060-4314-000 • Rev. C - May 2004
MK VI & MK VIII EGPWS Pilot Guide
39
Geometric
Altitude
continued
The Geometric Altitude is computed by blending a calculated
Non-Standard Altitude, Runway Calibrated Altitude (determined
during takeoff), GPS Calibrated Altitude, Radio Altitude Calibrated
Altitude (determined during approach), and Barometric Altitude
(if available). Estimates of the VFOM for each of these are deter-
mined and applied in order to determine its weight in the final
altitude. The blending algorithm gives the most weight to alti-
tudes with a higher estimated accuracy, reducing the effect of less
accurate altitudes. Each component altitude is also checked for
reasonableness using a window monitor computed from GPS Alti-
tude and its VFOM. Altitudes that are invalid, not available, or fall
outside the reasonableness window are not included in the final
Geometric Altitude value.
The Geometric Altitude algorithm is designed to allow continued
operation when one or more of the altitude components are not
available. If all component altitudes are invalid or unreasonable,
the GPS Altitude is used directly.
The Geometric Altitude function is fully automatic and requires
no pilot action.
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