Originally Posted by
UFO-flying-Airbus
Regarding a transponder-I was thinking that Hungary didn't need one because the owner is currently flying there without one(?)
It's OK to fly without transponder within the country, outside of controlled airspace, but
border crossing requires a C-mode transponder and radio contract with Budapest Information. Hungarian AIP also states that you have to cross the border at a designated reporting point, and must submit a flight plan at Hungarocontrol, at least 60 minutes before the flight.
The good thing is that if your destination is within another Schengen country, you won't need any customs/passport control before departure.