Originally Posted by
TBL Warrior
Not possible according to EGPWS logic, unless flap was not set to landing or gear not down....
Yes it is possible. In Honeywell's EGPWS system, there is also a 'Terrain Clearance Floor' mode. From their EGPWS manual (my highlighting):
The Terrain Clearance Floor (TCF) function (enabled with TAD) enhances the basic GPWS Modes by alerting the pilot of descent below a defined “Terrain Clearance Floor” regardless of the aircraft configuration. The TCF alert is a function of the aircraft’s Radio Altitude and distance (calculated from latitude/longitude position) relative to the center of the nearest runway in the database (all runways greater than 3500 feet in length).
On short finals the TCF is a sloping plane (100'/nm) starting anywhere from 0.25-2 nm from the threshold increasing to 400'AGL at 4.25-6nm from the threshold. The actual distance depends upon the accuracies of the runway's known position and the aircraft's ANP. Even if you are correctly configured and on a stable 3° descent, you can activate a 'Tow Low Terrain' warning if you are below the nominal 3° path and penetrate the TCF. Derfred's Simex with a 10hPa (300') error perfectly illustrates the TCF mode in action.