But I still don't know how you get from a technical system description to the operational procedure 'you select TA when you have a problem (such as an engine failure), and this tells other TCAS equipped aircraft that you will not (cannot) manoeuvre if an RA situation occurs.
That comes in the checklist for any situation that leads to shutting down an engine:
4 Transponder mode selector . . . . . . TA or TA ONLY