I work with rail safety SW. We only need 2 channels (SIL4) since emergency brake is always an option. It's possible to use 2 flight computers if they have internal safety redundancy such as lock step. If so 2 computers is just fine. Reading this article it seems they are not. OMG!
For relevant and interesting reading I would recommend looking up QF72. It was an Airbus back in 2008 that did a brutal nose dive due to a single faulty angle of attack sensor value. Sound familiar?
It might have been a bit flip due to cosmic (or other) radiation but the root cause was never determined. It's a long story.