Mode S transponder - can you tell?
Chaps I am lead to believe the carriage of a Mode S transponder is now compulsory when IFR in controlled airspace.
If I were to arrive in your airspace around the country in a light twin with just standard Mode C, would you deny me a transit or approach and ask me to exit such airspace? How can you tell from my return whether I am Mode S or not, and how often do you come across such instances?