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Old 20th Aug 2023, 16:54
  #103 (permalink)  
India Four Two
 
Join Date: Jun 2002
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For the USA to file nonstandard phraseology differences with ICAO would fill a volume as thick as a telephone directory.
It’s unfortunate enough that they persist with feet and statute miles for visibility, pounds and ounces, US quarts and gallons, and inches Hg for altimeter settings,
There are about 210,000 aircraft in the USA and 97% are GA. Almost all the GA aircraft will have altimeter sub-scales in inches Hg only. Add in about 30,000 Canadian aircraft plus a few hundred (?) more from Mexico and Colombia and you can see why North America will never switch to HPa.

The other units mentioned will also never change - there is too much entrenched infrastructure that uses those units.
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