Assembly Resolutions A18-13 Appendix J (18th Session of ICAO Assembly, Vienna, 1971), A21-21 Appendix F (21st Session of ICAO Assembly, Montréal, 1974) and A22-18 Appendix F (22nd Session of ICAO Assembly, Montréal, 1977) resolved that the units of measurements to be used in civil aviation shall be achieved on the basis of the International System of Units (SI), except in those cases where non-SI units are permitted for use together with the SI units, in the interest of safety of international air transport. On 23 March 1979, the Council adopted the 4th edition of Annex 5 changing the title of this Annex to Units of Measurement to be used in Air and Ground Operations, which increased the scope to cover all the aspects of the air and ground operations, made provision of a standardized system of units based on the SI, identified non-SI units for use in international civil aviation, and provided for the termination of the use of certain non-SI units. Provisions of Annex 5 are regularly amended to reflect the changing environment, such as the definition of units or technical improvements towards a safer aviation.
The latest amendments of Annex 5 deleted the references to temporary non-SI units.
ICAO maintains liaison with the International Organization for Standardization (ISO) regarding the standardized application of SI units in aviation.