ICAO SARPs Bilaga 2 (Luftregler) anger:
3.5 Time
3.5.1 Coordinated Universal Time (UTC) shall be used and shall be expressed in hours and minutes and, when required, seconds of the 24-hour day beginning at midnight.
3.5.2 A time check shall be obtained prior to operating a controlled flight and at such other times during the flight as may be necessary.
Note.— Such time check is normally obtained from an air traffic services unit unless other arrangements have been made by the operator or by the appropriate ATS authority.
3.5.3 Wherever time is utilized in the application of data link communications, it shall be accurate to within 1 second of UTC.
Ovanstående bör gälla för nästan alla länder när det gäller internationell civil luftfart. Militärer och okontrollerade flygningar omfattas inte av ovanstående.