Pat wrote: >The ICAO issues a world standard for the use of all >civil aviation authorities and commercial air operators >around the world. Their world standard instructions >are written in SI (metric) units and published >in the 'Blue Book'.
Hello Pat, I have posted to the mailing list on this topic a couple of times. There is a lot of misunderstanding about the ICAO, not least because the relevant document cannot be posted online without paying for it. However, if we are trying to dispel misunderstanding, then we should attempt to get better knowledge so we can shoot down the popular myths. This is particularly important if we are writing to publications etc. The ICAO Blue Book is no longer in force. It was changed in 1979 and they now classify countries as 'SI' and 'non-SI'. The relevant document is not online without charge but here is an excerpt that somebody posted to the risks digest: ****************************************************** [begin quote] Measurement of: ICAO Blue SI non-SI --------------- ---- ---- -- ------ Distances used in Nautical miles Nautical miles km nm navigation reports and tenths and tenths Relatively short metres metres m distances Altitudes, elevations metres feet m ft and heights [...] Dimensional units to be used in air/ground communications applicable for the following countries or FIRS: [excerpts] France: ICAO (8) (60) Switzerland: SI/non-SI United Kingdom: Blue (63) United States: Blue (33) [Relevant footnotes:] (8) Altitudes and heights on IAL charts in feet (33) Relatively short distances in feet [...] (60) [...] (63) [...] There are presently 69 footnotes explaining non-standardized measurements. [end quote] ****************************************************** >Because nations such as Australia, Canada, New Zealand, >South Africa, and the UK tend to use planes made in >the USA they simply go along with the lead on ICAO exceptions >given by the USA. The major reason for the dominance of 'feet' is not the manufacturer, it is due to problems of operations. Incidentally, the appropriate term used in the aviation community is 'aircraft'. The US does not use the same units as the UK for horizontal distances. >However, with the push of a button, all of the displays in the >cockpit can have conversion factors applied, This is not true. I hope you don't mind. Terry
