Technical data

Product Specification
HIF-2121/R5 CAGE CODE: 97896 SCALE: NONE SIZE: A DWG NO: 965-1176-601 REV: D SHEET 89
6.7.1.3 Control Inputs
Installations provide discrete terrain display select switches in the cockpit for each display. These are momentary contact
switches that are processed by the EGPWS input processing and signal selection block as inputs to the Wx/TERR select logic.
For some fully integrated displays this selection is provided via a display controller.
In addition a Terrain Inhibit switch may also be provided to deactivate the enhanced functions of the EGPWS.
For some installations, display switching via separate terrain select and weather select switches is supported. If the EFIS is in
a proper display mode then pressing the weather select switch will cause weather to be displayed if it is not, and to be
deselected (blank image) if weather was already selected. Alternately, pressing the terrain select switch will cause terrain to
be displayed if it is not, and to be deselected (blank image) if terrain was already selected.
All installations require input of cockpit-selected range scales for each display. Installations may optionally provide this on
single or dual ARINC-429 broadcast buses. Two ARINC-429 buses are provided for ARINC-708/708A split and
consolidated control.
6.7.2 Local Terrain Processing
The local terrain processing block extracts and formats local topographic data and terrain features from the related databases
creating a set of digital elevation matrix overlays for use by the terrain threat detection and display processing functions.
Additionally, data for the nearest runway is also extracted for use by the terrain threat detection and display processing
functions. Processing for the topographic and runway database are described in the following sub-sections.
6.7.2.1 Terrain Surface Data
Local terrain processing of topographic surface data updates a set of digital elevation matrix overlays that are positioned with
respect to aircraft position. Each matrix element contains the highest terrain altitude with respect to mean sea level in that
element’s area. Elements where terrain data are not available are marked invalid.
6.7.2.2 Obstacle Data
In addition to terrain surface data, the terrain database contains obstacle data. The obstacles data is presented on the screen
like terrain (same coloring scheme), and cause visual indications for warning and caution alerts like terrain. The current
obstacle database is obtained from NOAA, it includes obstacles in the United States and parts of Canada, Mexico and the
Bahamas.
Obstacle alerting is activated using the configuration module.
6.7.2.3 Nearest Runway Data
Data for the nearest runway are extracted and processed for use by the terrain threat detection and display processing
functions. Data are extracted from the same airport database used by the Terrain Clearance Floor functions (see section 6.3).
This database contains data on all runways 2000 feet or more in length with either published endpoint coordinates or adequate
information to extrapolate the endpoint coordinates. The contents of the database are processed by the local terrain
processing into nearest runway center position, nearest runway threshold position, and nearest runway altitude for use by the
EGPWS. These data are updated when the terrain threat detection and display processing functions are performed.
6.7.3 Terrain Threat Detection
The terrain threat detection and display processing block performs the threat analysis on the terrain data within computed
caution and warning envelope boundaries below and forward of the aircraft path. Results of these threat assessments are
combined with background terrain data and data for the nearest runway and formatted into a terrain display image which can
be displayed on a Weather Radar Indicator or an EFIS display in place of the weather image. In the event of terrain caution
or warning conditions, a specific audio alert is triggered and the terrain display image is enhanced to highlight each of the
types of terrain threats.
During takeoff, terrain cautions and warnings are inhibited by the terrain takeoff guard described in section 6.0.6.