After you file an IFR flight plan and load it into that panel thing with all the buttons by clicking FPL then "Load FS flight plan", how do you get it to follow the GPS nav? I can get it to follow any headings I put in, but I can't get it to use GPS for navigation. Basically I'm trying to get it to say LNAV and for the life of me I can't get it up again. It used to follow that GPS line perfectly, now I don't remember how to get it to work!!

Can anyone help me with this? Thanks!!