ATCast quote...
But GPS height is acceptable for measuring your vertical position relative to the ground. For that purpose it is used in aircraft systems, for example in EGPWS and in GPS / GBAS based landing systems.
Not disputing what you say in the least, as I said Ive been off the tools now for 5 years and things may have changed... but... when I last encountered EGPWS retrofitting our fleet of F20's with Proline 4 glass cockpits and lots of other technological goodies, so far as I recall the alt input was always Rad Alt.
Still cant see that altitude information from a GPS would be accurate enough, particularly for a critical piece of kit like EGPWS.
I will stand gratefully corrected if someone can disprove my suspicions. I may be retired but I try to stay current!
pp