General > General Technical Chat
why is the US not Metric
TimFox:
Going back to the original question: Please note that the US does not use the term "Imperial Units", except to refer to specific items such as the Imperial gallon and pint, which differ in magnitude from the US "Customary Units" the US gallon and pint.
Simon:
Quite, there are 3 systems on the go although the UK officially does not use imperial.
tooki:
Oh yeah, I just remembered another US unit that's used worldwide: the foot, in aviation. Flight levels are practically always* in feet, because having a consistent system is far more important than which system it is. Switching would likely lead to some crashes during the transition period. With there being essentially no advantage to switching, the risks involved in switching just don't make sense, which is probably why aviation has stuck with feet, despite ICAO recommending a switch to metric since 1979.
(Given the altitudes in question, the unit used is essentially totally arbitrary, since one's "feel" for a unit in everyday life can't translate to the huge altitudes involved. And the actual amounts don't really matter, insofar as it's air traffic control telling a pilot what flight level to use.)
*Except China, Mongolia, North Korea, Kyrgyzstan, Kazakhstan, Tajikistan and Uzbekistan. Russia actually used to use metric flight levels, but in 2017, actually switched from meters to feet.
Simon:
Something like flying altitudes are indeed best not messed with.
boffin:
--- Quote from: tooki on October 28, 2019, 06:33:27 pm ---Oh yeah, I just remembered another US unit that's used worldwide: the foot, in aviation. Flight levels are practically always* in feet, because having a consistent system is far more important than which system it is. Switching would likely lead to some crashes during the transition period. With there being essentially no advantage to switching, the risks involved in switching just don't make sense, which is probably why aviation has stuck with feet, despite ICAO recommending a switch to metric since 1979.
(Given the altitudes in question, the unit used is essentially totally arbitrary, since one's "feel" for a unit in everyday life can't translate to the huge altitudes involved. And the actual amounts don't really matter, insofar as it's air traffic control telling a pilot what flight level to use.)
*Except China, Mongolia, North Korea, Kyrgyzstan, Kazakhstan, Tajikistan and Uzbekistan. Russia actually used to use metric flight levels, but in 2017, actually switched from meters to feet.
--- End quote ---
It's ugly in the aviation world (Canada, light aircraft example)
Fuel, sold in litres, but you care about weight (in lbs), and consumption (in US Gal/hr)
Altitude in hundreds of feet
Visibility is in statue miles (metres in Europe)
But speeds (wind, and your aircraft) in kts
Directions in degrees true (if you read it) or magnetic (if you hear it)
Runway directions in degrees magnetic (except far north where it's deg true)
Air pressure in inches of Mercury (altimeter settings) and/or Hectopascals (weather reports, and for altimeter outside of North America)
Temperature (Celsius for air, Fahrenheit for engine gauges)
How we don't end up with more Gimli Gliders, I'm not sure
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