Task: Text to Code
Input (English): What is the airport code of the airport with the most flights?
Output (English): SELECT T1.AirportCode FROM AIRPORTS AS T1 JOIN FLIGHTS AS T2 ON T1.AirportCode  =  T2.DestAirport OR T1.AirportCode  =  T2.SourceAirport GROUP BY T1.AirportCode ORDER BY count(*) DESC LIMIT 1