a Caution altitude floor
_ The caution altitude floor (or terrain floor) is computed as a function of aircraft altitude with respect to nearest runway altitude and range to the nearest runway threshold position. This parameter represents a distance below the aircraft. The relationship to the nearest runway threshold location prevents undesired alerts when the aircraft is taking off or landing at an airport. The system is compatible with terrain clearances allowed for by regulatory approach and departure design criteria.
b Caution look-ahead distance
_ The caution look-ahead distance is computed from aircraft ground speed and turn rate to provide an advanced caution with adequate time for the crew to react safely. Depending on the situation this distance roughly corresponds to between 40 and 60 seconds for advance alerting.
c Warning altitude floor
_ The warning altitude floor is set to a fraction of the caution altitude floor, as illustrated in the upper part of this illustration. (Ref. Fig. 018) The warning altitude floor is computed as a function of aircraft altitude with respect to nearest runway altitude and range to the nearest runway threshold position. This parameter represents a distance below the aircraft. The relationship to the nearest runway threshold location prevents undesired alerts when the aircraft is taking off or landing at an airport.
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d_ Warning look-ahead distance
The warning look ahead distance is a fraction of the
caution look ahead distance (computed from aircraft ground
speed and turn rate) to provide an advanced warning with
adequate time for the crew to react safely.
(d) Terrain Displays and Alerts (Ref. Fig. 019, 020) The terrain awareness alerting and display function maintains a background display of local terrain forward of the aircraft for cockpit display. In the event of terrain caution or warning conditions, an aural alert and lamp outputs are triggered. The background image is then enhanced to highlight related terrain threats forward of the aircraft. The background terrain is depicted as variable density dot patterns in green, yellow or red. The density and color being a function of how close the terrain is relative to aircraft altitude. Terrain alerts are depicted by painting the threatening terrain as solid yellow or red. The set of digital elevation matrix overlays is processed by the terrain display algorithms into a matching set of display matrix overlays and passed to the radar display output processor. The display matrix overlays hold display attributes rather than 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:
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Enhanced GPWS - Terrain Background Display Legend
Figure 019
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Enhanced GPWS - Terrain Background Display on ND
Figure 020
R 1EFF : ALL 1 34-48-00Page A24 1 1 Config-1 Aug 01/05 1 1 1CES 1 -------------------------------------------------------------------------------| 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 | | ------------------------------------------------------------------------------- 中国航空网 www.aero.cn 航空翻译 www.aviation.cn 本文链接地址：A320飞机维护手册 AMM NAVIGATION 导航4(30)
