That is true, and the relationship is defined by the US, ICAO, and ISO Standard Atmospheres (these all agree as far as they go. As a space-faring nation, the US has defined it to an altitude MUCH higher than commercial aviation.) It depends on the lapse rate of temperature which varies from equator to poles and with weather, so it is simply an agreed standard, precise but inaccurate.
The main reason to fly pressure contours but maintain the fiction it is altitude is to control vertical spacing of aircraft. The pressure increment varies between each possible assigned altitude and would be confusing. By pretending they are altitudes, the arrangement is more understandable. Since everyone follows the same pretense, no harm done. At low altitudes, an altimeter correction is used, so the altimeter reads correctly on the runway of the airport supplying the correction (a good thing), and readings and flight assignments are called altitudes. At higher altitudes (18000 ft for the US) this correction is not made, standard pressure is used instead and it is called flight level. BTW, while most of the world flies in feet, the Standard Atmospheres are defined in metric. When a foot reading is required, it is converted (0.3048 m/ft). The US document is available as a scanned pdf free. The other two have to be purchased. ________________________________ From: Pat Naughtin <[email protected]> To: U.S. Metric Association <[email protected]> Sent: Sun, April 18, 2010 8:08:08 PM Subject: [USMA:47167] Re: Air flight altitudes in meters Dear John, Jim, and All, My understanding is that air craft actually measure pressure in something like kilopascals and that this pressure measurement is then changed (dumbed down ?) to a measure that implies that a measure of length has been made somehow. I suppose you could dangle a mass tied on a piece of string out the window of the plane so that it drags along the ground, but it sounds impractical! By the way, some approximate conversions from pressure to height might go something like this: Pressure Altitude kilopascal metres 100 0 90 1 000 80 2 000 70 3 000 65 4 000 60 5 000 45 6 000 40 8 000 22 10 000 19 12 000 15 14 000 10 16 000 7 18 000 4 20 000 3 25 000 1 30 000 Cheers, Pat Naughtin Author of the ebook, Metrication Leaders Guide, that you can obtain from http://metricationmatters.com/MetricationLeadersGuideInfo.html PO Box 305 Belmont 3216, Geelong, Australia Phone: 61 3 5241 2008 Metric system consultant, writer, and speaker, Pat Naughtin, has helped thousands of people and hundreds of companies upgrade to the modern metric system smoothly, quickly, and so economically that they now save thousands each year when buying, processing, or selling for their businesses. Pat provides services and resources for many different trades, crafts, and professions for commercial, industrial and government metrication leaders in Asia, Europe, and in the USA. Pat's clients include the Australian Government, Google, NASA, NIST, and the metric associations of Canada, the UK, and the USA. See http://www.metricationmatters.com/ to subscribe. On 2010/04/19, at 05:57 , John M. Steele wrote: It is my understanding that European air space is controlled in feet. > >The Wikipedia article on "flight level" shows a metric structure for Russia, >China, Mongolia, North Korea and various CIS States (non-European former USSR >satellites). Everybody else flies in feet (I think). > > > > ________________________________ From: James R. Frysinger <[email protected]> >To: U.S. Metric Association <[email protected]> >Sent: Sun, April 18, 2010 3:13:10 PM >Subject: [USMA:47149] Air flight altitudes in meters > > >My impression had been that all air flight altitudes were given and heeded in >terms of feet. But this article implies flight altitudes in meters. >http://www.foxnews.com/world/2010/04/17/european-skies-largely-remain-fly-zone/ > >Jim > >-- James R. Frysinger >632 Stony Point Mountain Road >Doyle, TN 38559-3030 > >(C) 931.212.0267 >(H) 931.657.3107 >(F) 931.657.3108 > >
