I am not able to automatically intercept the glide slope. I understand that in "nav" and "app" mode on, the nav1 radio set to the prescribed ils frequency and active (I hear the morse code beeps), and at prescribed ailtitude for intercepting the slope, the plane should automatically intercept the glide slope (and cause the "alt" light to go out) and begin the descent. I can't get this to work. First of all, the plane will not track the approach (autopilot on) unless in "gps" mode. As soon as I press "nav" the plane stops tracking the approach. When I expect the plane to automatically capture the glide slope, it just keeps on going at prescribed altitude. If it makes any difference, I have the "hdg" set to the runway bearing and I have armed the spoilers. What am I doing wrong?