I wouldn't say aircraft rely on TCAS advisories to avoid other traffic. TCAS is there as a support. Avoiding other traffic involves a lot of different systems including ATC and of course the pilots eyes. For a UAV to employ the same techniques it would require a forward facing camera, a radar (very heavy equipment for a UAV to carry) and an air-ground radio relay to carry local ATC broadcasts to the UAV operator. All these additions carry a weight and cost penalty and ultimately some one will have to be on the ground listening to ATC and watching radar. Of course, the UAV will be programmed to disseminate radar information and respond to TCAS, but it will still need someone on the ground to control the UAV in response to an ATC transmission. And therefore, the question is this: If the UAV requires even more complex technology than is currently in use AND a pilot of some description on the ground where is the cost benefit of a UAV?
Flying in war zones is great, if it's shot down nobody dies, but in civy space will a UAV cost more to operate than its equivalent manned aircraft? I think it would, in which case, in the cost/benefit world we live in who would buy and operate one?
FLR