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M
4C
ODE
Continued
18
Mode 4C is based on an EGPWS computed Minimum Terrain
Clearance (MTC) floor, that increases with Radio Altitude. It is
active after takeoff when the gear or flaps are not in the landing
configuration. It is also active during a low altitude go-around
if the aircraft has descended below 245 feet AGL.
At takeoff the Minimum Terrain Clearance (MTC) is zero feet.
As the aircraft ascends the MTC is increased to 75% of the
aircraft's Radio Altitude (averaged over the previous 15
seconds). This value is not allowed to decrease and is limited
to 500 feet AGL for airspeed less than 190 knots. Beginning at
190 knots, the MTC increases linearly to the limit of 1000 feet
at 250 knots.
If the aircraft's Radio Altitude decreases to the value of the
MTC, the EGPWS caution illuminates and the aural message
"TOO LOW TERRAIN" is enunciated.
EGPWS caution lights extinguish and aural messages cease
when the Mode 4C alert envelope is exited.
If the Aural Declutter feature is disabled, mode 4C alert
messages are repeated continuously until the Mode 4C
envelope is exited.
060-4241-000 • Rev. D - March 2000
MK V & MK VII EGPWS Pilot Guide
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