Even up to a CAT IIIB approach, pilots still have a decision height where you go around if you don't see the runway or the approach lights. That's not very high

Even up to a CAT IIIB approach, pilots still have a decision height where you go around if you don't see the runway or the approach lights. That's not very high for CAT IIIB (15m), but pilots are trained to abort and are basically waiting with their hands on the throttle. You can find stories of people aborting landings when already over the threshold. Here's a sim of some pilots aborting a CAT IIIB. https://m.youtube.com/watch?v=o9s2jQixK9w https://m.youtube.com/watch?v=o9s2jQixK9w Additionally the tighter the tolerances on the landing, the closer everything has to agree. In better weather there are also physical glide slope indicators like the PAPI lights. These are the four lights to the side of the runway, if you're too low they show all red, too high they're all white. You want half red half white. They're entirely passive.