andrewr I think you need to to read up on how TCAS works. The only thing that is accurate about TCAS is the altitude. Both bearing and distance are best guess worked out by an algorithm using a few assumptions on the signal strength. Generally accurate enough to visually identify the target, however I have experienced seeing a TCAS target to the left of my flight path when in fact we had visual contact with the aircraft and it was to our right. Too many pilots put too much faith in the bearing and distance of a TCAS target. Also seen target jumping around as system tried to work out the correct bearing in relation to us.