A300/A310 aircraft only, refer to 4.1.2.1 – EGPWS Mode 6: Excessive Bank Angle)
2.
Enhanced TAWS functions for predictive functions (e.g. forward looking capability)
3.
Optional functions (e.g. peaks mode, obstacle detection, RAAS function on EGPWS).
The following sections describe the TAWS functions regardless of the product
designations (EGPWS or T2CAS). Operational differences are highlighted when
necessary.
Note 1: In this brochure, EGPWS refers to P/N 965-1676-002 and T2CAS refers
to T2CAS standard 2.
Note 2: For the description of the EGPWS RAAS function, refer to 5.11 –
Description of RAAS.
4.1.1. TAWS PRINCIPLES
The TAWS processing may be depicted as in Figure 4-1. The TAWS captures the aircraft parameters from various sensors and systems. Based on its databases and algorithms, the TAWS evaluates the aircraft situation regarding the surrounding terrain, and triggers alerts and indications in the cockpit when a risk of CFIT is identified. Based on the same database, the TAWS also displays the terrain on ND for the awareness of flight crew.
The distance to the terrain/obstacle is determined according to the topography recorded in the terrain/obstacle database (plains, hills, mountains). In addition, the terrain displayed on ND is made up from the terrain database.
An outdated terrain/obstacle database may lead the TAWS to incorrectly evaluate the CFIT risk or to trigger nuisance alerts. Therefore, it is recommended to always get the latest terrain/obstacle database in the TAWS.
Note: The Obstacle database is specific to EGPWS only. The Aircraft Performance database is specific to T2CAS only.
4.1.1.1. TERRAIN DATABASE
The terrain database has a worldwide coverage and is defined according to a standardized Earth model: the World Geodetic System revised in 1984 (WGS84). The WGS84 defines the characteristics of the reference ellipsoid (semi-major axis, semi-minor axis, prime meridian, equator, etc). Based on this model, the Earth surface is divided into grid sets. For each element of the grid sets, the highest altitude above MSL is recorded and defines the terrain altitude in this element.
In order to optimize the database size, the grid set resolution varies according to the flight areas:
EGPWS T2CAS
-5 NM x 5 NM -2 NM x 2 NM -1 NM x 1 NM -0.5 NM x 0.5 NM -0.25 NM x 0.25 NM (airport vicinity). -In en-route areas: 3.0 NM -In terminal areas within 22 NM from the airport: 0.5 NM -In final areas for mountainous airport (within 6 NM from airport if elevation is 2 000 ft or more): 0.25 NM.
Grid set resolution
4.1.1.2. OBSTACLE DATABASE
At the time of writing the brochure, only EGPWS contains an Obstacle database, which includes artificial obstacles worldwide. Thanks to this database, EGPWS displays obstacles on ND.
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