The Nav button in the Autopilot will not engage until some form of altitude function (VS or FLC) has been selected first. So you could be hand flying and desire to have the AP takeover and navigate to the next waypoint in the flight plan but Nav will not engage whether or not you've already pressed AP. The light flashes when you press the button, but then goes off the second you let off on the button. However, if you engage VS or FLC and then select Nav, it will engage. Don't have this issue with other X-Plane planes. Please advise on how to correct this. Thanks.