There's a fundamental difference between the two. Airplane autopilots are basically scripted, and operate fully within the parameters set by the pilot. There is almost no intelligence, and very little adaptivity there. The pilot needs to reprogram the autopilot manually when the flight plan changes, for example. Flight conditions can change in many ways that require the autopilot to be reprogrammed, reconfigured, or even switched off. Airplanes have actually crashed more than once because the pilot configured the autopilot incorrectly.
I don't know much about trains, except that fully automating without adapting all the rail infrastructure is more difficult than you would imagine, for example because there is basically no standardization in how semaphores are placed, for example.
This is a long way off from the world of "Enter the destination from my garage, take a nap, and wake up an hour later at my destination," of "Full Autonomy." There is a distinct inflection point of utility where Autonomous vehicles require you to be paying attention to take over in emergency, and the point at which that is no longer required.
I thought both were already highly automated?