MSL-G is based on an internally calculated geometric altitude
by the TAWS. Geometric altitude is the height above MSL
derived from GPS. It represents the aircraft's calculated height
above MSL and serves as the reference altitude for color-
coding of the TAWS terrain display and as the input to the
TAWS look-ahead algorithm. Because it is derived from GPS
altitude, this reference altitude often differs from corrected
barometric altitude. The geometric altitude, which might be in
error by 100 feet or more, is not to be used for navigation. It is
presented to provide the crew with additional situational
awareness of true height above sea level upon which TAWS
terrain alerting and display is based.
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