Originally developed in the 1970s, the ground proximity warning system (GPWS) became a requirement for all large turbojet aircraft following several accidents involving controlled flight into terrain (CFIT). GPWS provided flight crews with audio and visual warnings when terrain closure rates indicated the possibility of flying into terrain or an obstacle. These warnings were derived primarily from the aircraft’s radio altimeter, which provided actual height above the ground. This system revolutionized terrain awareness and CFIT prevention, but it lacked the ability to look ahead of the aircraft to predict rising terrain.
Enhanced GPWS, or EGPWS, was developed in the late 1990s. Improving on the original design and utilizing GPS location and a worldwide terrain database, EGPWS was able to provide extra time to respond to terrain alerts. Instead of relying only on actual aircraft position and height above terrain, the system was capable of predicting unsafe aircraft ORGaltitudes. Before the aircraft begins alerting of actual terrain closure, it utilizes the terrain database to warn the flight crew of impending conflict.
In addition, situational awareness is enhanced while operating in areas of rising terrain with displays that show surrounding terrain height in relation to the aircraft. This allows flight crews to easily see where the terrain threats are in order to make quick decisions should terrain clearance become a factor, such as when an engine failure is experienced and climb performance becomes insufficient.
EGPWS provides other safety alerts. For example, it gives warnings that indicate the landing gear and flaps are not properly configured for landing, as well as if the aircraft begins to lose altitude during a climb, or develops excessive rates of sink during descent and landing. In addition, EGPWS can provide warnings for wind shear that can help flight crews react more quickly to a loss of aircraft performance caused by wind shear.
