Mode 4 - Unsafe Terrain Clearance - Honeywell MK VI Pilot's Manual

M 3
ODE
Continued
M 4
ODE
Unsafe
Terrain
Clearance
16
The aural message is only enunciated twice unless altitude loss
continues. Upon establishing a positive rate of climb, the EGPWS
caution lights extinguish and the aural alert will cease.
Selecting flap override on turboprop aircraft increases the al-
lowable altitude loss, enabling optional pattern work without
unwanted warnings.
Mode 4 provides alerts for insufficient terrain clearance with re-
spect to phase of flight, configuration, and speed. Mode 4 exists
in three forms, 4A, 4B, and 4C.
• Mode 4A is active during cruise and approach with the gear
not in the landing configuration.
• Mode 4B is active during cruise and approach with the gear
in the landing configuration and flaps not in the landing con-
figuration.
• Mode 4C is active during the takeoff phase of flight with either
the gear or flaps not in the landing configuration.
Mode 4 alerts activate EGPWS caution lights and aural messages.
For turbofan (bizjet) aircraft, to reduce nuisance alerts caused
by overflying another aircraft, the upper limit of the airspeed ex-
pansion portion of the Mode 4A/B alerting curve can be reduced
(from 1000) to 800 feet. This occurs if the installation identifies
an airplane type providing the 1000 foot upper limit and the
airplane is above 250 knots with gear and flaps not in landing
configuration and a sudden change in Radio Altitude is detected.
This is intended to eliminate nuisance alerts while flying a hold-
ing pattern and an aircraft overflight occurs (with 1000 foot
separation).
Mode 4 airspeed expansion is disabled (upper limit held at low-
est airspeed limit) 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 and Geometric Altitude data. This change to the Mode 4 en-
velopes further reduces the potential for nuisance alerts when the
aircraft is not in the landing configuration.
Several Mode 4 alert envelope variations are defined as an option
in the installation configuration. In the following Mode 4 discus-
sions, the most common limits are provided with the alternates
identified in parenthesis. For a specific application, refer to the
installation documentation to obtain the defined configuration.
060-4314-000 • Rev. C - May 2004
MK VI & MK VIII EGPWS Pilot Guide