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Flight Management System (FMS) for the Agusta AW139/AB139 Helicopter
GPS altitude displayed is the World Geodetic System 1984 (WGS--84)
height above the ellipsoid (geoid height + height above mean sea level
(MSL)). The GPS altitude is not relative to pressure altitude, but is
referenced to an earth--centered earth--fixed (ECEF) coordinate
system. Pressure altitude is not relative to the same reference frame,
but relative to the standard pressure or local pressure settings.
Therefore, significant differences are possible between GPS altitude
and pressure altitude. This concept is displayed in Figure 6--61.
GPS ALTITUDE
HEIGHT ABOVE MSL
HEIGHT ABOVE ELLIPSOID
EARTH'S SURFACE
WGS- -84 ELLIPSOID
fms055995.01
Figure 6- -61
GPS Altitude vs. Pressure Altitude
A28- - 1146- - 181
Navigation
REV 3 Mar 2009
6-75
Honeywell International Inc. Do not copy without express permission of Honeywell.
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