You look through the HUD until you see the runway or not. I found in flying the HUD if you are in actual instruments and you get down to decision altitude and you are still in the clouds you can be looking out and the runway will materialize through the HUD. At that point you make your visual transition. So you don’t have to transition from the PFD, look up and see if you see anything, look back down and look back up again. You look through the HUD until you see the runway or not.

Paul provides a thorough description of a HUD system – what it is, how it works and what you use it for.