[scott00]

One key difference is how much time operators have to figure out what's going on before action is necessary. If an aircraft autopilot fails, time before crash is likely measured in minutes, so the pilot taking 10 seconds to snap back into pilot mode still gives a pretty good likelihood of a favorable outcome. In a car, 10 seconds of no or bad driving on the part of the autopilot is pretty likely to cause a collision.

Even so, it's been implicated in crashes, notably Air France 447.