Greetings
Thanks Rainboe
RTA was invented by Smiths (grey box) ahead of anybody (in fact the smiths FMS is the most advanced) and its RTA was/is valid for any flight phase with a 6 sec precision, on top of that you have an RTA window, to be used for example if you are Oceanic (+/_ 3 minutes )
IT is only at a later stage that ICAO saw a good tool for FANS, and for timed Approaches.