radalt and weight on wheels
I'm not an RA expert, but on many aircraft the "Weight on wheels" discrete (boolean) is broadcast to almost all avionics. A simple enhancement might be if the RA notices negative or very low height for, say, 10 sec without "Weight on wheels" true, it shuts itself down as unserviceable?
I don't know whether this would have prevented this accident, but it would have made the AT disconnect explicitly.