Going Down and Increasing speed

Hi , there. I wrote some codes , which make the camera turn upwards when you press down arrow key , and downwards when you press up arrow key. My system is like airplane system. Simple plane actually , so how can i make my player to speed up if it's going down ( i mean if our character looking down )?

The object's forward vector will tell you something about whether the object is moving up or down, and to what degree. For example, if the z axis is forward and +y is up (as is Unity's convention), then the object is moving downward when forward.y < 0, and the degree to which the object is heading downward is proportional to abs(forward.y). You can then make the speed proportional (in one way or another) to that value.