Planes are complicated, and you can't test for all n! different things that can go wrong. I think the case that: a) an MCAS sensor is giving incorrect data AN

Planes are complicated, and you can't test for all n! different things that can go wrong. I think the case that: a) an MCAS sensor is giving incorrect data AND b) the data is leading MCAS to set the trim to the max AND c) the plane is going so fast that the force of the air over the elevator is too great to manually override AND d) the plane is too low to temporarily drop altitude to reduce the force on the elevator to allow a manual override I don't think this is an obvious set of things to foresee happening, especially D. It's the same way with software. There's just too many things to think of, and errors that slip through the test cases are inevitable. I've had what I've considered to be pretty thorough test cases and had a bug that was "obvious". I'm not excusing Boeing, but it isn't gross incompetence either.