Below is an context that describes a sql query, paired with an question that provides further information. Write an answer that appropriately completes the request.  # noqa: E501
### Context:
CREATE TABLE FLIGHTS (DestAirport VARCHAR, SourceAirport VARCHAR); CREATE TABLE AIRPORTS (AirportCode VARCHAR)
### Question:
What is the code of airport that has the highest number of flights?
### Answer:
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