E-GPWS modes 1-4 with GPS deferred.

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Depending on the level of technical detail being considered perhaps both views of GPS’s use in Mode 4 have merit.
GPS appears to be used in Mode 4 as in the text below. If GPS is not available we might assume that Mode 4 reverts to the basic system – it works as the old GPWS, but EGPWS may still be available via an alternate nav source.
This reversion probably does not warrant any MEL comment, but there should be some reference to the alternate nav source for EGPWS if the nav accuracy is less than GPS.

Extract from Honeywell Pilot’s Guide MkV & VII,
‘With version -210-210 and later models, Mode 4 airspeed expansion is disabled (upper limit held at lowest airspeed limit) when the Terrain Alerting and Display (TAD) function is enabled and available. This is due to the enhanced alerting capability provided with TAD, resulting from high integrity GPS Altitude and Geometric Altitude data. This change to the Mode 4 envelopes reduces the potential for nuisance alerts when the aircraft is not in the landing configuration.’