As I just came across an article in a newspaper saying that a mid-air crash was avoided because one of the aircraft was equipped with TCAS, I was asking myself if this system was not a standard in all civil aircraft.
In this case a DC9 from Aeropostal, that was enroute from Caracas to Puerto Ordaz received a warning by TCAS. An aircraft of another (not mentioned) airline had a loss of cabin pressure and left its cruising altitude until finally being on the same level as the VH aircraft.
Due to the warning system the VH pilot could react and change his route to avoid a crash.
I am sure that all new aircraft are equipped with TCAS, but there seem to be some older ones that don't have TCAS. Why is there no international regulation forcing ALL airlines to put the system in their older aircraft ?
Here the source (in spanish):