Hi West Coast,
On your aircraft with GPS deferred are there any references in the MEL to E-GPWS accuracy in modes 1-4 for terrain avoidance?
Very interesting point. Having a look at the MEL for our A320/330 equipped with the latest TAWS architecture the answer is no, although the main position reference for terrain display is the GPS position.
In plain language, minus GPS, are the remaining nav inputs to the FMS you fly sufficient to provide position fixing to still be accurate to the same degree
They are but...
Broken down even more, minus an obvious sign like a map shift, are you sure that E-GPWS terrain warning received is truly on your path of perhaps offset due to accuracy?
Here's the point. You may be subject to spurious or false alerts as the main source of informations in the absence of a valid GPS input would be the actual FM position, which in case of a map shift (or erroneous FM position) could lead to false alerts.
I know I will react as if it was, but curious if the accuracy minus GPS is addressed in your MEL.
As far as I can see (hopefully somebody else will be more specific) there is no reference to that in the MEL.