Annex XV of the Monitoring Decision states in Part 2 that for the purpose of identifying the aircraft operator defined by Article 3(o) of the EU ETS Directive, the ICAO designator in box 7 of a flight plan is to be used or, in the absence of such a designator, the aircraft registration marking is to be used. It appears that there is no uniform system, criteria or procedure for the application and issue of ICAO designator codes.

Where the aircraft operator cannot be identified then the legislation stipulates that the owner will be responsible.