Tor,
Yes, TCAS is ACAS (its just the 'brand name' if you like)... the reason the European's haven't used it mandatorily up to now, was that the US bought it in without proper certification/trials etc (in the European's opinion). The original system was thought to have too many glitches. Since then, version 6.04a has come out in the States, and Europe has mandated ACAS version 7 (enhanced, so that there are less false TAs and RAs) for implementation on all commercial a/c in the near future (determined by weight).
411A, behave yourself :-)... I don't know about GPS apps, but there were plenty of sensible reasons at the time for not bringing in TCAS. Saying that, the loyalty to products developed in your own region is prevalent both sides of the Atlantic! That attitude is slowly disappearing, but it has been a problem. There are now a lot of joint FAA/Eurocontrol teams, looking to implement products/concepts on both sides of the pond.
10W, ASAS (Automatic Separation Assurance System), using ADS-B, will NOT be a replacement for TCAS. Although the Americans are trialing a conflict detection and resolution system within this system (under their SafeFlight 21 programme), it is not thought that the 'safety net' of TCAS will be lost. In fact, it is a large bone of contention as to how much duality there can be between the two systems (in terms of processing data, and displaying it).
For more info on the above, there's tons of websites around including:
http://www.faa.gov/safeflight21/ http://www.ads-b.com/Content/index.htm
Also, a quick note on ACARS/FANS. As 10W said, ACARS is one version of an air-ground datalink, currently used by the airlines (for ops, amongst other things). However, the ACARS system is not especially robust... therefore, an Aeronautical Telecommunications Netowrk (ATN) is in development to provide better control of message routing (also security and reliability is said to be improved). This is only the comms part of the FANS package - surveillance functions (ADS-Contract) and navigation functions (GPS) are included as well.
RS.
[This message has been edited by RevStar (edited 07 November 2000).]