As has been mentioned by a few previous posters, a direct GPS input to EGPWS to is necessary for the unit to operate to its maximum capability.
GPS input to the navigational suite (FMC) does not guarantee the same protections as GPS direct input. You can still have map shifts with GPS input to the FMC. In fact, on Honeywell units, GPS direct input has unique software that provides additional protections close to the surface.
The creator of GPWS and EGPWS, Mr. Don Bateman of Honeywell, had this article in the FSF magazine AERO SAFETY World recently.
flightsafety.org/asw/aug08/asw_aug08_p18-20.pdf
It has been my passion to try and convince my airline to install GPS direct to our EGPWS. Most of our aircraft are not wired this way.
Boeing recommends it ….Airbus recommends it (yes, I have the documentation)….Honeywell recommends it.
To my knowledge, all aircraft built by Boeing and Airbus have left the factory in this configuration in recent years.
What I cannot understand is why this has not been a FAA (and other worldwide regulatory agencies) mandated upgrade.
….by the way, the FSF publication is available free online, with e-mail notification of a new issue available. Should be on every aviators Bookmarks.
AeroSafety World Magazine | Flight Safety Foundation