30 seconds to go
I just spotted this in Ghostflyers post,
When you get an RA, you are 20 to 30 seconds from collision.
You should have already had a TA ('Traffic,Traffic') which is 35 to 45 seconds from possible collision.
Mode C and S transponders will also give you height information.
Displayed as the difference in hundreds of feet between you and the target, it also says + or - so you know if it's above or below.
If you both have Mode S the RA manoeuvre will be co-ordinated.
If the other aircraft has a transponder but no TCAS, yours still works.
regards