What is the contribution of GPS data to the navigation of large aircraft? Do GPS data dominate barametric data?
---- Original message ---- >Date: Sun, 18 Apr 2010 18:10:10 -0700 (PDT) >From: "John M. Steele" <[email protected]> >Subject: [USMA:47170] Re: Air flight altitudes in meters >To: "U.S. Metric Association" <[email protected]> >Cc: "U.S. Metric Association" <[email protected]> > > 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
