Technical data

Product Specification
HIF-2121/R5 CAGE CODE: 97896 SCALE: NONE SIZE: A DWG NO: 965-1176-601 REV: D SHEET 24
FIGURE 1.3.2-4: TERRAIN DATABASE REGIONS – PACIFIC
1.3.2.1 Terrain Alerting
The Terrain Awareness alerting algorithms continuously compute terrain clearance envelopes ahead of the aircraft. If the
boundaries of these envelopes conflict with terrain elevation data in the terrain database, then alerts are issued. Two
envelopes are computed, one corresponding to a terrain caution alert level and the other to a terrain warning alert level, as
described in section 6.7.3. The algorithms are designed to meet the following criteria:
• Operational compatibility - minimal unwanted alerts during normal flight operations and approach procedures
• Improved Terrain Awareness warning times - provide adequate alert times for all flight phases and conditions
• Robustness - tolerant of aircraft position errors, altitude signal errors and database errors
The caution and warning envelopes use the Terrain Clearance Floor as a baseline, and “look ahead” of the aircraft in a volume
which is calculated as a function of airspeed and flight path angle. Simplified diagrams of the terrain caution and warning
envelopes are shown in Figures 6.7-2 and 6.7-3 of section 6.7.
If the aircraft penetrates the caution envelope boundary, the aural message “Caution Terrain, Caution Terrain” is generated,
and alert discretes are provided for activation of visual annunciators. (Note that some installations may use the aural message
“Terrain Ahead”). Simultaneously, terrain areas which conflict with the caution criteria are shown in solid yellow color on the
terrain display, as described in section 1.3.2.2.
If the aircraft penetrates the warning envelope boundary, the aural message “Terrain Terrain, Pull Up!” is generated, and
alert discretes are provided for activation of visual annunciators. (Note that some installations may use the aural message
“Terrain Ahead, Pull Up”). Simultaneously, terrain areas which conflict with the warning criteria are shown in solid red color
on the terrain display, as described in section 1.3.2.2.
1.3.2.2 Terrain Display
The MKVI/MKVIII EGPWC outputs a display of terrain data in KC Picture Bus (KCPB) or weather radar format per
ARINC-708/708A (ARINC 453). The terrain data can be displayed either on a shared weather radar indicator or, if the
aircraft is equipped with a Display Switching Unit (DSU), on a Honeywell UDI compatible display. If a weather radar
indicator is used, when the terrain display is present it replaces the Weather Radar display. The terrain display can be made
available to the flight crew at any time. When the conditions for either a terrain caution or a terrain warning are detected, the