Mode 2B provides a desensitized alerting envelope to permit
normal landing approach maneuvers close to terrain without
unwanted alerts. Mode 2B is automatically selected with flaps
in the landing configuration (landing flaps or flap over-ride
selected) or when making an ILS approach with Glideslope
and Localizer deviation less than 2 dots. It is also active during
the first 60 seconds after takeoff.
With version -210-210 and later models, Mode 2B is selected
when the aircraft is within 5 NM (10 NM with version -218-
218 and later) and 3500 feet of the destination airport
(independent of configuration) and 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. The Mode 2B envelope is selected in order to
reduce the potential for nuisance alerts during an approach.
The graph above shows the Mode 2B envelope.
Mark V and Mark VII EGPWS Pilot's Guide
Rev H, August 2011