I know that the GR4 is fitted with Mode S transponders and that these have hex codes allocated for the transponders ID, that these transponders can be linked to an ACAS system and information exchanged between them.
So is it a case here that this part of the GR4 avonics upgrade was only the transponder and therefore the chance to fit some sort of CWS was missed at the time?
If so I think we missing a safety milestone in doing so.