[GeoStL] Re: GPSr use in commercial aircraft

  • From: "Bruce S" <bruces1321@xxxxxxxxxxx>
  • To: geocaching@xxxxxxxxxxxxx
  • Date: Sat, 16 Aug 2003 19:50:03 -0500

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I think that my Garmin Vista determines altitude by sensing barometric
pressure. In an aircraft cruising at 37000 feet, the inside cabin altitude
is maintained at about 8000-9000 feet. Thus wouldn't the GPSr only read
cabin altitude and not the actual height above ground ?

What is the general altitude measuring source in GPSr's?

You are correct that the vista's default is to the barometic pressure to determine the altitude and since the cabin is pressurized you are getting the reading of the elevation it was pressurized to. When I have taken short flights my elevation shown was around 5000 feet when was flying at around 24000 feet. You can change the settings or at least see what the triangulated altitude using satellites but don't remember how it is done on vista. With the vista it can auto calibrate itself thus correcting for changes in barometric pressure. Also man manually calibrate when at a know elevation. In general the elevation from barometric pressure is more accurate than that from the satellites.

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