Flight Safety:
Interesting thoughts...
all the planes I have flown with TCAS require that the transponder be selected to the TCAS/TA/TA position...if something goes wrong with the transponder, the TCAS drops out and a warning message occurs.
So, in this case, did the Legacy crew notice any TCAS problems? Which might have indicated transponder problems.
also, why didn't ATC notify Legacy of intermittent transponder?
In the USA, if radar contact is lost with a flight, ATC is duty bound to inform said flight: RADAR CONTACT LOST
I do think there may be a "mechanical" component to the collision, and mentioned earlier there might be an intermittent fault in the cable between transponder and antenna...a good transponder and a bad antenna= no transponder for practical purposes.