It absolutely could be, though. Or you could use half an ethernet port. The idea of a data diode is fine, it's the [lack of] implementation that's at fault.

I mean, those movies being played on the back of seats aren't being run through a serial port. Given the move to an "on demand" scheme, they're not one way. The data diode is clearly meaningless when there's obviously two way traffic.

I don't understand. You wouldn't store the movies on the avionics systems in the first place. That's all inside the infotainment system, on one side of the diode. The things going over the diode would be stuff like current location and tire pressure.

Ultimately the whole point of having these systems connected on both cars and planes is to save weight on wiring. Their data diodes are just vlans.

Which are often insecure, making them not actually data diodes.

Which is where we started.

And still the problem is not the idea of a data diode, it's implementation.