I'm sorry but hitting the engine block of a C152 at 300mph is going to have a seriously negative impact on the controllability of an airliner.
Mode S is the answer and mandatory Mode C would be a leap forward. Think about it chaps. The last ten years alone have seen Ryan and Easy alone put an extra 150 Boeings into UK skies. Everything is expanding at breakneck speed and its only going to get worse. What's a bit ropey now will be unacceptable in another 10 years time. And I include the use of airspace by the fast jet community.
The US has universal RIS everywhere. We don't have that and we never will. Given the topsy turvey piled on top of itself complex airspace we have to live with on this congested Island it wouldn't work very well anyway.
See and avoid is rubbish. An invention from the 30's that relies on Big Sky Theory. The hours I've spent trying to spot 757s coming head on at 10 miles and not being able to... Just because YOU don't fly anywhere near any other type of commercial flying doesn't make a good argument for saying therefore nothing should be done nationwide.
I'm all for keeping the cost down. Lets have Mode S for GA and lets get the CAA to subisidise it and levy a special quarter percent tax on every airline ticket for a year. That would cover it all easily.
Cheers
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