All this and the code needs to be written correctly especially with regards to edge cases. Thousands of planes have been flying around the world for several decades now and we still see unique accidents or slip-ups that have never occurred before.

Think of all the edge cases that need to be accounted for with all the different variables out there from weather to people misbehaving on the plane. It's only going to take one freak accident to have people not want to board a self-flying craft ever again.