Icao Doc 8585 [extra Quality] -

: A list of aircraft operating agencies and authorities followed by their assigned designator and state.

Once accepted, your code is published in the next edition of ICAO Doc 8585. The entire process typically takes 90 to 180 days. icao doc 8585

Modern air traffic management systems are automated. If your airline does not have a valid 3LD in Doc 8585, the computer will reject your flight plan (ICAO FPL). You cannot legally file an IFR flight without a designator. : A list of aircraft operating agencies and