Following an exchange on the RTf just recently, I wouldn't rely at all on TCAS to show you the picture. Some versions don't display non-threatening aircraft, which can be as little as 1000ft above, MINIMUM separation!!! The a/c in question is commonly used on commuter routes in England/Europe, and the pilot actually asked for the level/type of the opposite direction flight to check his TCAS, and then said it could be faulty as it wasn't displayed. Another pilot on freq. then jumped in to say theirs was the same (diff type a/c) and explained the limiting extent of TCAS, much to my own personal shock.
