Here’s a fact: Machines can do things infintely better than humans can.
Here’s another fact: The more machines we add to the cockpit the safer air travel will be.
Here’s another fact: Humans can also do things and make decisions machines can’t.
Conclusion: We must add both. Only machines isn’t as effective as it could be. Only humans is basically the same as a flying tube dedicated to slaughtering people. Both together, obviously with a lot more machines than humans, can achieve the best safety.
For example, US Airways flight 1549.