3LDs were designed to assist in the identification of airlines in flight. These designators consist of a unique three-letter code which can be used for aircraft identification in a flight plan and/or a telephony designator which may be used as part of an aircraft's radiotelephony call sign
The 3LD Online Request System facilitates States in the assigning of three-letter and telephony designators to agencies/airlines. The 3LD system allows airlines to make requests for designators themselves directly, and have those requests automatically forward to the 3LD Focal Points each State for approval before assignment.
3LD State Focal Points may make their request by email to 3LD@icao.int
 Please note: These ICAO designators are not to be confused with the IATA two-letter reservations codes.