Just a word from an avionics engineer so don't get mad if this is impractical.
TCAS provides a Traffic Advisory (TA) to the crew when it detects a possible conflict. The crew are thus made aware of the conflict some time before a Resolution Advisory (RA) is issued and can locate the threat aircraft on their display. Both crews in this accident would have been aware of the conflict for some time. Might it not be good idea to have crews report Traffic Advisories to ATC whenever they occur? I don't know how often they occur , so maybe in practice, it would cause chaos to have every TA reported. Nevertheless, in this accident, if either or both crews had informed ATC of the conflict when their TCAS systems issued a TA, the controller would have had his attention directed back to the priority area in time to take appropriate action. A Resolution Advisory is meant to be a "Last Chance" warning. Although the TCAS design intent was for Traffic Advisories to give crews time to avoid the need for Resolution Advisories, in practice it isn't always possible for crews to visually acquire the threat aircraft.
Maybe it is now time to include ATC in the warning loop, but I suggest they be brought in at the beginning when a Traffic Advisory occurs, rather than wait for the Resolution Advisory to be issued. Its too late then - once an RA is issued, effective Air Traffic Control has already failed.
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Through difficulties to the cinema