEIGHT (Potential Energy).So, LMK what trouble you are having and I am, sure we can get you VNAVing happily.TTYS,