Originally Posted by slim_slag
That document looks like it was once used to justify Mode S for airline use. Fair enough. What they appear to have done is decided it's time to force it on the rest of the world, and added a load of stuff about Airproxes (used over 60 times but not defined once).
Take out all the legitimate stuff for airlines and Mode S and there is nothing left of substance except the possible need for GA to have mode C near busy airports. They said you only needed Mode C too, not Mode S
That may all be the case, but don't count on the CAA coming to their own conclusions themselves. Help them see it.