Originally Posted by Blumie
I've heard the "traffic, traffic" warning on flights before... so long as the appropriate corrective action is taken
There is no corrective action in response to a TCAS traffic advisory (TA, "Traffic, traffic"). The only time corrective action is applied is when there is a Resolution Advisory which could be any number of directives such as "Climb, Climb", "Maintain vertical speed", "Descend, Crossing, Descend", etc.
when was the last time a commercial aircraft was involved in a mid-air collision?).
There has only been one collision involving a TCAS equiped airliner. An ATC error had the two aircraft on a crossing course at the same altitude. The TCAS gave the appropriate commands but one of the airplanes ignored TCAS and followed the conflicting instructions received from ATC.