bold from me
Originally Posted by
Craggenmore
In addition to the basic GPWS functions, the GPWS has an enhanced function (EGPWS) which provides, based on a worldwide terrain database:
A) A Terrain Awareness Display (TAD), which predicts the terrain conflict, and displays the terrain on the Nav Display. The Terrain Awareness and Display (TAD) function computes a caution and a warning envelope in front of the aircraft, depending on the aircraft altitude, the nearest runway altitude, the distance to the nearest runway threshold, the ground speed, and the turn rate. When the boundary of these envelopes conflicts with the terrain, or with an obstacle memorized in the database, the system generates the relevant alert. On the 'Bus you get 60 secs for an amber caution and 30 secs for a red warning.
B) A Terrain Clearance Floor (TCF), which improves the low terrain warning during landing. A terrain clearance floor envelope is stored in the database for each runway for which terrain data exist. The Terrain Clearance Floor (TCF) function warns of a premature descent below this floor, regardless of the aircraft's configuration.
The EGPWS uses the geometric altitude. The geometric altitude is calculated by means of a specific algorithm that uses the following as inputs : The pressure altitude, GPS altitude, radio altitude, and data from the terrain database.
If you receive a caution or warning you are required to do something about it!
EGPWS is only as good as the database, isn´t it?
Wasn´t an E-jet attempting to land at Suvarnabhumi confused by a warning that no airport existed there? What is a pilot supposed to do about EGPWS warnings related to nonexistence of runways, or obstacles that only exist in database (since demolished/collapsed)?