West Coast
Cosmo
As noted, GPS does play into the equation. Especially for mode 4 which is where my primary concern is.
No it doesn't:
Mode 4 - Radio Altitude Based Alerts: TOO LOW, TERRAIN
Unsafe terrain clearance at high airspeed with either landing gear not down or flaps not in landing position. Follows DON’T SINK if another descent is initiated after initial alert, before climbing to the altitude where the initial descent began.
TOO LOW, FLAPS
Unsafe terrain clearance at low airspeed with flaps not in a normal landing position.
TOO LOW, GEAR
Unsafe terrain clearance at low airspeed with landing gear not down.
TAWS - Look Ahead Terrain Alerts (GPS): TOO LOW, TERRAIN
Descent below unsafe radio altitude while too far from any airport in the terrain database.
CAUTION TERRAIN
40 to 60 seconds from projected impact with terrain shown solid amber on the navigation display (in expanded MAP, center MAP, expanded VOR, or expanded APP modes only).
TERRAIN TERRAIN PULL UP
20 to 30 seconds from projected impact with terrain shown solid red on the navigation display (in expanded MAP, center MAP, expanded VOR, or expanded APP modes only).
The aural alert "TOO LOW, TERRAIN" is used by both systems, but still it they are two independent systems. If TAWS doesn't work (for any reason), GPWS mode 4 alerts are still available as they are only radio altimeter based (+ combinations of barometric altitude, airspeed, and airplane configuration).
All the above is pretty much copy paste from the OMB.
