Strikes me that visual acquisition is one of the least reliable of methods of keeping aircraft apart. It's all too easy to sight an aircraft, and then, because of the background clutter or change in motion geometry, lose it again. The most famous
example happened in West Coast's back yard. At least a contact, once on TCAS, tends to stay on TCAS.
Jerricho, what do you expect as a response to your traffic call? Are you using it for reducing standard separation? If so, do you accept "traffic in sight" as the criterion for reducing separation, or do you require a positive confirmation that the pilot of the following aircraft can maintain visual separation?