I think the way it would work (could be way wrong as well, just an idea), is that if for whatever reason the wire control lines were not working, it would automatically kick in the wireless part of the system. i.e it is dead until it knows that the wire control is out of action, OR, there was some other hardware failure or request to kick it in, all over the hard physical way, so that it would not be open to terrorist/nutter threats.
I'm afraid that's way too simplistic. You cannot hand over from one control system to another, either manually or "automatically" as you put it, unless and until you are sure that the secondary/standby system is working correctly.
This is a basic system design problem.
Q. How do you know that the standby system is working?
A. By running it continuously, off-line, and comparing its parameters with those of the primary system.
followed by:
Q. When the primary system gives failure readings, how do you know whether it's giving a false negative or the standby is giving a false positive? Think of the consequences if your 'automatic' control makes the wrong decision...
Bear in mind also
AndoiP's very valid second paragraph. There
will be intermittent failures of the radio system, and these should correctly be ignored during 'normal' operation when the wired system is working. But this apparently flawed arrangement doesn't lend confidence to switching over to it when 500+ lives are on the line.
The world isn't ready for this.