Originally Posted by gpn01
So, if the future scenario is that the whole of UK aviation (that's EVERY glider, light aircraft, microlight, balloon, hang glider, UAV, helicopter and ultralight) is entirely controlled, as the CAA would like it, by Mode-S equipped facilities then a German Cessna 172 decides that he wants to fly to the UK will he/she need a Mode-S tranponder fitting ?
I think it extremely unlikely that he/she would need one "fitting" as I would be very surprised if German requirements were less onerous than our own.
Note that according to ICAO SARPs, as NS suggested, altitude-reporting transponders have been required for all flying machines for at least 5 years.
By the time the Mode S requirement comes in, I imagine this will all be within EASA's remit.