Originally Posted by
WeeJeem
Call me old-fashioned, but I personally would be more than a tad nervous about using a traffic separation system where the inherent error associated with my estimated ("probable") altitude can vary significantly, depending on a) what satellites my GPS receiver happens to be using at the time, and b) what lattitude I happen to be flying at (and ditto for all other aircraft in the vicinity).
Without intending to advocate for GPS derived altitudes, b) shouldn't be much of a concern. Altitude errors which are a function of latitude would affect all aircraft at the same latitude. And you have to be at the same latitude to collide.