Technical data

Product Specification
HIF-2121/R5 CAGE CODE: 97896 SCALE: NONE SIZE: A DWG NO: 965-1176-601 REV: D SHEET 96
6.7.4.4 Terrain Test Display
During manually initiated self-test (see 6.10.6), the terrain alert aurals are included in the GPWS audio test outputs.
Additionally, a test display is output to the EGPWS display devices. This terrain test display exercises the complete set of
EGPWS colors and dot patterns.
6.7.4.5 Mode Annunciation
For some installations a 6 character mode annunciation display window is available to the EGPWS. For these installations the
system transmits encoded ASCII characters on its ARINC 429 output for use by the display.
Under normal conditions GPS position is used for the terrain display. When GPS is not available the system can default to
IRS position, or possibly to FMS position. This will be annunciated in the message window as follows:
When GPS position is being used, the message window displays GPWS or TERR in cyan letters.
When FMS position is being used, the message window displays GPWS-F or TERR-F (in cyan letters).
When IRS position is being used, the message window displays GPWS-I or TERR-I (in cyan letters).
For some installations, terrain awareness manual inhibit will cause INHIB (in cyan letters) to be displayed.
6.7.5 Terrain Database
As shown in Figure 6.7-1, local terrain processing extracts and formats local topographic terrain data from the EGPWS terrain
database for use by the terrain threat detection and display processing functions. This terrain database divides the earth’s
surface into grid sets referenced horizontally on the geographic (latitude/longitude) coordinate system of the WGS-84.
Elements of the grid sets record the highest terrain altitude (above MSL) in that element’s respective area. Grid sets vary in
resolution depending on geographic location. Because the overwhelming majority of “Controlled Flight into Terrain (CFIT)”
accidents occur near an airport and the fact that aircraft operate in closer proximity to terrain near an airport, higher resolution
grids are used around airports. Lower resolution grids are used outside of airport areas where aircraft altitude enroute makes
CFIT accidents unlikely and for which detailed terrain features are less important to the flight crew.
Digital Elevation Models (DEMs) are available for most of the airports around the world today. In cases where the data are
not currently available, DEMs are generated in-house from available topographic maps, sectional charts, and airline approach
plates. The process of acquiring, generating, assembling, and updating the database is governed by strict configuration
controls to insure the highest level of data integrity. DEMs from external sources are inputs to this process and are checked
and formatted for generation of the EGPWS Terrain Database.
The EGPWS terrain database is organized in a flexible and expandable manner. Using digital compression techniques, the
complete database is stored in non-volatile memory within the LRU. Updates and additions are easily accomplished by
inserting a single PCMCIA card in a card slot on a smart cable connected to the LRU. Status LEDs on the smart cable allow
the operator to monitor the database load progress and completion.
6.7.6 Obstacle Database
The obstacle database is a separate file from the terrain database. The obstacle database is included with the terrain database
in the terrain database PCMCIA card. Both files are loaded into the EGPWS with the obstacle database being accessed by the
EGPWC application only if enabled via configuration module option. The obstacle data is processed by the display
processing function in the same fashion as terrain is presented on the display as terrain (coloring scheme), and causes visual
indications of warning and caution alerts like terrain.
6.7.7 Internal Magnetic Variation Database
Using the International Geomagnetic Reference Field (IGRF), which is a series of mathematical models of the earth’s main
magnetic field and its secular variation, a global grid of magnetic variation values was generated using one degree intervals in
latitude and longitude. The resulting table is embedded into the EGPWC. Using two-dimensional interpolation, magnetic
variation is calculated for any position between the grid points. The internal magnetic variation database is included with the
terrain database in the terrain database PCMCIA card.
6.7.7.1 Use of Internal Magnetic Variation Database
For the EGPWS terrain display output true heading is required. Magnetic track or magnetic heading is required for envelope
modulation and mode 5. On some aircraft types one of these signals is not available. In that case the EGPWS sums magnetic
variation with an available signal to compute the required signal. So, magnetic variation is needed when: