Hi,
Have been struggling with this also:
But getting some good help. The 787 is child’s play compared to the 737.
Key to getting the VNAV to work is to make sure that relevant waypoint on the approach have the correct altitudes in them. They will if you use the flight planner. As suggested above check the LEGS and get rid of discontinuities.
The VNAV screen also needs the correct cruise altitude in it… the flight planner defaults to FL350.
Then to descent on the VNAV you need the altitude of the point to which you are descending in the altitude selector. Then it will calculate and execute the T/D time to descent and a green logo will appear on the map.
I am going to get this puppy to hunt as I am still stuck getting the ILS to work but have good instructions.
It flys at better FPS than the 787.