Technical data

Product Specification
HIF-2121/R5 CAGE CODE: 97896 SCALE: NONE SIZE: A DWG NO: 965-1176-601 REV: D SHEET 87
6.7 Terrain Awareness Functions
Revision History
Effectivity
Date - Modified By Description of the Updates App. Cfg.
29-NOV-99 Peter Bateman Initial release and entry into PVCS -001 -001
24-MAY-00 Susie Wright SCR 4942: General document cleanup. -003 -003
06-JUN-00 – Susie Wright Document only change – Deleted proprietary note from footer. -003 -003
02-JUL-01 – S. Wright Added review comments -008 -008
30-JAN-02 – N Paterson SCR 6325: Para 6.7.4 revised MSL to GSL -010 -010
The Terrain Awareness component of the EGPWS is divided into the functional blocks shown in Figure 6.7-1 with an
interface to an optional cockpit display. The highlighted blocks monitor aircraft position with respect to local database-
cataloged terrain and provide rapid audio and visual alerts when a terrain threat is detected. Terrain threats are recognized
and annunciated when terrain violates specific computed envelope boundaries forward of the aircraft path. The terrain
database also includes the obstacle database (see Note) providing similar annunciation when cataloged obstacles violate the
same envelope boundaries.
The Terrain Awareness alert lamps and audio outputs behave in the same manner as the standard GPWS mode alerts. Any of
the following: Terrain Caution Alert, Terrain Warning Alert, obstacle caution alert or obstacle warning alert will initiate a
specific audio alert phrase (see 6.7.4.2 and 6.7.4.3).
Complementing the terrain threat alerts, the EGPWS also maintains a synthetic image of local terrain forward of the aircraft
for display on EFIS Navigation Displays (NDs), Multi-Function Displays (MFDs) and Weather Radar Indicators.
The EGPWS may be configured to automatically de-select the weather display and pop-up a display of the terrain threats
when they occur. The logic used for these configurable controls also provides an external input for predictive windshear
alerts that can override a terrain display and revert to the weather display with the corresponding windshear data.
The EGPWS provides up to two optional external display outputs, each with independent range-scaling control in the same
fashion as a weather radar with more than one indicator. Changes of range scaling to one display do not affect the other
display. Each of these two independent outputs may be used to drive more than one display.
The blocks in Figure 6.7-1 are described in the following sub-sections. The specific databases, audio output function, and
display output processor are described in other related sections of this document.
NOTE: The terrain database may contain obstacle data if available.
6.7.1 EGPWS Input Processing and Signal Selection
The EGPWS input processing and signal selection function conditions and formats aircraft data into proper form for use by
the EGPWS while insulating the EGPWS from variations in aircraft type and configuration.
6.7.1.1 Display Configuration
There are several configuration inputs defined as a function of the selected aircraft type. These define the type of display and
how it is enabled by the pilot, including (for some cockpit avionics architectures) optional automatic pop-up of the terrain
display during Terrain Awareness alerts. Although ARINC-708/708A provides the basic format for the standard radar display
bus, there are variations between manufacturers that the EGPWS is designed to handle.