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时间:2011-10-12 14:19来源:蓝天飞行翻译 作者:航空
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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 (ND’s), Multi-Functional Displays (MFD’s), or 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 displays outputs, each with independent range-scaling control in the same fashion as 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.

2.2.10.1 TERRAIN AND OBSTACLE DATABASE
The EGPWS Terrain Database is the earth’s surface divided into grid sets and cells referenced to the geographic (latitude/longitude) coordinate system of the World Geodetic System 1984 (WGS-84).  Elements of the grid sets include the highest terrain altitude (above MSL) in each cells 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 not important to the flight crew.
Digital Elevation Models (DEM’s) are available for most of the airports around the world today.  In cases where data is not currently available, DEM’s are generated 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 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 via a PCMCIA card interface.
The Obstacle Database (in MK V and MK VII -204-204 and later, and MK VI and MK VIII) is a separate file included within the terrain database. Both files are loaded into the EGPWS in the terrain database PCMCIA card.  The obstacle database is accessed by the EGPWC application software only if obstacle alerting is enabled by installation configuration. The obstacle data is processed by the EGPWS in the same fashion as terrain, and is presented on the display as terrain (uses same coloring scheme).
 
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