I can't help pointing out that the new ADS-B mandate would not improve the safety of this situation at all. This is part of the lie about ADS-B.
Secondly, have I missed something? Why is there a focus about calls on CTAF and monitoring CTAF frequencies when all the aircraft were outside the CTAF zone at the time? Surely this is a failure of all concerned to be correctly on the AREA frequency and making calls. I would have expected the Metroliner to make a number of descent calls on the AREA frequency. And I would have expected the C152 to change its single VHF radio to AREA frequency at the CTAF boundary. If this had happened, wouldn't they have both talked to each other?
Surely this highlights:
a) That CASA / ASA discouraging non ATC related calls on area frequency is a source of confusion about what frequency is best to have an aircraft to aircraft dialogue meaning that aircraft outside the CTAF are using it to stay off the area frequency and
b) the reality is that our airspace really requires 2 radios now.