activewaypoint.
What kind of aircraft are you flying?
I'm currently flying a GV with the Honeywell SPZ 8500 system, and the V-NAV works pretty well. I do find it a little rough in entry so I usually start with a 1000 fpm descent, with VS, about 5 miles prior to the FMS calulated TOD point, and when I intercept the calulated vertical path, engage V-NAV. If a speed restriction is included with a specified crossing restriction, you will have to descend quicker then profile in order to make the speed/altitude crossing.
I've flown other aircraft with Honeywell FMS's (F900A, B, EX and GIVSP)and they operate in the same manner.
