The Enhancement is actually a set of smart logic that does a bunch of things, using the terrain data base, obstruction data base, inserted obstructions from a ground station, and air data, attitude, GPS position, heading etc:
1) The EGPWS predicts where you will be in 30 and 60 seconds, and looks to see if something is in the way. It warns you if so, aurally and visually.
2) It displays a continuous display of terrain and obstructions as if there were weather radar tuned to dirt and towers. On the ground prior to takeoff, you would see a field of small circles that are all the towers (masts?) in your area, for example. Nice stuff.
3) The system also looks at your profile to see if you are entering the classic traps, such as descent after takeoff. If so, it warns you. It also does this for normal approaches, and also for nose up tail strikes. There are about 30 situations that are programmed in as possible blunders that it attempts to see before you do.
While we can do lots with crew coordination and training, it is actually nice to have a device that "sees" the dirt that you can't see, and tells you about it.
I will try to post a few slides on it in a few hours, and update this post with the link.
if it seems like I am selling EGPWS, I am, in a way. I was the program manager on the Sikorsky push to get the first helo EGPWS certified, on an S-76, and worked with the FAA and Allied Signal (now Honeywell) on it. This was not an effort borne out of selling helicopters, but actually an effort to keep them flying longer! We held no rights to the work we did, and at least one other manufacturer is flying the system that we developed.