The graph below shows how the upper boundary of the Mode 2
alert envelope varies as a function of the aircraft speed. As
airspeed increases from 220 knots to 310 knots, the boundary
expands to provide increased alert times at higher airspeeds.
With version -210-210 and later models, the Mode 2A upper
limit is reduced to 1250 feet for all airspeeds 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. The Mode 2A envelope is lowered in order to
reduce the potential for nuisance alerts during an approach.
060-4241-000 • Rev. D - March 2000
MK V & MK VII EGPWS Pilot Guide