"who can authorise aircraft in a TMZ to switch off their transponders? "...and how ? Would this mean that everybody would need to have a radio tuned in to a designated frequency ? Cue frenzied feedback about "my glider/parascender doesn't have a radio/no space/already at max weight, etc etc". Suppose it'd resolve the issue of garbling when you have 20+ gliders all circling within a 50 metre radius of each other and all using Mode-S.
Does beg an interesting question though....if you're TCAS equipped, operating in a TMZ, and all the GA in the sector has been told to switch their transmitters off....Who tells the TCAS enabled pilots that they'd better start watching out ?
Seperate point made earlier provides an interesting scenario too whereby you have intensive Mode-S transponding GA below controlled airspace but climbing, at the same time as you have controlled, TCAS equipped aircraftdescending towards the bottom of their operating zone. Would this mean that TMZ buffer zones would be needed around the TMZ's ? That'd then constrict much of GA into an even smaller area. There's likely to be a few nasty crunches under that scenario.