but there is NOTHING in TCAS procedure that stops you visually aquiring and avoiding a possible collision before it ever gets as close as an RA.
Well, tell me how many crews maneuver
before a TCAS RA?
I'd guess about 0.0000001%
Unless you're a trained Air Force fast air pilot with interception skills I doubt a pilot can accurately gauge a collision risk.
If every time a pilot looked out and saw an aircraft that looked like it was at co-altitude and risking a collision course and reacted as suggested, there would be aircraft climbing and diving all over the skies.
No I am not "contending" that we sit back and wait for TCAS...but again, with 900 kts of closure for two aircraft approaching head-on, please explain how long the average pilot has to:
a/ see the the traffic
b/ determine whether there is a collision risk, and
c/ make an appropriate maneuver to avoid this collision (all being done visually).