I've just met an airline on Devau with 4-letter code, despite system does not allow to create an airline with code longer than 3 letters. How's that possible?
It’s a relic of the past.
There was a time when holdings didn’t operate any flights, they always needed a subsidiary. So holdings didn’t have a code at all. When this was changed to the current system, existing holdings got a 4-letter code assigned
Thanks, now I know :)