Technical data

Product Specification
HIF-2121/R5 CAGE CODE: 97896 SCALE: NONE SIZE: A DWG NO: 965-1176-601 REV: D SHEET 97
There is no direct source of true heading, but there is a source of magnetic heading.
There is no direct source of magnetic track, but there is a source of true track.
6.7.8 Geometric Altitude
Geometric Altitude is a computed aircraft altitude designed to help ensure optimal operation of the EGPWS Terrain
Awareness and Display functions through all phases of flight and atmospheric conditions. Geometric Altitude uses an
improved pressure altitude calculation, GPS altitude, radio altitude, and terrain and runway elevation data to reduce or
eliminate errors potentially induced in corrected barometric altitude by temperature extremes, non-standard altitude
conditions, and altimeter miss-sets. Geometric Altitude also allows continuous EGPWS operations in QFE environments
without custom inputs or special procedures by the flight crew when operating in a QFE environment.
6.7.8.1 Required Inputs for Geometric Altitude
The Geometric Altitude computation requires GPS altitude with Vertical Figure of Merit (VFOM) and RAIM failure
indication along with standard (uncorrected) altitude and radio altitude. Ground speed, roll angle, and position (latitude and
longitude) are used indirectly and are also required. Additionally, corrected barometric altitude, Static Air Temperature
(SAT), GPS operational mode and the number of satellites tracked are used if available.
The required GPS signals can be provided directly from an external ARINC 743 / 743A receiver or from the optional internal
EGPWS Xpress GPS Receiver card. Standard altitude, corrected barometric altitude, and SAT are provided directly from the
ADC. If SAT is not available, Geometric Altitude is computed using standard altitude with a corresponding reduction in
accuracy.
6.7.8.2 Altitude Calculation
The Geometric Altitude consists of three main functions: calculation of non-standard altitude, calculation of the component
altitudes and VFOMs, and the final altitude signal blending. Additional logic exists to handle reversionary modes and signal
reasonable checking for each component altitude. An overview of the Geometric Altitude function is shown in Figure 6.7-7.
NON-STANDARD
ALTITUDE/VFOM
CALCULATION
GPS CALIBRATED
ALTITUDE/VFOM
CALCULATION
SIGNAL
SELECTION AND
REASONABLNESS
CORRECTED
BAROMETRIC ALTITUDE
GEOMETRIC
ALTITUDE
STANDARD
ALTITUDE
RADIO ALTITUDE
RADIO ALTITUDE
CALIBRATED
ALTITUDE/VFOM
CALCULATION
TERRAIN DATA
ALTITUDE
SELECTION
SAT
VALIDITY
RUNWAY
CALIBRATED
ALTITUDE/VFOM
CALCULATION
NEAREST RUNWAY
ELEVATION
POSITION DATA
CORRECTED
ALTITUDE VFOM
CALCULATION
SAT
ROLL ANGLE
GPS ALTITUDE/VFOM
GPS SENSOR STATUS
RAIM FAILURE
TABLE 6.7-7: GEOMETRIC ALTITUDE BLOCK DIAGRAM