Engineer brains are just a type of neural network too, which also have a probability of putting out bad code. Space exploration budgets run into the hundreds of millions of dollars each and recruit the brightest people on the planet to design and program software, yet there is a long list of projects that failed due to code errors. Mars probes have failed to reach the planet, orbited too low and burned up, crashed into the surface, or landed successfully but later overwrote critical memory due to a flawed software update.

The AI doesn't have to be perfect, but only offer a lower error rate than humans.