J430
EGPWS modes are varied and can be quite daunting to comprehend. BOSTON has given you the best starting point for understanding it, the videos are very functional and assist in understanding the concept. I will attempt to explain it while keeping it as simple as I can. There are 6 basic modes that provide reactive warnings based on inputs of Radio Altitude, IAS and Vertical Speed (amongst others) to the GPWS, and then the predictive functions of the EGPWS take into account GPS position relative to a data base of terrain, obstacles and runways.
TCF (Terrain Clearance Floor) and RCF (Runway Clearance Floor) provide protection around a data base aerodrome. Provided the aircraft remains above the TCF envelope for the runway in the data base , warnings are not triggered. However the GPWS will still provide annunciations/warnings in MODE 1 excessive vertical speed, MODE 2 Excessive Terrain Closure Rate, MODE 3 Alt loss after T/Off, MODE 4 Unsafe Terrain Clearance and MODE 5 Glide Slope Deviation. On top of this the TCF is constructed to provide a stepped protection area that would be detailed on BOSTONS link to the Honeywell site. Simplistically put, it slopes from the runway elevation to 400' at 5nm. (Approximate) If you descend below this envelope you will still get a GPWS warning.
There certainly is an inhibit function for the EGPWS (Terrain Inhibit) that prevents spurious warnings on approach to an aerodrome not held in the data base. Hence the aircraft flight manual will usually if not always require that terrain inhibit be selected when on approach to an aerodrome not contained in the data base (A/D's less than 2000'). But even with this function selected the GPWS basic MODES 1 through 6 will still be operational.
Crew also have the ability to select GPWS flap override, this is one method of inhibiting part of mode 4 to have the GPWS ignore flap setting if a flapless approach is required, however mode 4 will still be operational in its other functions eg. TOO LOW GEAR.
Selecting the gear down also satisfies part of the Mode 4 function, if it didn’t then you would receive spurious warnings on approach below 500 feet AGL.
I couldn’t possibly hope to detail the full working and modes of the EGPWS/GPWS here, but I hope the brief summary from my failing intellect helps a little.