The instrument landing system necessary for auto landing is out of commission in SFO on runway 28L, due to construction, so the Asiana pilots had to make a manual landing, something they rarely do. That is why thy crashed. I'm on the road at the moment, typing this on my phone, I'll give more details when I get home. I'll be making a manual landing at LAX tomorrow, about 2pm local time. Be sure to watch CNN, I'll wave to you Ding!