The problem is, the computer is designed by the human and hence has Human errors. You can’t elminiate human error until the lord god Buddha himself pilots airplanes.
Driverless cars may well become the norm but the thing is that when they go wrong, they can just stop... the first time a pilotless plane goes wrong there’ll be no one flying them. As an analogy, I’m pretty sure we could perform major surgery on someone with a robot - but if it got it wrong, would you be prepared to undergo the knife of one in the future?
As long as safety-critical systems continue to be built by humans, there’ll be a human nearby to takeover when needs be. Automated Cars/trains/and similar ‘simply switch off’ systems are usually more of an inconvenience when they go wrong, rather than a pile of bodies.