Can someone please advise the protocol to be followed if dispatching with TCAS RA U/S and subsequently receiving a TCAS TA.
Difficult to say there is a "protocol" - down to the Capt to decide if it is acceptable?
If the other aircraft's Mode C is working but TCAS RA is "U/S", I still see no change as RAs are the result of a mutually agreed action plan (You descend, I climb OK?). If that mutual confirmation of what the other aircraft needs to do isn't there, the working TCAS's RA will not be made, that's a basic design feature I thought.
Not sure I agree? TCAS in 1 ac, and Mode C in other means the TCAS equipped aircraft will avoid by itself.
As above, I think it "improbable" that you would know, or could even have, TCAS RA U/S but TA working? Since you do not avoid on a TA alone, you are left with ATC and visual avoidance as your tools in the box. The airspace environment might lend itself to the probability the other ac is TCAS equipped - and indeed, whether the Capt deems the MEL item acceptable in the first place.