Here's a copy of our technical notice issued when we first saw it!
The new standard of EGPWS provides four main improvements to these ‘enhanced’ functions.
1. Use of the GPS position rather than FMS position
The principle of the new EGPWS is based on a GPS position rather than the FMS1 position. Both the EGPWS computer and the aircraft architecture have been modified to acquire the pure GPS position data from ADIRU1 instead of FMS1. If the position from ADIRU1 or from both GPS sensors is unavailable, the EGPWS will revert to the FMS1 position. The function cancels the
possible effects of FMS positioning errors due to map shifts or inconsistent navigation aids.
2. Peaks Display and Obstacle Warnings
The Obstacle function uses an obstacle database (including man-made obstacles) to produce obstacle conflict information. When the Terrain Awareness Display (TAD) is activated, obstacles are displayed in a similar fashion to terrain, using the same colour scheme. In addition, two new
audio alerts have been added to allow differentiation between terrain and obstacle warnings. For an obstacle caution, there is an ‘OBSTACLE AHEAD’ audio caution and for an obstacle warning, there is an ‘OBSTACLE AHEAD PULL UP’ audio warning.
The Peaks function allows display of the surrounding terrain in all phases of
flight, with the terrain displayed relative to sea level rather than aircraft altitude.
The LCD displays fitted to the A320/1 have two digital values displayed in
bottom right corner; the top figure representing the elevation of the highest
terrain/obstacle in view and top bottom figure representing the elevation of the bottom of the lowest colour band (low density green). These elevations are given in hundred of feet above sea level. The CRT ‘Peaks’ displays differ from the LCD display due to colour/memory restrictions of the CRT system. The CRT display has limited colours and a single figure in the top right corner representing the elevation of the highest terrain/obstacle in view.
3. Use of ‘Geometric Altitude’
The new EGPWS uses a ‘Geometric Altitude’ rather than pure barometric altitude. This ‘Geometric Altitude’ is a blend of GPS altitude, pressure altitude, radio altitude and terrain elevation data. This combination reduces or eliminates errors in barometric altitude caused by extreme temperatures and altimeter miss-sets.
4. Automatic de-activation of the enhanced modes (TAD/TCF)
The EPGWS has an automatic de-activation of the enhanced modes (Terrain Awareness Display/Terrain Clearance Floor), equivalent of TERR set to OFF, when the FMS and/or GPS goes to a “Low Accuracy”.