R 1EFF : 001-049, 051-099, 101-105, 151-199, 1 34-48-00Page A37 1201-214, 401-499, 1Config-1 Aug 01/05 1 1 1CES 1 altitude for each matrix element. These attributes are computed for the background and terrain threat areas and kept small (one byte) to reduce memory requirements and transfer time to the radar display output processor. The aircraft position and aircraft heading are used at the radar display output processor to extract a specific sweeping image ahead of the aircraft from the display overlays. Each element of the output display matrix overlays holds a single display attribute byte with fields for the colors, patterns, and symbols shown in the following table:
-------------------------------------------------------------------------------| Color | Threat | -------------------------------------------------------------------------------| Solid Red | Warning terrain (approximately 30 seconds from | | | impact) | |---------------------|-------------------------------------------------------| | Solid Yellow | Caution terrain (approximately 60 seconds from | | | impact) | |---------------------|-------------------------------------------------------| | High Density Red | Terrain that is more than 2000 ft. above aircraft | | | altitude | |---------------------|-------------------------------------------------------| | High Density | Terrain that is between 1000 and 2000 ft. above | | Yellow | aircraft altitude | |---------------------|-------------------------------------------------------| | Medium Density | Terrain that is 500 (250 with gear down) ft. below | | Yellow | to 1000 ft. above aircraft altitude | |---------------------|-------------------------------------------------------| | Medium Density | Terrain that is 500 (250 with gear down) ft. below | | Green | to 1000 ft. below aircraft altitude | |---------------------|-------------------------------------------------------| | Light Density Green | Terrain that is 1000 to 2000 ft. below aircraft | | | altitude | |---------------------|-------------------------------------------------------| | Black | No close terrain (Ref. NOTE in para. D.(1)(d)1_) | |---------------------|-------------------------------------------------------| | Light Density | Unknown terrain | | Magenta | | -------------------------------------------------------------------------------
1 Background Display
_ (Ref. Fig. 020) The background display is computed from the aircraft altitude with respect to the terrain data in the digital elevation matrix overlays. Where terrain data are available and sufficiently close to the aircraft altitude, they are
R 1EFF : 001-049, 051-099, 101-105, 151-199, 1 34-48-00Page A38 1201-214, 1Config-1 Aug 01/05 1 1 1CES 1
presented in background color dot patterns reflecting the
projected separations shown in this illustration.
(Ref. Fig. 019)
Different dot density patterns and colors are used to
represent terrain altitude bands with respect to the aircraft.
Areas with no terrain data available are painted with the low
density magenta. Known terrain sufficiently below the aircraft
altitude is black.
NOTE : Terrain is not shown if more than 2000 ft. below____
reference altitude
AND/OR
Terrain is not shown if terrain elevation is within 400
ft. of runway elevation nearest the aircraft.
2_ Terrain Caution Alert
R (Ref. Fig. 021A)
When the conditions have been met to generate a terrain
caution alert, a specific audio alert and light output is
triggered and the background image is enhanced to highlight
the terrain caution threats.
At the start of a terrain caution alert, the terrain awareness
function triggers the caution audio alert phrase TERRAIN
AHEAD. The phrase is repeated after seven seconds if still
within the terrain caution envelope.
During a terrain caution alert, the GPWS legend of pushbutton
switches 4WZ and 5WZ is on.
During a terrain caution alert, areas where terrain violates
the terrain caution envelope along the aircraft track, and
within plus or minus 90 deg. of the aircraft track, are
painted with the caution color 100 per cent yellow.
3_ Terrain Warning Alert
R (Ref. Fig. 021A)
When the conditions have been met to generate a terrain
warning alert, a specific audio alert and light output is
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