BendixKing KTA 910 System KTA 970 - Manual (Page 48)

Rev 2
KTA 870/KMH 880 Pilot’s Guide EGPWS Functions and Features
006-18265-0000
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AIRCRAFT ALTITUDE
In addition to the altitude information provided by the GPS, the GA-
EGPWS uses uncorrected barometric pressure altitude information from
the aircraft’s encoding altimeter, blind altitude encoder or transponder.
This altitude information allows the system to do two main tasks.
First, by using a special “derived-altitude” developed by Honeywell called
“Geometric Altitude”, the GPS and uncorrected pressure altitude infor-
mation is blended together by the system to provide accurate altitude
information, which is using the same Mean Sea Level (MSL) reference
as the terrain, obstacle and runway databases in the system. The blend-
ing functionality of “Geometric Altitude” means it is much less susceptible
to errors or malfunctions in the use of normal altimeter systems. (The
pilot is NOT required to enter an altimeter setting specifically for the GA-
EGPWS system).
Where aircraft are routinely operated in extreme weather conditions
(either hot or cold), Honeywell strongly recommends the optional temper-
ature input be used with the GA-EGPWS. This additional factor in the
blending formula of “Geometric Altitude” provides an even more accurate
vertical position to the system, and prevents serious discrepancies
between actual altitude and “Geometric Altitude” under extreme temper-
ature conditions, especially during rapid climbing or descending flight
profiles.
The second benefit of using “Geometric Altitude” in the system is that the
pilot will now have an independent monitor of altitude. The system can
detect an abnormal difference between “Geometric Altitude” and the
uncorrected pressure altitude. Optionally, the system can provide a voice
callout and display a message to the pilot should such an abnormal dif-
ference occur.
Geometric Altitude