Well I myself felt Lookforshooter made some good points! Nice to see some non airline 'SOPS only' folks in here. One thing for sure, I never saw a TCAS unit installed that talked to the ground prox, then argued with each other over who took precidence. The fact is, each unit operates independently...one worries about traffic the other about terrain. Both can and will squak, and have squaked at me in the pattern at mountainous airports at the same time. The fact is if you have a flock of airliners above you, mountains below...the PILOT will have to make a decision, not the box. Obviously there are those in here that are very uncomfortable with that.