Not necessarily so
212man – “EGPWS; they have their own GPS which gives true height.”
A). Not all EGPWS installations use or have GPS embedded; shame on those operators who don’t. Beware FMS / IRS drift!
B). Those EGPWS that do use GPS still require the ‘geometric altitude’ software update. Most updates are free, as are all revisions to the terrain and obstacle databases. See
www.egpws.com Operation/pilots guides, General info/operational updates, and What’s new/new press release ‘getting the job done’.
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Unless specifically authorized everything else is forbidden.