The International Civil Aviation Organization (ICAO) assigns four-letter codes to airports. For example, the code for Kahului Airport in Hawaii is PHOG.
Airports in northern Europe have codes that begin with E, and airports in southern Europe have codes that begin with L. If an airport is in northern Europe, the second letter can not be A, C, J, M, O, Q, R, U, W, X, or Z. For airports in southern Europe, the second letter can not be F, R, or U. The remaining letters of the alphabet can be used in the second position.
For all regions of Europe, there are no restrictions on the third or fourth letter of the ICAO code; all 26 letters are allowed.
How many ICAO codes can be issued in Europe?