Actually, it is nominally based on height above sealevel. Sitting on the runway, with altimeter correction dialed in, it will read the published height of the runway above sealevel.
At cruise levels, no altimeter correction is used and reading is called flight level. It is the height above sea level IF sea level were at 15 °C, 101.325 kPa, and a lapse rate of -6.5 K/km to the stratosphere (11 km), and zero lapse rate above that to 20 km. Further it it uses a height variable called geopotential height, the height that would be true if gravity were constant with height. There is a transformation between that and geometric height in the standard. ________________________________ From: James R. Frysinger <[email protected]> To: U.S. Metric Association <[email protected]> Cc: U.S. Metric Association <[email protected]> Sent: Sun, April 18, 2010 8:47:07 PM Subject: [USMA:47168] Re: Air flight altitudes in meters Altimeters work off of atmospheric pressure readings, Pat. But the readout is in terms of height above terrain. So assignments and reports are always in length units. No human pressure to altitude correlation procedures are used. Jim Pat Naughtin wrote: > 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 > <http://www.metricationmatters.com/>for more metrication information, contact > Pat at [email protected] > <mailto:[email protected]> or to get the free '/Metrication > matters/' newsletter go to: http://www.metricationmatters.com/newsletter 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] >> <mailto:[email protected]>> >> *To:* U.S. Metric Association <[email protected] >> <mailto:[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 >> > -- James R. Frysinger 632 Stony Point Mountain Road Doyle, TN 38559-3030 (C) 931.212.0267 (H) 931.657.3107 (F) 931.657.3108
