W.r.t.
what if the target is slowly closing with you from the right hand side on a converging course and alongside at your altitude - say half a mile away in cloud? - surely in that instances the potential infringement of the TCAS bubble around each aircraft will cause a RA - where one should climb and one descend - so making a turn should have very little effect on that.
Also, and certainly when two aircraft operate at fundamentally different speeds (e.g. fast jet versus turboprop - as posed by 'garp' ) turning might be inappropriate, but surely
only if the aircraft stay at the same altitude (which is what TCAS is supposed to prevent).
All I'm wondering is that where aircraft are subject to a RA, and as such they should be
diverging w.r.t. their altitudes, would a turn maybe also be of some value - albeit not in all 'normal' RA instances, but instead just perhaps of benefit for those instances when somebody does not comply with their RA - after all, what we're looking at here is a scenario where ATC has failed to keep you apart, TCAS is telling you both to do something but one of you isn't, so what other choices do you have ?
Admittedly though, there's no two ways about it, but due to the 'uncertainty' of the position and movement of each aircrafts respective TCAS bubble - certainly from the perspective of the pilots - it's probably a tough choice as which direction you should turn, if at all.
Of course if the answer is to throw technology at the problem maybe what's really needed is TCAS that's hooked up to GPS (make it compulsory) that way you'll get highly accurate heading, speed, height information and as such the TCAS unit should be able to triangulate a position and so produce a more appropriate RA maybe with 'roll' guidance - uhm, would we then still need ATC ? …… only kidding
Ps. (hence the edit) Ghost - bravo, an excellent posting !!!