2.2.12 GEOMETRIC ALTITUDE (GPS REQUIRED)
Geometric Altitude (for MK V and MK VII -206-206 and later, and MK VI and MK VIII) is a computed pseudo-Corrected Barometric Altitude (computed altitude “Above Sea Level” - ASL). This is designed to ensure optimal operation of the EGPWS enhanced functions through all phases of flight and atmospheric conditions. Geometric Altitude uses GPS Altitude, an improved pressure altitude calculation, Radio Altitude, and Terrain and Runway elevation data to reduce or eliminate errors potentially induced into Corrected Barometric Altitude by temperature extremes, non-standard altitude conditions, and altimeter miss-sets. Geometric Altitude also allows continuous EGPWS operations in QFE environments without custom inputs or special operational procedures.
2.2.13 WEATHER RADAR AUTOTILT (MK V AND MK VII ONLY)
MK V and MK VII EGPWS (-210-210 and later) provide an automatic Weather Radar tilt angle capability. The Auto-Tilt function uses aircraft altitude above the terrain and the terrain database to generate an optimum tilt angle for the Weather Radar. The Auto-Tilt angle results in minimum ground clutter on the display while maintaining the optimum weather detection capability. With manual tilt control, there can be over-scan where weather cells and terrain are below the antenna beam scan resulting in a blank display. Alternately, under-scan, where the antennas scan is hitting the ground below the weather cells, results in ground clutter display. The calculated tilt angle is transmitted on the ARINC 429-output bus (labels 061, 062, 063, 064, and 065) for any compatible Weather Radar system. See the appropriate Part Number ICD for complete Label definitions.
2.2.14 SYSTEM DISPLAY AND ANNUNCIATION
In addition to the aural (voice) alerts provided over the cockpit speaker and interphone system, the EGPWS drives cockpit annunciators and/or Electronic Flight Instrument Systems (EFIS) with system status and alert annunciations. For some EFIS displays, the EGPWS is designed to interface and display the EGPWS terrain video as well as alert annunciations directly onto the EFIS without the use of external relays or annunciators. This is referred to as an “integrated” EFIS display. For other displays (some EFIS and all Radar Indicators), the terrain video is relay switched into the display system externally taking the place of weather radar video. In this case, external switching and annunciation is required. This is referred to as a “Bolt-On” display. The interface and display characteristics are defined for each display system and programmed into the EGPWC as part of the configuration software.
Cockpit annunciations can vary somewhat aircraft to aircraft or operator to operator. In addition, several system options are defined by the installation configuration. One of these is EGPWS lamp format. For MK V and MK VII, two formats are provided; Lamp Format 1 and Lamp Format 2. For MK VI and MK VIII, only Lamp Format 1 is currently available. These are described and illustrated below.
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