Originally Posted by
ShyTorque
Not true. It requires one aircraft to have TCAS and the other to have a working transponder.
Then still the one without could collide with another one without. I guess you couldnt manage the ”one has, the other dont” in forhand. If it was possible I guess bo one needed TCAS.
Conclusion, every A/C in the country or world should have it. You could make it every A/C minus one if one could guarantee the function on every TCAS.