I have no real experience in aviation but I was on the site just out of curiosity. On This question, the top answer states that attempting to land with only the instruments would almost certainly lead to a crash, which surprised me. I understand of course that it would be much more difficult to land without being able to see the airfield, but what factors make such an extreme difference? Also, some computer systems can land a plane, and obviously such computers are using only instruments - what capabilities or information do they have that a pilot doesn't?
As a secondary question, could there be circumstances where it is relatively safe (or at least not catastrophically dangerous) for a human pilot to land using only instruments? For example, would it make a difference if you were landing on a salt flat, completely level and with arbitrary clear space in all directions? Are there certain planes where attempting a manual landing with only instruments might be practical?
Edit: To synthesize/summarize what I understand from the answers so far:
- Planes capable of automated landing have additional, high-precision instruments that most planes don't have
- Computers are able to continuously monitor many different instrument inputs and respond appropriately to them all, while a human pilot would struggle to manage so many different streams of information simultaneously